An Ecological Stud/ of Zeiraphera Diniana Gn

AN ECOLOGICAL STUD/ OF ZEIRAPHERA DINIANA GN. (= GRISEANA HB.) (LEFITOPTERA : TORTRICIDAE) ON CONIFERS IN BRITAIN.

KEITH R. DAY

Submitted for the degree of Ph.D. London University Imperial College, 1977. ABSTRACT Zeiraphera diniana Gn, a pest of conifers in the family Pinceae, undergoes population fluctuations which are characteristic for different parts of its geographic ' , range aTrid_for.the host species on whose needles the larval stages feed. The width of host range, whiCh includes Larches, Sprrces, Pines .and Firs, has induced the evolution of incipient physiological races to cope more readily with the particular developmental and *ecological problems of living on a narrower spectrum of conifer species.- The extent of introgresSion of sympatic strains is apparently a function of thoSe environmental factors which change throughout the geographic range and which may mediate clinal variation in the expression of certain physiological attributes. A number of budmoth pop-6.16tibris in Brig aih were examined in detail for their phenological relationships with certain host plants. The degree of coincidence necessary for the first larval instar and . the resultant mortality due to asynchrony was studied for a population on Pinus contorta Doug. and the joint phenology of Larix - spp. and egg/larval populations from a number of localities are described. The delayed consequences of winter temperature for egg developmental rates and for the subsequent age distribution of larval populations is discussed as a possible factor in the dissolution of barriers to the introgression of sympatric races. Aspects of the nature of polyphagy, the possible race 3

characteristics of female moths during oviposition;______and the survival rates of eggs at high temperatures were investigated experimentally. It is concluded that populations•of Zeiraphera diniana Gn. 'Britain on

.diff-ererLt hos l,s tend to interbreed making . the deline- ation of discrete race units difficult The major determinants of population change are •sought through the compilation of population budgets for separate communities on Japanese'Larch and on Lodgepole Pine. : Sampling procedures. lead to the identificb.tion•of important mortality'processes and their temporal variation during the period of this study.

CONTENTS page ABSTRACT - 2 INTRODUCTION 8 1. . Principle interactions of the budmoth with its various host plants and the definition -of . ecotypes 11 '1.1 The sampling sites and their historical

association with populations :of Z. diniana.. 17 • I 1.2 Conifer phenology and post-diapause egg development : 24 1.2.1. The experiMental determination of survival rates for newly hatched larvae feeding-.upon developing vegetative pine buds 29 1.2.2. The' appraisal of pine bud growth in the field (1971 and 1972) and the estimation of hatching-time in

natural egg populations 42 1.2.3. The extent of insect/plant synchrony and theoretical survival estimates

based on field and laboratory data _ 49 1.2.4. The potential of the male inflorescence of lodgepole Pine as a larval food

source 54 1.2.5. Variation in post-diapause development of eggs from different ecotypes and

locations. 63

1.2.6. The phenology of Larch, its spatial variation in the field and coincidence with larval populations. 75 1.3 Larval population.age structure estimates. 89 1.4 The response of larval populations to three coniferous food .plants. 97 '1.5 The choice of coniferous hosts for oviposition. . 122 1.5.1. The effect of the larval food plant' on the selection of oviposition sites in female Moths. 125 1.5.2. The choice of host plant by ovipositing females of different ecotypes. 128 1.6 Some temperature effects and an historical. appraisal of known population "outbreak" periods. 135 1.6.1. Historical records. 137 1.6.2. Experimentally determined diapause egg mortality. 144 1.7 The relative frequency of morphotypes in field populations and some general inferences 155 2. A quantitative assessment of Zeiraphera diniana populations in the field 169 2.1 The study areas. 2.1.1. Hope Forest, Derbyshire ..171 2.1.2. Langdale Forest, Yorkshire 174

2.2 The sampling programme : methods and

procedure• .- 176 2.2.1. . Direct egg counts. 176 • 2.2.2. Estimates of numbers entering larval stage. • ...., 178 2.2.3. Larval stages sampled on conifer

foliage. 181 • i • t 2.2.4.. : Pupal samples. 185 Adult.saMples: 1:88; 2.2.6,- Estimates" of fertility and fecundity . of female moths in the field. 190 • 2.3 Sampling equivalents. 192. 2.4 The distribution of Z. diniana: in the population samples; 194 2.4.1. Changes the_ .values_ of, .k._.±hroughout__ _ _ the life history. 195 2.4.2. Distribution of eggs. 197 2.4.3. Distribution of larvae. ---204 2.4.4. Distribution of pupae. 207 2.5 The population budgets. 211 2.5.1. Eggs. 211 -.5.2. Loss of larval stages from the population.222 2.5.3. Larval parasitoids . 229 2.5.4. Virus disease. 242 2.5.5. Pupal mortality 244 2.5.6. Variations in natality. 246 CONCLUSIONS 252

ACKNOWLEDGEMENTS 26 1

BIBLIOGRAPHY. 262 APPENDICES 282 PLATES 302

ADDITIONAL PUBLICATION INTRODUCTION For more than a century, populations of Zeiraphera diniana Gn. have been the concern and interest of those who have witnessed. their remarkably regular fluctUations in density. These cyclic populations form a special case in-the field of animal ecology, although by no means a unique one among thoSe phytOphagous insects which are forest defoliators. In many ways ecologists have a particular obligation to study oscillatory phenomena which, because of their recurrence, lend themselves to a repeated and thorough. analysis of the mechanisms which generate change and their relationship to less predictable ecological events. This very predictability of the fluctuations of cyclic populations has leant to' them an air of apparant simplicity; but only relatively recently has headway been made towards an understanding of the crucial processes responsible. Baltensweiler, who has made an outstanding contribution to an evaluation of the population ecology of Zeiraphera in the Alps and other areas of Central Europe, reviews 20 years of research which started as an animal population census in the Upper Engadin valley of Switzerland and has continued as a multi-faceted and interdiciplinary study of the complex interactions of the insect with its environment (Baltensweiler, 1968 and 1976: in preparation). Not least among these interactions are the reciprocal qualitative changes which occur in the insect pest and the larch host (Benz, 1974), and the patterns of 9

population fluctuation which differ among the sampling strata (Auer, 1971b). It is in agreement with Wilson (1968) that many investigators have called for pariallel studies of insect populations in optimal and sub-optimal parts of their range; here might the important relationships of regulatory and disturbing processes be profitably assessed (Richards and Southwood, 1968). In this type of study careful consideration must be given to the diversity in the kinds of fringe area that will be present for a given species.(Wilson, 1968), and the nature of genetic heterogeneity and environmental . variability which will enhance the persistance of such marginal populations (Birch, 1970). It was with this in mind and against a background of fragmentary; but nevertheless tantalising, information about Z. diniana in Britain, that the present studies were initiated. The moth is first recorded in England in 1846 (MacDougall, 1922) and has since been noted from various parts of Northern England and Scotland and quite exceptionally, from Ireland (Barret, 1885). About the population ecology one thing is certain; density fluctuations are not characteristically cyclic. The increasing importance of Z. diniana as a member of the lepidopterous fauna of 'British coniferous forests is partly the result of a rapidly expanding forest area (Crooke, 1958) dominated by young conifers and given to 10

the monoculture of rather few tree species. An increase in the relative abundance and/or distributional area of . -a'tree species will be followed in time by an increasing complement of phytoph-agous insect species (Southwood, .1961; Opler, 1974) of which Z. diniana is surely an example'in the case.of the conifers on which it preferent- ially feeds. The basic biology of Z. diniana.is adequately reviewed .in many recent papers dealing. with this insect' (eg. Bovey, 1966) althoUgh some accounts (Clark, Geier, Hughes and Morris, 1967), while. attempting'a synthesis,' have been misleading in their interpretation of the . "life system". It is an univoltine insect with non- overlapping generations which makes the collection of population data in the field and the subsequent analysis of the results a relatively simple matter. The most meaningful results, however, are only forthcoming from a long term study which capitalizes on these attendant advantages. A strategy of investigation has been employed here which attempts to answer central questions about observed population patterns attributable to genotypic and phenotypic variation within the species. Complementa-y research on the population parameters of non cyclic populations, advocated by Baltensweiler (1968), is also pursued. 11

1 0 - Principle interactions of the budmoth with its various host plants and the'definition of ecotypes.

Principally Z. diniana has been documented as a .pest of 'the European Larch (Larix decidua Miller). On this host plant the.budmoth has been known to undergo its most remarkable population fluctuations (Auer 1961, 1968; Auer, Baltensweiler, and Bovey 1959;. Badoux 1952 Baltensweiler 1962a 1962b 1962c 1_963a 1963b 1965 1967' 1969; Bovey 1958, 1966; 'coaz 1894; Enderlein 1'913; Esche'riOh 1909, 1931; von EtZel'1880; Fuchs 1913; Jahn 1958; Schimitschek and Jahn 1952; Leuzinger 1938; . Maksymov 1959; Maresch 1881; Meyer 1947; Schernthaner 1892; Thomann 1929). Such records are particularly noteworthy in that they describe periodically high population densities of Z. diniana on European Larch almost exclusively from the alpine region of Central Europe. Bovey and Maksymov (1959) review the occurrence of morphologically distinct forms of the budmoth on other conifers in the Alps. These host plants include the cembran pine Pinus cembra L., the soots pine Pinus silvestris L. and the mountain pine Pinus Lugo Turra (= P. montana Miller). A complete list of host species at other locations is given in Table 1. It is immediately evident that a wide range of coniferous hosts in the family Pinaceae are selected by populations outside the Central European alpine regions. This is especially true in view of the fact. 12

that published records invariably refer to economically damaging populations'.

Davall (1857) was, in effect, the first forester to notice that the insect "has .many varieties" and this opinion has since been crystallized by Thomann (1929) who distinguished a "race" which, developing on Iarix decidua, hatched from the egg stage earlier than those which developed on Pinus cembra or Pinus silvestris. Bove' and Maksytov (1959) re—established. this observation by experiment and introduced the terms "IarchfOrm" and "Pineform" for these deVelopMentallyl and as it appeared, morphologically distinct. races. The authors . conclude that "These two colouration types are not dependent upon the food, because the caterpillars of the first instar on Pine and those of the second on 1 Larch conserve their characters" . That the larval colour forms or morphotypes are genetically induced and are subject to quite different mortalities on a number of food types has been further confirmed by Day andi Baltensweiler (1972). It seems likely that, under normal conditions in the Central European Alps, the integrity of sympatric strains of Z. diniana is per- petuated by ecological and temporal isolation. Despite this, Baltensweiler (1970) has recorded regularly

1. Because the colour form of each individual is not definite until the fifth instar it is difficult to see how they might have been known at an earlier stage. 13

changing proportions of certain morphotypes in the larch population during the course of a complete population oscillation and has linked this with possible determinants of population change. No record b of -similar frequency switches in the alpine Pine population are yet available. A knowledge of the occurrence outside the Central EUropean Alps of different forms of Z. diniana has been hampered'by incomplete description and inadequate standardization of the known c6lourtypes„ .A. scheme drawn up by the Swiss ecologiSts and established in.the.literature (Baltensweiler1970, Day and Baltensweil er1972) is now available. The older records must, therefore, be treated with caution. MacDougall (1922) for example describes caterpillars of an intermediate polymorph predominating in large populations on Pine and Spruce. The exact colour types, combination of colour features.. and the proportions of each within the population are. not given. MacBougall's observations are noteworthy for the reason that they are inconsistent with information on the predominance of colour morphs in pine populations from other sources. However, a means of quantifying such observations is invaluable for a further insight into the population processes of the budmoth.

In considering the principle interactions of the budmoth with its various host plants it is necessary to attempt to answer three central questions. • 14

Firstly, how.consistant is the concept of colourtypes. with one of ecotypes — where morphological.or physiological characteristics suit an individual to a particular ecological niche? In turn, what are the. advantages of these physiological characteristics under different conditions, i.e. for populations on..

_ different food plants?. . Finally, how do the:colourtypes in the population under investigation relate'. •to the population regulating processes operating?' •

•• 15

TABLE 1 Host plant Location Author Larix dahurica Siberia Florov:1952 Turcz. decidua Carinthian Alps , Kurir 1947: Miller leptolepis Hope Forest, Kirkland and Siebold England . Paramonov.T957 ..Schonhery 1964 laricina N. America .MUtuura 1966 (Du Roi) K. Koch . .) ,occidentalis N. 'America. Mutl..mr.a .1966 Nutt. . americana N. 'America Geiler and Michx. Theile 1966 sibirica Transbaikalia and Florov 1942 Ledeb. Irkutsk, U.S.S.R. Prozorov 1940 Eastern Siberia Pleshanov et Larix sp. Oxford DistriC., Waters 1929 England Czechoslovakia , Pfeffer 1930 Picea abies L. Czechoslovakia _Pfeffer 1930 Bohemia and Saxony Prell 1930 Komarek 1929 Erzgebirge Sachsse 1933 Theile 1967 Scotland MacDougall 1922 engelmanni N. America Keen 1952. Parry sitchensis Sbotland MacDougall 1922 Carr. Hope Forest, Kirkland and England Paramonov 1957 *Abies concolour N. America Keen 1.952 Gordo and Glend. pectin.ata S. Sweden Lekander 1951 16

Pinus uliginosa Czechoslovakia Pfeffer 1930 Neum. silvestr_i_s• Scotland MacDougall 1922 , L.. Norway Bakke 1969 silvestris Switzerland Bovey and var. Maksymov 1959 engadiniensis mugo Turra. • Denmark Fritz 1903 Jutland Boas 1923 contorta Hope Forest, Brown 1970 Doug. England. (pers. comm.) *Pseudotsuga N..America Keen 1952 taxifolia (Poir) .Britton

* Mutuura and Freeman (1966) use Z. improbana (Walker) for Z. diniana Gn. of American authors. Differences from European conifer feeders include the genitalia and maculation. 17

1.1 The sampling sites and their historical association with populations of Z. diniana

Since Britain is said to. lie on the edge of the geogi.aphical range for this palaearctic species any spatial variation in what Turnock (1572) and' others term "population patterns and life systems" in dif- fere/it part6 of :this country remains a matter of interest, in the present study. Current knowledge of the series of host .'plants available to.certain' "ecotypes" of Zeiraphera'diniana (see Table 1) is reason enough to ensure that some account be taken of populations in different areas. For these reasons a number of forest locations were considered as poten-

tial study areas at the start of these investigations. 11:_list is given below and in Figure 1.

Preliminary samples in 1969 - showed rather low populations at both the Cannock and Hope sites and although Hope was further from base facilities at Imperial College Field Station, Silwood Park, it was chosen for an ongoing study owing to a more promising history oL budmoth outbreaks. A second intensive study area was chosen late in 1970 when it was learned that high populations had been present at Langdale Forest during that year. The Langdale and Hope sampling sites are described in more detail later. Of the remaining locations listed, some•were used for the aquisition of experimental material and others, 18 Figure 1. Population centres and sampling sites for Zeiraphera diniana Gn. in Great Britain (numbering as in text.)

Ake ALTITUDES 91° OVER 800' a.s.l. 19

despite extensive searches, were less rewarding.

Limited records of Z. diniana populations in Britain are available. Those provided by the Pores— try Commission are indicated below and although some

• notes on collected adults are present in the literature (Waters 1929, Barret 1885) they are too scant to'be',.pf much use here.

20.

1. Hope Forest N.W. Conservancy, 0.S. Sheet 102, G.R. 103925, latitude 53°26N, altitude 1500 a.s.l. (Snake Pass) to 600 a.s.l. (Ladybower Reservoir). . tree- spy- Picea sitchensis/Larix leptolepis/ Pinus contorta (P. 61). approx. area 230 acres • *** 1955-57 (Kirkland and Taramonov 1957) ** 1964-65 Damage confined mostly to Picea.'sitchensie.

2.Langdale Forest N.E. Conservancy, 0.S. Sheet 93, (Wykeham High Moor): G.R. 96, latitude 54°.21N, altitude 750 a.s.l. tree spp. Pinus contorta P. 59, 60, 61, 63) / (some) Pinus silvestris / (some) Larix leptolepis (in peripheral belts). approx. area . 300 acres. *** 1970 on 170 acres.

3.Harewood Dale Forest: N.E. Conservancy, 0.S. Sheet 93, . • G.R. 9699, latitude 54°23N, altitude 650 a.s.l. .tree spp. Pinus contorta (P. 60) ** 1970 21

Cannock Chase N.W. Conservancy, 0.S. Sheet_120,_. (Beaudesert): G.R. 0414, latitude 52°43N, altitude 600 a.s.l. tree spp. 1) Pinus 'silvestris (P. 64) •;approx, -area 30 acres * * 1967 tree spp. 2) Larix leptolepis Picea sitchensis (P.28) approx. area 60 acres *** 1965—

5 Burford: Private farm yoodland, 0.S. Sheet 144, G.R. 245160, latitude 51°50N, altitude 650 a.s.l. tree spp, Larix decidua (approx.' P 30) / Pinus silvestris approx. area 2 acres 1969-72 on L. decidua only:

6. Rothbury Forest: N.E. (E) Conservancy, 0.S. Sheet 71, G.R. 0198, latitude 55°18N, altitude 1000 a.s.l. tree spp. Pinus contorta (P58, 59, 62, 63, 64) approx. area 280 acres. *** 1970 (about half the total area affected) (J. Stoakley in litt.) 22

7. *Radnor Forest: Wales S. Conservancy, O.S. Sheet 128, G.R. 2066 latitude 52°16N, altitude 1200 — 1700 a.s.l. tree spp. =Iarix leptolepis (over the greatest area)

8. Mortimer Forest: N.W. Conservancy, 0.S. Sheet 129, G.R. 4065, latitude 52°17N,altitude 700 — 100 a.s.l. •tree'spp. Iarix leptolepis and Pinus silvestris

9. Selm•Muir: . Scotland S. Conservancy,. 0.8. Sheet 61; G.R. 096F.1. latitude 55°52N, altitude 750 a.s.l. tree spp. Picea sitchensis and Pinus contorta ** 1968

10.Keswick: Private woodland, 0.S. Sheet 82; G.R. 2722, latitlide 54°36N, altitude 500 — 700 (approx.) tree sppo larix decidua *** 1925 (probably only a few acres)

11.Gisburn Forest: N.W. Cbnservancy, O.S. Sheet 95, G.R. 7457, latitude 54°1N, altitude 600 — 1000 tree spp. Picea sitchensis / Pinus contorta / Pinus silvestris *** 1964 23

12. Windsor Forest: O.S. Sheet 169, G.R. 940716, latitude 51°26N, altitude 250 a.s.l. tree spp. Larix decidua

Indices of population density.. *** high based upon ' records. of. ** 'medium visible damage . or other notes. . * low—present .

Quite extensive searches revealed no Z. diniana populations'in these areas during the present study. 24

1.2 Conifer phenology and post-diapause egg development

The phenology of the annual vegetative growth of the coniferous host plant appears to' be critical ,- in-detcrmining the survival of freshly hatched budthoth larvae (Bovey and Maksymov, 1959). Eggs of.all forms of Zeiraphera diniana enter an obligatory diapause shortly after the completion of embryonic gastrulation. They remain for several months in their oviposition sites under the: surface'irregularities-of foliage. - producing branches.' During this period.eggs.may be subjected to extreme low temperature and indeed a temperature regime of +2°C for 120 days is most effective in terminating diapause and inducing least egg mortality (Bassand 1965). A gradual increase in spring temperature favours a resumption of embryonic morphogenesio and the newly hatched larvae appear in late spring. The exact time of emergence will depend on the_ambient temperature and humidity during the periods of diapause and postdiapause development (Bassand 1965) when a definite relationship with these environmental conditions and egg mortality rate will also exist. In addition the choice of oviposition site will influence the ratio of post-diapause development through the agency of direct radiation on eggs or exposure only to air temperature (Baltensweiler 1966). The nature and rate of egg development in relation to climatic 25

conditions in the European Alps is, therefore, well _documented for larchform budmoth populations, although less is known of the status of populations.of other ecotypes.

The influence of environmental factors such as temperature and rainfall on the appearance of new. • foliage and inflorescences of potential host plants has not been fully investigated. Thus, it is not yet possible to attribute the rate of growth of new and available plant material and the rate of egg development to. some common sequence of climatic factors. Some attempts have been Made to coMpare the vegetative phenology of certain conifers (Schober and Seibt, 1971) and Baltensweiler (1971) has given an account of comparative phenology of larch over an altitudinal profile in the Swiss Alps. Simak's (1970) work on Larch phenology demonstrates the highly complex relations of bud—break, flushing times and of shoot growth to photoperiod and temperatures-- Since Larch needle growth is dependent upon conditions during the entire course of bud formation, it seems likely that the extent of insect/host asynchrony will show coniderable geographical variation. Working with five Pinus species Lester (1967) investigated the foliar ontogeny of seedlings and noted responses to photoperiod and temperature which are generally reported for dwarf shoots elsewhere. Van den Berg and Lanner (1971), in the course of their studies of 26

bud morphogenesis of Lodgepole Pine describe briefly - the seasonal course of terminal shoot elongation in this species and'Lanner (1971) notes that although pine shoot length is largely predetermined by bud- organogenesis in the previous year, the groWth rate of shoots fluctuates considerably and is susceptible to current environmental conditions including light and temperature.. Further details of the initial vegetative phenology of some conifers are given in later' chapters.

.Alpine populations of the larch budmoth are said to experience optimal climatic conditions at elevations of 1800m (a.s.l.) where egg hatch coincides with the appearance of Larch needles in their most favourable condition (Baltensweiler 1963, 1966, 1968). Some aspects of insect/Larch asynchrony'at other altitudes in the Alps have been studied Baltensweiler. (1963) and further work is in progress on the lower •Swiss plateau (Graf 1974). The problem examined here concerns interactions of host plant and emerging larva under climatic conditions nearer the edge of the geographical range of Z. diniana than the Central European Alps. A parameter of particular significance is the mortality experienced by populations of emerging larvae on different host plants at different stages of their vegetative development. In Part 2 an attempt has been made to assess the possible effects of such mortality on the gross population dynamics of the 27

insect under natural conditions.- Here, laboratory---- experiments on early feeding by larvae and field estimation Of conifer phenology are brought together

in an attempt to quantify their joint effects on the

..,eceIogiral isolation of ecotypes and indicate the ' sanctions imposed, through this type of larval mortality, on the geographical range of this species,

The description and consequences of insect/ plant asynchrony have been important considerations in a number .of insect population investigations. Eidt and Little (1970) review the literature on insect control through induced asynchrony and Eidt and Cameron (1971).demonstrate that the association between Choristoneura fumiferana and its host Abies balsamea is such that anything which affects synchrony between the two will inevitably effect budworm survival.

