- 1 -

THE BIOLOGY OF FEAT ER-WINGED BEETLES OF THE GEflUS

Om. PTINELLA WITH PARTICULAR REFERETXE TO CO XISTEI;CE AND PARTiil

by

VICTORIA IOTA TAYLOR B. Sc. (Lona.)

A thesis submitted in partial fulfilmentsof.the

requirements for the derce of Doctor of Philosophy.

September 1975 Imperial College Field Station,

Sill-mod Park, Ascot,

Berkshire. 2

TABLE OF CO_ ITS Page no. Title page 1

Table of Contents 2 Abstract 5 Introduction and literature review 7 Section 1: The biology of P.aptera and P.errabunda with additional notes on F.taylorae. 1.1 Habitat 36 1.2 Distribution

1.3 Life history 47 1.4. :Votes on morphology 59 1.5 Gut analyses of adults and larvae S2 Section 2: Field sampling and collections of Ptinella

2.1 SAmpling method oo 2.2 Develol-ment of extraction technique 69 2.3 Application of sampling technique to natural populations 73 2.4 Field collections of Ptinella 82

2.5 7:easurement of subcortical temperature 90

2.6 Discussion

(i) The association of species 101

(ii)'That is a population? 106

(iii)Species distribution and the problem of colonisation 108

(iv)The microclimate under bark 111 Section 3: Laboratory experiments on the biology and fecundity of P.aptera and P.errabunda (including data for P.taylorae)

3.1 Culture methods 115

3.2 Response of Ptinella to physical parameters of the environment

(i) Relative huLtidity tolerance 120

- 3 - Page no. (ii) Temperature tolerance. 124.

3.3 The effect of tel.merature on the life history

(i) Fecundity and oviposition rate 126

(ii)Frolaortion of e.gs hatching and duration of the eg stae 129

(iii)Ddration of timature sty. ;es 133

(iv)Duration . of pre-oviposition period. 158

(v) Duration of total pre-reproductive reri•d. 158

(vi)Fre-reproductive mortality and fertility 14.0

(vii)Sc:: ratio- 14.1

3.4 The estination of life table statistics at different temperatures 163

3.5 Discussion

(i) The effect of relative lit.t.iidity 150

(ii)The effect of temperature 154

(iii)r m and the species habitat 160

Section 4: Competition experiments with P.a.Dtera- and P.errabunda

)1-1 "xperi,aents 164

4.2 Discussion 171

Section 5: 77in,-; poly.dorphit;m and se:: ratio in Ftinella

5.1 Jing poly.Aorphism and sex ratio in field collections 174.

5.2 The effect of ternerature on wing polymorphism and se:: ratio of P.aptera in culture 186

Coinarison of reproductive potential of apterous 5.3 and alate females 192

5.4- Discussion

(i) Wings and the environment 200

(ii)Inhertitance of wines 205

(iii)The reproductive significance of win3s 207 Page no. Section 6: Discussion

0.1 Co:Apetition and coexistence 211

6.2 Asexuality - an advantage for colonists 218

6.3 Faracio::ical fecundity 294.

6.4- Snviron::ontal and genetic deterLrination of morph? 225

6.5 Strategies in a heterogeneous environment 226

6.6. 3piloo_te 229

Su .r ark 231

Ackno-.:ledgements 235

References 236

ppendi:: 1: A -oroble.0 of long standing 247

Apnendix 2: Statistical formulae used in anal-rsis of data 2)+8

Appendi:: 3: Differentiation of larval in stars 250

Appendi:: Result's of field collections of Ptinella 251

Append.1:: 5: Results of field. sampling of Ptinella 257

Appendix 6: Results of laboratory experi:Aents with Ptinella 265

,Appendix 7: Results of' comeetition ex-oerinents with Ptinella 278

Appendix 8: ;Ting polymorphism and se:: ratio data 281 ABSTROT

The biology of Ftinella aptera and Ptinella errabunda has been studied

with a particular view to investigating the problems of ecological and genetic

stability of a system involving intimate co-existence and parthenogenesis in

one member of the pair.

Both species have been shown to be multivoltine with overlapping

generations; P.aptera is bisexual but P.errabunda is parthenogenetic.

Field collections and laboratory observation suggest: that the ecological

requirements of both species are similar - both ai-e primarily unspecialised

mycetophagea and are largely restricted to the subcortical zone of trees in

a particular state of decay, by their specific humidity requirements demonstr-

ated in laboratory culture. Furthermore, some degree of coexistence between

P.aptera and P.errabunda is suggested by field sampling data, and competition

was implied. It is suggested that coexistence is in such cases transient

or may be a consequence of superabundance of resources.

Controlled laboratory rearings show that the potentially doubled fecundity

predicted for a thelytokous species is not realised by P.errabunda. However,

the experiments, carried out over a range of temperatures, show a significant

separation of the species with temperature on the basis of reproductive performance. These conclusions are supported by the results of competition experiments in which P.aptera predominated at 20°C and P.errabunda at 15°C.

The differential adaptation is considered in relation to subcortical temperature measurements.

The incidence of alary polymorphism has been investigated in field collections of Ptinella and in laboratory rearings. A seasonal effect was observed with a significant increase in alate females in late summer.

Temperature has been shown to affect alate production in culture implying a physiological switch sensitive to adaptively relevant parameters of the environment. Hbwever, a genetic basis for the polymorphism is implied by the higher proportion of alatae - . the progeny of alatae compared with the progeny of apterae.,

The wing polymorphism is also associated with a reproductive polymorphism, laboratory rearings showing significantly greater fecundity of the alate morph in contrast to all other non-social insect wing polynorphisms for which comnarable data exist.

The distributions of P.antera and P.errabunda are considered in terms of habitat availability and colonising ability. The successful wide spread of the apparently invading P.errabunda is attributed in part to its partheno- genesis. The limitation of P.antera is considered to be partially a consenuence of problems associated with colonisation in a discontinuous environment and also as a result of the species'diminished reproductive efficiency at low temperatures relative to that of P.errabunda.

Other species of the genus are considered in an attempt to determine the origin of P.errabunda. It is concluded that it is almost certainly of New

Zealand origin together with a new species Ptinella taylorae which was discovered in the course of this work. - 7 -

INTRODUCTION AflD LITERATURE REVIEW

.... none are bstter calculated to .... controvert the idea, thLt such

elaborate, and almost incomprehensible orcanisation, could be the result of a

fortuitous calbination of atoms, " (::atthews, 1872).

This reference , oblieue and (in choice of the word "fortuitous") rather

inaccurate, to Darwin's revolutionary idea of evolution by natural selection

cones in the introduction to a monocraph of the Ftilii-daP- the only monocl--rh

yet ae votcd to the family of the 7;Orld's sm.ellest beetles. So impressed was

the author, the Reverend A. 7.-L, Lthews, by the diversity and complexity of his

minute eubjects that he felt unable to accent that their forms h-a been

derived by any natural process. All the data alined in the present study of

species of this family, however, seem consistent with the contrary view:

they succest that not only the species morpholocy (with the minutae of

construction so fustifably admired by ::atthews) but also, integrated with

this, their life hi stories and habits, have been moulded by forces of natural

selection.

The Ftiliid beetles of the cenus Ftinella comlvirte some twenty to thirty

described species distributed throughout the world. early ae. 1072 the

scientific neclect of this family was la Tilented by 1:_atthews (Aopendix le) and certainly from the biolocical point of view this situation' has scarceiv improved over the last hnide:ed years (Dybas, lo insects have not only resulted in their 1-,c:_nt; much overlooed literally, but has also made them difficult subject for scientific stu,-,y.

The aim of the current work is to investicate a case of apparent coexistence between closely related ec'-- of i'lllie-e wh ich is made more stri::ing in ecolo-ical terms by one of the s-eecf.es bein3 iy.rthenonetic and both being noli7r-orr,hic The species studied, Ftinella a '.era (GuorInnevill and rt5nella errabunda (Johnson), are the two predominant species of P-inella in Britain (although this situation may be changing, see reference to

Ptinella cavelli (Baer) in Johnson,' 1975 ) • Data onr their bioloPv and habits may be hoped to be of more than specialised interest and to contribute

something to a general understanding, both ecological and evolutionary,

of those phenomena mentioned.

Coml5etition and Coexistence.

The idea of one variety replacing another in a population due to

superior competitive ability was, of course central to Darwin's t:ieory of

evolution by natural selection. But discussion of the conditions for

replacement to occur between "two species which contend for the same food"

(Volterra, 1928) and of the dynamical process of such replacement began in

earnest with the theoretical work of Lotka (1925) in the United States and

Volterra (1928) in Italy. The differential equation which has as solution

the logistic eouation describing the growth of a single population was

generalised to cover.the interaction between two species. The model can be

considered as the theoretical basis for the laboratory experiments of Gause

(1932, 1934), Crombie (1945), Birch (1953) ana•notably Park and his co-workers

(Park, 1954, 1962; Neyman, lark and Scott, 1956) and many others besides.

Pour possible outcomes of competition derived from the equations were illustrated graphically by Gause and 71itt (1935). In two cases the displace-

ment of one species by the other was predicted depending on their relative competitive abilities; the third case involved an unstable equilibrium such

that the outcome would depend on the initial densities of the species.

Finally it was shown that if the competition coefficients are such that, by an increase of its own density, each species is harming itself more than it

harms the compY6itor, stable coexistence may be maintained indefinitely.

The ecological implications of the Lotka-Volterra equations were at least partially appreciated by Gause (1934) who wrote "as a result of compet- -9-

-ition two similar species scarcely ever occupy similar niches". In 1944

an anonymous author reporting the British Ecological Society SL,mposium of

that year referred to "cause's contention" that two species with similar

niches could not coexist indefinitely. However, Udvardy (1959) has pointed

out that it should be called Grinnell's axiom om the basis of a remarkably

clear statement of the idea published in 1928. Cinnell wrote that "no two

species in the same general territory can occupy for long identically the

same ecologic, niche. If by chance, the vagaries of distributional movement

result in introducing into a new territory the ecologic homologue of a species

already endemic in that territory, competitive displacement of one species

by the other is bound to take place. Perfect balance is inconceivable".

Stateents of what has been alternatively termed the competitive exclusion

principle have taken a number of forms. Some authors have given a limited

form whereas Hardin (1960) Debach (1966) and MacArthur (1972) amongst others

prefer a more apriori, albeit empirically trivial definition. For example

Hardin (1960) says simply "complete competitors cannot coexist". But of course without further explanation this fails to avoid ambiguity.

The early laboratory experiments of Cause and others generally fulfilled

the predictions of the Lotka-Volterra equation: one or other of the competitors in a pair went to extinction. However, in relation to the natural situation these results were.paradoxical since naturalists reported that, contrary to the exclusive principle, similar species commonly coexist. Furthermore

direct evidence of competition is rare. Such observations resulted in dichotomy amongst ecologists - some, notably Birch (1957), Cole (1960) and

Ayala (1969, 1970) regarding the principle as trivial whilst Hardin (1960),

Hutchinson and Deevey (19/4-9) and MacArthur (1972), whilst admitting it to be obsolete in empirical terms consider it to be an important basic theorem in the understanding and interpretation of biological communities. Birch's attack was based on the failure of logistic equations to describe adequately - 10 -

the growth of, populationz and Ayala (1970) made the same criticism in his

claimed invalidation of the principle. In his experiments with Drosophila pseudoobscura and Drosophila serrata he showed that the two species, whilst

competing for food as larvae and for space as adults, were able to coexist for long periods whilst harming each other more than themselves (Ayala, 1969).

However, Gause himself had realised and pointed out the limitation of the application of the equation to simple organisms'(such as yeasts and protozoans) whose population growth is normally adequately described by the logistic equation (Gause and Witt, 1935).

Field ecologists in applying the principle to natural populations have considered it in its evolutionary context, investigating the circumstances in which competition is reduced or absent thus permitting coexistence. Such work involves detailed analyses of the niches of coexisting species and problems arise in the use of the term "niche" and its definition. It was used by Elton (1927) to describe the function or role of an organism in its environment relative to food and enemies in particular. After many years of confusion when various alternative definitions were used by different authors,

Hutchinson (1957) formalised the concept using ilacArthur's term "funaPmental niche" and defining it as an n-dimensional hypervolume such that any point within it corresponds to a state of the environment where the species concerned would survive indefinitely. Although theoretically staisfying, it is impossible to quantify such a hypervolume completely in any real environment.

Generally certain parameters believed to be of importance in determining the immediate environment of a species are selected for detailed analysis together with interactions of other organisms in the habitat, to derive an approximation of the realised niche of the species. The definitions of niche, habitat and ecotype have recently been clarified and reexpressed in a more universal form in a very useful paper by Whittaker, Levin and Root (1973).

It is generally thought that changes in animal populations may be determined to a greater or lesser extent by two types of events - density dependent and density independent. Density dependent mechanisms may act on

populations in such a way as to maintain them at densities below the carrying

capacity (K) of the environment. If such a situation occurs where two species

are sharing the same potentially limiting resource in the consequent absence

of competition both may coexist indefinitely. Intraspecific competition is

particularly important in this context. Broadhead and Wapsphere (1966)

were able to show that intraspecific competition for oviposition sites

amongst two closely related species of the psocid Yesopsocus, almost certainly restricted the population at a level at which intraspecific competition for

for food was insignificant. The species were thus able to coexist. A

similar explantaion is given by Fontin (1961) for the stable coexistence of

the ants Lasius flavus and Lasius niger even in the presence of apparent competition for food underground. In these cases when intraspecific competition regulates each population independently, the requirements for the stable coexistence described by the Lotka-Volterra equations are excatly fulfilled.

Coexistence may also be facilitated by "frequency dependent fitness"

(Ayala, 1970); at low population densities one species might be superior in performance. But as its population increases, the effects of intraspecific competition reduce the rate of increase such that the second species is relatively superior in reproductive performance. Rather similarly Gause (1970) and Ayala (1970) attribute the coexistence of Drosophila species in the latter author's experiments, to changes in the relative fitness of different stages of the life history. D.serrata is superibr in larval competition and

2.1yseudoobscura in adult competition (Ayala, 1969). Hutchinson (1961) has put forward the idea that the diversity of phytoplanktonic species coexisting in the relatively unstructured environment of the open sea, is due to a

temporally non-equilibrium situation, different species being favoured at

different times due to fairly regular changes in environmental factors.

However Richerson, Armstrong and Goldman (1970) maintain that coexistence

is a consequence of variation between patches of water with a low rate of - 12 -

mixing. A temporal balance of advantage may contribute towards maintenance

of chromosomal polymorphism observed as seasonal changes in chromosome

stricture within the populations by Dobzhansky (1945) for D._pseudoobscura.

As Varley, Gradwell and Hassell (1973) have pointed out there is an analogy

between competitive coexistence and maintenance of genetic polymorphism.

A balance of advantages permitting coexistence may also be facilitated

by spatial factors. Thus Lack (1945) suggested that where two species have

similar niches that meet on an environmental gradient, competition in the region of overlap may be intense. However, repletion of the population by migration from the areas optimal for each species may stabilise coexistence in the zone of overlap. Hutchinson (1957) suggests that breeding refuges may be used by species in a similar way.

In the intense competition for space in the sea-shore intertidal zone,

the importance of predators in maintaining species diversity has been convincingly demonstrated by Paine (1966). Selective predation prevents one species from monopolising the resources and reduces the effectiveness of interspecific competition (Connell, 1961). Predators and parasites have also been seen by Varley, Gradwell and Hassell (1973) as indirect agents permitting coexistence between species whose populations they regulate below K.

Broadhead and 7:apsphere (1966) visualise a situation where a predator or parasite common to competitors, by selectively attacking the common species at any point in time, could maintain a stable coexistence between the competitors. However no examples of this have yet been recorded.

Unstable regimes of coexistence are commonly associated with transient habitats. Yutchinson (1957) notes the reduced likelihood of competitive replacement occurring in successional communities where food may be superabundant during any particular stgae. Selection pressures in such situations are likely to act to increase colonising ability rather than competitive ability (see below). Coexistence may also be unstable when one species is replacing another as may occur when alien species are introduced -13-

into a native fauna. Examples of such displacement are reported by Bess

et al (1961) and Debach and Sundby (1963) for hymenopterous parasites.

However, it is important to notice in this context that cases of apparent

corpetitive displacement may in fact be spurious. A number of observers

have attributed the population decrease of the red squirrel Sciurus vulraris

to competition with the introduced grey Sciurus carolinensis. As Shorten

(1954) has pointed out this is far too simplistic an interpretation of the

situation. The decline of S.vulraris, is at least in part, due to the

extensive destruction of its habitat and reduction of its populations by

disease and probably several other factors.

Careful study of cases of apparent coexistence of species by Lack (1945)/

Croker (1967), MacArthur (1958), Brian (1957) and many other authors, have

shown that competition is probably absent since their precise niches differ.

Presumably this is the consequence of selection pressures minimising inter-

specific competition. It is apparently possible for such differences to be

accentuated in times of competition for a normally superabundant resource.

Zaret and and (1971) observed that the niche overlap of certain tropical

fish was extensive in times of abundant food, whereas when food was La short

supply niche separation was considerably greater. Of course the possibility

of certain forms of food becoming unobtainable to one species but not to

another during the changed physical conditions imposed by drought cannot be ruled out. The importance of interspecific competition in the evolution of

differences in food size ranges, feeding behaviour, etc. in permitting diversity of species in stable habitats in particular, has been emphasised by Hutchinson (1959), Kopfer and racArthur (1961) MacArthur (1965), Schoener

(1965) and Harper et al (1961).

Turning now to the problem of the apparently coexisting congeneric

Ptiliidae, 5-t is clearly necessary to establish initially the extent and manner of coexistence of the species and especially to consider whether their coexistence stable. Only then can the relationship be referred to the various foregoing models to determine which explains the coexistence of

Ptinella most satisfactorily. Parthenorenasis.

If coexistence is shown to occur to any extent between P.aptera and

P.errabunda the problem is further exacerbated by the presence of partheno-

genesis in one member of the coexisting pair. Since the basic m.ichinery on which competitive interaction works is the reproductive potential of the respective species, the theoretical doubling of this by parthenogenesis should give that species so characterised greater intrinsic competitive ability relative to the bisexual one. The mitigating factors required to overcome this advantage must be substantial. Even if coexistence is shown to be absent, the general biology of parthenogenesis leads to expectations of differences in the habitats and biology of parthenogenetic species relative to their bisexual counterparts.,

Parthenogenesis may be defined as the development of unfertilised eggs and as such is a modification of a pre-existing system of sexual reproduction.

It occurs throughout both plant and animal kingdoms and falls naturally into two categories depending on the sex of the progeny. The genetic, evolutionary and ecological implications associated with each system however, are completely different. The reproduction of P.errabunda is apparently thelytokous since only female individuals have been recorded (Johnson, 1975 ). In this form of parthenogenesis, eggs develop without fertilisation into exclusively female progeny; it is thus equivalent to a purely asexual process. The cytological and genetic aspects of thelytoky have been reviewed comprehen- sively by 'White (1973). Hot all species or biotypes exhibiting thelytoRy use it as the exclusive means of reproduction and a number of cases of apparently pure thelytoky have been found, on closer investigation, to involve a sexual phase. The regular alternation of asexual and sexual reproduction is known as heterogo.ny (Bite,

1973) or cyclical parthenogenesis. Its implications cannot be compared with those consequent of thelytoy since the sexual phase introduces the genetic variability characteristic of sexual reproduction and as such is absent from -15- a purely thelytokous species. It is therefore important that, before any

predictions are made concerning apparently thelytokous species, the possibility of the regular occurrence of males, no matter how rarely, should be eliminated.

For example it would make the case very different if males were merely rare, inconspicuous or shortlived as was found to be the case for Orchesella villosa and Sminthurides aouatica (L'ayer,1957). Determination of the method of reproduction at any one time in heterogenous species has been shown frequently to be under environmental control.

The occurrence of cyclical thelytoky is understandably correlated in most cases with those kinds of niche which rather regularly repeat a demand for colonising ability and high reproductive potential. The aphids provide excellent examples of. the "benefits" achieved by this means of reproduction.

The paedogenetic Cecidomyiidae are rather similar although their c1rromosome_• behaviour is more complex. Pure thelytoky has the same advantage of cyclical thelytoky except it lacks these stemming from the annual or occassional sexual phase with its consequent genetic recombination. The near universality of sex shows that these advantages are important although it is not yet wholly clear what they are (Vlilliams, 1975). Thus pure thelytoky may be a rather hazardous achievement in the direction of cyclical thelytoky when the latter may be regarded as ideal. Trialeurodes vuorarium and various thelytokous thrips apparently fit this category, Again, many cases are multivoltine, r-strategist colonising species. But other thelytokous species e.g.

Solenobia triDetrella (Seiler, 1961) are of a quite different character; indeed the rather random distribution of the occurrence of thelytoky seems a bar to any general theory.

The repeated independent origin of thelytoky is reflected in the diversity in the -genetic machinery effecting it. ',',`Ili to (1973) recognises two broadly different mechanisms by which the perpetuation of the chromosome number in ensured. Apomixis describes the total supression of meiotic reduction division - maturation division is thas mitotic and therefore purely - 16 -

replicatory in nature. Associated with this mechanism, mutation causes

accumulatlon of heterozygosity. In autonixis meiotic reduction takes place,

consecuently the chromosome nurber must be restored by fusion of nuclei

produced in the meiosis or fusion of cleavage nuclei in pairs; such fusion

results in an overall tendency towards increased homozygosity. It is

characteristic of both apomixis and automixis, that with the abolition of

fertilisation, the genetic variability derived from the different genotypes

of the patents is totally absent. Thus a genotype favoured by selection

whilst bisexual, would be expected to become fixed and perpetuated on becoming

parthenogenetic (Mite, 1973). In automiotic forms a certain degree of

variability would be expected to arise from the crossing-over of chromosomes

during meiosis, however, this effect would be expected to be small compared

to that in sexual reproduction. Once parthenogenesis has become established,

the major source of variability will presumably derive from mutation at

individual loci and structural rearrangements of chromosomes.

Despite the differences between the two types of thelytoky, the overall

evolutionary implication is probably the same for both apomicts and automicts:-

in the long term thelytoky represents a "blind alley" (Darlington, 1958) and

ultimately the lack of variation that could enable species to adapt to

changing environmental conditions will result in their extinction. However,

this view was challenged by Suomalainen (1961). He claimed that his

biometrical studies of otiorrhynchine weevil populations showed geographical

differences between parthenogens attributable to variation in the gene pools

of the populations and arising after the adoption of thelytokous reproduction.

This, he concluded, implied that at least in parthenogenetic polyploid

populations of weevils selective change could still take place and hence

evolution "fitting" the parthenogens to their new environments. More

recently Williams (1975) has expressed similar views concerning the evolution- ary potential of asexual populations. Yinite (1973) on the other hand interprets

biometrical variation such as that shown by Suomalainen as the consequence

of polyphyletic origin of either thelytoky or polyploidy, or both in these - 17 -

weevils. Expression of mutant alleles would be limited where the original

allele was represented in at least double dose. In the absence of any

evidence that species or biotypes have reverted from parthenogenesis to

bisexuality (Williams points out the lack of evidence to the contrary - that

such reversion has not taken place) it seems likely that in the long term

at least, the idea of thelytoky as an evolutionary dead end is correct.

Nevertheless, it is of interest to look for common ecological and

historical factors among the various groups that have become thelytokous,

and also to consider a priori what the advantages are and the situations

where the immediate advantage would be expected to be most marked. That

advantages do at least sometimes exist is shown by the successful estblishnent

of parthogenetic biotypes in bisexual groups.

The most immediately obvious advantage of a parthenogenetic species over

its bisexual counterpart is that of increased effective fecundity and, as noted above, this is particularly problematical in cases of coexistence of parthenogenetic and bisexual biotypes and species. In addition to the shedding of the meiotic load by parthenogenesis, the need_ to expend enemy on mate-finding or courtship is obviated. Thus parthenogenetic females can devote their total resources as adults to feeding and reproduction. Neverthe- less, such benefits may be of limited importance since in a number of species it has been shown that the potentially doubled_ fecundity is far from realised.

In Drosophila marlobeira up to forty per cent of the progeny may be inviable

(lairdy and Carson, 1959) and Stalker (1956) has observed twenty-five per cent inviability in Lonchoptera aubia. Similar results have been obtained by

Petersen (1971) for the collembolan Isotorna notabilis which suffers a thirty- seven per cent egg mortality although it is not yet clear whether this species exhibits facultative, seasonal or obligatory parthenogenesis. Presumably such a failure is often due to the genetic imperfections of the system such as incorrect fusion of meiotic nuclei or deleterious cross-overs. In invest- igating the situation in P.tera and P.errabunda it is thus esr,ential to - 18 -

compare the fecundities achieved by both species under the sue conditions.

Pew such studies have been undertaken. For the Arctic sinuliid CArmnuais

Downes (1964) has recorded an average of approximately twenty r s per

breeding cycle whereas temperate bisexual blackflies produce hundreds.

However, this case is probably somewhat misleading since the exigencies of

the Arctic environment may have an overriding effect in reducing reproductive

performance. 7.7bite (1970) has argued that if reproductive performance was

of prime importance in the evolution of parthenogenetic forms, the systems

should have been perfected by selection. But work by Bergerard (1951;,) on

the phasmid Clitumnus extradentatus and by Stalker (1956) on Drosophila larthenogenetica suggests that after initial success in selectively increasing the proportion of virgin eggs developing parthenogenetically in these bisexual

species, further improvement of the character rapidly falls off, ultimately to zero. In the absence of crossing with a bisexual population further progress' will depend on the occurrence of suitable mutations and so will be very slow. To summarise, in the known cases fecundity is not doubled by the advent of thely:;oky, as might naively have been expected. Usually there is some moderate. increase: yet this may not be the major advantage of thelytoky.

The potential ability of each parthenogenetic individual to initiate a whole new colony is another obvious and less disputable advantage of thelytoky. Obviously too this potential would combine well with any increase in effective fecundity towards creating the facies of a habitual colonist species. In a temPorary habitat when resources are abundant for a limited period of time, a strategy of very rapid increase in numbers to exploit an unpredictable supply would be expected to be selectively advantageous

(Southwood, :72.y, 'Hassell ana Conway, 1974). In such a situation the slower trend to improve adaptation of a sexual species would be relatively less important in terms of selection over the short period. when the habitat is suitable. It is interesting to note that inbreeding and apomixis in plants - 19 -

are most co non among weed species that characterise the early and most

temporary stages of succession. ..n analagous situation would_ be expected

;n animals in habitats of fluctuating ecological suitability (17ayr, 1963)

subject to similar selection pressure. Chiselin (1974), for example, observes

that evolution of parthenogenesis has occurred during the colonisation of

freshwater environments by some bisexual marine groups. Rotifers and

gastrotrichs found in the most transient freshwater fools exhibit a large

number of asexual forms. The brine shrimp Anemia salina (Stella, 1933 and a_2:,esni, 1956) is faced with the problem of exploiting an environment

particularly prone to temporary disappearance. The distribution of its large

number of genetically variable, thelyW:ous biotypes is discontinuous as a

consequence of the nature of the habitat and although local populations may be large, the probability of extinction must be considerable.

The rotting wood habitat in which Ptinella is found appears to constitute a similarly short-lived, discontinuous environment. The time over which conditions may be suitable for a particular species is necessarily limited and may be taken as representing a stage in succession. Indeed Elton (1927)

has suggested the use of rotting logs for studying the ecology of succession.

Thus parthenogenesis has arisen independently on a number of occassions amongst the rotting wood fauna. Pour species of Diplopoda in Fennoscandia that are typically found under the bark of rotting wood are, in this region at least, parthenogenetic (ralmon, 1949). One of the four, Froteroiulus fuscus is the most cosmopolitan of Fennoscanaian aiplopoas even occurring within the Arctic circle. Presumably its parthenogenesis enables it to exploit isolated patches of habitat and to make the most of its ability to disperse passively carried on driftwood. In addition to one of the subjects of the current work (F.errabunda) parthenogenesis has also evolved both in the same genus in Ptinella cavelli (Johnson, 1975 ) and in at least one

World Genus Euruzae. Dybas (1966) has reported_ five cases of apparent

parthenogenesis in the latter Genus whose species he found in the rotting - 20-

wood and forest floor detritus in Florida. Tn particular, he notes the

extension of one species' range outside its normal distribution, in sawdust

piles over a large area of the United States. Fresumably parthenogenesis

has helped to make this "opportunistic" extension of range possible.

The wood-rotting macro-fungi effectively form subhabitats of the rotting

wood environment and the same selective pressures would be expected to

operate on the fauna exploiting these niches as on that of rotting wood

itself. Lawrence (1967) has investigated the distribution of bisexual and

parthenogenetic biotypes of Cis fuscipes in the United States. From an

hypothesised centre of invasion in the north-west, the parthenogen is

believed to have either displaced the bisexual type in the south-east, or

colonised the area more rapidly and successfully than the bisexual form.

Further, Lawrence has suggested that the exclusive occurrence of the

parthenogen in the large, environmentally "suitable" area of the mid-west,

is a direct consequence of its high dispersal and colonising ability. This

has enabled it to exploit the exceptionally discontinuous environment

attributable to modern methods of agriculture. A similar explanation would

account for the apparent colonisation of oceanic islands by the parthenogenetic

biotype subsequent to its accidental introduction. Parthenogenesis was

included by Lindroth (1957) as one of the six characters desirable in insects

to facilitate establishment in the New World after crossing the Atlantic in

shipping ballast. Five parthenogenetic species of beetles (Amischa analis

and four species of Otiorrhynchus) that he recorded associated with ballast

sources in southern England, had successfully established themselves in

New Foundland.

The immobility of higher plants has obviously contributed to increase

selection pressure for hermaphroditism and parthenogenesis (Stebbins, 1957) and it seems reasonable to expect an analogous situation in relatively

sedentary animals. In this context it is interesting to note the occurrence

of thelytokous biotypes in the flightless Psychid moth Solenobia triouetrella - 21 -

(Seiler, 1961). This is the only family in the otherwise highly active

Lepidoptera in which parthenogenesis occurs commonly, and perhaps it

represents, in part, a mechanism in overcoming the problem of mate finding in

situations where high selective advantage is to be Gained from wing reduction.

Similar cases are exhibited amongst the otiorrhynchyne weevils (e.g. Suomalainen,

1947) and both the wingless tettigonid Sago redo (ratthey, 1941) and the

apterous grasshopper 7!oraba virgo (',;alite, Cheney and Yey, 1963) are partheno-

genetic. Although it is not clear to what extent the selection pressures

that favoured loss of wings are still operative in the current habitats

of these species, it seems reasonable to consider parthenogenesis as a partial

alternative to wings in achieving success in dispersal and colonisation. Of

course there are many parthenogenetic species that are winged (or which, like

Ptinella, have winged morphs), nevertheless a statistical association between

parthenogenesis and flightlessness seems indicated. The potential for lone colonisation (and implied... absence of necessity to encounter a male) may

help to explain this.

Despite the foregoing evidence that parthenogenesis whould be strongly

selected in particular ecological situations in response to requirements for dispersal and reproductive increase, -,;bite (1973) believes that there is more substantial evidence to support the view that the overriding advantage conferred on a species by thelytoicy lies in the exploitation of the pre- existing heterotic condition, but with the loss of the genetic load associated with the maintenance of heterozygosity. This implies that thelytakous species are generally unable to make adaptive modification to changing environmental conditions, resulting in their confinement to relatively narrow, constant invariable niches. Such an interpretation could be applied to explain the absence of parthenogenesis amongst marine organisms and highly motile groups which are inevitably exposed to fluctuating conditions. Although this theory appears to conflict with the preceeding observations, the two interpretations are not totally incompatible. It is feasible to predict that - 22 -

in certain circumstances the advantages gained by increased dispersal power

and reproductive potential might enable a parthenogenetic species or biotype

of low adaptive ability to be selected in the short-term over more plastic

bisexuals. Sago peon, 27oraba virPo and Drosophila man-abeira may all be

regarded as parthenogenetic forms restricted to rather widely separated

populations in special habitats. It appears that the spread of such species

and in particular the phenomenon of predominance of parthenogenetic biotypes

as extensions of a bisexual range, must be a conseauence of the continual

exposure of genetically different biotypes to new niches by vitue of their

potential for dispersal. Ultimately some new areas would be expected to be

colonised by chance. Evidence for this having occurred is suggested by the

association of various p-rthenocens with the creation of new habitat as a

result of human activity and subseauent to glaciation.

Parthenogenesis has often been reported in association with what can

perhaps be thought of as "unsaturated" environments which provide relatively

invariable ecological niches. :ere the rewards may be thought of as being

considerable for strongly heterotic biotypes with high powers of colonisation

and of generally high adaptiveness. Little ability to undergo further

adaptive change will not matter against such advantages, except in the long

term. Even then it is possible that a new parthenogen may be able to

"break away" from the bisexual race to replace the old. Areas exposed after

glaciation and as a result of man' s activity have already been mentioned in

this context; to these may be added: northerly, Boreal and Arctic environments.

Apparently associated with such conditions is the phenomenon named by Vandel

(1`928) geographical parthenogenesis. This describes an observed tendency for exclusively female progeny to predominate in the northen latitude of

particular species' ranges. Vandel (1928., 1934, 19W) showed that the

parthenogenetic Trichoniscus coeleb,s has a wide distribution through France,

the Baltic, Scandinavia and Iceland whereas the closely related bisexual

Trichoniscus elisabethae is restricted to damp mountain regions of southern

France. Interestingly T.coelebs also extends into the southern :s.gions but - 23 -

only in the "unfavourable" areas of the arid "carrigues" of the French

!'eclitterranean Coast. Similar patterns have been well documented for the

aiplopoa Polyxenus lacurus (Palm6n, 1949), chrysonelids (Suomalainen, 1965) and the otiorrhynchyne weevils. The latter have been the subject of extensive

study by Suomalainen (1940, 1947, 1953) who concluded that parthenogenesis

and its associated polypoidy have been particularly successful in this Group

since parthenogens are Generally more wiacly distributed than the related bisexuals. Ten species found in the eastern Alps exhibit both bisexual and parthenogenetic bietypes.

Suomalainen (1962) has suggested that the different distributions of poly-floid types are due to broader ecolo ,-1.cal tolerances and requirements of poly-oloias. In 1940 Vanrel had expressed a sexewhat similar view ascribing the success of parthenogenetic species studied_ by himself, to their polyploidy which conferred on them (according to him) greater vigour and ability to withstand harsh conditions. 3oth views are unsubstantiated. Clearly when investigating the occarcence of parthenogenesis in a species or renus, the possibility of a -eographl_cal pattern in the method_ of reproduction ;lust be considered.

The problem of coexistence applies not on„'' to parthenogenetic and bisexual populations occurring together, but also to sympatric parthenogenetic

I:aryotypes. Stalker (1.-?56), in his study or parthenocenesis in Lonchonte,'a dulia is one of the few authors who hays considered the evolution of the system at least partially,: in ecological terms. :e concluded that when the four karyotype ranges overlap distinct genetical and physiological differences between the karyotypes re-lt in sufficient niche differentiation to permit coexistence within the terms of the competitive coexistence principle.

The Arctic environment has been staled by Downes (1962, 196.1+) and, apart from the problems of the stringent clirmtic factors, it may be reasonable to consider the selective pressure in such situations as analagous to those already described as likely to operate in transient environments. - 211. - 7

Downes believed tat with respect to Fisher's sig:oid curve for realisation

of diversification, the Arctic fauna is still below the level at which

co-nyetition would be expected to cone into play (compare with conditions

for coexistence above and characteristics of transient environ-lents below) .

The same author has recorded a number of parthenogenetic species amongst

the chil-onomlas and simulilds. He has suggested that they may represent

relatively imperfect genotypes which, because of their advantages both in

colonisation and effective fecundity in a short reproductive season, are yet the best genotypes available to exploit the Arctic envtron-lent.

Unfortunately, in the absence of adequate studies of the ecological

significance of thelytoky, the problem of its evolution and maintainance alongside bisexuality can only be approached in a rather intuitive and

speculative way. But this review has at least shown that it, is too simplistic to consider all naturally accurring parthenogens as cases of a single phenomenon with universal basic Caus©. and consec;uence. 11 the evidence available suggests an adaptive state attained under different circumstances by independent means and in response to a variety of reouirements. Thus in attempting to interpret the phenomenon in P.errabunda all the foregoing possibilities must be considered.

Poly-mouhism,

The striking wing polymorphism exhibited in the genus Ftinella has been noted by a nu-iber of authors (e.g. ::attire;: s, 1872; Britten, 1926; Johnson,

19p). polymorphism is recorded in a large number of genera in a wide range of insect orders, all stages of wing reduction being observed from macroptery through degrees of brachyptery to aptery. Usually a species is monomorphic or dimorphic for its wing condition, but sometimes intermediate individuals are fairly common. There are essentially two kinds of problem associated with polymorphism; firstly how it is"engineered", whether by purely genetic determination, by physiological mechanisms, by c- -ironlentally - 25-

controlled switching mechanisms or by come combination of these. Then there

is the problem of how the mechanism, whatever it nay be, is arrived at and

stabilised by natural selection. Further, any polymorphism may ideally be either genetic in the sense of its having genotypes obligatory sedentary or migratory, or what is sometimes referred to as "non-genetic". In the latter all individuals share the same capability of changing during development in response to a particular level of some environmental factor. Of course this is incorrectly termed "non-genetic" since presumably the form and setting of the switch is genetically controlled. These two extremes represent an idealised situation, in reality polygenic variability results in mechanisms falling somewhere between -these. two. There ''is also a considerable amount of evidence 'to suggest that most polyElorphisms are a conbination of genetic . and environmental.

Physiological mechanisms underlying wing polymorphism have been the subject of much debate and are discussed by Johnson (1969). The most satisfactory general hypothesis that has emerged is known as the ontogenetic hypothesis. This suggests that behavioural responses associated with flight are directly related to a prT.rticular developmental stage of the adult, both being under the sane hormonal control responding to environmental factors

(Johnson, 1965; Kennedy, 1956). Thus migratory females are commonly sexually 1-rnnture. Southwood (1961) has put forward a more specific hypothesis to explain the determination of migratory activity in Keteroptera. Tie has pointed out the juvenile characteristics of brachyptery (perhaps the reduced level of eye development and pigmentation of other organisms can be considered in a similar way), and links them to environmental factors determining levels of juvenile hormone. This would explain the mass production of migratory individuals under certain conditions. 'Then low temperatures are associated with wing reduction, the - effect is due to excessive juvenile hormone - a state termed tlHefatbetclytl. "Frotothete1e on the other hand describes the depression of the influence of the same hormone at hiP-4 temperatures resulting -26-

in adult characteristics in larvae. The Ecteroptera as far as engineering

polymorphism are concerned would seem to represent e::amples of so-called

"non-genetic" or environmental determination.

Genetic aspects of wing polymophism have recieved little attention,

but a purely genetic explanation features in the work of some earlier authors

Jackson (1928) claimed that her breeding experiments with the dimorphic weevil Sitona hispidula supported the view that the brachypterous condition behaves as a simple !:enclelian dominant and Lindroth (194.9) adheres to the hypothesis that brachyptery is determined by a dominant gene, macropterous individuals being homozygous recessives. A similar idea of determination at a single locus was further developed by Brinkhurst (1960a and b) for aquatic bugs such as Gerris najas and Vella saulii where alates occur only rarely and ih localised habitats. He postulates a lethal allele (A) with a dominant phenotype. Thus the homozygote (AA) is lethal but the heteror,,ycote (Aa) produces a consistently short-winged phenotype. The recessive homozygote (aa) produces long winged or short winged progeny depending on the prevailing temperatures at vittelogenesis. High temperatures result in the production of macropters. Presumably the ontogenetic hypothesis may also be applied to this situation to some extent, in terms of "susceptible" genotypes. Brinkhurst has also suggested that the lethal gene had disappeared from many populations and species in the absence of selection favouring it. Such selection would, however, occur in temporary pools and similar unstable habitats where macropterous individuals are recorded. There is however, no direct evidence to support this hypothesis and such a common lethal gene seems inherently rather improbable. It is possible that controlled breeding experiments and detailed ecological investigation might generate a more feasible hypothesis.

However, Caswell (1959), although reluctant to speculate, has produced from breeding experiments, alatae which apparently have a genetic basis. In cultures of Callosobruchqs maculata the proportion of "active" individuals in the population was shown to decrease through time, a similar result being - 27 -

obtained by 'Teilington (1957) for 3,7alacoso3la. The results of crossing

individuals from the "old" cultures with "new" individuals showed a variable

percentage of "active" progeny. Crosses between "old" individuals produced

four point five per cent active progeny whereas comparable breeding using

"new" parents resulted in twenty--nine point two per cent of the offspring

being active. The implication is that the absence of certain unidentified

environmental factors selecttng for "activity" from the cultures resulted in

reduced production of the forms. Other genetic hypotheses concerning poly-

morphism are those of Kettlewell and Kinne. The former has postulated a

dominant gene (M) for migrants (Kettlewell, 1952) and the latter claimed to

have shown a genetic switch mechanism in C-ammarus duebeni (Kinne, 1953).

The evolution and stabilisation of wing polymorphism may be favoured in

terms of natural selection by a variety of environmental conditions. Hacknan

(1964, 1966) has reviewed the phenomenon in Diptera and Lepidoptera. In the

case of the Diptera he concluded that, with the exception of marine and

parasitic habits, most incidences are associated with what he called

"terricolous and geophilous" habitats. The view that the frequently observed

reduction of wings of species inhabiting islands is a precaution against being

"blown off" (Darwin, 1859; Huxley, 1943) he refuted, pointing out that the

species concerned are not generally found in habitats exposed to wind but in

cryptic habitats, often deep in forests. Similar arguements may be applicable

to brachypterous and apterous mountain species. Although cryptic habits are

also associated with wing reduction in some Lepidoptera, Hackman has suggested

that at least in some cases it can be explained in terms of the"reumann-Eggers;

Downes" theory of optimisation of reproduction in situations of environmental

stress and isolation. Reduction of wings or flight apparatus is normally

associated with a relatively_ increased reproductive potential. Presumably the

proportion of resources normally devoted to flight activity and development of

musculature and wings becomes available to increase fecundity. The first step - 28 -

in such reduction seems to be degeneration of wing musculature (Young, 1961).

The major exception to this is the positive correlation of wings with

reproductive castes af ants and termites (wilson, 1953). Dixon (1972)

compared the fecundity of brachypterous and macropterous alatae of the aphid

Drepanosiohum dJ.xoni and showed that the macropterous individuals that retained

the ability to fly throughout adult life were less fecund than the

brachypterous forms. This lead him to suggest that in this species the strong

selective advantage of wing reduction is increased fecundity. However, it

appears that Atillsfabae has a significantly different system; despite the

net reproductive rate of the al-tes being only seventy per cent that of the

apterae the intrinsic rate of increase of the former is only slightly lower

than that of the wingless morphs. This is apparently achieved by earlier

egg production by alatae (Dixon and IA•atten, 1971). The extent to which this

explanation can be extended to other associated forms of degeneration (eyes,

pigment) is not clear. Obviously selection will act more quickly if there is

also direct disadvantage in the maintenance of wings as might occur for

example in species that burrow or are restricted to movement in confined

spaces - examples of these might be termites and litter organisms.

In his extensive studies of Pennoscandian Carabidae, Lindroth (1949)

has suggested that the stability, restriction and isolation of species

habitats will all favour brachyptery. He rejected Darlington's view

(Darlington, 194.3) that the brachyptery renders an individual more viable

than its macropterous counterpart. Alternating periods of climatic stability

and variability such as must have occurred during th last Ice Age, Lindroth

maintained, would favour dimorphism. The noticeable concentration of apterous

forms along the rest coast of ITorway could be a consequence of the lam

glaciation when pockets of suitable habitat were isolated and their populations

subjected to strong selective pressure for wing loss.

It is generally accepted that the evolution or maintenance of migratory

members of relatively sedentary species has often taken place in response to -29-

selection pressures imposed by transient habitats (Johnson, 1969). The

occurrence of wing polymorphism is closely associated with populations in

habitats where aptery confers selective advantage, but where the same habitats

are.: suitable for only a limited period of time. The species must thus expend

energy dn the production of colonising individuals if it is to survive.

The concept of migratory activity related to habitat stability has been

developed over several years by Southwood in particular (Couthwood, 1960a,

1960b; Greenslade and Southwood, 1962) and culminated in his hypothesis that

the basic function of migration is to enable organisms to follow locational changes in their habitats (Southwood, 1962). The problem of distinguishing between trivial and migratory movements is unlikely to :.rise in considering

polymorphic species. Southwood (1960a)considered the population regulatory role of migration to be secondary but nevertheless of scPe importance in colonising species lacking any complex mechanism for regulation. Instability of habitats is a matter of degree, but Southwood gives many examples of habitats that must be considered. decidedly unstable, (these include several communities and organisms dependent on them, temporary pools, plant and animal debris) and he reviews the migratory activities of species associated with them. The relation of wing dimorphism to habitat instability is illustrated by Young (1961) for irew Zealand species of Corixidae and

1.rotonectidae. In unstable bodies of water subject to drought, the populations are almost exclusively winged individuals with fully developed wing musculature and pigaentation predominate.

The wing polymorphism in Ptinella generally takes the form of a distinctive dimorphism the alate morph having the' Leather wings characteristic of the family. TLe usually more numerous apterous forms are characterised by complete loss of-wings and eyes, and reduction.of_pigmentation. nngs are "prim Live" in the Coleoptera and their reduction has presumably taken place in response to selective pressures. Reduction of wings is frequently - 30 -

correlated with other changes in morphology In p:.,rticular reduction of ocelli

ana to a lesser c;:tent compound eyes. lialnus (1945) has discussea this

correlation suggesting that the chief function of the ocelli in flight is

associated with phototonus and equilibrial orientation (flying with the

dorsal surface upwards). Cornwall (1955) however has (leionstrcItel a close

relationship between the ocelli and the sensitivity to light of the anterior

:art of the compound eye in CalliThora (Diptera) and Locusta (Orthoptera).

ralmus further noted that the variation in reduction reaches its ultimate

form in certain Australian termites whose soldiers lack winrs, ocelli and

compound eyes. in f act the wingless morphs of Ftinella are equally ey:trene,

and there also eNists a range of polymorphic subcortical insects which

also be aczerThea as 4ternite-11',:e" in their almost constantly correlated

reduction of wings, eyes and riglon.tation (:ailton and Taylor, unpublished ra.s.)

Sl -alar reduction is also observed amongst other elliptic species - litter and

soil organisms and in particular troglodytes. Thus cave-dwel ling ptiliias

of the ',eller Fi-r-nilinn ana::aThinella (Joseph, 1882; Dybas, 1960) are

eyeless, wingless and pale in colour.

The degree of habitat stability is not onlyimportant in the evolution

of wing polymorphism but also plays a vital role in determining the ecological

strategies evolved by species. Such a role was inferred by Dobsbanshy (1950). He argued that in the fluctuating climates and physiological stringency of temperate areas, the most effective selective forces would be

imposed by factors of the physical environment. In the more stable ecosystems

of the tropics, the absence of gross climatic variation and catastrophes

should result in the maintenance-of populations around the level set by the

carrying capcity of the environment. Selection in such situations is

predominantly determined by biotic interactions.

Development of the concept of life historical strategics evolved, in

response to natural selection (Cole, 1954; Lewontin, 1965) resulted in the - 31 -

statement by Cody (1;66) of what he called the principle of allocation of

time and cnerGy. This postulated that the proportion of total energy intake

and activity output per unit of time that an organism directs towards

reproduction will depend on the stability of the habitat. In applying the

hypothesis to the consideration of brood size in birds Cody reasoned that the higher mean brood size produced by temperate species is a direct response to

the characteristic climatic instability, the latter, by inflicting density

independent mortality, prevents populations from reaching the carrying

capacity of their environment. In the tropics, however, where populations

tend to be regulated by population prossuTes in the absence of climatic fluctuation, selection favours individuals producing smaller broods. The consequent: energy "surplus" diverted from reproduction may be expended in increasing the chance of survival of the offspring. The maximisation of the rate of increase (r) and effectively of the carrying capacity (K) by natural selection in ecological strategies has been referred to by Irac...!Lrthur and

Wilson (1967) as r-selection and Kr-selection respectively. Species that are r-selected evolve towards maxi= production whereas E.-selected species tend to evolve towards maximum efficiency in the utilization of limited resources.

Effectively both types of species evolve towards maximum reproduction but they do so in different -days. The same authors considered the strategies that island species would be expected to exhibit. They predicted that although on initial colonisation species would be r-selected, once the community had reached equilibrium K-selection should predominate. Such a model is tentatively supported by Cody's data on clutch size in different

Geographical locations (Cody, 1966). The concept of r- and K-selection has been clarified by Roughgarden (1971).

Hairston, Tinkle and Wilbur (1;70) and Pianka (1970) have described the relation of strategy tc5• habitat in terms of a strategy continumwith r-selection dominating one extreme and K-selection the other. Recently - 32 -

Southwood, 7!ay,Trassell and Conway (1974) have more explicitly related

strategy to the temporal duration of the habitat in terms of species' generation time. They contend that if the time for which a habitat is

"suitable" for the species concerned is relatively little larger than the average generation length of that species, selection will favour individuals producing the maximum number of offspring to potentially contribute to the next generation in a newly colonised habitat. If, in such circumstances, the population exceeds K, this will not adversely ai'fect the next generation because it will be in_ another location.:_whengeneration time iS-shdrt-relative to duration of the habitat, K-selection, it is predicted, will minimise density dependent mortality and increase both overall efficiency of resource- exploitation and competitive ability . The concepts were expressed in a model which included a value for "overshoot" of the population relative to

K and the subsequent return to eouilibrium. Colonising species came within. the unstable extreme of the continuum.and thus. will' be strongly. r-selected.

Gadgil and Solbrig (1972) have considered r- and K-selection in terms of responses to density independent and density dependent mortality supporting their theoretical approach with data for weed species. This has resulted in predictions approximately equivalent to those of Southwood et al although. the latter authors' approach is concerned with community organisation.