A similar conclusion was reached by Schutte (1957) . for the oak tortrix; here oak bud break and caterpillar --- hatch were not always synchronous, but because individual trees flush at the same time relative to other, adjacent . trees in subsequent years, at least small pockets of the populatio., are able to survive no matter what environmental conditions induce overall asynchrony.

Sindelar and Hochmut (1972) have pointed out that the coincidence of developmental stages of pest and host plant forms a basic prerequisite for the maintenance of high pest population density and note that 28

late flushing forms of oak, as described by Schutte. (1957), are resistant to the attack of green oak tortrix. The same authors conclude from their:own work on the Larch mining moth, Coleophora r laricella, and larch-gall-midge, Dasyneuralaricis—that- infestation rate in different Larix decidda proven . ances is at least partly dependent on the earliness - and rapidity of Larch flushing. This i6 consistent. . with the observations of Ohnesorge.(1958),. who found.. that late flushing. Norway Spruce was resistant to . . Pristiaora abietina. Also Varley - and Gradwell (1968)..: have suggested that the key factor. for the determination of winter moth population size at Wytham Wood maybe a • product of the newly hatched caterpillars inability to exploit unopened oak buds.

1.2.1. The experimental determination of survival rates for

newl hatched larvae feedina u•on develo in ye etative pine buds

------has7been suggested by Bovey and Maksymov (1959), Itozhkoir (1966) and established in Section 1.4 of this present work that only'the extreme pineform of Z. diniana •will zurviVe. in all its larval stages,on Pinus or Picea spp.. whereas other forms, especially the larchform, will sustain high -mortality.. Two further determinants of larVal survival on pine are the age. of the larva and the developmental stage of the host bud. The following series of experiments demonstrate the influence of a range of bud types on first instar survival immediately after hatching.

Materials

Eggs from an exclusively pineform population were used. Larvae feeding on the foliage of Pinus contorta (Doug) var latifolia (Lodgcpole Pine) in the sampling site at Langdale Forestry .(described in Part 2) were collected during the course of field investigations and reare:: to adulthood according to standard laboratory rearing schemes. In order that a minimal egg and subsequent larval mortality might be attributable to parental influence, conditions for adult-nutrition, mating and oogenesis were kept as close as possible to those advocated by Meyer 1969 and Benz 1969. In turn those eggs laid were incubated under standard conditions 30

of temperature and, as far as possible, humidity, (Bassand 1965)to yield maximal rate of egg eclosion at a time of year when pine buds at suitable stages of development could be obtaihed from the-original forest. sampling site.-

Thus, during May 1972 diapausing eggs were removed from an ambient.+2°C. temperature and:alloWed to complete post—diapause development at 1.5°.C. Suitable. Lodgepole pine buds were selected as widely as possible • from trees in a mixed provenance of coastal and. inland • types.

Methods

Various parameters have been used to indicate growth rates of aerial foliage in the field. BaltensWeiler and collaborators (Jaccard 1965, in Baltensweiler 1971) have used Larch needle growth for whole trees and have also employed a graded series of developmental stages, dependant mainly upon colour, to . indicate gross phenolcgical features-,of whole forests 1 •.at distance. In other instances, aerial surveys have been employed to achieve a comparative measure of foliage development, (Marshall 1968). Some fine measurement of the growth of Lodgepole Pine buds is needed here which will relate as far as possible to the requirements of the individual larva. It was decided that the division of the early stages of bud expansion into 6 categories would offer sufficient 31

gradation from buds where new needles are entirely covered by bud scales and are inaccessible to searching larvae to buds where more advanced needle growth has made them inedible. The 6 categories are shown and described in Figure 2 and Plate 1.

Russ (1971) has shown the effects of territorial ,behaviour in three species of Microiepidoptera; it was felt that larval density may also have.•a certain influ. ence ,on survival and that this is determined by the frequency of IarVal enooUnters rather than' by direct competition for new feeding. sites. Newly emerged larVae were contained with a single Pine bud at 5'densities (1, 2, 4, 8, 16 larvae per bud) with replicates for each bud class in a 5 x 6 block design. The size of the pine buds in replicates was kept 'constant, a maximum being determined by the size of containers used (57 x 37 x 23 mm with-aids). 32 Figure 2. Details of the development of needle shoots within a bud of Pinus contorta (developmental classes 1-6). c.f. Plate 1.

RESI N - AND SCALE STRANDS

BUD SCALES • NEEDLE SHEATH • SCALES PAIRED NEEDLE LEAVES EX POSED BASE OF N EEDLE SHOOT 33

It was found unnecessary to provide the pine buds with nutrient solution during the short period of the experiment. Each Container, having been supplied with its requisite number of-first instar caterpillars, was placed in a 1500 -terdi room with simulated 16 hour daylength. Freshly hatched caterpillars were separated from ineubating'eggs.twice a day so that no experimental caterpillar was starved, for too long. After 3 days the containers at 1.550- were examined-and the mprtality of larvae. noted... In . . a few cases larvae were alive,. but had not fed, and these were also included in the mortality figures. A total of 1560 first instar caterpillars were used in this experiment in a total of 390 containers. The number of replicates in each category are shown in Table 2.

Results

The experimental data are summarised in Figure 3 and in Tables 2 and 3. The analysis of variance (Table 4) of this data shows that highly significant changes in survival rate occur with both changes in density of larvae and on buds at different developmental stages. Adjacent shoot classes were tested as paired values (Wilcoxon signed rank test) for differences in survival and significant survival changes between densities are only emphatic between densities of 2 and 4 (1) = 0.05)0

Numbers of first instar larvae surviving (percentages in brackets) on 6 stages of bud development Table 3 at 5 different densities bud developmental stages

1 2 3 4 5 6 TOTAL

4(20.0) 15(75.0) 16(80.0) 11(55.0) 11(55.0) 5(25.0) • 62(51.7) e

rva 9(22.5) 33(82.5) 29(72.5) 24(60.0) 20(50.0) 11(27.5) 126(52.5) la - :

f 6(15.0) 4 6(15.0) 20(50.0) 20(50.0) 18(45.0) 15(37.5) 85(35.4) o 8(10.0) 161(33.5) oo 19(23.8) 38(47.5) 40(50.0) 27(33.8) 29(36.3) ity

1 20(25.0) 13(16.3). 126(26.3) _. o, 10(12.5) 15(18.8) 42(2.5) 26(32.5) Dens

TOTAL 48(18.5) 121(46.5) 147(56.5) 106(40.8) 95(36.5) 43(16.5) ' 560(35.9)

Table 2

Numbers of experimental replicates

a) density of larvae 1 2 4 8 16 b) no. of containers per category 20 20 10 10 5' c) total larvae per category 20 40 40 . 80 80 (a x b) Figure 3. The percentagesurvivaloffirstinstarlarvaeonshootsatdifferentphenolOgical.stages(developmentalclasses).

0 L A RVA LSU RV IVA L 50 90 - 1 0 1 BUD (SHQOT) DEVELOPMENTAL CLASSES. • 2.

3 4 1,ar■.tal density(perbud) 5 16 •,- 1 4 n 8 2° . • 6 36

Table 4

Analysis of variance for percentage larval survival in Table 3

Source of variation di SS MS Fs Between bud classes 5 7945 1589 20.15*** Between larval . ., 4 3258, 814.5 10.33*** densities . .Ei+or .20 1577 . 78.9 , Total - 29 12780 , . • • .

F 0.001 (5,20) = 6.646

F 0.001(4,20)= 7.10 37

Conclusions

During the winter, Lodgepole pine buds retain an oblong--ovate form and are covered externally with grey- ish red lance shaped and fringed bracts-or-scales which are coated with exuded resin. In this - s't-age" are quite unacceptable. as food for Zeiraphera larvae and the persistant needle leaves from the previous growing season have long passed a :stage of nutritional... Suitability. Late spring growth follows, a pattern' of bud expansion -and elongation where the resinous bracts. part gradually to reveal firstly the light brown, membranous scale leaves and latterly the tips of the green needle leaves which are enclosed by the former. This temporal sequence is indicated in Plate 1. Further bud, or by this time shoot, elongation not • only increases the e::-Tesure of shot shoot bases and the distance between needles but a7.so heralds an increase in the size of needles themselves and a further development of their xerophilous characteristics.

The influence of these changes on larval survival rate has been under investigation in these experiments. In bud group 1 resinous bracts ewer the edible needle leaves and although this class includes some buds where expansion has taken place, larval entry to the bud and subsequent survival is minimized. A considerable increase in survival rate occurs for bud group 2, an increase which is maintained also for group 3. In both 38

groups needles are exposed. There is a significant •decrease in survival rate from group 3 to 4 and again from 4 to 5. These decreases correspond to the changes in the xerophilous nature of the needles and to the increase in distance between short shoots (needle groups) as noted above. The latter may well be closely connected with the amount of protection neces- • ,E sary for feeding larvae. Many authors (e.g. Escherich 1931) have noted that the characteristic silken tubes spun between Larch needles provide a useful Clue.t the recognition of Zeiraphera diniana caterpillars on this host plant. On Larch the first attempts at feeding are usually along the edge and towards the apex of a single needle. Subsequent feeding will include several needles which are drawn and spun together. These not only ensure adequate nutrition for the caterpillar for at least the first 2 or 3 instars, but provide valuable protection in an otherwise exposed situation. On pine the earliest feeding sites are again toward the needle apices which, as they are appressed to the main stem in groups 2 and 3, provide a good site for the primary silken galleries. It is as needle and shoot extension proceed that the potential feeding site becomes spatially divorced from the "shelter" site. The idea that a protected feeding site is essential to young larvae is reinforced when it is seen that practically all third instar larvae feed between two or three adjacent shoots (like those 39

shown in 2 of Plate 2) which are pulled and grow .together bound by silk. Very few third instars are Sound outside such a protected site.

There are also highlysignificant changes in larval survival related to density on a single bud. Mortality increases dramatically at larval densities greater than 2 per bud when relativa availability of food or suitable feeding sites do not appear to be limiting. Mortalities recalculated as k-values (Varley.and Gradwell 1968) are plotted against log10 larval'density in Figure 4for each bud class. In this way mortality resulting from crowding is shown to be weakly density dependent (undercompensating) for most bud developmental stages (1-5) and strongly denbity dependent on well developed bud stages (6). Competition for a limited food resource is well known in insect larvae where "scramble" competition may operate (Nicholson 1954); in some cases mortality results, not from absolute food shortage but from forms of conflict, mutual interference or territoriality (Munro 1967). Some form of intra-specific disturbance-may thus be expected to occur in Zeiraphera diniana although this phenomenon has not been investigated further. Evidence exists for the occurenee of territorial behaviour in three species of Tortricidae investigated by Russ (1971); the larvae exhibit a vibrational communication which deters competition from neighbouring individuals and regulates population density. In this case the feeding 40

Figure 4. The relationship of log first instar mortality (k) to log density of larvae on pine shoots of 6 developmental classes.

• 1

Cw 0 ■4

03 1013A34 3INc S3SVJ.S 1VIN

•6

1.0 1.5 2.0 2.5 LOG LARVAL DENSITY/10 BUDS X 41

. strategy employed differs radically from:those Diprionid sawfly larvae which feed gregariously on the needles of Pinaceae (Knerer and Atwood 1973) .j_n order to benefit from the establishment of mutual — ' feeding.sites; the oviposition patterns of female -sawflies are appropriate to the degr3e of gregariousness found in the larvae. 42

1.2.2. The appraisal of pine bud in the field 51971 and 1972) and the estimation of hatching time inaILLLLLEa=112-11LLIrla The relationship of bud .development to larval survival in the laboratory is directly relevant to the interpretation of insect/plant phenological information from the field. A composite picture of the comparative effects of asynchrony from year to year may be developed by combining these sets of data.

Methods a) Pine bud growth

The rate of elongation of individual pine buds was measured throughout the initial growing season. Seven Lodgepole pine trees were selected within the 156 hectare sampling site and a bud chosen from each of 3 branches. The buds were then measured from a marked base to tip at 5-7 day intervals (1972) and 3 day intervals (1971) for a total period of 55 days (both years). Marked trees within the forest (where trees were on average 3-4 m high) were located by white plastic labels.

Because final bud (shoot) length is variable, individual measurements were difficult to relate unless recalculated as a percentage of terminal length. Since the rate cf bud elongation levels off in mid-June the length at this time was chosen as a standard and individual lengths changed accordingly. Van den Berg.. 43

and banner (1971) confirm the seasonal course of shoot elongation for Lodgepole Pine found here. Under normal conditions potential shoot length is governed:by the number of anatomical "stem units" (Doak 1935 in Van den Berg—and-Lahner, 1971) present -ill—the—bud-; whlah-- in Lodgepole Pine has a particularly early developmental . ' schedule. Thus, final shoot length is largely predetermined in the preVious 'growing .season and may reasonably • . form a basis for recalculating elongation rate. It is • f difficult to.equate rate of'shoet elongation wih,other measures of larval survival and it is therefore U_Sed. • here only to reinforce further phenological estimates.

The method of bud categorization used in 1-.2.2 above and similar to a system employed by Schober and Seibt (1971) for Spruce buds, was again applied to a •selection of buds f2om the Langdale sampling' site. Buds to be examined tiere chosen singly from every third or fourth tree on a diagonal Walk across the plot. 'In this way about 30 :buds were collected once a week froM the end of April until early June. Whereas bud elongation measurements were made in 1971 and 1972, the method of bud categorization was used onl: in 1972; incomplete records are available for 1971.

b) Train,ha- hedfi./s-tins-Lar larvae

Upon emergence from the egg, young caterpillars are positively phototactic acid can be trapped during their search for food at the periphery of the pine tree. 44

On Lodgepole pine the eggs seem to be aggregated at particular centres on a branch (see Section 2) and at fairly high levels of infestation (as in 1971 .and 1972) it is quite possible to locate eggs in their natural situation-foi'e)E-periment-ai use.

Baltensweiler (1972) has used a series of sticky . . ,bands at the ends of experimental branches in order. to,

trap emerging first instar"larVae. *A similar device was used here;. eggs were located at oviposition.sites in the field and. without'disturbing their.. immediate • surroundings, bands of white, Waterproof Sellotape were attached on either side of the trimmed branch (Plate 3 ). Just before hatching was due-to commence the bands were coated with a sticky glue (0.-sticko), •which for complete and continued effectiveness needs renewal at 3 or 4 weekly intervals; Caterpillars trapped on the sticky..bands were counted and removed at approximately weekly intervals and hatching rate depicted as a 'cumulative frequency curve. Difficulty. . , in counting the tiny Li (1st instar) caterpillars was overcome by recognition of the black head capsule .and . use of a hand lens.

Rates of post-diapause development are apparently different for egg .batches located on the south. side tree or exposed directly to solar radiation in the sub-alpine regions (Baltensweiler. 1966). This is not so for similar egg batches at lower altitudes, but as 45 a precaution experimental branches were chosen at 3 compass directions from each of 7 trees and finally the results combined to avoid any possible directional bias. Twenty—one branches were used, each was close to a tree chosen for bud measurements. Some buds, damaged during measurement were not included in, the final data.

Results a) ,Complete phenological measurements'for pine bud elo'ngation in 1971 and 1972 are_given. in Appendix 10' The increase of. mean length 'of pine-buds with time is shoWn for these two years in Yigure 5. As the rate of elongation appears not to differ for the two years it is assumed that the frequency of bud developmental stages (bud classes) shows approximately the same distribution in the- 1971 field conditions as they did in 1972 for the corresponding phenological interval. That - is to say that "coincidence" in 1972 differs from that in 1971 only by the (approx.) 41 days .which separate 50% larval hatching date (Figure 7). It is thoughtthatthis assumption is.valid in view of the' .fact that the two bud samples recorded fol. 1971 show . similar bud frequency distribution to the corresponding bud samples for 1972 (Figure 6). This assumption is implicit in the calculation of the theoretical survival rates in Section 1.2.3.

b) The rates of larval hatch in the field are represent,A as cumulative frequency curves for 1971 and 1972 in Figure 7. Figure 5. The elongation of Pinus contorta shoots calculated from field measurements at Langdale (1971 and 1972)

I 0 MEAN AND 95°/0 CON. LIMITS z LIJ • 1971 Tlil h ( 19 BUDS ) LIJ z • 1972 ( 20 BUDS) 1 00 0 2 Li 0 0 0

— 50 I 0 z w 0 CO

22 26 30 4 8 12 16 20 24 28 1 5 9 APRIL MAY JUNE

Figure 6. Frequency distributions and their means for Pinus contorta shoota,in 6 develoumental.classes. (Langdale 1971 and 1972) MEAN BUD CLASS FOR EACH SAMPLE

1971

•

A A , 50 50

'10 BUDS IN EACH CLASS 50 50 5 50 50 50 . . t , . . „ P „ „

1972

(NJ-

, t , 5 14 17 20 23' 26 29 1 4 7 10 13 MAY JUNE Figure 7. The timing of. egg hatch in field pcipulations at Langdale (1971 and 1972).The percentage cumulative frequencies'of trapped first instar larvae are given for May and June. 100 Y C EN QU ) FRE

°/0 50 ( H C ATIVE L GG HAT E CUMU

14 18 22 26 30 . 15 MAY 49

1.2.3. The extent of insect/plant synchrony and theoretical Survival estimates based on-field and laboratory data

•Method

By suparimposing_the rate of egg hatch on data for the rate of bud development it is.possible to estimate that on any particular day a definite number of first instar larvae will hatch and that these larvae will have at their disposal pine buds of certain develop- -Tiental classes definite proportions. In'the following Calculations it is at first assumed that local variations in egg density will play no part in the determination of population survival. So, although increase in density of larvae per bud depresses survival rate (Figure 4). it has been taken that larval density is not greater than 2 per bud (from 1971 and 19722-Tre1d results y.

The sum of survival rates for each day should be an estimate of total survival in any particular population, but to-simplify the description of population survival in the following model, appropriate estimates have been made on only threa occasions during the period of egg hatch. Any theoretical population, characterised by the'temporal difference between egg hatch and bud break, can then be assigned a survival rate by these simple calculations. The following formula calculates S, the proportion of the hatched population which survives:- CUMULATIVE FREQUENCY EGG HATCH o Figure SURVIVAL ESTIMATES( S )* 8. 100 class, isalsoindicated. 50 0 10 respective larvalsurvivalestimatesonPinuscontortabuds.Budgrowth,interms ofthemeanbud.. Percentage cumulativefrequenciesofhatchedeggsfor 13 MAY 21 5 theoretical pbpulations(4 29 JUNE . - E)andtheir 14 >6 1 o 2 40 3 5 6> 0

co r) w m 51

3 7 E z bit . rit . nt t=1 i=1.

where. b = the proportion of larvae feeding it on bud class i at time t.

= the survival. rate of larvae feeding on bud class i at time t

=the number of larvae hatched between time t and t 1

, ValueS for b' assume that hatching larvae.are assigned 'to'buds in the class —.proportions which occur in the

• • field.. Values for r ate derived from survival rates of larirde at densities 1 .and (Figure .3). Values for n are derived from cumulative frequency hatching curves (Figure 7) and if 3 nt = 100, S will be a percentage value. t.1 Values of S, together with the respective. population cumulative frequency hatching curves are plotted in Figure 8. Three theoretical and two real populations are used here as exponents of the relative asynchrony described above,

.Conclusions

'The results from theoretical survival estimates show surprisingly little variation over a credible range of asynchronous situations. Hatching situations A and E (Figure 8) are almost certainly extraordinary for natural populations although, firm evidence for this can only come from several years observations. If 52

asynchronous situations outside the bounds of A and E. .are unlikely; a variable mortality due to a "coincidence"

. .problem. would also seem unlikely from year to year, if only those factors used in the above model for S.are considered. Very few additional factors are likely to increase survival in the field from the levels which were experimentally demonstrated (Figures 3 and 4)

although many may..decrease survival rates. Assuming ' 1 .experimental conditions (in 1.2.1) did not favour any , . , one replicate group More than another it seems that the.

highest survival rate (83%):could not be:bettered by • r more than 10% in the field. This implies that the i .1 theoretical survival rates (S) calculated here are also theoretical maxima for the same material in the field. If this is so, a large (30%) and constant Li mortality which is more or less independent of population density should be discernable in Zeiraphera-diniana populations at Langdale from year to year.

The theoretical estimates are not intended to simulate the exact mortality effects on counterpart. natural populations, but rather to.-demonstrate the possible magnitude of variation in survival rates. of • populations in different synchrony situations. The strictest comparisons between these estimates and corresponding estimates of larval survival in the field (Section 2) would therefore be misleading. Some general conclusions may be drawn, however. The field estimates for early larval mortality (which would include 53 a component for the inability to establish on pine buds) are in noticeable disagreement with the figures derived above (i.e. 1971 observed:83%, calculated 39%11972 observed 0f, calculated 46%). It has already been stated that- -many- .other factors.could:_furthf:.r reduce ahe___ survival rates of newly hatched larvae (e.g. adverse weather conditions). It has been difficult to Tcstu:Late on additional factor having the potential to increase survival rate in the field. The following • inve'stiatiOns'reVeal the gignificande."Oianother food . . . supply; hitherto exclUded from the experimental studies,. 54

102.4 The potential of the male inflorescence of Lodgepole pine as a larval food source

No mention is made in the literature. of the availability of male inflorescences of.pine - to hatching budmoth larvae although some authors have described them as feeding on the flowers of Larch (Florov 1942) and of Spruce (Escherich 1931). Slizynski (1971) 'reports the. interesting case of the black arches moth Ocneria (= Lymantria) monarcha L. which feeds sliccessively on the male inflorescence, the May needles and.eVentuaIlY the perennial needles of Pinus silvestris. This moth has a similar life cycle to the bud moth.and it would seem that the use of the male flowers as a food source immediately after hatching is of significant importance to the survival rate of the caterpUlars. Again, Graham (1963) notes that mature Abies balsamea trees are more susceptible than immature trees to heavy attack from Spruce budworm because the male strobili provide' food early in the year when opening of vegetative buds lags behind production of larvae. Heron (1964) showed experimentally that staminate flowers of Pinus glauca - (Moench) exerted a greater -phago,_Aimulant effect on Spruce budworm larvae, than did either new vegetative shoots or mature needles owing to the greater .concen- tration of total sugars in the former.

Like most other coniferdles, Pinus contorta is monoecious, the female cones being borne subterminally 55

and occasionally on the young shoots and persisting ' for several years. The male inflorescences are detected firstly as a distinct swelling at the. base of the winter bud and they become evident an yellow to reddish groups of oval cones at the base.of- the young shoot during late spring (see Plate 1). Most important is the fact that they develop in advance Of:the terminal vegetative shoot.. While the terminal shoot remains.in. a rudimentary stage of development the sporophyllS borne upon the cone-axis stay:tightly Packed at,tleir outer- most edges (as in Plate 1).. Further changes involve :a • rapid lengthening of the cone axis which separates the sporophylls allowing them to dry and freely shed the mature pollen. Because of the rapidity of.the cone axis elongation it May be surmised that, although cones .are available as focal before the vegetative shoots, they are available forra. s-hort time onl-r.

Distribution of male flowers

Lodgepole pine begins coning about 6. - 8 years (Dallimore and Jackson, 1961). The trees under consideration at Langdale were 10 years old ir. the first year of sampling (planted 1961) and only one quarter, approximately, were not producing male flowers in 1972 (Table 5). One feature of their distribution within trees was very roughly assessed; 15 trees were selected randomly from within the sample plot and two branches sampled from each tree. One branch was chosen from each of two Table...2 The distribution of male flowers between top and bottom sections of the crown (Lodgepole Pine)1972

Tree no. Top Bottom Terminal number %' terminal number % shoots with fls. with fls. shoots with fls. with fls.

1 10 3 30 , 39 35 , go

2 20 9 45 2:"! 9 41

3 18 10 56 31 ' .' 23 ' 74 4 . 6 2 ' 33 18 . - 14 78

5 16 , 0 . .., . ' 0 107 2 39

6 17 0 • 0 1+7 • 17' . 36

7 9 '6 67 . 33 • 26 79 8 12 2 17 • 56 • . 29 . 52 . 9 5 o . . -0 . - ' 9 . . • - 0: o- . 10 7 0 . 0 .17 o. , 0. 1 ! . 9 . . 11 23 2 . 4o.. 33 ,,83 .

12 8 • 0 • 0 ii.:. 0' 21 0 0 .- ' 13 . 8 0 0 ...... 14 14 2 14 29 . . : . 13 45 . . . . . • 15 12 . 0 • 0 43.. 1 . 2 + me,.n 2.- s.e. 12.33 — 1.41 2.40 +— 0.86 18.07 -+ 5:90 37-00. I .41 . . •16..13 -1. 3.75 41.271-8.86. 5?

levels within the crown — the top- half and the bottom half. The total number of terminal shoots for each branch was noted and also the number of those shoots bearing male flowers. The results are given in Table 5. • . _ '" ----• 'The.results show that there are significantly greater proportions of male flowers on branChes from the lower half of the crown than from the top half (P <0.005) Overall about 40% of the shoots on these

• trees possessed male flowers (this utilizes the correct assumption' that there are- equal number Of branches in each half of the crown);

Distribution of budmoth larvae in relation to male flowers

During the course of experiments in 1.2.1 above, • _ the male inflorescence was not tested as a food Source and the collection of field data did not include the classification of male flowers into developmental stages. Routine rearing of first instar (Langdale) caterpillars on male inflorescences before cone axis' elongaticn had taken place showed quite high larval survival rates. Inflorescences can therefore be regarded as a suitable food source during at least part of their development.

In view of the high proportion (40% above) of shoots bearing male flowers and their nutritional suitability it was thought likely that they would also provide a "desirable" pabulum under field conditions. 58

The distribution of budmoth larvae on new shoots was investigated for the 1972 Langdale population 2-3 days after hatching had commenced (Figure 7). A single ',shoot was randomly selected from each of 150 sample

• trees and soon as possible afterwards the number and position of first instar caterpillars were noted (see sampling methods in Section 2). Each "shoot" sample* constituted the total current spring bud growth issuing from'a single Shoot of the previous year (leaders were, avoided to preserve,. the correct growth habit). The resultS are given in Appendix 2 and summarised iii Tables, 6, 7, and 8. Greater numbers of larvae were feeding on male inflorescences than on the vegetative parts of the buds (P <0.001 ). Even on buds at developmental stages 2 or 3 (optimal for survival in 1.2.1 above) there were more larvae on flowers. It is therefore concluded that where both male flowers and vegetative shoOt-s are present, more larvae were feeding on the former. This holds at least for the first 30% of larvae hatched at Langdale in 1972. The contingency Table 7 however, illustrates the fact that perceptibly similar numbers of larvae occurred_ on shoots with and without male flowers. Conclusions In 1.2.3 above theoretical larval survival estimates, based partly on laboratory data for survival on vegetatiVe pine shoots, were not in accord with field observations.

* a 6— branch sample unit = 141.9 shoot samples. 59 Table 6 The number and position of larvae in shoot samples • (Langdale 24.5.72)

position of larvae

bud class inforescence . vegetative' shoots____L

1 2 1 -

1 ' . . 0' - 1 0 . . 0. 2 1 .

. • • 2 . • . . 0 '. . ...' . . 1:1.• ' •0 : . 1 0

1 .1 3 0

1 ' '0 .

1 f. o .

2 . 0 • •:. 1. . 0

. . 1 . .0 • n t,. 0 '4'

1 5. 0

3 .1 % 0

1 0

• 1 0

2 0 Wilcoxon signed— 28 2 ranks test ***sig. (p = 0.001)

shoots with no larvae : 46 60

Table 7

Contingency-table for association between larvae and

. shoots with male'flowers number oflarvae per shoot sample 0 1 2 3 total sample shoots 50 14 5 .3 70 with flowers

without flowers 69 11 5 85

total 119' 25 10 1 155

2 = 7.815 talc, = 3.338 n.s. 0.05 [3]

Table 8

Contingency table for association- between flowering • and bud development number of samples in each bud class

1 2- 3 4 -5 •6- . total sample shoots 10 45 12 3 • 0 0 70 with f:Jwers

wfthoUt flowers 9 30 25 10 2 9 85

total - 19 75 37- 13 2 9 155

2 2 = 16.750 talc. )1/41= 25.50 0.005 [5] 61

Part of the discrepancy lies in an apparent increase in •field larval-sUrvival.(in at least one year) above that calculated. The significance of the male inflorescence for larval survival is thought to be high although of Short duratiCn, but no quantitative information on this is available. It is, however, of :considerable '-interest that newly hatched larvae are found in greater numbers on male inflorescences. This does not necessarily indicate any preferential dispersal by the larvae. since the flowers are always encountered first . by 'peripherally dispersing,. newly hatched caterpillars,' (Figure 9 ).

Table 7 gives evidence that numbers of larvae on reproductive and flowerless shoots do not differ significantly and so at least in the earlier stages of larval dispersal there seems not to be ady particuldr selection of reproductive shoots.

Estimations in 1972 have shown that a sizeable and variable proportion of shoots bore male flowers

(top 18.07-4.90%; bottom 41.17±8.86%, Table 5).. There was a tendency for flowers to accompany- shoots in the. _ lower bud developmental classes (contingency Table 8). The presence of the male flowers, although accessible for a short time only, could and probably does contribute to significant increases in larval population survival and "damps down" variations in mortality that could normally be expected as a result of imperfectly synchronous insect/plant phenologies. 62

Figure 9. Scheraatized branch of Pinus contorta indicating initial dispersal of hatched larvae and the percentage distribution of eggs among the most important oviposition sites (1971 Langdale)

LIGHT

10/0• CURRENT BUD BUD MINES SCALES • 3%

POSITION OF NEW MALE ST ROBI LI

.1 0/0 NEEDLE BASES AND SHEATH SCALES

"FRASS" AND OLD 4, 25 °/0 MALE STROBILI

411) 70 °/0 OLD BUD SCALES 63

1.2.5 Variation in post-diapause development of eggs from •,. different ecotypes and locations

The preceeding discussion has dealt with the developmental synchrony of budmoth larvae:and pine. A fundamental determinant of this relationship is of course the length Cf the diapause period in the egg stage. Bassand (1965) has clarified the embryological details of-egg development and gives further information . on the nature of variations in duration' of the various stages of diapause and the mortality within them which is attributable to sub-Optimal temperature and humidity regimes. Bassand chose to work with material selected from natural populations on alpine larch stands (Haut-Valais and Brianconnais).

His results are comparable with those of Bovey and Maksymov (1959) and Day and Baltensweiler (1969, unpublished). These authors show that eggs with the shortest duration post-diapause development (p-d dev) are always the issue of predominantly dark polymorph. populations (LARCHFORM). .Furthermore, these are separable from eggs of light-polymorph populations (PINEFORM) by a noticably longer p-d dev in the latter. At the extremes of "ecotype" and for alpine populations hatching at quite different times on the relevant host - plants. Interbreeding of polymerphs at opposite colour extremes and of intermediate colour types produces unpredictable lengths of p-d dev in the resulting eggs. 64

The aforementioned investigations have involved the use of insects collected in the Swiss Alps. The present work is concerned with verifying similar relationships in English Topulations which are widely - dispersed--and -often occur-in_mixed_Sp.ecies:standsof_L host trees. A relatively easily measured physielegical parameter, p-d dev. duration may also reveal the. similarity of otherwise of English and:Swiss ecotypes-;

• Pre-treatment of experimental eggs

To eliMinate al.1.0ther likely bourcesof. influenee. on the rate'of.post-diapause develOpment; the larvae:i pupae and adults of the parental generation and the eggs themselves were exposed to similar.and controlled microclimatic conditions, particularly with respect to temperature. In all cases budmoth larvae of the 4th or 5th instar were collected in the rield and laboratory reared to the pupal --otage on the ;vegetative Shoots of their natural host plants (see methods, section 1.4). Larvae in the 5th.instar were examined and standardized. for colourtype (1111 to 7445). Although many adults were reared and made available for mating, poor mating' success and a desire to use spc.ific colourtype crossings limited the total number used in these expprimehts to 28. Females were mated and allowed to lay eggs in experimental cages (see methods, section1521located in a constant environment room (temperature 20°C; relative humidity approx. 65%; overhead illumination 16 hours per day). Frequently large egg batches were laid and

65 t'

these were used whole rather than risk undue disturbance during the separation of adjacent eggs. Selected experimental egg groups were removed periodically and placed in 30 x 6 mm glass tubes .with plastic stoppers where they- remained until---the larvad--hatched_._ ___Over__1000 _ laboratory reared eggs were used in,all.'

Experimental methods

A variety of temperature regimes will, successfully eliminate the.obiigatory diapause with minimal'egg mortality (13ssand 1965). For practical..bonvenience and • for purposes of comparison; the eXperimental eggs were held at the temperatures described below prior to hatching.

Groups 1 — 8 Pre—diapause - diapause post—diapause

duration/days 10 10 180 measured _ temperature °C +5 +2 +15

During the nost—diapause developmental_ period the tubes. were examined on Wooden racks at 1—day intervals and any hatched first instar larvae removed with a camel—hair brush. The length of post—diapayse development was said to be that time in whole days from the start of exposure to a temperature of 15°C (i.e. dater 180 days at 2°C) to the time of hatching. Groups 9 and 10 . The estimation of egg population size in the field (Section 2) provided materia from'two forestry sites (Langdale and Hope Forest), which here given an 66

additional but less exact compariaon_cf the_rates of egg development of both populations which are included as specific groups in 1-8. Since these eggs were collected dUring February 1972 and held at the same_temperatures subsequently, any differences in hatching time are likely to be the result of developmental differences and not of: climatic discrepencies prior to 'February. .Hatched caterpillars were removed from collecting tubes at daily intervals.

Groups 11 and 12

Two egg groups were held at &nista/it tetperatures corresponding approximately to long term monthly mean •temperatures at the northern forestry sites. Hatching was recorded as before.

Month Au S 0 N - - - A-p--- — - - monthly mean 14 12 9 5 4 3 3 4 6 tem.p °C (Buxton) experimental 15 15 10 10 5 2 5 5 10 constant temperature

Group 13

By way of comparison, data is .alSo included here of budmoth eggs from Switzerland (LenZburg and U. Engadin) which were incubated at +2°C for 193 days. It was not possible to simulate successive constant temperatures approximating the long-term monthly means for the Upper Engalin and thus the comparison (Figure 10) may be considered a rough guide only to the differences in rate 67

Table 9

. . Mean duration of post-diapause development for egg groups 1 - 8

egg morphotype location number mead s.e. group of parents of eggs duration no. 0'1 . y • , n p-d dev. 1- 1131 , 1121. Hope 66 - 4.409 0.124 . 2. 1111 1,131 Burford 29 5.035 0.1,36. .3 ' ..6645 6645 Hdpe 136 6.882 0.123 4 . 3331' 3333 Langdale. . 63 7.540 0.150 5 2111 1111 Hope 71 8.958 0.310 6 7442 Hope 220 9.177 0.109 7445 Langdale 7 7445 7445 Langdale 226 11.443 0.202 8 . 7445 Langdale 25 . 7332 Hope 15.920 0.428

Non-significant differences between means tested with the Student-Newman-Keuls test are underlined below (P =-'0.05) •GrOup 1 2 3 4 5 6 7 8 68

Figure 10. Frequency distributions for the hatching egg populations (11),.(12) and (13).

O o cv)

Oti CV SE PAU DIA F RT O TA R S TE F A

- O S cv Y A D

O 0

0 0 CV ON11-01VH ADNI31-1038d 0/0 . a FREQUENCY 25 10 Figure 11.Frequencydistributionsforthehatchingeggpopulations (3) and(5). 5

DURATION OF P.-DDEV. 69 10

ov ,

20 DAYS

70 Figure 12. Frequency distributions for the hatching egg populations (2), (6) and (8).

50 2 T

)— U Z Li I 25 D • 0 w CC Li_

5 101 '5 20 DAYS DURATION OF POST-DIAPAUSE DEVELOPMENT

Figure 13. Frequency distributions for the hatching egg populations (1), (4) and (7).

I I 5 10 15 20 25 DAYS DURATION OF P -D DEV 72

of egg hatch produced by temperature regimes in Switzerland and Northern England. A further account of monthly mean temperature differences'for certain • locations is given in Figure 14. • Afte-r-indubation at +2°C, --the--Swissseggs were. placed at 10°C. It is at this temperature that egg groups 11-13 commenced hatching.'

Results

The measured duration of.post-dfapause.deVelop- ment for groups 1-8 is summarised. in Table ;9 and.presented as a series of frequency distributions. in Figures 11, 12 & 13 Numbers of larvae hatching per day are shown in Figure 17 for groups 9 and 10 and. similarly in Figure 10 for groups 11-13.

Discussion

Considerble variation is 2-pparent in the rate of egg development from different parents. Groups 1 and 8 are separated.by a difference between their means amounting to 11 days (at 15°C). 'Tal'ents of similar colourtype often produce eggs which quite clearly have • dissimilar developmental rates. Groups 1, 2 and 5 for example are derived from almost completely black colourtypes and yet 5 has an unexpectedly long egg development. In the same way the eggs from light colourtypes (3, 6, 7 and 8) are at variance. 73

Representative field egg populations for 1972 (Groups 9 and 10) demonstrate one overall trend implicit in Table 9. This ins that the Hope population, with a wide range of larval colourtypes,'hatahes appreciably earlier than the Jiangdale' population with a 'range of colourforms limited to the light end Of the series:., At best, then, it is possible .only to_relate.diffe ences in egg developmental rate to location and :submit that a number of exceptions to the findings. of.Bovey • and MakbymoV (1959) do occur, • . Figure 10, illustrates the effect of. previous' temperature experience on eggs during' diapause. Groups 11, 12 and 13 all hatched at +10°C, but almost 200 days at +2°C, causes the Swiss population (13) to hatch over a' very much shorter period, Low temperatures during diapause periods of 2C0 days are characteristic of the Alps (Figure 14), whereas higher winter temperatures are characteristic of the' Northern England forestry sites. It may be expected, then, that populations from these . latter sites would ,hatch over a longer period if hatching - took place at the same temperatures as alpine populations.

General inferences are that British populations hatch late and over a prolonged period due to the existance of winter temperature conditions sub—optimal for the elimination of diapause and re—activation of egg .development.

Figure 14. A comparison of monthly mean air temperatures (40 years Meteorological Office records) at three recording sites nearest to important population centres for Z. diniana. The approximate periods in which eggs are diapausing are also indicated.

EGG DIAPAUSE PERIODS ... HOPE

111111111111111•1111111111111111111■11 ENGADINE

•15 -

•10 -

u o w a .5 .

w a 2 w

- 5 -

-10 J F M A M J J A S 0 N

• MIDDLETON ST.GEORGE (LANGDALE)

• BUXTON (HOPE)

• SWISS ALPS ( ENGADINE) 75

1.2.6 The phenology of larch, its spatial variation in the field and coincidence with larval populations

In preceeding sections the relations'between first . . instar budmoth larvae and' pine development-have been . studied in some detail. An inquiry into the comparative phonology of Larch over an altitudinal and latitudinal 'profile acts as a. final adjunct to this.theme. :Surveys of Larch growth were necessarily, limited to such areas and times that•would'indicatel. in a broad.way,. 'the- , • . favourability of otherwise Of the host:Vegetat'ive. Phen- ology to 1)rospeetive budthoth populations,

The position of European Larch (Larix decidua Miller) as the major host of Z. diniana in the Central - European- Alps is well recorded in the literature. Baltensweiler (1971) I- asbeen making very thorough records of Larch needle phenology throughout this region since 1961, and has linked these data with similar records for the date of egg hatch. It seems that insect/ host synchrony is equally good overthe altitudinal pro- - file studied (550 — 2120 m.a.s.1.). but that other biotic or climatic processes (Baltensweiler, Giese' and Auer 1969) may be responsible for less acceptable population growth conditions on Larch at lower altitudes. In Britain not only lower altitudes, but also higher latitudes are experienced, a combination producing a quite different climatic regime which could :reasonably be expected to have repercussions on the insect population at any 76

number of occasions throughout _a generation. Despite_ the_

relative abundance of European and Japanese Larch in Britain (11,2mmel, Irvine and Jeffers 1950, 1951) the largest and most numerous budmoth outbreaks recorded. are those on Pine and Spruce (MacDougaI11922). Where mixed-stands of Larch and Spruce occur it is often Spruce which has the higher liopulations in outbreak `periods (Kirkland and Paramonov 1957). Pine and especially Spruce have been the subjects'for more widespread and more frequent attacks in. the Carinthian' Alps of Czechoslovakia and East Germany (Drell 1930, Theile 1967); This apparent switching of important host plants away from the indigenous Larch stands of the Central European Alps is a problem of prime importance in Britain. A partial solution may be sought in these comparative studies.

Methods

Measurements of Larch needle growth. and budmoth egg hatch were made—dUring the Spring and early Summer of 1971 and 1972. Three locations were chosen and are listed over the page:— 717

• Loc'ation Eggs Larch Needles Silwood From early Spring Larix decidua adjacent Park, egg samples at Hope to the field station Sunninghil.l. and Langdale, and and in Windsor Great from field collect— Park. ed material' (1970, 71) naturalised at Silwood.

Hope Forest Low populations Larix leptolepis on at Hope made few the Snake Pass records possible. (GR 103925) and adjacent.to the road as far as the reservoir.

Langdale ' Natural egg Larix leptolepis along :Forest populations on the intercompartmental :Pinus contorta belts adjacent to the sampling area.

In addition, occasional "spot" sampleS from other locations were taken to verify the phenological relationships„

Needle measurement

Larch needles are born _in_faaci_caes_on_511Dr.t_ahoat2___ which may persist for many years on the older branches. Older shoots such as these are probably very important since it is these which are nearest to the ovipositiOn ---- sites of female moths and thus the likeliest to be encountered by newly enclosed and . wandering first instar larvae. Extensive oviposition on the newer shoots at the apex of - branch can only be expected where epiphytes such as the lichen Parmelia aspidota (Bovey and Maksymov 1959) are growing (see also Section 1.5). The location of the eggs on a tree, therefore, makes the choice of needles for measurement a biologically important one. Baltensweiler (1971) chose 10 tres at• each site and 78 froth each selected a branch 1.5 — 3.0 metres above ground and marked 6 'short shoots on each. The mean length of needles 0/':these, measured at weekly intervals, was taken as representative of larch growth at that site if 3 were proximal and 3 distal to the second or third years . terminal bud scar (Jaccard 1965). A similar procedure was followed here except that fewer assumptions could be made about potential oviposition sites and, *so that all extremes of needle length could be accounted for, all lieedleS'were measured on' some whole'branches. The actual measurement taken was one fi.om the'tip of the longest needle in each fascicle to the visible base of the needle at 'the point of contact with the old bud scales. Shoots under long term surveillance were. distributed as follows at the two main sites. --- Site Trees Branches/ Short shoots Total tree branch

Langdale 3 3 6 54 Silwood 3 2 6 . 36

As stated above periodic samples were taken within whole branches including up to 1000 shoots.per sampling occasion.'

Larval emergence

This was monitored in the field by regular observations of "sticky traps" as described in Section 1.2.2. Information (reproduced in 1.2.5) on the emergence time of egg populations completing their diapause development under field conditions at Silwood'Park is also used here. Figure 15. Egg hatching (percentage .cumulative frequency) and Larch needle, growth (mean shoot needle length) at Silwood Park, 1971.