The mechanisms by which reproductive output can be maximised depend on variations in the pattern of life histories. Cole (1954) attempted to determine the evolutionary factors underlying the variety of temporal patterns of offspring production showed (having first made several simplifications such as the very unbiological one that the population can be in exponential increase without check) that the advantage to a species of changing from a single litter to repeated litters was only about equivalent to adding one individual to the single litter. Clearly the impact of such an advantage depends on the brood size. The balance of the physiological cost of changing strategy against that of increasing the number of progeny should determine whether -33-

iteroparity would evolve in such a situation. Cole's models have subsequently

been modified and extended by Hamilton (1966) and Cadgil and Bossert (1970).

All these discussions emphasise that the relationship between brood size and

age at the commencement of reproduction in determining the capacity for

increase is very significant. Decreases in age of first reproduction have a

markedly greater effect on r than an increase in brood size. Lewontin (1965)

emphasised the importance of this relationship in strategies of colonising

species in particular. He predicted that selection would have acted to

minimise development time in such species under strong interdemic selection

by virtue of the high failure rate to which colonisation episodes are subject.

Further, any variability in development time would be similarly reduced

whereas that on fecundity on which selection pressure had not been so

strong would be expected to be greater. In the model that he considered, a

ten per cent reduction in the age of first reproduction should be eqUivalent

to an approximately one hundred per cent increase in fertility.

Ptinella fits into the category of a colonising species since it

inhabits a transient environment. Nevertheless despite its successional

characteristics the sub—oartical zone of rotting wood is comparatively rich

in species and thus a balance in evolution of polymorphism and strategies

somewhere between those associated with the extremes of the stability

continuum would be expected to have been evolved in Ptinella.

Although the problems of coexistence, parthenogenesis and polymorphism

and life history strategies have been considered indepndently in the foregoing review, it is evident that they are all closely inter-related in adapting

species to their habitats.

Taxonomy.,

Ptinella aptera was first described by Guerin-:Meneville (1839) being at that time assigned Ptilium apterum. It was subsequently transferred to the Genus Ftinella described by rotschulsky (184.5) and includes the formerly

separate species, pallida (Erichson) and tennuis (Siki) (Beseuchet and Sundt,

1571). The only comprehensive work on the Ptiliidae is Matthew's monograph

of the Trichopteryeidae (= Ptiliidae) (atthews, 1872). This includes

general accounts of the life stages of ptiliidis and also a description of the larva made from Ptinella larvae of undistinguished genus. A pupa of the

Ptiliidae was described by Perris (1846). These descriptions have been

critiscised by Hinton (194.1) who described the immature stages of

Acrotrichis fascicularis, and stated that the Ptiliidae are fungal feeders in all stagesof their life histories. Matthews (1872) had supported Ferris' view (Perris, 184.6) that the bettles are predacious, an inpression gained from examination of the mouthparts and behavioural observation. No account of the biology of the Ptiliidae exists in the literature apart from observations made by collectors on the species habits (Dybas, 1566). Thus, as with other members of the genus, the habitat of P.aptera is recorded as being beneath the bark of a variety of species of trees (e.g. Fowler, 1889). Matthews recorded the species from Europe and the Candy Islandsand Beseuchet and Sundt

(1971) report its distribution in Europe and Morroco, noting its more common occurrence in western Europe.

So great is the difference between winged and wingless ,morphs of

P.aptera, that GilImeister (1845). originally thought that the alate form was a distinct species and named it Trichoyteryx Ratisbonensis. The degenerate apterous morphs so typical of the genus (Britten, 1926) are almost always

(but see mention of P. cavelli below) more abundant than the winged forms

(Beseuchet pers. comm. and Beseuchet and sundt, 1971).

Prior to the commencement of.this study P.errabunda had not been distinguished from the superficially similar P.aptera. Detailed observations, however, showed that there was a separate species. often occurring with the latter, which was consistently distinguishable on taxonomical features of the genus - namely spermatheca and their thorax shape. This conclusion was - 35 - confirmed. by Johnson (pers. cor,t.i.) who described the species as P.errabunda

(Johnson, 1975). After a scrutiny of early collections, he recorded the older t specimen was one from Viandsor Forest, collected in 1925. As far as is yet known the species is Iyholl,y parthenogenetic since no Liales have been found.

Two further sPecies new to the British fauna are also considered in the current study. Ftinella ca.velli has been described from rew Zealand (Brown,

1893) and from Britain (Johnson, 1975) and. is notable for its size, apparent parthenogenesis, and absence of apterous forms. The other species Ptinella taylorae has not previously been described and was discovered during the course of this work. It is known only froia the British Isles and is absent from early collections. In his description of the species Johnson (in press)

Points out close similarities to 17ew Zealand. species. Zt is the opinion of

Johnson that P. errabunda, P.cavelli and F.taylorae have been introduced to this country from rew Zealand. -36-

SECTION 3.

Tal BIOLOGY OF P.APTL'In AND P.Eirt ?ABU:. IDA .:11TI

ADDITIONAL NOTES ON P.TAYLOaA3.

1.1 Habitat .

Ftilid beetles of the Genus Ptinella are found characteristically

beneath the bark of dead trees and in rotting wood. Of the whole dead wood

environment the subcortical Zone is probably the most faunisticly diverse and densely populated and it is in this habitat that F.antera, P.errabunda and P.taylorae are most- frequently found. The subcortical zone provides a habitat of high potential energy for species able to exploit it. Although only a for insects are able to utilise the cellulose directly by means of bacterial EITMbionts, saprophytic fungi are able to break down the wood and make it available to other organisms, thus supporting a large mycetophagous fauna. Two broad categories. of fungal decay of wood are distinGuishable: white rot is caused by. fungi that can Ettack aIl-oonstituents of wooa, whereas the brown rot is associated with fungi that are unable to decompose

These rots have differential effects on the rate of decay and properties of the dead reed and presumably affect the fauna dependent on them. Nevertheless many of the mycetophaes.are fairly cosmopolitan with respect to food supply.

P.utera and P.errabunda, are certainly amongst the more cosmopolitan of rucetophagous insects as gut analyses demonstrate (see 1.5 below) although they,.appear to be rather specific in their -physical recuirements, particularly the relative humidity of their micro-habitat. ::ark,cr of the woodrotting fungi show specificity with regard to tree species ana especially with the broad-leaved/softwood division. This specificity is not reflected by F.antera and P.errabunda, they have been collected from a ride range of tree species both broad leaved ana. SoftWooa. Any tendency for a particular species of tree to be more frequently populated by ------Ftinella than other species is almost certainly a reflection of the different subcortical conditions in the different tree species as they decay. The apparent "preference" for Pagus sylvatica -37-

observed durIng the study was at least partially due to its abundance and to

being the dominant species in much of the south of England where collections

were made. The apparently shallow rooting system of Paws in the topsoil on

chalk resulted in large numbers of wind-blown nature trees providing favourable

sites for Ptinella. Despite the abundant dead and dying Ulmus_2rocera,

Ptinella Ildre rarely collected from this species, in general the bark of

diseased trees dries out very rapidly and falls away exposing the sapwood

beneath.

The rate of decay of dead wood and hence, to a large extent, the duration

of its period of suitability as a habitat for Itinella, is highly variable.

A distinct pattern of increasing rate of decay with decreasing latitude can,

however, be observed. Thus in northern boreal forests the rate of decay

is sufficiently low to allow- timber in all stages of degradation to accumulate.

In the tropics, on the other hand, the turnover is generally very rapid. In

the temperate forest of Britain the variability is almost as etre_le

delending on the nosition of the dead wood. (An -oarticular its or

relative to solar radiation), its size, Its typo, its characteristic

susceptibility to decay and many other factors. Thus the succession of

decay may extend over more than 20 years in a lar-e fallen -,'arus or less

than 2 years on branches. Elton (1966) has distinguished four types

of rotting wood: (1) dead or ;;ring wood on 14 ving trees; (2) dead standing

trees or boles; (5) fallen logs (covering branches to cnti -- trees,

the important factor beinil; their contact with the ground); (4) dead stumps. All of these Blton records as having certain differences in their associated

fauna and fIora and Its develolnent. 'oth P.aYYte— —. oa and P.erraoncla have however, been collected from e=„,..iples of each of these sites on more than

one occassion, again suggesting their cosmopolitan habits. The decay of wood may start frpn laracitic attack on living trees, or via wounds or insect damage. Alternatively it may not commence until the tissue is already dead as a consecuence of senescence or being blown down by -33--

wind. The particular fungi attacking the wood are to some e.- tent dependent

on how the tissue has become susceptible to infection and laLarik (1974) has

considered successions of fungi in these two categories and further subdivides

them. On living wood there are successions associated with wounding,

_ parasitic attack, fire damage, and insect attack. Successions on dead wood

are based on whether the trees are fire killed, wind felled, felled and left

as trunks in contact with the grouna, and branches and slash. Such categories

are however, inadequate to describe the complexities involved. Cartwright

and Findlay (1958) have described the "double-frontea" attack on dead wood

that occurs in many cases, internal infection by Lasiaiorycetes resulting

in heart rot and the invasion externally by a great variety of both decay

and non-decay fungi and moulds. is decay proceeds there is generally a

concurrent shrinkage of the woody tissue (Cartwright and Findlay, 1953) and

with the drying and cracking of the bark, the latter tends to become detached

from the underlying saowood. However, this is not invariably the case since

it was observed diring the course of this study that white rot would often

proceed to an advanced state without the decayed sapwood losing intimate

contact with the bark and thus preventing the formation of a subcortioal

zone. On any section of rotting wood the subcortical zone is almost invariably

discontinuous and especially so on large trunks. A variety of fungal

successions may become established in different parts of the wood within

centimetres. of each other. It is impossible to schematise such successions It it (1 arik, .1974) due to the complexity of the interactions of all the factors, physical ana biotic, that affect them. such discontinuity with aifferi.ng

rates of decay probably renders the habitat favourable for species such as

rtinella for a longer period of time, different parts of the wood becoming

available at different times. This applies narticularly to trees that have

fallen entire; the smaller branches decay and dry out rapidly whereas the

decay of the bole may proceed over 'many years. Despite such variability - 39 -

there are recognisable p. ';terns of species in the dead rood coemunity. In

one of the few quantitative studies of rotting wood fauna, :rarer (1955, 1968)

showed that a croup of about twenty dominant sieclez occurred regularly in

natural and synthetic logs in contact with the ground. Although the dominance

within this group of species was variable, the pattern was shown to be

consistent. Larkin and Elbourn (1964) on the other hand, considered dead

wood in live oak trees (predominanty -Alecus robur) and E'oundea lower

diversity of species and a generally lower abundance. At least part of this

difference was attributable to the lower moisture content of the dead wood

not in contact with the ground. 2urthemore the fauna of wood on the ground

is supplemented by free exchange of litter species. Ptinella is not one of

these litter organisms, and has not been to en from litter samples during

the course of this stucy. P.aptera and P.errabunda are apparently confined entirely to dead wood and predominately to the subcortical zone. Hevertheless observations suggest that if the air ha-aidity is particularly high, individuals iday feed on the outer surface of the bark in cases where thls i s covered by moss and lichens.

The major physical factors affecting the distribution of insects in the subcortical region are moisture and temperature. The moisture content of wood shows considerable variation dependent on a large number of factors.

In the early stages of fungal succession the water content is generally high (:Aari, 1974) and results in a relative humidity in air s7Jaces In the wood of about 1R:.- Such a high relative humidity is suboptimal for many s»ecies of fungi. As decay proceeds the water content of the wood decreases permitting greater fungal development. in the later .stages of decay the dry atqosl:shere in the `.rood may adversely affect the fauna, Ptinella being

Particularly susceptible as a result of their requirement for high relative hunidity (see Section 3). However, the drying effect is counteracted by the tendency for rotting wood to absorb water from the soil and to became waterlogged by rain. even if whi_te rot occurs e::tonsively in the heartwood and sa-owood., an un,lecayed layer often remain- outside the sairc;oo: enabling an at 1-„I here of hih relative iimiiity to li,:rost in the o )bcortical sone.

The metabolic activity of the decay fungi contributes to the at lozpherc

moisture and the L,eneral resistance to decay of the bark which may fora a

relatively impermeable outer coverinP,reducing water loos from the zone and the orcanismo within it. The overall moioture content of the wood is further influenced, by its degree of e:,:josure, the amount of bark cover ana in thickness, its relationship to the soil and many other factors.

Temperatures in the subcortical reGion are similarly variable depending on many of the same factors that affect moisture content. Of these the degree of cynosure to solar radiation is most 1-anortant. Graham (1924, 1925) and Haarl/v and. Petersen (1952) have consj2ered subcortical temperatures and concluqe that for Jog, in full sunlight temperatures mau be as high as 46°C

(Haarl/v tersen, .1952 - ::ountain pine lo,-) and 65°C ('2A‘aham, 1921k - white pine lo). Such temperatures may be a limiting factor affectin: both fun,:al ,:;rowth and insect po2u1ations. 21ton- (1966) has referred. to the

"stel-.1 1 e" nature of clez:a 10,;.s c:..--,)020:7_ to full sunii,:;ht in open park-land.

The concept of rotting wood being an environment bu!!ered from seasonal climatic variations is clearly rather simplistic. But aor-filte the e::treme fluctuations in moisture and temperature, much of the subcortical one does show aelayed and reduce2 reaction to external climatic chan:es and can reasonably be called. 'buffered'.

Little is ]moim of the predators and parasites in the subcortical habitat al though 1.7ri:in and Llbourn (1964.) remark on the fotr-ntlaDly- difficult to e',11rilat sunTllY of yoey; r"e2a.lnly the diversity of or:anis is exists to emploit it. The only pred_ators actually observed. attachinG Ptinella were

Staphylinia beetles; on several occasions these a-cre seen ta::.Inc- 1 inella

athou,:h no other predators or parasites -;:evo identi-Piea qur4 n: the course of the study they unaoubtealy exist and. form an important fart- of the rotting. wood habitat. The =tent of 3car. od. as an env:.rontent in Britain has decfc,as:.i

consifcrably over the last thousand years (Hariond, 197)) as a lir,?ct

conseclionce of human activity; clearing forest to ma7:e arricultural land

available and rianaging remaining woodland. Such - Aanage.lint normally involves roll-loyal of dead wood as a precautIon against the s-orca'l of Cocay fungi that may be parasitic on living trues. Thus, des2ite the c::tensive planting or coniferous and mimea woodlana by the Forestry Commission during this century, the decline of rotting wooi has continued. This has apparently resulted in loss of a number of species associated with deaa wood from the

British fauna and has limited. the •distribution of others_ (Osborne, 1965).

Trnen woodland has peristed it is often only as isolated patches ana this too ha: p,'esumably contributed to the decrease of many dead wood species whose dispersal powers are often limited.. The major remaining areas of forest providing a continuous rotting wood environment are the remote forests of upland. Britain and, in southern areas,.the oha royal hunting forests. :alch or the collecting of material for the current study was carried out An those latter areas in ';iindsor Forest and the 7ew Worest in particular, part of the former area having been designated for the preservation or the lead wood habitat.

The habitat is de-cribed further on the basis of detailed observations in Section 2.

1.9 DiSt"IbUt1031..

3z;: s-,-,ec4es of It4 n211a are currently founa in rotting wooa in the

British Isle-. Or these r.al.teraana F.er.f2Z-mnaa are the most wLa-spr--;aa ana abunaant although r.eavelli_ is a-oparently increasing ra,icUy. I

lonticollis and. ine11a it (:Iecr) are all rccorded from Britain and =nropc ( Besuchet and. Sundt, 1971). ::ol,evcir, no such records emist for 7' csvelli• and. F.t--710,--0 The major diagnostic character of morpholo-y used in deterainln: the ta-lono .ic relatonshp of

Itinella is the si.aye of the -flnrm-tir,c-t in this way it is possible to

suGcst oriGIns of these species, which are probably lccr,.ely restricted in

Europe to Britain, by deterqinins the distribution of their closest relatives.

Johnson (1975, in press) has added Y.errabun021, P.cavelli and P.tclorae

to the British list and by detailed examination of early collections of

Ptiliidse has established the earliest recorded dates of the species beinG

found in Britain. The earliest known specimens of P.errabunda are those

collected by Donisthorpe from "Andsor orest in 1925. HavinG initially been

identified as Y.aryeera, Johnson's re-oxanination has shown them to be

P.errabunda. The first specimen of P. cavelli found in this country was

taken in 1936 from Temple, ::idlothian. P.errabunda and F.cavelll are easily

dlstincuished by the lar,e size and consistent presence of wincs in the

latter srecie-,. .tavlo,-ce is very similar to P.errabunda in size and ;:eneral

appearance and the shafe of the spermathe=3.reseble each other clo-ely.

7:owever3 F tavlorce" -7,"— only discovered during the course of this work when

it was identifies in a collection from Furnace, Co. :"ayo, Ireland, ;'?:de in

AuGust 1975. Cubscuiv-ntiv a male 1-Linella collected v;ith r.errabunda from

2reshfield, LanOashire by Johnson in 3epte_lber 1972 1 identified then a,

.14a2:Lreon re-ex aril is thought to be 1-4LZ_orc_2 (pers. conn.),

particularly as the s-ocles has more recently been collected fcom the same

site. _Pro-, conp,7.rison with other Ftiliids, Johnson concludes (pers. con'.)

that both these srecies are of :ew Zealand oriln, in the sper..:_theca

shape shows stronG similarities to those of at least two known :ew ealand

sfecies - Ftlnolla and watt. Other less 'L:i.1C.f f,"DCC:I.CE are recorded rran::adaG-a-car, Tristan da Cunha and :Jt. Helena. ::one of

the described :]"_:.^o-!?tan species -ticular resemblance to F.erra-ounda or F.tavlorae as far as sperwLatheca shape is concerned. F.c-vellj au:,.nod"

17ew Zealand species already described in that country where it is apparently one of a Group of very snecics. It is thus, reasonable fer.Johnson - A.3 -

(1975) to coneDn(7e that all Vireo sIec:;cs are relat1vily recent introThctions

from row Zea1and.

The recorded distributions of P.a ,,tera P c-rlscbundc and F.tm-lorae are

given in Figures 1.1, 1.2 and 1.3. F.a-te.('a has been recorded throoghout

much of 2ancland and has been collected from a single locality in Scotland.

During the course of this work the species wJ.s. found to predominate in many

of the localities whenacollections were made. These uere based lcrely in

the south or :nsland and in particular Ber:sii:e, 3-crry and Ha_Tr:li-r.e. In contrast Johnson (1975, pers. coal.) reports that P.crrabunda is consistently

--'.ore abundant than P.aora in his collections concentrated larL;e3,y in areas of central and northern Britain. P.errabunda has also been recorded through- out southern Britain although in certain areas such as 'dindsor Forest, the

1:ew Forest and various Faf;us gavatica woodlands on the Borth Downs in

Surrey, they were rather localised in distribution. It is thus concluded that the distributions of tera and P.errabunda certainly overlap on a geographic scale although the latter species is more widespread than P.autera.

The distribution of P.ta-lorce in Britain (Yisure 1.3) is apparently very limited and restricted largely to western coastal areas notably Furnace and Pontoon in Co. L'ayDwestern Ireland, Kilve and the Quantociss Hills in

Somerset, the 2orest of Dean (all collected during this study) and from at least three sites in South Lancashire - For,aby, Ainsdale and. Preshfield

(Johnson, in press). The proximity of such sites to the major Darts of

Bristol and Liverpool is noted by Johnson, the Irish sites are however, somewhat problenatical in tills context.

The hew Zealand species 1.cavelli is such _lore cos_opolitan in its distribution than P.taid= although it aimears to be restricted largely to northern Britain where it seems to be extending its distribution. It has been recorded in large nuubers from sites in northern Bngland by Johnson

(1975) but was encountered on only one occasion in the current study, at a - 41 .. -

..

Ptinella ..

..J Hll!',, ... • leo ,

9 o I~

J'I' I l' ~"~f\ ,. ,'t--t-.-.-----!~...x:::j / v~--~'~·~------+_------I_------4_------~------~~:.----~O '~ t:: o .. ,

Figure 1.1 The l:norm dintribution of F.f:l~t.EE::§:' in the British Isles.

(dc.'1tr. Jolmson e.nd collections). - 4-5

.. \.Y.V' ,.., !-~. Y 7" .....17 17 ~ ..2 r~ - ~' I ~ , ~~~ 1 _,9- Ptinella ~~ ,II • .. '( ~ errabunda ~~~ ,,1 '\,)I. ,.'" o. t~~~ I, ~' r""I... i;.1 1/ I .. 7 R ./. 0 11M, .JI"'~ . I I ,), ~ . Hlll', ) . . I ... • , lee J . ~,.t-~ j , ~ J.7 .: .. A-l ....l: ~ ~.; .'"~ ~ \J ~ N""> ..., « n I' 5 I- ~~ .J - "I'" ,. t" J1fI ~ / ... \ II( 'rY' l J/f I" ~ "" ~ I ... " ", - ~~~ .<1\ ~ , ~..., 11 --, , 7 J I ,~ 1 .tf1Y • IJ l ~. ..-. ... ~ ...J' ... I'" J"'1' .a -:.... oL .- ,;...... :z 1;;. 17;"'- " m "',= l'.>: -I ...... --. II'"'" 0 ,. • I ( III I"" ".,. 0 1 0 , . 7 OI!! ~ or::: .... r ~ ° r1'- ...... 1- .J .11 J. - )- I!J'. .~J-i.. '<'"i~11 t:J ~ ,~ ., v / ,. r\ .~ , /.'. .. 0 1 :. of

Figure 1.2 The knorrn distriou-cion of P .~~1-:£"OUl1~ in the British Isle s

(clata Jolmson e.nQ. collections). - 46 -

I ,.. , .. ", ....

I '~~~~++~HHH++++++rHH~~++~~~ { ,

A

IJ 1 l . .In ~" w~~R+~HH~+r~HH~~--~ ~ r

t o o,:::t:====+=~ It oJJ ..a. '"

M-v--~U+------+------~----__ ~ ______~ ____ ~~~----~O/" -c . 0 J ,

Figure 1 . 3 The known distribution of R taylorae in the British Isles (data collections and Johnson) - 4.7 -

site in a valley on Dartmoor near the village of ronsworthy. This is

undoubtedly the southernmost extreme of its range recorded to date. Freviously

Carmarthen was considered to be the limit in range in a southerly direction.

1.3 Life history.

There are no published accounts of the life history of any species of

Pstnella and the taxonomic descriptions of the iumture stages given by

::atthews (1872) and Ferris (184.6) are regarded by _Tinton (1941) as inadecuate

and misleading. The latter author has described the Laimature stages of a

species in another ptiliid genus - Achrotrishis fascicularius (Herbst).

The immature stages of P.a-otera, P.errabunda and P.tqlorae and their

course of development are very similar, and where no distinction is made the

,following account applies to all three.

The eggs are deposited singly or in groups, in cracks and crevices in

the lower part of the bark or the sapwood. They are ovoid 0.4 mm long,

0.2 ma wide, opaque and cream in colour slightly tinted with a shade of

pink (Figure 1.4). The surface of the egg is externally sculptured and the line of the dorsal cap is just visible becoming Dore indistinct shortly before

eclosion. The larva emerges by forcing open the cap along the pre-marked

line apparently by exertion of pressure -by the head. -3closion is complete

within a couple of mlnutes. The observation of all stages throughout the

year suggests that eggs are laid more or less continuously, the beetles

thus being multivoltine. In general, is Mature stages were rather less

abundant in winter presumably as a result of oviposition and developmental

rates decreasing at low temperatures (see Section 3). Females seem to show

no consistent pattern of behaviour as far as oviposition sites are concerned.

Sometimes the eggs are laid in large nuwCoers. in a group of up to 20, even

on top of each other on.spme occasions,but at other times they are deposited

singly. Possibly the availability of suitable sites determines whether

the eggs are laid in groups. Unfortunately little information was available

concerning ovipositioh in the natural habitat since the eggs were seldom -48-

found due to their small size and the structural complexities of their

microhabitat.

The larvae (Figure 1.5) are of the primitive coleopterous type described

as campodeiform (Boving and Craighead, 1930). Such larvae are normally

associated with a predacious habit and it was the opinion of Perris (191..6)

and. Hatthews (1872) that Ptinella larvae are subcortical predators. However,

this belief has been repudiated by Hinton (1941) and there was no doubt

whatsoever from the observations made in this study, that the larvae and

adults are primarily mycetophagous. Not only have all active stages been observed feeding on fungal hyphae, spores and yeasts in culture, but gut

analyses of wild caught specimens have confirmed that these items form the basic diet in the natural situation. There is no obvious difference between the diet of adults and larvae although the more extensive gut analyses of adults (Section 1.5) show that algal cells and a certain amount of unidenti- fiable material are also taken. That the spore contents are utilised by the animals is suggested by the presence of many ruptured spores in the

posterior region of the gut. Since the larvae are not predacious but nevertheless are campodeiform, this could perhaps be an adaptation for predator avoidance. As, effectively, herbivores they are highly susceptible to predation and their adaptation for active locomotion presumably increases their efficiency in avoiding predators. Their behaviour is characterised by brief spells of rapid movement in an approximately straight line followed by a second's hestitation and often a change of direction, before locomotion comiences again. Such activity is observed in cultures and also when bark is removed exposing the subcortical zone. The reaction on being disturbed in this way appears to be a more exaggerated form of the normal activity.

This form of behaviour is probably typical of many Ptiliidae since it has also been noted for A.fasicularius by Hinton (1941). Presumably the high degree of mobility not only enables the larvae to escape from predators but permits them to move to more favourable areas within the subcortical - 49 -

Figure 1 . 4 Ptinella err X100

Figure 1 . 5 P. aptera instar 2 larve-X100

Firure 1 . P. artera riipaX100 -50-

zone when conditions become suboptimum in one particular area.

In natural and cultural conditions larvae are sometimes observed in

dense aggregations. Often such groups are associated with localised abundant

sources of food such as mats of fungal hyphae or patches of sporulating

moulds. On other occasions aggregations are not so clearly related to any

obvious factor and the possibility of some form of proto-social grouping

cannot be entirely dismissed.

Three larval instars have been observed in each of the three species.

Uo differences were discerned between the larvae of these species and thus

in all experiments where larvae were used, they had to be taken from laboratory bred pure cultures derived from adults of known species. Furthermore the only apparent difference between successive instars is the overall size.

3.:easurements of the. total length of larvae and the width of the head capsule were taken from individuals, mounted live in a drop of water on a microscope

slide. The individuals were. observed under a magnification of x150 and the dimensions noted by means of an eyepiece graticule. The animals were measured alive since specimens preserved in alcohol showed tremendous variation in the degree of distension of the abdomen. However, the variation was insufficiently reduced by this method of observation to determine any significant difference between the lengths of the different instars. Themean head capsule widths of thirty larvae, ten from each instar (the instar number being determined by recording every ecdysis for each individual reared in isolation) are presented in Table 1.1 together with the results of application of - student's t-test to the data. The results snow a significant difference between the head capsule widths of the three instars for i'.antera, however, the possibility of significant variation between populations could not be eliminated since relatively few larvae of known instar were available for examination. The few measurements made on F.errabunda larvae were of tLe same order as those for P.aTitera thus precluding any simple distinction of the two species larvae. Tt was concluded that without more extensive

- 51 -

Table 1.1. ;:ean values of head capsule width in different larval instars of P.aptera with results of Student's t test for significant difference.

unit .7 0.0 2 trim Lean width head capsule in units Standard error

Instar I 7.71 +0.09 Instar II 8.78 +0.09 Instar III 9.62 +0.05 Comparison t value degree of freedom probability Instar I and instar II 8.54- 18 P < 0.001 Instar II and instar III 7.83 '18 P < 0.001

Table 1.2. Lean proportions of different gut contents in adults and larvae of Ptinella.

Mean proportion gut contents with standard. error. (sauple size in brackets)

Species: P.aptera P.errabunda Gut contents Aseptate septate hyphae Aseptate septate iiyphae spores spores spores spores

:axed population 0.77(5)- 0.21(5) 0.02(5) 0.70(5) 0.27(5) 0.03(5) field caught daults +0.19 +0.20 +0.02 +0.19 ±0.19 +0.02 Single species populations field 0.61(5) 0.54(5) 0.05(5) 0.54(5) 0.33(5) 0.13(5) caught adults +0.19 +0.21 +0.04 +0.17 +0.18 - +0.15 Single species populations laboratory 0.58(5) 0.38(5) 0.03(5) 0.77(5) 0.42(5) 0.01(5) reared larvae +0.1 +0.19 +0.02 +0.19 +0.24 +0 lamed population field caught larvae 0.57(5) 0.40(5) 0.02(5) (snecies indist-. - inguishable) +0.23 +0.24 +0.02 - 52 -

measurements of a much greater number of individuals, larvae of different

instars could only be reliably distinguished by observation of their

development from the e;gg stage. The duration of the larval instars and of

all the developmental stages is somewhat variable depending on prevailing

environmental conditions, particularly temperature (see Section 3 for

experimental data). The humidity requirements of the larvae are discussed in Section 3. Following ecdysis to the third instar and a subsequent period of

active feeding of variable duration, the larva becomes generally inactive

and passes through a transient non-feeding prepupal stage prior to pupation.

This stage is marked by a general swelling of the thoracic region and an

overall shortening of the body. The prepupa has normally become attached to

a suitable substrate by the tip of the abdomen. In laboratory cultures, where

the substrate was plaster of Paris, a pupation chamber was often excavated

from a small hole or bubble in the plaster. Such sites are difficult to

observe in their entirety on wood since removal of the bark tends to destroy

the upper covering of the chamber. Nevertheless it seems likely that where

the substrate is suitable, excavation of a pupation chamber occurs.

The pupa is obtect (Figure 1.6) and is creayv white in colour. A day

or so before eclosion of the adult, the pupa becomes progressively darker.

Nevertheless, the callow adult is pale yellowish in colour on emergence and only gradually darkens during the-pre-ovipasition period.

In each of the three species there are two adult morphs, a "reduced"

apterous form and a fully developed winged morph. P.aptera and P.ta:.lorae

are bisexual, but P.errabunda has only been found as females. Furthermore,

eggs have been shown to develop without fertilisation to produce normal adults

which also produce offspring from unfertilised eggs. No evidence was found

for any form of gynogenesis, such as that found for Ptinus mobilis (itoore,

Tioodroffe and Sanderson, 1956), since spermatozoa were never observed in the

spermatheca of any specimens, either taken from natural conditions or reared - 53 -

in cultures. It is therefore concluded that F.crrabunda reproduces by

thelytokous parthenogenesis, In the bisexual species the sexes are not distinguishable externally. Furthermore, it is scarcely possible to separate the three species without examination with the aid of a microscope. After a certain amount of collecting experience however, if two of the species occurred together it was often possible to make a fairly reliable distinction based on a subjective impression. In particular, with mixed populations of

F.tvlorae and P.errabunda, the former species was generally, recognisable by a slight tendency for it to be darker in colour and greater in overall size. In order to examine the animals under the microscope, it was necessary to imobilise them, since otherwise they continuously move around preventing the anatomical features characterising the species from being observed clearly. Conseruently a method for identifying the species alive was developed and this also enabled the sexes to be distinguished without killing the insects and dissecting out reproductive structures. The method consisted of placing an individual (or sometimes as many as five together) in three or

four drops of distilled water from a finely drawn Fasteur pipette, on a microscope slide. The animals were held relatively immobile beneath a 15 m diameter coverslip which was gently lowered onto the surface of the drop.

Often the beetles were still able to move around to some extent and occasionally if too much water was usedl they escaped. Kevertheless, it was normally possible to examine the animals under x150 magnification on a Wild 120 microscope. The spermatheca in females and the adeagus in males, were usually visible through the cuticle and body- wall thus enabling the animals to be sexed with absolute certainty. If these structures were obscured by body contents or other structures it was often possible to discern them by means of phase contrast microscopy. The diagnostic species featUres of spernatheca and thorax shape were likewise distinguishable by means of this method. The beetles were ayTarently able to withstand periods of at least five minutes, held in drops of water as described, without any discernibly adverse effects; the greatest source of mortality was a result of the water

evaporating underneath intense illumination and the coverslip squashing the

insects. With practice it was possible to identify and sex individuals of

all three species with negligible mortality. Animals were removed individually

from beneath the coverslip by means of a few hairs on a paint brush.

P.aptera was originally described by Guerin-Meneville (1839). Both of

the apparently new British species have been described by Johnson (1975, in

press). The three species are, as has already been described, separated on the basis of the shapes of the spermathecae (Figure 1.7) and to a lesser extant the thorax (Figure 1.8). The spermatheca shape is the more reliable

characteristic since the thorax shape shows a certain amount of variability both within and between populations of each species. The spermatheca of

P.aptera is clearly distinguishable from those of P.errabunda and P.taylorae,

appearing oblong with a sac-like bulge at one end. The other two species have very similar, almost ring-shaped spermathecae, that are only distinguish- able by subtle differences in shape and proportion. However, the shape of

the pronotum facilitates separation of the two species. In P.errabunda the

sides of the pronotum are rounded but in P.taylorae and indeed in P.aptera

also, the posterior side margins are sinuate. P.taylorae and P.aptera are also separable with reasonable accuracy by inspection of the thorax, since the indentation of the pronotum is slightly greater in the former species

and the anterior sides are less rounded. Furthermore, the subjective

impression of the larger size of P.taylorae is confirmed, that species being

slightly longer than Eaptera. The differences between the two morphs are consistent for the three species. The apterous morph is pale yellowish brown and eyes and wings are absent (Figure 1.9). In the elate fora the feather wings characteristic of

the family are fully developed and are folded beneath the elytra, the apices of which are ►ore rounded than those of the apterous form. The compound eyes are also well developed and the overall pigmentation is heavy, giving

- 55 -

Figure 1 . 7 Ptinella spermathecae X 400

P. tavlorae

7;--,ire 1 . Ptinella thoraces X 100

F.tEvlorae P.erral,unda

Tirure 1 . 9 Apterous adult P.aptera x 100 - 56 -

the insects a dark brown colouration. An "intermediate" form was also observed to occur with a very low frequency. This form was paler than the alate and although the compound eyes were present they were only poorly pigmented. The wings appeared to be shorter than those of alates suggesting a parallel reduction to that recorded by pybas (1966) for Burygyne intricata.

Nevertheless, on detailed microscopic examination the wings were found to be fully developed with the appropriate number of marginal hairs, the reduced appearance being due to a lower degree of pigmentation or chitinisation of the hairs and of the animal as a whole. It is not clear to what extent this is a consequence of some deficiency or failure during development, or even a recurring mutant. On the other hand it may merely represent an extreme form of phenotypic variation.

The feather wing in Eurygyne has been described by Dybas (1966) and a general and rather inadequate description was given by Liatthews (1872) for the family as a whole. Both authors remark upon the consistency of the wing structure within the family with the notable exception of Nossidium and genera related to it. The wing in Ptinella is essentially the same having a long, narrow, sclerotised proximal section which phases into a more flattened distal section on which marginal hairs articulate. The entire surface bears microtracheae. The marginal hairs are long, and flexible at the base where they are almost transparent as a result of reduced chitinis- ation. The wings are normally folded beneath the elytra in a characteristic pattern described by Forbes (1926) for Achrotriuhis and by pybas (1966) for

Burygyne; the pattern is the same for Ptinella. Folding starts with a convex bend at the base and subsequently follows concave, concave and convex transverse folds. When the wings are folded, the marginal hairs are visible ihrough the elytra lying Tarallel to the margins of the wing struts. The extension of the wings has been observed to be variable, taking place very rapidly on some occasions but less rapidly on others when the rings may be carried partially unfolded, but still beneath the elytra, for a period of -57-

time. The re-folding of the wings is usually rather slower and both

activities have been observed to be associated with rhythmic contractions of

the abdomen. Presumably hydrostatic pressure is the underlying mechanism.

The exact stimuli that elicit a response of flight activity in Ptinella

are obscure, although in the laboratory it appeared to be induced in some

instances by an increasing heat or decreasing humidity stimulus as individuals

were held under a bright light source. It was not possible to discern from

observation whether flight, when it occurred, was active or merely passive

relying totally on air currents. There has been much discussion concerning

the aerodynamics of flight activity in very small insects and the controversy

as to whether it is active or passive in feather winged species remains unresolved. The incidence of the morphs is discussed in Section 5.

In addition to actual flight, alate individuals show a high decree of activity particularly under conditions of increase& temperature and reduced humidity. Unlike the apterous morph they are apparently positively phototactic and move away from the subcortical zone to the surface of the bark, from where they presumably disperse. However, there must presumably be a form of threshold for flight activity that permits dispersal by flight, but also ensures colonisation on landing on a potentially favourable habitat. Some kind of reversal of the phototactic response is apparently implied. The mechanism controlling this behaviour is probably hormonal but under environ- mental control. Although the responses of either morph of Ptinella to light were not investigated during this work, what could be termed mass disp,:rsive or migrational activity was observed. In one situation a colony of P.aDtera was maintained in a perspex culture box containing pieces of wood. At one corner of the box a tube lead through into a plastic container; the culture box was covered with thick, black cloth but the other container was left' uncovered. ,'Then the box was exic]ined after a period of time, it was found that a large number of alates had accumulated and died in the small plastic container exposed to the light. On opening the. culture the wood was found - 58 -

to be fairly dry, although there were still apterous Ptinella on it and it

undoubtedly represented a more favourable environment than the small plastic

container. It was also observed that most of the alate females had been

inseminated, implying that mating may occur prior to dispersal. There is

also some evidence to suggest that a tendency towards dispersal may occur in

alates in the total absence of light. In many of the competition cultures

(see Section 4) that were maintained in darkness in constant temperature

rooms, large numbers of alates (apparently the vast majority of the alate

population) were found dead around the rims of the butter dishes where the

lids fitted. It is suggested that a sharp increase in activity relative to

that of apterous individuals resulted in accumulation of alates where dead

apterous beetles were seldom found. Presumably such dispersive activity

would carry them on to the upper surface of logs from where they could fly

or be blown off by air currents. Possibly the major function of the eyes

is to ensure that the alates move towards the light and consecuently away

from the surrounding litter where a simple activity response might take them.

The apterous adults of Ptinella are Often found in large nuMbers beneath

bark, feeding in a similar manner to their larvae and apparently on the same

food (see above). Their locomotion is reminiscent of that of the larvae

but the frequency of stopping and turning appears to be rather less and the overall activity is lower. Immediately after bark is removed, or the animals

have been disturbed in any other way, the beetles "freeze" for a few seconds before fleeing under adjacent bark. Contacts between beetles in crowded

situations are frequent and normally result in a brief pause during which

the antennae may touch and are moved especially rapidly. Subsequently they normally retreat before turning and moving off.

:sating behaviour in Ptinella appears to be relatively uncomplicated but has rarely been observed, although what are assumed to be males have been seen to pursue other individuals (their sex was not distinguished).

If a femle iwas encounered and submitted to the male's attentions, -59-

copulation took place, the pair appearing to remain coupled facing in

opposite directions for some period of time - at least several minutes.

Further details were not clear. On insemination the spermatozoa are passed

into the female enclosed in What is interpreted as being a more or less

spherical spermatophore. This passes up the spermatheca duct to the

seer: atheca where the spermatozoa are maintained ready to fertilise the

eggs as necessary. Subsecuent to a pre-oviposition period of variable

duration and to mating, the eggs are fertilised and matured singly in the abdomen. The rate of maturation Llay be very rapid, the egg increasing in

size until it almost entirely fills the abdomen in a matter of hours. I/ maNLaula number of 5 eggs have been observed to be matured in F.antera over a period of 24 hours at 30°C. In the parthenogenetic P.errabunda the eggs develop without fertilisation, however their aaar:iLluia recorded rate of maturation was only 1.5 per 24 hours period. Whether this is a conseouence of their Parthenogenetic reproduction, or whether they have an intrinsically lower fecundity, is not clear, although the fecundit . of the ap=entl,r related, bisexual P.ta,Tlorae is of the came order. Since the hi :h rates in r.al-Itera were only achieved at 30°C, at which temperature both F.errabunda and P.trlylorae were unable to survive to breed, suggests that the greater rate of egg maturation in P.aptera is at least in part a consecuence of increased metabolic activity at the higher

1.4 :rotes on mor.pholoz.

The internal Idoriphilogy of Ftinella has been briefly consilered by

.172,tthey:s (1872) in his monograph on the Ftiliidae. The :lorpholo--,r of the digestive tract is descrilJed together with an.account of what he term 5 the

"reproductive organs" but which is in fact restricted to the (1.1.es..,:as and spermatheca. During the current study an attempt was made to elucidate the structure of the ovaries and the testes. Lccauae of the diminutive size of the beetles their dissection to exPose internal organs was extrel...a,y - 60 -

difficult and rather haphazard. The following technique was used: an adult

beetle was killed by asphyxiation with carbon dioxide, and placed with its

dorsal surface uppermost in a groove in a small 'bed" of molten wax on a cavity slide. The cavity was then filled with insect saline. The procedure was carried out under the high power objective (total magnification x50) of a stereo microscope. A tungsten needle, drawn to a fine point by electrolysis, was then used in order to remove the cuticle from the dorsal surface of the abdomen in such a way as to expose the internal organs. Unfortunately this part of the procedure was very difficult to perform since the cuticle was relatively tough and as it was removed, it more often than not carried most of the body contents with it. Without micro-manipulation equipment a tungsten needle was the only instrument that could be controlled with sufficient accuracy to effect any form of dissedtion of the beetles. Once the cuticle had been removed, any organs that were distinguishable could be removed on the end of a finer tungsten needle and mounted in insect saline beneath a coverslip, for examination at a higher magnification and using phase contrast.

Despite an extensive search the expected acrotrophic ovarioles were never conclusively identified. The male reproductive organs were, however, often clearly visible through the intact body wall, their presence being distinguished by the extremely long spermatozoa. On dissection and more detailed examination it appears that a single testis is present as an enormously enlarged_ body in contrast with the normally small size of the organ in comparison with the female reproductive organs. The testis is elongated and sac-like and when dissected out exceeds the length of the abdomen; consecuently it is curved almost into a complete ring in the abdomen. At the distal end the spermatogonia are visible and subsequently zones of maturation and transformation are distinguishable. These zones are concentrated in the most anterior part of the testis, the remainder accomodating the mature spermatozoa. The average length of a single spermatozoan is about 2.0 ma. The modification of the testes, is thus apparently to facilitate production and accomodation of the - 61 -

relatively enormous spematozoa. The significance of the size of the spermatozoa of Ftinella is unknown. As a result of their large size, it

seems likely that only relatively few sperm may be stored in the female

spermatheca at one time. Thus regular reinsenination is required to enable the female to realise her maximum reproductive potential in favourable

environmental conditions. Clearly further information is required on the detailed structure and functioning of the reproductive organs, sperm transfer

and fertilisation, in order to determine the selective advantage associated with the evolution of such a modified male system. It is interesting to note the apparent normality of the female reproductive system in P.errabunda,

although again the ovaries were not identified. The spermatheca shows

remarkably little variability in shape and size, which is perhaps surprising

since it is functionless in the species as it appears to exist in this

country. In several thousand individuals examined, none had spermatozoa

in the spermatheca. If an organ is functionless for any length of time, selection ceases to act to maintain it in its most optimal achieved form..

This generally results in variation and ultimately in atrophy. Dybas (1966) found a similarly high degree of uniformity in the spermathecae of partheno- genetic species of Bury me and he concluded that the method of reproduction

was probably of recent origin in the group. It is also conceivable that in

its country of origin (almost certainly New Zealand), P.errabunda might now,

or at least in recent times, have had a bisexual race or closely related

species with which genetic exchange has tai place. An attempt, was made to determine the chromosome nuldbers of

P.errabunda and P.taylorae in order to suggest possible phylogenetic

relationships betreen.them, in particular to determine whether the partheno-

genetic P.errabunda exhibits polyploiay as do many thelytokous species. Two techniques were used initially in an attempt to observe the

chromosomes - the aQetrorcein squash technique (Grimstone and Shaer, 1972)

and a rapid. Feulgen squash method (1.1aQDonald and Harper, 1965). . The former - 62 - was ado-eted for extensive use since it wes very cluick and simele and apparently

Cave completely adevate results. A survey of chromeomee in Coleoptera has been made by Smith (1953, 1960), however, no Ptiliidae were included.

The chromoson number is most easily distinguishable at metaphase of cell division; however, the location of actively dividing cells is often problem- atical. Robertson (1966) used gonads of adults and the brains of larvae- for chromosomal analysis of the Chrysomelid beetles of the genus Callierepha and remarked on the particular usefulness of the testes as a source of materiel eSi3Alarly John and Shaw (1967) used material exclusively from the testes of two day old adult male Dermestid beetles. Other authors, however, have concentrated on larval and pupal material in investigating

Coleopteran chronosomes. (Sanderson, 1960; Takagi and Takeshi, 1966). Since the testes of male Ptinella (P.aptera in thin case) were fairly easy to re: ove intact from the body, investigation was concentrated on gametogenesis divisions in, the male germ cells; it was from these that the only succeererul preparations were obtained. In many species there is only a brief iDeriod, normally at the beginning of adult life, when production of spermatozoa takes place. Although it was not possible to accurately determine the age of Ptinella from which successful preparations were obtained, it seems that spermatozoa formation is not confined to a single period of adult life. In most of the preparations actively dividing cells were not visible and thus the chromosomes were indefinable. However, on two preparations cells were observed undargoingemeiotic division and sets of chromosomes observed from each are reproduced in Figure 1.10. The chromosomes are minute end even at a magnificationof 15000x it was not Dossnlc to distinuish conclusively which ::,ctaphas/anaphase was to2.:;n; place. 7:evertheless, hay were interpreted'asel2 pairs of chromoeoelen ,:7ore EL7tin;.puis:IeL.

1.5 C-ut analyses of adults and larvae.

In order to determine the feeding hebits of adults and larvae of F.retera - 63 -

Fic,ure 5.10 P.aptera chromosomes from testes of adult.

Magnification X 4,000 and P.errabunda, and in particular to deteriline whether any significant difference in diet exists between the two species, gut analyses were carried out on field caught (adults and larvae) and laboratory reared (larvae) individuals. Methods of diet analysis that have been applied to species of

Collembola, a relatively unspecialised group of detritivores, and their limitations, have been considered by McMillan and Healey (1971) and Anderson and Healey (1972). These authors have developed a quantitative technique, of analysis to investigate the diet of coexisiting Collembola. The method_ involves filtration of gut contents from a sample of individuals onto a

Millipore filter from which a sample of grid squares are selected randomly and the number of particles of various categories are scored. An attempt was made to apply this technique to Ptinella but the size of the gut is so small that mass bulking was found to•be impracticable. An alternative method was therefore employed in which the gut was dissected out on a microscope slide, squashed and mounted. in polyvinyl lactophenol. The slides were subsequently examined under phase contrast at a magnification of x600.

The numbers of particles were counted under the broad categories of aseptate spores, septate spores and hyphae. Amounts of yeast and unidentifiable material were assessed qualitatively since particles, could not be distinguished.

Qualitative observationson the gut contents were also made.

The procedure was carried out on both mixed and single species populations of Ptinella brought into the laboratory in their intact habitats. Five adults of each species were taken from the mixed population and five from the two single species population. Five larvae were also taken from the mixed site but since their species could not be identified the data were supplemented by analysis of five larvae of each species derived from laboratory cultures. The numbers of particles in each of the categories were expressed as proportions of t're total number for each individuals. ::ean proportions for each species were calculated together with their standard -65-

error which were compared within.and-between'speoies (Table 1.2). The data show that a large variety of fungal spores apparently form

the basis of the diet for active stages in both P.aptera and P.errabunda,

and fungal hyphae of varying dimensions forming a lower proportion of the

.food intake. Yeasts and unidentified material were present to a varying

degree and occasionally algae were identified. The variation in prol,ortions

of the different components of the diet and in their relative size was

considerable within each species and no significant difference was recorded

between the species or between adults and larvae.

It is included that no evidence was found to suggest niche separation

of P.aptera and P.errabunda on the basis of differential food utilisation,

the general impression gained being that both species are cosmopolitan

rycetophages. However, in order to further substantiate this view more

emhaustive investigation would be reruired covering a large number of sites

and taking the possibility of seasonal variation in food supply into account.

The data are, however, consistent with those of Anderson and Healey (1972)

for woodland populations of the Collemhola species Tomocerus minor and

Tomocerus longicornis. -66-

SECTION 2

FIELD SMILING AND COMMTIOITS OF PTESLLA.

2.1 Sampling method.

Although the analyses of collections of field-caught Ptinella provide

useful information on the gross population relationships of the species and their habitat requirements, some form of systematic sampling is required

to investigate the degree and stability of coexistence between species of

Ptinella. Such sampling, it was also hoped, would show the species particular

habitat requirements. A method was therefore devised for sampling Ptinella

populations on fallen trees and logs. Samples were taken by means of a cylindrical steel punch (Figure 2.1) following the method described by Furniss (1962) for sampling beetle-infested bark. A sample size of 25 cm2

was selected since this was approximately the maximum size that could be conveniently. punched out of the bark on a ranee of trunks of different

sizes, without being distorted by the, curvature of the bark. Since populations of P.aptera and P.errabunda frequently occur at high density, it was also considered that numbers of individuals taken in a 25 cm2 sample would_ be sufficiently high to make results meaningful and amenable to statistical analysis. Samples were taken systematically as opposed to randomly since the surface of a fallen tree is so complex that random selection of stations is impracticable. In order to cover the two basic aspects of sun and shade, samples were initially taken at intervals of 0.5 m along a median line on the upper and lower surfaces of the trunk. It was not always possible to take samples from the highest and lowest points due to obstruction by branches; in such cases samples were taken from the nearest accessible areas of bark.

The lower size limit on branches that could be sampled was approximately

30 cm circirmference. Initially it was planned to take samples from the same trunk at regular intervals during the year. For this reason sites had to be selected that provided a sufficiently large surface area to permit - 67 -

Figure 2.1 Diagram of cylindrical steel punch used for taking bark sc,r2pleE,.. -68-

a number of destructive samples to be taken without causing total disruption

of the habitat. Essentially this meant finding an entire fallen tree with

widespread and dense populations of both 12ta2:tera and P.errabunda. Initial collections were made from prospective sites in an effort to establish whether these requirements were fulfilled.