1971. SILWOOD PARK EGG SAMFLES E . HOPE ; •

TCH LANGDALE 0 co HA 100 9. GG

z E LU LU 3m CY 3 EN

LU U • 0 I. 0 I- 0 FREQ 25 , 2 0 Ui • z m - tf) LU 15 , rjj -1 o m w 2 D 5 m Z 0 Y, 0 —.o ' 0 15 25 1 10 20 30 APRIL MAY (J) z co • w U 0 w M 0 Z 0U E < 3 0 - Figure 16.Egghatching(percentagecumulativefrequency)andLarchneedlegrowth (mean'shootneedlelength) -

A-1-1 > "O" 0 100 50 at Langdale,.1971. APRIL 20 I

MAY 10 I • 20 1971 LANGDALE EGG SAMPLES HOPE ----(seetable10) LANGDALE 30 1 JUNE 15 25 5

a u-lt-uH ION313 -1.033N !OOHSNVIA1 Figure 17. Egg hatching (percentage cumulative frequency) and Larcli needle growth (mean shoot needle length) at Silwood, 1972.

1972 SI LWOOD PARK EGG SAMPLES HOPE • LANGDALE •

K m > z w 8 z 25 mM 0 r m 15 r m 6 5 = 3 -

Tigure.18. Egg hatdhing.(percentage -cumulatiye frequency) and Larch needle growth (mean shoot needle length) att Langdale, 1972. 1972 LANGDALE • 'EGG SAMPLES HOPE ----- LANGDALE o E I E ' co • 100

z Z w >- I Uz 0 w 0 CO co 0 (r) w 50 25 m 0 0 w I 6M 115 = L11 5 3 Z OoO 3 o 0 • .10 • 20 . 1 10 20 APRIL MAY JUNE Figure 19. Egg:hatching (percentage cumulative frequeny) and Larch needle growth (mean shoot needle length) at three Swiss locations, 1971. Re-drawn frOM Baltensweiler (1972).

• SWITZERLAND 1971 EGG SAMPLES 0 ' NEEDLE MEASUREMENTS 0 o

LENZBURG( 550m) BRIENZ (1300m) ZUOZ(1800m) 100 U IN

OF NV3 O IS r. 001- 1 3N 50 25 3 14 - 3 E 15 Nal IO H MULATIV

5 W CU W

/0 0 10 20. 30 APRIL MAY

Table 10 The coincidence of egg hatch with Larch needle length

Location of year origin of egg a b difference Larch population date of 50% date of 10mm a - b egg hatch needle- length days

Silwood 1971) Hope (LARCH) 25.4 20.4 . 5 1972) 24.4 6.4 . ;18

1971) . Langdale (PINE) 19.5 '20.4 ,29 1972) 13.5 6.4 . :37 •

Langdale 1971) Hope (LARCH) 8.5 1.5 7 • 1972) , 7.5 . - 29.4 , • 8 1971) Langdale(PINE) 22.5 1.5 ;21 . 1972) 16.5 19.4 27 . +Lenzburg 1971 indigenous 14.4 14.4 0 (550 m.a.s.l.) , . . • +Brienz 1971.. indigenous: •25.4 27.4 ...... -2 (1300 m.a.s.l.) . - i- • , 1 . +Zuoz 1971 indigenous . .. 16,5 1 0 16.5 . . 1 (1850 m.a.s01.) . . . . • I'. the result here is derived from a hypothetical LARCHFORM population at Langdale which uses Silwood data and assumes the difference between, the dates of 50% hatch of the population in Figure 15 will remain the same at the more northerly latitude. .This was necessary aS no natural Larchform population was avilable at Langdale.

from Baltensweiler 19.72 Figure 20. Frequency distribution for needle length samples from a branch of Larix decidua (Sunninghill, April 1971)

TOTAL SHOOTS = 1040

t.r) H 0 0 I (1/ 10 Li_ 0 >- U Z LU D 0 LU 5 x LL

r . .. i . .. i 5 10 15 20 SHORT SHOOT NEEDLE LENGTH mm • 86 Figure 21. Needle length frequency histograms for Larch short shoots from trees at five locations (April 3rd 1972) . The upper four are along an altitudinal profile at Forest._

100 • . SNAKE PASS 366m

- . •50 . . . . .

, ., . • . . 50- . . . . SNAK E INN 320m

HAGG FARM 50 241m ENCY

EQU 20 FR

/ . . 0 .

• 50- RESERVOI R 183m

50 SUNNI NGHILL 61m

20- t.-1 I

C 1 2 3 4 5 6 7 8 9 10 11 12 13 t 14 '15 LARCH SHOOT NEEDLE LENGTH mm 87

Results

The results are displayed in graphical form (Figures 15 - 18) needle growth being more or less linear in the early stages and the cumulative percentage frequency agg hatch producing a sigmoid curve against time. Mean needle length between 6 and 18 mm has been marked on the graphs because this is the optimal needle length for larval development (Baltensweiler, 1969). To account for a wide distribution of needle lengths on a.tree the proportion of shoots with needles between 6 - 18 mth has also been .plotted. This, then, is an index of "fitness" of Larch for larval establishment at any time during the period of measurement.

The date at which 50% of the egg population has hatched is tabulated and the difference_ (in days) bet- _ ween this and the date at which mean Larch needle length is 10 mm is also given for comparison. The greater the disparity between these dates the worse insect/plant . synchrony will be (10- mM n.l. is taken as a convenient norm for synchrony from the data obtained at Zuoz by Baltensweiler, 1971).

Conclusi:.ns

1) Pineform (Langdale Forest) larvae, because they hatch from eggs with a long post-diapause development, are hopelessly out of phase with the corresponding Larch needle growth. They are considerably more out of phase than Larchform (Hope Forest) larvae whose eggs invariably 88

hatch earlier (Table 9). Difference in lengths of_post7_ diapause development suit individuals to particular host plants but_in doing so make other host plants unavailable.

.2) Some minor coincidenCe differences may exist between years .and.between locations although these differences are not testable; theoretical data has been used in part (see footnote to Table 10). The. differences in any case are not striking but suggest that in some climatically abberrant years coincidence relatidnships could be more favourable..

3) • All British populations here hatch much later in relation to Larch needle growth than do any of the Swiss populations despite the fact that in terms of egg hatch the Larchform populations lie somewhere "between " the Lenzburg and Zuoz sites of the altitudinal profile (Figure 19). Thus, the chances of L1 larvae establishing themselves successfully on Larch in Britain are considerably less favourable than in the sub—alpine areas__ of Switzerland, but-may be better in some years (eg. 1971).

4) The curves describing Proportions of optimally sized nelles present (6 — 18 mm) serve to reinforce the above points. Because thicker branches have fewer short shoots than does thinner and newer growth, and these shoots tend to flush earliest, the frequency curves for needle length tend to be skewed (Figure 20). If anything this would favour very early hatching larvae-, uncharacteristic of the populations studied here. 89

1.3 Larval population age structure estimates

- Introduction

In many forest insect populations it is known that climatic effects can lead to direct or indirect mortality - in a susceptible proportion of individuals in that ..„population (Shepherd 1959 ; Witter; Kulman and Hodson '1972). The persistance, of populations of insects in any area depends primarily on their ability to survive ex- , :tremes of weather• or indeed any physical component of their environment which potentially unfavourable to. the majority Of individUals. Avoidance of such unfavour-- able conditions is the prerogative of mobile populations (Southwood 1962) and those with behavioural patterns.. which enable them to escape temporarily from an adverse environment (Green 1962). Tolerance of severe conditions, for example the lethal influence of low temperature, has evolved in many insects (Salt 1950 ; Andrewartha 1952) and in some is enhanced by an ability to acclimatize to severe environmental conditions (Colhoun 1960) and thus in time to tolerate even greater'severity. This is the case with the overwintering eggs of Z. diniana (Bakke 1969).

Where severe climatic conditions are unprolonged, but also unpredictable in the life history of the insect, avoidance may also be achieved by a widely distributed age structure so that individuals from any single and susceptible age group appear in the fieLd over a relatively long period. Baltensweiler (1966) promotes this argument 90

for populations of Z. diniana which seem, in the Alps at •least, to have. a heterogenous larval age structure in ' most years at high altitudes but homogenous larval age 'structure in some years at lower altitudes. He terms heterogenous-".. a population' which may comprise 'simultaneously proportions of three or more instars ...". It is suggested that at lower altitudes larval age structure is such that all.adults appear'in the field more or less simultaneously. Since unfavourable - weather conditions for :oviposition are more frequent at these altitudes, catastrophic mortality may be the result. . However, if eggs appear in the population over. a long period due to - a heterogenous age structure, there is less risk of all eggs falling foul of an apparent high summer temperature • mortality suggested in the regressiOn analyses of Baltensweiler, Giese and Auer (1971).

Heterogenous populations (for age structure) are produced at alpine altitudes by direct solar radiation impinging on exposed and "shaded" egg microhabitats (Baltensweiler 1966). Those eggs on the upper surface of Larch branches- hatch significantly earlier than those 'which are located on the lower surface and therefore exposed only to ambient air temperature. No such solar radiation effects are experienced at lower altitudes where eggs hatch more or less simultaneously and a hothogenous age structured larval population is the result. The nature of age structure at British altitudes and latitudes is the subject of this study. 91

The causes of age distribution, other than those out lined above, must also be considered.

Methods

Larval samples were.taken from conifers during May and June. Four variables influence the data:- '

Source of samples (location) •Langdale Forest Hope,Forest. Rothbury ForOst*

Host plant species (ecotypes) Larix leptolepis Pinus contorta

Sample, date (approximately End of May . 3 occasions - exact dates are Beginnin•cfJune. given in Table.11). End of. June

Annual variation 1970 1971 1972

Samples do not cover all combinations, of these variables but standardized comDa2isons are available for most. • A further comparison:.is,possible witlOialtensweiler's (1966) figures where a broad criterion for age structure . was established.

As far as possible samples of budmoth larvae were selected at random from groups of trees at each site. In most cases population density -as low and all larvae encountered in a branch to branch search over several trees were collected. Individuals were examined soon after collection and, before instar determination by eye was assured, maximum head capsule width was noted

* Rothbury samples were kindly collected by R. Brown & J. Stoakley, Forestry Commission. 92

• and instar assigned later. Thus age structure by instar class rather than absOlute. _ age distribution is under examination here. 'As a check for parasitism, all larvae (on samples) were individually reared to maturity.

Results

The number of larvae in each instar as a proportion of the total in that sample form tha essential data in Figure 22 and Table. 11. An adjustment ha's been made to this data with'respect to instar length. The probability that a larva will be fOUnd in a particular instar is proportional to the lengthOf time spent between ecdyses at constant temperature (and apprOximate constant R.H.W Some instars are much longer than others in these circumstances so more realistic representation of the field data is sought by dividing the actual number found in each instar by ci (a correction factor for instar the percentage of the total larval life spent in instar under constant environmental conditions). Final numbers for each instar are calculated as a percentage. Thus, in Figure 22 results for each column are described.by the expression

100 Where n; is the number of larvae in in.starxcolleOted in the field sample.' Cx ni = 1 C. and C. is the constant for instarx (see Table 11)

Table 11 Age structure of larval populations as percentage values

Nos. larvae in each instar ci (see text)

instar Lccation Year Date 1 2 3 - 4 5 Total Larvae 1 Hope 1970 20.5 - 5.7 42.3 43.0 • 9.1. 24 , Forest 2 1971 23.5 .2.2 19.2 58.6 • 18.8 . 1.2 6o

3 1972 31.5 5.2 49.7 . 41.7 3.4 24

4 1971 6.6 23.7 11.0 :57.9 ' 7.5 23

5 Langdale 1971 24.6 •2.0 20.2 .67.7 10.1 220. Forest 6 1972. 22.6 0.5 116.1 52.8 30.2 0.5 144

7 Rothbury 1971 14.2 3.5 40.2 . 2.3 69 9.6 11 4 Forest (pine) 8 1971 24.6 1 2.1 21.4 66.6 10.0 37 (pine) 1 . i 1 8.8 . 70.4 19.8 • . 0.9 . 9 1971 24.5 I 39 (pine) i +Trimmis 1964 60.2 37.4 2.3 • . +Zuoz 1964 1.2 4.4 59.5 4.8 c c c C 2. 3 4 5 constants 12.09 12.73 16.29 37.55 from Baltensweiler 1966 a based on estimates of mean instar length for larvae developing on Larix decidua at 15°C constant temperature (see Section 1.4) 95

. Conclusions

Most of the British samples (1 — 9)- illustrated in Figure 22 show heterogenous larval age structure; :three instar classes are each-represented by 10% or more .of the total population. The only notable exc3ption to this is the late hatching 1972 population at Hope (3). It is interesting to see that most of these. samples Indicate greater age spread than d4 the Swiss populations referred to by Baltensweiler'(1966) as heterogenous, e.g. Zuoz 1964 (11). None are as homogenous as Trimmis 1964 (10) although (10) and (11) are themselVes not dissimilar.

For the same year populations at Hope (3) and . Langdale (6) are phenologically separated by about three weeks. This confirms the role ---trfat-ebbt-Srid-d—vari-atibri- (in duration of post—diapause development) plays in their temporal separation. This observation is repeated for 1971 in (2), (4) and (5).

The effect of delayed egg hatching due to annual climatic variation is generally recognisable in the larval populations of different years (5 and 6 reflect the cumulative frequency hatching curves of Figures 15 and 17 above), although such annual differences carried through to later stages in the life history, are unlikely to have any marked consequences for the population. 96

The dissimilarity of egg microhabitats which produces population age distribution heterogeneity in the Swiss Alps (at altitudes 1500 m.a.s.l.) is not a cause of the same phenomenon-at lower altitudes (Baltensweiler . 1966). If. an explanation is sought in a prolonged hat- ' ching period it may be seen in Figures 15 and.19 that 'the cumulative frequency hatching curves have differing slopes. Table 12 clarifys this, giving the duration

• of egg hatch for the median 95% of the population.

Table 12

Time (days taken for 95% of the larval population to• hatch. Population centres are arranged- in order of increasing larval age distribution heterogeneity.

Ienzburg Zuoz " Hope Langdale

1971 6 9 17 19

1972 15 21 97

1.4 The response of larval populations to three coniferous food plants

First indications that populations of z: diniana might show variable responses to an ,array of trophic

conditions were given by Bovey and Maksymov (1959)• , who investigated quite clear cut:distinctions between =two sympatric-races on Pine (Pinus mugo, Pinus. bilvestris. var. engadinenSiS and Pinus cembra) and Larch (1.1ari • • decdua). Such ideas on sympatric rades'haVe needed •. serious revision in the light of reports of. mixed populations• of-all colour forms on a variety of host plants (MacDougall 1921, Kirkland •and Parmonov 1957). Objectivity was brought to the classification of colour . forms by Baltensweiler (1970) although it is still convenient to speak of dark (Larchfom), intermediate and

•light (Pineform) colour types. In the same paper it is suggested that the predominance of-intermediate forms on • •. Larch at lower altitudes is due to the effect of the selection pressure- of high summer temperatures for the more temperature resistant eggs of intermediate forms (Baltensweiler and Vaclena, in preparation). This idea will be examined later in relat:on to conditions prevalent in Britain. The existence of differential mortality in populations of dark and intermediate colourtypes under conditions of trophic stress (Day and Baltensweiler 1972) led to the•hypothesis that the trophic condition of the host plant plays an integral 98 part in the insects population dynamics. An argument for this is built upon the following factual information from the ELgadine populations on Larch.

1) During a complete population cycle the rrapartions of dark, and intermediate larval colourtypes change in a manner, as predictable as the population oscillations. themselves (Baltensweiler 1970).

Owing to fluctuating larval population density and periodic_defoliation'of large proportions 'of the current years needle growth in each'tree (Auer 1968), the annual ring increment (Badoux 1922) and the trophic

condition of subsequent_years .larch______needles (Benz 1974) also varies cyclicly. 3) Mortality of dark morphotypes is higher than that of intermediate types under conditions ofTrophic stress (Day and Baltensweiler 1972). 4) An unknown (residual) Mortality(s) acting in delayed density dependent manner is the key factor in driving the population oscillations (Varley and Gradwell 1970).

The fact that proportions of different ecotypes in the population are a result of the previous years trophic conditions does not preveL.G theM from also 99 being instrumental in determining the current years . larval mortality. Thus from year to year items 1-4 (previous page) are inextricably linked. Although this theory has much credence, vitalrparts. are, as yet, unverified,. For example, it is not yet known • that the key factor is early larval mortality. Further work may reinforce the .idea. of such a feedback Mechanism and. add to the growing knowl.edge. of trophic effects on the population dynhmics.of. forest insect's (Kozlowski 1969; .Dixon.1970; Verzhutshii, Dokiichuk and Zhitova 1971;. Victorov 1971; Bombosch 1972; Sindelar and Hochmut Iunderstadt, Schwarz and Dinish 1975). Differential susceptibility (of-a population to the same host plant in different developmental stages was demonstrated in sectio 1.2.2. Variations in mortality were the result of,physical (bud scales, resin) rather than trophic_barriers. It is now timely to examine the consequences of feeding on a range;c:T coniferous. ho,pts for populations of ecotypes representing natural populations. This will help to quantify the relationships of ecotypes observed in the field and clarify the position of Spruce feeding formd and those on Japanese rather than European Larch. In addition to numerical mortality of budmoth larvae a number of other developmental parameters are scrutinized in the following experiments 1 QO which were carried out during the period March—May 1971. Methods and Materials Experimental design

Budmoth larvae were allbwed to complete-- --or attempt to complete their entire development on natural diets of conifer needles. Martality, instar length and weight were, monitored until.pupation. occurred. Eiglit'groups of larvae were allotted to the following test matrix which .takes.aebount of larvae from three localities fed on three• species of conifer host. Langdale 'Hope ' Burford

Picea sitchensis a d f SS a—h group code used Larix leptolepis b e in JL figures and Larix decidua h tables - EL

The larvae These were hatched from eggs obtained from selected breeding. Larvae in the fOurth or fifth instar were collected from each of the three localities where populations oc arred on the host plants listed below. Each larva was checked for 1 colourtype and reared individually to the pupal and adult stages. Pairs were then placed in standard cages (Meyer 1969) where mating and oviposition took place. Eggs were collected, placed in glass

1. See following page. 101 vials and incubated at the temperature suitable for diapause outlined in section 1.2.5. Such precautions are necessary since it is known that- environmental conditions experien6ed during egg diapause_are liable to influericelongevity:of_: later stages (Bassand 1965). Larvae were thus produced from the following source material:- Locality Langdale , Hope Burford Natural Pinus Larix . Larix host: contorta leptolepis decidua

Parental 7445. . .3231 2231 .. 6335 2131 . 2111.. colour 7445 4331 1131. types 7446 3231 1111 . 7447 1131 3231. Y. 6446 2131 2121 The rearing programme Upon entering the post-diapLase incubation period the eggs contained in glass vials were checked daily, and twice-daily at peak-hatch periods, for emerged first instar larvae. These were transferred with a fine hair bru7;12 to individual glass tubes containing a white card label ancl, a fresh shoot of the appropriate host foliage. Each tube was capped with a finely perforated poly-thene stopper and placed vertically in a wooden rack to be incubated at +15°C. Some 290 first instar caterpillars. were

1. The coding recognises colour variation from completely black to completely orange (or yellow). Four morphological features are typed in sequence, head capsule, pronotum, anal plate and general body colour. Each shows continuous variation in the proportions of black and orange cover which are estimated and recorded as a numeral for each morphological feature. An entirely black larva is given as 1111 and completely orange as 7447. 102 dealt with in this way. Subsequently an external check on each tube was made daily and any visible signs of ecdysis were noted. Cast skins are not normally eaten but since early intarb fees within a silken_tube_it.is not alwayS possible to•bee them. without undue disturbance. At 3-day intervals all- . remaining food, silk, faeces and cast_integument were removed and replaced with a fresh quantity:of'. food. At some of these intervals froth the third • instar OnwardS- each caterpillar was accUrately weighed and from this time also, caterpillars were accomodatt3d in 4 x 2 cm (Siam.) glass tubes.' Some time after the 4th ecdysis larvae were examined for colourtype. Pupation took place in the 4 x 2 cm. glass tubes and when the pupal integuMent had hardened each was 1.,laced . in a similar tube with a basal layer of,plaster-of-paris and charcoal mixture.. When moistened, _humidity was maintained and could be roughly checked from the appearance of th?, base during the 3-week. pupation period. Host plants European Larch (Larix decidua,) Japanese Larch (Larix leptolepis) and Sitka Spruce (Picea- sitchensis) were .chosen as a suitable basis for comparison in this experiment. Britain has been widely afforested with all three species and Zeiraphera diniana populations are known from each. 103

For practical reasons no species of pine are represented although fcr broad comparison the results from Section 1.2.1 remain relevant. Larch needles can be encouraged' to break bud

prematurely by bringing small branches into"a warm . humid and artifically lit environment:while providing them with tap water (Baltensweiler, per. -comm.). Successful results can be obtained from January onwards'for the purposes, Of.this experiment such:a technique was'employ.ed for a short period' only during March. FOrthe'completion:of. the . experiment twig- samples were obtained from two reasonably mature local Larch trees. Constancy of. needle length was thus assured, at least'for the earlier instar larvae, between 4-10 mm. Immediately' before feeding the whole dwarf shoot was-removed 'and could be placed "in the tube with no damage to the needles themselve0. Owing to a .much later bud-break than Larch, Spruce foliage was not naturally available. Thus, two container grown Sitka Spruce were pre-cooled for two months and maintained in a-heated green- house for several weeks before 11.:;e. Normal buds were produced under these conditions and utilized soon after the bud-scale cap had been broken during the swelling process. Care was taken to avoid taking too many buds from each branch and from each tree. In this way all experimental larvae

Table 13 Mortality ,of larliae fed, on different host plants

group :origin . host n numerical mortality in total each instar mortality t 1. 2 3 4 5

c 'Langdale EL 54- 4 • 4 1 9 16.7 1 b JL 82 6 1 4 3 T . 14 17.1 a %-, SS 27. 4 • '3 1 8 29.6

e • Hope . JL 23 6 2 2 10 43.5

d SS_ 11 7 1 8 72.7

h Burford EL 22 - 3 4 2 1 10 45.5 ,., g JL 24 10 4 2 . 16 66.7 f SS' 40 34 5 1 . 40 . 100

% instar 64.3 20.9 10.4 4.3 100 mortality 105

Table 14

Percentage _'total larval mortality and group comparisons

LANGDALE [ HOPE . BURFORD SS .29.6 (0.02*) 72.7 (n.s.) 100 (n.s.) (n.s.) (0.02*)

JL 17.1 (0.01**) 43.5 (n.s.) 66.7 (n.s.) (n.s.)

EL 16.7 45.5. (o.O1**)

Probability level at which there is a significant difference between adjacent groUps is given in brackets. n.s. not significantl -P>0.05---

Table 15 Instar lengths for larvae fed on different host plants.. Mean instar length. (days) s.e. Mean length of Group Origin Host 1 2 3 4 5 larval stage (days) n c Langdale EL 6.00 I 0.03 3.40 I 0.07 3.58 t 0.07 4.58 t 0.16 10.56 I 0.40 28.32 t 0.28 43 b JL 5.75 -1 0.57 3.16 t 0.06 3.29 t 0.10 4.7' 1 0.09 12.00't 0.06 28.99 I 0.24 68 a SS 7.58 ± 0.53 4.26 ± 0.33 5.05 ± 0.47 5.00 t 0.36 11.95 t 0.22 33.84 ± 1.34 19 e Hope' JL 5.00 1- 0.27 3.64 I 0.34 3.55 t 0.24 4.27 t 0.30 11.00 t 0.57 27.45 ± 1.08 11 d SS 5.33 I 1.20 6.00:1:1 2.00 5.33 ± 1.86 6.33 ± 0.89 15.67 t 2.73 38.67 I 5.80 3 h Burford EL 5,5 1- 0.15 3.17 10.11 3.50 I 0.19 4.17 + '0.27 10.92 I 0.65 27.25 11.01 12

g JL 6.0 ± 0.00 3.00 t 0.00 3.57 I 0.20 3.71 t 0.42 10.29 -1 0.75 26.57 1 1.00 7

Table 16

Mean length of larval stage with group. comparisons(days

Langdale Hope Burford SS 33.84 38.67 None surviving (0.02*) JL 28.99 (n.s.) 27.45 n.s.) 26.57. (n.s.) (n.s.. EL 28.32 27.25 107 were reared more or less synchronously. Results Mortality during the larval stages . The results are given in Table 13 of all recorded mortality other than accidental death. Fatalities during each instar are tabulated and the, percentage mortalities of each-experimental group are are further. compared in Table 14. In all cases where larvae had died the food substrate was examined for ' signs that feeding had taken place and'fur.almoSt all fatalities this had not been the case. L1 , • Fatalities in' later instars Were once again associa- - ted with low or negligable food consumption'and there were very few instances where normal quantities of foliage had been eaten by larvae which did not successfully pupate. Length of larval instars The mean length of each larval.instar for those larvae surviving to the pupal stage is given in Table 15, together with the mean total lengths of larval life which are again compared in Table 16. Larval and pupal weights Larval weight for each indi,idual surviving to the pupal stage is plotted as a function of time in Figures 23 to 31. The characteristic form of each plot may be subject to some distortion due to the timing of weight measurements in particular groups. For example the typical decrease in pre-pupal weight Figure 23. Changes in fresh weight of larvae surviving until pupation in group a.

DAYS AFTER ECLOSION 109

Figure 24. Changes in fresh weight of larvae surviving until pupation in group b. (means and 95% confidence limits are given for males and females).

45 GROUP b

r 30 cc 25 0 I- 0 20 LTJ

15 cc z Lu<1 10 2

1 5 10 15 20 25 30 35 DAYS AFTER ECLOSION

950/0 CONFIDENCE LIMITS d, 110

Figure 25. Changes in fresh weight of larvae surviving until pupation in group c. (means and 95% confidence limits are given for males and females).

13.1 w 330 cc .< ii. 0 E__ 25

[i] 20 if) w cc u_ z 15 < w 2 10

5 10 15 20 25 30 35 40 DAYS AFTER ECLOSION 95% CON. LIM. Figure 27. Changes in fresh weight of larvae surviving until pupation in group e

mg 25 E

20 F LARVA T O 15 EIGH H W 101- FRES

10 15 20 25 30 35 40 45 50 DAYS AFTER ECLOSION Figure 26. Changes in. fresh weight of larvae surviving until pupation in group d.

30-

5 10 15 20 25 30 - 35 ' • 40 '45 DAYS AFTER ECLOSION 113 Figure 28, Changes in fresh weight of larvae surviving until pupation in group g.

GROUP g

35 rn E 30 w cc 25 O I 0 20

I (r) w 15 cc

5 10 15 20 25 30 35 DAYS AFTER ECLOS ION 114.

Figure 29. Changes in fresh weight of larvae surviving until pupation in group h.

O .cr

O N O OSI 0

N ECL R FTE A

DAYS O

IC) O 0 3VAeiV1d0 11-1013M HS3LI3 1 Table 17 Pupal weights of Z. diniana fed on different host plants

Group Origin Host Mean pupal weight s.e. n sexual difference (mg)

c Langdale EL ?. 31.40 0.71 26 5.48 - •

coil 24.89 0.76 17 sig. P > 0.001

b JL 29.11 ? 0.63 38 2.11 • dr 27.00 0.73 28 sig. P =0.05

a SS 26.22 1.72 9 ' 5.60 64 20.62 1.32 10 sig.. P=0.02

e Hope JL ?. 24.27 1.24 6 '1.53

cr 22.74 1.15 5 not significant

h Burford. EL 27.46 1.12 '5 5.45 cr 22.01 1.48 7 sig. P =0.02

g • JL .? - dr' 23.26 1.06 5 116

Table 18

Mean pupal weights and group comparisons (mg) a Langdale HOpe - Burford SS 20.62 (0.001***)

JL 27.00 (0.054, ) , 22.74 (n.s.) 23.26 • 1 (n.s.) (n..s.) EL 24.80 ' (n.s.)

Langdale Hope Burford . SS 26.22

JL 29.11 (0.01*) 24.27 (n.s.) EL 30.28 27.46 (n.s.) 117

and at each ecdysis is often not indicated. Pupal weight is alSo recorded in these figures and means for each experimental group are given. in Table 17. Group comparisons are given in Table 18. Discussion The influence of trophic conditions on .,population fluctuations will be realised through the mortality of feeding stages and the qualitative differences which affect the survival or natality of the .subsequent population. Such effects haVe been ()User- Ved.fer larval populatiOns of three biotypes (Langdale,. Hope and Burford), which have fed c.n• three host plant species. Larval mortality which is of primary importance, has been measured as total mortality for each population and for each instar period; as expected greatest mortality occurs during the first instar and is related to negligable food consumption. Although total mortality increases for each biotype group in a host plant series EL

that the polymorphism is to some extent characteristic , of the biotypes Langdale, Hope'and Burford. Further substantiti,le evidence for this is to be found in the pupal weights of surviving larvae. The groups of 2'Hope. male_pupae which as larvae had continued to feed on Japanese Larch weighed on average 17% less than their Langdale counterparts. More Significantly `the same difference was apparent between the'female pupae; Benz (1970) has also shown a:good correlation Metween i pupal weight and fecundity. Pupal weight •. differences for groups on different hosts-are found only in male Langdale pupae fed on Sitka Spruce and Larch. Other comparisons for Sitka Spruce are of course absent owing to a low survival rate of Hope and Burford larvae. Altwegg (1971) however, generated higher survival rates'using anti fi a3 ddets-and-found _ _ the pupal weight of female Z. diniana to be 15% higher where Larch needle powder had been used instead of Spruce (Picea abies) in the food medium; the larvae were all of the Swiss Larchform. In almost all cases there are sexual differences in pupal weight. Closely linked with larval and pupal weight are rateb of development measured in terms of instar length and total duration of the larval period. Although this latter value is only significantly different for one comparison (Table 16) the changes in larval weight with time (plotted in Figures 23 to 31) show variable patterns for all surviving larvae 120 except those Langdale larvae on both species of Larch where weight change is relatively constant. Less rapid deVelopment on Spruce (5 days or 14% difference at 15°C) may be partially advantageous in delay- ing the oviposition period under natural conditions but is unlikely to offset the disadvantageous features of increased larval mortality and a reduced fecundity 'implied in the lower pupal weight of females. Cert- ainly Variations in instar length will contribute to

;population age distribution hetei'bgeneity, a characteristic of natural populations discussed in a previous: • section. A general conclusion is that polyphagy and monophagy are not clearly separable racial characteristics for Z. diniana but that the Pineform (Langdale) larvae exemplify increased rather than absolute tolerance of certain trophic conditions. The sub- stitution of Sitka Spruce for Larch as a natural host plant incurs "trophic stress" in a greater proportion of individuals in the Larchform (Hope and Burford) population, but even .on 'Larch, mortality of Pineform (Langdale) larvae is less. If the evolution of phytophagous insects generally proceeds towards a narrower rather than a broader host plant range (Dethier 1964) then a reduction in tolerance to trophic characteristics of certain hosts may be expected to follow in the wake of a reduction in host range imposed by other limitations which show 121 similar polymorphic expression in those populations. Baltensweiler (pers.comm.) has recorded high larval mortality'of'Swiss Larchform larvae on Larix leptolepis for which mortality has not beenobserve.d to be any greater than for Larix decidua in—these investigations. This may be an indication of the more 5pecialist nature of the polymorphs on'Swiss larch, the integrity of such a polymo'rphism being maintained by more rigorous ecological and. temporal isolation from sympatric morphs capable Of feeding on other conifers. 122

1.5 The choice of coniferous hosts for oviposition In the light of investigations in Sections 1.2 and 1.4 it has been established that certain differences exist between biological races of. Zeiraphera_diniana which .-are. partially_assoolated__L_ with distinct colour forms of the late instar lar-

vae. Insofar as these differences contribute, to the increased survival of these races on respective.. coniferous hosts, it would be expected that the females of each race. would possess the. appropriate , • oviposition behaviour which allows -the progeny to • maximise such physiological advantages. Bovey and Maksymov (1959) in a series of field experiments showed quite conclusively that the Larch and Pine races with which they were dealing in the Swiss Alps laid the great majority of their eggs on their named . hosts wheh presented with a choice of Larch, Pine and Spruce branches. Thus the larvae of-each colour— form (extreme dark and extreme light) appear more or less exclusively on Larch or Pine hosts and other - . .developmental distinctions serve to increase the ecological isolation of two races. In England and Scotland different colour types have appeared in variable proportions on a surprising variety of host conifers. Larval censuses at Hope show a complete range of colour types on Japanese Larch, where Larch and Sitka Spruce are intimately associated in the same stands. The idea that 123 particular colourforms favour oviposition on their relevant hosts must be in some doubt. One possible determinant of oviposition choice by female moths involves the theory of "larval memory" or Hopkins' host selection prihciple which.pbstulates . • - that the females of phytophagous insects tend to oviposit upon the same 'plant species•as their own -val food plant. Despite a large number .of insect species tested, the general validity. of this principle has yet to be proved (Thorpe 1930, Dethier•1954,' Wiklund.1974). The most polyphagous grOup. of Zeiraphera diniana, light colour type .larvae from Lang- dale, were utilized in an experiment hereto assess. the effect of larval foodplant species on adult oviposition choice. Factors stimulating oviposition in -Z. diniana have been investigated by Benz (1969) and most important appear to be the presence of afresh larch twig, perceived by the antennae, and a spermatophore with

seminal fluid and viable spermatozoa, in the recep- taculum. In addition, ovipositiont is one of the factors which, acting as a feedback-mechanism, stimulates oogenesis. Other factors of general impor-. tance to oviposition are light and adequate adult - nutrition (Benz 1970). Altwegg (1971) confirms the stimulating effect of the green larch twig on oviposition and proposes that such stimuli perceived by the antennae are potentiated from contact 124 chemoreceptors of the tarsi. A number of visual, olfactory or tactile stimuli originating from the host plant may be responsible for oviposition behaviour in microlepidoptera (Deseo 1970). In

Choristoneura_fumiferana_(C.lem.) both:ahape_and_s_u___• _ face texture of the host leaves influence•oviposition (Stadler 1974) when females are confronted . with,a . choice of host species., The potential for conifer host discrimination is highlighted by egg laying Diprionid sawfliesreViewed .by Knerer'an Atwood. (1973), which virtually' ignore very .vigorouS .trees possessing leaves with high water content. and have a predilection for the same weakling trees from one generation to the next. At a finer level of habitat selection Robert, Ourisson and Wolf-(1968) mention the action of substances responsible for the stimula- tion or inhibition of the localisation of eggs during oviposition of the Gelechiid moth Scrobipalpa ocellatella Boyd. Altwegg (1971):has shown that Spruce (Picea abies) and pine (Pinus silvestris). will not replace larch twigs as suitable sites for oviposition when using adult females of the "Larchiorm" ecotype of Switzerland. This investigation seeks to clarify the question of host species choice by individuals from the aforementioned mixed British budmoth populations. As indicated two slightly different experimental situations were used to separately investigate the possible variables attributable to larval food experience and those associated with the predisposed oviposition behaviour of "ecotypes".. 125

1.5.1. The effect of the larval food plant on the selection of oviposition sites in female moths Methods and materials Larval budmoth were reared iildiVidually on . fresh shoots of Japanese Larch'(Larix.leptolepis)„,_. European Larch (Larix decidua) and Sitka Spruce (Picea sitchensis). These larvae originated from parents, of the light type (7445) Langdale stock which themselves were collected in the field during the larval stage. They are shown in Section 1.4 to be polyphagous and. • . . therefore suitable for this experiment.: Rearing. techniques were the same as those used in SectiOn 1.4. Pupae were allowed to undergo normal development and emerging adults were introduced into metre cubic wooden frame cages, covered in fine gauze and placed in an open air insectary. .Lrtificial light was provided in daylight hours but twilight conditions allowed to preVail along with natural conditions. The cages were provided with 10% sucrose solution in a cotton 1001 stoppered glass vial supported on wire and the cages gf:ven a fine water spray daily to maintain humidity. A choice .of three host plants was given to the ovipositing females; two of the larval food plants Larix leptolepis and Picea sitchensis were made available and in addition the natural host of Langdale ecotypes, Pinus contorta was used. A fresh twig of each was set erect in a plastic beaker containing water and supported by a 126

hole'in the lid, a thicker twig without foliage was set . upright next to each foliage twig. The surface of these thick twigs.was to be representative. of the natural sur- 'faCe oviposition sites corresponding to each host species and did not hold epiphytic lichens. The foliage and oviposition twigs were replaced in the cage periodically and those: removed were carefully examined for eggs. A total of three .cages were used corresponding to the three larval rearing groups and •a total of 15 heal- . thy females oviposited in each. .Equal numbers of males were available in each cage. Results Eggs were laid almost exclusively on the oviposition twigs provided. The numbers on each are recorded in Table 19. The -two—way—analys-i-s--o-f—var-iance------for Table 19 evidences the fact that no discernable differences were found between grOups reared on different larval hosts but that preferences for different hosts at oviposition are highly significant.

(P = 0.005). Overall the host plants- were preferred in the order Pjcea sitchensis> Pinus contorta> Larix lepolepis. 127

Table 19 Numbers of eggs laid by female Z. diniana given a choice of three natural host plants (usual abbreviations)

Oviposition Larval food plants site - JL EL SS Total LP ' 543.(31) 688 (35) 330 (25) (31) SS 902 (51) 1176 (59) 1006 (75) r(61) JL 312 (18) 132 (6) 5 (0) (8) Ttalo eggs per 15 yy ' 1757(100)' S 1996(100) - 1341(100) 5094 .(100)

' percentages in brackets.

Two-way anova without replications for Table 19

MS F Source of d.f. SS S variation Among food plant 2 73245 36623 1.89 n.s. groups Among oviposition 2 1166589 583295 30.12 ** sites '

Residual 4 . 77465' 19366

Total 8 1317298

F.05 [2,4] = 6.94 F. 005 t2,4] = 26.3 128

1.5.2. The choice of host plant by ovipositing females of different ecotypes Methods and materials

Adult females. I derived from larvae fed on Japan- eSe Larch,,were confined with a single male each in individual cages modelled on designs used by Meyer ''(1969), Altwegg (1971). and Graf (1974). Sucrose 'solution (10%) was provided by means of glass tubes in the'-lid of each cage. Fresh foliage twigs of Sitka Spruce, Lodgepole Pine and Japanese Larch were set "upright at the inner. perimeter of each cage so that the proximal ends of each twig were immersed in water provided in the plastic beaker below. Three types of oviposition site were tried in intimate association with the foliage twigs (Plate 4); the most suitable design, a blotting paper strip backed with green tape and stuck with a narrow band of sellotape to the inside of the cage, was eventually used in this experiment. In addition to making the eggs laid immediately visible (Meyer 1969) it also has for this experiment the advantage of ensuring Contact with a single foliage twig during oviposition. Four trial groups were taken as representative of four larval colour type categories (Table 20). Groups 1-3 were bred from material collected at Hope Forest and Group 4 was bred from Langdale larvae. Each group comprises 5 females and thus Table 20 Numbers of eggs laid by female Z. diniaria given a choice of three natural host plants

Group 1

Oviposition Colourtype in larval stage mean no. + Site 1111 • 1111 1111 1111 1111 eggs/site - s.e. LP 7 66 19 23 66 36.2 12.4 ss 77 5 49 5 41 35.4 13.8 1 JL 38 0 42 81 55 43.2 ;13.2 Total eggs 122 71 110 109 '162 114.8 '14.6 per female

Group 2

Oviposition Colourtype in larval stage- ... , mean no. site 2231 2311 3231 3231 2131 ,eggs/site ; = s.e. LP 62 39 23 70 27 44.2 9.4 ss 19 96 59 38 77 57.8 13.7 JL o 34 22 24 17.8 6.o, . . . 130 128 . 119.8- . 110.7 Total eggs 81 ' 144 ' 116 l' per female . . I . '

Group 3

Oviposition Colourtype in larval stage . mean no. + . site 4331 4343 5443 5343 . 5333 eggs/site j - s.e.

LP 4o 6 63 38 107 - 50.8-. -‘ 16.7 , ss 122 72 57 ' . 56 36 68:6 14.5 J1., 23 • 24 5 22 .• 1. 15.0 5.0 Total eggs 185 102 125 116 :144 . 134.4. . , 14.4 per female Table 20 continued

Group 4 Ovinosition Colourtype in larval stage mean no. site 6441 6443 7445 7445 . 7445 eggs/site . 4.: s.e. IP 2 66 19 38 27 . 30.4 10.7 . ss . o 48 48 25 29 . 30.0 8.9 JL 84 27 ' 41 84 109 69.o 15.2 Total eggs 86 141 108' 147 165 129.4 14.2 per female -

Overall means It 3.e. (%) LP 40.4 ± 6.o (37) ss 48.o = 6.9 (39) • JL 36.3 ± 7.0 (29) 131

Table 21

Two—level 'lusted anova for Table 20

• Source of il.f. S.S... MS Variance variation V •Fs . components as percentage of overall . variance Among groups 3 397 132 '0.06 11.5% . . • . Among ovipobit—• 8 16791. 1099 . 2.86* .24.0% , ion sites within V V . • groups • . Among females of 48 35300 .735 — '64.5% the same colour type Total 59 52489 — —

F•05 [8,403 2.18

* P < 0.05 132

20 cages were used in all. The_cages were_keptat 20oC constant temperature and artificial light was . given for 1-5 hr/day (including short twilight periods). Results The numbers of eggs laid by each female on each oviposition site are given in Table 20 and a two-level 'nested analysis of variance outlined in Table 21. There is no evidence of a significant difference in the oviposition habits of different grOups. but again significant differences (P = 0.05) -are in evidence between the eggs laid on each oviposition site. The order of preference foi' each site is as before, Picea sitchensis> Pinus contorta > Larix aeptolepis. Discussion It is clear that "memory"-of-the-larval-host-i-s,-- for those hosts tested, not an important component of adult oviposition behaviour. The polyphagous, "pineform" larvae were involved here, but Altwegg (1971) was also unable to validate the host selection principle when rearing "larchform" larvae on media containing powders of Spruce or Pine needles. Two parts to the sensory information of an ovipositing female moth can be considered. Firstly the tactile, visual and, most importantly, chemosensory information perceived by sensillae on the antennae and tarsi. These are provided by the foliage twigs alone but secondly the 133

tactile and possibly chemical stimuli perceived by the ovipositor at the time of egg deposition must convey information on surface topography, important for correct location of the eggs. There are considerable differences iri the bark structure of Larch, Pine and Spruce and the localisation of eggs differs accordingly but i,ince the preferences for each host were similar

'even where artificial sites were present these pref— 1 erences may be more'readily attributable to stimuli :. from.the.foliage twigs. It was.not possible, to.demonstrate any differences between the colour types usf-d or indeed between Hope and Langdale moths for host preferences of the type described by Bovey and Maksymov (1959) and Altwegg (1971). Whereas the larval stages are quite sensitive to different food plants it seems that the female budmoth is much less specific in her choice of host plant for oviposition, a conclusion which contrasts with the situation found in the Spruce budworm Choristoneura fumiferana. In this insect the larvae are less specific than the female moths (Stadler 1974). A survey of winter egg distributiOn at Hope Forest (Forestry Commission, Report on Forestry Research for 1958, internal publ.) showed an abundance of eggs on Picea sitchensis in a mixed stand with Pinus contorta, Pinus cembra and Larix leptolepis, which was not obviously related to the proportional 134 representation of these trees in the forest or to the total lengths of tdigs in each species. The moths responsible for such a host preference were identified at the time as predominately "pineform". Field samP- ling at Hope.in 1970 and1971Showed a small population of eggs on Iarix leptolepis but none on Picea sitchensis, a reversal of the trend described above and one whiCh is not borrie out by this experimental work where- material representative of Hope populations'was used. To explain field and laboratory results atisfaetorily. may require further experimentation on the gross orientation of Moths to their host plants. -The - preference for landing sites that match cryptic colouration as described for Agonopteryx pulvipenella (Malcolth and Hanus 1973) or the ability to distinguish foliage from a distance may well be important here. 135

1.6 Some temperature effects and an historical appraisal of known population "outbreak" periods Studies on the relationships of climate and weather to fluctuations in insect population numbers are