The anterior edge of the sampling tool was sharpened so that it could be hammered into the bark until the sapwood was reached. The punch, with the sample in it, was then withdrawn and the exposed area rapidly "swept" with

an aspirator to collect all insects present. The sample was then forced out of the punch into the polythene bag in which the tool had been placed immediately after its withdrawal, thus reducing the chance of beetles escaping from the bark. In practice their reaction to disturbance tended to carry them into the crevices in the bark. The 2 x 1 inch aspirator tube was then sealed with a polythene closure and placed in the same polythene bag which was subsequently knotted and labelled with the sample number. On returning to the laboratory a little 70,% alcohol was added_ to each tube in order to preserve the insects for subsequent identification. The bark samples were carefully removed and each was quickly placed on a 20 x 20 cm square of gauze with a mesh size of 1 x 1 mai, lying on a white enamel tray. The gauze was then folded around the bark and made fast with an elastic band. After checking the tray for escaping individuals the sample was weighed and placed in a plastic cup ready for extraction (see 2.2 below). After extraction the following measurements were made on each sample in the initial sampling method: the thickness of the bark and the crevice depth. It was considered that theoe measurements would be of interest since they often varied considerably. The samples were then rewrapped in their pieces of gauze and dried in an oven at 600C to constant weight. From these data the moisture content of the wood was calculated as a percentage of the dry weight. 6i -

2.2 Development of extraction technique.

The size of Ptinella is so diminutive and the bark in which they may

hide is so, complex in structure, that hand sorting and dissection of bark

samples inevitably resulted in under estimation of the numbers of beetles

present. It was therefore considered desirable to develop an efficient

extraction technique for removing Ptinella from bark samples. The technique

was loosely based on the high-gradient cylinder extractor for soil animals

described by I:acfadyen (1962) with a number of simplifications permitted by

the nature of the material and the beahvioural responses of the beetles

concerned. The principle underlying this method of extraction is the response

of Ptinella (and many other micro-arthropods) to temperature and humidity

gradients. The extractor effectively sets up steep temperature and humidity

gradients with temperature increasing and relative humidity decreasing in

the sample with time and conditions of relatively low temperature and high

humidity existing in the collecting vessels. Tile response of Ptinella to

both of these factors and to humidity in particular is compatible with the

use of this method (see Section 1 and 3).

The gauze-wrapped samples were placed in plastic drinking cups (diameter

6.5 cm at the top) containing distilled water to a depth of approximately

3 cm in the bottom. The 6auze was sufficiently fine to prevent the bark from

crumbling into the collecting vessel, but the holes permitted the majority

of the subcortical animals and certainly the Ptinella, to pass through into

the cup. The cu-os were then set up in the extraction apparatus (Figure 2.2).

They were supported a little below the level of the samples by a rectangular

piece of hard-board (116.5 cm x 71.0 cm) in which circul=ar holes had been

cut. The hard-board in turn rested on a tank (106.5 cm x 61.0 cm) through

which water flowed slowly at a continuous rate acting as a cool water bath.

The apparatus was designed to hold 72 samples simultaneously in 12 rows of

.6, each suspended so that the bottom third of the collecting cup was immersed

in the cool water. Heat was applied directly above each sample by means of Figure 2.2 Perspective diagram of high temperature/humidity

gradient extractor.

.K A water B cool water tank 106.5 cm x 61.5 cp. x 20.0cm C hardboard sample holder 116.5 cm x 71.0 cm

E collecting vessel - dipmeter 5.75 cm (12 rows of 6) F sample 25 cm2 G light bulb 15W (12 rows of 6) H hardboard light batik holder 106.5 cm x 61.5 cm

J metal frame K chain support 39.0 cm L water inlet 0.75 cm /i water outlet 0.75 cm

• ' • • • / • /2 / / I • •• - -... r • • •„.. ••••••

N- - 72 -

ordinary light bulbs (15 W) sot in a piece of hard-board with a metal frame.

This in turn was suspended from the frame supporting the entire apparatus by means of a link chain at each corner, attached at both ends by means of

a nut and bolt. Thus the entire frame could be easily raised whilst samples or cups were placed in their holders and subseouent1y lowered until the bulbs almost touched the samples. The overall dimensions of the extractor are given in the diagram (Figure 2.2). The heat generated by the light bulbs rapidly desiccated the bark setting up the required heat and humidity gradients.

These were further increased by a layer of expanded polystyrene 1.5 cm thick fitted on top of the hard-board, insulating the lower halves of the cups from the heat above. The samples were normally left in the extractor for a minimum period of 2+ hours, the collecting cups being exchanged for fresh ones after this period to enable the extracted animals to be examined or preserved for subsequent examination. Since Ptinella were able to survive for up to 72 hours, and possibly longer, floating on the surface of the water in the cups, it was possible to extract thew from the bark alive. The majority of Ptinella were extracted within the first 24. hours. However, the time taken for complete extraction was dependent on the time that the bark took to dry out, which in turn was related to the nature. and thickness of the bark and its initial water content. The efficiency of the extractor was tested by introducing known numbers of P.aptera and P.errabunda adults and larvae on to. bark samples. .that had previously been heat sterilised to exclude the possibility of beetles already beins present in the bark. The subsequent saturation of the bark with water resulted in the discs being made favourable to the beetles. They were maintained for at least 12 hours in a culture jar with a dry plaster of .Paris base to ensure that the beetles became well established in the bark. Twenty such discs were,set up each with 10 beetles and 5 larvae. P.aptera individuals were introduced onto 10 of the discs, and 10 had P.errabunda on them. After checking to ensure that no individuals had left the discs, - 73 -

the latter were set up in the extractor as described. After 24 hours the

number,. of adults and larvae in the collecting vessels was counted. The

results are summarised in Table 2.1 and show that for adults the method was

10c5 successful for both species in each of the 10 replicates. All the

Ptinella were extracted in the first 24 hours. The extraction of the larvae

was less efficient and several were observed to have become stuck to the sides of the collecting vessels where they.becaLe desiccated. Since no way

was hnorrn by which the larvae of the different species of Ptinella could be

distinguished, those collected from samples were not considered. Ten elate

individuals of each species were set up on two discs in a similar way and

again extraction was l00-7: efficient although the test was slightly less

reliable since it was based. on only two replicates. Nevertheless it was concluded that for the extraction of F.aptera and P.errabunda adults from bark samples, the extractor developed was highly efficient and permitted

the number of adults in such samples to be counted with a high degree of accuracy. As far as other subcortical species were concerned, many were extracted by this method, particularly Collembola, mites and various small larvae; larger species were unable to pass through the gauze but many of these, such as the Staphylinidae,were normally collected in the aspirator as they were less easily able to hide in the bark.

2.3 Application of sampling technicue to natural

populations.

The first application of the sampling method was made on a fallen Farms

cy-lvatica at High Standing Hill, Unasor Forest in Berkshire. The tree was a well grown, nature. specimen whose main trunk had broken off at a height of approximately 5.6 m from the ground. Heartrot • had apparently decayed the heartwood of the trunk resulting in weakening such that it had apparently broken in two in a strong wind. The tree was' am:ongst other broad-leaved species on the side of a vest facing slope. However, the space left in the canopy when the tree fell was sufficiently great for parts of it to, potentially - 74 - at least, receive direct sunlight for several hours during the day.

Sampling was carried out on 6th May 1973 when it was believed that the tree had been fallen for at least 2 years. This conclusion was reached subjectively

on the basis of the examination of the dead wood and its state of decay, and

. in particular the smaller branches. The characteristic bootlace-like

rhizomorphs of Axmillaria mellea were found ramifying extensively beneath

the bark and fruiting bodies of the same fungus were observed. It seemed

likely that a parasitic attack by this fungus had caused the initial heartrot.

As a sampling site the majority of the trunk and Main branches appeared to be

in a condition that would provide a favourable habitat for Ptinella and a few

trial collections from various points confirmed this view. A total of 100 samples was taken from 109 stations at the site by the method described above. They were taken from the standing bole, tr•:o sections of main trunk, two math branches leading directly off the latter and two side

branches of the main branches. At each station the height from the ground of

the point where the sample was taken was measured, together with the circum-

ference of the trunk at that point. The texture of the bark and the wood

is ediately beneath the sample was -subjectively assessed and given one of six possible ratings: smooth and unrotted, spikey and unrotted, smooth and

spikey, spikey and rotted, smooth and rotted, and flaky. The colour was

also noted as one or a mixture of the following categories: white, brownish,

light brown, dark brown. The samples were nmbered, odd numbers representing sites on the upper surface and even numbers representing those beneath the trunk. The distance to the nearest section of missing bark was also measured.

The total surface area of the tree was estimated as accurately as

possible. The percentage of samples that were unrotted and the percentage from which the bark had peeled off were calculated together with the overall

density of Ptinella per sample area. The results are given in Appendix 5.

It did not seem feasible to summarise the results since the variation in conditions between samples was so great. Only a single individual of

P.errabunda was taken and only 16 P.aptera. rove than half of the latter — 75 —

occurred in 3 samples suggesting a contagious, irregular distribution. The

percentage moisture content of the bark beneath which Ptinella were collected

exceeded 400 of the dry weight, resulting in a relative humidity in the

subcortical zone of approximately mpg. In all but one sample the wood_ and bark were dark brown or brown in colour and,mre always fairly well rotted.

Crevice depth however, was variable as was the distance to the nearest area

of missing bark. The single P.errabunda was collected in a sample with two P.aptera.

The total surface area of the tree was approximately 100.3 m the total area sampled being 2,725 cm2 (about 0.03;0). Of the 109 sample stations 11.9370 were unrotted and a further 8.265 had no bark at all. Thus if the samples taken were sufficient to reflect the tree as a whole, it was estimated that a total area of 20.195 was suite certainly unavailable to Ptinella. Overall densities of Ptinella as estimated by sampling are given in Table 2.2 where they are compared with densities recorded at the second sampling site. A close correlation was observed between position of a sample and whether the bark was unrotted or missing altogether, a slow rate of decay being associated with the lower surface and a very rapid rate often culminating in loss of bark occurring on the upper surface. The total density of Ptinella (Table 2.2) on the fallen tree was estimated to be 62.39 individuals/m2. It appeared from the above results that the density of beetles on this apparently suitable site was too low and the variability of the subcortical habitat was so great as to make systematic sampling impracticable. Thus for its use on other sites the method was modified.

Since the 25 cm2 samples were apparently too small for sampling Ptinella populations over the diverse area of a tree trunk, a modified method was used at the second site in another area of Windsor Forest. For convenience the same sampling instrument was used, but at each site a central sample was taken and subsequently six more were taken from the bark immediately surrounding the first. These samples could then be considered either singly or joined together to fora•a larger sample area of 175 cm2. A uniform - 76 -

Table 2.1. Test of the efficiency of the extraction apparatus over 24. hours.

llean proportion adult Mean proportion larvae extracted. (with S .E . ) extracted (with S.E.) i .Etultna apterous 1.00+0 1.64+0.05 P.errabunda apterous 1.00+0 0.66+0.03

P.aptera alate 1.00+0 P.errabunda alate 1.00+0

Table 2.2. Population densities of Ftinella on fallen Fasus sylvatica at

two sampling sites in Windsor Forest.

Site 1 (May 1973) Population density per 25 cm2

(i)Excluding debarked. areas 0.18

(ii)Excluding unrotted areas 0.17

(iii)Excluding all unfavourable areas 0.20 Estimated absolute population per 1 m2 surface area of fallen trunk: 62 Estimated absolute population of the entire site . (surface area 100.3 1,32) : 6,238

Site 2 (October 1973) Estimated absolUte population per 1 m2 surface area of fallen trunk: 3,64.0

Estimated absolute population of entire site (surface area 33.0 m2): 120,120 -77-

F.gylvatica trunk was selected, trial collections having indicated the presence of both P.aptera and P.errabunda on the tree. The beech was a mature specimen in mixed woodland on the edge of a predominantly softwood area. It had apparently been uprooted by wind and had fallen across a naroow gully with marshy ground in the bottom of it. The first 7.4 m from the root end was remarkably uniform and sampling was concentrated along this section. There were few external signs of subcortical variability with the exception of some patches of moss and cracks in the bark. The trunk was orientated in a south- westerly direction and was in intermittent shade from the immediately surrounding conifers and Fagus. Sampling was carried out in October 1973. Starting approximately 1 m from the roots, 10 sampling stations were marked out at intervals of 0.5 m along the upper surface of the trunk. Samples were treated as already described but fewer measurements were made on the habitat, thus only the colour of the bark, its thickness, the state of the rot and its moisture content were measured. Furthermore these measurements were only made on the central sample at each station. The results are given in full in Appendix 5 and are summarised in Table 2.3. Although large numbers of Ptinella were taken in the samples (mean number per sample was 9.1) all belonged to the sane species, P.aptera. The sampling could thus yield no information on the coexistence of the two species although the distribution of P.aptera alone was of some interest. The results show an overall increase in the density of P.aptera with increasing distance from the roots of the tree when the samples are considered in their groups of seven. The physical characteristics of the subcortical habitat were remarkably consistent throughout the length of the trunk that was sampled and no correlation could be discerned between factors measured and the number of*Ptinella collected in each sample. The total population density of Ptinella at this site was estimated to be 3,640/m2 of tree surface area (excluding the side branches whose surface area was not measured).

The sampling technique was further modified for application at the third - 78 -

Table 2.3. Number of Ptinella in 10 175 an2 samples collected from a -fallen F.sylvatica in Windsor Forest in October 1973.

Sample Numbers of 11.1cluksra no. apterous males alate males apterous females alate females total I 1 14. 9 23 '2 18 5 13 3 39 4 65 3 23 31 6 44 4 19 3 16 31 2 68 5 34- 1 3 38 0 .33 2 35 27 8 80 7 4.3 2 2 65 3 27 1 35 25 10 81 9 32 14 2 101 10 46 1 52

/4-0 637 Total 294 29 27h- -79-

site selected. The circular punch was dispensed with altogether and a

100 cm2 rectangular area of bark was used as the sampling unit. This permitted

the collection of individuals from areas of bark inaccessible to the punch

sampler. The site fell into 5 broad categories, all parts of the bole of an uprooted F.gylvatica on the North Downs in Shere Manor Estate Surrey.

The tree was on the edge of a stand of mixed broad-leaved species and there

were a number of other mature beeches nearby, two of which had also fallen

but at a more recent date. Samples labelled. A were taken from a section out

off from the main bole, lying about L..5 m from the latter and largely over-

grown by Pteridium aauilinum. Station B was a similar section of trunk lying immediately anterior to the main bole although not in physical contact with

it; it to was partially covered by P.equilimul. The remaining three locations

were on the main bole. This wau not entirely resting on the ground, only

the bases of two branches were in immediate contact with the soil. Thus only the lowest parts of the trunk were shaded by grass and P. ac ninum.

Station C was the most distal projection of the intact trunk and was approxi- mately 2 m from the ground. The fourth area of bark (D) from which samples were taken was the base of a side branch, the latter having been detached.

This situation was fairly well shaded by the rest of the trunk above it.

The final group of samples, E7was taken from the main surface of the trunk which was approximately 2.5 m in length. The selection of the sites was not random. Small pieces of bark were removed from different points until populations of Ptinella were located. The 100 cm2 samples were then taken from the adjacent bark area. Sampling was carried out in June 19Th- and a further brief search of the site was made a year later in June 1975.

The same basic principles of sampling were used as at previous sites.

However, the 100 cm2 sample was measured out as a 10 cm x 10 cm square on the bark and was then cut out using a sharp sheath knife. On returning to the laboratory the bark was divided into pieces that would fit conveniently into the mouths of the extractor vessels. Apart from these deviations, the -80-

procedure was followed as already described. The search of the site in June

1975 was not done on a systematic sampling basis since much of the habitat

had been destroyed by the previous sampling and searching. The five locations

were inspected and as many Ptinella taken as could be found. The beetles

were taken in an aspirator only, no bark being taken back to the laboratory

for extraction. The results of the sampling and the collecting from the site are presented in Tables 2.4 and 2.5.

The data show the complete absence of P.aptera from the two detached

sections of trunk A and B. On the main bole however, both P.errabunda and

P.aptera were found. From the distal projection C, the three 100 cm2 samples taken each had mixed populations of the two species in an approximately

1:1 ratio, P.aptera being slightly more abundant. The three samples from site D were similarly mixed although in, the two furthest from the trunk, F.errabunda was considerably more abundant. In the third sample the number

of each species was approximately equal. The remaining samples taken from

the ulper surface and sides of the bole were more variable in composition. P.errabunda was present in only three of the total of eight samples and in

trio of those P.aptera was considerably more abundant. In the third, the two

species were approximately esual in abundance. Only a single alate individual of P.aytera was collected in all the samples although 22 of the elate morph

of P.errabunda were taken, 16 of them being from the first site where the

proportion of alates was calculated to be 0.13 of the population.

The fungal decay at the different sampling stations was variable. All

had subcortical.areas where the sapwood was smooth and dark brown in colour

with varying amounts of mycelium visible and large cuantities of frass. Drier areas of white rot were also widespread and in fact the bole was largely decayed in this manner with areas of habitat more favourable to

Ptinella being relatively isolated. It.was concluded that the tree had

probably been fallen for at least 5 years its relatively shaded situation and its bulk helping to Maintain a fairly high water content and thus moist - 81 -

Table 2.4. Number of Ptinella in 18 100 cm2 samples taken from 5 stations on a fallen F. sylvatica at Shore laulor Estate, Surrey in June 1974.

Sample NuMber of P.aptera Number of F.errabunda number apterous alate apterous alate total i apterous alate , total male male female female

Am 51 8 59 A2 59 8 67

B1 28 28 B2 12 12

01 4 6 10 8 8 02 2 7 9 7 7 03 6 6 6 22 11, -4-'

Di 1 1 2 53 6 59 D2 3 4 7 46 46 D3 8 8 1 17 13 18

El 13 14 32 E9 9 8 17 07 E3 17 [.23 L.0 El 14 19 ,1- 33 3L 34 26 2 E;), 17 9 2 .17,,J0 8 10 10 E7 8 6 24 2 Es 6 6 .

Total 121 4 121 7 253 334 22 356

Table 2.5. Numbers of Ftinella taken at 5 stations from F.svlvatica at Shere Manor Estate in June 1575.

Sample Number of P.aptera Number of P.errabunda number apterous alate apterous alate • total apterous alate total male male female female A 12 1 13

B 9 9 C D 1 2 3 7 7 E 7 5 1 13 2 2 - 82 -

conditions beneath the bark.

The search made a year later failed to reveal any Ptinella at station C; however, small populations were taken from the remaining sites. 'These

collections, although of insufficient size to be truly representative of the Ptinella populations at the site, do at least show that the species

composition was maintained over a period of a year.

2.4 Field collections of Ptinella.

A large nudber of general collections of Ptinella were made from a variety of sites throughout thecouzDeof the study. Dead wood. :• in a suitable state of decay (assessed by experience) was examined for Ptinella and any

that were found were collected in an aspirator fitted with a 2 x 1 inch

glass tube. If the animals were reouired alive a little bark or frass from

the sUbstrate was placed in the tubes with them in order to maintain a high relative humidity. Men the beetles did not need to be kept alive a little

70% alcohol was added to each tube to preserve them. The site, date of collection and tree species were noted for each collection together with any relevant data. On some occasions pieces of bark from heavily infested wood were taken back to the laboratory in sealed polythene bags. All visible Ptinella were collected in an aspirator and any remaining were removed by means of the extractor after the bark had, been cut into suitably sized pieces.

The species, sex and morph of each individual collected was determined by examination under the microscope as described in Section 1. Some specimens were made into permanent preparations by preserving them in 705 ethanol followed by washing in distilled water and mounting on a microscope slide in polyvinyl lactophenol. The preparations were then sealed with a cover- slip and allowed to dry in an oven at 600C for about 36 hours. If recuired, the preservation in alcohol could be omitted and the animals mounted directly in the mountant which also acted as a clearing agent.

•The records of species, sex and wine morph were summed for each site - 83 -

and are presented in Appendix 4.

During the collection of specimens various nualitative observations

were made on the distribution of Ptinella relative to theirhabitt. 'To

single particular form of dead wood provided a favourable habitat for

Ptinella. Thus they have been collected from such diverse sources as entire

fallen trees, dead standing trees, dead branches on living trees, bark

covered fence posts, cut logs stacked or lyri.ng on the ground and, even on

one occasion from a sawdust heap. The latter probably represents the most extreme divergence from the normal habitat. The density of individuals was

very variable some apparently favourable, extensive sites having only small

scattered :.7coups of the beetles, whilst on the other hand some small logs had very high densities. 'Ihatever form the wood was in, it was observed that the bark was normally coming away from the sanwOod and was often cracked in places, tips providing an extensive subcortical zone. Men ,the bark was removed the surface of the wood where theleeties were collected was invariably moist. Yost frequently the sapwood.ras dark brown in colour due to staining from insect frass and fungal products and the surface was often slimey. In other areas of the subcortical zone however, there was frequently a thick mat of fungal mycelium on which the beetles and their larvae were observed to feed in often dense aggregations. Two such fungi were identified as a species of Ibriednia and the common mould

Trichoderma, viride. Often the high density of mycetophagous insects feeding in the sobcortical zone apparently controlled the aevelo_ment of the byphae.

The presence of Stereum sporophores on dead wood was found to be a fairly reliable indicator of decay conditions generating a subcortical zone favourable to Ptinella. Another fungus that was regularly identified on logs where

Ptinella were found was Armillaria mellea. This cosmopolitan species was common on both softwood and broadleaved trees. Although often associated with colonisation of dead stumps it also caused heartrot in standing trees, resulting in their death. Areas of woodland with actively parasitic infections of A.mellea provided the 'oast productive collecting sites. Once the fungus has become parasitic it may spread rapidly through an area attacking the bases of trees and subsequently the heartwood. In living trees the infection may not be particularly noticeable from without, but it weakens the tree making it vulnerable to being blown down by wind. Once fallen the decay may be very rapid and extensive as the dead or dying tissue is invaded. by saprophytic wood-rotting and non-rotting fungi, moulds and bacteria. The mycelium of

A.mellea forms a dense white mat beneath the bark which dies and contracts away from the sapwood. At this stage the round, brownish-blacks bootlace- like rhizomorphs ramify over the sapwood beneath the bark. Ptinella were often collected in large numbers from amongst these rhizomorphs. Although the fungus causes a white rot (i.e. it is able to break down both the cellulose and the lignin), the wood surface is often dark brown as described above.

The duration of the period over which such sites present favourable habitats for Ptinella has been considered in Section 1.

The collecting data show that P.errabunda and F.aptera were generally widely distributed through southern England and frequently collected together from the sane site although the former species was most frequently collected from sites in 'the older forest and woodland. areas, such as Mndsor Forest and the New Forest. These localities represent more or less continuous areas of, woodland that have been in existence for hundreds of years with relatively little disturbance in the way of removal of dead or dying wood. Although

P.errabunda was also found in such areas its distribution was generzaly smaller and disjunct. :lowever, where conifers haa been planted within t.iece areas, P.errabunda was also found in abundance. In fact the results suggest an overall tendency towards absence of P.antera from softwoods, P.errabunda, predominating in such sites. On only two occasions was P.aptera taken from conifers. In both cases the trees were fallen, well grown Pinus sylvestris, with much thicker bark than was found on smiler conifers typical of the forestry plantations. One of the sites was at Brock Hill in the New Forest -85-

where the Pinus concerned was in a stand of mature trees of the sane species

adjacent to mixed hardwoods. However, within 50 metres of the site were a

number of small Douglas fir (Pseudotsua menziesii) logs in a plantation.

The latter sites supported populations of P.errabunda.

P.taylorae was found to be very limited in its distribution and never

occurred in the same collections as P.aptera although it was found with

P.errabunda on several occasions. When P.taylorae was found during the course of this study it was always taken from dead branches and trunks of Quercus petraea with a thick covering of lichen and moss on the outer surface of the

bark. The data from the collections were plotted in a cell diagram (Figure 2.3)

with numbers of P.errabunda along one axis and numbers of P.antera along

the other, the numbers being grouped in blocks of 10 with the exception of the first group (1-9). aci site was allut:;ed to its appropriate cell depending on the numbers of each species recorded, thus the number in the cell gives the total number of sites at which a certain number of each species was found. Sinilar diagrams (Figures 2.4' 2.5) were plotted for the sites under classification of dead softwood trees and dead broad-leaved_ trees. A further set were drawn representing the seasons summer and winter, the latter including the months October to March, the remainder being termed summer (Figures 2.6, and 2.7). Ideally the collections should have consisted. of one or more samples of regular size, however, the variable nature of the habitats and size of the populations made such sampling impracticable. Collections were made from some sites on more than one occasion. Whether these data were included together, or regarded as representative of separate sites depnded on a subjective assessment of the relationships of the collections to one another and on the times at which the collections were made. For example, if two collections were made within a week of each other at adjacent stations, they were suaaed. However, where a large site was visited repeatedly over long -86-

intervals of time, the records were considered to be effectively from different

sites to take into account the likelihood of changes that may have occurred over the intervening time.

Of a total of 88 collections made largely in central southern England between 1972 and 1975, 26 were found to contain both P.aptera and P.errabunda.

Since some collections consisted of only one or a few individivals the actual number of sites whei the two species occurred together was probably slightly underestimated at 29.55g. This figure suggests coexistence of the two species at least at the level of sites. P.aptera occurred in a total of 39 sites and was exclusive of P.errabunda in only 13 of these. In contrast, P.errabunda occurred in 75 sites and was exclusive to L9 of them. Obviously these figures would be altered slightly if sites were considered in the geographical sense only, however, the difference is so marked that a significant trend is almost certainly reflected. Despite the apparently greater frequency of P.errabunda, inspection of Figure 2.3 shows that there is a tendency for P.aptera to be more abundant than P.errabunda in the sites where both were collected. In 18 out of the 26 sites where both species occurred, P.aptera was more abundant than P.errabunda and generally there was a considerable numerical difference.

The figures for the different tree types show a very strong negative association between P.aptera and softwood species already remarked upon above.

In both the cases where P.aptera was recorded on Pinus? P.errabunda was present in greater abundance. P.aptera was apparently absent from the remaining sites. The data for the seasons (winter and soriner) reflect the same sort of predominance of P.aptera insites where the two species were collected together.

There did appear to be a tendency for a greater number of sites occupied by

P.aptera alone to be found during the summer months. . Nevertheless, the two largest, exclusively P.aptera collections were made at one Fagus site

(described in detail above) in October of two successive years. There was also a tendency for P.errabunda dominated mixed collections to be found

-87—

Fi8ure 2.3 Species cor.:osition of field colleetionc of Ftinella.

2 2 130 . 120 / / 1 110 1 / 100

90 1 . . 80 .

/ .

da 1 n 70

bu / • a /

err 60 P. ■ 1 1 . No. 50 . 4 . / 40 . 4 1' 1 30 4 1 /. 1 20 11 1 2/ 1 1 10 20 5' 3 1 1 1 1 1 . 3 5 2 1 1 2

0 1 10 20 30 40 50 60 70 80 90 100 110 120 130+

No. P. aptera Fioare5 aad 2.5 afecies co:aposition of field collection of

Ptinella aifferen'; Free trees.

Figure 2.4 SOFTWOOD

2 • • 120 / e

100 1 • ' • • • 80 • 1 • •' No. 60 • P. errabunda • • 1 • 40 • 1 • 2 ..' 20 e 5 1 . 5 A' 1

1 20 40 60 80 100 120 + No. Raptela

Figure 2.5 BROAD_LEAVED

2 ,/ 120 ,' 1 , 100 . . 1 ,I 80 . , , No. 60 , 1 Penabunda 1 . . 3 ,' 40 3 A' 1 2 1 / 1 20 6 2' 1 _ 1 15,41 3 1 1 1 1 1 1 2 5 2 1 2 0 1 20 40 60 80 100 120 + No. P.aptera - 89 -

Figures 2.6 and 2.7 Srecies composition of collection of P.al)tera for different seasons.

Figure 2.6 WINTER

1 , e 120 • • . • 100 e

1 I ° 80 • •

No. .9' 60 I P.errabunda • 2 .." 40 3 ;I°

2 1 e ' 20 6 1 ,' . ' 1 12 ,1" 1 • 1 1 2 2 3 • A 0 1 20 40 60 80 100 120 + No. P.aptera

Figure 2.7 SUMMER

2 1 , , 120 I' 1 1 ,' 100 1' ,' 80 1 .' ,' No. 60 P.errabunda 1 ,' 1 2 ,' 40 1 ," 1 2 I' 1 20 5 ,2' 1 8 ,4' 2 1 1 1 1 1 1 2 2 2 0 1 20 40 60 80 100 120 ÷ No. Raptera -90-

during the winter period. No doubt the somewhat confused seasonal variations

in collections were largely due to biased collecting of one sort or another.

Had a much greater number of sites been represented, interpretation of the results might have been more meaningful.

P.taylorae was collected from only five locations (Appendix 4) and there was thus insufficient data for any interpretation of the species' relations with P.errabunda, with which it co-occurred on some occasions, to be attempted.

2.5 Measurment of subcortical temperature.

In considering the temperature adaptations demonstrated in the laboratory for the species of Ptinella, it is important to relate the performance and activity of the species to the temperature regimes of the natural habitat.

Few attempts have been made to investigate subcortical temperatures, the most comprehensive study being that of Haarlp(v and Petersen (1952) who studied day-time temperatures under bark of living and dead .Sitka spruce (Picea sitchensis) for a period of. 20 days during June. There are however, no comparable published data for hardwood logs.

Subcortical temperatures were measured on a fallen beech at Silwood

Park over 2 periods of 10 days in the months of June and December. Measurements were made using 9 thermistors in conjunction with a Grant multipoint temperature recorder (Model D) which was set to record automatically at 15 minute intervals.

The thermistors were inserted beneath the bark either at a natural fissure or a knife slit. Care had to be taken to ensure that the entire thermistor was underneath the bark and that the latter did not split. This was achieved by pushing the probe at least 2 or 3 cm inside from the opening. The latter was then packed with sawdust and plugged with plasticene. It is believed that major inaccuracies occurred in all the data as a consequence of the crude method employed for making measurements, the microclimate presumably being disrupted. In the absence of more refined enuipment and techniques a limited amount of data was obtained with a view to demonstrating any gross -9i-

correlation or variation of subcortical temperatures with air temperature,

thickness of bark and, for summer records, incident light. Because of these inaccuracies two extreme categories of bark thickness were selected for study: very thick - 2 cm (on the main trunk), and very thin - 0.2 to 0.4 cm. These

were either in full shade of surrounding vegetation or the trunk itself, or

were exposed to varying degrees of shade by surrounding trees. The latter

effect was-further modified by cloud shadow which was recorded for each site. In the December measurements absence of cloud cover was not observed during two 24 hour periods of continuous observation. Standard air temperatures were obtained from the Silwood Park meteorological records. Four sites were

selected ( 2 exposed and 2 in constant shade) and the temperatures plotted (Figures 2.8, 2.9, 2.10 and 2.11) for two 48 hour periods.

In the'first period in June there was no Cloud cover during the entire

day, the thermistors were observed to be unshaded by surrounding trees for between 3 and 4. hours during the middle of the day. The maximum temperature

of 48.50C was recorded at 13.00 hours at site 1, the thermistor being under thin bark on a side branch; the site was exposed for the full period. The

temperature increased by 25.5°C over a period of two hours. The rate of increase was less for the thick bark exposed to the sun, being 20°C in the same two hour period. When these sites became shaded soon after 13.00 hours, the temperature fell rapidly at site 1 although site 2 showed a slight lag phase and then fell sharply. The sudden increase in temperature at site 2 at 19.00 hours was due to a brief period of exposure to the sun. Only at one time did the temperature at either of these sites fall to the same level as, or below, the air temperature, this was at 6.00 hours when the air temperature was rising. The maximum temperature reached in a shaded site was 25°C at 14.00 hours (site 4), the minimum was 11°C (site 3) at 5.00 and 6.00 hours. The temperature at site 3, characterised by thin bark, only exceeded the air temperature at one time. During the day, temperatures at site 4. appro::imated - 92 -

the air temperature, but in darkness it remained approximately 3.5°C above the air temperature. The reverse pattern was true for site 3. During period 2 light cloud cover persisted throughout the period,

consequently the air temperature was lower during the day, but higher during

the night than during period 1. The maximum subcortical temperature recorded

was in the unshaded site 1 (34°C) at 12.00 hours; the minimum was 13°C (site 3, 4.00 hours). The peaks on the temperature Graphs for the exposed sites were due to increases in light intensity, although sunlight was never maximal. Temperatures at exposed sites or shaded. site 4, never fell below the air temperature at any time during the period.

In the December recordings the theriiistors were positioned beneath thick and thin and loose and tight bark. Overall temperatures were highest at site 4 although the maximum temperature recorded was at site 3 (11°C between 11.00 and 12.00 hours in period 2). During period 1, there was little variation in air temperature over the 24. hours and the variation in subcortical temperatures was low and consistently between about 2.5 - 1.0°C below the former. Sites 3 and 4 in particular recorded almost identical temperatures throughout being slightly higher than 1 and 2.

Period 2 was characterised by a rapid drop in air temperature from 14.00 hours (11.500) to a minimum at 7.00 hours (1.5°C). Subcortical temperatures reflected this decrease apparently with little time-lag, sites 1, 2 and 3 recording temperatures approximately 1.0 - 2.0°C below the ambient temperature. The maximum temperature (11.000 was recorded at site 3 where the minimum temperature of -1.000 was, also recorded (7.00 - 8.00 hours). At site 4 the subcortical temperature was initially 1.5°C , below air temperature and maintained this level until 15.00 hours when it had dropped to 0.5°C below.

Subseruently it decreased steadily but remained approximately 1°C above the air temperature until the latter increased at 8.00 and 9.00 hours.

The measurements made during December are bellevcd to be less meaninGful than those of the June periods since greater precautions were taken In the Figure 2.8 Subcortical temperatures on a fallen beech

Silwood Park - June Period I - total absence of cloud cover Sites 1 & 2 full sun 10.15 hours to 13.00 hours and four. 15 minutes around 19.00 hours. Symbol Site Bark Situation

A 1 thin sun

0 2 thick sun

• 3 thin shade • 4 thick shade o air temperature • soil 2 inches grass minimum

Temperature o in C.

Time in hours Figure 2.9 Subcortical temperatures on a fallen beech Silwood Park - June

Period II - total light cloud cover but light intensity variable.

Symbol Site Bark Situation

A thin sun

0 thick sun

• 3 thin shade • 1. thick shade

air temperature

♦ soil 2 inches

0 grass minimum 50

40_

Temperature

in °C.

— 13'.' ,Ar..• -.. ••••• -.....411,.. - --2:...._ A' .... 20 ...-• .. .. -- ... .A..., .. 0 "A, • "... s -. 0 .... -*".• / A- .1' *". ..---0 0-- =AL- - - •„ --0...„„ ..-. --.0 ...-- o - • - - - A- - - • -

10 2 24 6 Time in hours

Figure 2. 10 Subcortical temperatures. on a fallen beech

Silwood Park - December

Period I - total cloud cover

SyMboll Site Bark

• 1 thick O 2 thick, loose

• 3 thin A 4 -thin, loose air temperature

soil 2 inches

grass minimum

30

Temperature

0 In C.

20_ •

- - - -0 - - - - ❑ - CI- -0- -0 - -

0 12 18 24 6 Time in hours Figure 2.11 Subaortical temperatures on a fallen beech Siiwood Park - December Period II - total- cloud cover. Symbol Site Bark • 1 thick 2 thick, loose 3 thin thin, loose

. ❑ air temperature soi1.2 inches grass minimum (-3°C) 30 _

20 O • Temperature ;

o in C.

0 - 0 - -0- - ❑Al 10 - - - - -a- - --A-

- -0 0- -0, -

12 18 4 6 Time in hours - 101 -

latter period to ensure that the thermistors were well under the bark and insulated from the surrounding air.

2.6 Discussion.

(i) The association of species.

The results reflect the reports of many authors on the col.iplexity of

dead wood as an environment (e.g. Graham, 1925; Elton, 1966). It is this

complexity and its effect on the distribution of Ptinella that has been shown

to preclude the regular sampling of the habitat in order to investigate the

population dynamics of these beetles, through the absence of sufficiently uniform sites where the two species occur together. The destructive nature of the sampling is also a considerable draw-back to such intensive sampling.

"Sven if samples of bark are replaced there is no doubt that the underlying habitat is radically affected by what often amounts to the disruption of the humid microclimate. Inevitably the distribution of Ptinella is also affected.

Amethod of sampling dead. logs for Ptinella has been devised using a circular punch to produce 25 am2 sample discs of bark. Although the method appeared to be efficient since the beetles pause for a moment on being disturbed and can thus be collected rapidly in an aspirator, there was at least one source of potential mortality. The possibility of individuals being crushed by the pressure from the compression of the bark by the punch could not be eliminated. However, there was no evidence to suggest that such mortality was an important factor in the sampling. Any form of mortality or escape of individuals into the surrounding subcortical zone would. have resulted in underestimation of Ptinella populations.. There appeared to be no such problem of potential underestimation attached to the extraction method developed to remove adult beetles from the bark samples. This method based. on a high temperature/humidity gradient has been found to be approximately 100; efficient for extraction of adult Ptinella. Although initially designed to accomodate 25 cm2 samples, it could have been adapted to take samples of greater or lesser size if necessary. - 102 -

Applying these techniciues to the sampling of Ptinella in the field

produced disappointing results. At the first site selected for intensive

study a pioneer collection had indicated the presence of both P.aotera

and P.errabunda in reasonable numbers on severalparts of the tree. neverthe-

less, despite the apparent external uniformity of the site, the degree of variability in the subcortical zone had been underestimated. A total of

only 17 Ptinella were taken in 100 samples on various parts of the tree. More Ftinella would certainly have been,collected had a greater number of

samples been taken from the site, but to yield results that could have been

subjected to statistical analysis the number of samples reauired would have

been impracticable. Furthermore, such intensive sampling would clearly have rendered the site unsuitable for further investigation to consider the effect

of time on the Ptinella populations, as a result of destruction of a large part of the habitat by removal of bark in sampling. At the second site where

sampling was applied the method was modified so that seven 25 cm2 samples were taken at each station. Clearly such a six-fold increase in sampling would have increased the number of Ftinella collected but this would still,

almost inevitably, have resulted in too small a number for analysis of the

degree of coexistence between the species and their relationship to physical parameters of the habitat. It had been hoped that the measurement of moisture

content, bark thickness, crevice depth and the other assessments of the habitat might be relatable to the distribution of the two species. But it appears that although certain broad correlations could be made between the

presence of Ptinella and for example moisture content, colour and texture

- of the wood. and bark, other measurements, although possibly significant in

some cases, were largely trivial. It was concluded that the complex inter- actions of numerous physical and biotic factors in the subcortical zone

determine the distribution of Ptinella, primarily by their modification of

the basic factors of humidity, temperature and food supply. Considering the

sampling in the light of information from subseuuent sampling and collecting, - 103 -

it is almost certain that the assessment of parameters in the manner described

would not permit distinction between populations of P.aptera and P.errabunda

to be made. Their differential requirements, if they exist, are too subtle to be demonstted in this way.

The second site seledted for sampling was apparently exceptional in its

relative uniformity that extended even to subcortical conditions. Furthermore,

the density of Ptinella was sufficiently high to make statistical analysis

of the data possible. However, the absence of P.errabunda from all of the

samples and the ,enerally low variability of the assessed factors, prevented any meaningful conclusions on the interactions of the two species from being reached.

Comparison of the population densities of Ptinella at the first site with those at the second site, demonstrates the tremendous variability between favourability of one habitat and another. Assuming that the entire surface area of the main trunk of the FaPus at site 2 to be, like the area sampled, favourable to Ptinella,, the total populations of the bole (33.0 mg in surface area) was estimated to be 121g20 individuals compared to only an estimated 6,258 individuals on site 1 (surface area 100.3 m2). It is concluded that where conditions are.favourdble for Ptinella,populations may be substantial.

Although the sampling at the third site on the North Dorms in Surrey, could not provide data on the overall distribution of P.aptera and P.errabunda on the tree as a whole, the data is considered to be sufficiently represent- ative to show that localised coexistence of the two species does occur. Furthermore, the collections made a year later suggest that such coexistence may be maintained for a period of time that considerably exceeds their generation times. It is not possible to draw far-reaching conclusions concerning coexistence between P.aptera and P.errabunda on the basis of a single intensively studied site. Nevertheless, it is suggested that such intimacy of coexistence (i.e. within a 100 crag area of apparently continuously - 101a.-

favourable habitat) occurs at.other localities where mixed collections of the two species have been taken.

Despite the fact that mixed populations appeared to have persisted over at least a year, a situation of totally stable coexistence is not necessarily implied since the possibility of one or both species population densities being maintained: by reinvasion from areas of slightly different microhabitat specific to each, cannot be ruled out.

The complete absence of 12.azbera from the two detached sections of trunk compared with the mixed populations on the bole may be interpreted in several ways. Since only two 100 cm2 samples were taken from each of these stations, the possibility of P.antera being present in very small numbers on, or in, a very localised situation cannot be eliminated. However, this appears unlikely since the logs were carefully searc#ed in order toseleot the sampling points, the majority of the remainder of the habitat apparently being unsuitable for

Ptinella. It is possible that subtle difference in the species requirements has resulted in the distribution pattern observed, but again the seemingly wide range of microhabitats from which both species have been collected and the incidence of large mixed populations at this site, suggest that the two species broadly overlap. The presumed superiority of P.errabunda in dispersive ability, has already been mentioned and it is suggested that it could have been important in determining the species distributions observed at this site. It is conceivable that successful colonisation of the main part of the trunk by

P.aptera could have been facilitated by the greater diversity of conditions on this large log, as opposed to the only limited variety of microhabitats on the small sections that had been sawn off. Once one, or more, populations of P.aptera had been successfully established, environmental factors that are implicated in determination of alate production (see Section 5) could probably be avoided by the beetles. Thus with only minimal alate production, the adjacent logs may have remained uncolonized by P.antera. P.errabunda, on the other hand, with its potential ability to establish colonies through single - 105-

individuals might be expected to have a greater chance of colonising all the

available habitat. This may have resulted in the exclusively P.errabunda populations on the logs.

However, another factor that may have been involved in the apparent

exclusion of P.antera from the logs, is the greater reproductive efficiency

of P.errabunda at 15°C (Section 3). Since it was noted that both trunks were at least partially shaded by dense herbage, it is suggested that the

subcortical temperature would have been relatively low (probably remaining below 20°C for most of the year) perhaps permitting competitive exclusion of P.aptera by P.errabunda by virtue of the latter speciesIgreater reproductive potential at low temperatures.

The predominance of P.aptera at all but one of the sampling stations on the basal section of the bole, could perhaps be interpreted in terms of competitive superiority of this species at high temperatures (around 20°C and above). Such an interpretation is consistent with the observation that none of the upper surface of the trunk was shaded by grass or ferns and it .was potentially exposed to direct sunlight for at least part of the 24. hour period. Thus generally higher subcortical temperatures would be expected on this part of the tree than on the logs and P.aptera might have had a significant reproductive advantage. If competition did occur between the two species on the main bole, the area %where P.errabunda dominated the nixed species samples, may be inter- preted as a region where the two species distributions met. A subjective impression that much of the bark at the base of this short projection was still attached to the sapwood, suggests that this area may have been isolated and had perhaps been colonised by P.errabunda enabling it to form a pure species population. In conclusion, there is some evidence from the sampling and collecting carried out at the Shere Manor Estate site, to suggest that intimate coexistence between P.errabunda and P.aptera may occur. revertheless, there is also - lo6 -

evidence that nicy be interpreted as suggesting that the two species may

compete for some resource in limited supply, the outcome of the interaction

possibly depending on. local differences in subcortical temreratures. If this

is the case, the observed coexistence of P.a,)tera and I.errabunda may be a consequence of superabundance of resources in the particular locality

concerned. Alternatively it may represent a teuporal balance of competitive

advantage of the two species or merely a transient state.

(ii) What is a populction?

One ::iajor problem involved in the assessment of Ftinella populations is

that of definition of the population unit. It is clear from the frequent

aiscc,ntinuities of the habitat that populations must often be small and

restricted. However, in the conditions provided by a dead tree such as the

second sampling site, it was impossible to estimate the extent of a -population.

Theoretically the activity characteristic of the s.::ecies could, if the

subcortical zone was suitable throughout the length of the tree, enable the

beetles and their larvae to mix freely throughout the entire habitat, thus

constituting a single large population unit. The samples would thus represent a sihgle population. of Ftinella. However, it is almost certain that at

points along even as uniform a habitat as this site appeared to represent, discontinuities in the extent of decay and the effect of cracks in the bark could probably result in localised areas of microhabitat that are unfavourable for Ftinella. The insects should, theoretically at least, be able to cross

such areas but the extent to which they will move from an optimal area to a less favourable habitat is not clear. Presumably if the insects' immediate environment becomes less favourable, perhaps as a result of high

population density or deterioration of food, the stimulus is sufficient to

"carry" them through suboptimal conditions to a more favourable microhabitat.

The extent to which failure of the bark to separate from the underlying sapwood represents a barrier to extension of populations of Ftinella,, is unknown - 107 -

At the first sampling site it is clear that the populations that

existed could not be thought of as forming a single continuous unit, the

environmental discontinuities. being considered to be too great to permit

free interchange of individuals from one locality to another. :owever, it is

uite.possible that Gene flow could occur between localised population units

as a result of activity of alate adults, although in the absence of further

information on the behaviour of this morph and the dispersal mechanism, this

cannot be established. 3xperiments in which Ptinella, are marked, released

and subsequently recaptured, would be needed in order to clarify the

situation.

The initial establishment of populations of Ptinella, whether by

repeated colonisation or by a single "founder" individual, is a further

problem in considering the extent of population units. In situations where

dead 1:ood provides a relatively continuous environment over a large area,

multiple colonisation seems most likely. Nevertheless, on some occasions

colonisation of isolated sites might result from successful establishment of

a single individual . Although such a possibility is not precluded for

P.aptera, since evidence has been found showing that alate females MAy be

mated before dispersal, the parthogenetic reproduction of P.errabunda would

obviously increase the chance of single individuals of this species

establishing new colonies. Such pioneering individuals of P.errabunda

could theoretically, realise their full reproductive potential in isolation,

whereas P.aptera would reauire =insemination to achieve this.

Until the problems concerning establishment of populations of Ptinella

and their extent are further clarified, the degree of intimacy of coexistence. between P.aptera and P.errabunda will, to some extent at least, remain obscure. -108-

(iii) Species distribution and the problem

of colonisation.

The collections of Ptinella that were made from a large number of sites

cannot, as has been pointed out, be regarded:as population samples since the

size of area from which they were taken is not uniform. However, the data

have been used to consider the distribution of Lta:-L- a. and P.errabunda relative to each other (in southern England in particular where P.abtera is

often found extensively and coexisting with P.errabunda) and to the habitat assessed subjectively. The possibility that collecting was incomplete, all

parts of the habitat freouented by the animals not being searched and thus

resulting in a bias in favour of one or other species, cannot be ruled out.

The general procedure of collecting any animals seen either on the sapwood

surface or on the bark in an aspirator meant that if one species was more cryptic in habit than another, there would have been a tendency for it to be

consistently underustimated. However, on the occasions when bark was taken

back to the laboratory and the animals removed using the eXtraction technique

described, there was no evidence of proportionately more of one species

being collected by this method. It is thus concluded that the collections probably broadly reflect the distribution of P.aDtera and P.errabunda. The observations made on the habitats from which collections were taken

suggest that both species occur in broadly the same kind of habitat. This

comprises the subcortical zone of rotting Wood at a particular stage of

decay, such that the requirements of the beetles (especially concerning humidity conditions) are fulfilled. The subcortical region has been described by Elton (1966) and is considered in general terms in Section I. It is also apparent that the distribution of Ptinella is related to the fungal micro- flora idj, so far as this affects the physical conditions immediately beneath the bark. Detailed consideration has been given to the honey fungus A.mellea, since this species was found so often to reflect the presence of a subcortical habitat favourable to Ptinella and was one of the major subjective means of - 109-

assessing whether a particular site was likely to support populations of the

beetles. There was a danger of bias when such indicators were used, so that sites not affected by Armillaria might not have been searched sufficiently

thoroughly. In order to counteract such bias any dead wood that was found was inspected carefully for signs of the presence of Ptinella.

expression of collecting data in the form of cell diagrams has shown

an apparently greater tendency for P.antera to be found. with P.errabunda than as pure species groups. Furthermore, all the data indicate a greater overall distribution of P.errabunda in the areas of southern, south western, and western England where collections were taken. Nevertheless, when P.aptera occurs in the same collections with P.errabunda, the former species is almost invariably numerically predominant. Since the collections are only broadly representative of the Ftinellu populations, too much emphasis cannot be placed on interpretation of the data. However, several suggestions may be made to explain this very Liarked tendency for predominance of P.antera at mixed sites.

Perhaps the most obvious explanation is one that invokes competitive inter- action between the two species; predominance of P.aptera could result from its greater competitive ability in a situation where a particular resource shared by the two species is in short supply. Alternatively the two species might be occupying subtly different niches, P.errabunda's niche apparently being less extensive than that of P.aptera in such sites where the two occur together. A further possibility is that the history of colonisation of the site may determine the proportions of species to some extent. Thus in an

"old forest" area with abundant dead wood, P.errabunda would probably have little or no advantage over P.aptera in colony foundation and the species composition could be a result of the reproductive capacities of each species under the prevailing conditions and chance. The explanation based. on species differences in habitat, probably does not apply in this situation since

P.errabunda was on some occasions found in considerable numbers on apparently very similar sites to, but in the absence of, P.aptera, Nevertheless, if - 110-

competition occurred between the two species at the sites where they were

collected together, coexistence could have resulted through the ability of

P.errabunda to exploit a different microhabitat. But in the absence of

considerably more intensive systematic sampling over a period of time, no satisfactory conclusions can be reached.

The cell diagrams that were plotted for the two categories of tree type

- broad-leaved and softwood, merely reflected the observations made from the

collections, that there was a marked absence of P.aptera from softwood species.

On only two occasions was P.aptera taken from softwoods and both of these were small populations from Pinus vlvestris. Both trees were mature specimens

with thick bark (1.5 - 2.0 cm) and lying close to mixed woodland. Many of the other collections from softwoods were made in Forestry Commission

plantations and were thus from trees under 50 years of age. Furthermore,

it was observed during the source of collecting that on most occasions, in

extensive areas of plantations, some apparently suitable trees and logs were uncolonised. This implies failure of the dispersal mechanism of Ptinella to

enable them to reach some sites. Considering the problem in terms of

colonising individuals, the parthenogenetic P.errabunda would be expected

to have a distinct advantage over P.aptera because of the ability of a single

individual to realise maximum fecundity on initiation of a new colony. A female P.aptera, on the other hand, would require a male to be present to facilitate reinsemination in order to realise maximum reproduction. It

seems likely that in the "old forest" where P.aptera is abundant, the problems of dispersal are reduced by the more or less continuous availability of

habitat over several hundred years. But in the plantation areas of more recent origin, modern forestry techniques aimed at reducing disease, result in extensive clearance of dead wood; habitat favourable for Ptinella is thus often extremely discontinuous. As far as colonisation is concerned 'the problems posed by such a habitat must be considerable. As has been suggested above, parthenogenetic reproduction would be expected to permit greater efficiency in colony foundation and hence in the ability to exploit at least

some of the niches, available in plantations. The incomplete colonisation of

such areas, as indicated. by the apparent absence of Ptinella from favourable

sites, suggests that dispersal in discontinuous environments is a major

problem for Ptinella. It is suggested that this problem of dispersal under- lies the general restriction of P.aptera to "old forests" inferred from the

collecting data and also noted by Johnson (1975). The single record of

P.aptera taken from a sawdust pile is somewhat anomalous in this context, although the conditions in such situations may have favoured the survival of a colony in a timber yard for a considerable number of years after the initial colonisation. The overall restriction of P.aptera populations in

Britain probably reflects the decrease in forested areas, or at least in areas Of continuous woodland. Osborne (1965) has discussed the effects of forest clearance on Coleoptera and Hammond (1974) has listed some ten species of beetles, associated with dead and decaying wood, that are recorded from deposits dated. post. 9000 B..P. but which are unknown in Britain today. The spread of certain Coleoptera associated with coniferous woodland in this century, apparently facilitated by the planting of conifer plantations, has been reported by Hammond (1974) and it is possible that P.errabunda fits into this group. However, the fact that the species is equally widespread on broad-leaved trees virtually eliminates the possibility of its introduction as a softwood dependent species. The evidence suggesting that P.errabunda and P.taylorae are, like P.cavelli, New Zealand species which have become established in Britain, is discussed in Section 6.

(iv) The microclimate under bark.

The subcortical temperature measurements made on a fallen beech during

June demonstrate the effects of solar radiation and bark thickness on the climate beneath the bark. Although the measurements are unsophisticated, the magnitude of the differences involved is sufficiently great to enable several - 112 -

conclusions to be.drawn from the data. The great increase in temperature

due to direct sunlight was slightly modified by the bark thickness. Presum-

ably the thin bark at site 1 acted as a relatively good conductor facilitating

the very rapid temperature change. Where the bark was thicker, the volume of air in it resulted in a greater degree of insulation of the sUbcortical

zone; consequently the temperature increase was slower and the maximum value recorded was 7.5°C below that recorded under thin bark. The insulation effect

permitting rapid increase in temperature was again demonstrated during period

2 when an increase in light intensity, despite cloud cover, resulted in rapid increase under thin bark whereas a lag phase was recorded under thicker bark. It might have been predicted that a similar insulation effect would exist around minimum temperatures, resulting in a slower decrease in temperature beneath thick bark. However, there was no evidence of this since the minimum temperatures recorded were all similar. It is possible that this effect was present but the tendency for rapid heat loss through thin bark was ameliorated by the higher temperature reached by the wood itself, where the insulation against heat loss would be greater. This would result in an overall decrease in sUbcortical temperatures that would differ little between thin and thick bark in the absence of full sunlight. This view was supported by the data from shaded sites when the temperatures were higher beneath thick bark and lower beneath thin. The low temperatures of the latter were probably considerably modified by ground level temperatures which were lower than those recorded for the air. Shaded bark showed_ a time lag in following the changes in air temperature, whereas exposed sites tended to reflect them almost immediately, apparently as a result of the larger temperature differential involved. It is interesting to note the insulation effect of thick bark in shade where a minimum temperature of 17°C was recorded (period

2) when the air temperature was 12°C. As has already been noted the December measurements of subcortical temperatures on the same tree are inadequate. However, it seems that in - 113 -

General the temperatures are lower than the prevailing air temperature,

presumably being affected by the proximity of the sites concerned to ground

level where lower temperatures are recorded. The differences between

temperatures recorded at various sites did not differ sufficiently for any

meaningful conclusions to be drawn concerning the effects of bark thickness during these periods.

The importance of relative sun and shade has been reported by other

authors, notably Haarl/v and Petersen (1952). They measured subcortical

temperatures on standing Sitha spruce (Picea _sitchensis) and LIbuntain pine (Finus mugo) and compared them with temperatures recorded by themselves and

other authors under the exposed bark of logs of the same species, and the

Lodgepole pine (Pinus contorta var. latifolia). The conclusion that they

reached was that temperatures below the bark on dead wood and stumps were

higher than those on living trees, attributing this to the lower water content

of the bark and of the underlying wood of the former. Similarly, variations in temperature were more rapid. beneath dead bark. The same authors showed

that although the temperature recorded in wood is lower than that of the bark

L.Imediately above it, the difference is eliminated, at night. Although these measurements were made on living trees, they lend some support to the interpr- etation, expressed above, concerning the effects of wood temperature on

subcortical temperatures. Although Haarl/v and Fetersen (1952) compared the temperatures beneath the bark of dense and thinned stands of trees, the data are not directly relevant to fallen trunks which, in natural forest situations, may be subject to only a very short period of direct solar radiation. It is considered that the dead beech on which the recordings were made in the current study repres- ented a fairly natural, mature, deciduous woodland situation with the effects consequent of artificial thinning or dense planting being absent, the tree having fallen naturally, leaving an area immediately above it free of canopy cover. It is clear, from the data, that although the periods when a particular - 114. - area of bark is in full sun may be very infrequent in a natural situation, their effect :hen they do occur is considerable. The Great importance of shade from surrounding vegetation, particularly canopy, even in periods of cloud cover has been emphasised by HaarlXv and Petersen (1952). They .shored that the presence of bark scales had an effect on temperature that was comparable to shading. Graham (1925) has investigated the subcortical habitat and its fauna on a variety of softwood species (Finus strobus, Pinus rosiness.) Pinus banksiana,

PiQea canadensis and Abies balsamca) and reached similar conclusions. He also emphasised that subcortical temperatures on the underside of logs are equivalent to those recorded in full shade. The colour of the bark was also expected to be important in determining subcortical temperatures.

Graham concluded that the distribution of insects under bark, although determined to a large extent by availability of food and prevailing relative humidity conditions, may sometimes be limited by temperatures beneath the ' bark. Such findings would seem to apply to species of Ptinella and are of particular importance in relation to the demonstrated differences between reproductive performance of species at different temperatures (Section 3).

Clearly investigations in this direction need to be extended, relating accurate subcortical temperature measurements made with minimum disturbance to the mieroclimate, to light intensity, ground and air temperatures, physical characteristics and dimensions of the bark, and temperatures of the wood imediately beneath. Such data should ideally be obtained for a wide range of tree species in a variety of situations, and should subsequently be related_ to Ptinella populations. - 115 -

SECTION 3.

LABORATORY EXPERMENTS ON 2--M BIOLOGY AND FECUNDITY OF P.APTERA AND P.ERRABUNDA (INCLUDING DATA. FOR

P.TAYLORAB).

3.1 Culture methods.

There is no account in the literature of the maintenance of Ptiliidae

in culture. All cultures were initially set up using adults (apterous

morphs only) and occassionally larvae, taken in an aspirator, from their

natural habitat. Eggs could not be collected since they were very difficult

to locate in the cavities of the rotten wood and bark; similarly pupae were

seldom found. Although the larvae were often abundant under bark they

suffered high mortality in aspirators as a result of their small size and fragility. Stock cultures were maintained in an outdoor insectary. Two methods were found to be satisfactory, the principle in both being the maintenance of the natural habitat in as intact a state as possible. Thus pieces of bark (maximum size 20 cm by 20 cm) under which Ptinella were found to be abundant, were packed into 30 cm by 30 cm polythene bags which were then rendered more or less air-tight by knotting at the top. This maintained the relative humidity inside the bag at around 109g. Such cultures could often be sustained for up to a year, providing they were opened periodically and sprayed with water. The most successful stocks, however, were those in which an entire section of a rotten branch was kept sealed in a large polythene bag. Obviously this was only practicable when a particular branch was found to support a high population of Ptinella, a suitable section could then be sawn off intact. The small stock culture of P.taylorae from Furnace,

County Mayo, has been maintained in this way for a period of 21 months without significant deterioration. The bag was opened once every L. to 6 months and the log sprayed with a little water to maintain high humidity conditions. - 116 -

A variety of other methods for stock and large scale experimental culture

were developed and tested. In all cases the closer the conditions in these

Cultures approximated to the natural habitat, the more successful they were.

Lengths of dead branch were heat sterilised (15 lb per square inch at 121°C for 20 minutes) and reinfected with wood-rotting fungi. They were placed in glass jars that had previously been sterilised in the same way. The relative humidity was maintained by standing the wood on a layer of water-saturated plaster of Paris or sand in the bottom of the jars. When fungal growth had become established known populations of Ptinella were introduced. Unfortunately the success rate with such cultures was low, the wood frequently becoming contaminated by the growth of moulds. The latter apparently inhibited the growth of the wooll-rotting fungi and produced conditions.unsuitable for

Ptinella. Similar attempts were made using thin strips of sound wood which had been heat sterilised and subsequently saturated with water. Glass jars were lined with these strips. Debris collected from beneath the bark of rotting, wood where Ptinella were found, was introduced into these cultures and if fungal development was adequate (subjectively assessed as presence of a mat of hyphae and spores between the glass and the wood strips) populations of insects were set up in them. Again this method, although highly successful on two occasions, was subject to failure through lack of development of wood-rotting fungi in the presence of considerable infections of contaminant moulds. One further method of culture was attempted using a pine sawdust medium. However, even if the wood-rotting fungi became established, contaminants were introduced. by the animals themselves. Populations of Ptinella failed to become established in any of these cultures. The successful stock cultures were maintained in the outdoor insectary, in the laboratory (for immediate availability) and in constant temperature rooms at 15°C and 2000. No further attempts were made to extend development of these particular methods of culture, the alternative stock cultures on bark and intact wood in bags being more efficient and less time-consuming to set up. -117--

Extraction of individuals from the stock cultures described was often

time consuming. Consequently a number of stocks were kept for immediate access,

in 10 cm diameter glass containers with a layer of plaster of Paris in the

bottom and sealed with "Bakelite" screw tops. Approximately 1000 relative

humidity was maintained in the cultures by ensuring that the plaster of Paris

was saturated with water. This culture method was a modified form of that

used by GOto (1960) for Collembola. Food was provided in the form of baker's yeast pellets which developed their own flora of contaminant moulds. Such

cultures were particularly useful for maintaining large numbers of beetles for a relatively short period of time between their collection and their use in experiments. They were kept at 20°C and 15°C in constant temperature rooms.

The best stocks were Obtained by leaving contaminated yeast in the cultures and adding fresh when the supply apparently ran short. It appeared that the dense populations in these cultures (approximately 2 animals per cm2 surface area) were sufficiently high for adult and larval feeding to control the spread of hyphae of contaminant moulds, thus reducing the major mortality factor (see below) due to adults and larvae becoming entangled in hyphae.

Although both the adults and larvae are able to bite through the hyphae, if the population density was low this had no significant effect on the spread of hyphae through the culture. Cultures were checked weekly (if not in constant use) and the plaster of Paris moistened with distilled water if required. In some cases when such a culture was first set up hyphae were controlled. by daily removal by means of a red hot needle. Any water that condensed on the sides of the containers as a result of temperature fluctuations, was removed regularly since both adults and larvae are easily trapped in drops of water and drown. Controlled laboratory experiments were carried out under highly artificial conditions. Individual parts of beetles were placed in 2 inch by 1 inch glass tubes with plastic closures. The tubes were filled to a depth of about 3 ems with pure plaster of Paris which, if it was kept more or less saturated - 118 -

with distilled water, enabled a relative humidity of approximately 100; to

be maintained under conditions of constant temperature. Pellets of baker's yeast were supplied as food initially, but this was found to support a large

microflora. An alternative method was devised using tiny squares of filter

paper on which a very concentrated suspension of yeast cells had been smeared.

This was easily removable if, after a few dgys, it became heavily contaminated,

however, an unforseen preference of the adults for the edges of the paper for

oviposition resulted in its having to be abandoned. Eventually the most

successful method was found to consist of smearing a little of the suspension

(made from baker's yeast pellets in distilled water) directly onto the plaster

of Paris and clearing the contaminants with a red hot needle every other day.

Resmearing was carried out when necessary. Despite these precautions mortality

due to fungi was high in the cultures. In the small surface area a pair of Ptinella was particularly susceptible to becoming entangled in hyphae which

apparently then "invaded" the insects' tissues resulting ultimately in the death of the latter. Larvae were particularly susceptible and in highly

contaminated cultures, eggs were also infected by moulds and failed to develop.

To overcome the problem of contamination an attempt was made to develop a completely sterile technique of culture. Culture jars with "Bakelite" screw tops were heat sterilised at 15 lb per square inch at 121°C for 20 minutes and the plaster of Paris was subsequently moistened with sterile distilled water. However, maintenance of a pure, contaminant-free yeast supply was problematical, bacterial contaminants being particularly difficult to eliminate. Further, surface sterilisation of the beetles in O.Z mercuric chloride was only partially successful unless it was repeated until the gut was empty and infection by this means reduced. Even then it appeared that spares were trapped in the mouthparts and-on setae and readily became established on the yeast. The treatment of the animals with the mercuric chloride resulted in a high mortality rate and eventually it was decided that no great advantage would be gained by further developing the technique which - 119 -

was abandoned in favour of the less controlled but undoubtedly more successful methods described.

The method was slightly modified to facilitate observations of

individuals over a period of time for some experiments and for life history

studies in particular. Glass tubes 2 by 2 inch containing plaster of Paris to a depth of 2 cm were used. Small yeast pellets or smears of cells were provided as food and the tubes were made air-tight by sealing with polythene closures.

In all cultures where plaster of Paris was used and eggs or individuals needed to be observed, care had to be taken to ensure that as smooth a surface

as possible was obtained. Beetles showed a strong preference for oviposition

sites in bubbles and cracks in the plaster. To provide "controlled" oviposition

sites, lines were made in the plaster by drawing a needle across the surface before it solidified.

Cultures for use in competition experiments had to be able to accomodate a potentially high number of individuals and to be as standard as possible.

Initially they were set up using perspex "butter" dishes with a 2 cm layer of plaster of Paris in the bottom. A standard quantity of yeast was added as a food supply. However, it soon became apparent that such attempts at standardisation of conditions were unsatisfactory since the development of contaminants could not be controlled and a high proportion of the "competing" populations failed to become established. In an attempt to reduce mortality and to make conditions resemble the species' habitat more closely, standard sized (25 cm2) discs of bark under which Ptinella had been found in large' numbers were dried in an oven at 60°C for .2 weeks to destroy all adults, larvae, pupae and eggs that might have remained undetected in the bark.

The discs were resaturated- with water and then placed in the culture dishes. When the microflora had begun to develop, the experimental populations were introduced. The size of the bark discs could be varied together with the amounts of yeast provided as additional food. - 120 -

During all experimental work apterous individuals were used, unless

otherwise stated, since these were the most abundant morph normally making

up more than 95% of the total population collected in the field.

3.2 Response of Ptinella to physical parameters of the environment.

(i) Relative humidity tolerance.

Ptinella species have only been recorded from microhabitats characterised by a high relative humidity (Johnson, 1972, 1975, in press). The importance of body size in the water relations of insects has been noted by many authors

(e.g. Bursell, 1974) and the high surface area to volume ratio of very small insects may in part, be responsible for their frequently observed dependence on environments with a consistently high level of relative humidity.

The precise humidity requirements were measured for P.aptera and P.errabunda in order to determine any differencei in tolerance that might permit them to exploit microhabitats of slightly different microclimate, coexisting only in narrow overlap zones. Such separation on the basis of humidity tolerance has been observed for anopheline mosquitoes (Pittendrigh, 1950). Experiments to determine the response of Ptinella to humidity were set up at 2000 in a constant temperature room. Humidity was maintained at a range of levels in a series of desiccators using solutions of potassium hydroxide at different concentrations (Solomon, 1951). Regimes were set up with the following relative humidities: 15% 55, 55g, 75,g, spg, 85g, 9z, 95%, 97% and 1000 (distilled water). Six adult individuals of each species were selected and placed in 2 x 2 inch culture tubes which had been positioned in the desiccators 48 hours earlier to allow them to equilibrate. Instead of being sealed with polythene closures, each tube was covered with a piece of fine muslin secured by an elastic band. This allayed free movement of air but prevented the insects from escaping. One of these experimental cultures was set up for each species at each relative humidity. All cultures were - 121 -

checked hourly for the first 10 hours and subsequently every 12 hours. The

number of dead individuals in each culture was recorded. The relative humidity

at the surface of the plaster of Paris was checked at the beginning and end

of the experiment using cobalt thiocyanate papers examined and assessed by

means of a Lovibond comparator. The experiment was repeated at all relative hmidities, except 975, when further animals were available.

It was observed that prior to death the beetles became inactive although

tactile stimulus produced response in the first stage of inactivity. There

then followed a Stage when the animals, although completely inactive, could

be revived on introduction to an atmosphere of 1005 relative humidity.

However, death was relatively easy to diagnose since the beetles were noticeably

dehydrated and appeared contracted. This seemed to be a direct result of

dehydration. In the lower relative hmidity conditions the animals were

noticeably active initially before becoming moribund.

The results of the two replicates of the experiment are presented in

Appendix 6 and are strmarised in Figure 3.1 as a graph of relative humidity (R.H.) against the tine at which 50' mortality was reached or exceeded.. The

graph shows that despite the high degree of variability amongst individuals

in both species, the humidity tolerance of P.errabunda tended to be slightly

lower than that of P.aptera. Individuals of neither species could apparently

survive for longer than 11 hours at 955 R.H. or 34. hours at 97;:, R.H. (this point is not included in Figure 3.1). Both species, with the exception of a single individual P.aptera were shown to survive for at least 9L hours at R.H. with no visible sign of deterioration or physical stress. This

indicated that death in the other cultures was not due to lack of food or

other factors, but to water loss. Attempts were made to repeat the experiment using larvae, but the

latter were so fragile that many were dn,laged during handling and it was

almost impossible to determine the mortality due to water loss. However, it

was clear from observations that the survival time of larvae at 95, and below was even shorter than for adults (larvae were not tested at 97)). Figure 3.1' Time of median mortality for P-..aptera and P.errabunda at different relative humidities -.temperature 20°C. 8 _

7_

6_

H 5_ tv Time for Median mortality 4 _ in hours a_

2_

A p.aptera

0 P.errabunda •

0 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

% Relative humidity - 124. -

The effect of relative humidity on the eggs was observed by placing

eggs in 2 x 1 inch cultures into the desiccators and recording those relative

humidities at which eggs hatched. It was -shown that resistance of eggs to desiccation enabled hatching of larvae at 8qi, R.H. and above although the larvae did not survive after hatching in the humidity regimes below locc•

(ii) Temperature tolerance.

Although temperature sets upper and lower limits to the actual survival

of insects, these may be considerably above and below the range over which

the animals are normally active and reproducing. A simple experiment was

carried out in order to investigate the range of temperatures over which

Ptinella are active and to determine approximately the upper and lower lethal

temperatures. Six individuals of each of the two species were placed in 2 x 1

inch culture tubes sealed with polythene closures to maintain 100;, R.H. One

tube for each species had previously been allowed to equilibrate for a period of 48 hours at each of the following temperatures: 30°C, 25°C, 20°C, 15°C,

100C, 50C and 0°C. The activity of the animals was observed at each temperature at 6-hourly intervals for a period of 24. hours. Subsequently they were checked again /1.8 hours after the start of the experiment. The experiment was repeated and the results of both replicates are Given in Appendix 6. The total number of individuals of ec.ch species seen to be active at any time during the five observation periods was plotted against temperature in Figure 3.2. It is immediately clear that the activity range of P.aptera is centred about higher environmental temperatures than that of P.errabunda. Below 5°C both species were inactive although a low degree of response was produced by tactile stimulation of P.aptera and active movement resulted from stimulat- ion of P.errabunda at this temperature (although all were relatively active after the first 6 hour period). At 000 or below, activity could not be induced, unless the temperature was increased. The activity of the beetles at the upper end of the range increased with temperature for both species being 125 -

FiGure 5.2 Yumbevs of F.aptera and F.errabunda active at different teppera.tureL. in five observ:Aion3 (total population 6 at each ternEerature).

10 20 30 Temperature in 0C - 126 -

expressed at 25°C and 30°C as a high degree of activity. However, after 12

hours at 30°C the activity of F.errabunda had apparently declined and after

4-8 hours 0.83 of the population of this species had become totally inactive or dead.

Individuals of P.taylorae and P.cavelli were also subjected to a temperature of 30°C and were found to die within 72 hours as did all

P.errabunda individuals. The observations on these species, although very

limited, suggested a range of activity resembling that of P.errabunda more

closely than that of F. aptera.

3.3 The effect of temperature on the life history. (i) Fecundity and oviposition rate.

The effect of temperature on egg production in insects has been invest-

igated by a number of authors and is of particular interest in Ptinella.

Dybas (1966) has assumed that the small size of Ptiliidae and the large size

of the eggs that mature singly, filling two-thirds of the abdomen, must

restrict the fecundity of these beetles. However, the often very dense populations of ptiliids have been reported by molly collectors and were

freciuently observed in the course of this study. The foregoing experiments

suggested that the differences in activity at various temperatures between

the species should be reflected in similar variations in fecundity and

oviinsition rate. A range of five temperatures was selected covering the activity range of both species. Ideally pupae of the same age or newly emerged adults should have been used to start the experiments. However, the problems of culturing made the supply of a large number of suitable individuals impracticable.

Instead individuals were selected from cultures maintained at appropriate

temperatures for at least 2b, hours previously (with the exception of

P.errabunda at 30°C which was set up from cultures at 25°C). Observation

had suggested that during the pre-oviposition period the pigmentation in all - 127 -

of the three species considered is not fully developed. Consequently animals

for fecundity experiments were selected subjectively on the basis of their

degree of cuticular pigmentation. Unfortunately this meant that the possibility

of any given female having laid eggs previously could not be completely

eliminated.. However, it seems likely that the majority of the insects had.

not previously oviposited and thus the experiments should give fairly reliable data on the total fecundity.

Individual females of P.aptera,. P.errabunda and P.taylorae were placed

in 2 x 1 inch culture tubes. In the case of the two bisexual species, a single adult male was placed with each female. Active males with almost full

pigmentation were used and if a female subsequently ceased to produce eggs,

the male was replaced. The aim of this was to reduce the probability of a female running out of sperm if the male failed to re-mate. Similarly if a male died it was immediately replaced. The cultures were set up in constant temperature rooms at 1000, 1500 0°C, 25°C and 30°C with twenty replicates at each temperature in the case of P.aptera and P.errabunda. The highly localised known distribution of P.taylorae and the existence of only a single stock culture prevented the nee of more than eight replicates and all of these were kept at 20°C. Eggs in the cultures were counted every alternate day and when the number of eggs in any culture became difficult to count under a binocular microscope (normally when in excess of 20) the female (and male where applicable) were transferred to a new culture. The same procedure was followed if a culture became particIlar4 heavily contaminated, such that the activity of the beetles was impeded by fungal hyphae. If a female died prior to oviposition the fact was recorded and when possible the cause of death was identified subjectively as either being accidental or "natural". Thus in some cases it was quite clear that a female had died as a result of becoming tangled in hyphae and such mortality was regarded as a direct consequence of inadequate culture methods and termed "accidental". Regardless of the cause of mortality these females were repleed to ensure a cohort of 20 reproducing - 128 -

females for subsequent analysis. The deaths of the females were recorded but if they had oviposited prior to death they were not replaced.

The results are presented in detail and summarised as fecundity schedules

for each species at each temperature (Appendix 6). The number of eggs laid in each two day time period is plotted in the form of npyrnmids" along a time

base for each female, thus providing a visual display of the variation in

individual patterns of oviposition. Beneath these is plotted a female survivor-

ship curve based on the same data. The total egg production of the cohort of

20 females is plotted as a histogram along a similar time base. The schedules only cover the adult life of females. The duration of the pre-oviposition

period used in plotting the graphs was a mean value derived from another experiment (see below). Inevitably this resulted in inaccuracies' in expresding the pre-oviposition period since it was impossible to establish precisely the tine that had elapsed between emergence and beginning the experiments for each individual. In practice, the mean for pre-oviposition period was used and only if full pigmentation was observed prior to oviposition, was a- further length of time added. Such undesirable inaccuracies could only have been eliminated by using individuals whose emergence date was known and, as explained above, this was impracticable in the circumstances.

The mean cumulative total of eggs was plotted with time over the mean female lifespan for P.aptera and P.errabunda at each temperature and or

P.taylorae at 20°C in Figures 3.3 and 3.4. The results show that at 15°C there was a slight tendency amongst some of the population of P.aptera to produce more eggs in the latter part of adult life. However, there was relatively little evidence of an overall fall off in egg production with increasing longevity. At 15°C the total egg production of the experimental populations of P.aptera and P.errabunda was similar, but at'20°C there was a marked increase in egg production by P.aptera whereas that of P.errabunda was of the same order as at 15°C despite the increase in the daily oviposition rate. The increase in egg production by P.aptera, was - 129 -

even greater at 25°C and 30°C; however, P.errabunda showed only a slight

increase in oviposition rate at 25°C and the longevity was greatly reduced,

being comparable to that of P.aptera at 30°C. The high degree of individual

variation in egg production is shown by the schedules. The schedule for

P.taylorae is not directly comparable with those of P.aptera and P.errabunda

since the cohort was of only 8 individuals as opposed to 20 for the other two

species. However, the graph of cumulative number of eggs plotted against time

permits such a comparison to be made. It is apparent that for oviposition rate

and egg production at 20°C values for P.taylorae approximate .those of P.aptera

more nearly than they do those of P.errabunda. The graphs also show the

relatively consistent nean rate of oviposition throughout the mean duration'

of life for each species at each temperature, although in P.errabunda at 2000

and 25°C after an initial linear increase the oviposition rate decreases with

increasing time. In P.aptera this fall-off is less marked. The oviposition rate of P.aptera is greater than that of P.errabunda at all temperatures above 15°C, although at the latter temperature the two are very similar.

The reduction in mean female life-span with increasing temperature is also illustrated. Values of the mean longevity of female Ptinella are presented in Table 3.1. There is no significant difference between the values for

P.aptera and P.errabunda at the some temperatures at 15°C and 20°C. However, at 25°C the longevity of P.errabunda is significantly lower - 29.10 days (4. 2.60 days) compared with 38.40 days (± 3.32 days) for P.aptera. The mean longevity of P. taylorae does not differ significantly from that of either

P.aptera or P.errabunda at 2000. Male longevity appeared to be slightly lower than that of female, however the difference was probably not significant.

(ii) Proportion of eggs hatching and duration

of the egg stage.

The variation with temperature in the proportion of eggs hatching was - 130 -

FL_;ure 5.3 Gra7h of me,:,n cumulative tot.7.1 .07"!S 1:ith time at aifferent temperatures - P.a,Dtera. OC

0 25 C 80_

60 _ Cumulative 0 no. eggs 20 C

40 o 15 C

20

20 40 60 Time in days . Figure 3.4 As 3.3 - P.errabunda. 80

Cumulative no. eggs Rtaylorae 20 0C

0 15:C

20 1000

20

40 60 80 Time In days - 131-

measured for all species. Between 10 and 20 females were placed in 2 x 1 inch

culture tubes and maintained in constant temperature rooms at 10°C, 15°C, 20°C, 25°C. and 30°C. The animals had been recently collected and thus a period

of 5 days was allowed to enable the insects to become adapted to the experi-

mental temperatures. After the initial 5 days the animals were transferred

to fresh cultures. Thereafter the culture vessels were changed daily, thus

ensuring that all the eggs in a tube had beenproduced within a single 24

hour period. Exceptions to this procedure were cultures at 10°C and those of P.aptera at 15°C when the oviposition rate was very low. In such cases a culture was maintained and eggs were destroyed until the peak 24 hour period of oviposition was thought to have been reached; only then were the Ptinella transferred to new cultures. The major drawback of this experiment was the high degree of contamination by fungi in the absence of activity of adults or larvae. Initially 20 replicates were set up (30 for P.aptera at 30°C due to the rapid rate of ovipositi6n), but the number of cultures unaffected by fungi was aslow as 5 (P.aptera at 20°C). It had been observed that the fungi attacked eggs, presumably destroying or damaging them. Consequently it was decided that in order to eliminate gross distortion of data as a result of mortality due to fungi, any cultures showing fungal growth around eggs should be abandoned. The cultures were inspected daily and the usual precautions against fungi were taken. In order to measure the duration of the egg stage it was necessary to remove the larvae in the 24 hours immediately after they hatched. The fragility of the larvae, however, was such that few of them survived removal from the culture vessel even on a single hair of a paint brush. Since larvae were required. for other experiments (see below), the procedure of daily removal and counting of larvae was only followed for the first two cultures of each species at each temperature or for sufficient to provide egg stage duration data for at least 20 eggs; (the only exception here was for P.taylorae for which suptlies of all stages were very liaited) and for P.aptera at 15°C. -132-

Table 3.1. Mean longevity of adult Ftinella at aiffcrent temperatures.

Mean longevity in days (with standard error -S.E.) Temperature Species P.utera P.errabunda P.toirlorre in 0C Snmple sine 20 )0 15

10 57.20+4.00

15 58.70+3.06 53.90+3.4.8 20 39.00+3.72 38.00+3.92 39.76+3.56

25 38.40+3.32 29.10+2.60

30 26.50+2.18

Table 3.2. Proportion of eggs of Ptinella hatching at different temperatures.

Prol.crtion of eggs hatching (numbers of eggs in brackets)

Temperature Species: li'.aptera P.errabunda P.taylorae in 00 10 o 0.75 (77)

15 0.64. (61) 0.76 (251) 20 0.82 (99) 0.55 (128) 0.82 (84.)

25 0.83 (298) 0.4.1 (61)

30 0.83 (534.) - 133 -

It was normally quite si,aple to determine whether an egg had hatched,

since the area of the chorion through which eclosion takes place was, if not totally absent, distinct.

he proportion of eggs hatching for each species at each temperature was calculated by summing the data over all the cultures since the number of eggs

in each culture shaved considerable variation and was so:Jetties low. The

data are summarised in Table 3.2. For P.aptera the proportions.of eggs

hatching at 30°C, 25°C and 20°C were similar and relatively high, of the order

of 0.83; but at 15°C the success falls off raridly and at 10°C eggs did not

hatch for the entire period of observation (150 days). P.errabunda however,

showed an opposite pattern although the proportional hatch at any temperature

was considerably lower than that of P.aptera (0.76 maximum hatch achieved at

15°C). The hatching success of P.taylorae at 20°C was estimated from 5 cultures and a total of 84 eggs and was found to be 0.82 - the same value as

that calculated for P.antera at 20°C.

The mean duration of the egg stage was calculated at all temperatures for both species and plotted as a reciprocal against time (Figure 3.5). Both

P.aptera and P.errabunda show a inverse relationship between duration of this stage of the life cycle and temperature. _,egression equations (Appendix 2) were fitted to the data and found to be significant for P.aptera (P = 0.05 -

0.0* but not for P.errabunda (P = 0.10). The results .are summarised in '

Table 3.3..

(iii) Duration of immature stages.

The effect of various temperatures on the duration of immature stages of the life cycle (from hatching to emergence as an adult) was investigated by observation of individual larvae from the 24 hours during which they hatched to the time when they emerged as adults. In order to facilitate this, 2 x 2 inch culture tubes were used. Larvae were transferred on the tip of a hair during the 2) hours following.their hatching in the previous exi,eriment. The 1314.

Table 3.3. Mean duration of egg stage of Ptinella at different te,Iperatures and results of linear regression analysis of reciprocal of duration on temTerature.

Mean duration of egg stage in days with Standard. error (no. of eggs in brackets) Temperature Species: P.aptera P.errabunda P.taylorae in oc 10 46.36+0.58(25) 15 50.40+3.66(8) 33.40+0.61(30) 20 12.52+0.21(42) 20.76+0.48(25) 15.00+0.27(11) 25 10.44+0.08(50) 21.65+0.41(20) 30 7.66+0.11(50)

Regression coefficient 0.0070+0.0012 0.0018+0.0005 Degrees of freedom 2 2 t value 5.802 3.422 Probability P=0.05-0.02 P=0.10

* denotes faL;2.7.2e, of eggs to hatch - 135 -

high mortality of these larvae as a result of transference has been noted.

A total of 10 individuals of each species at each temperature was observed

daily until they emerged as adults, the immature stages being recorded to

determine the number of larval instars and their duration. If an inditidual

died (mortality due to fungal contaminants was high in this experiment as a

result of the limited activity of the larvae in their destruction/control of

the hyphae) a replacement culture was set up. In order to eliminate the

possible effect of temperature during the ggg stage affecting subsequent

development, larvae were taken from cultures at their respective temperature.

Consequently, due to the relatively small number of larvae and the delay in

their availability as a result of the long duration of the egg stage in

cultures at 15°C (P.aptera), 1000 (P.errabunda) and 25°C (P.errabunda - due to

the generally low degree of success of this species at 25°C) only 5 individuals

were followed through. In each of the 3 species, 3 larval instars were distinguished. The

results are set out in. Table 3.4.. Although the duration of instars is variable, there is a consistent inverse relationship with tenperature. The

trend of differences between lengths of instars at a single temperature

tended to be highly variable from one temperature to another. The duration

of the pupal stage varied with temperature in much the sane way as the larval

instars. At 20°C and e:bove, the nean duration of the immature stages P.errabunda was slightly greater than that of P.aptera. But below 20°C those of P.aptera here greater than P.errabunda. A graph of the reciprocal of the total duration of intiature stages, was plotted against temperature (Figure 3.6) and the results of the regression analysis on this data are given in Table 3.4. Regression coefficients for both P.a7)tera and P.errabunda were significant (P = 0.01 for P.antera; P = 0.01 — 0.02 for P.errabunda). Comparison of the coefficients and their standard errors showed that they were

significantly different. A single value for the duration of the total immature stages was -136-

Figure 3.5 Regreor;ion of reciprocal of mean duration of egg stage on temperature for P.aptera and P.errabundf A

0.12_ b = 0.0069 _ P.0.156--0.02

0.10_

0.08 _ A 1 Days

0.06

0.04 _ b =0 0018 P.= 0.1.

0.02 _ A P.aptera

0 Rerrabunda

20 30 Temperature in °C. Figure 3.6 RegresciOn of reciprocal of mean duration of inmature. stage on temperature for P.aptera and P.errabunda.

0.10 b=0.0044 P=0.01

0.08

0.06 b=00028

1 P=0.01-0.02 Days

0.04

0.02 A P.aptera

0 Rerrabunda

10 20 30 Tempeiature in °C. - 137 -

Table 3.4. Variation in the mean duration of imuature stages of Ptinella with temperature and results of lin7:ar regression analysis of reciprocal of duration of total Li mature period on temperature.

;:ean duration of immature stages in days with standard errors (no. of individuals observed in bracl:ets) Temperature Stages: Inctar 1 Ins'car- 2 Instar 3 pupa total in oc (i)P.aptora

15 (5) 13.60+0.51 9.80+0.73 14..60+0.51 11.20+0.37 49.20+0.66 20 (10) 4.60+0.22 3.70+0.21 5.60+0.31 5.80+0.39 19.70+0.42 25 (10) 2.50+0.17 2.30+0.15 4.90+0.31 5.00+0.21 14.70+0.34 30 (10) 2.10+0.26 2.40+0.22 2.40+0.16 4..50+0.27 11.40+0.43 (ii)P.errabunda

10' (5) 12.80+0.8475.40+0.51 34.20+0.49 14.80+0.80 57.20+0.80 15 (10) 5.90+0.2313.20+0.33 13.90+0.28 7.70+0.26 40.70+0.58 20 (10) 6.20+0.36 6.10+0.23 5.30+0.30 6.90+0.23 24.50+0.34

25 (5) 3.20+0.20 5.00+0.32 4.80+0.37 4.20+0.37 17.25+0.86

.1.:ean duration of total inAature stages for P.ta7lorae at 20°C = 23.75+0.85 days.

Regression coefficient for reciprocal of P.aptera P.errabund.a total duration iivature stages on temperature with S.E. 0.0044+0.0001+ 0.0028+0.0003 Degrees of freedom 2 2 t value 10.752. 8.1165 Probability P = 0.01 P=0.02-0.01 - 138 -

calculated for P.taylorae. The result is a mean derived from four individuals

followed through to adult energence. Due to the extreme scarcity of first instar larvae of this species, an attempt was made to minimise larval mortality

in the cultures by making conditions ,..-4.40 "naturnitt nosRible- To achieve this, small sauares of suitable bark - 3 cma - were heat sterilised and permitted to develop a small fungal microflora. Seven newly-hatched larvae.were introduced into two cultures, 3 from one 24. hour Period and 4. from a subseaUent one. The cultures were maintained at 20°C and examined daily. The date on flhich adults emerged was recorded. The mortality in these cultures was almost 525 since only 4. adults emerged. The mean value for the total duration of immature stages in this species did not differ significantly from.that of

P.errabunda at 20°C.

(iv)Duration of pre-oviposition period.

The effect of temperature on the duration of the pre-oviposition period was measured by taking individuals during the 24 hours immediately after emergence and, in the cases of P.aptera and P.taylorael sexing them and placing individual females in 2 x 1 inch c3zlture tubes. Two fully pigmented males were placed with each female to ensure mating and 5 replicates were set up for each species at each temperature. The tubes were inspected every 2L. hours and the date on which oviposition commenced was recorded. Three replicates were set up for P.taylorae at 20°C. The results are given in Table 3.5 expressed as mean values for each of the species at each of the different temperatures. The duration of the pre-oviposition period did not differ significantly between the two species at any one temperature and followed an inverse relationship with temperature.

(v)Duration of total pre-reproductive period.

The mean values for developmental time for the two species at each temperature and for P.taylorae at 20°C were added to the respective mean

-139-

Table 3.5. ::ean duration of the pre-oviposition period of Ptinella at different temperatures.

rcan duration of pre-oviposition period in days with standard errors (no. of individuals observed in brackets).

Temperature Species: P.aptera P.errabUnda P.trjlorae •in 00 •

10 15.00+0.34(5)

15 12.00+0.77(5) 11.40+1.12(5)

20 6.00+0.45(5) 5.60+0.51(5) 7.00+0.58(5)

25 4.00+0.32(5) 4.20+0.37(5)

30 3.40+0.51(5)

Table 3.6. Duration of pre.-_reproductive period of Ptinella at different temperatures (sum of mean values for duration of e'eg and inriature stages) and results of regression analysis of reciprocal of pre-reproductive period on temperature.

Duration of pre-reproductive period in dwfs

Temperature Species: P.aptera P.errahunda P.taylorae in 0C 10 118.56 15 111.60 85.50 20 38.22 50.86 45.75 25 28.98 43.10 30 22.46

Regression coefficient (with S.E.) 0.0023+0.0003 0.0010+0.0001 " t value 8.423 8.045

Probability F=0.01-0.02 F=0.01-0.02 pre-oviposition periods to derive a value for the duration of the pre-reproduc-

tive period (including the egg stage). The results are presented in Table

3.6. This data was plotted as a reciprocal against time and the regression

coefficients were calculated for each species, tested for significance and

compared with one another. Both coefficients were significant (P = 0.01 -

0.02 for both species) and their stanaord errors were found to be non-over- lapping indicating"significant differenos (Figure 3.7).

The length of the total pre-reproductive period is consistently shorter

in P.aptera than in P.errabunda, except at 15°C. The latter value for P.aptera was 111.60 days and was thus only slightly shorter than the

developmental time of P.errabunda at 10°C. P.tsylorae, with a total value of 45.75 days for development at 20°C is closer to the value for P.errabunda (50.86 days) than P.aptera (38.22 days).

(vi) Pre-reproductive mortality and fertility.

The value for pre-reproductive mortality covered the period from hatching

to oviposition. Ten individuals were placed in butter dish cultures, one for each larval instar for each species at 150C, 20°C and 25°C and at 30°C for P.aptera and 100C for P.errabunda. Five replicates were used and the cultures were checked at weekly intervals. A week after adults were first observed in the cultures, the bark was removed and carefully dissected and the number of adults recorded. Due to the lack of suffioient larvae it was not possible to carry out this experiment with P.tsylorae. The results are presented in detail in Appendix 6;some'eultures were aborted as a result of excessive fungal or bacterial contamination. The results show the mortality in the instars summed, a rough estimate of death-rate was made for each instar by subtraction. Thus the mortality in the third instar and pupal stage was subtracted from that derived from cultures set up using second instar larvae etc. The populations were too small and the replicates too few to make these estimates particularly meaningful. Nevertheless, it did appear that where the overall developmental mortality was high, in P.aptera, at 15°C and P.errabunda at 10°C and 25°C, the highest level of mortality apparently

occurred during the third instar-pupal stage. This could merely have been a reflection of the longer. duration of these two stages considered as one in the

experimnts. The causes of mortality were not identified.

A mean value for the total pre-reproductive mortality of Ftinella was

obtained by addition of an estimate of prekwiposition mortality to the mean

mortality occurring in cultures set up from first instar larvae. These data

are given in Table 3.7, the former estimate being included in brackets. The

data for this estimate were obtained from the fecundity experiments described

above, the number of individuals dying before oviposition being recordedinum

mortality of pre-reproductive stages of P.errabunda is lower than the minimum

recorded for F.aptera (0.40 + 0.02 + 0.05 pre-oviposition mortality). The maximum mortality noted for either species was a value of 0.58 + 0.05 for

P.aptera at 15°C. Fertility was also estimated from the fecundity experiment, the number

of females dying without producing any eggs being recorded for each cohort.

Although the populations were relatively small, there was some evidence for

decreased fertility of P.aptera at 15°C. The results are displayed in Table 3.8. The fertility of P.taylorae was apparently. rather low at 20°C although

the population size was too small to permit any great importance to be attached to such an estimate.

(vii) Sex ratio.

The values for the relative numbers of males and females of P.aptera

and P.taylorae were calculated by summing the results of as many rearings as were available. These included cultures in the previous experiments where adults were bred from known apterous parents. 'Zany of the data were obtained from fecundity cultures that remained sufficiently uncontaminated for some animals to survive to adult emergence, at which time sexing was possible.

The data were summed and an overall sex ratio calculated for P.aptera at each - 142 -

Table 3.7. ::ean proportional riortality of pre-reproductive stages of Ptinella at different teLiperatures.

1:ean proportion iv.ing rith standar& errors

TeuTerature Species: P.aptcra P.errabunda in 0C No. of populations 10 5 o.4.6+o:o6 15 5 0.58+0.05 0.22+0;02 (+0.05) 20 5 0.48+0.0 (+0.05) 0.32+0.04 25 4 0.47+0.06 0.42+0.08 (+0.05) 30 5 0.40+0.06 Figure in brackets represent adult pre-oviposition mortality

Table 3.8. Fertility of female Ptinella at different temperatures.

Proportion of females lgying eggs (no. females in brackets)

Temperature Species: naptera Pierrabunda •.112. 1L,2/1211.!a in oG

10 0.95 (21) 15 0.91 (20) 1.00 (20) 20 1.00 (20) 0.95 (21) 0.89 (8)

25 1.00 (20) 1.00 (20) 30 1.00 (20) - 13 -

temperature in terms of proportion of progcny that are female. The results

are summarised in Table 3.9 as the overall propartion of•females. The results show a sex ratio slightly biased in favour of males. The sex ratio for

P.taylorae at 200C was estimated to be 0.45 (females as proportion of total progeny). It is thus very similar to the value calculated for P.aptera at 200C: 0.46.

3.4. The estimation of life table statistics

at different temperatures.

The reproductive potential of a species depends on numerous environmentally determined factors such as longevity, fertility, duration of immature stages etc.. However, there exists for every species a fundamental ability to replicate itself at a particular rate; this has been defined by Andrewartha and Birch (1954) as the innate capacity for increase (Lotka's intrinsic rate of natural increase). This property of a species is difficult to measure since it is readily modified by prevailing environmental conditions. Any estimate of this statistic (rm) must include the specification of the environmental regime under which the estimate was made. The calculation of rm from data on natality and mortality was demonstrated by Lotka (1925) and despite the problems concerned with its accurate estimation, the innate capacity for increase reflects the level of reproduction optimised by natural selection for a given species under a specific series of environmental factors. It is thus of great relevance in the investigation of the reproductive performance of closely related species exhibiting a greater or lesser degree of coexistence. In order to determine the reproductive potential of P.aptera and

P.errabunda and its variation with a single, controlled environmental parameter - temperature - the data from the foregoing experiments were used. An attempt had been made throughout the experiments to minimise the variation in parameters other than temperature, keeping relative humidity and food supply optimal. In the absence of the standard life table data for a cohort of

mothers, statistics were calculated for individuals using mean values for the duration of the pre-reproductive period, the proportion of eggs hatching,

the proportion of individuals surviving to reproductive age, fertility of

females and the sex ratio. These population means were used in conjunction

with the egg production and longevity data for the individuals of each species at each temperature (derived from the fecundity e::poriments) in order to

estimate the mortality and natality of the individuals. The calculation of reproductive statistics was performed using a programme (W.D.Hamilton,

unpublished) on the C.D.C. 6600 computer. The output of the programme

consisted of values for the gross and net reproduction rates, the multipli- cative rateaef increase, the innate capacity for increase and four estimates

of generation time. Only three of these statistics were used for subsequent

analysis. These were selected as being the most useful in reflecting

reproductive performance and also because they were calculated directly from

the data independently of each other. They are as follows:

the innate capacity for increase rm given by q-rmx1xFx = 1

the net reproduction rate Pao given by • Ito = tlxFX

mean length of generation (the mean age of parturition for a cohort of mothers) VIZU given by 7IZU = 2: xlxFx 1xFx The values estimated for the two species were compared over the three

temperature regimes where both effectively reproduce (i.e. 15002. 20°C and

2500) using an analysis of variance for a factiorialdesign incorporating an orthogonal polynomial breakdown to take into account the relationship between

the statistics and temperature in each species. The analysis was performed using the programme LL 02V (analysis of variance for fact orial design, Health

Sciences computing facility; U.C.L.A. version of July 22nd, 1965) on the CDC 6600 computer. The breakdown for the species was ignored, but that for temperature investigated the relationship between each species and variation

- 145 -

Table 3.5. FeJale se= ratio of Ptinella at different temperatures.

Proportion of fannies (no. of individuals in brackets)

Te:.-Terature in 0C 15 20 25 30

(i)P.aptera 0.49 (198) • 0.46 (336) 0.47 (138) 0.43 (69)

(ii)P.ta:lorae 0.45 (20)

Table 3.10. Linear and quadratic - conparisons and variance ratio test of life table statistics of P.aptera and F.errabund.a at 15°C, 20°C and 25°C.

(i)rri Interaction a.f. Mean sauares Variance ratio F Linear 1 0.0094 156.5000 quadratic 0.0002 3.1667 "Error" 0.0001

(ii)ao Interaction Linear 1053.4437 98.4748 * quadratic 1 1.8431 0.1723 "Error" 10.6976

(iii)W.Z.U. Interaction Linear 1 8384.2697 128.8017 Quadratic 1 3485.9326 53.5520 "Error" . 65.0944

0.01 level of probability for F 6.87 for 1 and 114 degrees of freedom (d.f.)

* denotes significance at the 0.01 level of probability. - 146 -

in temperature. A variance ratio test was then employed to determine if the

relationship of the statistic differed significantly between the two species.

The results of the analysis are set out in Appendix 6. The results of the F test are given in Table 3.10. The linear sums of squares are highly

significant for both rm and Ro showing that the values are approximately

fitted by a linear regression ecuation, but the regression coefficients for

the two species differ with a high level of significance (P<( 0.01). However,

for 701 both the linear and quadratic, sums of squares were significant

indicating the absence of a simple relationship between this estimate and

temperature. It is clear that the values and the effect of temperature on

them are significantly different between the two srecies. Mean values for the

statistics are given in Table 3.11 for both species over the range of

temperatures investigated. The graph of rm with temperature (Figure 3.8) for the populations shows a direct linear relationship for P.aptera over the temperature range. The intercept on the tenTerature axis implies that the rate of increase will be negative below about 13°C. The graph for P.errabunda, although apparently more or less linear between 10°C and 200C shows a fall off in the rate of increase at 250C. Results of a linear regression analysis are given in Figure 3.8.. The regression coefficient is significant for P.aptera but not for P.errabunda. Ro for P.aptera shows a rapid increase over the range 15°C to 25°C increasing only slightly thereafter to reach a recorded maximum at 3000 (Figure 3.9). For P.errabunda however, Ro increases rapidly from 100C reaching a recorded maximum at 1500 and then decreases in a linear relationship at 200C and 25°C. The reciprocal of generation time plotted against temperature (Figure 3.10) fits an approximately linear relationship for both P.aptera and P.errabunda. Results of linear regression analysis show significant regression coefficients for each species (1, = 0.01 - 0.02) although they are not significantlyy different from each other.

The maximum value of rm for P.errabunda was recorded at 20°C (0.0248 4. 0.0017). It did not differ significantly from the corresponding value for

P.aptera (0.0257 ± 0.0023). However, the maximum for P.aptera was almost -11+7-

'able 3.11. :"ean values of life table statistics for Ptinella at aifferent temperatures.