- _,among the_oldest and continue to be among. the most widespread studies in population ecology. . Henson (196B) gives a comprehensive review of the form such inves- 'tigations have taken and points to the usefulness of a combined approach to tiometeorologicai work, involving experimental studies, .micrometeoroldgical investigations and a knowledge of the relevant syn'optic climatology. The work of Baltensweiler (1966 a) and Baltensweiler, Giese and Auer' (1971) along an altitudinal profile, and of Baltensweiler (1964, 1966 b) over wide areas, represents examples of such an approach. A mainly retrospective atudyi- such -as-that-of--- Baltensweiler (1966b) in which the appearance of foliar damage by Zeiraphera diniana in European Spruce forests is correlated with long term changes in the weather, has a number of points to recommend it, in spite of the pitfalls inherent in correlation analysis. Firstly, use is made of forest records and meteorological observations which are already available, and . secondly a broad basis for a Second level of more detailed investigations is established. The realisa- tion that Z. diniana exhibits several distinct population patterns in different parts of its 136

Palearctic range and that these are recognisable in .geographic terms (Baltensweiler 1966 b), allows for the emergence of an attractive idea that climate determines an equilibrium population density upon which density related population procebses, and variations in the weather, may act. Care must be taken, however, not to :.exclude the possibility that climate also indirectly 'determines-such population patterns through the impoverishment of parasite complexes and influence on food. availability, as Aiscussed by Turndck (1972) for the.Larch Sawfly, Pristiphora erichsonii (Hartig.). Indeed, climatically induced insect/plant phenological asynchrony discussed in Section 1.2.6. may be critical in the determination of an equilibrium larval population density by limiting food availability in most years. An examination of the response cf populations to climate may be made using the guideline that least abiotic mortality is probably experienced where populations are observed frequently at high densities and at regular intervals — the so called "optimum areas" (Baltensweiler 1964). For Z. diniaha these occur only in the zone of the alps between 1700 and 1900 metres a.s.l. The following investigation examines the hypothesis that when the weather (as indicated by temperature only) aspires to that of the optimum areas, then population increase is evidenced. Some temperature effects, highlighted by the first part are followed up experimentally in the second part of this investigation. 137

1.6.1. Historical records The basic features of this analysis are that temperature exerts a favourable, unfavourable or indifferent influence on Zeiraphera diniana. in all its stages and_this may or may_not._be manifest_ as population mortality. Temperature at any particular. time of the year (and by implicatiOn on any. particular budmoth Stage. since it is univoltine), may vary spatially in the form. of climate and from year to year.as a funotion.of the weather. If the effects,of.tempprature on budmoth populations are defined in advance.it should be possible to observe the effects. of favourable temperature indir-. ectly as population increase. Before this result can be achieved a number of simplications and assumptions must. be made. Temperature Monthly mean temperatures are, derived from the means of daily maxima.and minima as' recorded at Buxton, Derbyshire by the' Meteorological Office. A single value for monthly mean teMferature ignores. all but the broadest temperature trends for that month.. and is compared with a long term (47 year) average value for each month derived from the same data; Dev.Lations from the long term average are recorded in Appendix 3 and are the basic values used.in this analysis. Population increase This is not an easy value for' which to gain infor- 138

mation retrospectively. Published_accounts_are available of some large populations in Britain (MacDougall - 1922, Kirkland and Paramonov 1957) and other "outbreaks" are recorded by the Forestry Commission (pers. comm.). •Front-this-information it is possible to define certain .periods when population increase was taking place some British locations: to a greater or lesser extent and other periods when population increase did not take place or at least did not lead to readily observed "outbreaks",and forest defoliation (latent period). Known population outbreaks and the' relationships of the Latent period with two increase periods are illustrated in Figure 30. It will be seen that the years 1951-52 and 1958-60 are excluded from either the Latent or Increase periods. The duration of each of the latter cannot be exactly deteiailhe-E.--Bizti-C cra= cesses may have been responsible for population decrease in some years (particularly 1958-60 at Hope) despite the possible climatic favourability of those Periods. Alternatively, population increase may be generated by a favoJrable climate in some years although it may only be after a number of generations that this is realised as visible damage to conifers. Thus, years such as the aforementioned which do not readily fit either the Latent or Increase categories have been excluded. Temperature and the life history of Z, diniana The effect of temperature on some of the critical

Figure 30. Periods of partial defoliation (outbreak periods) caused by larval populations of Z. diniana, and their locations.

KESWICK CANNOCK /\ LOTHIANS & HOPE HOPE SELM MUIR N .WALE5-7\ .ZL A

L A TEN T INCREASE INCREASE 140

stages has been thoroughly reviewed by Baltensweiler (1966 b) in relation to populations in mid-Europe (Czechoslovakia and the. German Democratic Republic) on Spruce. A similar approach is adopted here. Monthly mean temperatures may be haveia_favourable (+), unfavourable (-) or indifferent .(o) effect on the population depending on the sign and'magnitude of the temperature deviation and upon which stages in the life . history they are expected to act. Thus, normal temperatures for the months September.to March.are likely ta

be higher than those optimal for egg diapause develop-. is ment and minimal egg mortality (Bassand 1965). In this case any positive deviation from the long term monthly means can be regarded as detrimental or at least in- . different to the population of eggS in the field. Conversely, a negative_deviation can be regarded as favourable. In April and May post-diapause development proceeds and egg hatching occurs. .1t was found in section 1.2.6 that field egg hatching fcr populationS an Larch and Pine is generally late in relation to foliage production and since warm spring temperatures tend to hasten hatChing more than foliage development, any deviation > +1°C will increase insect/host coincidence favourably. The caterpillar population which hatches will reach the pupal and adult stages early if June and July temperatures are high. If eggs are laid early, mortality might ensue Table 22 Months in which mean temperature is judged to be favourable or unfavourable to budthoth populations over two periods from 1930 - 1966

Jan Feb Mar Apr May June July Aug. Sep : Oct - Nov Dec

Key to the determination of favour- a a a b b- a c a a. . a a a able temperature dev4?.tions • • , • , Latent period 21 yrs. 2,12 14 10 15 19 13 19 12 ..10 ! 10 10 11 (1930 - 1950) + 9 7 11 6 2 8 2. 9 11 11 11 10

11 yrS, Periods of population increase : 2 4 5 , 5 9 10 .5 7 2 !. 6 5 5 6 (1955 - 57, 1961 - 66) + .7 6 6 2 1 . '6. . 4 9 5 6 6 5

Significant difference • between periods (Fishers exact test of independence) P = • 0.039*

a temperature deviation4(0°C )÷ioc

• II < -1°C 142

as a result of high temperatures in late summer (Baltensweiler, Giese and Auer, 1971) and therefore a premium may be placed on low June and particularly low July temperature. Similarly eggs laid in August should suffer 'less mortality if deviations <0°C occur. The final modal, based on a quite intimate knowledge -of pcssible thermic response in a budmoth population,. `determines.the classification of actual monthly mean temperature deviatiOns as favOurable (+) or unfavourable/ ;.indifferent (2) for the two periods whiCh are compared on a 2 x 2 contingency table.for each month using Fisher's exact test of independence. (Sokal and Rohlf, 1969). These results are given in Table 22. Discussion The chief distinction between the Latent and Increase periods are shown with this naive model in the August temperature deviations from the long term monthly means. There are fewer favourable years for August temperature in the Latent period but, conversely, more favourable years for the periods- of population increase (sig. P = 0.04). It is immediately of interest that "summer" temperature deviations (data from July, August and September monthly means) are also of greatest significance in the similar anlysis of Baltensweiler (1966 b). In the latter case, greater detail of population densities are available and it was possible to distinguish progradation and gradation periods 143

. (in which there were more, favourable summers) from a latent period. This suggests that the a priori assumption, that negative temperature deviations from 13.8°C (August mean) favour population increase (by decreasing

mortality), is of greatest importance. - Of course, it is by no means evident from this

information what the exact bioJogical implicatiOns t5f. higher than'. average August temperatures are for British populations. Both adults and eggs are present.in the field during this month d.although eggMortality waS tacitly assumed for the purposes of establishing a testable model here, adult mortality. (or _variations in natality) may also be consequences of higher than average temperature conditions. 144

1.6.2. Experimentally determined diapause egg mortality_ The results of an elementary model suggest that an egg mortality related to temperature may be important during. the earlier stages of diapause in the field; a_conclusion also implicit in the.more elaborate data examined by Baltensweiler (1966 b). - More direct evidence comes from multiple regression analyses of egg mortality and temperature data collected at four alpine sites (800 — 2100 m.a.s.l.) at which different .patterns of population fluctuation occur (Baltensweiler, Giese and Auer 1971). The results Imply that diapause mortality was strongly associated with excessively warm temperature conditions from oviposition through mid- winter. Elsewhere (Baltensweiler, 1968) it has been stated that summer temperatures above 30°C are lethal to newly laid eggs, but no quaiiti-t-87ti-ve—e'Crid-e-ri-ce - for — this is given, and although the effects of only two temperatures (11° and 20°C) on prediapause eggs were observed by Bassand (1965) there is reason'to suspect that, all other conditions being optimal, the higher - temperature induced a 20% increase in egg mortality. With this evidence in mind an investigation of egg mortality during the prediapause period was under- taken. Four sources of variation were examined, these were temperature, the duration of exposure, variation attributable to different morphs and variation of eggs from fcmalns of the same morph. Results are given for two separate experimental situations. 145

Methods and materials In the first experiment egg batches were obtained from laboratory reared moths of four morphotypes (Table 23; eggs from a single pair' represent each morphotype). Oviposition took place at 2000' and batches of eggs were collected as soon as possible afterwards (usually within a few hours). These batches were sorted, with as little manipulation as possible, into groups of 20 eggs placed in plastic stoppered glass tubes (30 x 6 mm). The tubes were held in wooden racks at one of two temperatures (250 C., 3000) for one of three pdssible periods (5; 18 or 24 hours), and subsequently at standard temperatures for the remainder of the diapause period (10 days at 15°C, 180 days at 2°G, and then at 15°C until hatching). Mortality of eggs during the initial incubation period was said to have occurred wheri- e-gp-- dIlap-sut-or failed- to resume development after diapause had been eliminated. Post-diapause mortality was recognised in eggs which showed evidence of resumed embryogenesis but failed to hatch. A second experiment using a similar procedure examined more fully the extent of egg mortality variation attributable to parental replicates. A number of different matings produced eggs to represent each of 5 morphotype groups. A total of 20 adult pairs (males and females homogenous for morphotype) were used and 1645 eggs obtained from these. The numbers of eggs for 146

Table 23

The effect of Temperature, duration of exposure and parental morphotype on the•pre—cliapause mortality of eggs. (Mortality of eggs per batch of .20), •

Temperature (°c) Duration (hours) Morphotypes ..,. A B ,C D

25 5 t 0 0 .0 18 . 7 1 . .. ' 24. . . . ' 6.4 6 ' 1

• • 30 18 16 • 2 ' 5 1 24 12 1 7 3

(28.6%)

Key to morphotypes Field source, types A Hope Forest • 1111. 21 21 B Hope Forest 2131 4311 C Hope Forest 6445. 6445 D Langdale 7445 7445 . Total % mortalities for each variable 25°C 30°C 5 hrs. 18 hrs. 24 hrs. A B C D 12.9. 22.1 4.4 23.1 25.0 37.5 6.7 18.3 7:5 147

Table 24

2 x 3 x 4 Factorial anova for pre—diapause egg mortality

df SS MS F Source of variation S Temperature • 1 20.17 20.17 7.23* Duration 2 83.25 41.64 14.92** Morphotypes , 3 148.33 49.44 17.72**

Temp, x Duration 2 2.58 1.29 <1, ns. Temp. ' x ,Morphotypes 3 33.50 •11.17 4.00 ns Duration x Morphotypes 6 65.42 10.90 3.91. ns Temp. x Dur. x Morpho— 6 16.75 2.79 types Total 23. 370

F.05 D ,,1 = 6.99

F [26] = 14.5 F = .005 [3,6] 12.9 148

Table 25

The effect of temperature, duration of exposure (during the pre-diapause period) and parental morphotype on the post-diapause mortality of'eggs (per batch' of 20)

Morphotypes * • • Temperature (°C) Duration (hrs.) A B " 'C . .D

. . 5 . 8" 2 • 0 - 2. • 25 • 18 8 . 24. : 6 . 2......

5 "12 4 . 0 2 30 18 3 1 1 .4 24 9 3 . 0

82/48o (28.2%) Total % mortalities for each variable 25° 30° 15his. 18hrs. 24hrs. A' 17.5 16,07 '1,8.8 - :16.3 16.3 , 38.3 .16.7 1.7 11.7

* as for Table 23 149

Table 26

2 x 3 x 4 Factorial anova for post—diapause egg, mortality

Source of_variation df' SS. MS • • F - :•

Tamperature 1 .0.16 •0.16 <1.ns: Duration 2 1.33 , 0.67. . <1 ris . 172.50 . 57;50 13.10- Morphotypes . . 3 .

Temp.' x Dur. •2 12.34 .6.17. - 1.41p.s. Temp. x. Morph. :3' . 3.17 1,06f . 2 <1 ns Dur. x Morph: .6- • - 24.00 ' 4.00 . <1 ns

Temp. x Dur. x Morph. 6 26.33 4.39

Total 23 239.83. • .

F 12.9 .005 E326.

Table 27 The influence of parental morphotype on pre - and post-diapause mortality (°0) Parental Replicates + Morphotype diapause 1 2 3 4 5 6 7 mean s. e. mortality + A pre- 11.4 4.7 16.1 23.4 13.90 - 3.94 post- 75.0 4.7 22.6 10.2 • 28.13 t 16.07 B pre- 3.5 5.4 ' 16.5 66.7 23.03 - 14.84 post- 4.9 0 26.4 0 18.85 ± 11.82 C pre- 1.0 4.3 0 1.77 - 1.30 post- 4.0 2.5 0 - 2.17 -+ 1.25 D pre- 23.5 46.2 7.0 38.6 12.1 0 14.5 20,27 I 6.37 post- 2,9 7.7 7,0 17.5 7.3 0 2.2 6.37 t 2.17 - pre- 5.4 10,6 8.00 1.- 2.60 post- 6.5 35.0 20.75 - 14.25

Total eggs used = 1645 mean mortalities pre-diapause 13.39 3.90 post-diapause 15.25 - 4.79 1 Table 28 Two-level nested anova with unequal sample sizes for Table 27

Source of variation df SS MS

Among morphotypes 4 146.83 36.71 0.771 ns Between diapause 5 1705.82 341.16 1.17 ns mortalities within morphotype groups

Within parental 8742.45 291.42 replicates 30

Total 39 10595.10

Key to replicates ( o1 x morphotypes 1 2 3 4 5 6 7 A 1111 x 2121 1121 x 2221 1111 x 211 1111 x 2111 B 2131 x 3331 3331 x 3211 3231 x 301 4331 x 3333 . , c 6445 x 6445 6443 x 7442 5342 x 7425 • D 7445 x 7445 7445 x 7445 6444 x 7445 6445 x 6335 7445 x 6433 7444 x 7445 7445 x 7445 E 4333 x 3231 3331 x 3331 152

each replicate group were different and mortalities are represented as percentages of the total eggs in a group. Once again oviposition took place at 20°C' but standard incubation followed immediately and mortality was noted in the normal manner. Results The mortality of eggs (eXpressed as number dead,' 'batch of .20-) is given fOr prediapause and post diapause' periods in Tables 23 and 25 respectively (abnormal. temperatures); 'percentage. dIapause mortalities .are given in Table 27 (parental replicates); . Factorial anova Tables (24 and 26) and a nested anova Table 28 corresponding to each are presented. Prediapause mortality It is clear from Table 24 that prediapause mortality in the first experiment has '„,ignificant variance components related to temperature (13, = 0.05), duration of experimental period:(P = 0.005) and morphotype representatives (P '0:05) although no first order interactions between these yariables are apparent. .The gross effects of the three primary variables are made more meaningful when consideration is given to the total percentage mortality in each variable category; there is a trend for mortality to increase with temperature and duration of exposure, and differences between groups of eggs from particular females may be observed. Table 28 shows however that variation among morphotypes is not significant in the second experiment. 153

Post diapause mortality Table 26 indicates that post diapause mortality is not related to the treatments given to eggs during the period of initial incubation, but that group (morphotypes) variation exists: Once again, replicates introduced 'in the second experiment give no basis to variation on the grounds of morphotypes alone

(Table- 27). Discussion Although a trend, of increased lore—diapause egg , mortality has been shoWn to occur between temperatures o of 25 and 30 C and for prolonged exposure to each; the absolute mortalities experienced are not as great as might have been expected. An exposure of 24 hours to , a temperature of 300C only induced 29% mortality in eggs of the first experimental—se-rri-es-. -This —rather surprising result which is not in agreement with the claims of Baltensweiler (1968 and elsewhere) points to the possibility that eggs are polymorphic for high temperature resistance in different parts.of their geographic range. The selective importance of this is as great as it might be for resistance to low winter temperatu_es experienced in the extreme northern parts of its range;*Bakke (1969) has measured the super cool- ing points for eggs from the mountainous regions of Southern Norway and found them to be greater than —500C which seems exceptional even for Z. diniana. A source of considerable variation in pre—diapause 154

mortality is once again between_family groups and seemingly unrelated to morphotype. Although it would_ seem likely; the heritability of high temperature resistance yarrants further' investigation. As expected, there is a Connection between August temperatures, egg mortality and periods when field populations do not gene7:ally increase to "outbreak" 'proportions. This substantiates the work of'Baltens- weiler, Giese and Auer,(1971) but also Suggests that after a series of years 'with excessively warm August temperatures the remaining population will be dominated by relatively temperature—insensitive eggs. A strong selection pressure would act on a population with a wide range of temperature resistance as shown in these experiments. 155

1.7. The relative frequency of morphotypes in field •populations and'some general inferences A large part of this work has referred to the classification of final instar larvae as morphotypes. The reason underlying the descision to group parts of the population according to colour criteria is borne out by the otservations of Maksymov (1950), Bovey and -Maksymov (1959) and others who discovered the existance of "sympatric" races of Z. diniana in the "optimum" parts of its geographic.range. 'Two. races accorded with the extreme colour forms Of the series used by Balten.sweiler (1970) and here, and in addition they were confined . to quite distinct host species. They were thus designated "Larchform" and "Pineform" and some developmental characteristics appropriate to their respective host plants were furthar_eviden_ced,_ _ using such colour criteria and developmental or behavioural characteristics as a model for racial integrity . certain paradoxes have been shown in these investigations-:-. British populations do not appear to bear the same discrete racial characteristics typical of sub—alpine populations in Central Europe. Be- ore further discussion of these points the actual frequency of larval colour types in field populations must be considered. The two field populations examined in detail were at Langdale (Pinus contorta) and at Hope (Larix leptolepis) although some limited samples of populations at Burford (Larix decidua)

Table 29 Morphotypes of larvae in field samples1970_ 72 Head capsule 1 2 3 4 6 7

Hope 1970 2 3 1 Thoracic 6 4 4 2 1 1 2 Shield 3 1 3 1 1 9 3 4

Hope 1971 1216 6 4 2 7 2 4 1 1 1 1 2 6 2 4 5 2 1 6 2 1 3 1 3 1 4 1 1 4

Hope 1972 42 9 19 10 3 12 4 4 2 3 11 4 S 5 11+ 3 1 3 1 3 1 6 1 6 1 1 1 1 2 4 3

Langdale 2 1 1 2 3 4 1 1 3 4 1971 3 1 2 2 4 4 2 1 1 5 6 2 1 1 1 6 2 16 15 ■••■ 2 20114 4 1• 1 10 55 2 21 214 Langdale 2 1 197 2 3 1 1 3 2 1 1 1 3 3 2 5 2 7 52

Burford 1 1 1 2 4 1970 2 :2 1 2 1

1 2 3 4 ANAL PLATE

Table 30 Larvae from field samples grouped in morphotype categorids A - P Head Capsule 1 2 + 3 4 + 5 6 + 7 Anal Plate

0 1+2 3+4 •r1 1+ A B E F I J C.) "CI rt5 r-' ;..4 2 0 •r.i 3+ C D G H K L 4

SAMPLE A BC D .E . FGH i I J K L M N 0 P. Z • Hope 1970 2 3. 20 8 4. 2 2 1 13 55 Hope 1971 20 9 ' ' 23 . 31 2 3 4 3 2 7 1 19 124 Hope 1972 57 22 37 36 2 3 1 4 1 15 20 198 Langdale , .1971 3 1 13 17 1 2 1 8 12_ 5 9 12 365 449 Langdale . 1972 2 . . 6. 7 1 1 3 . 10 2 98 130 Burford 1970 1 1 6 10 5 3 ;1 2 29 Burford 1.971 5 1 6 Cannock . 1970 2i 2 4 11 • 3 i 58 Figure 31. Percentage frequency of final instar larvae in each of the morphotype categories (from Table 30) from Langdale and Hope Forest.

ABC DE.FGH I J K LMNOPO

30 HOPE 1970 155

r--1 -,

20 HOPE 1971 ,_ 2.124 . ,

I , ...... ' . )-20 HOPE 1972 E195 • 8

z 60 - LANGDALE 1971 - 2449 •

ce 4 _J U_ 0 2 C

r—i 0

LANGDALE 1972 0 0 6 2130

. _ A BCDEFGH I J KLMNOPQ MORPHOTYPE CATEGORIES ( FROM TABLE 30)

■ ------Table 31 Changes in morphotype composition of larval populations in- consecutive\years.