(i) Intrinsic rate of natural increase i per female per. (with S.3.) Temperature Species: P.aptera P.errabunda P.taylorae in °C 1 10 0.0109+0.0007 15 0.0057+0.0000 0.0212+0.0006 20 0.0257+0.0023 0.0248+0.0017 0.0230+0.0017 25 0.0471:+0.0022 0.0195+0.0020 30 0.0657+0.0033 (ii)Net reproductive rate Ro in females per female per generation (with S.E.) 10 .5..61+0.60 15 2.53+0.25 10.29+0.78 20 5.20+0.72 6.24+0.72 4.33+0.47 25 10.36+1.15 3.61+0.43 30 10.64+1.23 (iii)Generation time W.Z.U. in diz7s (with S.E.) 10 147.68+2.23 15 11,2.35+2.12 109.65+1.72 20 57.15+1.74 67.80+1.93 63.11+1.51 25 2.61+1.92 56.86+1.28 30 34.90+0.95

Means of values for 20 female P.antera, 20 P.errabunda and 8 P.taylorae. Figure 3.7 Regression of reciprocal of ..Jean. duration of pre-reproductive eriod on ternterature for P.c..-:stere. and P.erraounda.

b = 0.0023 P = 0.01-0.02 0.04

0.03 b =0.0010 P =0.01- 0.02 1 Days

20 o Temperature in C.

Figure 3.8 Variation of rri :L,:i- rature in P.a--)tera and F.e:rabunda.

b = 0.0040 P < 0.001

A P.aptera

10 20 Temperature in 0C.

— -- ?iGure 3.9 Variation of Pi'.0 pith teloperature in P.a7:,tera and P.errabunda.

10_

8_

6_

R o females per _ generation 4

2

0 P. errabunda

10 20 30 o Temperature in C.

FiGure 3.10 Rezression of reciprocal of W.S.U. on terxcerature for P.aptera and P.errabunda. 0.-03 b= 0.0014 P=0.01-002

b = 0.0008 P=0.01-0.02

0.02

1 WZU in days

0.01

A Raptera

0 R. errabunda

20 30 Temperature in °C. -150-

three times that value (0.0657 + 0.0038) and was recorded at 30°C. At 15°C

the value for P.aptera is approximately one third that of P.errabunda at the same. temperature, the latter value being only slightly below the maximum

recorded at 200C. P.errabunda shows a positive rate of increase at 100C. A single individual P.aptera at 15°C registered a negative rate of increase.

For RO values there is a similar pivotal temperature at 20°C above which

P.aptera shows higher values than P.errabunda and below which the pattern is

reversed. The maximum values of Ro did not differ significantly but were recorded at 15°C and 30°C for P.aptera and P.errabunda respectively (10.29

± 0.78. and 10.64:, + 1.23 ). Values of rm, Ro and MIZU were also computed for P.taylorae at 20°C. They were compared with the corresponding values for

P.aptera and P.errabunda using Student's t test for significant difference

between means of two small samples. The analysis was carried out on the Wang

advanced programming calculator 720 B (Appendix 2). No significant difference

was found between P.taylorae and either P.aptera or P.errabunda for values of rm and Ro although a significant difference (P = 0.05) was recorded from

P.aptera for VIZU (Table 3.12).

3.5 Discussion. (i) The effect of relative humidity.

The relative humidity tolerance experiments have shown that both P.aptera and P.errabunda are only able to survive in a very limited range of humidity conditions approximating the saturation point. Neither species was apparently able to survive for more than 314 hours at 97 R.H. which represented the highest R.H. regime that was set up below the saturation point of 100;1 R.H.

Since the Lovibond comparator has a 5% margin of error at high humidities and 97% R.H. was the highest humidity that could be accurately generated using volumetric methods described in the literature (Solomon, 1951), the range of humidities between 97g and 100% R.H. was not tested. The slight difference - 151 -

Table 3.12. 0ormarison..of life table statistics between P.tvlorae and.

P.aptera and P.errabunda at 203C us4ns Student's t test.

1:ean standard error t value degrees of Probability free dola ru intrinsic rate natural increase/female/dad P.aptera 0.026 +0.002 0.7081 26 P2> 0.10 P.tavlorac 0.023 +0.002 0.6511 P.errabunda 0.025 +0.002 26 P > 0.10

Ro net reproduction in fe:iales/female/Generation P.aptera 5.203 +0.722 26 P. 0.10 0.733 P.tcvlorae 4-.331 +0.473 1.603 26 P > 0.10 - P.errabunda 6.236 +0.721

generation ti:Je in days 57.153 +1.735 LLIvItEa 2.035 26 P .1=0.05 P.taylorae 63.105 +1.505 1.4.57 P.errabunda 67.802 +1.951 96 P > 0.05 - 152 -

between the median - lethal times of P.aptera and P.errabunda is of insufficient

r. ,finitude to be statistically significant and it would thus a-ppear that coexistence is not facilitated by differential relative humidity tolerances

of the species. 3ven if significant differences ei2erged in the 97,.. R.H. to

100;` R.H. range it seems probable that such niche differences would not be

sufficiently great to separate the species in ecological terms. The normal

variations in microclimatic conditions would probably be of this order and

tolerable, for relatively short periods at least, by both species. lievertheless,

it is possible that the ability of individuals of the two species to recover

from short periods of exposure to conditions of low relative humidity might

differ sufficiently to permit them to have species optiTna in slightly different

microhabitats under bark. Since the observations of field populations show

no evidence of this, it is concluded that a species separation on the basis of relative humidity tolerance similar to that suggested. by Paviour-Smith (1960a) for species of Ciid beetles, probably does not exist between P.aptera and

P.errabunda.

The inability of both species to tolerate prolonged periods of relative humidities at or below 97% R.H. and possibly those even closer to saturation, implies that this factor is of considerable importance in limiting their distribution by determining the areas beneath rotting bark where they can survive. The lower tolerance of larvae to adverse humidity conditions, although not demonstrated. conclusively by controlled experimentation, is a result that would be predicted since the larvae are particularly susceptible to water loss as a result of their high surface area to volume ratio. Presumably the apparently "thin" integument is relatively permeable to water loss by evaporation thus making the larvae dependent on an almost saturated atmosphere to maintain their water reserves, Investigation of the extent of these in all stages of the life history and the means by which water loss is regulated and replenishment facilitated, are required to further determine the environmental water requirements of Ptinella and the extent to which these are realised in the rotting wood habitat. - 153 -

Since solutions of potassium hydroxide were used to determine the relative

humidity tolerance of Ptinella, the possibility of the insects being adversely affected by proximity to the caustic solution cannot be eliminated.. Although

the dead individuals showed :symptoms of death as a result of desiccation such

effects could have been the result of the breakdown of water loss regulation

at death, or even an effect of the chemical on the mechanism of regulation.

Nevertheless, in some cultures where individuals almost certainly died as a

result of dehydration, relative humidities of around R.H. were recorded. It is thus concluded that the data reflect with a reasonable degree of

reliability, the humidity tolerances of P.antera and P.errabunda.

Presumably the strict humidity requirements of Ptinella tend to restrict

them to the sub-cortical zone reducing the likelihood of their straying into

the less optimal litter. However, they are problematical in the consideration

of the dispersive/migrational activities of elates which move from conditions of relatively optimum humidity to considerably less suitable conditions.

Although only two alate P.aptera were tested at 95; R.H., both were observed to live longer than apterous forms under the same conditions. Thus it is suggested that the increased pigmentation of the cuticle reflects greater impermeability to water loss - an adaptation that presumably permits alates to survive longer periods of adverse humidity conditions. In order to further clarify this problem, data on the humidity tolerances and preferences of alates are required. If possible these should be supplemented by data on the responses of both apterous and alate forms to fluctuating conditions of relative humidity. The resistance of the eggs of Ptinella to desiccation at lower relative humidities is presumably an adaptation permitting their survival through short periods of adverse microclimatic conditions in which their immobility renders them particularly vulnerable to desiccation. The ability of larvae and adults to respond actively in such situations might facilitate their survival despite their more limited tolerances. - 154 -

(ii) The.effect of temperature.

The experiments to determine the effect of temperature on the activity

of Ptinella have shown this factor to be of potential significance in influen-

cing the relative distribution and abundance of P.aptera and P.errabunda since

they have been shown to have differing ranges of temperature over which they are active. The range for P.aptera apparently extends from around 15°C to

30°C and probably even higher, whereas that of P.errabunda is from around

10°C to 25°C and possibly a little higher. ability of P.aptera to function normally at 30°C contrasts sharply with the death of P.errabunda

after about 48 hours at this temperature. Conversely the latter species is

active at 10°C and 1500 when the activity of P.aptera is severely curtailed.

Despite the relatively limited range of te:aporatures over which the two species

are active their physiological tolerance permits them to survive much greater

extremes, both surviving at 0°C, the lowest temperature for which data were

available. However, reproductive physiology is apparently more critical and

the temperature range over which reproduction occurs is limited in co,Jparison with the tolerable range for survival. The effects of temperature on insect reproduction have been reviewed by

3ursell (1974). Despite the fact that reproduction was investigated at only four temperatures in each species, the general relationship of increasing oviposition with increasing temperature was shown. A general relationship between oviposition rate and temperature has been demonstrated for a large number of insect species. There is a rapid increase in rate until maximal oviposition is achieved fairly near the upper reproduction limit, subsequently it falls off rapidly with any further increase in temperature. This relation- ship was clearly shown for P.errabunda but it seems likely that maxi ima oviposition was not reached in the experiments with P.aptera at 30°C, thus the subsecuent reduction in oviposition rate was not observed. The results demonstrated the orientation of the reproductive range of P.aptera about a -155-

higher temperature range than that for P.errabunda reflecting the differential

activity and tolerance ranges of the two 3DOCiOS.

Individual e:;g production in P.aptera and P.errabunda was shown to be

highly variable and there was no consistent, reduction in ovi7)osition at the

end of adult life that might be predicted as a consecuence of senescence.

This suggests that. in the.majority of cases the total adult life span was not

realised under the cultural conditions employed for. the experiments. 1:Tever-

theless. an:inverse r.olationship between teperature and longevity was de,ons-

trated for both snecies implIring either realisation of the life span or

temerature dependent mortality. The moderating effect of the tei.perature

longevity relationship on that between temperature and oviposition was

clearly demonstrated in P.errabunda where the mean cumulative egg production at 25°C and 20°C was exceeded by that at 15°C when oviposition rate is lower but longevity is significantly higher. Throughout the temperature range investigated, the oviposition of P.aptera was higher than that of P.errabunda at the sane temperature.

The proportion of P.aptera eggs hatching has been shown to be approximately constant over the normally active range of the species with a marked decrease in egg fertility, or increase in egg mortality at 15°C. It is not clear what proportion of the failure of eclosion is due to egg mortality and what is due to infertility of eggs. It is possible that a decrease in sperm viability at low temperatures could result in greater infertility of eggs at 15°C than in those observed at higher temperatures. The total failure of P.aptera egg6 to hatch at 10°C and for development to be followed through the iamature stages, resulted in this temperature regime being excluded from experiments further investigating the effect of temperatures on reproduction in P.aptera. In

P.errabunda the proportions of eggs hatching are considerably lower at 25°C and 200C than those recorded for P.aptera at the same temperature. However, at 15°C the success in hatching exceeded that for P.aptera at the same temperature. The causes of the failure of eggs to hatch at higher temperatures -156-

are not known although inviability of sperm at high temperatures cannot be

ruled out. Such explanations in terms of sperm inviability cannot, however, be applied to P.errabunda in which the eggs develop without being fertilised.

The failure of P.errabunda to achieve the high levels of hatching success

exhibited by P.aptera is consistent with the results of other authors working

on parthenogenetic' races and species (Stalker, 1956; Petersen, 1971). Although

an intrinsic difference between P.errabunda and P.aptera with respect to the

proportion of eggs hatching cannot be ruled out, it is suggested that the

lower hatch success of P.errabunda is &consequence of an imperfect mechanism

facilitating parthenogenetic reproduction. It is interesting to note that the

proportion of eggs hatching recorded for the bisexual P.taylorae at 200C is identical to that for P.aptera at the same temperature. This suggests that there may not be any great intrinsic variations in hatching success

between species of Ptinella.

An inverse relationship between duration of developmental stages and temperature has been recorded by a number of authors (e.g. Howe, 1953) and

is predictable from the response of metabolic rate to changes in temperature.

This in turn reflects the fundamental activity curve of enzymes with respect

to increasing temperature. Both P.aptera and P.errabunda have been found to exhibit a similar relationship between duration of the immature stages and temperature although estimated regression coefficients for the responses of the two species. are significantly different, reflecting their differential adaptations with respect to temperature. The validity of the fitting of regression equations to the data is questionable since an exact linear relation- ship is unrealistic in a biological system inevitably subject to intrinsic variation. Nevertheless, regression analysis was considered useful in many cases where it approximated the data fairly closely and thus permitted meaningful comparisons to be made between the two species. A similar inverse relationship was found to apply to the variation of the egg stages with temperature in P.aptera, but although similar between 10°C and 20°C in - 157 -

P. errabunda, at 25°C the tine elapsing before eclosion is greater than at

20°C. This slight decrease is typical of developmental rates just below the upper extreme temperature.

The summation of the duration of the developmental stages to give the total pre-productive period reflected the basic effect of temperature on development resulting in the expected inverse relationship between the duration of the total pre-reproduction period and temperature. The significant difference between regression coefficients for P.aptera and P.errabunda clearly

demonstrated the adaptation of P.errabunda to a lower temperature ranze than P.aptera.

The absence of information on the causes of pre-reproduction mortality precludes any useful interpretation of the data for variation of mortality with temperature. However, it may be concluded that mortality is likely to be greatest at the extremes of the temperature range over which the animals- are active. Thus mortality was greatest in P.aptera at 15°C and below, and at 10°C and 25°C in P.errabunda. It seems likely that somewhere above 30°C

P.aptera would show a similar increase in mortality as the upper temperature extreme was approached. Since it was impossible to maintain any of the cultures entirely free of contaminant fungi, it is probable that an important component of the overall mortality was the direct result of infection of individuals by the fungi and of their becoming trapped by fungal hyphae. Possibly the reduced rate of development at low temperatures together with the reduced activity of the animals under such conditions, results in a higher degree of mortality of this kind. NO data were available on mortality as a result of parasitism or bacterial or viral infection. The combination of the data on fecundity and mortality, modified by the appropriate values for sex ratio and fertility, has enabled expressions of the reproductive capacity of P.aptera and P.errabunda to be estimated for each of the temperatures considered in the experiments. Of these values the innate capacity for increase is the most useful in this situation where the -158-

species have been maintained under conditions as nearly identical as possible.

This permits direct comparisons to be made between the species at each temp-

erature. As Andrewartha and Birch (1954.) have pointed out, rm is the only meaninr-r'ul statistic for comparing the rates of reproductive increase of different species, since they chance with changing age structure of the

population. By definition, rm applies to a stable age distribution.

The values of rm for P.aptera, P.errabunda and P.taylorae at 20°C are

not significantly different, the populations increasing by a factor of

0.024 per day. However, this value represents a maximum for P.errabunda

whereas that for P.aptera is almost three times as great, reaching its recorded maxim= at 30°C (although it may exceed this at a slightly higher

temperature). It thus appears that parthenogenesis, far from doubling the

potential rate of increase of the population, has apparently little effect

on reproductive output. The possibility that the parthenogenetic P.errabunda

arose from a species of considerably inferior reproductive ability, cannot

be ruled out but unless this is the case the implication is that increased reproduction rate is of relatively little selective importance in the evolution

of parthenogenetic species or races of. Ptinella. White (1970) has expressed a similar opinion concerning the evolution of parthenogenesis. It has been shown that the effect of temperature in modifying rm is considerable for both the parthenogenetic P.errabunda and the bisexual P.aptera. Since the mean value of rm for P.aptera is very much lower than that for P.errabunda at 15°C and 10°C, the latter species would be expected to have a considerable reproductive advantage in situations where mean temperatures are of this order. Conversely the reproductive potential of

P.aptera is greater at or above 200C. Although the number of eggs produced by female P.errabunda at 20°C is slightly lower than that at 150C, the

intrinsic rate of increase is greater at the former temperature since the acceleration of developmental rate at 20°C is relatively more effective than

the corresponding increase in fecundity, as the females produce more of their

eggs earlier; this effectively reduces the generation time. - 159 -

The net reproductive rate is an estimate of the number of females produced

which survive to reproduce in the next generation. However, the value derived

from the experiments described above is of limited interest since no account

is taken of natural mortality by predation and parasitism. Furthermore, the estimationwould be expected to vary from one generation to another as a result of differences in the age structure of the population concerned. Its main interest lies in consideration of how rm is influenced by the total expected reproduction of the female. Generation time is also of great importance in thtscontext. Thus although the total reproduction of P.aptera at 2500 is not significantly different from that of P.errabunda at 15°C, the effect of temperature in decreasing the age of first reproduction results in rm being at least twice as great for P.aptera, the generation time having been approximately halved. Similar results have been shown by other authors ( . . Siddiqui and Barlow, 1972) for the other species of insects:

It is important to emphasize the artificial nature of the determination of the life table statistics. The aim of the laboratory experiments was to approximate conditions as nearly as possible to the optima for both species but,as has already been described, the culture methods could not be controlled sufficiently to achieve this in the laboratory. The approximations made during the computation of the statistics and the means by which the life table data were extracted from the laboratory data obviously limit the decree to which conclusions may be drawn from the results. However, the differences between the values obtained seem to be sufficiently great to justify their interpretation where possible.

It seems likely that naturally occurring populations of Ptinella do not exhibit a stable age distribution in the early stages of colonisation or as a consequence of population fluctuations. As has already been noted. the statistic rm, by definition describes reproduction in a population with a stable age distribution and thus the extrapolation of laboratory derived -160-

values of life table statistics to populations of Ptinella in the field are

only made with the greatest caution. 2urthermore, no attempt was made to

investigate the natural mortality of field populations of Ptinella and thus

the possibility of differential mortality between the two species resulting

in modification of values of rm cannot be eliminated. However, the extreme

plusical similarity of all stages between the two species, suggests that

predation and parasitism would not have a differential effect.

The results of the foregoing experiments with P.taylorae at 200C provide physiological evidence to support the taxonomic evidence for relatively close relationship between P.taylorae and P.errabunda. The similarity of the proportion of eggs hatching to that recorded for P.aptera as opposed to

P.errabunda is, as, has already been described, probably attributable to the decreased viability of eggs consequent of the parthenogenetic reproduction of P.errabunda. Apart from this P.taylorae shows a distinct trend towards similarity to P.errabunda in other life history values. The value for the fundamental statistic rm is lower than that of both P.errabunda and P.aptera.

(iii) rm and the species habitat.

In conclusion, all the data for fecundity, duration of stages and other life history parameters are integrated to generate values for the innate capacity for increase. Although relationships of the various values are reflected in rm, it is this statistic that is of ultimate importance as far as consideration of the overall potentials of the two species is concerned. The estimation of rm for P.aptera and P.errabunda under controlled conditions has shown that the temperature range for reproduction in P.errabunda is significantly lower than that for P.aptera. The two species are thus adapted to different environmental conditions, with respect to temperature, reflecting their differential activity ranges. The significance of these findings is greatest when they are considered in relation to conditions in the species habitats. — 161 —

The, results of subcortical temperature measurements on a fallen beech log have already been discussed in the previous section, and the overriding

importance of the effect of light intensity on the bark surface has been

emphasised. It is not clear how maximum ten:peratures (48.5°C recorded at

one site in full sun) affect Ptinella, although presumably behavioural

responses enable them to move to areas at lower temperatures. The range of

activity of individuals beneath bark has not been assessed in an;' way but

it is assumed that the observed- mcbilii7 of the species in cultures and during collection from logs, reflects a relatively wide area of aotivity in

the natural habitat. Furthermore, it is likely that short exposure to maximum

temperatures may not result in death. Despite the extreme temperatures recorded in sun and shade it is more likely that the significance of light

intensity on subcortical temperatures, as far as Ptinella are concerned., lies in the mean temperatures, and their effect on the innate capacity for increase. There are certain situations where high temperatures would be expected to limit the distribution of Ptinella. This could have explained the

observed absence of Ftinella from some logs in artificial clearings or other open areas of land where high light intensity may be recorded for up to 12 hours in a day. However, it was suggested in Section 2 that the period of exposure to the sun of a site in a natural forest situation is more likely to be of the order of 2 or 3 hours. Obviously factors such as topography may have an important effect. Within the environment of a single log lying on the forest floor there may be considerable variation from one part to another and some particular points may be in more or less permanently heavy shade from surrounding herbage. Theoretically such coilditions would favour

P.errabunda, whereas the high temperatures of the subcortical zone on the upper surface exposed to the sun would provide conditions more suitable for

P.antera. Although field data did not provide conclusive evidence of species separation on so local a scale, as a result of differential temperature - 162 -

effects on reproduction, this could theoretically at least, facilitate

relatively intimate coexistence between the tuo species.

On a wider geographical scale it is suggested that the relative reduction

in shading associated with the seasonal loss of canopy cover in deciduous

woodland, enables F.antera populations in such situations to maintain a

positive rate of increase despite the mean air temperatures in winter being

below the level for successful reproduction for this species. This is

supported by the observation of active larvae and adults (including recently emerged individuals) under bark during winter. Extending this idea it is

suggested that the permanent shading of logs in coniferous and other evergreen, forests would be expected to severely impair the reproductive-capacity of

P.aptera and temperatures may be insufficient to permit a positive value for rate of increase to be achieved. In winter the temperatures may be so low as to totally inhibit reproduction. Under such conditions P.errabunda„ with its overall adaptation to a lower range of temperatures, would be expected to be able to maintain population growth throughout most of the year. The possibility of an insulation effect dependent on bark thickness has already been suggested (Section 2) and could be of importance in this'context. The higher mean subcortical temperature predicted for deciduous forest logs or those unshaded in clearings may reduce the reproductive success of

P.errabunda. This would be expected to apply in particular to thick barked deciduous logs in sunlight where, the effects of incident radiation may be supplemented by heat generated by decaying wood (Cartwright and Findlay, 1958).

Such differential temperature-determined distributions on the larger scale could result in transient coexistence of P.aptera and P.errabunda at certain sites. Such coexistence over an area could be maintained by recruitment of individuals from localities of species optima. Latitudinal and altitudinal differences in distribution are also predicted from differential temperature adaptation although local climatic conditions of cloud cover, for example, would modify these differences. - 163 -

In order to investigate the significance of differential temperature adaptation of P.aptera and P.errabunda further, the effec:3s of fluctuating temperatures on the reproductive performance should be considered. Much attention has been directed at the effects of fluctuations in temperatures on reproduction and the subject has been reviewed by Hagstrum and Hagstrua

(1970). However, Burrell (1974) has concluded that observed accelerations and retardations may be largely spurious, the effects of temperature on development being the same whether the temperatures are fluctuating or constant. Por more detailed study of the possibility of very localised temperature differences permitting apparent coexistence of F.antera and

P.errabunda in a single log, accurate microclimatological information is required. This presents considerable technical problems and in Particular such measurements are inevitably distorted by the unavoidable disturbance of the microenvironment. -164.-

SECTION 4. COLTETITION EXPZIIIITENTS ?IITH P.APMRA,

Mm P.ERRABUNDA.

4.1 Experiments.

Laboratory experiments on competitive interactions between two species

have been carried out by numerous biologists in the time since Cause performed

his pioneer work with yeasts and Paramecium (Cause, 1932, 1934.). More recently several authors (e.g. MacArthur, 1972) have maintained that such

an approach is of limited importance, suggesting that the experiments

should be approached in such a way as to demonstrate the niche diversification

that enables similar species to coexist indefinitly. Nevertheless, in the

absence of any reliable data concerning the extent and stability of co-existence

in Ptffnella, or detailed information on the species habitat requirements,

it was concluded that a classical approach involving placing the two species

in a situation of potential conflict would at least yield some information that might clarify the species ecological relationship.

3xperiments were set up to investigate a situation of direct competition between P.aptera and P.errabunda. It was hoped that the experiments would demonstrate competitive displacement of one species by that competitively superior to it, and would also show the effect of initial density on the outcome of such competition. The cultures used in the competition experiments are described in Section 3. Initially the cultures were set up in as standardised a manner as possible. Conditions in these cultures were highly artificial to enable them to be controlled as accurately as possible in all replicates. A total of four experimental situations and three controls were set up, each with five replicates with the exception of the "food limited" experiments where only two replicates were used. Two controls were set up for P.aptera: a "numerical" one in which the total number of individuals was the standard population size of 12 used in the experimental

- 165 -

cultures.. and one in which there were 12 females in the population, the

total n-2.11'er of individuals in the culture being 24, the number of males

bein3 based on the assumption of a 1:1 sex ratio. The composition of each of the cultures is given in Table 4.1.

Table 4.1. Species composition of cultures set up to investigate the

competitive interaction between T.aptera and P.errabunda.

Culture P. aptera P.errabunda

Ro. males :To. females Total No. females A 5 5 10 2 experimental 4 4 8 4 populations 3 3 6 6 2 2 14. 8

Single OOP 12

species 6 6 12

controls 12 12 24.

Competition experiments were carried out in conditions of approximately

mpg R.H. and at two temperatures: 20°C and 15°C. Two regimes of food

supply were also used. In "standard" cultures food was judged to be relatively abundant, but in "food limited" cultures the quantity of food provided was reduced considerably. As described in Section 3, the initial culturing method in which conditions were highly artificial had to be abandoned in favour of a modified method that approximated natural conditions

more closely and permitted survival of a greater number of Ptinella. The

discs of wood on which the animals were placed were taken by means of the

circular sampling punch from a uniform P.sylvatica log on which both P.aptera

and P.errabunda had been found. Discs of bark were selected such that their texture and thickness (1.0 cm) were as uniform as possible, and two were

placed on top of each other, with the surface of the bark outermost, in - 166 -

each culture. In the "food limited" series of cultures the bark discs were

cut into auartertand two pieces were placed together in each culture. These bark discs were sunposed to provide the food supply of fungi for the organisms but it was supplemented with dried baker's yeast. In "standard"

cultures three large grains of yeast were supplied but in those where the

food sulDply was restricted only a single small grain was added to each culture.

The initial cultures set up were maintained for only a month after which

time almost all the Ptinella were found to have died irrespective of species.

The modi-ried cultures were, however, maintained where possible over a period

of 6 months in darkness in constant temperature rooms at 1500 and 2000. The individuals used to set up experiments were taken from a variety of sources and each was carefully examined under the microscope to determine

its species and sex before being introduced into the cultures. At the end

of the 6 month period all the beetles visible on opening of the culture

were collected in an aspirator and those remaining in the bark were extracted by means of the heat/humidity gradient extractor. The number of individuals

of each species, their sex (in the case of P.aptera) and their wing morph, were recorded for each culture. It was not possible to make regular counts of the population since this would have required collection of the individuals by means of the extraction apparatus. Inevitably this would have resulted in high mortality of immature stages and radical alteration of the micro- habitat. Approximate estimates of the adult populations were, however, made at intervals of two months during the experiments. The bark discs were carefully removed into new culture jars and all adults observed in the old cultures were collected in an aspirator. The bark was then separated with as little disturbance as possible and gently shaken over the old culture. Any individuals observed were again collected in the aspirator. Finally the bark was replaced and the new culture vessels checked for animals that had escaped. The adults were then placed in these cultures whilst each -167-

was identified and sexed before being replaced in the original cultures.

The cultures were checked fortnightly to ensure that the relative humidity

was maintained at the required level, distilled water being added when

necessary.

The results are given in Table 4.2 and in detail in Appendix 7. Only the data for the "standard" cultures at 15°C and 20°C are given in the

table, since in the majority of the "food limited" cultures the final

populations were very low if not altogether extinct. The results for each

series of replicates have not been joined to give mean values since the data

are so variable. Furthermore, the results of the two bimonthly recordings

were also found to be highly variable and of apparently little value in

interpretation of the competitive situations; they are therefore included

in the Appendix only.

It became Quite clear within the first month after the cultures were

set up, that any attempt at standardisation of conditions in bark cultures

was optimistic, since the development and type o2 the microflora on the bark

was never consistent between cultures. Thus the microenvironment was equally

variable and little useful interpretation could be placed on any results

derived from such unstandardised experimental conditions.

One interesting phenomenon that was observed from the bimonthly records

was the production of a large proportion of alate individuals in the first

generation. rhny of these winged adults were lost from the population

since they apparently left the relatively favourable habitat in the bark discs

and on damp plaster of Paris, the majority being found dead in the small gap

where the lids fitted onto the bases of the culture dishes. The production

of alates in this manner was recorded for both species and in some cultures

the proportion of alates was maintained, unusually high levels (as high as

0.42 of the total population in one P.aptera culture) being recorded in the

final populations. - 168 -

The total populations in the experimental cultures after 6 months showed a ?sigh degree of ap'Jarently random variation and the same sort of

variability was also observed in the control cultures. However, there was

a distinct tendency for there to. be, a considerably greater density of

F.aptera in cultures at 20°C. In the control cultures at 20°C, the

P.errabunda populations were particularly siaall. However, the bimonthly

records for some of the latter cultures showed populations in excess of 100

individuals and in fact many of the experimental cultures had larger

populations of both species at the bimonthly recording times. In a total

of 9 out of la cultures in which populations of Ftinella survived,

P.errabunda had invariably had an initial numerical advantage over F.antera.

21t 15°C however, P.errahunda was predominant in all but one culture.

In this particular population, P.errz.zbund,2,...was extinct and only 3 P.antera

individuals rere surviving; inspection of the intermediate recordings

suggested that this culture had failed to become established initially.

It was interesting to note that in contrast to the extinction of P.errabunda

at 2000, P.aptera only reached extinction in one population at 15°C despite the predominance of P.errabunda. Furthermore, the bimonthly records at 15°C aid not show a dramatic population increase and subseouent decrease before termination of the experiments. Alates were apparently less abundant in cultures at 150C than in those at 20°C. A slight trend was observed for the highest proportion of P.aptera in populations to be associated with initial numerical advantage of that species. The results of the controls merely reflected the enormous variability in the populations although some rather large populations were observed for P.errabunda at 15°C.

The results of the "food limited" experiments showed no consistent pattern partly because so few individuals survived in the cultures and also since only two replicates were set up. Five of the fourteen cultures set up at 200C became extinct. However, none actually reached extinction at 15°C where P.errabunda appeared to predominate. -169-

Tc:ole 4..2. Results of competition experiments between P.ap.tera and P.errabunda over a period of 104 17Ts at 20°C and 15°C (5 -replicates)

(±) Standar120°C

.rt‘ Culture: B C D ..LJ F No. P.antera 3 3 3 33 34. 11 ITo. P.errabunda - - - 1 Proportion P.antera 1.00 1.00 1.00 ).53

No. P.a-otera 22 21 5 34 4 4 No. F.errabunda - - - - 2 Proportion P.antera 1.00 1.00 1.00 1.00

No. P.antera - 1 - 11 - 38 ITo. P.errabunda - - - - 4 Proportion P.antera - 1.00 - 1.00

No. P.antera 57 9 4.6 10 40 28 'To. P.errabunda - 9 • - Proportion P.aptera 1.00 1.00 0.84. 1.00

No. P.aptera 52 16 12 22 1]. ITo. Peerrabunda - - 3 10 Proportion12.1a. :tera 1.00 1.00 1.00 0.88 -170-

Table 4.2 continued.

(ii) Standard 15°C

Cult:tre• : A B C D No. P.antera 16 2 19 No. P.errabunda 129 57 10 6 2 111+ • Proportion P.antera 0..I1 0.03 0.00 0.03

No. P.antera 3 13 7 7 21. 16 No. P.errabunda 5 13o 112 41 119 Proportion P.antera 0.38 0.09 0.06 0.15

No. P.aptera. 24 22 8 16. 7 NO. P.errabunda 71 61 101 46, 139 Proportion P.artera 0.25 0.27 0.07 0.2'6

No. P.antera 1 1 3 2 50 9 No. P.errabundn 37 9 - fl -. Proportion P.aptera 0.03 0.10 1.00 0.15

No. P.aptera 16 16 2 , 1 No. P.errabunda 30 52 54 29 Proportion P.aptera 0.35 0.24. 0.04. 0.03

- 171-

I, 0 iscussion.

As a result of the null nu ler of replicates used and the tremendous

variability in cultural condiLions, re at care has to be excerised in the

interpretation of the data. It had been hoed that the initial method of

culturing, Involving the use of :roast alone as a food suTply, would produce

at least ',-,a.Jatively uniform conditions for the experiment. However, conditions

in these cultures were inaaecivate to sustain populations of Ftl.nella for

even one month ana furtherriore, the yeast developed contaminant microflora

of high variability. The rirovision of the wood discs in subseuent cultures

at least supplied a potentially greater variety of conditions for the beetles

and a more balanced and varied food supply. The variability in microhabitats arising on these apparently similar pieces of bark was primarily a result of fortuitous dominance by one or more species of fungi. In cultures where

populations were small or.where total extinction had occurred, the bark was characteristically ary and coated with thick mats of white mycelium. Such desiccation occurred despite the regular addition of water in an attempt to maintain a high relative humidity in the cultures. Although water was added directly to the bark the fungal mycelium formed a water repellent mat off which the water drained onto the plaster of Paris.

Bearing in mind the caution with which. the data must be interpreted, certain general trends have, nevertheless, been suggested by the results of thecompetition experiments. In particular the effect of temperature on the interaction between the species has produced some interesting results.

At 20°C it was shown that P.aptera predominates in all cultures regardless of the initial population densities. This implies some form of competitive superiority of P.aDtera over P.errabunda at this temperature. With the evidence of the bimonthly data it appears that in some cultures at least, the population of P.errabunda decreased considerably after an initial period of increase. This coula suggest that the composition of the final populations - 172 -

does not merely reflect differences in the effective fecundity of the two

srecies, but that some interference nay have occurred between them in respect

of one or more renuirements that were in short supply. However, an alternative

explanction that does not invoke competitive interaction is that conditions in the cultures could, at some time, have become untenable for P.errabunda

(at any or all stages of develornent) although relict populations of P.antera were able to survive and subseouently build up the populations. Such an interpretation implies a difference in the tolerance or recuirements of the two species. Possibly the high population density attained by P.errabunda in some cultures resulted in over-exploitation of the available resouroea.

This could explain the dramtic increase and subsenuent decrease of populations in three of the P.errabunda controls. It might be tentatively suggested that the survival of P.aptera over P.errabunda in unfavourable conditions is a consequence of the greater genotypic diversity resulting from the bisexuality of the former species. Such variability might have resulted in a greater range of tolerances.

At 1500 the pattern of species predominance was reversed with P.errabunda forming the greater proportion in almost all populations. This appears to be a direct consequence of the greater reproductive efficiency of P.errabunda at 15°C (see Section 3) together with density independent mortality within the cultures. The survival of P.antera in all but one experimental population suggests the possibility that, had the experiments been carried out for a longer period of time, a different outcome might have been observed. With a mean pre-reproduction period of 112 days as opposed to 86 days for p.errabunda, only one generation of adults could be produced in the 6 month period. In addition to being able to produce two generations, P.errabunda also has a significantly higher fecundity at 15°C (see Section 3) and thus would certainly be expected to predominate numerically even in the early stages of competitive interaction, if it exists. Thus in order to obtain further evidence for the presence or absence of,such interactions between - 173 - the two species in these cultures, experiments should be maintained for a considerably longer period of time.

It had been hoped that experimental cultures in which the food supply was severely curtailed would enforce direct competition for food between the two species and result in displacement of one by the other. Such displace- ment was in fact widespread with a tendency for P.aptera to persist at 20°0 and P.errabunda at 15°C. However, these results based on only 2 replicates can in no way be regarded as reliable since the final population densities were so low as to suggest that extinction may have been purely random.

One major source of inaccuracy common to all the experiments was the fact that only the adult population was considered, the assessment of the II-mature stages being impracticable. Obviously, if such data had been available the interpretations suggested might have been different. - 174 -

MOTION 5 MING POLT.:ORPHISU AND SEX RATIO L' jayrii,

5.1 ',tang -1:olymorphism and sex ratio in field. collections.

The numerical dominance of the apterous morphs of Ftinella has been noted by t=onomists (::atthews, 1872; Britten, 1926; JOnson, 1972 ) and is thought to be characteristic of the genus. The only exception recorded in the literature is the species F.cavelli (Johnson, 1975) of which only alate individuals have so far been found. The distribution of mate and apterous morphs and the ecological significance of the polymorphism have not been investigated previously.

The proportion of winged morphs of P.aptera and P.errabunda in the field was investigated by analysis of the data from collections of Ptinella taken from a number of different sites at various times during the years 1972-1975.

The collecting methods and their limitations have been described in Section

2. The disjunct distribution of the species and the nature of the habitat precluded the application of systematic sampling methods. No collections of P.aptera were made during February, November and December and none of P.errabunda during November and December. The absence of collections for these months does not denote the absence of Ptinella populations at this time of year, but rather reflects the generally reduced activity of Ptinella at low temperatures (see Section 3) and the problems of observing them when they are relatively immobile. They have in fact been observed under bark during all months of the year. It is possible that at the onset of low temperatures they may retreat into the decaying heartwood either directly or via scolytid galleries where the microclimate may be more buffered from external temperature changes. Although some attempt has been made to collect

Ptinella from heartwood, especially during the winter they have not been found there.

The animals collected were examined alive if they were to be used for -175-

cultures or experiments. If they were not re:•uired they were preserved in

7011,:: alcohol and subseouently mounted in polyvinyl lactophenol on microscope

slides. The mountant acted as a clearing agent thus making the spermatheca

readily distinguishable and permitting rapid species and sex determination.

The procedure for examination of living specimens has already been described

(Section 1). The high degree of pigmentation associated with the possession

of wings sometimes made observation of the spermatheoa difficult. Although

the shape of the hind angle of the pronotum is diagnostic, a certain amount

of variation in this character in both species made it necessary to regard

the shape of the spermatheca as being the only totally reliable means of

distinguishing the species P.aptera and P.errabunda. However, in alates

in particular, the thorax shape had to be used to distinguish between females

of P.taylorae and P.errabunda since the differences in spermatheca shape

were often too fine to be visible in the presenCe of concentrated pigmentation.

Inspection of individuals by means of a microscope set up for phase contrast

microscopy often improved the definition of the spermatheca beneath the

pigmented exoskeleton. If it was impossible to identify an animal alive it was preserved in alcohol and mounted as described.

The species, sex and wing morph were recorded for all individuals. The data are given in detail in Appendix 4.

The data on both numbers of each morph and of each sex, were analysed by means of a programme MD.Hamilton, unpublished) run on the C.D.C. 6600 computer. The basic output of the programme gave proportions of winged males, winged females, all winged individuals, and proportions of males amongst winged individuals and wingless individuals and the overall male sex ratio. Since both degree of alary polymorphism and sex were expressed as proportions; 'it was possible to plot the proportion of rings in males and the proportion of wings in females on axes expressing wing proportion at the zero and unity extremes of a scale renresenting sex, expressed in terms of the proportion of females (Figure 5.2). The slope of the line joining the two points could then be regarded as a regression coefficient -176- for the regression of the degree of alary polymorphism on sex. ath a base

axis unity, the coefficient was simply calculated as the difference between the proportion of winged females and that of winged males. An overall value of the coefficient was derived by summing the data for all collections. The

programme also included a facility permitting the joining of the data for each site into any groups rewired, setting up the appropriate contingency tables and testing for departures from the Null hypothesis of independence by means of a chi-squared test. Contingency tables were set up for proportions of winged and wingless morphs in males, the same for females and sex ratio of the whole sample. Equations used in testing the contingency tables are given in Appendix 2. The approximate 2 test is invalid if apy of the expected values in the contingency table are less than 5. units. Such low values result in uncertainty in close decisions on significance. In these cases it may be possible to execute an exact test of the data using the equation:

)c2 = (a+b) (c+d) (a+c) (b+d) n !a!b!o!d! However, this method applies only to a 2 x 2 table. Predicted values below

5 were indicated in the output and thus it was possible to decide how much meaning could be attached to the interpretation of a particular value.

Although in some cases data could be summed so as to generate expected values greater than 5 or to form a 2 x 2 table that could be tested exactly, it was clearly invalid to do this for data from different sites. High values of 2 in such situations would. only permit a statement to the effect that there was a strong possibility of departure from the Null hypothesis independence.

The basic data from the collections of P.aptera and P.errabunda were joined and tested for months, Seasons and a year. The appropriate 2 values are given in Table 5.2. Due to the consistently low proportion of winged individuals in the Ptinella populations at any particular site, the predicted numbers of winged males and females were, in the majority of cases, -177— less than five. Thus the results have to be interpreted with caution. The proportions of winged individuals in each population together with their standard errors are given in Appendix 8, the values summed for months being summarised in Table 5.1. Although these values show a great range of variation from one site to another they do reflect overall trends that are distinguishable in the analyses for months and over the year.

There is apparently no simple pattern of significance from one month to another for P-nptsra luales. The data for June, for example, generate a X 2 value of 68.96 (P <0.001 for 9 degrees of freedom). Similarly and October give values that are probably significant. None of the predicted val es fsr numbers of winged males in each month was greater than 5.

However, the value for June was so large that there can be little doubt in the validity of rejection of the Null hypothesis of independence between the variables of presence and absence of wings and different sites. The )C2s for July and April (2.72 and 3.96 respectively with 5 degrees of freedom) are almost certainly insignificant. The females of the same species appear to exhibit a more consistent rejection of the Null hypothesis, X 2 values for hay, June, July and October probably being significant at the P = 0.05 level of significance. The amall proportion of alate females recorded for August is based on only two samples and is thus likely to be misleading.

In conclusion, there seems to be an overall pattern of increase in proportion of winged females during the summer and autumn months. Furthermore

SOME relationship between the development of wings and time of year is implied by the significant X 2 generated by summing data over three-monthly periods. Only the figure for spring is based on a sufficiently small population to cast any doubt on the significance of the observed values.

Despite summing, the data for wings in males is still insufficient to produce entirely reliable estimates of significance. However, all values of X 2 for seasons are significant at the P = 0.05 level and probably reflect a relationship between the months of each season and the proportion - 178 -

Table 5.1.. FrO',:ortions of winged LaLLviauals La collections of field caught

P.a.oterl• c• -mimed for lionths and seasons.

Proportion of winced inclividuals•with standarl error

in :J. i.e in fe..2ales total population January 0 0 0 ::arch 0 0.010+0.006 0.004+0.003 AIDril 0.018+0.006 0.010+0.005 0.014+0.004 May 0.032+0.018 0.046+0.026 0.038+0.015 June 0.014+0.007 0.036+0.011 0.025+0.007 July 0.030+0.021 0.202+0.043 0.129+0.027 August 0.067+0.032 0.254+0.048 0.161+0.031 Septe:Jber 0 0 0 October 0.070+0.011 0.110+0.014 0.090+0.009

Spring 0.012+0.004. 0.013+0.004. 0.012+0.003 Snmer 0.024+0.008 0.104+0.015 0.065+0.008 Autumn 0.063+0.010 0.100+0.012 0.080+0.008

Total 0.029+0.004 0.060+0.006 0.044+0.003 - 179-

NI 2 , lde 5.2. estst for contingency tables on data of wing po3.3r.orphisa and sex ratio in field caug!it P.antera.

Coanarison Degrees of X 2 values freeaaa alary/aptery alary/aptery sex ratio in males in Jales Between sites in month 17.arch 2 0 ( ) 0.06 ( ) 1.24 ( ) April 5 3.96 ( ) 1.12 ( ) 0.57 ( ) May 2 6.40 (*) 8.20 (*) 1.84 ( ) June 9 68.96 (**) 41.04 (**) 7.65 ( ) July 5 2.72 ( ) 13.24 (*) 2.33 ( ) August 1 0.57 ( ) 0.01 ( ) 1.91 ( ) October 1 19.50 (**) 52.92 (**) 7.87 ( ) Between months in seasons Spring 2 9.03 (*) 6.24 (*) -5.17 Summer 2 5.99 (e) 36.89 ** 4.76 Autumn 1 4.26 (*) 8.38 * 1.31 Between seasons in year Year 2 33.45." 63.01 ** 7.15 *

* denotes significance at the 0.05 level of probability ** denotes significance at the 0.001 level of probability ( ) denotes predicted value in test of 5. - 180 -

of the male population that is winged.

The results of summing the data over an entire year show a relationship

between seasons of the year and the proportion of both males and females in

the populations that are alate, both X 2 values being significant at the P = 0.001 level.

The proportions of the elate individuals that are male are given in

Appendix 8 and although not tested for significance, these values summed

for nonths (Table 5.3) show a tendency to fall from around 0.5 in spring

to between 0.1 and 0.2 in summer and early autumn. This implies that the

increase in alates in,these seasons is largely the result of an increase in

the numbers of alate females in the populations.

The results of analysis of collections of P. errabunda are displayed in Table 5.4. Variation in the proportion of winged individuals between sites is, as for P.aptera, considerable. The X 2 values resulting from testing the contingency tables set up for months are shown in Table 5.5. ,Jr9. Despite the low numbers involved; theYV— values are probably sufficiently large to justify the conclusion that the degree of alary in populations of

this species is also related to the time of year. The proportions of winged individuals in the populations of P.aptera and P.errabunda, are plotted against time in months in Figure 5.1. Both species show an increase in the proportion of alates, from a low level in winter and spring to peal:s in surer and early autumn (July for P.errabunda and August for P.aptera). There is no significant difference in the absolute values of the maxima for the species. Table 5.2 also includes the results of contingency table analysis of the sex ratios of P.aptera populations at the different sites. None of the

)‹2 values, derived by joining the data for months was significant at the level of P = 0.05. The summing of the data over seasons generated meaningfully insignificant values of X 2, implying that no relationship exists between sex ratio of a population and the site where it occurs or the tine of year. - 181 -

Table 5.3. Pro.._L- Ortipns of 121e inaividuals collections of flel caught F.artern suLuea for Lionths and seasons.

Fro-:ortion of male individuals vith stand:.r1 error

17.onth in :-.1a tae in al)terae in total population Jrnual7y 0 0.300+0.120 0.300+0.145 I:arch 0 0.555+0.019 0.552+0.019 Ar,ril 0.6 43+0.128 0.510+0.016 0.512+0.016 :".ay 0.500+0.204 0.597+0.040 0.554+0.039 June 0.266+0.121 0.515+0.021 0:510+0.021 July 0.100+0.067 0.475+0.043 0.427+0.040 August 0.182+0.082 0.487+0.047 0.4.38+0.04.2 Septeber 0 0.4.52+0.02:4 0.452+0.0/4 October 0.396+0.051 0.517+0.016 0.506+0.016

Spring 0.522+0.104 0.53+0.012 0.534+0.012 Swim 0.179+0.051 0.504+0.018 0.483+0.013 Autmln 0.396+0.051 0.510+0.015 0.500+0.015

Total 0.341+0.036 0.520+0.008. 0.512+0.008 - 182 -

Table 5.4. Pro7ortions of 7in,3ed individuals in collections of field caught P.errabund_a summed for months and seasons.

Month Proportion of winged_ inftiv.;.:11.1als with str,ndard errors January 0 February 0

March 0.016 ± 0.007

April 0 ray 0 June 0.069 + 0.008 July 0.175 + 0.029 August 0.148 + 0.032 September 0.087 + 0.059 October 0.074 ± 0.018

',linter 0 Spring 0.007 + 0.003 Suumer 0.091 + 0.008 Autumn 0.075 ± 0.017

Total 0.060 + 0.005 - 183 -

Table 5.5. X 2 tests for contincency tables on data of wing po1,ymor-ohiam in field caught F.errabunda.

Cooparison Degrees of freedom )(2 values alarY/aptery in Between sites in month feuales :larch 12 67.71 (*) June 13 41.21(*)

July 8 '43.32 (*). August 7 66.84 (*) October 9 '49.21 (*). Betueen months in seasons Spring 2 5.95 * Sumner 2 25.26 (**) Autumn 1 0.04 Between seasons in year

Year 2 64..72 (**)

* denotes significance at the 0,05 level of probability ** denotes significance at the 0.001 level of probability ( ) denotes predicted value in test of < 5. Figure 5.1 Variation in the proportion of winged individuals 'with time for field collected F.aptera and P.errabUnda.

•

P. APTERA, F. ERRABUNDA

0.20 0.20

0. 18 _ 0.18

0.16 _ 0.16

0. 14 _ 0.14

• O. 12 .. ► O 0.12 _ ► co 0.10 _ c 0.10_ ► 0 0.08_ ► a 0.08 a. 0.06 ► • 0.06

0.04_ 0.04

0.02 _ 0.02

• III 0 J A M J JY A J F M J JYI a%I Months Months

• based on 1 site • based on 1 site - 186 -

However, it was interesting to note that semmation of the entire data for

seasons generated a sicnifi cant value of ;K2 (7.15; P = 0.05 for 2 degrees of freedom) suggesting the presence of a relationship between sex ratio and

the season of the year when the population was sahiplea. The sex ratios for the data for each month (Table 5.3) show a tendency towards bias in favour of males (if figures for months when only one site was sampled are considered invalid and ignored). In July this bias is sharply reversed due to the presence of a higher proportion of females in faar out of six sites concerned.

The same trend is reflected in the data for August although only two sites were considered. It appears that the significant value of X.2 for the year is the result of a slight female bias of the sex ratio in summer (0.48 f 0.02 males) compared with the significantly different bias in favour of males in spring (0.53 + 0.01).

The overall relationship of wings to sex in field caught Ptinella is represented in :Figure 5.2. Monthly values of the regression coefficient were variable but showed a sharp increase in July and August reflecting the observed increase in winged females. The coefficient is very small since alates form only a very small part of the total population.

5.2 The effect of....-rierature on wing and sex ratio of P.aptera in culture. ••••■•••■••••■•■•■••••■■•

Temperature is a factor that has been implicated in the determination of wing development in some polymorphic species (Johnson, 1969). Since this is a factor that can be readily controlled in laboratory experiments and furthermore, observations of field populations of Ptinella had suggested that an environmental factor such as temperature changing through the year might determine the degree of wing production, the effect of temperature on the latter was investigated.

Data were collected as described in Section 3, from successful rearings of progeny of known apterPus parents in a variety of cultures. Further - 187 -

.119.,:;ure. 5.2 Ovc.:,:-11 reL,rceeion ex2rc.Jein: the relationship of wings to

sex in field caught and reared. P.antera.