Sample site Year Number' of G-statistic + df Log.number larvae typed larvae per field sample unit (Instar 4 - 5)

Hope 1970 55 0.2355 21.776* 11 Hope 1971 124 0.4430' 17.470n.s. 11 . . Hope 1972 198 ' 1.1265

Langdale 1971 449 1.3979 22.046* 12 Langdale 1972 130 1.5955

1 X20.05 Ell = 9.675

X20.05 [12]= 21.026

for homogeneity of morphotype comparisons between years. See Table 30. 160

and Cannock (Larix leptolepis) were also taken. Larvae . taken in samples were simply reared to the fifth instar and colour typed in the usual way. Total numbers of larvae typed in different years were variable and the results for three morphological criteria (head capsule, , • pronotum and anal plate) are given in Table 29. Resu) is Colour types for each morphological criterion 'are clearly associated (Table'29). MOrphotype :proportions in Hope and'Iangdale:populations differ radically although representatives of all major colour types are found in both (Table 29 and 30). By amal- gamating some of the colour distinctions in Table 30, a more general comparison of populations between years has been made in Table 31. Proportions of morphotypes are differently represented in populations between 1970— 1971 (Hope, P = 0.05) and 1971 — 1972 (Langdale, P = 0.05). In Figure 33 the morphotype proportions are shown as percentages for the Hope and Langdale populations, the significant changes are seen to be towards greater proportions of dark individuals (Hope 1971) and greater proportions of intermediate individuals "(Langdale 1972) These changes do not, however, represent major switches of emphasis in population composition but rather small alterations which may arise through a gradual selection in a single generation. Baltensweiler (1970) has noted similar changes for cyclicly fluctuating populations on Larch which in 4 generations result in a substantial 161

switch from predominantly dark types at high population density to predominantly intermediate types at low population density. Interestingly enough changes at Hope, As recognised 'above, are also concurrent with increases in larval population density (Table 31).

;-- 162

Discussion The relative abundance of feeding Zeiraphera diniana caterpillars on Pinus contorta at Langdale Forest has facilitated an analysis of mortality in young stage larvae and its relations to phenological characteristics of both insect and host plant. The developmental stage. of the vegetative bud is an important factor in determining larval survival; the risk to the population is spread, howeVer, by variations in the timing of bud elongation between trees and by a prolonged larval hatching period. Survival estimates are therefore rather uniform from year to year ayld in addition, possible' mortality is damped down by the availability of male flowers on older trees. Larvae show a distinct preference for feeding on this reproductive tissue and there may be selection pressure for shorter periods of post: diapause egg development to take advantage of it in some years. The heterogeneity of bud break prevents the timing of larval hatch being precisely selected for and, as for the winter moth (Varley and Gradwell 1968), selection pressure is from two directions; as Singer (1974) argues, early hatching larvae of the winter• moth are partly selected for by the accumulation of toxic chemicals in the oak leaves later in the season -(Feeny, 1970). In Zeiraphera diniana the rapidly changing xerophilous nature of pine needles must also be a strong selection pressure for earlier hatching larvae. 1 163

Provenance differences in Pinus contorta may account for some phenological variation;•in some cases the earliest flushing provenances remain noticably freer from larval damage (Stbakley 1970). If this is substantiated then a simple form of cultural control .'may result from planting these early developing Lodgepole races in areas where Zeiraphelradini'ana is known to be a 'threat. Similarly, the avoidance of profusely flowering coastal provenanbes (Cannell 1975) may discourage severe attack. Differential susceptibility of Lodgepole • pine provenances (as found with attacks of Rhyacionia buoliana, Esbjerg and Feilberg 1971) may take effect through other physiological race differences such as resin production which makes Scots and Corsican pine more resistant to the pine shoot moth (Harris, 1960). The coincidence of Larch budmoth larval populations with the flushing of species of Larix in Britain is generally poor. The eggs hatch late when compared with the food plant phenology and in a population such as that on Larix leptolepis at Hope Forest there exists forms whose hatching characteristics are very variable. This could be an indication that there is much interbreeding between populations which under different circumstances are confined to appropriate host plants by their adaptive characteristics. In this way Swiss populations seem to be ecogenotypic and among those associated characters are larval colouration, post-

diapause duration, survival of larvae on different 164

hosts and appropriate oviposition behaviour (Bovey and I4aksymov 1959).- Light colour type larvae at Hope Forest are in some cases able to hatch early and the females seem to have an inappropriate oviposition behaviour which, overall, increases their chances of survival on Japanese Larch. The result at Hope is a larval population whose colour types are very variable and whose other physiological characteristics are equally unpredictable. The variation in larval colour and the continuous variation of other physiologiCal characters are probably under the control of polygenes. Some characters of the populations investigated, for example tolerance of •trophic stress, may also be continuously variable and polygenic, but exhibit themselves as threshold characters in the manner described by Robinson (1971). The genetic integrity of populations with different characteristics may only be maintained under the auspices of a progres- sive ecological separation; a single population tends to fragmentate along the division introduced by the most important elements of a polymorphism. This would seem a. reasonable explanation for the origin of - distinct Larch feeding polymorphs from the polyphagous Pine or Spruce feeding polymorphs of Central and Northern Europe. Larch forms, with a narrower range have capitalized particularly on the widespread and native Larch forests of the European Alps and Eastern Siberia where today they show their most remarkable population cycles. 165

In Britain, the coming into contact of previously separated, but not genetically isolated populations is essentially phylosynapsis, a term coined by Hubbell (1956). The outcome is the production of mosaic— discordant intergradation. of numerous, small- local populations which differ from one another. in the incidence, degree of intermediacy of :and association between

-the characters by which'the "parent" populationsiare. distinguished. 'It is interesting that this should oCctir in areas which are sub—optimal for populatlbn increase and for this reason are regarded as climatically -fringe . locations. Carson (1955) has considered the genetics of some marginal populations of Drosophila robusta and concludes that types which are highly adapted to varied conditions in their main areas of distribution (and exhibit.chromosomal polymorphism) will not be represented peripherally; there will be less polymorphism at the edge of the range. The success of more generalised types in marginal situations is related to the requirements associated with environmental variability which may also be one reason for the continued persistance of Z.diniana populations with such variable characteristics in fringe areas on Larch hosts. Accordingl:, the distinctions between prominent population polymorphisms, or even sibling species (in the sense of Mayr, 1942) are blurred. If increased gene exchange between Z. diniana populations results in the success and increased persistance of marginal populations there is a contrast with other 166

species where introgressive hybridization of allopatric races results'in decreased fitness of the hybrid geno7 types; the .case of Bupalus piniarius Linn., whose northern and southern British races hybridize in : a narrow belt, ' would seem to be an example (Cbckayne 1912). • .A problem which has been hinted at in Section 1.4 is.the predominance of Spruce feeding forms at Hope in ''some years (notably 1957, Crooke and Bevan 1958). and the virtual absence of caterpillars on Spruce but light 'populations on Larch for other years as noted during this study. The charaCteristics of the latter populations and their colour type composition (Tables 29 - 31 and Fig. 33) Would suggest that most of the necessary pre-adaptations for spruce feeding exist as a reservoir in these Larch feeding populations. Possibly the switching of importance from one host-to-an-oth-e-r—is- arbitrated by climatic conditions and the intimate association of Japanese Larch and Sitka Spruce at Hope Forest. A switch from Larch to Pine would certainly seem less likely owing to their dissimilar vegetative phenologios. Consideration must be given to the possible reasons ior gene exchange between otherwise host specific populations. In Section 1.3, populations on Larch and Pine were described as heterogeneous for age distribution, a concept used by Baltensweiler (1966 a) whose work on Swiss populations provides a useful comparison. The results of such heterbgeneity it is 167

suggested might be to buffer the population against environmentally catastrophic effects acting on specific age. intervals and to antennuate the.periods a population will spend.entering and leaving these age intervals. ',_This_impliea.also that populations with fundamentally different phenologies will tend to be represented'in the same stage simultaneously in the field which for the adult populations will mean an increase in the probability of interbreeding and increased gene'exchange. Clearly this will occur to any great extent only in situations where the populations are not widely separated spatially and where preferential mating does not operate. Although this last point has not been tested experimentally, results from Section 1.2.5 and elsewhere would. suggest that successful matings between ecotypes are easily obtained. Age distritnItnii—h-ete-roge-n-eTtywila also decrease the abundance of adults in the field at any particular time which, while decreasing mating success in a population whose sexual encounters depend on non-oriented searching, will not adversely effect Z. diniana females which attract males by pheromonal stimuli (Roelofs, Garde, Benz and Von Salis 1971). Finally, climate and weather may also determine the conditions favourable for the increase of populations on specific host plants or of populations with particular phenological characteristics. In this way the composition of discrete populations may change along with the variable expression of weather. In particular, the 168 effects of excessively warm August temperatures on egg populations, discussed in Section 1.6., will mitigate less against populations on Spruce and Fine. Their later phenologies facilitate the avoidance of possible egg mortality during the later summer. 169

2. A. quantitative assessment of Zeiraphera diniana populations • in the field Field studies of Zeiraphera and the analysis of the major determinants of population change (Auer, 1968) have suffered in-the past-from all-inadequate-knowledge--- of mortality processes operating on uninvestigated'stages during the life cycle (Varley and Gradwell, 1970). A. hitherto unknown process (or processes) appears to be •driving those Alpine population oscillations and emerges as the key factor (sensu Varley and Gradwell, 1960) from a simple analysis. The inclusion of data.-.on variations . in the fecundity of female moths during a. cycle (Baltensweiler, 1968) does not radically alter this. It would- seem, therefore, that two complete life tables, constructed during those two critical years yhen.the magnitude of kr (the rridual k value) ls at its maximum and minimum, would clarify the situation. This is of . course only possible as a result of the regularity of the population oscillations. With the less predictable British populations it is hoped that a description of the mortality processes within a limited number of generations will reveal some- thing of the quantitative differences in population growth between two areas and between these and the cyclic Swiss populations.- It is of great interest to . discover what differences may exist in the predominance of density

related mortality processes iP each area in the way that Whittaker (1971) has compared populations of Neophilaenus 170

spumarius (Homoptera : Cercopidae) in different parts of its range. Klomp (1966) gives a comprehensive example of how life table data may be used in the analysis,of population change for the pine looper (Bupalus piniarius). Like ot4her forest insects Bupalus take-S-the -ideal—subject- for a long term study of this kind owing to the extent and persistance of the forest habitat (Varley, Gradwell and Hassell, 1970. The systematic construction,- preSen- . tation and analysis of life tables for insects'is reviewed by Southwood (1-966). and,HarcoUrt (•1969). • In con unction with the constructiori: of populatign budgets the dispersal of some stages is also described. Since the dispersal of insects within a habitat will both influence and reflect denbity related mortality proces6es and in some cases will determine the magnitude of density unrelated processes, trio investigation of spatial patterns is crucial to an interpretation of the life table dtaa. 171

2.1 The Study Areas

2.1.1. Hope Forest, Derbyshire Chosen for intensive study by virtue of its historical association with g. diniana populations (see section 1.1 and Figure 30), Hope Forest is situated within the Peak District National Park and is characteristically at a •‘.• relatively high altitude and northerly latitude (Figure 1). During .the 1957 outbreak, the most severe and widespread of recent forest problems attributable to this insect; the area within the forest most heavily affected by feed ing larval stages was towards the upper end of the Snake Pass near Lady Clough Moor at an altitude of 1500 feet above sea level. It was here among a compartment of • , Japanese Larch and Sitka 'Spruce that.a sample site of 1,700 m2 was selected: A plan of the site together with some other features is given in Figure 32, and an elevational view from the opposite side of the steep sided valley is shown in Plate 5. A second view at one side of the site illustrates more clearly the terrain and its altitudinal position within the afforested valley, (Plate 6), while the juxtaposition_ of Larch and Spruce in a closed canopy habitat is indicated in Plate 7. Considerable practical difficulties were experienced in sampling in this habitat not least of which were those due to the slope of the ground and the river flowing in the valley; the latter restricted the transport of samples on numerous occasions. Details of the investigations surrouding the 1957 Figure 32. The sampling area at Hope Forest (Derbyshire). Forest limits are indicated by stippling, N the species of trees by letter codes (in text), and the aspect shown in Plate 5. is marked.

100 m

BOUNDARY FENCE

SAMPLING AREA

J L / SS

JL/ SS/ LP PLATE 5

0 0 GH LP CLOU LADY

SNAKE FASS , HOPE FOREST 173

infestation are given by Kirkland and Paramonov, 1957 and. Crooke and Bevan, 1958; it is recorded that Sitka Spruce was particularly severely affected, more so in fact than Japanese Larch (egg counts on winter branches , • - - bear this out, Brown, R. pers. comm.).. The sampling - programme, commenced in 1970 (this work), shows.ilui.:te the .reverse at.a lower population denSiiy, to the extent that . Sitka Spruce was not systeMatically .Sampled,in the study. area on most occasions. Lodgepole pine also odours in • peripheral belts and in:some nearby situations:at-Hope, is inteiTlahted with the other two conifer species; in no instances from 1970-72 were larval stages found on this host. 174

2.1.1. Langdale Forest, Yorkshire Prior to 1970 dangerously high population levels . of Z. diniana were unknown within this.Forest area but during the summer of that year the Forestry.Commission' discovered an infestation covering some 170 acres of. Wykeham High Moor planted with:Lodgepole Pine, •The-: effects of such a population are shown in Plate 8 where. the badly damaged tree in the middle ground contrasts with the relatively unaffected tree i'the.foreground Once again greatest damage was .experienced- at very nearly the highest altitide (750 feet above sea level), and fl- was here that a sampling area of 156,250 m2- was selected. This is shown in Figure 33 and Plate 9 gives an impression of the most southerly side of the plot whereas Plate 10 gives a-general aspect of the surre'Inding forest area from a distance. Within the sample" area the trees.were all Pinus contorta of 'uniform age but variable size and undoubtedly of mixed provenance. Investigations commenced in the autumn of 1970 and continued through 1972,. Surround- ing the Lodgepole Pine compartments were belts of Japanese Larch and adjacent were extensive and more mature compartments of Scots Pine; neither of :Aese conifers showed much evidence of larval populations during this period,

Figure 33 175 The sampling area at Langdale Forest (North Yorkshire). Forest rides are indicated by stippling, N and roads by parallel lines. The aspect shown in Plate 9. is marked.

100m

FOREST RIDES

LP SAMPLING

/\-- LP

PLATE 9

WYKEHAM HIGH MOOR , LANGDALE FOREST 176

2.2 The sampling programme: methods and procedure During the course of its relatively simple 'life cycle, the budmoth may be found in, and moving 'between, three habitat zones; the. non-foliar portion.of the conifer ' _ • canopy (eggs), the foliar canopy (larval stages) and the ground litter layer below the latter.(pupal stage).. . . Except in tne unusual circumstances of complete defoliation where late instar 'larvae may diSperse in search of a/terna-' tive host trees.(Bovey, 1966),.dispersion-Rnd migratory • movement,between forest:areas is a functiOn of•the adult male and female insects: To some extent the appearance. of populations in each zone is attendant upon the weather and the particular species of host plant.- These influence the timing and placement'of each'developmental stage during the-year. With these considerptions in mind a Sampling programme was designed, the aim of Which was to obtain. numerical estimates of- absolute population density, for. as many life stages as possible for the two sampling locations during the period allocated to this study. As is usual with such investigations a number of useful estimates of stage specific mortalities were obtained as a result of the population count.-. The methods employed for each estimate are described and discussed under the following headings.

2.2.1 Direct egg counts Eggs laid by female moths in the late summer and early autumn remain in their oviposition sites until 177

or May of the following year when they hatch. Methods are available for the extraction of eggs from plant surface tissues by washing (Condrashoff,, 1967; ,Retnakaran and French, 1971), but were thought inadequate for the eggs of Z. diniana which are frequently jammed or lodged in crevices or ,ephipytes according to the branch surface topography. It was decided that direct searching of twigs and branches cut into manageable and standard lengths would be. most effective. Low population density of eggs at Hope Forest during the study period meant that no direct count samples were taken here. At Langdale whole branches were taken from selected trees (see 2.2.3), cut into 18 cm. lengths and examined under a binocular, microscope at about x10 magnification. These Pinus contorta branches were mostly fl'uo—or aeafy- lichens, which in any case are best soaked in water first for easier examination (Baltensweiler, pers. comm.). Most eggs were located by teasing back old'bud scales at the nodes or by carefully examining the current years larval "f2assnl. Some eggs were located _between needles at their bases or among the dwarf shoot scales or, rarely, among the scales of a newly formed terminal bud. Distinctions were made between yellow, healthy eggs, those which were partially collapsed (often a result of abiotic mortality) or partially evacuated (the result of predation), those which were parasitized and those which had hatched in the previous generation. All eggs were retained and completed their incubation under standard

1. used here to include silk, exuviae, faeces and uneaten foliage. 178

laboratory conditions; any further mortality could thus be included in the estimate of "unhealthy" eggs. Hand sorting and searching branches in this'way Was time consuming hut.resulted in a highlevel of accuracy which could be roughly checked by re-incubating searched branches and debris and looking for hatched caterpillars during the post-diapause period; few were found.

2.2.2 Estimates of numbers entering the larval 'stage The strongly phototactic behviour:of:neWiy. hatched first inatar caterpillars can be exploited in a number of ways in order to trap and collect them, either under field conditions (see 1.2.2) or in the laboratory with field sampled material. A simply constructed device,.used by Baltensweiler (1964) and called by him a photoeclector, was used to estimate the numbers of eggs hatching on larch and spruce branch samples (Hope) or on pine branch'samples (Langdale). The photoecleetrs (Figure 34) were made from metal 5 gallon containers with lids (Metal Box Co. Ltd.) and were provided with single holes at the lid and base end. The inner surface of each container was painted_ black and allowed to dry thoroughly for several weeks before use. The lid hole was covered with fine cotton gauze and a glass funnel and tube collecting device fixed securely to the basal hole. The container was 2/3 filled with branch material cut into manageable lengths and then stacked along the walls of an outside Figure 34. The photoeclector used for estimates of numbers entering the larval stage. In use the drum contains branch samples cut into manageable lengths. 5 - GALLON DRUM

t:j%iiLIGHT REMOVABLE LI D

COLLECTING TUBE 180

insectary at air temperature. Care was taken to ensure that cireulation of air was maintained behind the containers to inhibit condensation within them and that the collecting end faced a constant light source provided by flourescent tubes. The 3 x 1" tubes were examined each day subsequently and all first instar Z. diniana removed, together with parasitic Hymenoptera and the larval stages of some other Lepidoptera which frequently appeared in samples. Quite often7a single container would accomodate a whole branch sample, but where samples. were larger more than one was used. • To some extent the number of containers available placed an upper limit on the number of samples which could be examined in this way. Branch samples (see' 2.2.3) were taken in the field as soon before hatching in the natural situation could be expected to take place (in most cases_ a few weeks before). The efficiency of the extraction was checked with marked egg batches in normal containers and the hatching rate of these and the actual number of first instars collected were compared afterwards. 1 181

2.2.3 Larval stages sampled on conifer foliage Sampling methods for extensive investigations of larch budmoth populations in the alpine regions of .Europe have.been reported by Kaelin and Auer, 1954, and Auer, 1961 and 1971b. Their procedure involved the direct counting of fourth and fifth instar caterpillars on whole branch samples and this has. essentially been the method adopted here. Techniques involving the chemical knockdown of insects from a sample of conifer foliage, while labour saving, are unlikely to take a sufficiently large proportion of the earlier instars which remain within their foliar gallery feeding sites (Plate 2) and will differentially sample parasitized and unparasitized individuals'of later instars. In fact the characteristic feeding sites on conifers (Escherich, 1931; Bovey, 1966) are distinctive enough to help the search considerably although they may not be used on their - own as a population index, since confusion often arises with the larvae of other Tortricids, particularly Spilonota lariciana common on -Japanese and European Larch throughout Britain. Other indirect methods for estimating Z. diniana larval population density may be useful for extensive studies or at high densities but are likely to be no more than a useful check for life—table studies. They include the collection of falling faecal pellets (examples are discussed by Southwood, 1966) and the measurement of radial increment in stem wood (Mott, Nairn and Cook, 1957) which has been used by Badoux, (1952). 182

The variation in distribution of feeding larvae within a branch of a single tree makes the whole branch a reasonable sampling unit particularly since it represents the. habitat universe of. the insect for more than 10 months of the year. For example on Larch all parts of the branch represent potential sites for developing eggs, although the older (and more proximal) parts .of the branch are preferred. The hatching larvae generally Comiqence feeding On the first available and healthy short shoot with which. they come into contact although as a result of their phototactic behaviour they will move towards the distal' shoots of the branch during their larval lives. Thus, although position within the branch will change throughout metamorphosis, the branch'remains a viable habitat unit from egg to fifth instar larva. Auer (1971b) sampled whole branches within the larch crown and obtained about 7.5 kg of branch material per tree; an estimate of population intensity was then expressed as numbers of caterpillars per 1 kg branch sample.' Auer's trees were, howeVer, several times larger than the larch sampled at Hope Forest and a smaller quantity of foliage per tree was considered appropriate for these investigations. Two or, in some cases, three branches per sample tree were taken, each randomly selected from two (or three) levels in the crown (lower, middle and upper levels) which would then represent any population variation which may exist between them (Baltensweiler, pers. comm.). The uppermost branches and 183

leader shoot were regarded as a single branch which was not sampled to retain the normal growth habit of the tree. Sample trees were selected at random throughout the plot at Hope Forest and up to (but usually less than) 24 samples were taken on any single sampling occasion. Failure to detect an appreciable egg population on Sitka Spruce in the mixed sample stand resulted in few, if any, samples' being taken from year to year,. but when they were taken', sampling followed, the same routine. Estimates of population intensity were finally expressed as numbers of insects per branch sample. The open canopy and different growth form of Finus contorta at Langdale facilitated some modifications to. the branch sampling plan.' Whole branches were necessarily sampled since eggs may be laid in any part-of the canopy. Variation in populations in the upper_ and lower halves of the canopy were accounted for by selecting one branch randomly from each and combining these with similar branches from two other adjacent trees. The final 6 — branch sample represented canopy level differences and variations between adjacent trees. Areas for sampling within the plot were distributed regularly to cover the whole plot but the tree group for sampling was chosen by random pacing within an area. Up to and usually

fewer than 23 6 - branch samples were collected in this way on any single sampling occasion. Distribution of the population within the branch habitat changes radically after hatching from the egg. 1.84