MALE FEMALE

0.10 .ALATE

0.08 _

WINGS

Proportion 0.06 _ 'elate

0.04 _

0.02 _

0 0.02 0.04 0.06 0.08 1.00 Proportion female

SEX

field caught b= _ 0.0302

reared b= 0.1716 - 188 -

cultures were set up with pairs of apterous beetles in Perspex pill boxes

(diameter 5 cm) on a plaster of Paris block 1 cm thick provided in order to maintain 100;-0 relative humidity in the chamber. A small piece of heat sterilised bark reinoculated with fungus was supplied to furnish the micro- habitat. Cultures were maintained in constant temperature rooms at 15°C,

20°C, 25°C and 30°C and were inspected regularly for the presence of adult progeny. The latter were removed from the cultures, sexed and the presence or absence of wings was recorded.

The possibility of a simple genetic basis for the ring polymorphism was also investigated in cultures at 20°C. The cultures were set up as described above. Virgin alate females were selected, as soon as possible after emergence, by examination of the spermatheca. If the females had been fertilised the sperm were visible either in the spermatheca or as a tight mass in a spermatophore, during the pre-oviposition period when the degree of cuticular pigmentation was relatively low. Ten alate females thus selected were placed singly in cultures with an alate male and the progeny recorded.

The results of rearingswere analysed by means of the same computer programme used for the analysis of the field data. The proportion of alates in the progeny of each pair is given in Appendix 8 and summarised for the different temperatures in Table 5.6. Inspection of these data shows the great variation in the distribution of winged individuals amongst progeny of apterous parents at 15°C, 20°C and 25°C. The total absence of alates amongst the sixty-nine individuals reared at 30°C suggests that at this particular temperature alates either form a very low proportion of the population in both sexes, or the develorment of wings may actually be inhibited at this temperature. The data from the rearings were summed for each temperature an also in a variety of combinations to produce contingency tables and their X 2 tests. Only those that are meaningful and non-repetitive are presented in Table 5.7. The comparison of numbers of alate progeny from rearings at each temperature generates a significantX2 for the relation - 189 -

Table 5.6. Suinary of proportions of alate individuals and male sex ratio in progeny of F.aptera reared at different temperatures.

Temperature Proportion of alate individuals (wita S.E.) sex ratio (with S.E. in oc In males in fe:aales in total pop. in total population 20 progeny of apterae 0.045±0.015 0.287±2.035 0.157±0.019 0.538+0.026 20 progepy of alatae 0.182±40.082 0.478+0.074 0.302±0.059 0.324+0.057 20 progepy of total 0.059.1.0.016 0.327+0.032 0.192+0.019 0.505+0.024 15 progeny of apterae 0.010i-0.010 0.062±0.025 0.035±9.013 0.510+0.036 25 progeny of apterae 0.0204.0.014 0.138+0.037 0.076+0.019 0.530+0.037 30 progeny of apterae 0.000 0.000 0.000 0.000

Progeny of all apterae 0.028+0.008 0.174+0.019 0.096+0.010 0.532+0.017 Progepy of all parents 0.035+0.009 0.207+0.020 0.118+0.011 0.516+0.017 All progepy with alatae 0.050+0.012 0.321+0.028 0.177+0.016 0.535+0.020 All progeny without alatae 0.000 0.000 0.000 0.478+0.029

All field caught P.aptera 0.029+0.004 0.060+0.006 0.044+0.003 0.512+0.008 -190-

be been wings in females and temperature. Reversion to the actual proportions

shows that the maximum proportion of alate offspring from apterous parents

is found at 20°C (0.29 ± 0.(4). The. 2s for wings in males at different temperatures are apparently non-significant as are those for the sex ratio.

The proportion of alates that were male is about 0.15 and is not significantly

different at 15°C, 20°C and 25°C. Comparison of the progeny of apterous parents with those of alates all

reared at 200 generated significant -A.2 values for all classes considered, although the predicted value for winged males was less than five in one

instance. Hovever, the latter was sufficiently large to reflect a probable

significant de...)arture from the hypothesis of independence of proportion of

wings in male progeny and parental morph. The test of the sex ratio showed

a marked relationship between proportion of males and females in progeny and their parentage. Referring to the proportions in Table 5.6 and Appendix

8, the data show a marked bias of the sex ratio in favour of females amongst

progeny of alate parents. The X 2 values for alate females is also significant, shorting a relationship between wings in females and the morph of their parents, the proportion of alate females being far greater in the offspring of alate parents. The proportion of the alates that were male

was consistent regardless of the parental morph. The results of all rearings in which alate progeny were present were compared with those from which alates were entirely absent. The analysis showed sex ratio.is insignificant being independent of the presence of alates

amongst progeny (the other .X.2s are trivial). Finally the data were summed over all rearings and were compared in a 2 x 2 contingency table with

the total data for field caught P.aptera (Table 5:7). '.3‹ 2 is shown to be

highly significant for wings in females (X 2 = 95.57 P 0.001 for 1 decree of freedom) but is not significant for either wrings in males or sex ratio.

The value of the latter in particular is very low (X2 = 0.03 P> 0.05 for 1 degree of freedom) and referring to the actual proportions, there is no - 191 -

Table 5.7. X 2 tests for contingency tables on data of wing polyorpl-lista and. sex ratio in reared and collected. P.aptera.

Comparison Decrees alary/aptery alary/aptery - sex ratio of freedom in nales in females

X2 X2 All progeny of arterae, totals for all te::Teratures 3 4..60 30.66** . All progeny, totals for all telaperatures 3 7.66( ) 41.98** 1.07 Progeny of apterae at 2000 and progeny of alatae at 2000 1 6.68(*) 6.05* 10.55* A11 progeny with alatae and all wit lout alatae 1 7.34(*) 60.60** 1.96 Total reared and total field cuaght 1 0.39 95.57** 0.03

denotes significance at the 0.05 level of probability and ** at the 0.01 level ( ) represent values based on exs;,ected, nu:Scer of < 5

Table 5.8. Results of student's t test coi.iparing ::can cumulative egg production and oviposition rate of apterous and alate Ptinella at 20°C

P.aptera P.errabunda apterous alate apterous alate dean no. eggs laid (withS.n.) 29.35-14.07 56.86+4..56 17.55+2.02 31.16+6.11 t with 33 d.f. and probability . 48 P <0.001 2.77 P=0.01-0.02 Oviposition rate in no. eggs/ day (with S.73.) 1.51+0.15 3.13+0.12 0.90+0.04. 1.12+0.10 t with 24. d. f. and probability 7.80 P < 0.001 2.23 P=0.05-0.02 -192-

significant -difference between the overall sex ratio of field caught and

reared specimens (0.51 4- 0.01 and 0.52 t 0.02 respectively).

The overall regression coefficient relating wings to sex in the culture

populations (Figure 5.2) was considerably greater than that calculated for

the field caught populations (-0.17 as opposed to -0-.05). However, it was approximately the same as the high values recorded in July and August in

the field (-0.17) and apparently reflected the high numbers of winged females in the cultures at 200C, particularly those derived from alate parents.

5.3 Comparison ofKlunliELEllie22fLamterous and alate females.

Inferior reproductive performance has been reported by several authors for alate individuals of wing polymorphic species (e.g. Dixon, 1972). In order to investigate the phenomenon in Ptinella fecundity schedules were constructed for alate females of P.aptera and P.errabunda using the methods described in Section 3. Due to the inadequate supply of alate individuals in both natural populations and cultures, it was possible to set up only fifteen pairs of winged P.aptera and six of P.errabunda - all at 20°C

(Appendix 8). Mean values of the number of eggs laid per female are presented in Table 5.8 for alate P.aptera and P.errabunda, together with the corresponding values for apterous morphs of the same species at the same temperature. The values were tested for significant difference using Student's t-test the calculations being performed by means of a Wang programmable calculator. In both species alate females are shown to produce a greater total number of eggs than apterous individuals (Table 5.8). P (0.001 for P.aptera and P = 0.01 - 0.02 for P.errabunda. Since it seemed probable that variation in longevity between individuals was more likely to be a consequence of inadequate culture techniques than an intrinsic characteristic, the results are also expressed as oviposition rates. These were shown to be significantly - 193 - different at the P <0.001 level (P.aptera) and between F = 0.02 and 0.05 levels (P.errabunda). Apterous P.antera produced a mean number of 1.51 ±

0.51 eggs per day, whereas alate females of the same species averaged twice as many ; 3.13 + 0.12 per day. The difference between the morphs of P.errabunda was not so great (0.90 ± 0.04 eggs per day for apterous females, and 1.12 + 0.10 for alate individuals) but was significant between the P = 0.02 and F = 0.05 levels.

7urther,investigation of these interesting, but surprising, differences of fecundity in population terms, was carried out by the estimation of values of life table statistics for the experimental winged populations of both- species. The methods by which data were obtained for the statistics have already been described in Section 3. Unfortunately the absence of winged individuals from laboratory cultures of P.errabunda prevented independent measurements of duration of pre-reproductive stages, survival, and proportion of eggs hatching, from being made. With the exception of pre-oviposition period, these values were obtained for progeny of alate P.aptera and the results are summarised in Table 5.9 Frith corresponding.apterous values. However, it must be pointed out that it was not possible to detect whether a developing individual would emerge as an alate adult. The use of progeny of alates for the measurements was aimed at maximization of the chance of at least some of the progeny being alate (for further discussion see below).

The value for the sex ratio was the only measurement that differed between alate and apterous individuals; that for alates being biased in favour of females (0.59 females) whereas the apterous population exhibited a sex ratio favouring males (046 females). The measurements used for alate F.errabunda were, with the exception of a value for fertility, derived from the fecundity experiments, those obtained for the apterous population of the came species at 20°C. The mean values for intrinsic rate of increase, net reproductive rate and generation time are presented in Table 5.10 with the corresponding -194-

Table 5.9. Mean values used in the estimtion of life table statistic3 for apterous and alate Ptinella at 20°C.

P.aptera. P.errabunfta alate apterous alate apterous ::can duration egg stage in days with S.3. 12.25+0.29 12.52+0.21 as for 20.76+0.4B apterous (no. of eggs) (20) (42) (25) Mean duration of larval and pupal stage in days with S.E. 19.10+0.55 19.70+0.42 24.50+0.34 (no. individuals) (10) (10) (10) Mean pre-oviposition -neriod in days with S.E. as for 6.00+0.45 It 5.60+0.51 apterous (no. individuals) (5) (5) Total pre-reproduction period in days 37.35 38.22 tt 50.86 Sex ratio-proportion of females 0.59 0.4.6 It 1.00

(no. of individuals) (D4-5) (336) . Proportion eggs hatching 0.78 0.82 tt 0.55

(no. of eggs laid) (11) (99) (128) Proportion individuals surviving to reproduce 0.56+0.05 -0.52* 0.06 0668+0.04

(no. of individuals) (5) (5) (5) Proportion of feuales laying eggs 1.00 1.00 0.86 0.95 (no. of females) (15) ( 20) (7) (21)

* denotes proportion of adults dying before reproduction =0.05 - 155 -

Table 5.10. Comparison of mean life table statistics between apterous and alate morphs of Ptinella at 20°C with results of Student's t test.

P.aDtera P.errabunda alate apterOus alate c12terous

17;o. of females 15 20 6 20 ru increase per mean female per day (with S.E. 0.049+0.001 0.026+0.002 0.033+0.003 0.025:;-0.002 8.813**(t1) 2.327 deGrees of freedom 28 24

Ro females per mean female per (with S.E.) Generation 13.868+1.2065.203+0.722 11.656'4288 6.236+0.721 t 6.4,95** 3.031 degrees of freedom 33 u- mean generation (with S.E.) time .in days 5.053+1.34. 57.153+1.73574.692+2.71o67.802+1.931 0.906 1.792 degrees of freedom 33

denotes significance at 0.05 level of probability ** denotes significance at 40.001 level of probability t1 corrected t value for unequal variances. -196-

figures for apterous morphs. The values were compared for apterous and alate

populations of each species by means of Student's t test for significant

difference. The results of the significanoetest are given in Table 5.10

The intrinsic rate of increase is significantly different between morphs

in both species, being greater for alates. The net reproduction rate shows

a similar pattern but no significant difference is obtained between estimates

of generation time for winged and wingless morphs of both species.

In female Ftinella the shape of the spermatheca is normally clearly

distinguishable when an individual is examined under a microscope using a

transmitted light source. In the course of sexing individuals for fecundity

experiments it was observed that the size of the spermatheca was apparently

greater in alate females than in apterous feales. Since spermatheca volume

is certainly correlated with high reproductive output in Apidae, measurements

were made in order to determine whether the spermatheca volume in female

P.antera reflects fecundity. The shape of the spernatheca in F.antera is

irregular, however, it roughly approximates an Plipse with a 90° bend in it.

The volume was therefore calculated on the basis of this figure._ Using

an eye-piece graticule in association with a 1:113. :20 microscope, the total

length and breadth of the slermatheca was measured in forty-eight preserved

specimens or Y.antera, collected from a variety of sites, mounted in polyvinyl

lactophenol. The depth "as measured by focusing from the dorsal surface of

the organ down to the ventral surface using the graduated fine focusing screw

facility on the microscope. The measurements were fitted to the equation

for the volume of an elir-

volume of elipse V = 415 abc

whore a, b and c are lengths of

The individuals on which the measurements were made coneriseil two

randomly sclected populations - twenty-four elate and twenty-four apterous fer.ales collected from natural populations: measurement . of the val'mic

of the spermatheca was time consuming and measurements of depth had to be

repeated several times to obtain an accurate estimate, a linear regression - 197 -

analysis was applied to determine the relationship between volume and a

single convenient dimension, the total long axis of the spermatheca. The

results of the analysis are given in Table 5.11 where both the correlation

coefficient and the regression coefficient are presented with the aiTropriate

t value. The regression is also represented graphically in Pig • _5 ._3 . The

high value of t shows significant de,mrture of the calculated regression

coeficient from the hypothetical value of zero for absence of relationship.

This showed the close linear relationship between the values of spernatheca

volume and total long axis length and suggested that it would be valid to

use the latter dimension in comparisons between the spermatheca volulce of

dir-?erent individuals.

The data on spermatheca volume and total long axis length were separated .

into two classes depending on whether the individual was alate or apterous.

The means of the two groups were compared by means of Student's t-test

calculated by means of the ;Tang calculator; the results are given in Talle

5.12. The mean volume of the spermatheca for alates was 9.35 + 0.27 x 10-5mA

whereas that for apterous individuals was 5.84 + 0.14 x 1155mm3. The high

value of t confirmed the significance of the difference between these values.

The mean length of the spermatheca of the alate females was 0.215' mm and

was 0.171. mn for apterous females. The t value was considerably higher

than that relating to volume. Apparently this discrepancy was due to

several extreme values of the latter which were associated with immaturity of the individuals concerned. It was observed that the spermathecae in

these cases were, like the entire beetle, poorly chitinised. Although the total long axis measurement was probably a relatively accurate estimate of what the total spermatheca length would have been once sperm were present inside it, the depth and thickness were distorted. It is suggested that

this resulted, at least in part, in the greater observed variation in volume.

In order to eliminate the possibility that variation in spermatheca

size merely reflects variation in the overall body size as opposed to the -198-

Table 5.11. Results of linear regression analyses relating to spermatheca size ia 24 apterous and 21 alate P.ai)tera.

(i) Regression of volume ontotal.long axis length of sermatheca. Mean total long axis length in mm 1.930 x 10-1 + 0.054 x 10-1 ::ean volume in mm3 7.590 x 10-5 + 0.003 x 10-1 Regression coefficient 0.076 Computed t value 11.143 F4:0.001 Correlation coefficient 0.854 P 4 0.001 (ii)Regression of total long axis length of spermatheca on thorax length Mean thorax length in ma 1.720 x 10-1 + 0.007 x 10-1 :.:ean total long axis length in in 1.9501E10-1 + 0.034 x 10-1 Regression coefficient -0.109 Computed t value -0.148 P:, 0.10 Correlation coefficient -0.022 P], 0.10

Table 5.12. Comparison of iman spermatheca volume and long axis length between apterous and alate morphs of P.aptera with results of

Student's t test.

apterous

Mean spermatheca volume (with S.3.) in mm) 9.35x10-5+0.27x10-5 5.84x10-5+0.14x10-5 Correlated t value (ti) 11.39 Probability P < 0.001 Degrees of freedom 35 Mean total long axis length of spermatheca (with S.E.)in mm 2.15x101+0.17x10-1 1.71x10-1+0.15x10-1- t 19.48 Probability P < 0.001 Degrees of freedom 46 — 199 —

Figure 5.3 cession of spernatheca volui:ie on tot.1 lone; axis lenEtn of speriaatheca in alate and. airLerouo- F.aptera.

12_

• 11

b = 0.076 P< awl

9_

Spermatheca volume in mm3x 10 5 8_

7

6_

5 _

o apterous

4 _ ■ elate

016 0.18 0.20 0.22 0.24

Length of spermatheca long axis in mm - 200 -

,presence or absence of wings and:the associated differences in fecundity,

the length of the thorax was measured. The distance between the centre of

bhe anterior margin of the pronotum and the mid-point on the hind margin

was measured on each of the individuals. The dimension was used to rerresent

a measure of an independent variable of body size. The regression of the total long axis length of spermatheca on thorax length is drawn in Figure 5.4 and the relevant regression and correlation coefficients are presented in

Table 5.11. The graph illustrates the absence of association between

spermatheca size and thorax length and_ the separation of the data into two

Groups on the basis of sperratheca size alone, the two groups exactly coinciding with the two different morphs.

5.4 Discussion. (1) Wings and the environment.

•The incidence of winged and wingless individuals amongst wing polymorphic species has been attributed to two mechanisms, simple genetic determination or a certain genetic flexibility in development permitting presence or absence of wings depending on prevailing environmental conditions at a critical stage in the life history. Evidence in the vast majority of cases suggests that the wing polymorphism is environmentally determined.

In Ptinella the numerical dominance of the apterous morphs recorded in the literature, has been supported by the data from all populations from which collections were made, with the exception of a few sites where the proportion of alates was particularly high. The proportion of alate and apterous individuals has been shown to -waxy considerably between sites, although the sizes of samples were frequently so small that much of the variation was probably a result of sampling error. The summing of the data for each month has shown a trend towards a relationship between the proportion of apterous and alate individuals in a population and the time of year, for females of both P.artera and P.errabunda. This trend was not however, apparent in males although the distortion of results due to the inadequacy -201-

Figure 5.4 Regression of total long axis length of spermatheea on tiox

length in alate and apterous P.a,Aera.

0.24 _

• •

• • 0.22 _ ■ ■ • • • ■ • • ■ • • • ■ • Length of ■ • spermatheca ■ long axis 0.20 _ in hin b= -0.109 P >0.10

0.18 _ 0 0

0 0 0 q3 o 0 0 ❑

0 0 0.16 _ OD

❑apterous

ilOakite

0.14 1 6.15 0.16 0.17 018 0.19

Thorax length h mm - 202-

of }C 2 values when expected values in the contingency tables are less than

five, has already been discussed. :yen summation of the data for seasons

did not result in high expected values for proportions of alate males

although the significant values of X 2 for spring, summer and autumn for

both sexes probably reflect a trend towards increasing proportions of winged

individuals in populations during summer and early autumn. Such a trend

definitly exists, for F.antera females at least, environmental conditions at

these times of the year being implicated in the control of the polymorphism.

The specific conditions that might determine whether wings develop or not

are obscure, although a subjective impression of "deterioration" of the

habitat was recorded at most sites where the proportion of alates was

noticeably high. In such situations the population was frequently dense and often restricted to a small area, apparently isolated by the unsuitability of the surrounding habitat, the latter commonly being very dried out.

The distribution of alate individuals in populations of P.errabunda is shown

to follow a similar pattern of variation through the year as that described for P.aptera. For both species a sharp increase in the proportion of alates in summer to reach peaks in July (P.errabunda) and August (I.IlLesa) and a subsequent decrease in October has been shown. In the case of P:aptera it was into.Inesting to note that the proportion of winged individuals that are male falls from about 0.5 in spring to only about 0.2 of the summer population implying that the seasonal effect on wing development is considerably greater for females than males. It is not clear how this differential wing development is controlled. Further samples for all months, ideally with data on physical factors of the habitat are required in order to clarify this trend and relate it to the prevailing environmental conditions. Unfortunately the highly variable nature of the habitat and the destructive nature of the sampling are such that this approach is severely limited. As a result of the relatively

small amount of data available for analysis, summation had to be carried out indescriminately over the three year period during which collections were made, thus obscuring annual variation in proportions of alate individuals -203-

in populations. Observations at least, suggest that in addition to the recorded

seasonal variation in alary development, there may be further variation based

on the age of the colony.

One factor which changes corresppn,lingl7r with season and which could

thus effect an increase in alates in summer, is temperature. The effect of

this factor on P.aptera has been investigated under controlled laboratory

conditions. The proportion of alates in the progeny of any pair, is shown

to be variable although this mutt, in part, be due to sampling error since

the number of offspring of a single pair of parents that reached adulthood

was limited as a result of the cultural problems already described (Section

3). Contingency table and X 2 analysis of the summed_ data for progeny at

.each temperature have shown a significant relationship between development

of wings and temperature in female P.aptera. The highest proportion of

ringed female progeny occurred at 20°C - 25°C (.29 .03 to .1L- ± .04)

whereas wings were absent from all individuals reared at 30°C. The absence.

of wings in the latter could have been due to physiological effects at this

temperature resulting in inhibition of wing develolnent. Alternatively it

might simply have been due to chance, the number of progeny observed being

sufficiently small for there to be a finite possibility that alates would not

be represented. The proportion of individuals with wings was low at 15°C

suggesting that at the extremes in the species range of activity, the

mechanism for ring development might be rendered non-functional.

The comparison of the overall proportions of alates in cultures with

those in field populations has shown that there is very little difference as

far as males are concerned. The proportion of alate females however, is

significantly greater in laboratory reared populations and the overall

fraction of alates, both male and female, is higher in cultures. There are

several possible explanations for his phenomenon. The field caught data

was, as has already been described, derived by a rather haphazard method

of collecting the animalrl. Since the alates exhibit a high degree of activity it seems likely that some of them, were overlooked during collecting,

especially those that were reacting with positive phototaxis and had reached

the outer surface of the bark. Furthermore, their persistence in a po7mlation

would be expected to be lidited, altLough neither the nature of the stinuli

that result in flight activity, nor the ti-._e that elapses between emergence

and flight, are known.

Ptinella mny Have broadly overlapping generations and thus it seems

likely that if alates arc produced as a regular proportion of each generation,

their numbers would be fairly reliably reflected by the data. Similarly,

equal proportions of slate individuals would be expected at all temperatures

if the mechanism is simply genetic. The laboratory data suggest that

temperature is at least one of the environmental factors affecting a pheno-

typically plastic genotype, alates being inhibited at extre.2es of the

temperature range over which reproduction takes place. If the polymorphism

is essentially temperature dependent, the low values observed in the field

collections could be a consequence of low temperatures under bark during

the developmental period. The increase in sulaaer could be attributed to correspondingly higher temperatures at this time of year. The possibility that the temperature effect observed in culture is spurious, seems to be

highly unlikely. Although conditions in the cultures were not perfectly

standardised, there was no consistent difference observed between the cultures at different temperatures. It is conceivable that subtle differences in

food supply existed.

The casual observation of populations in neglected cultures suggest that temperature is not the only factor that can affect wing development.

In several such cultures the observation of winged individuals in large numbers was associated with decreases in humidity as a result of drying out of bark. A subjective assessment that food becomes restricted, implies that wing development is determined in immature stages exposed to such conditions. - 205 -

(ii) Inheritance of wings.

:UtiiOUgh the evidence discussed so far tends to support the hypothesis

that the polymorphism is environmentally controlled, breeding experiments

using alate Parents hint at a genetic basis. In these experiments it has

been shown that the proportion of alates amongst the Progeny is significantly

greater than that in the progeny of apterous parents although the proportions

of the sexes in alates rep ains unaffected. A further series of controlled

breeding experiments extended over several Generations needs to be carried

out before any conclusion can be drawn and a Genetic hypothesis postulated.

ITevertheless, the results do imply some degree of Genetic basis for the

polymorphism possibly similar to that of Callosobruchus maculatus (Caswell,

1959). One possible hypothesis is that particular polymorphic genotypes

result in phenotypic similarity with respect to wings; but under certain

environmental conditions the expression of wings is permitted in one genotype.

The explanation of the polymorphism in genetic terms is problematical

for P.errabunda. Since this species reproduces by pcmthoGenesis, a simple.

Genetic basis for the polymorphism is apparently precluded. MnGed dispersives

initiating a colony would be expected to produce a clone of alate progeny

with a more or less identical genome to that of the mother. Unfortunately,

data foralatebreeding experiments was not obtained for this species. The

fact that no alate P.errabunda were obtained in the standard culture conditions

similar to those described for P.aptera, suggests that the mechanism may be

different in the two species. However, such a gross difference between two

species so similar in other ways would seem unlikely. It is tentatively

suggested that the threshold for development of wings is hider in the

parthenogenetic species. This issupported by observations on alates made

in Section 4 when apparently the conditions in the competition cultures were

such that a high proportion of winged P.errabunda was recorded. Casual observations of one site showed a population of P.errabunda that was almost - 206

totally elate. Possibly this species is potentially fully winged but the

expression of wings is, as in P.a7)-tera environmentally deter,lined. It is interesting to note that the one species of Ptinella (P.aavelli), in the British

fauna that can without doubt be said to be a New Zealand species and that is now abundant in this country, has been recorded only as the winged morph.

Turthermore ,lince no males have been found, it appears to reproduce partheno-

genetically. However, the foregoing is moi-oly speculative and further

eml'eriments with "P.errabunda are required in order to determine the nature

of the mechanism of the polymorphism and the stages at which development

of wings is determined.

The polymorphism is further complicated in P.aptera by a distinct bias

in the sex ratio in favour of females amongst alate individuals. It is

apparent from the field data that a greater proportion of females are winged

than the fraction of males that are alate, although alates are z;eneralllr so scarce that this has little effect on the overall sex ratio of the

population. This is supported by the results of the laboratory rearings in

which the sex ratio of the progeny of alates reared at 20°C is 0.32 4. 0.06

(proportion of males), the proportion of fe:.,ales that are alate being 0.48

+ 0.07 as opposed to 0.18 + 0.0 for males. As has already been noted the sex ratio within alates is constant regardless of parental morph. Amongst the apterous individuals there is a slight male bias in the sex ratio. This, coupled with the fact that despite the proportion of alates in the population being low, the sex ratio is female biased, results in an overall

sex ratio that approximates,a 1:1 ratio. The sex ratios calculated for the summed field data and the laboratory data do not differ significantly,

their great similarity suggesting that the method used to collect the field

populations gives a reliable representation of Ptinella populations in the

field.

A trend towards a female biased sex ratio is also recorded amongst apterous offspring of alate parents as opposed to that exhibited by those -207-

of apterous parents at the same temperature.

It is not clear how the female biased sex ratio is achieved in alates.

It is possible that it arises through differential mortality of males and

females during development, a r,reater proportion of males failing to reach

adulthood. The data on sex ratios supports such an explanation, although

some means of genetic determination is not ruled out. Since females mate

before flight in laost cases, the selective advantage of wings in :males is

not so great although the function of winged males is, presumably, to permit

variability and greater realisation of the female reproductive potential in a new colony. Re.inselaination is necessary to achieve the latter.

(iii) The reproductive significance of wings.

It has been shown that the alate morphs of P.aptera and P.errabunda are significantly more fecund than the apterous morals. This increased fecundity is sustained by the other life history parameters and results in an increased reproductive potential in terms of the intrinsic rate of increase. Such a finding has not apparently been reported in the literature before in any but the social insects. In the latter it has probably been an Laportant stage in the evolution of the social system, ringed queens being responsible for the production of the entire colonies. The worker castes of many of the termites and ants show similar adaptations to apterous Ptinella. The differences in the intrinsic rate of increase and the net reproduction between apterous and alate P.aptera and P.errabunda have been shown to generate highly significant values of t (8.81 and 6.50 for rm and Ro respectively imptukE2). Although the sample number was smaller for P.errabunda, the differences were significant at the 0.05 level of probability

(t = 2.33 and 3.03 respectively). No significant difference was shown between the generation times of alate and apterous individuals of either species. The duration of the stages of the life-history, mortality, fertility and percentage hatch were found to be relatively similar for apterous and - 208 -

alate P.aptera. The only exception is the sex ratio which was shorn to be female biased in alates.

The increased fecundity of alate P.aptera and P,errabunda is paradoxical in these non-social species since it is difficult to see how the apterous morph could have evolved in the presence of a uore fecund winged morph.

The selective advantages of loss of wings must be Very considerable to overcome _theintrinsic alate advantage of greater reproductivity. The dispersal polymorphism could presumably have been achieved without recourse to aptery by behavioural polymorphism such as has presmicbly been evolved in the fully winged species P.cavelli. One possible explanation of this paradox is that when first evolved, aptery facilitated increased reproduction

(as in many polymorphic species) and together with morphological reduction adapting it to the species cryptic habits; conferred considerable selective advantage on the apterous form. In this way the wingless morph became predominant, the reproductively inferior alate :,morph being maintained to effect dispersal and.colonisation. The limited powers of dispersal of dead wood insect species is noted by Hamiaond (1974.) and thus strong selective pressure for increasing fecundity of alates would be expected to exist, particularly if some degree of environmentally mediated but genetically based difference is involved in the polymorphism. If such super-fecundity, evolved in alate Ptinella it must be assumed that the mortality suffered by dispersives, and the cryptic adaptations of aptery, are sufficiently great to maintain the polymorphism balanced in favour of the apterous morph. Inevitably the criticism can be made that the data on life history do not necessarily represent alate individuals since there was no way in which alates, or potential alates, could be distinguished prior to emergence as adults. The generally low proportion of alates in all cultures prevented detailed investigation of this particular problem. Clearly, with establish- ment of a successful culture method for maintaining alates, this would demand further consideration, since it is possible that differences in - 209 -

life history could prevent the reproductive potential observed,from being

realised. The increase in reproduction by increasing fecundity suggests

that the duration of the life cycle has already been minimised. Hamilton

(1966) and Lewontin (1965) have pointed out the greater relative advantage

gained by reduction of the length of the cycle as opposed to increase of

fecundity. This has been regarded by Pianka (1970) as one of the character,-. istics of strongly r-selected species; it would appear that the environmental

pressures that result in r-selection apply to P.aptera and P.errabunda (for further consideration of strategies and selection see Section 6). The increase in reproduction of alates is reflected by an increase in the volume of the spermatheca in P.aptera (the problem was not investigated

in P.errabunda). It was shown that the mean spermatheca volume increased from 5.8h. x 10-5 mm3 in apterous morphs, to 9.35 x 10-5 mm3 in alates, apparently implying an almost double potential for storage of sperm. The

selective advantage' for the latter is great for a dispersive morph of a species that depends on reinsemination to realise its full fecundity. If, as seems likely, the vast majority of females are inseminated prior to dispersal, their potential as colonisers would be benefitted by any increase in the number of eggs that could be produced on invasion of a new site, thus increasing the chances of successful establishment. Apparently a similar development has taken place amongst the Apid.ae where the spermatheca may be relatively enormous. In this case it apparently facilitates the production of all offspring by the queen from a single mating. It was shown that the total long axis length of the spermatheca may be used as a reliable and easily measureable expression of volume for comparative purposes. The regression coefficient for spermatheca long axis on volume was 0.03 and when tested against the theoretical zero of indepmnd- ence, it generated a highly significant t value of 11.14. This would enable measurements to be easily made when comparing individuals from different populations. -210-

The increase in zpermatheca size was shown to be independent of body size, the regression of total long axis length on thorax length generating a regression coefficient which when tested gave an extremely low value of. t (-0.15). Hamilton (pers. comm., and hamilton and Taylor, in preparation) has suggested that the origin of sociality in the termites may have resulted from selection pressures associated with the rotting wood environment. A number of species found in the habitat exhibit wing polymorphism and reproductive phenomena such as parthenogenesis. It is concluded that of these species, Ptinella is apparently most termite-like in terms of its very extreme alary polymorphism and the quite exceptional finding of the increased reproductive potential of the alate morph. - 211 -

SECTION 6

DISCUSSION

6.1 Colaretition and coexistence.

Field sampling and collecting have established. that F.aptera and

P.errabunda occur over :Each of the sa;:_e- area of Britain occupying broadly

the - habitat although P.errabunda is much the more widely distributed

of the two. However, in southern .3ngland- where P.antera is locally abundant,

there is no doubt that the species coexist in the same localities and at

the same sites, at least at the level of individual tree trunks. In view

of the problem already discussed concerning definition of populations it has

not been possible to estblish the degree of intimacy of the observed

coexistence in population terms. FUrthemore, the field data were insufficient

to deterAine the degree of stability of coexistence between the two

species. In one case re-examination of a site, a year after sampling had

first been carried out, revealed a distribution pattern of the species that

differed little from that initially observed, thus suggesting some degree

of stability of the association of the species. Nevertheless a potentially

competitive situation exists between P.aDtera and P.errabunda presenting the

question of how the species are able to continue to coexist.

Inevitably it has not been possible to determine the precise niches of

P.aptera and P.errabunda; however, their general requirements and responses

to some of the major environmental factors have been compared. There is no evidence to suggest that the species differ in their food requirements or

preferences in either the larval or adult stages. Thus the coexistence

described by Lack (1945) and Croker (1967) including niche differentiation on the basis of food supply, probably does not apply to the two Ptinella

species. Similar conclusions have been reached for two at least partially mycetophagous coexisting species of Collembola (Tomocerus minor and T.longico-r rnis) (Anderson and Healey, 1972). As far as physical factors are concerned, no evidence was found to suggest that coexistence was facilitated by differences - 212 -

in humidity tolerances of the two species although the possibility of such

differences existing near the saturation level cannot be entirely eliminated.

7owever, temperature was found to form the basis of a potentially important

species separation through its differential effects on both the range of

tolerance and activity and on the reproductive performance of the species.

P.antera was shown to be adapted to the range of temperatures between 15°C

and 30°C (or slightly above) the maximum rate of increase that was recorded

being achieved at 30°C, P.errabun41, on the other hand, had an active range

between 10°C and 25°C exhibiting its maximum recorded rate of increase at

2000. It is thus possible that direct competition between the two species

may be avoided as a result of their adaptation to different temperatures.

Although the results of the laboratory experiments in which F.artera

and P.errabunda were placed in situations designed to subject them to direct

competition, were insufficiently standardised. to be particularly meaningful,

there was a general trend that was interpreted in terms of a temperature

dependent competitive advantage of the species. Thus at 20°C P.aptera

apparently had a competitive advantage over P.errabunda, whereas at 15°C

the situation was reversed with P.errabunda dominating. A simple model has

been constructed in order to demonstrate that the outcome observed in the

competition experiments can be predicted from the differential rates of

increase exhibited by the two species at 15°C and 20°C(Figures 6.1 and 6.2).

The values for intrinsic rate of natural increasearm) derived from the fecundity experiments (Section 3) have been converted to finite rates (A ) by the formula:

N= erm per generation

Using the values for the generation times of the two species at 15°C and 20°C

(Section 3), the population that would be predicted for each species in

successive generation is given by the formula:

Ntia = X Nt where Ntia is the size of a population after one Generation of increase from - 213 -

Fir:Lire P2ojoctea tipn _1.1c.1-ease in co.inetiti.m F.“ P.err,.bunaz observed -3;u1-,tion cine3 t terlin ; 2

600

500 • P. aptera 20 C. o A 15 C. • P. errabunds 20°C. o O 15 C. 400

Number of 300 females

200

.100

100 200 Time in days

Experiment terminated

P. aptera P. errabunda - 214. -

a population of size U.. The graphs representing the expeCted increase of

populations of eclual nul,-ibers of P.aptera and F.errabunaa (N = 1:.) at 15°C

and 20°C are given in figure 6.1 and 6.2. The Observed mean numbers of adult females in the competition populations.(B) after 6 months are presented in the figures. It is clear that the cultural environment did not permit unlimited po,.:121:-..tion increase either as a result of conditions being so stringent as to result in excessively high density independent mortality, or through limitation of resources for which-individuals would be expected to compdte. The outcomes of the competition experiments starting with initially eoual densities of females arc consistent with the species predominance predicted from their rates of increase, although the actu.A. values are very considerably smaller, suggesting that competitive advantage was based on differential rates of increase.

The species separation demonstrated im the laboratory could clearly function on a geographical scale to determine the species distributions.

However, the subcortical zone of decaying wood - has been shown to be highly variable as far as temperature is concerned aepending on the intensity of solar radiation on the bark surface, the thickness of the bark and other factors. Thus degree of canopy and herbage shading may have a considerable effect on microclimates beneath the bark.• It has been suggested that the observed absence of P.aptera from coniferous plantations is at least partially a consequence of the consistently low temperatures under permanent canopy cover. Such temperatures would probably be well below 15°C for much of the year and thus would not permit P.aptera to maintain a positive rate of popula- tion increase. However, P.errabunda's physiological adaptation to a lower range of temperatures would be expected to enable this species to establish and maintain colonies in such areas. Furthermore, measurements of subcortical temperatures have.shown that a similar effect is possible within a shaded log in more open deciduous woodland and if part is exposed to direct sunlight a sufficient range of temperatures should exist to permit coexistence - 215 -

of the two species, each in its area of mioroclimatic optiaam. On this basis

it :light be predicted that such logs could. sustain populations of P.errabunda

on their lower surfaces which are penAanently shaded, P.aptera predominating

on the ul)per surfaces el:osea to sunlight by virtue of their ;:;reater re'.Dro-

ductive efficiency at Higher temperatures. However, the data from

and collection was ambig-uous and a prog-r=e of accurate subcortical

temrerature neasr.re::ent and intensive sampling of Ptinella 1Dopulations would

be recaired to further clarify the situation.

Coexistence of two competing slpecies may be facilitated by means other

than niche differentiation. Temporal balances of advantage, such as those

visualised by Dobzhans:y (1911.5), or freouency dependent fitness (Ayala, 1970),

may enable a relatively stable state of coexistence to exist. between species,

but no evidence was found to suggest this in mimed populations of P.alYtera

and P.errabunda. However, it is conceivable that the temperature separation

already described could have functioned in some situations to permit a form

of temporally based coexistence.

Another -form of relatively stable coexistence has been demonstrated. by

Connell (1961) and Paine (1966) for intertidal organisms. In this case the

balance is apparently based on differential predation. Since the natural

mortality of Ptinellawas not assessed in the course of the study, it is

possible that P.aptera and P.errabunda are subject to differential rates of

mortality. However, selective mortality of two species that are so similar

in physical characteristics seems rather improbable.

The situations of coexistence already discussed facilitate relatively

stable associations between species. There are however, a number of

circumstances in which an unstable or transient form of coexistence nay be

observed; frequently they may be associated with habitat instability

(Hutchinson, 1957). One particular form of transient coexistence may occur

on invasion of a species' habitat by a non-endemic species as was described

for species of isopod- Ascellus by Williams (1962). Pew cases of competitive

displ:.ce2ent have been studied(Debach and Sunny, 1955) and Cro rwell (1968) - 216 - but presninably whilst it is tal:in;. lace the two sic:cies concernea nay coexist in so:e instances. since there is much taxono:dc and historical evidence to

'2uest that P.erraLunda is of :rew Zealand origin and has been introduced

Into 73ritain dur!ng this century, it is '30,0?:ule that this snecies is aisnlacing the enclomic F.antera. It is not -essible to trace the introduction and subser-Izent si.rcaC. of F.errabunda in the same way as Paviour-Smith (1960b) has been able to deaonstrate the invasion of Britain by the Australian fungus beetle Cis bilamellatus. The diminutive size of Ptinella and their cryptic habits have resulted in their being overlooked by many entomologists and the records that do exist tena to reflect the zeal and range of particular collectors rather than the actual distribution of the species. Furthermore, the distribution of F.antera prior to the first records of F.errabunda is eaually uncertain. Presumably the endemic species of Ptinella have, like many other organisms associated with decaying wooa, been adversely affected by continuing destruction of the habitat. Although this woula have startea with early human activity of forest clearance, it is probably in the last

500 years that the natural habitat has been decimated and continues to decline with modern methods of forestry and further clearance of areas of established woodland. Thus it is not clear whether competition with the non-endemic

F.errabunda or merely destruction of habitat has resulted in the pre sent, rather limited., distribution of P.aptera. In the north of Britain it is likely that annual mean temperatures are generally too low to permit extensive populations of F.antera to become established and possibly the greater reproductive efficiency of F.errabunas under such conditions may have resulted in displacement of the former species and a general contraction of its range in northern areas. However, the widespread distribution of F.errabunda is probably largely a consequence of its ability to exploit habitat that is effectively unavailable to F.aptera.

Although a potentially competitive situation arises where F.antera and

P.errabunda coexist, there is no conclusive evidence to suggest that - 217 -

P.errabunda and. P.aptera compete for. resources in short supply. The

coexistence of species in transient habitats may be permitted by the failure

of the populations to exceed the carrying capacity of the environment for the

fhiration ofthe period when the habitat is favourable. In such situations

the species are reproducing in an unlimited environment and differences in the

composition of the mixed populations are a consecuence of differential

rP.production rates and the history of colonisation of the particular site

concerned. Thus the predominance of P.a7tera in many mixed populations may

be the consecuence of environmental factors, such as temperature, permitting more rapid population increase than that effected by P.errabunda.

The assessment of whether food supply for Ftinella is superabundant or whether it in fact limits populations, is problematical. It :night be assumed that the food supply of species which are effectively unspecific n'cetophages in the subcortical zone of a decaying tree would be unlimited relative to the populations concerner% Both density independent factors and density dependent mortality, due to predators for example, would be expected to limit population growth such that the carrying capacity of the environment is not reached. Nevertheless, the great diversity of subcortical conditions observed on rotting wood might be expected to result in semi- isolation of both mixed and single species populations of P.aptera and

P.errabunda in "islands"of favourable habitat. In such limited areas population growth between microclimatic catastrophies could result in the overshooting of the carrying capacity and a situation of direct competition between the two species. Whether the duration of the suitability of such sites would be sufficiently long to permit competitive displacement is not clear, although the reproduction rates observed in the laboratory suggest that, in some cases at least, it may be. Any prediction of the probability of such localised populations as those visualised occurring is precluded by the problems associated with definition of population units.

In conclusion the data concerning the distribution and coexistence of

P.aptera and P.errabunda and the nature of their habitat, although ambiguous, - 218 -;

surest that an interpretation in terms of a simple fundamental interaction between the species is unrealistic. It seems most likely that the spatial and temporal heterogeneity of the environment results in a similar variability in the basis of coexistence between the two species and, indeed also between

P.errabunda and P.taylorae.

6.2 Asexuality - an advantage for colonists.

The selective advantages that have lead to the evolution of asexuality from pre-existing sexual reproductive mechanisms in a variety of anim,,ls, have been variously attributed to advantages of increased fecundity, fixation of successful heterotic biotypes, colonising ability, and, for relatively immobile species,independence of males. All the observations made on

P.errabunda during the course of the current study demonstrate that this species has evolved asexual reproduction in the form of pure thelyto4.

The possibilities of seasonal occurrence (heterogony), rarity or cryptic nature of males were effectively eliminated. 2urthermore, one particular form of parthenogenesis that night have been predicted from the situation of coexistence of a bisexual and a parthenogenetic species was shown to be absent in P.errabunda. Described as gynocenesis, it is the phenomenon whereby the egg of a purely parthenogenetic species requires the stimulation of sperm penetration in order to develop; the parthenogen is thus dependent on a closely related bisexual host for successful reproduction. This method of reproduction has been recorded in detail for Ptinus mobilis and its bisexual

"host" Ptinus clavipes (Moore, Sanderson and Woodruff, 1956). However,

P.errabunda was shown to be independent of P.aptera in its distribution and on no occassion were spermatozoa observed in the spermatheca of some 3,500 collected or laboratory reared specimens of P.errabunda that were individually examined.

Having established that P.errabunda reproduces by thelytoky in its observed range at least, and that a certain degree of coexistence with

P.aptera occurs, the reproductive advantages of a parthenogen in facilitating a potentially doubled fecundity and the observed coexistence of the two - 219 -

species are paradoxical. .Although increased fecundity is the most irmnediatel,y

obvious advantage for a species evolving parthenogenesis it has been shown

that this doubled potential is not realised in P.errabunda. As has been

observed for other species such as Lonchoptera dubia (Stalker, 1956) and

Drosophila mangabeira (11Urdy and Carson, 1959), the egg viability is low,

significantly lower flLfact than for both the bisexual species P.aptera and

P.taylorae. Furthermore the oviposition rate of P.errabunda at a given temperature is significantly lower than that of P.aptera under comparable conditions. It has become _apparent that P.aptera and P.errabunda are not as closely related as had been suspected. initially when P.errabunda was thought to be a parthenogenetic homologue of P.aptera; thus the problem of how bisexual and parthenogenetic species could have evolved and been maintained alongside one another, is to some extent obviated. On the basis of comparative morphology and responses to temperature, P.errabunda is considered to be more closely related. to P.taylorae. If the egg viabilities of the two species are compared, that of P.ern....q3unda is again significantly lower implying that lack of success in hatching is associated with a change from bisexual to parthenogenetic reproduction. Effectively the potentially doubled. fecundity predicted for

P.errabuncla is reduced to a slight advantage (in terms of the innate capacity for increase) of F.errebunda over P.taylorae at 20°C, comparisons with

P.aytera being complicated by the adaptation of P.aptera to higher tempera-4 tures.

Since increased fecundi-6y was clearly not so great an advantage in

P.errabunda as would have been expected, it is concluded on the basis of the current work that the greatest advantage of parthenogenetic reproduction to r.err.sbunda and probably to many parthenogenetic species and races, probably lies in the potential of each individuals, at any stage, to initiate a colony. In his account of the parthenogenetic species of the Ftiliid genus

Euryrynej Dybas (1966) concluded that the overriding selective advantage conferred by the change from bisexuality to parthenogenesis is the conse suence of increased.. fecunaty, considering the advantages of colonisation - 920-

to be of secondary importance. :owever, it is sa7gested that, as for

F.errabunla, so the greatest advantage of e2fective asexuality in parthenogeneti

species of -2u77:-;ne is based on more effective colonising c:bil3ty. The

ronincj wool habita'6 may generally be re-arCed as a transient habitat of

disjunct distribution 1966; Southwood, 1960a); thus its associated

faun 'e deuenent on - ore or less regular colonisation episodes for their

survival and evolution of -flarthenogenetic reproduction would he expected to

he favoured by selection. The relativoly high incidence of asexual reproduction in this environment has alrealy been discussed. That the advnnta=es of a parthenogen in terms of colonizing ability are realised in

P.errabunda is apTcrently demonstrated by the distribution of this species relative to the bisexual F.antera. The extensive conincidence of P.antera's

distribution with old forest areas where rotting wood provides a more or less continuous habitat has already been Outside such areas the records for the species are relatively scarce, the woodland being dominated by extensive areas of softwood plantations and local isolated areas of deciduous woodland and forest remnants. The habitat available to Ptinella outside the old forests is thus largely discontinuous and perhaps parallel to that described for Cis fuscipes by Lawrence (1967). The distribution of

P.errabunda is not limited in the same way as that of P.aptera and although the species' reproductive efficiency at lovr temperatures has been inferred as enabling it to become established over a wider range than the bisexual species, its :=eater ability to colonise isolated patches of habitat may be even more important. Lawrence (1967) attributed the success of the parthenogenetic

Cis fuscipes in colonising the patchy habitat of the raid-western United

States to its asexual reproduction. Thus the observed, almost exclusive, occurrence of P.errabunda in forestry plantations and in isolated areas of deciduous woodland is probably largely a consequence Of its superior colonising ability, this advantage being supplemented in evergreen forests by the greater reproductive efficiency of the species relative to P.antera, at the lower temperatures consequent of- perranent shading of the habitat. -221.-

urt'lerriere, the dispersive abilities of reerrabunda nay facilitate raid ' ex--;1-)'!;at;on by the spec .es of newly available habitat and the increase of

populations to such an extent that colonising individuals of P.aptera are unable to become established.

In his study of dispersal in beetles, Linciroth (1957) included parthenogenesis amongst the desirable characteristics of species for long- distance dispersal in ship's ballast. 7-xon7,-:;cal evidence

,ply that the three species of Ptinella recen';ly the British fauna

(Johnson, 1975, in press) are almost certainly long-distance immigrant species

4'-or 7c,w Zelanq; furthermore two of the three species (F.errabunda and

P.cavelli) are apparently parthenogenetic, in Britain at least. Although the evidence is scant, the following suggestion is made to explain how these species could have been accidentally introduced and the nart that partheno- genesis may have played in their successful colonisation in Britain.

Approximately 300 years ago Britain Tr.s self-sufficient as far as timber resources were concerned, but with the heavy demand of the Industrial

Rovplution and subsecuently the First World lar, the reserves were exhausted and both softwoods and hardwoods were imported on an enormous scale. Although

New Zealand has never been a major timber source, between 1922 and 1931 large quantities of hardwoods were imported. In 1925 17,297 cubic yards of the Puriri cVitex lucens) alone were exported to Briatin (Timber Trade

Federation of the United Kingdom, pers. comm.). Although no break-down was given for the other species they probably included those specified as being imported in 1945 (Brough, 1902) in particular the southern beeches

(Nothofapus fusca and Nothofagus menniesii), the Rata (iletrosideros excelsa),

Rena-Rewa (Knic;htia excelsa) and Tawa (Beitschmiedia tawa). Softwoods also formed a high proportion of imports from New Zealand in 1945 including the

Yauri pine (Agathis australis), the Rimu (Dacrydium cuyressinun) and the ratai

(Fodecarpus spicatus). However, the latter were generally transported ready cut as planks whereas, even in 1945, much of the hardwood was shipped in the form of untreated logs. The adaptation of P.errabunda P.cavelli and - 222-

P.taylorae to a relatively low range of temperature, together with the strong association of P.cavelli identified from specimens from Westland and apparently related Groups of the other two species, with the.South Island of New Zealand suggest that they are perhaps adapted to subcortical conditions in the ever-

southern beech (Nothofagus) forests where the forest floor is in more or less continuous shade - "There is, however, one undeniable characteristic of the forests (of New Zealand). They arc gloomy ..." (Laing and Blackwell,

1927). It is not difficult to visualise some parts of NothofLzrs (or other hardwood) timber being nartially decayed and car=,-inG with it thc associated subcortical fauna. Thus a means of tian1,-,ertation of the beetles existed.

A number of other New Zealand species of Coleoptera have become established in Britain (Hammond, 1974) and it seems lihely that South Island 3-zecies in particular are climatically pre-adapted to conditions in Britain which are broadly similar to those encountered in I:ew Zealand.. The Ptinella species would be expected to be similarly pre-adanted. It seems lilcely that all three species concerned were introduced, probably repeatedly, in the 1920's and 1930's as .fie scribed, on Laported timber. It appears that P.errabunda and P.cavelli were able to spread ra_AdJ,y and e::tensively whereas P.tavlorae rpparently exists as localised populations. It appears more than coincidental that the former species are parthenogenetic whereas P.te;ylorae is bisexual.

It is interesting to note the possible association of localities from which

P.ta3rlorae has been collected with the west coast ports of Liverpool and

Bristol perhaps reflecting confinement to the areas immediate surrounding the points of introduction. However, the distribution on the west coast of

Ireland is somewhat problematical in this respect, although the snecies mzy be more widespread in that country, and the possibility of the species being pre-adapted to high rainfall of the west coast cannot be eliminated.

Nevertheless, it seems reasonable to conclude that the highly successful establishment of P.errabunda and P.cavelli (in northern Britain at least) has been Greatay facilitated by their ability as parthenogenetic organisms, to - 223 -

initiate colonies from single pioneering individuals whereas the limitation

of P,taylorae may, at least in part, be a conserluence of its bisexuality and

consequently relatively lower colonising ability.

In view of the foregoing it appears that the selective pressures

favouring evolution of parthenogenesis must have been effective in New Zealand

and in the absence of information concerning the conditions and locations

where parthenogenesis was evolved, apy hypothesis concerning it must be purely

speculative. Nevertheless, current advantages observed , presumably reflect to

some extent those that favoured the evolution of this method of reproduction

in Ptinella.

There is thus much evidence to suggest that parthenogenetic species have a definite advantage over bisexual forms in terms of dipersal ability and thus selection would tend to favour such forms in transient habitats.

Furthermore, in the case of P. errabuhda, the predominance of the apterous morph and the apparently greater selective disadvantage of the dispersive ringed form would be expected to increase selective pressures favouring greater efficiency of the latter morph, and thus parthenogenesis.

Unfortunately it has not been possible to consider parthenogenesis in

Ptinella with respect to the belief of Waite (1973), that the overriding importance of thel:)-toky lies in its fixation of heterozygosity without the genetic load encumbent with its maintenance in a bisexual system. The compatability of White's view, implying a tendency for partheno gens to be restricted, specialised biotypes, with the evidence for advantages conferred in dispersal and to a lesser extent reproduction, has already been discussed.

Thus despite P.errabunda's opportunistic colonisation of newly available habitat, the apparent limitations of P.aPtera and the exacting physical recluirements of these species of Ptinella suggest that P. errs can

probably be considered to be a somewhat restricted species confined to a relatively narrow and invariable niche. - 2214.-

In conclusion, the investigation of the biology and distribution of a

bisee7ual and a parthenogenetic species of Ftinella lends strong support to

the view that increased dispersive and colonisation efficiency, as opposed to

simply increaser'.: reproduction, is a major selective force that favours evolution

of parthenogenesis particularly amongst species inhoItting transient

environments.

6.3 Paradoxical fecundity_pplymorphism.

Although feather-wings are characteristic of the Ftiliidae, most specieS of Ftinella exhibit physically extreme alai- polymorphism with a predominating apterous, eveles morph. Furthermore, the current study has shown that this is accompanied by a remarkable, albeit paradoxical, physiological polymorphism in the form of super-fecunaity of alate morphs compared with the apterous forms, unparalleled as yet, in any of the literature on insects outside the social lymenotera. stable polLrlorliam implies a balance of advantages f or each form and it is simple to visualise the way in which simple alai- polymorphism would_ be maintained in Ftinella with the high cost of alate aise-,ersal being balanced by the need for colonisation in a temporally unstable habitat. 1Towever, with an increased fecundity associated with the alate morph it is difficult to explain how selection could have favoured the evolution of a reproductively inferior form in the presence of a winged morph of significant];' greater reproductive potential. It is reason- able to assume that the mortality of dispersive individuals in a temporally and spatially heterogeneous habitat mast be considerable, particularlY in the case. of the species of Ftinella investigated in the current study whose

1;.mits of physical tolerance are narrow. ::everthelees, it would seem more reasonable in terns of evolutiona7y cconoe,y for a simple behavioural dimorphism to be evolved in the fecund alate morph than for a physically reduced, re-rroductively inferior morph to be favoured by selection. It appears that lacavellia_ a_ has evolved just such a behavioural 1--poeloii,a Ln and this species - 975-

is apparently successful existing in alate form only in the same sort of

habitat as the alary polymorphic P.a'Aera and P.errabunda. There thus any ears

to be no Great disadvantage associated with maintenance of wings beneath the

bar:: although the dispersal activity of P.cavelli demands further investigation.

Tn view of this it is tentatively zugflezted that tlIc evolution of su-:er-

,:'ecnnity in alates could have occurred subseruent to the estalient, by

:election, of a nossibly initially superior, apterous morph. The came heavy

mortality of individuals leaving the rather narrow optimum subcortical

conditions that would result in selection favouring wing eye reduction,

would. similarly loc.a to selection-ressure for increased fecundity of dispersives

to ensure ma::imwl -,:roductivity of the few successful colonists. The surer- fecundity thus evolved has -cresu2ably failed to enable the d1wte for.a. to displace the retroductively less efficient apterous morph as a result of the .lortality involved in dispersal. Dybas (1966) has suggested that the reduction in wing hairs exhibited by the species 22a202111tricata1 an island nember of an otherwise non-polymorphic genus, is an adaptation to reduce mortality as a result of flight activity although he attributes it to the somewhat dated concept of Darwin (1059) of winged island species being subject to mortality a., a result of being blown out to sea. Regardless of the precise nature of the selective forces involved, the remarkable similarity botr,-en protortions of individuals with fully c7eveloped wings in E.intricata and P.antera and P.errabunda collected at the same time of year (6.5? - 7.01 for E.intricata and between 6.05 amd 8.0,7L. for P.aptera) suggests that the mechanism underlying the polymorphism of both species is probably the same, reflecting similar needs to balance the advantages of wing reduction on the one hand and the need for dispersal on the other.

6.4 Environmental and genetic determination of nor h?

The control of alary polymorphism has, in most cases, been demonstrated

to be closely linked with environmental factors. General evidence from - 226-

cultures of P.aptera and P.errabunda, collecting data and field observations

suggests that in Ftinella the polymorphism is at least partially environmentally

controlled. Thus high proportions of winged individuals are recorded at certain times of the year (late summer) and at particular localities where

conditions for the beetles may be considered to have deteriorated. However,

a simple interpretation of the mechanisms of control based on the ontogenetic

hypothesis seems unlikely. Factors of food supply limitation, papulation

density or unfavourable humidity conditions could all be involved in determining

wing development but breeding experiments using alate P.aptera have suggested

that a genetic basis to the polymorphism is also involved perhaps paralleling

the situation in Cc.11osobruchus maculata (Caswel1,1959). The proportion of

winged individuals in the progeny of alate parents is significantly greater than that in the progeny of apterae, however, a Mendelian interpretation

of the form visualised by Kettlewell (1952), Kinne (1953) or Brinkhurst (1959,

1960b) is probably too simplistic. The overall implications concerning the

alary polymorphism of P.aptera clearly suggest a genetic mechanism controlled by environmental switching although further controlled. breeding experiments.

are required to clarify the situation. In particular the fecundity of all offspring of alate parents should be considered in an attempt to determine the degree of association between wings and super-fecundity. Furthermore,

the strong correlation of wings with a female biased sex ratio, although relatively easy to explain in terms of selective value, is not so easily interpreted in terms of the mechanism by which it is achieved.

6.5 Strategies in a heterogeneous environment.

The transient nature of the rotting wood habitat and its irregular and often disjunct distribution, result in a high degree of both temporal and spatial heterogeneity relative to species which, like Ptinella, are associated with particular stages of the rotting wood succession. Whilst the discontinuous incidence of the habitat and its ultimate deterioration require an efficient dispersal mechanism in species associated with it, the potential diversity 227 -

of decay conditions observed at a single site implies that the duration

of favourability of the site relative to the generation time of Ptinella may be relatively long in many cases. Thus, as has been described, selection

will favour a balanced alary polymorphism, furthermore, the reproductive

strategies evolved by the species are determined by the same selective

forces imposed by the two-fold heterogeneity of time and space. In a habitat that is clearly so unpredictable Ptinella would be expected to have evolved

in the direction of maximisation of production to result in maximum exploit-

ation of a frequently unsaturated environment, their populations being

limited largely by density independent mortality (Southwood, May, Hassell

and Conway, 1974). In terms of the r-selection,/:-selection continuum, a stronly r-selected strategy is implied. Although the concept of the selection

continuum is only meaningful in comparison of species'stategies, it may be concluded from the study of both the life histories and basic ecologies of

P.aptera and P.errabunda, that these species.are adapted to fit into the

r-selected end of the range. Moreover, the correlates of r-selection listed

by Pianka (1970) are apparently fulfilled by both P.aptera and berrabinida, although the repeated reproduction of both species is apparently anomalous, being associated with K-selection. It seems thatthis is the inevitable consequence of the evolution of small body size and the needs of the active campodeiform larva. In order to produce the latter, the food supply laid down in the egg must be considerable and as a result each egg is relatively enormous compared with the body size. Only a single egg can be matured in the abdomen at one time and in order to realise the total potential egg production of at least 100 eggs, repeated reproduction over a fairly long life span in necessary. Dybas (1966) concluded that this would seriously limit the reproductive potential of Eurygyne since he assumed that the duration of adult life is short and the rate of egg maturation slow. However, it is likely that he underestimated the reproductive potential of the genus which is probably similar to that exhibited by Ptinella. Despite its - 228 -

Table 6.1 Coarison of dou-Jling times of Ptiiella with those of predouinately r-selected species and, for contrast, a 1:-selected species.

Species Temperature doubling Source in 00 tiue in days Holm sapiens (2aiwanese population) c.14,892 Hamilton 1966 P.antera 15 121.61 Hiptus hololeucus (beetle) 25 112.84 Andrewartha n Birch 1954 P.errabunda 10 63.59 2:icrotus acimatia (vole) 55.45 Kendeigh 1961 Rattus norvegicus 47.15 Nendeigh 1961 P.errabunda 25 35.46 P.errabunda 15 32.69 P. taylorae 20 30.14 P.errabunda 20 27.97 Cis bilauellatus 24 27.08 Paviour-Smith 1963 P.a-otera 20 26.97 Gibbiurn psylloides 25 20.55 Andrewartha A Birch 1954

P.aptera 25 14.62 P.aptera (elate) 20 14.15

P.aptera 30 10..55 Rhizopertha douinica 29.1 8.37 Birch 1953 Calandra oryzae 29.1 6.30 Birch 1953 Daphnia ilex 2.40 Hamilton 1966 Schizosaccharo, ces kephir yeast 0.48 Gause 1932 - 229-

limitations the reproductive performance of the genus compares favburably

with that of other animals in terms of population doubling times. The times of 11.22LpE1. and P.errabunda are compared with those of other species largely at the r extreme of the continuum in Table 6.1, doubling time being estimated from rm values by means of the formula:

doubling time = loge 2 rm

These high rates of increase although natural mortality was largely excluded

are apparently achieved by rapid development, early reproduction, rapid egg

maturation (at least 10 eggs in a single 49 hour period at 3000 for P.aptera).

It appears that the relative uniformity of duration of the pre-reproductive period reflects its minimisation under strong selection, that has not however,

acted to such a great extent on fecundity. Thus as predicted by Lewontin

(1965), the total egg production is rather variable from one individual to

another. As far as P.errabunda is concerned the slight reproductive increase

probably consequent of evolution of parthenogenesis may perhaps be regarded

as one stage further in the selection for reproductive advantage, with the bias in sex ratios suggested by Hamilton (1967) reaching its ultimate potential for reproduction as pure thelytoky.

6.6 Epilogue.

Although the results of this study of the biology and ecology of Ptinella pose a number of general problems, it appears that many of the adaptations of Ptinella may be interpreted, without recourse to the Divine intercession invoked by the Reverend Matthews (1872), as the results of evolution by means of natural selection, such that the species is fitted to a habitat characterised by a high degree of temporal and spatial heterogeneity.

Furthermore, although few of the data are, in themselves conclusive, many aspects of the species biologies have been shown to lend support to current ideas on broad evolutionary and ecological concepts of species interactions - 230- and adaptations under the selective pressures imposed by a heterogeneous environment. 1. The aim of the study was to investigate the biolo-,r of two species of

Ptiliidae and where possible, to relate the findings to the broad ecological

and evolutionary phenomena of competitive coexistence, parthenogenesis,

polymorphism and ecological strategies. The literature on these subjects

and on the species considered in the study was briefly reviewed.

2. The life history of Ptinella was studied in laboratory cultures and by

field observation. The pattern is the sane in all three species considered

P.aptera, P.errabunda and P.taylorae, and with the exception of alate

individuals, all stages are confined to decaying wood - principally the

subcortical zone. They are multivoltine, eggs being matured and laid singly

throughout the year when prevailing temperatures permit. Larvae are

campodeiform and develop through three instars, the results of gut analyses

demonstrate ultilisation of an apparently common food supply by all stages

of both P.aptera and P.errabunda, the diet comprising fungal spores , hyphae, yeasts and unidentified material.

3. Absence of males, and of sperm from the female spermatheca in all

individuals, and the ability of unfertilised eggs to develop to produce

normal adults lead to the conclusion that P.errabunda reproduces by pure

thelytoky.

4. A technique for sampling field populations of Ptinella was developed but was shown to be severely restricted by the heterogeneity of the rotting wood environment.

5. Results of field sampling and extensive collection of Ptinella showed that P.aptera and P.errabunda may apparently coexist in the same habitat. Furthermore, evidence suggested that competition for resources in short supply - 232 -

may occur, the outcome probably depending on the prevailing temperatures. In such cases it is suggested that coexistence may be permitted by surer-

abundance of resources or may represent a transient state or a temporal balance of advantag es.

6. Laboratory studies on humidity tolerances of Ptinella suggested that relative humidity is an important limiting factor in determining the

distribution of. P.aptera and P.errabunda since prolonged survival was not observed at or below the maximum humidity tested of pg.

7. The effect of temperature on the activity, development and reproduction

was studied in laboratory experiments. A significant difference in temperature

adaptation was demonstrated for P.aptera and P.errabunda, litatera was shown to be active from 15°C to at least 30°C with a maximum rate of increase

(rm = 0.066) at 30°C, but P.errabunda was active between 10°C and 25°C with a maximum rate of increase nearly one third that of F.aptera (rm = 0.025 at 20°C). Outcomes of competition predicted from this data were realised in laboratory competition experiments between the two species.

8. It was noted that the potentially double fecundity associated with parthenogenesis was not realised by P.errabunda, the proportion of eggs hatching being significantly lower than in bisexual species.

9. The implications of differential temperature adaptation were considered in relation to observations of the species habitat and distribution and to results of subcortical temperature measurements made on a dead Fagus sylvatica in fairly typical "old forest" surroundings. It was concluded that subcortical temperatures (maximum 48°C) are potentially limiting for Ptinella populations and furthermore patterns of sun and shade may provide sufficient diversity of microclimates to permit spatial separation of species optima. - 233 -

10. The data from collections were analysed with respect to the incidence of alary polymorphism. Alates were shown to form a consistently low proportion (0.04) of the population but in both species a significant seasonal effect was detected in collections maximum values being recorded in July and August (0.16 and 0.18 for P.aptera and P.errabunda respectively) suggesting an environmentally controlled polymorphism Possibly based on temperature.

11. Laboratory breeding experiments showed a relationship between alate production and temperature in P.aptera with apparent breakdown of the mechanism towards the extremes of the activity temperature range.

12. Genetic control of the polymorphism is also inferred. Breeding experiments demonstrated a significantly higher proportion of alates in progeny of alate parents. It was therefore suggested that alary polymorphism in Ptinella is based on polymorphic genotypes generating phenotype similarity with environmentally controlled expression of wings in one genotype.

13. The first case of apparent reproduction advantage of an alate morph outside the social insects was recorded for P.aptera and P.errabunda. The problems concerned with the evolution of the apterous morph in view of this were considered. I:orphological study of the morphs demonstrated the reflection of increased fecundity in the significantly increased size of the spermatheca of alates.

1l. Differential distribution of P.aptera and P.errabunda was observed from collecting data, P.aptera being generally restricted to "old forest" areas of southern England in particular where the species was predominant. P.errabunda, however, was shown to be widely distributed. through the British Isles.

15. A species new to the British List (P.taylorae) was found on the west coast of Ireland and Was subsequently found in a few localities on the west coast - 2314.- of England. It was concluded. that, together with P.errabunda and P.cavelli, P.tvlorae is a species introduced from New Zealand during the last hundred. years.

16. The successful spread of P.errabunda was attributed to its parthenogenetic reproduction and it was suggested that the potential colonising ability of each parthenogenetic individual is perhaps the most important selective advantage of this form of reproduction, at least for species associated with transient environments.

17. The restricted distribution of P.antera was attributed largely to the problem of colonisation in a discontinuous environment and partially to displacement in northern areas by P.errabunda which is reproductively superior at lower temperatures.

18. It was concluded that the overall biology and ecology of P.aptera and P.errabunda reflect the strong r-selection associated with the high temporal and spatial heterogeneity characteristic of the rotting wood environment. - 235 -

ACIGIOWL7.',DGELONTS

I should like to express my sincere thanks to my supervisor Dr.X.D. Ha.lilton for his invaluable guidance and encouraL.ement throughout the course of this project.

Particular thanks are due to Professor T.R.B.Southwood for his constructive criticism and helpful advise in the preparation of the thesis and for allowing me the use of the facilities of the field station.

I am especially indebted to Colin Johnson of the Entomology

Department, Manchester. Museum, for making his data on the national distribution of Ptinella available to me and for much interesting and helpful discussion. I should also like to thank Dr. Levy (Imperial College) for discussion on ticiber decay and Dr. Bevan of the Forestry Commission, Alice Holt and regional officers of the Forestry Commission for advice on sites for collection of speciricns. Finally I r.m indebted to the Natural Environment Research Council for the financial support of this project. - 236 -

REFERENCES * Original paper not seen by author.

AnDERSON,J.M. & HEALEY,I.N. (1972) Seasonal and interspecific variation in major components of the gut contents of some woodland Collembola. J. Anim. Eco1.41, 359-368. ANDREVIARTHA,H.G. & BIRCH,L.C. (1954) The distribution and abundance of animals. Univ. of Chicago Press, Chicago, 782 pp. AYALA,F.J. (1969) Experimental invalidation of the principle of competitive exclusion. Nature Lona. 224, 1076-1079.

.AYALA,F.J. (1970) Competition, coexistence, and evolution. In: Essays in evolution and Genetics in honor of Theodosius DobzhanstEt edt. /LK...Hecht Z LC.Steere, 121-158. Appleton-Century-Crofts, New York. BARIGOZZI,C. (1956) Differentiation des genotypes et distribution geographique dtArtemia salina Leach: donne-es et problems. Annee biol. 33, 241-251. BERORItRD,J. (1954) Parthenogese facultative de ClitumnUs extradentatus Br. (Phasmidae). Bull. Soc. tool. Ft. 79, 169-175. BESS,H.A., BOSCH,R. VAN DEN& BARANOTO,F.H. (1961) Fruit fly parasites and their activities in Hawaii. Proc. Hawaii ent. Soc. 17, 367-378.

BESUCHET,C. & SUUDT,E. (1971) Ptiliidae, In: Die E..fer ritteleuropas. Band 3 edit. H.Freude, K.W.Harde & G.A.Lohse, 329-331. Goeke 2: Evers, Krefeld. BIRCH,L.C. (1953) Experimental background to the study of the distribution and abundance of insects. III. The relations between innate capacity for increase and survival of different species of beetles living together on the same food. Evolution, Lancaster, Fa. 7, 136-1/1b. BIRCH,L.C. (1957) The meanings of competition. km. Nat. 91, 5-18. BOVINGIA.G. & CRAICHEAD,F.C. (1930) An illustrated synopsis of the principle larval forms of the order Coleoptera. Entomologica am. 11, 1-351. BRIAN,A.D. (1957) Differences in the flowers visited by four species of bumble-bees and their causes.. J.Anim. Ecol. 26 71-98. BRINKHURST,R.O. (1959) Alary polymorphism in the Gerroidea (Hemiptera- Heteroptera). J. Anim. Ecol.. 28, 211-230. BR_D1KHURST,R.O. (1960) The distribution of the water-bug Venn saulii Tamani, with some notes on alary polymorphism. Proc. R. ent. Soc. Lond. SA) 91-92. -237-

BRITTEN,H. (1926) No. IV Coleoptera, Ptiliidae (Trichopterygidae). Trans. Linn. Soc. Lond. 19, 87-92. BROADHEAD,E. WAPSPHERE,A.J. (1966) Lissopsocus populations on larch in England - the distribution and dynamics two closely-related coexisting species of Psocoptera sharing the same food resource. Ecol. 1;slalca 2i, 327-388. BROUGH,J.C.S. (1962) Timbers for woodwork. Evans, London, 232 pp. BURSELL,E. (1974) Environmental aspects. 1. Temperature and 2. Humidity. In: The_ physiology of Inseota. Vol. 2, 2nd edit. /1.Rockstein, 1-84. Academic Press, New York. CARTWRIGHT,E,ST.G. & FINDLAY,W.P.K. (1958) Decay of timber and its prevention. 2nd edition. Her najesty's Stationary Office, London, 332710. CASTJELL,G.H. (1959 Observations on an abnormal form of Callosobruchus maculatus (F1 Bull. ent. Res. 50 671-680. CODY,M.L. (1966) A general theory of clutch size. Evolution Lancaster, Pa. 20.„ 174-184. COLE,L.C. (1954) The population consequences of life history phenomena. Q. Rev. Biol. 29, 103-137. COLE,L.C. (1960) Competitive exclusion. Science, N.Y. 132, 3/i.8-349. CONIELL,J.H. (1961) The influence of interspecific competition and other factors on the distribution of the barnacle Balanus balanoides. Ecol. Lonogr. a, 61-104. CORNTELL,P.B. (1955) The functions of the ocelli of Calliphora (Diptera) and Locusta (Orthoptera). J. exp. Biol. 32, 217-237.

CROIZER,11.A. (1967) Niche specificity of Neohaustorius schmitzi and Haustorius sp. (Crustacea : Amphipoda) in North Carolina. Ecology, 40, 571-975. cra3=,A.c. (1945) On competition between different species of graminivorous insects. Proc. Soc. (London), (B), 132, 362-395. monELL. ,K.L. (1968) Rates of competitive exclusion by the Argentine ant in Bermuda. E2222a, 49, 551-555. Diat=a-TON,C.D. (1958) Evolution of Genetic systems. Oliver a Boyd, Edinburgh. DARLIUGTON,P.J. (1943) Carabidae of mountains and islands: data on the evolution of isolated faunas and on atrophy of wings. Ecol. llonogr. 225, 37-61.

DARITM,C. (1859) The origin of species by means of natural selection. Penguin Books, 459 PP. -238-

DEBACH,P. (1966) The competitive displacement and coexistence principles. A. Rev. Ent. 21, 183-212. DLBACH,P. w SUNDEY,P,A. (1963) Competitive displacement between ecological homologues.- Hilgardia1.2t, 105-166. DIXON,A.F.G. (1972) Fecundity of bracbypterous and macropterous alatc.e in Drepanosiphum dixoni (Callaphididae, Aphididae). Entomologia exp. a1 p1.. 15, 335-340. VoRATTEN,S.D. (1971) Laboratory studies on aggregation, size and fecundity in the black bean aphid, Aphis fabae Scop. Bull. ent. Res. ol, 97-111. DODZHAI:SIZ,T. (1943) Genetics of natural populations. IX. Temporal changes in the composition of populations of Drosophila pseudoobscura. Genetics, Princeton' 28, 162-186. DOBZHAI:Sia.,T. (1950) Evolution in the tropics. Solent. 23, 209-221. DOMES,J-k. (1962) What is an artic insect? Can. Ent. 51.1v 245-162. DOWIES,J.A. (1964) Arctic insects and their environment. Can. 2nt. 96, 279-307. DTBAS,H. (1960) Anew genus of blind beetles from a cave in South Africa. .Fieldiana, Zool. 20 399-405. DYBAS;H. (1966) Evidence for parthenogenesis in the featherwing beetles, with a taxonomic review of a new genus and eight new species (Coleoptera: Ptiliidae). Fieldiana, ;Lod. 22, 11-52. ELTON,C. (1927) Animal Ecology. Sidgwick & Jackson, London 207 pp. ELTON,C. (1966) The pattern of animal copmunities. Methuen, London 432 pp. FAGER,E.W. (1955) A stu 1 of invertebrate nonulations in deca in• wood. Unpubl. D. Phil. Thesis, Oxford. niversity, 154 pp. FAGER1E.'7. (1968) The community of invertebrates in decaying oak wood. J. Anim. Fool. 2, 121-142. *1+O1iBES,W.T.1% (1926) The wing folding patterns of the Coleoptera. Jl. N. Y. ent. Soc. 34, 42-686: 91-139. FOWLER (1889) The Coleoptera of the British Islands. Vol. III Clavicornia. Reeve, London, 399 pp. Fumuss,lut. (1962) A circular punch for cutting samples of bark infested with beetles. Can. Ent.. 21,- 959-963. GADGIL,11. & BOSSERT,W.H. (1970) Life historical consequences of natural selection. Am. Nat. 104, 1-24. - 239 -

CADCIL,M. SOLBRIG,O.T. (1972) The concept of r- and Er-selection: evidence from wild flowers and some theoretical considerations. Am. Nat. 106, 14-31.

ITSE,G.F. (1932) Experimental studies on the struggle for existence. 1. :axed populations of two species of yeast. J. exp. Biol. 21, 389-402. GAUM, G.F . (1931,.) The struggle for existence. Williams n Wilkins, Baltimore. CAUSE,G.F. (1970) Criticism of invalidation of principle of competitive exclusion. Nature, Lond. 227, 89. GAUSEI G.2.TIITT,A.A. (1935) Behaviour of mixed populations and the problem of natural selection. Am. Nat. 6.25 596-609. GEIOLET)::,,T. (1974) The econo s of nature and the evolution of sex. University of California Press, Berkeley, 54• pp. *GIIESISMRP.C.J.F. (1816) Trychopterigia. In: Deutschlands Fauna vol. 17 edit. J.Sturm. GOTO,H.E. (1960) Simple techniques for the rearing of Collemhola and a note on the use of a fungistatic substance in the cultures. Entomologist's mon. lag. 96, 138-140. 0.1=,S.A. (1924) Temperature as a limiting factor in the life of subcortical insects. J. econ. Ent. 17, 377-383. GRAHAU,S.A. (1925) The felled. tree trunk as an ecological unit. Ecology, 6 597-411. GREENSLAD2,P.J.11. a SOUTHMOD,T.R.E. (1962) The relationship of flight and habitat in some Carabidae. Entomologist, 95, 86-88. GRMSTOITE,A.V. & SICAER,R.J. (1972) A guidebook to microscopical methods. Cambridge University Press, London, 134 pp.

*GUER1N-MENEVILLS (1839) Rev. zool. BAUMAN. & PETERSEN,B. (1952) Measurement of temperature in bark and wood of Sitka spruce. (English summary.) Forst. ForsVaes. Danm. 21, 43..•91. HACKMAN,W. (1964) On reduction and loss of wings in Diptera. Notul. ent. 44, 73-93. HACKMAN, 71. (1966) On wing reduction and loss of wings in Lepidoptera. Notul. ent. 1}6 1-16. MAGSTRUU,D.W. & HAGSTRUM,W.R. (1970) A simple device for producing fluctuating temperatures with an evaiustticrnof the ecological significance of fluctuating temperatures. Ann. ent. Soc. Am. 63) 1385-1389. - 24.0 -

HA.LaSTON, N G-. MIME, D .17 • & WILBUR, H .B (1970) Natural selection and the parameters of population growth. J. 21, 681-690. HAIECLION,W.D. (1966) The moulding of senescence by natural selection. J. their. Biol. 12 12-45. H4.201TON,W.D. (1967) Extraordinary sex ratios. Science, N. Y. 156) 477-488. HA:2IOND,P.11. (1974) Changes in Mae British coleopterous fauna. In: The chance_ flora and fauna of Britain. edit. D.L. Hawksworth, 323--Kg Academic Press, London. Hil_RDINIG.. (1960) The competitive exclusion principle. Science, N. Y. 131, 1292-1297. • HARPER, J .L , CLATWORTHY J .N. ,T.T.ANAUGHTON, I .H. & SAGAR, G .R. (1961) The evolution and ecology of closely related species living in the same area. evolution, Lancaster, Pa. 15, 209-227. HINTON, H .E (1941) The immo.ture stages of Acrotrichis fa scicularis (Herb st. ) (Col., Ptiliidae). Ent. mon. "rag. lb 24.5-250. HOWE,R.W. (1953) The rapid. determination of the intrinsic rate of increase of an insect population. Ann. Appl. Biol. 4,) 13/4.-151. HUTCHDISODT, G.E . (1957) Concluding remarks. Cold. Spring Harb. Symp. auant. Biol. 22, 415-427. HUTCHINSON,G.E. (1959) Homage to Santa Rosalia, or why are there so many kinds of animals? Am. Nat. 2_3, 14.5-159. HUTCHEISON,G.E. (1961) The paradox of the plankton. Am. Nat. 22, 137-1'4.6. HUTCHINSON,G.E. & DEWEY, E S ( 194-9) Ecological studies on populations. SLtzr,v e r of Biol. Progress. Vol. I, 325-329. Academic Press, New York. HUXLEY, J. (194.2) Evolution. The modern synthesis. Allen Unvan, London, 645 PP. JACVSON,D.J. (1928) The inheritance of long and short wings in the weevil Sitona hispidula, with a discussion of wing reduction among beetles. Trans. Roy. Soc. Edinb. 1,5 665-736. JOHNIB. & SHAW,D.D. (1967) Karyotype variation in Dermestid beetles. Chromosoma, 2a, 371-385. JOHNSON,C. (1972) La faune terrestre de L'isle de Sainte-Helene, pars 2, Ptiliidae. Ann3.s. lats. r. Afr. cent. ser. 8to toologie No. 192, 91-96. JOHNSON,C. (1975) Five species of Ptiliidae (Col.) new to Britain, and and corrections to the British List of the family. Entomologist's Gas. 26, 211-223. 241 -

JOHNSON,C. in press. A third immigrant species of Ptinella Motsch. new to t'lz; british fauna. Entomolgist's Gas.

JOHNSON,C.G. (1963) Physiological factors in insect migration by flight. Nature, Lond. 198, 423-427.

JOHNSON,C.G. (1969) Migration and dispersal of insects by flight. Methuen, London, 763 pp.

*JOSEPH,G (1882) aystematisches Verzeichniss der in den Tropirstein-Grotten , von Krain einheimischen Arthropoden nebst Diagnosen der von Verfasser entdeckten und bisher noch nicht bescriebenen Arten. Berl. ent. Z. 26, 1-50. KAXRIK,A.A. (1974) Decomposition of wood. In: Biology of plant litter decomposition. Vol. I edit. C.H.Dickinson & G.J.P.Pugh, 129-174. Academic Press, London. Kamus,H. (1945) Correlations between flight and vision, and particularly between wings and ocelli in insects. Proc. R. ent. Soc. Lond. (A) 20, 84-96. KENDEIGH ,S.C. (1961) Animal ecology. Prentice-Hall, Inc. N.J. 468 pp. 1CNNEDY,J.S. (1956) Phase transformation in locust biology. Biol. Rev. 31, 349-370. • HETTLE1ELL,H.B.D. (1952) A possible genetic explanation and understanding of migration of continuous brooded insects. Nature, Lond. 169, 832-833. K1NNE,0. (1953) Zur geologie und Physiologic von Gammarus duebeni Lill j. Biol. Zbl. 260-270.

KLOFFERIP.H. 6:11ACARTIMR,R.H. (1961) On the causes of tropical species diversity : niche overlap. Am. Nat. 95, 223-226. LACK,D. (1945) The ecology of closely related species with special reference to cormorant.(Phalacrocorax carbo) and shag (P.aristotelis). J. Anim. Ecol. 14, 12-16. LAING,Ral. & BLACKWELL,E.W. (1927) Plants of New Zealand. 3rd edition 71bitcombe a Tombs, Christchiarch, 499 pp. LARKIN,P.A. ELBOURN,C.A. (1964) Some observations on the fauna, of dead wood in live oak trees. 211a, 15, 79-92. LAMENCE,J.F. (1967) Biology of the parthenogenetic fungus beetle Cis fuscipes TSellie (Coleoptera:Ciidae). Brevicora No. 128, 1-34. morTIN,R.c. (1965) Selection for colonising ability. In: The genetics of colonising species edit. H.G.Baker& G.L.Stebbins, 77-79. New York. LINDROTH,C.H. (1949) Die fennoskandischen Carabidae. III. G6teborgs K.Vetensk -0. vitterhSamh. Hanql. Ser. B. Vol 4. 911 pp. - 21.2 -

LETDROTH,C.H. (1957) The faunal connections between Europe and North America. Almqvist & Wiskell/Gebers, Stockholm, 334 pp. *LOTKA,A.J. (1925) 'Elements of Plysical Biolomt Baltimore. EACrIURTHUR,R.H. (1958) Population ecology of some warbles of north eastern coniferous forests. 3coloa 39, 599-619.

la0AATHUR,R.H. (1965) Patterns of species diversi r Biol. Rev. 142, 510-533. MACARTEUR,R.H. (1972) GeoPraphico.l.ecolow -_patterns in the distribution of species. Harter R.017, Ne17 York, 269 pp. MACARTHUR,R.H. l4WILSON,21.°. (1967) The theorq of island biogpographv. -Princeton University Press, Princeton, N. J..203 PP; • NAGDONALD,11.D. a HARPER,A...E. (1965) A rapid Peulgen squash method for aphid chromosomes. Can. J. Genet. ciTto14 2) 18-20. EACVADTEH,A. (1962) Control of humidity in three funnel-type. extractors for soil arthropods. In: Progress in soil zooloa edit.P.7.1Surphy, 158-168. Butterworths, London. 15E101,1410.,J.H. & HEALEY,I.N. (1971) A quantitative technique for the analysis. of the gut contents of Collembola. Rev. Ecol. Biol. Sol. 8, 295-300. EATTHUS,A. (1872) Trichoptenrgia illustrate, et descripta. A monograph of the TrichoPter72. London, 188 pp. 1.:AZTHEY,R. (1941) Etude biologique et cytologique de Saga Leda Pallas (Orthopteres: Tettigoniidae). Revue suisse Zool. 48, 91-102. LM1-3R,H. (1957) Zur Biologie and Ethologie einheimischer Collembola. Zool. Jb. (2/-sta85, 501-570. ITAYR,2. (1963) Animal species and evolution. Harvard University Press, Cambridge, class. 797 pp. MORE,B.P., )OODROPTE,G.E. akmaasol4L.R. (1956) Polymorphism and parthenogenesis in a ptinid beetle. Nature, Lond. 177, 847-848. MOTSC=ISKY,V. (1845; Ueber die Ptilien Russlands. Bul. Soc. Imp. des Nat. de Hoscou 18 pt 2, 504. ITURDY,17.H. GARSON,H.L. (1959) Parthenogenesis in Drosophila mangabeirae :'.slog Lm. Nat. 93, 355-33.

.NEYTTANIJ., PARK,T. & SCOTT? B.L. (1956) Struggle for existence: Ttibolium model: biological and statistical aspects. Proc. Berkeley_SM.math. Statist. Probpb. 1.4.1, 41-79. Univ. Calif. Press. OSBORNE,P.J. (1965) The effect of forest clearance on the distribution of the British insect fauna. Proc. Int. Corer. Ent. 12t1 ) London 122, 37-55. - 243 -

RkE71,11.T. (1966) Food web complexity and species diversity. L,71. Nat. 100, 65-75. FALEI:,E. (1949) The Diolopoda of eastern Pennoscandia. Ann. Zool. Soc. Vanamo 21, 1-54.- (1954) 7::::erimental stidies of interspecies competition. II. Temperature, humidity and competition in two species of Tribolium. Physiol. Zoo?. 27, 177-233. PA.RK,T; (1962) Beetles, competition and Populations. 3cience, N. Y. 133, 1369-1375. PA:TIOUR-SIITHITI:. (1960a) The fruiting-bodies of macrofungi as habitats for beetles of the family Ciidae (Coleoptera). Oikos, 22, 43-71. (1960b) The invasion of Britain by Cis bilamellatus Fowler (Coleoptera:Ciidae). Iroc. a. ent. Soc. Londe (A)25, 145-155.

PAITIOT.1-231T21-1,I:. (1968) A population stuay of Cis bilamellatus wood (Coleoptera, Ciidae). J. nim. :col. 37, 205-223. PERRIS,I% (1846) Annls Soc. ent. Fr. ser. 2 41 465. FETERSEN,H; (1971) Parthenogenesis in two common species of Collembola. ev. Ecol. Biol. Sol .,2, 133-138. PTAIE:A,E.R. (1970) On r- and Z-selection. Am. Nat. 104, 592-597. PITTSHDRIGH,C.3. (1950) Humidity behaviour and distribution of two species of Anopholes. Evolution, Lancaster_ Pa. 43-78. .POITTIN,A.J. (1961) Population stabi1i7Ation and competition between the Ants Lasius flavus (F) and Lasius nizt: (L.). J. Arum. Ecol. 30, 47-54. RICEDIRSON,P., A.T.:STIZONG,R. & GOLDMAN,C.R. (1970) Contemporaneous disequilibrium, a new hypothesis to explain the "paradox of the plankton% Proc. natn. Acad. Sci. U. S. A. 67, 1,710-1,714. ROBERTSON,J.G. (1966) The chromosomes of bisexual and parthenogenetic species of Calliranha (Coleoptera: Chrysomelidz.e) with notes on sex ratio, abundance and egg number. Can. J. Genet. Cytol. 8, 695-732. ROUGHGATIDEN,J. (1971) Density dependent natural selection. Ecology, 52, 453-468. aANDERSON,A.1.1. (1960) The cytology of a- diploid bisexual spider beetle, Ftinus clavizes Panzer and its trinloid gynogenetio form mobilis ;:oore. Proc. R. Soc. Bdinb. (B), 61, 333-350.

SCHOETTER,T.-1. (1965) The evolution of bill size differences among sympatric congeneric species of birds. Evolution, Lancaster, Pa. 19, 189-213.

a.37m, J. (1961) Untersuchunen caber die 3ntstehun7, der ParthenoEenese bei Solenobia triouetrella 72.2. (Lepidoptera, rsychidae). Z. 7ererbIehre, 92, 261-316. SHORTE. (1954) Snuirrelz. Collins, London, 212 pp. BARL077,C.k. (1972) Population srowth of Droso7ohila melano- • caster (Diptera: Drosophilidae) at constant and alterna temperatures. :nn. ent. Soc. in. 65, 993-1001. 3. X. (1953) Chromosome numbers of Coleol)tera. 7.:erecliV, Lona. 7, 31-2,3.

5.".airii, (190) . Chromosome numbers of Coleoptera II. Can. J. Genet. Clytol. 2, 67-33. SOL01:011,:j.:. (1951) Control of humidity with potassium hydroldel sulphuric acid, or other solutions. Bull. ent. Res. 42, 543-554. SOUTZ-700D,T.R.:3. (1960a) 'Migration - an evolutionary necessity for aF2nizens o.r. temporary hal-iitats. Proc. Int. ConsrJ;2.t...lienias,, 54-58. SCUTH7;00D,T.R.3. (1960b) The Mitt activiLy of Heteroptera. Trans. R. ent. Soc. Lond. 212 173-220. SOUTTinD0D,T.R3. (1961) A hormonal theory of the mechanism of winj polymorphism in Heteroptera. Proc. ent. 300. 32, 63-66. 3=:.:003,T.R..J. (1962) ::igration of terrestrial arthropods in relation . to habitat. Biol. Rev. E1, 171-214. SOUTHWOOD, T.R.3 MAY, HASSZLL, M. P. & CONWAY, G.R. (1974) Ecological. strategies and population parameters. Am. Nat. 108, 791-804. STALKER,H. (1956) On the evolution of parthenogenesis in Lonchoptera (Diptera). Evolution, Lancaster, Pa. 10, 345-359. STEBBINS, G41., (1957) Self fertilization and population variability in the higher plants. Am. Nat. 225 337-354. STELLA,E. (1933) Phenotypical characteristics and geographical distribution of several biotypes of Artemia salina L. Z. indukt._ Abstamm. -u. VerebLehre, 412-446. SUOMALAINEN,E. (1940) Polyploidy in parthenogenetic Our culionidae. Hereditas„ 16 51-64.

SUOLIALAINEN,E. (1947) Parthenogene se and PolIploidie bei Ras selkarf ern (Curculionidae). Hereditas) 23) 425-456. SUOMALAINEN,E. (1953) Die Polyploidie bei den parthenogenetischen Rissellkafer Zool. Anz. Suppl. 17, 280-289. - 24.5-

SUOHALAIIM,E. (1961) On morphological differences and e#olution of different polyploid parthenogenetic weevil populations. Hereditas, 4.7, 309-341.

SU0MALAII3N,E. (1962) Significance of parthenogenesis in the evolution of insects. A. Rev. Ent. 7 34.9-366. SUOLIALXITEIVI. (1955) Die polyploidie bei dean parthenogenetischen Blattkafer Adoxus obscures L. (Col. Chrysomelidae). Zool. Jb.(qyst.), 92, 183-192. & TAKESIII,K. (1966) Biology of some Scolytid ambrosia beetles attacking tea plants. V. Chromosome numbers and sex determination of tea root borer,aleborous germanus Blanford (Coleoptera: Sco3ytidae). Appl. Ent. Zool. 1 29-31. ITDVARDY,M.D.F. (1959) Notes on the ecological concepts of habitat, biotype and niche. Ecology", L0, 725-728. VANDEL,A. (1928) La parthenogenese geographique: contribution a l'etude biologique et cytologique de la parthenogenese naturelle. 1. Bull. biol. Fr. Bel 4. 22, 164-281. VANDEL,A- (1934.) La parthenogenese geographique. II. Les males triploides d'origine parthenogenetique de.Trichoniscussi ae Herold. Bull. biol. Pr. Belat g" 419-463. VANDEL,A- (194.0) La parthenogese geographictue. IV. Polyploidie et distribution geographique. 21211LilLat112:2.21911aLak, 94-100. VARLEY,G.C., GRAMELL,G.R. a HASSELL,M.P. (1973) Insect population ecology aziannaitiroach.. Blackwell Scientific Publications, Oxford, 212 pp VOLTERRA,V. (1928) Variazione e fluttuazioni del numero d'individui in specie animali conviventi. Abridged translation in: Animal ecolor. R.N.Chapman. McGraw-Hill, New York. 1ELLINGTON,W.G. (1957) Individuals differences as a factor in population dynamics; the development of a problem. Can. J. Zool. 51.1 293-323. CHENEY,J. & KSY,K.H.L. (1963) A parthenogenetic species of grasshopper with complex structural heterozygosity (Orthoptera: Aeridoidea). Aust. J. Zool. 21, 1-19. INITE,M.D. (1970) Heterozygosity and genetic polymorphism in partheno- genetic animals. In: Essays in evolution and ispnetics in honor of Theodosius Dobzhansky edit. U.K. Hecht & W.C.Steer 237-262. Appleton-Century-Crofts-Amsterdam.

WHEM,M.J.D. (1973) Animal cytology and evolution. 3rd edition. Cambridge University Press, London, 957 pp. -21.,.6-

laTTAKER,R.H., L3V1N,S.A. & ROOT,R.B. (1973) Niche, habitat and ecotype. Am. Nat. 227 321-338. WILLIAMS,G.C. (1975) Sex and evolution. Princeton University Press, Princeton, New Jersey. 200 pp. 17GLIAMS,W.D. (1962) Notes of the ecological similarities of Ascellus aquaticus (L.) and A.meridianus. Rao. gydrobiologia, 22, 1-30. NTIASON,E.O. (1953) The origin and. evolution of polymorphism in ants. Q. Rev. Biol. 22, 136-156. YOUNG,E.C. (1961) Degeneration of flight-musculature in the Corixidae and Notonectidae. Nature, Lond. 121, 328-329. ZARET,T.M. & RAND,A.S. (1971) Competition in tropical stream fishes: support for the competitive exclusion principle. Ecology, .„52, 336-34.2. -21+7 -

APPENDIX 1.

A PRO]3LEM OF LONG STINDMIG

"3ut the study of these insects, however interesting it may be, is involved in much obscurity, and presents difficulties, which,' comparatively few have ever ventered to encounter. Thus, it has happened, that, while the larger and more conspicuous sections of the same order have engrossed the attention and occupied the time of hosts of scientific naturalists, the

Trichopterygia ( Ptiliidae) alone have been left almost unheeded, or, at best, treated in a manner so imperfect and unsatisfactory, that confusion has been worse confounded, and difficulties multiplied without end".

Taken from Matthew's (1872) monograph on the Ptiliidae which represents the sole attempt published to date aimed at a comprehensive study of the family. — 28 —

AFF31.:DIX 2 S^ _TIBTIcAE FOZ.TULAE USED ET A.7ALYSTS OF DATA. (Dailey, 1959),

Table A2.1. Student's t test for counarison of t::o- wall sauples. (i) variance eruol. t= where s2 = 4(x _5:1)2 _ 772)2 n1 + n2 - 2 1n2 ni + n2 - 2 degrees of freedou.

(ii)variance unequal t' = c. — distributed like t with f degrees of freedom sl- + 22 nl n2

where f = 1 u = s12 / n1 ni - 1 n2 - 1 si2 / ni s22 ri2

Table A2.2. Linear regression analysis. Fitting regression line for the regression of y on x: y = a + bx where a = y- bY:

and b = (x - 7)(Y- = regression coefficient (x Y)2

Test for significance of regression coefficient:

t = b with n -2 degrees of freedou s / I( D where 13 = 0 - 249 -

Table A2.3. X 2 test for general contingency table (r rows and c coluins).

a b . . • A

•

• • • N

for (r - 1)(c - 1) degrees of freedom E where for first entry 0 = a and E = AWN

This method is only7reliable if no exrected value is less than 5.

The formula for the exact test of a 2.x. 2 contingency table is given in the text (Section 5). -2507

L.1-1:373= 3

rtriT • 171-•.(1- • n-ni T • •,"T • T -••1 ri • - ..i.1J• .

11C2 C,- f1M10 7Aat.I.0 of Tnsta.,' lcngth of P.cv Intr . P. lcrvae ih units la2v.ae in unit 7.1 1 413 1 7 (, 1 5, 0 C- Co --; (.5 5 .:, 9.0 3 67 3 2 r;9 2 , C.6 2 66 4. 7.5 1 59 1 02 57 1 7.8 1 61 1 8.5 , 52 2 0 9 2 53 2 67 n_ 7.6 1 72 3 8.0 1 7L. 3 7.9 1 78 3 8.8 2 61 3 9.2 2 41 1 9.6 3 46 2 8.0 1 70 1 7.8 1 63 1 9.6 3 83 3 9.0 2 64 1 0 t 3 76 2 7.6 1 63 3 9.4 3 57 1 9.0 ? 59 2 9.0 3 61 3 t test for cozTarison of licaa cal)sule widths of different instars given in te::t Section 1. t test for courson of body le ti's of aifferent instars in P.antera. Ins gars I II III :ean body in units 56.50 63.50 70.20 Standarrl c=or. 3.04 3.80 2.63 t value for II, III 1.44 1.45 De,:;rees of freedou 18 18 Probability 0.10 0.10 It is -thus concluded thr,t lcrval len.,:th cannot be used to aistinc;uishbetl:eeh insters of i.antera 1Prvae.

LuVA; = 0.02 mm

- 251 -

APFELIDIX RESULTS OF Pr3LD COLLECTIONS OFE4;:alla1

Table Ah..1. Collections of fiela caught P.antera taken between 1572 and 1975.

Date Location Site Nuuber of P.antera alate apterous ala.te apterous

14.7.72 Silwood Park(SU56) Pas 2 Shur loci: Row- (SU87) Ullzus 15.7.72 26.7.72 11 It. • . 11 3 6 3 8 15.7.72 ft 9 Pagus 1 1 31.7.72 Windsor .Great Park 1 33 10 (SU57) Famous_ bark 32 It If ft PZ.',EUS 7 1 16.8.72 3 It ft It It 2 24.10.72 11 R It It It 11 It 16 12 20 14 16.8.72 It 11 11 Ziercus 49 17 56 25.9.72 Silwood Park Pagus 57 69 22.7.74 tt 1 8 7 9 5.4.73 Windsor Forest Fagus 10 12 5.6.73 tI It 7 12 4.73 55 55 10.73 29 294 274 21.4.74 1 9 6 11 u It 3 7 It u 11 1 12 a3 10.74' 2 92 4 87 31.5.74 64 46 18.6.74 6 1 1 ft fl It It 6 4 O 0 It 12 1 5 5.4.73 If 6 7 18.4.73 Windsor Great Park Fagus 1 1 1.6.73 Silwood Eark Fagus 8 1.1 If 8 13 11.7.73 26.7.73 11 It .7 6 15 19 3.6.73 Wargrave Nill (SU77) sawdust 3 11. 30.1.74 GuildfordS.s.(11Q04) Quercus .-3 ".7 14.16.3.74 West Hanger (Noil.) Fays 379 303 26.3.74 Lyndhurst N.F.(SU20) Quercus 1 tt tt Pagus 1 3

tt It It 11 tt 11 3 4 It 11 It It ft 11 5 6 22.4.74 Lyndhurst (SU20) Fagus 6 364 4 328 11 If It 11 2 53 1 65 It 11 11 It 8 417 5 393 9.5.74 Hurtwood (TQ04) Pinus 1 30.3.74 Ranmore (TQ15) Fa7us 3 28 3 15 4.6.74 Hackhurst Downs Fagus 96 79 White Downs (Tc11/1. Fagus 36 2 34- II Fagus 6 14.6.74 II It It 9 11 It 7 It It It It It It 6 6

- 252- Table A4.1 continued.

Date Location Site Number of P.aptera alate apterous alate apterous

14.6.74 Tihite Downs .L.-..w....._.-_ _,us 12 6 19 It It It It It It 1 1 It II II If it 11 3 4. 11 9 II It It it 8 1 8 II II II II 11 11 12 1 13 It It It It 11 It 18 14 It 11 9 If It It 9 8 II II It It II 11 17 23 II It It ' It 11 11 . 14. 19 It II It tt 11 It 17 9 It It 11 It II ft 8 10 It It It It II It 8 6 It It II It II 11 6 ft H It 11 II It 97 89 6.7.74 Windsor Forest Fagus 1 1 14.10.74 Brockenhurst (SU20) Pinus 1 1 It H It Lyndhurst (SU20) -12Ya_.--'ua 2 6 1 3 20.10.74- 0 It 2 2 It It 11 11 11 7 12 It It 11 11 II 1 7 3 6 It II .9 It It 1 5 1 II II II It It lo 5 It It It It It 17 18 9 It II II It 7 12 It II 9 It It 12 1 8 9 9 It 9 It 3 3 It It 1 9 It 9 1 49 1 46•

denote collections from the same site (see text) Quercus = Quercus robur Fagus = Fagus sylvatica Ulmus = Ulmus procera Pinus = Pinus sylvatica

— 253 —

Table A4.2. Collection of field caught P.ertabunda taken between 1972 C 1975.

Date - . Location Site NuLther of P.errabunda

alate apterous

Silrrood Patk.(SU96) ' Quercus 1 9.7.72 — . Sambucus 54 15.7.72 Shurlock Row (SU87) - Ulmus 12* tl It n' 11 tl 2paa 6 31.7.72 Yandsor Great Park(SUn. Fagus bark 1 15* 11 11-.8.72 Pinus 1 27 11 11 tl 16.8.72 Fagus 1 10* It. tt It 0.0 It Quercus 38* 24.0.72 Ruscomb Salix 7 It 28.8.72 KAngley Vale (SU81) 1 25.8.72 Silwood Park Fagus 2 21* n It It 22.7.74 1* It 7 24.10.72 Windsor Great Park ' 11 II It It It II II 30* 37 29.2.73 Oaklea SaMbucus - 1 Windsor Great Park Fagus 12* 4.73 10.73 It 11 II II 3 2* 29.4.74 0 It II It 2* 18.4.73 Windsor Great Fark Fagus 1* 1.6.73 Silwood Park . FaFus 3* 11.7.73 •11 It II 1* 26.7.73 II It tt 2* 3 5.6.73 Windsor Forest Fagus 1 8* 11.6.73 Thetford (TL88) Pinus 9 27 13 11/4. 18 160 40 301 15 15.8.73 Co. Mayo Fir 2 18.10.73 Pontoon Co. Mayo Pinus 3 4.1.74 Badger's Mount (TQ46) Sambucus 36 q. • . 11 It 49 It ft 11 11 Querdus 10 ' It It •.11 1 II H It It It It Guildford S.1'. (TQ04) 30.1.74 - 5 It 11 It 11 11 17

11 II 11 It II II It 22 01..1.74 Guildford N.C. (TQ04) CratatIgus 8 30.1.74 II It II 7 15 1 0 It Quercus 2 30.1.74 H It It 11 11 It It II 6 24. 13.3.74 West Hanger (T(104) Larix fir “ Fagus 152* 14.16.3.74 .1 2 Lyndhurst H.P.. (SU20) Pinus 6.3.74 13 30.3.74 Pinchampstead (SU86) pinus n n It Bramshill Pseudotsuga 7 n It It Pinus 33' 22.4.74 Lyndhurst N.F. (SU20) Fagus 4* 3.5.74 Winterfold (TQ04) Pinus 138

-2514.- Table 4.2 continued.

Date Location Site NurJber of P. errabunda alate apterous 4.5.74 31ackheath (TV4) Pinus 44 it II It II Pinus 104 • 9.5.74 Hurtwood (P404) Pinus 4* 50.5.74 Raniaore (D.415) Fagus 3* 2.:.7.' Oriolton (s-I90) 1 14 II If It II It 1 13 II If It 11 11 0 38 2.6.74. Orielton korcus 7 /:..6.7/!. Oriclton Ziorcus 15 4.6.74 :ILc:diurst Downs F-12- 1 117* White Downs (TQ14) it 1 50* II II It 0 14.6.74 c) 51 3 59 16 110 8 7* 14* 29 28 12 40* 53* 46* 18* 117 34*

38 19.6.74 Silwood Park Castanea 33 6.7.74 Windsor Forest 12.122. 1 23.7.74 Hurtwood Pinus 27 50 1'4-8.74 HoLabury Hill (TQ14) Pseudotssa 9 1 , ft It :r r;11.:.,a....._...1 .,, .. Pinu s 4 6 14..10.74. Drockenhurst N.P.020) Pinus 15* 20.10.74 It It It 11 2 17

14..10.74 Lyndhurst N.F. (31720) ....=.---Fer,us 2 2* 20.10.74 It It It II 1 20.10.74 Brockenhurst NP. Pseudotsuca if (SU20) It ft It II 1111 ft 11 3.74`. Forest of Dean (6050) Quercus p. 3 46 tt 11 9 It ft Quercus p. 7 78 3.75 Abergvrsyn (81185) Quercus p. 14 ft II II Quercus p. 1 31 It it tt Quereusp.. 6 it 11 Lanafan (SN67) Quercus p. if It It It n 1 if tt It It Pinus 2 3 it II 11 Betula 1 11 5.75 listman's wood (SX68) Quercus, p. 2 It It Ponsworthy (SX77) 11 9 - 255 -

'lade continued.

Date Location Site NuLler of P.crabunda .late apterous • I 5.75 PonsT7orthy SX(77) =uercus p. 6 Vxntoc::::3 ft . 11 (L-ether stowey) ST(1:2) ct 22 it rr •2

denotes collections fro:A the same site (see text)

collections also containing P.antera

uercus = .;duercus oetraea

)uercus = (}uercus robur

Faus = Pa;-us sylvatica

Pinus = Pinus sylvectris

Ulmus = Ulmus nrocera Castanea = Castanea sativa

Betula = Betual pendula Cratageus = Cratageus .lonogyna

Larix = Larix decidua

PseudotsuGa = Pseudotsuga

-256-

Table A4.3._ ColleCtions of field caught P.ta7aorae taken between 1972 and 1975.

,Date Location Site Number of P.taylorae alate apterous alate I apterous

17.8.73 Furnace. Quercus p. 8 4 4 Co.Mayo ti It It ft It rt tt 7 4 18.10.73 tl If If 10 6 It R II II IT It It 23 4 9 It II tl tt tt 19 1 8 18.10.73 Pontoon - Fir 18 6 Co.Mayo II II If ft tt If 4 7 3.9.73 Mane (ST 14) Quercus P. 61 5 42 3.3.75 Forest of Dean (S050) Quercus P. 23 4 18 5.75 Quantocks Quercus P. 7 1 4 (Nether Stowey)(ST13) It It. II fl IT II 4 3 ft it 11 11 11 11 13 2 7 -2577

APPE3DEC 5

R3S:L23 OF =ID SA: 2122;(3- OP PTIILILLA3

'7 71.)le A5.1. ITI.Eoers of Ptinella in 109 25 C__12 :!=oleo colleCted frcx.,. a fallen ?.sylvatica at Tligh Stanaing Hill, Anasor in ray 1973.

Sanrole 7o. :TO. ht. circiri. ''',; 11,10 bark crevice tex.ture colour Llissi]to no. P.a. P.e. (:a) (E0 contenti- ,_ tnic,rness, • , Jel)th . bark A (u.:) (cm)

1 1 2.3 3.2 95.0 15 5 11. ;-) • 11.0 2 U720.T.T3D

3 2.6 3.2 104.6 15 5 5 W./B. 5.0 21. 1.5 3.2 68.8 14. 6 1 LB/B 0

5 2.4 3.1 103.4 15 14- 5 L.B. 2.0 6 1.7 3.1 112.5 14 4 4 LB/B. 0 7 2.3 3.0 98.7 16 5 5 W. 9.0 3 U.TaOTTED 9 1 2.1 3.0 110.9 lb. 06 3 D.B. 7.0 10 ULTOTT3D 11 1.3 1.6 116.8 10 6 4 LB/B. 0

1 9 0.9 1.6 49.0 3 2 2 LB/B. 13.0 13 1.2 1.4 124.8 9 3 4 D.B. 6.0 14 0.8 1.4 50.8 7 2 2 DB/LB 23.0 15 1.2 1.2 129.3 6 2 4 D.B. 0 16 UUROTTAD 17 1.2 1.2 114..3 6 1 4 D.B. 2.0 18 UHROTTED 19 1 1.1 1.2 122.5 7 4 3/4 LB/DB 4.0 20 2 1 0.7 1.2 83.9 10 4 4 D.B. 10.0 21 1.1 1.1 101.4 7 2 4 D.B. 0.1 22 1.0 1.1 103.7 7 1 1 L.D. 0.4 23 3 0.8 1.1 126.5 5 4 3 D.B. 0 24. 0.5 1.1 45.2 10 3 1 L.B. 0.4 - 258 - Table A5.1 continued.

Sample Ito. Ito. ht. cil-cu.1;; H.90 bar:: cl.evice texture colour missing :o. 1.a. P.e. (m) (u) content thicLness aryth bark (rm.) (1.4 (cm) 25 0.8 1.1 132.0' 7 3 5,14 LB/D3 0

n t 1 0.5 1.1 97.o 3 5 LB/B 0 27 0.7 1.2 119.6 7 1 4 B. 0.1 23 0.3 1.2 120.1 5 4 3 ',.„. 0.2 29 0.6 1.2 90.3 6 tk 5 J./B. 0.2

30 0.2 1.2 128.7. 7 2 2 B. 0.4. 31 0.4 1.1. 37.6 8 4 5 0.1 32 0.2 1.1 108.3 6 5 5 B. 0.3 33 1.9 1.1 59.6 6o 3 2 3. 0

• • 31; 1.6 1.1 63.6 7 2 5 4. 0.5 35 1.9 1.2 46.8 6 2 3 W./B. 0.1 36 1.6 1.2 54-.5 7 0 5 it•J. 0.5 37 4 1.7 0.9 68.5 5 4. 3 D.B. 0 38 1.5 0.9 49.7 0 5 71. 0.4. 39 1.8 0.6 68.9 3 1 3 D.B. 0 1+0 1.6 0.6 57.3 5 2 5 w./B. 0.3 4.1 2.0 0.5 43.0 3 0 4 D.B. 0 42 1.8 0.5 32.1 3 2 5 ',/. 0.2 4-3 BARK IISSIUG 2.0 0.5 68.0 3 2 3/5 D.B. 0 4.5 BARK IESSETG 46 2.1 0.2. 22.9 2 1 3 B. 0.7

4-7 BARK flISSING 48 2.1 0.4 40.0 3 1 2/4. D.B. 0.6 4.9 BAR:: i a SSITIG 50 1.9 0.4 28.4. 1 1 4 D.B. 0 51 3.0 3.2 103.9 18 0 4 D.B. 5.0

52 UNROTMID 53 2.6 3.2 115.1 15 3 3 L/DB. 14.0 -259- Table A5.1 continued. Sample Uo. ht. circua ;- 1-120 bark crevice texture colour missing . J.' 2 • . bark no. P.e. (11) (12) content S (11V.1) (_:a) 19.0 54 1.6 3.2 39.2 15 0 0 L.D. 4.0 55 2.6 3.1 96.6 14 3 L.B. 56 ROTTED - 11.0 57 2.4 3.o 105.7 13 0 5 J. 58 117:10TT3D - 15.0 59 22.9 3.o 53.,, 15 2 5 r. 60 1.3 3.0 41.7 12 0 0 L.B. 32.0 61 1.4- 2.8 105.9 12 0 4. D.B. 15.0 62 0.9 2.8 26.0 9 0 o B. 12.0 63 1.3 1.5 26.8 8 0 2 B. 2.0 64. UUROTT3D 65 1.2 1.5 103.8 8 0 4 D.B. 5.0 66 0.8 1.5 59.6 10 2 2 B. 43.0 67 1.2 1.2 109.2 8 5 4/3 D.B. 0 68 UNROTTED 69 1.1 1.2 96.9 7 4 4/3 D.B. 2.0 7o UITROT2ED 71 1.1 1.2 69.7 7 0 4. D.B. 0.1 72 UNROTT2D 2.0 73 1.1 1.1 63.4 6 1 2 L/DB. 74 =ROT= 0 75 0.9 1.1 105.7 7 3 3 D.B. 76 0.4 1.1 83.6 1 2 2 L.B. 0.3 0 77 0.7 1.2 84.2 8 •2 5 W. D.B. 0.2 78 0.4 1.2 119.9 6 .0 3 D.B. 0.2 79 0.3 1.2 94.6 8 2 3 80 0.6 1.2 66.5 10 0 0/1 B. 0 81 0.6 1.1 65.7 3 4 5 W. o 82 0.2 1.1 29.5 .7 0 4 D.B. 0.4. -260- Table A5.1 continued. • . 3:7-aple No. No. Ht. circua. c': H 0 bar:: crevice texture colour aissing no. P.a. P.e. (a) (m) conent thic].:ness del)th bark (ma) (ma) (cm) 83 1.9 1.0 58.2 6 2 3 D.B . 0 84 1.6 1.0 69.7 6 5 27.0 85 1.7 0.8 69.5 7 - 1 4 D.B. 5.0 86 1.5 0.8 48.6 0 5 W. 32.0 37 1.8 0.8 61.1 6 5 -J. 4.0 38 1.4 0.8 53.6 4 5 W. 13.0 39 1 1.9 0.5 74.9 3 3 D.B. 0 90 1.6 0.5 44.2 7 0 5 id. 0 91 1 2.0 0.4 67.3 3 1 3 D.B. 0 92 1.9 0.4 46.4 3 1 D.B. 0 93 BARK lESSEIG 0 94 2.1 0.4 23.4 2 1 3 D.B. 95 BARE: =SSD* 96 2.1 0.3 21.8 2 1 4. D.B. 0 97 BARK :as SING 98 2.0 0.3 27.0 1 1 B. 0.1 99 BARK laSSING 100 BARK!'ESSIM 101 UNROTTILD 102 1.5 4.8 59.9 11 1 4 D.B. 103 1.5 4.8 73.7 16 1 3 D.B. 104 1.2 4.8 84.2 19 2 0 L.B. 105 1.2 4.8 89.1 17 0 2 DAB. 106 4.0 4.0 93.5 20 2 5 W. 107 4.0 4.0 93.1 21 4 3 D.B. 108 1.6 4.0 104.7 34 8 3 D.B. 109 1.6 4.0 41.8 19 4 3 L.B. - 261 -

2able .A5.1 continued.

1 - 10 main trunk; 11 -32 rain side brnnch; 33 - 50 side branch;

51 - 60 main trunk; 61 - 72 main branch; 73 - 100 side branch;

'101 - 109 standing bole.

P.a. = P.aptera

P.e. = P.errabunda ht. = height off ground circum. = circunference of trunk , 0 content = water content as >J of dry weight of sample 2 missing bark = distance to the nearest missing bark.

Texture . - 0 smooth unrotting 1 spikey unrotted

2 smooth/spikey rotted

3 spikey rotted

4 smooth rotted

5 flakey

Colour white B. brownish L.B. light brown D.13. dark brown mixtlre

- 262 -

;'able A5.2. 2ruLibers of Ptinella in 70 25 cra2 sa.:Iples collected frou a fallen

2.371vatica in -jinlsor Forest in October 1973.

Sauple :71:=Ibers of E.aiDtera Stfocortical conditions at stations Dpe apterous alate apterous date total colour -texture bark co-ntent cr r.t.1

1 154.3 D.B. 3 19- 1 1

3 3 3

5 5 6 1 2 3

7 2 1 8 137.9 D.B.,(J 4 21

9 5 1 3 1 10

10 11

12 6 1; 3 2 15 13 2 2

14 7 5 12 15 12/!..5 B./W. 4. 18

16 1. 6 1 11 t 17 5 1 o 13 2 6 8

19 1 4 5

20 10 6 1 17

21 6 8 2 16

22 3 3 6 110.0 B. 14- 18

23 7 2 5 1 15 24 1 1

25 2 2 8 26 1 1 2 -• 263- 77:01 c 3a=le ::fors of 1:-.ora Su-boort...cc:1 conaitions at stc..tions no. itoro us al ate apterous alato 3Gojc,:i rf! colour te;:ture 111,.rk content thlcmess cf 9 bar:: in 27 1 1 8

2 1 20 .L. 1

29 2 1 3 129.5 D.B. 3 17

30 9 13 31 1 1

32 11 1 5 1 13

33 2 2 4.

3!..-- 3 3

35 9i 8 17

36 4 6 10 123.4 D.B./W. 4 15

37 7 3 10

38 5 2 1 8

39 9 .1 3 2 15

40 7 11 13

41 1 1 4. 6

)1-2 6 6

43 1:. 7. 1 12 115.9- D.B./17. 4 14.

3 3 0

45 10 l.i 2 16

46 7 1 h.-- 2 il.i

47 12 5 1 18

-48 2 3 2 7

49 5 1 1 .7

50 2 3 5 129.7 D.B. 3 15

51 13 13 26

52 1 3 4.

53 1 2 1 4.

5I. 6 1 6 13

55 1 1 - 264- - ~2.b1c A5.2 continued.

0-.... '3~ ..:: :le :;u.. i0cr~ '.L P. 2.. -\)ter!:~ SilOCol.. tica1 conclitio113 (.,0/- 1.1 3-GC'.tions no. ,,1 ,...~o [·.:;terous c.lc_te nJ?tcrous \-.,_~. Vv totr.l ,.j 1'iC.tO:" colour -cc:{ture b~~"':: co:rte:lt ..'G11ic:·:ne s S d' 0.:-.r~: :L."1. ~].m d' 9 ~ .?v-." 1:_ 7 1 12

1 "7 57 3 2 II- I 10 1]):-.0 D.B. 3 -)

/" 58 3 3 0

('\ 59 11 1 v 20 60 If- 2 6

61 2 I·I'" 1 1 8

D_"') 5 2 3 1 II

,.. -. ..;)) 3 5 2 5 20 128.1:- D.B. J1;- S'·~.- 5 8 13 3

55 1 5 1 7

I' ,.- 00

67 13 8 21

... r, 00 13 -Il' .30 .S9 7 6 13

70 7 1 3 1 17

f~ Hc..tcr content = 'water content as ;~ of d.:i:"'J. Y!eight of s::,.nple

Te:<:ture Colour

0 Sl':1ooth unrotted if. uhite

1 spi~·:ey unrotted B. bro17l1ish

2 sr:1ooth/spikey rotted. L.E. light bronn

3 spikey rotted. D.B. Jarl·: broun 4- srllOoth rotted / ~·.rl...,,-:ture 5 flu}:ey

- - - - 265 -

APPINIDIX 6

REST7LTS ILBORAT:027: VITH PTI:73LIA

Thble A6.1. ::ortnlity of Ptinella at different' relative humidities at 20°C.

Tile in hours

1 2 3 5 6 7 9 10 i 32 TriL.ber of LI:111/.11.0.1131z aeaa

Renlicates: 1 9 1 2 1 2 1 2 1 7 1 2 1. 2 1 2 1 2 1 2 (1) P.attero.

15 4 4 6 6

35 2 2 5h. 66

55 _ _ 5 6 6 6

75 32 64 66

8o 11 ■ 11 56 66 85 _ _ _ _ 31 4 4 66

90 _ _ _ _ 1 2 2 2 5 6 6 6

95 ______1 65 65 66

97 ______- -- -- 6

100 ______1 1 ■ ■ ■ ■ ■ ■

( ii) P. errab unda

R.J.L. 15 5 4 6 6

35 44- 6 6

55 23 66 75 1- 21 65 -6 6-

8o 11. 3 66

85 -- -- 11 65 66

90 -- -- 3 - • 6 2 64. 66

95 1 Mb 1 4 6 56 66

97 ■ ■

100 * * * * * * * * * * * * * * * * * * - 266 -

'able A6.2. Activity Itinella at different tezr:e2:atures over a pc3riod of 48

of ani_:::als observed to be active

Tenperature. °C: 0 5 • 10 20 25 30

Replicates: -1 2 1 9 1 7 1 2 1 2 1 2 1 2

(i) F.a-r;terr,

• hours , 0 - - - - 5 3 o 6 6 6 6 0 6 0'

4••• am 12 - - - - 6 5 6 6 6 6 6 18 - - _. - _. - 6 6 6 6 6 6 6 6

ma ON 24. _ - - - li. . 6 OP 6 6 6 6

40 ------G 5 6 6 6 6 6 6

Total 5 3 23 23 30 30 30 30 30 30

(ii) P.errabunda Time in hour:

6 lw• 5 6 6 6 6 6 6 6 6 6 6 6

12 1 6 o o 6 6 6 6 6 6 5 13 6 5 6 6 6 6 6 6 4. 5 24. 5 5 6 6 6 6 6 6 1 2

40 4 6 6 6 6 6 6 5

Total -5 7 27 28 30 30 30 30 30 29 17 18

-267-

Table A6.3. :brtality of immature stages of Ptinella at different temnerature.

(i) P.t2.2±,pra :.:ean proportion of population dying (with nuSoers of populations in brackets) Temperature in °C 15 20 25 I 30 Stage 1st instar adult 0.58+0.05(5)' 0.48+0.06(5) 0.47+0.06(4)- 0.40+0.06(5)` 2nd instar adult 0.46+0.05(5) ..0.42+0.05(4).0:28+0.04(5). 0.28+0.07(5) 3rd instar adult 0.30+0.03(5) 0.17+0.03(4) 0.14+0.05(5) .0.10+0.04(4)

1st instar 2nd instar 0.16 0.06 0.19 0.12

2nd instar 3rd instar 0.16 0.25 0.14 0.13

3rd. instar adult 0.30 0.17 0.10 0.10

(ii) P.errabunda Man proportion of population dying- (with numbers of populations in brackets

Temperature in 00 10 15 20 .25 Stage 1st instar adult 0.46+0.06(5) 0.22+0.02(5) 0.32+0.04(5) 0.42+0.08(4) 2nd .instar adult 0.34+0.05(5) 0.16+0.07(5) 0.26+0.07(5) 0.40+0.04(0 3rd instar adult 0.24+0.04(5) 0.08+0.04(5) 0.12+0.06(4) 0.26+0.05(5)

1st instar 2nd instar 0.12 0.06 0.06 0.02

2nd instar. 3rd instar 0.10 0.08 0.14 0.14

3rd instar adult 0.24 0,08 0.12 0.26

Values for mortality in each instar derived by subtraction of mean values for cultures from each other. — 268 —

Table .16.4. Anal'rsis of variance of life table:Statistics.of P.aptera and

P.err:abunda at 1500, 2000 and 2500%

(i) Intrinsic rate of natural increase r-1 factor decree of freedo-A. stras of squares scuares Species 1 1 0.00059 0.00059 Te=erature 2 2_ 0.00005 0.00405

Interaction 12 2 0.00957 0.00479 114, 0.00692 0.00006 Total 119 0.02518

(ii) rret reproduction no

factor decrees of freedoLl sims of squares mean squares

Species 1 13.941 15.941 Temperature 2 52.017 16.008 Interaction 12 2 1055.287 527.643 Residual 114 1219.526 10.698 Total 119 2320.771

(iii) Generation time factor decrees of freedom sums of squares mean squares Species 1 633.561 633.561 . Temperature 2 2 126641.762 63320.881 Interaction 12 2 11870.202 5935.101 Residual 1111. 7420.761 65.094 Total 119 146566.286

▪

- 269 -

Figure A6.1 ..Fecundity sched'ale for acIult fe_ale F.aptera at 15"t

a MESA a• a a •aa a 1•11a

la a • • a MMMMM Manila a a'

la a Slant a. as. an

a ma a a. a a •• MIMI a to 1.

▪ MMM Oat. lama

a. • all of Ma al

S OW • MMMMMMMMMMMM a • MMMMMM

Ma lama's.'

• la aiming& war MMMMMMMMMMM masa

2. a iit a a a 111. a •aaa • a imalaalialal ar a MMMMMMM a mesa a Mika

a ft a a •• ma a a ia s• on ma =omit ilia ma i■ gm as a

a a • •

Ma II= ANL lab MI6 r as a

a p • a a- a a • IS =lea& -20 N

C

6„ -1015

z0

5 -0

.1 I

0 10 20 Time in days 401 50 60 70 80 90 100

- 270 -

Figure A6, 2 Fecundity schedule for adult P.aptera at 20°C.

• I a III •

a a • Er s a a a

Ma

-a -smash" BILMAILINAIIL-K.11111LIMUNILAL-a--a-R- 11-11.114-1M-IlLar-11-L. •11■•

:0 ,...,-...... ■■./WM-ILA.MM.1142M.....111.....11.■.JIM.A.MAILMLIILMAI

111•11•0211.••■• a a a a a Mg .0 I M • r • r r

leruaAllt6belhoustaa1111116.16.6.1...

-10 C

O

5. -0

4.

:6 C V

2.

1

20 Time in days 0 10 40 50 60 80 90 100 - 27]. -

Figure A6.3 Fecundity schedule for adult female P.antera at 25°C.

jggeg_g

g r Mk IS

ty di

n MAILIMall3dhaiLAJMALL11.11111111WIMILMIL u fec

l

idua ma...1616.&11.1611111411.11.111.auIaiumm

iv taluraususam_challtRILLallm-. d In cl▪ ahl1111Wahmus_a_ia. .161L11116alluallamslamLua. NumilllnalbaillialsuralawmuLm.

. ■ IM NI Nummula.16111.. 20

rn 6. 10 4.:

4.

1

20Time-in days 40 10 50 6 70 80 90 100

- 272 -

Figure A6.4 Fecundity schedule for female P.aztera at 30°G.

MUM mamma 161611111.

20

rn

1 _10A 0 z

100 _ 0

10 20Time in days 40 40 60 70 80

- 273 -

Figure A.5.5 Fec'mdity schedule for adult female P.errabunda at 10°C.

• SOSO . a •

MO a a

■ ESI•S & ll a • Ala KM Oa. 1 1 ■ al

• as ••■ ■ ■ a ■ a a • a

MISSION IS mmmmmmm a s ASO it d n ■ ■ ■ OOOOO • fecu l a • a I. a alga a n ■ SU a ma

idu • Vann ■ a all OOOOOO a ■ moan a

iv a MMMMMM a a .. a..1.• a a a a a m• MMMMM a pa sLa a 0 d

In • It II ems ita a a Oa • aiaa a &ASO

IS San liaala1• agi aS• SUM a• OOOOO

a ■ a • a Sega a ••• MS

• a a MMMMMM •22M1

■ a a • • a a a MO

IS • • II fa a ■ IN [20

Qf

6 10 0 0

1

O 10 20 Time in days 40 50 60 70 80 90 100

- 2714. -

Figure A6.6 Fecundity schedule for adult .feLlale F.errc..,bund,..:. at 15°C.

a a II a 11ealLAILAUIL11LINLA pa alio a a a a ma. pram. • lb.

la A •• r N11 me Ai •• a a a IM a MI Ma r a a

pap, amnia a a g•I a a fa IN a a a a a a

C I II a a 6 • II • • a MMM a l• 0 0 • a ■ mmmmmmmm . Mm11 . -

MMMMM M_21•1• IIIJEM011 a a am a IN a • ■ 0

a • a • a a •

MIEN Well =Mall Mni“.

r. a • MI qi• • • • VP • • • • ma la ram • MMMMMM [30

6.

5

4

C

2

1

0 10 20 Time in days 40 50 60 70 80 90 100 -z75-

FLTure 11S.7 Fecundiy schedule for aault.feale P.erra-)ullaa at 20CC.

dapolm■aap.••••

•

■ a

ity a ■ • Oa II •I • d ■ sr • a a a ma a • fecun l a du

i .1.10.21610 11 11111111• div In a a, me • . ■ mars • ••••

11111111111AWI111 111M11111116-11"1.

111---11---111 0.1111111111111-1110 —20

C -10:E 60

d .0 50

40

10

10 20 Time i days 40 60 80 90 100 -276-

Fecundity sched-ale for a:_alt P.=:_bunda at 25°C.

6.11.1.111.16.

NM MEL sr se IN 10. • )ft La/LALJLJILI .■

V ■ s dm C 0 k mamma

V

C

111AMUM11201111LAIL

11LCAS11111111111La211WLAL. L1111---1111111111111SAILIUMMI--

20

a) C 6„, 10 •E U)

5„,

0 10 20 Time in days 40 50 60 , 70 80 90 100 - 277 -

Figure A6.9 Fecundity schedule for adult P.tgylorae at 20°C. it d l fecun

dua IN • as SIO i div •■ EN • Mi ■ • In • MI VS In

LALJLILAJEWL-LJW&M IJIMINIL-3-ALJLAUMUILJLIWARANAII--JLJEMANLJI 2-- V NM III

MO 20

C 3 10 'E

O

5

1

0 10 20 Time in days40 50 0 70 80 90 100

• - 278

APPENDIX 7 RESULTS OF COMMON IDCP.I.RILIEnTS WITH PTIHELLA

Table A7.1. Results of competition experiments between P.aptera and P.errabunda over a period of 184 days at 20°C and 15°C biLionthly recordings in brackets. (5 replicates)

(i) Standard 20°C C P. aptera P.errabunda 1 t apterous alate apterous alate total apterous alate total r CP e

A (5,4) (2,-) 3(1,5) (6,2 ) 3(14,11) B 1(11,2) (2,14) 2(5,-) (2,- 3(20,6) (1,-) C 2(4,3) (-,6 1(3,-) :(2,- 3(9;9) (20,-) D 12(3,4.) 3(8,1) 10 • 13(4,1 36(15;0) ..5(425,Y 1(103,-) F 16(4,14) (1,2) 16(5,12) 2(2,1) 51.(12,29) G 5(16,13) 1(5,1) 5(1448) (5,2) 11(40,34) • A 7(4,-) 11(3,6) 4(16,-) 22(29,6) -(7,-) B 11(6,3) 7(4,3) 1(2,1 2(14,6) -(1,-) C 2(7,1) 3(4,4) (4,.. 5(19,5) (4,-)R:=3 (1,-) -(5,-) D lh-(5,9) 19(8,4) 1(44) 34(2704) „(20,-), (1,-) (21,-) 2(57,9) 2(57,9) 3' 3(3,1) - 2,1 1(2,1). (2,-) 4-(9,2) • G 4(12,6) 2,- (17,5) 4(31,11) A (52-) 1(28,-) (4,-) -c4,-) C (13,4) (6,-) 1(73).) 2:-2.) -(22,9) (10,1) (2,-) •1(-,2) 10(-,3) .., 11(,-,5) (4,1) (1,-) -(5,1) 4(115,-) (7,-) 4(121,-) F (3,5) (3,1) 127) (3,-) -(10,11 G 15(21,6) (17,2) 23(10,6) 26,6) 38(74,20 A 24(4,17) (1024) 32(4223) 1(11,2) 57(29,46) B 3(6,7) (42-) 6(428 10,2) 9(24-217) C 24.(2,6) 22(1,3 . -4) 46(3,10) D 5(32-) 5(1,- 1,-) 10(5,-) 2,7 F 20(4,-) 20(31 1,1 G 11(3,-) 17(8,- 4,- 28(16,-) A 23(13,15) 2110,12) 111,1) 5140,28) (1,-) B 10 1,5) 1 -,1 1,10) C 9(10,1) 2 3,1) T,- 12 19,2) D 7(2,5) 11(1,7) 2 3,1 22(7,16) 3(10,6) 10(-,1) F 5(10,5) 9(4,3) (8,3) 34(27,11)

- 279 - Table A7.1 continued.

(ii) Standard 15°C u u P.aptera P.errabunda 1 t apterous alate apterous alate total apterous alate total u r e A 10(4,2) 6(2,3) (1,-) 16(7,5) 128(5,8) 1(1,-) 129(6,8) B 2(4,1) (4,3) 2(8,4.) 53(6,10) 4(2,3) 57(8,13) C (7,2) (11,6) (18,8) 10(15,12) 10(15,12) D 1(7,2) (7,11) 1 2(14,13) 62(26,-) (1,-) 62(27,-) 44(25,-). 44(25,-) F 7(13,7) 2(2,-) 6(12,6) 4(2,1) 19(29,14) G 3 2 5 A (1,-) 3(2,1) 3(3,1) 5(1,-) 5(1,-) B 4(-,1) (1,-) 8(6,4) 1(2,-) 13(9,5) 13(9,29) (3,2) 36(12, 31) C 3(3,2) 3(2,3) 1(1,1) 7(6,6) 107(3,21 5(1,2) 1114,31 D 2(-, 2) 5 7(-,2) 4(9,16 41 9,16 11(50,-) 8 119(50,-) F 1(2,-) 3( 2,-) G 4(1,1) 11(3,2) 1(2,-) 16(6,3) A 13(4,3) (1,-) 11(8,9) (2,1) 24(15,13) 70(5,4) 1(5,-) 71(10,4) B 10(12,5) 12(10,9) (6,1) 2126,15) 61(7,8) 0,-) 61(15,8) C 3(2,3) 5(5,3) 8 7,6) 10(10,9) 10(10,9) D 4(1,-) (1,-) 9(3,4) 3(1,-) 16 6,4) 46(2,6) 46(2,4) E 138(15,27) 139(15,27) 2(2,-) 5(3,4) 7(5,4) (3,2) (-,1) ' (1,-) -(4,3) A 1(6,10) 7,7 (-,1) 114,18) 36(-,13) i(-21) B (-(4 1 -,3) 9(-,10) C 1(-,1 2(-,1 (-,1) D (1,4) 2(2,6 2(3,10) u(-, 37) (-11) F 23(10,9) 26(8,12) 1 50(18,21) G 4(9,6) 1 3(8,4) 1(1,-) 9(13,10) A 7 6,2) (1,-) 83,6) 1(1,-) 16 11,8) 29 1,1) 30 1,1) B 7 4,10) 9 5,13) ( ) 16 10,23) 51 1,28) 52 8,29 2,6) 2 2,4) 2 4,10) 53 2,24) 51F 4,25 D 1 4,h) 14,2) (-,1) 1 8,7) 29 1,-) 29 1,18 23(-,30) 23 -,30

G 12(4,7) 5(3,3) 17(7,10) - 280 -

Table A7.1 continued. (iii) Food liidited 20°C 2 replicates - results after 184 days only.

P.aptera P.errabunda 1 t apterous alate apterous alate total apterous alate total r e A 1 1 B C D 2 6

G 2 3 5 A 1 1 • 2 2 B 1 2 3 c - 2 2 D - - E 12 12 F 1 1 G 1 3 4

(iv) Food limited 15°C 2 replicates.- results after 184 days only. A 2 3 5 10 10 B - 1 1 0 - 6 6 D - 7 7 E 3 3 F 2 2 4 G 1 1

A 12 12 B 3 1 4 13 13 C - 2 2 D 1 2 3 5 5 3 13 13 F 1 1 3 3

-281-

APPMIDDC 8 7L:G. POL'271:011.PittX: Al7D Sa RATIO DATA

Table A8.1. Proportions of winged individuals in collection3 of field caught P.a7)tera

Pro-cortion of win:ea individuals (7?ith 3.123.) "1:onth in 1.2ales in female:; in total population

January 0 0 0

:7arch O 0.010+0.006 0.004+0.003 O 0 0 0 0 0 Total 0 0.010+0.006 0.004+0.003 April 0.00 0 0 O 0 0 0.077+0.074 0 0.039+0.038 O 0 0 O 0. 0 0.019+0.007 0.013+0.006 0.016+0.004

Total 0.018+0.006 0.010+0.005 0.014+0.004 0 0 0 0 0 0. 0.100+0.053 0.167+0.088 0.122+0.047

Total 0.032+0.018 0.046+0.026 0.038+0.015 June 0 0 0 O 0.167+0.152 0.056+0.154 O 0 0 O 0 0 O 0 0 O 0.056+0.033 0.028+0.019 0.250+0.108 0.240+0.085 0.244+0.067 O 0.071+0.069 0.039+0.038 -282--

Table A8.1 continued.

Proportion of 7rined individuals (with s.E.)

17onth in _.ales in feJales in total population

June 0 0 O 0 0 Total 0.014+0.007 0.036+0.011 0.025+0.007 July O 0.333+0.272 0.143+0.132 O 0 0 O 0 0 0.029+0.025 0.236+0.066 0.145+0.040 0.111+0.105 0.438+0.124 0.320+0.093 O 0 0 Total 0.030+0.021 0.202+0.043 0.129+0.027 .August 0 0.250±0.217 0.091+0.0p7 0.076+0.036 0.233+0.050 0.167+0.033 Total 0.067+0.032 • 0.234+0.048 0.161+0.031 Septel-Jber 0 0 0 October 0 0 0 0.090+0.016 0.127+0.019 0.108+0.012 0.021+0.015 0.024+0:022 0.032+0.013 O 0.500+0.354 0.500+0.354 0.250+0.153 0.252+0.217 0.250+0.125 O 0 0 O 0 0 0.125+0.117 0.333+0.157 0.235+0.103 0.500+0.354 0.833+0.152 0.750+0.153 0.020+0.020 0.021+0.021 0.021+0.014

Total 0.070+0.011 0.110+0.014 0.090+0.009 - 283 -

Table A.8.1 continued.

Proportion of winged inaviduals (with S.E.)

:Onth in :.:ales in femnles in total population Spring 0.012+0.004 0.013+0.001; 0.012+0.003 Suimer 0.024+0.008 0.104+0.015 0.065+0.000 Autumn 0.063+0.010 0.100+0.012 0.080+0.008 Total sites 0.029+0.004 o.o6o+o.006 0.0h4+0.003 Table A8.2. Proportions of nolo individuals in collections of field caught P.antera.

ProFortion of ale individuals (with S.E.). :onth in alatae in apterae in total population January o 0.300+0.145 0.300+0.145 71:arch o 0.556+0.019 0.555+0.019 O 1.000 1.000 O 0.455+0.150 0.455+0.150 Total 0 6.555+0.019 0.552+0.019 April 0 0.455+0.106 0.455+0.106 0 0.500+0.248 0.500+0.048 1.000 0.480+0.100 0.500+0.098 0 0.462+0.138 0.462+0.138 O 6.500+0.354 0.500+0.354 0.616+0.135 0.515+0.018 0.516+0.017 Total 0.643+0.128 0.510+0.016 0.512+0.016 hay 0 0.582+0.047 0.582+0.047 O 0 0 0.500+0.204. 0.651+0.073 0.633+0.069 Total 0.500+0.204 0.597+0.040 0.594+0.039 June 0 0.368+0.111 0.368+0.111 O 0.706+0.111 0.667+0.111 0 0.421+0.113 0.421+0.113 O 0.429+0.187 0.429+0.187 O 0.349+0.038 0.349+0.038 O 0.514+0.060 0.500+0.059 0.400+0.155 0.387+0.088 0.390+0.076 O 0.480+0.100 0.462+0.092 O 0.322+0.037 0.522+0.037 0 0.300+0.036 0.500+0.354. Total 0.236+0.121 0.515+0.021 0.510+0.021 -285- Table A8.2 continued.

Proportion of i:ale individuals (with S.2.) 1::onth in alatae in apterae in total population

July 0 0.667+0.193 0.571+0.187 0 0.273+0.134 0.275+0.134 0 0.500+0.354 0.500+0.034 0.051+0.087 0.508+0.062 0.447+0.057 0.125+0.117 0:471+0.121 0.360+0.096 0 0.441+0.085 0.441+0.085 Total 0.100+0.067 0.4.75+0.04,3 0.427+0.040 August 0 0.700+0.14.5 0.636+0.145 0.191+0.086 0.467+0.049 0.421+0.044 Total 0.182+0.082 0.487+0.01;07 0.438+0.042 September 0 0.452+0.044 0.452+0.044 October 0 0.588+0.034 0.583+0.084 0.420+0.060 0.518+0.021 0.507+0.020 0.333+0.193 0.514+0.037 0.508+0.037 0 0 0 0.667+0.272 0.667+0.157 0.667+0.136 0 0.500+0.250 0.500+0.250 0 0.368+0.111 0.368+0.111 0.250+0.217 0.539+0.138 0.471+0.121 0.167+0.152 0.500+0.354 0.250+0.153 0.500+0.354 0.516+0.051 0.516+0.051 Total 0.400+0.051 0.517+0.016 0.506+0.016 Spring 0.522+0.104 0.534+0.012 0.534+0.012 Summer 0.179+0.051 0.504+0.018 0.483+0.017 Autumn 0.400+0.051 0.510+0.015 0.501+0.015 Total sites 0.341+0.036 0.520+0.008 0.511+0.008 -286-

Table A8.3. Proportion of ringed individuals in collections of field caught P.errabunda.

Month Proportion :-singed (with s.71.) Month Proportion rinsed (with S.E.) January 0 Mo,y 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

Total 0 0 February 0 0 March 0 0 0 0 0 Total 0 June 0 0 0.111+0.105 0 0.050+0.035 0 0 0.031+0.031 0 0 0.009+0.008 0 0.127+0.030 0.200+0.179 0 0.400+0.219 0 0.083+0.080 0.049+0.019 Total 0.016+0.007 0 April 0 0 0 0.020+0.019

- 0 0.117+0.017 Total 0 Total 0.069+0.008 - 287 -

Table A8.3 continued..

LI'onth Proportion winged (with S.E.) July 0 0 0 0.063+0.061 0 0.351+0.054 Total 0.175+0.029 August 0.036+0.035 0.091+0.087 0 0 0.118+0.078 0.900+0.095 0.400+0.155 Total 0.148+0.032 September 0.087+0.059 October 0 0.600+0.219 0 0 0.500+0.250 0 0 0.061+0.034 0.080+0.092 Total 0.074+0.018 Grand total all sites 0.060+0.005

- 288 -

Table A8.4. Proportion of winged individuals in laboratory reared P.aptera at different teziperatures.

Temperature Pair Froportion of winged individuals (with S.E.) in.oc no. in males in fe,mles in total population

20 1 0.044+0.043 0.143+0.094 0.081+0.04-5 apterous parents 2 0 0.143+0.066 0.078+0.038 3 0.028+0.027 0.238+0.093 0.105+0.041 4. 0 0.407+0.095 0.193+0.052 5 0.308+0.128 0.111+0.105 0.227+0.089 6 0 0.400+0.098 0.196+0.056 7 0.273+0.134. 0 0.177+0.093 8 0 0 0 9 0 0 0 10 0 0.800+0.179 0.333+0.136 11 0 0.500+0.354 0.167+0.152 12 0 0.750+0.217 0.375+0.171 13 0 0 . o 14 0 0 0 15 0 0.800+0.179 .0.333+0.136 16 0 0 0 17 0 0 0 18 0 0.500+0.354 0.167+0.152 19 0 0 0 20 0 0 0 21 0 0.750+0.217 0.373+0.171

Total 0.045+0.013 0.287+0.033 0.157+0.019 20 22 0 0.571+0.187 0.333+0.136 alate parents 23 0 1.000 0.667+0.272 24. 0 0.222+0.139 0.154+0.100 25 0 0.545+0.150 0.400+0:127 - 289-

Table A8.4 continued.

Temperature Pair Proportion of winged. individuals (with S.E.) in 0C no. in males in females in total population 20 26 0 0.500+0.354 0.333+0.272 slate parents 27 0 0.500+0.177 0.400+0.155 28 0.214+0.110 0.429+0.187 0.286+0.099 Total 0.182+0.082 0.478+0.074 0.382+0.059 15 0 0.111+0.105 0.056+0.054 30 0 O 0 31 0 O 0 32 0 O 0 33 0 0.167+0.152 0.100+0.095 34 0 0 35 0 O 0 36 0.143+0.132 0.250+0.217 0.182+0.116 37 0 O 0 38 0 O 0 39 0 O 0 40 0 0.125+0.117 0.056+0.054 41 0 O 0 42 0 - O 0 /1.3 0 0.3334.272 0.143+0.132 44 0 O 0 45 0 O 0 46 0 0.333+0.272 0.111+0.105 Total 0.010+0.010 .0.062+0.025 0.035+0.013 25 47 0 O 0 48 0.083+0.080 0 0.044+0.043 49 0 0 0 Table A8.4 continued.

Te:aperature Pair Proportion of winged individuals (with S.3.) in oc no. in males in femnles in total popuItaion 50 0 1.000 0.200+0.179 51 0 0 52 0 0 0 53 0 0.250+0.217 0.067+0.064 54- 0 0 0 55 0 0.200+0.179 0.111+0.105 56 0 0 0 57 0 0 0 58 0 0 0

- 291 -

Table A8.5. Proportions of male individuals in laboratory reared F.alltera at different temperatures.

Temperature Pair Froportion of male individuals (with S.E.) in oc no. in alatae in apterae in total population 20 1 0.333+0.272 0.:S47+0.082 0.622+0.0800 apterous parents 7 0 0.490+0.073 0.451+0.070 3 0.1674.152 0.6864.065 .0..632+0.064 4 0 0.6524.070 :0.526+0.066 5 0.800+0.179 0.5294.121 0.591+0.105 60 0 0.634+0.075 0.510+0.070 7 1.000 0.571+0.132 0.647+0.116 8 0 0.250+0.153 0.250+0.153 9 0 0.333+0.193 0.333+0.193 10 0 0.875+0.117 . 0.583+0.142 11 0 0.800+0.179 0.667+0.193 12 0 0.800+0.179 . 0.500+0.177 13 0 0.500+0.354 .0.500+0.354 14. 0 0 0 15 0 0.875+0.117 0.583+0.14.2 16 0 0 • 0 . 17 0 0.500+0.354 0.500+0.354 18 0 0.800+0.179 0.667+0.193 19 0 0.500+0.35+ 0.500+0.354 20 0 0 0 21 0 0.800+0.179 0.500+0.177 Total 1.155+0.048 0.609+0.028 0.538+0.026 20 22 0 0.625+0.171 0.417+0.1.4.2 elate parents 23 0 1.000 0.333+0.272 24. 0 0.364+0.145 0.308+0.128 - 292 -'

Table A8.5 continued..

Temperature Pair Proportion of Llale inaivicluals (with S.L. in 00 no. in alatae In apterae in total population • 20 25 0 0.4/4+0.166 0.267+0.114 alate parents 26 0 0.500+0.354 0.333+0.272 27 0 0.333+0.193 0.200+0.127 28 0.500+0.204 0.733+0.114 0.667+0.103 Total 0.15,+0.071 0.429+0.076 0.324+0.057 Total at 20 0.155+0.040 0.538+0.026 0.505+0.024 15 29 0 0.529+0.121 0.500+0.118 30 0 0.4.62+0.138 0J.:62+0.138 31 0 0.333+0.272 0.333+0.272 32 0 0.556+0.117 0.556+0.117 33 0 0.41:4+0.166 0.400+0.155 34. 0 0.500+0.177 0.500+0.177 35 0 0.500+0.250 0.500+0.250 36 0.500+0.224- 0.667+0.157 0.636+0.145 37 0 0.500+0.354 0.500+0.354 38 0 0.400+0.155 0.400+0.155

39 0 0.667+0.272 0.667+0.272 40 0 0.580+0.119 0.556+0.117 41 0 0.600+0.155 0.600+0.155 42 0 0.429+0.108 0.429+0.108 43 0 0.667+0.193 0.571+0.187 44 0 0.435+0.103 0.435+0.103 45 0 0.600+0.155 0.600+0.155 46 0 0.750+0.153 0.667+0.157

Total 0.143+0.132 0.524+0.036 0.510+0.036 -293-

Table A8.5 continued.

Telx:orf.-..ture Pair Proportion of ,-ale individuals (with S.3.) in oc no. in alatae in apterae in total population 25 L.7 0 0.500+0.158 0.500+0.158 48 1.000 0.500+0.107 0.522+0.104

,-,.1,./ c 0 0.165+0.135 0.615+0.135 50 0 1.000 0.800+0.179 51 0 0.600+0.155 0.600+0.155 52 0 0.400+0.219 0.400+0.219 53 0 0.736+0.110 0.733+0.114 54 0 0.500+0.250 0.500+0.250 55 • 0 0.500+0.177 0.444+0.166 56 0 0.273+0.134 0.273+0.134 57 0 0 0 58 0 0 0 59 0 1.000 1.000 60 1.000 0.400+0.219 0.500+0.204 61 0 0.667+0.193 0.571+0.188 62 0 0.667+0.136 0.533+0.129 63 0 0.333+0.272 0.333+0.272 64. 0 0.500+0.250 0.500+0.250 65 '0 1.000 0.600+0.219 66 . 0 0 0 67 0 0.769+0.117 0.714+0.121 68 0 0.667+0.272 0.667+0.272 69 0 0.333+0:193 0.333+0.193 70 0 0.556+0.166 0.455+0.150

Total 0.143+0.094 0.561+0.038 0.510+0.037 -294-

Table A8.5 continued.

Temperature Fair FroortioA of male individuals (with S.11.) in °C no. in alatae in aptcrae in total po-,:ulation 30 71 0 0.206+0.171 0.286+0.171 72 0 0.500+0.250 0.500+0.250

73 0.667+0.157 0.667+0.157

74 0.563+0.124 0.563+0.124

75 0.600+0.155 0.600+0.155

76 1.000 1.000

77 0.600+0.219 0.600+0.219

78 0.333+0.272 0.333+0.272

79 0.778+0.139 .0.778+0.139 Go 0 81 0 0 0 82 0 0.500+0.354 0.500+0.354 Total 0 0.565+0.060 0.565+0.060 -295—

Figure A8. 1 Fecundity Echedule for adult female P.aptera alate 20°C.

--JaMR4a .

V a 1.1.= &&

iifi•rMa LaMlina • • t

1111KINIMINUNalli AM at Ala 20

0) C 60

8

5

4

C 1

2,,

1

0 10 20 Time in days 40 50 0 80 90 100

-296-

Figure A8.2 Fecundity schedule for adult P.errabunda alate 20°C.

LaSALMILMUILIWLIWI L. ea MKS ■MI MMU ■

101

6 N - O

5 h

3 •

15

2„

1

50 60 70 80 90 100