•stage simply because all new foliage, available as food, grows terminally rather than throughout the branch as on Larch. Terminal bud groups alone may therefore be sampled with no fear of missing feeding larval stages ' on other parts-of the branch. Usually bud groups were Selected at random from within a tree and from randomly chosen trees and on some occasions buds were selected in the same way but from 3 adjacent trees as before. :Sampling-equivalents (following section) are given for different sized foliage units so that all estimates of : population intensity are presented as numbers per 6 — branch sample unit. Branches removed from a tree with secateurs or a small saw were cut into convenient lengths for packing into large, reinforced, brown paper bags in the field. Every effort was made to examine samples as soon after collection as possible but where delays were experienced the brown paper prevented undue condensation while remaining more or less insect—proof. Storage at + 5°C during examination kept all material fresh. VisUal searches for caterpillars on foliage samples were relatively simple and assumed to be 100% efficient. All larvae found were labelled and reared to maturity to check for colour type and parasitoids. • 185

2.2.4 Pupal samples There are numerous examples of insect populations whose pupal stages•have'been sampled by trapping them during their movement between habitat zones'(Varley and Gradwell, 1968 Klomp 1966). This is particularly useful in the case of arboreal insects which pupate in the litter layer and soil since a relatively unimpeded journey will take place and rather cumbersome traps may be used just, 'above the litter surfabe. Many Vepidoptera, including Z. diniana, "abseil" from'the foliage on a silk thread and, dropping often from branch to, branch, reach the sub-canopy litter quite directly. Dispersal from the area circumscribing the canopy is. often_ assisted by — strong winds during the descent although the surface area/weight ratio of a final instar caterpillar does. not allow for this to the same extent as for locally dispersing first instar caterpillars or, more graphically, for the analogous dispersal of "ballooning" juvenile spiders. Descending larvae were trapped on the smooth aluminium top of a amUnation larval descent/adult emergence trap (Plate11). The basic design follows that described as the Type 2, metal box by Southwood and Siddorn (1965) with a surface area of 0.42m2 which was coated in the field with 0-sticko, a powerfully retentive grease remaining efficiently sticky for a considerable time under these conditions. Caterpillars falling onto 186

these traps were completely immobilized and predation of the catch was prevented by the addition to the trap of •a raised chicken—wire,mesh. Traps were dispersed regularly throughout the *sample plots at Hope and Langdale but once again, randomly with respect to the position of trees. At Lang- dale caterpillars were caught even in quite open positions where some distance separated the canopies of adjacent trees. whereas at Hope a closed canopy produced a more •homogeneous situation at litter level and more problems: were experienced with the blockage of traps by falling conifer needles. Clearing of traps and re—application of grease was necessary at intervals in all situations since many other insects tended to obscure the trapping surface. In all, up to 25 traps were used-at Langdale and 19 at Hope Forest. Collections from traps were washed in acetone and stored in 70% alcohol for laboratory examination. To confirm estimates of larvae entering the pupal stage and to obtain live pupae; it was possible to take a:limited number of samples of litter to a depth of about 8cm and covering the same area as the combination traps (0.42m2) in both study areas. At Hope, with virtually no ground vegetation, these were relatively easy to collect and to sort by hand but real difficulties were experienced at Langdale where.a thick ground cover of heather (Calluna vuj.garis) prevented easy collection 187

and, more importantly, simple sorting of insects from the stem.and root material. Together with core litter samples they were useful for detecting the relative numbers of caterpillars which had descended for pupation (more fully discussed in 2.4) but gave no indication of relative.rates of predation or losses due to other causes when taken over a limited number of occasions. 188

2.2.5 Adult samples First estimates of adult population density were those given by emergence traps partially described above. 'Emerging adUlts were trapped by their initially photo— tactic movements in the only exit holes of the metal frame.provided with 3 x 1" glass tubes. These contained a cellulose aCetate baffle and were fixed to the frame by a' xylonite mould. It was once more necessary to clear heather at Langdale to ensure a reasonable contact - of the edges of the traprith the ground but at Hope no difficulties were experienced. The traps were moved around as often as possible, particularly in view of their dual function. The collection.of rigorous measurements of adult population density and dispersion (by mark=recapture • methods, for example) was not possible - within the framework of this study. During the daytime adults are relatively inactive resting among the foliage or on branches or twigs where they are cryptic. Their activity increases in twilight conditions when most matings and oviposition take place (Meyer, 1969). When inactive moths are disturbed they will fly short distances or quite commonly drop to the ground or to other branches. By vigorously shaking trees it is possible to obtain an estimate, albeit a very approximate one, of numbers of adults per tree. Clearly separated trees a-6'Langdale proved much easier to sample in this way. 189

Difficulties inevitably arise in accounting for... dispersive movements by adult moths from the sample area and immigration by others. While large scale dispersion will evidently take plaCe in years of peak. population-density (Baltensweiler_and:_YRn Saila,. 19_75)i_ when defoliation levels are relatively low among hobt trees no more than very local movements may be experienced. Thus, while consternation is expresed. at the necessity to assume immigration is equal- to. . emmigration thiS may not be'far. from a real pictue on. the available evidence. 190

2.2.6 Estimates of fertility and fecundity of female moths in the field Oogen:sis and oviposition are dynamic processes the life of female Z. diniana, both reliant on a number of environmental factors, feed-back mechanisms and some mutual interaction (Benz, 1969). They are,: both liable to be variable characteristics under

-natural environmental conditions potentially'responsible for important changes in natality. Attempts were made to measure 'the fertility of mated females in a field cage system where- they were confined on their natural host plant and provided with an adequate supply of 10% sucrose solution. Cylindrical cellulose acetate sleeves, 30 cm long (Plate 12) with fine cotton gauze windows and ends were attached in the manner indicated to-branches:In-- the field. These experimental branches were covered some time before use to ensure that no eggs were laid on them by adults from the natural population. At the beginning of August, 1971 (Langdale) and mid-July, 1971 (Hope), pupae were introduced into.the sleeves in 3 x 1 glass tubes affixed to the upper surface of each cage in a pos1,;ion where they would not collect rainwater. The pupae were obtained from natural populations and one male and one female placed in each cage as soon before eclosion as could be arranged. Some Iangdale cages contained 2 males and females each.' The cages containing dead adults and the branch on which' eggs were laid 191

It/ere returned to the laboratory at the end of September for examination. During the course of the adult flight period at Langdale a series of small random collections of adults were made to determine sex ratio of the population and the proportion of inseminated females. The dead adults were kept in 0.022 M phosphate buffer at pH7$ containing 6.7% formalin and 1% NaC1 (Benz, 1969) until they could be examined. Females were macerated' in warm 10% KOH'fOr. several minutes.and dissected when spermatophores.in the bursa could be counted The number of xipe eggs in' the ovaries wel.e'also counted bUt this yielded a limited amount of information since no previous history of these females had been recorded. 192

2.3 Sampling equivalents Field population estimates in this study were fundamentally of two types; those based on a branch or foliage sample unit and those obtained.from sathples' covering a known area of sub canopy litter.. The former must initially be regarded as an estimate of, population intensity since, over an extended period f. the trees will grow appreciably and the amount of. available habitat will increase: To. be- precise the ' number of branches per tree and numbers af..foliage

shoots per branch'will:inCrease. While Alle'SQ- are - important considerations. for an extended sampling programme the samples here were sufficiently large and taken over a relatively short Period that serious errors were probably not encountered by .conVeiling the. branch sample units to estimates o± population density. To relate all samples to a common unit of absolute population dehsity a serieb. of measurements between and within trees were made in the field. This' also acts as a check. on the . uniformity of samples and helps in the biological interpretation of the sampling results. These estimates are presented in full in. Appendices 4,5,6 and 7 and in som cases the final quantity has been arrived at independently in two-ways for accuracy. The essential equivalents are given in

Table 32. 19'3

Table 32

Equivalent units for branch samples and ground area in the sampling sites

Equivalent Langdale Hope Unit' -. Pinus contorta Larix Picea leptolepis sitchelLsis 2 * 2 ' 2 branch sample 0.43 m 1.45 m 0.47 m * emergence/ 0.98 samples 0.2,9 samples 0.90 samples sticky trap (0.42 m2)

* .6-branch samples

•The differences in sample weights between crown levels are discussed in Appendix 5 in relation to the selection of a sample unit at Hope Forest, and in Appendices 6 and 7 regressions of branch weight on length and on the number of bud-groups-peT-hi-anch given for measurements taken from Iodgepole pine at

Langdale. 194

2.4 The distribution of Z. diniana in the population samples The dispersion pattern of'each of the stages sampled yields valuable ecological information. 'Descriptions of the sampling data are giyen in Appendix 8 where each sampling distribution is compared with either.a Poisson or a negative binomial distribution, and the goodness of fit evaluated with a chi-squared test. Of all the sample sizes and stages tested in this way only a few-do not fit the negative binomial distribution; these are highly contagioub and mathematical descriptions of them t.end towards the logarithmic • series: For the analyses of variance simple logarithmic transformations to the data have been made. The exponent k of the negative binomial in each case furnishes a measure of the degree of clumping or contagion and is calculated fr-em-a---resonably-a,ccurate_ _ _ iterative solution given by Southwood (1966). 195

2.4.1. Changes in values of k throughout the life-history Hope Forest If estimates of k are based on whole branch sample units then it can be seen (Table 33) that in each of the three years. the distribution is progressively less contagious from the egg to pupal stage. This tends towards a Poisson distribution and is indicative of hovement of caterpillars between branches or more intensive losses (2.5.2.) in branches of highest insect density (parasitized individuals are included in all counts and do not, therefore, affect the dispersion pattern). 'Ail values of,l(the mean number' of 'individualS in an aggregation) are greater than 2 for branch samples. Langdale Forest. For terminal bud group samples (1972) the values of k given in Table 33 are fairly uniform... A sample equivalent of 18cm of branch length for the egg stage reveals a dispersion pattern with considerable amounts of clumping and thus the insects distribution changes radically during or shortly after the first larval instar. Following this a less contagious dispersion pattern is established and maintained until larvae leave the tree. Values ofj(Table 33) for terminal bud group samples are all less than 2 and in this case clumping is a result of environmental causes (Southwood, 1966). The clumping produced at oviposition seems to influence dispersal throughout that part of the life history spent on the conifer despite movements of the larval stages. 196

Table 33 Values for the exponent k of the negative binomial distribution for population samples at Hope and Langdale (see Appendix 8)

Single branch samples at Hope Forest. Values of A Olean no. of individuals in an aggregation) are given . in brackets. Samples

eggs mid-insta Idte-instar pupae (per larvae larvae 0.42m2) 1970 0.35 0.99 3.19 1.04 (2.21) (5.36) (3.80) (4.22) ' 1971 1.07 1.42 1.22 58:94' (5.24) (8.24) (7.66) (0.56) 1972 0.96 5.11 (13.4) (23.5)

Terminal bud group samples at Langdale (1972)

first instar mid-instar late instar larvae larvae larvae.. 1 bud group 1:01 2:50 2.23 (0.92) (0.62) (0.32) 5 bud groups . 1.27 2.59 (3.83) (1.46) 15 bud groups 2.82 2.63 (8.80) (4.33)

N.B. The terminal bud group has a branch length equivalent of about 18 cm. Numbers of eggs per 18 cm length follow a highly contagious distribution not described by the negative binothial. 197

2.4.2. Distribution of eggs Oviposition sites Within a foliage—bearing branch the position of eggs seems chiefly to be determined by the presence of fresh conifer needles and_crevices on'the branch or- twig__ surface which allow penetration of the short ovipositor while the egg is laid. An illustration in Meyer (1969 shows the attitude of the ovipositor which results ih. the eggs being concealed from the surface when they are finally depoited. In alpine.larch standS'where atmospheric pollution i6 minimal eggs ar'e usually laid, under growths of the lichen Parmelia aapidota which are particularly profuse on Darts of branches more than 5 years old(Naegeli, 1929; Thomann, 1929; Escherich, . 1931; Bovey, 1966). When epiphyte growth is not as prolifiC on larch, eggs are freoue/i-Gly laid at the base of dwarf shoots (Florov, 1942), the ,recurrent bud scales providing reasonable access to the probing ovipositor. Alternatively, the holes produced in dwarf shoots by mining larvae of Dasy:.eura laricis a..e utilized by the populations studied by Graf (1974'. The sites chosen on Japanese larch at Hope Forest are almost certainly those found to be used most often in'the choice experiments of section 1.5 ; ie. the scaled bases of dwarf shoots and lesions are cracks in the bark of older branches. When provided with thalloid lichens on laboratory branches, eggs will be laid underneath in 198

the same way that most artificial sites will be used; that-is to say egg laying females are relatively .unselective and will use any correctly "textured" surface. Thus, when presented with a variety of potential sites on Lodgepole pine in the field, most will be used to some extent. Figure 9 indicates the distribution of eggs (Langdale', Autumn 1970)1Detween several possible site .and emphasis is placed on the 25% in "frass and Male floWers" in Section'2.5.1. A small percentage were located in the old.bud mines of Rhyacionia buoliana which (like those of D. laricis above) will not enhance the survival chances of the hatching larvae in the following year. The great majority of eggs are laid under scales of the old bud scars. (Plate 13) a location also chosen by populations on Spruce (Pfeffei., 1930; Geller and Theile, 1966). Owing to the heterogeneity of potential sites in. the vicinity of fresh foliage the number of eggs laid together in a single site is not large. The mean number of eggs per batch (where each egg touchesand is cemented to at least one other egg in the group) is given below for the experimental branches (Section 1.5) and the field samples on P. contorta at Langdale.

batch size

Pinus contorta. 4.21 ± 0.36 Picea sitchensis 3.48 ± 0.26 Larix leptolepis 3.90 ± 0.49 Field 1970 3.32 ± 0.26 Field 1971 2.42 ± 0.14 199

Table 34

Analysis of variance for eggs counted on branches, Langdale 1970 a) Sampling unit : Single -branches-sele'cted from either the upper or lower ,crown of randomly.choSen trees.. Source of variation df. SS MS Is - between crown levels 1 0.62 0.62. 1;84 n..s. residual 17 ' '5.74 0..34 .. Total 18 6.36 - •

E0.05 • [1,17]= 4.45 b) Sampling unit* 18cm branch lengths from single branches as above Source of variation cf. SS MS Fs *** between branches 18 9.67- 0.54 3.26 residual 439 72.22. 0.16 Total 457 81.89

• F0.001 [15,120][1 =

* a log10 (x + 1) transformatior has been made on the data for the analysis of variance. •

200

Table 35 Analysis of v-triance for eggs counted on braAches, Iangdale 1971 * - a) --Sampling _unit • 18 cm lengths cut from 6-branch samples (2 branches from each cf 3 trees in a group) Source of variation df SS MS • Fs between groups " 6 1.39 • 0.23, 4.69*** (6-branch, samples) • residual . ' 1240 61.40 *0..05 .

Total 1246 • 62.79 - • F0.001 [6,12 =4.04

b) Sampling unit • 18 cm lengths cut from single branch s-ampies-rand-omly-Eeleated from trees Source of variation df SS MS Fs *** between branch 8 4.12 0.51 5.84 --+ samples - residual 176 15.50 0.09 Total 184 : 19.62 •

F0.001 [8,120] '3 '55

* a log10 (x + 1) transformation of the data has been made for the analysis of variance. 201

:Table 36 Analysis of variance for egg_iphotoeclector) samples from Hope, 1971 •* Sample unit Single branches from each of 3 crown levels (upper, middle and lower) in randomly selected Larch trees. Source of variation df, SS MS Fs Between trees 8 0.47 0.06 0.62 n.s. Between levels .2 0.60 0.30 3.23 n.s. within -trees • . . Residual 16 1..50 0.09 Total 26 2.57 59 F0.05 [8,16 =2.

F0.05 12,163=3.63

* a log10 (x + 1) transformation has been made to the data for the analysis of variance. 202

This confirms the observations of other authors on egg batch size of between 1 - 4 eggs on Larch and Spruce. However, this tends to obscure the fact that egg distribution on Pine is still highly clumped when a small sampling.unit (18cm branch length) is taken (Appeidix 8);. even larger units (2 and 6-branch samples) give strongly contagious results. An explanation probably lies in the fact that a single female moth will lay a-large number of eggs in a small branch length Provided that.she has foUnd an initially productive searching area. Variation between larger sample units The analyses of variance for egg samples show consistantly large components of variation between branches (Table 34b; Table 35b) at Langdale. There is, however, no significant variation between crown levels either at Langdale (Table 34a, upper and lower halves of crown) or at Hope (Table 36, upper, middle and lower sections of crown). This is less surprising at Hope where amounts of available foliage/branch in each level are probably similar (see note in Appendix 5). At Langdale the weights of foliage bearing branches are significantly different between levels but once again the amount of foliage per branch weight is proportionately greater for higher branChes. This leads to the situation described in Appendix 9 where there is a significant negative regression of eggs per 100gm branch weight on total branch weight. It would seem that the •

203

number of eggs laid bears a greater relationship to amounts of fresh foliage than to other parameters of branch size. Unfortunately the regression of Appendix 9 does not hold true for Appendix 10 where.the total. weight of the branch does not influence egg density. (eggs/100 gm). Significant variation between groups of trees • (6—branch samples). is only found on one occasion (Table 35a) at Langdale and in 1972 the variation component between these units is not significant . (Table 37).

Table 37 Analysis of variance for egg_lphotoeclector) samples from Langdale 1972

Sampling unit* • 2 branches, one from the upper half • of the crown and one from the lower ha:'_f, from each of„ 3 adjacent trees (group) for 20 groups Source of variation df SS ' MS •Fs between groups 19 5.02 0.26 1.01 n.s. of trees within groups 40 10.42 0.26 (between trees)

Total 59 15.45 70.05 0140] =1.84

* a log10 (x + 1) transformation has been made on the data for the analysis of variance. 204

2.4.3.Distribution of larvae The distribution of larval stages in the population samples is still very much product of adult disperSal and oviposition behaviour in the previous generation,. . despite the dispersal of freshly eclosed larvae in the spring. This is quite significant since it means that - - high levels of intra-specific competition will be, involved '

before larval density reaches . a point 14herer defoliation and consequent food shortage, is experience.d. -It. is.• . nevertheless likely that a more regular aarval dist;ci,bution;. will be asaumed- at higher population .density. • T,To analyses of variance are given for bud samples taken at Langdale in June and July 1972. The earlier instar samples (Table 38) show a highly significant variance component among trees within tree groups. Tlis may once again reflect the selective nature of moth oviposition or result from particularly- high larval mortalities on certain trees; perhaps the bud phenologies of certain provenance types are :,mportant here., No significant variation can be located either azong tree groups or within groups in the later larval sample (Table 39). 205

Table 38 Analysis of variance for larval samples (June 1972) at Langdale

Sample unit _Single terminal budgroupS.-r- 5 taken sat__ ,_ random from each of 3 adjacent trees.

Repeated for 24. tree• groups. Source of variation df SS MS. - Fs- Among,tree groups 23. 1.13- 0.05: 1.29 n, s-, Among trees (within . 4E '1.84 Y 0'..04 2.34- tree groUps) • :: within trees ' 288 4.71 0.02. . . Total 359 7.69 F0.05 [24,120] =1.61

F0.05 [24,0(2 =1.54

.001 [50,12g=2.02-

* a log 10 (x 4. 1) trainsformationhas been made to the data for the analysis of variance. , . 206

Table 39 Analysis of'-variance for larval samples (July 1971) 'atlangdale

-;Sample ,nits Single terminal bud groups. 5 taken at random from each of 3'adjacent trees. Repeated for 24 tree groups..

Source of variation df SS MS Fs Among tree groups 17 0.37 . 0.02 1.63 n.s. Ambng trees .(within :36 0.48 , 0:01 • 1.31 n.s.' tree groups) . . . within trees 216 2.21 0.01 Total 269 3.06 0.05 171,0q=1.67

0.05 [40,00r1 '39

* a log10 (x + 1) transformation has been made to the data for the analysis of 'variance. 207

2.4.4. distribution of pupae Zeiraphera diniana is said to leave the conifer foliage during the last larval instar and to pupate in the surface litterlayer after first burying itself and spinnirig a silken cocoon among the debris (Bovey, 1966). -Several accounts indicate that pupation will, on occasion, take place before this. Schimitschek and Jahn (1952) write that' very warm and dry weather in 1947' lead to acceleratedlarval development and many, pupated'among the. foliage bearing larch twigs in the. North Tirol of Austria:• 'fqacBougal (1922) found that pupae occurred quite commonly at the feeding sites on young pine shoots. A superficial population survey, in particular one at high population density, will tend to overestimate.the numbers staying in the tree. since parasitized caterpillars become progressively more lethargic but may still complete- their development within their feeding sites. Exceptionally, parasitoids may attack a larva late enough that its activities up to the pre-pupal stage are not noticably altered and a large proportion of parasitized larvae will consequently fall to the ground in the normal way; Phytodietus griseanae Kerr. is an. example of this (Figure 39). Apart from parasitism, other factors seem to be responsible for a significant proportion of pupae which remain in the foliage. Since temperature has already been mentioned as a possible influence, a simple 208

experiment was arranged to test,this. A set of 16 cylinder cages were erected, each containing a .vertically placed conifer twig (20 - 30cms high) .kept fresh with a water reservoir and d base layer of the appropriate conifer needle litter. A small •, 'number of these cages contained P. contorta twigs and the rest L. leptolepis, and each conifer was represented at least once at each of 5 temperatures. Between and.1Ofinal instar larvae from the Langdale FOrest population were 'introdUced ,brito the, conifer foliage and they were then left atthe assigned temperatures until they had.pupated. The results for the pupation sites of each group are presented in Table 40. Pupation site in the Larch cages was found to be

not independent of temperature (G-Test) although the greatest effect was at 5°C where 7 out of 9 larvae (63%) pupated in the foliage. Other temperatures did not contribute- to significant differences in the location of the pupatiOn- site (two sub-sets of data were tested for independence and the G-values were not significant; Table 40). Overall, however, about 20% pupated fa the foliage. Homogeneous results were obtained at the 5 temperatures using Pine and overall 16% pupated in the foliage. These results do not reveal any particular influence of high temperature but suggest that at "normal" field temperatures (eg. 15°C and 20°C) between 5 and 10% will pupate in foliage. In the field (Langdale, 1971) two independent Table 40 The number of final instar larvae choosing to pupate in litter or in the host plant foliage at 5 temperatures and for 2 host plants. .(Tests of independence of pupation site and temperature are given).

Host plant: Pinus contorta Pupation site proportion in Temperature°c Litter Foliage litter. (p)

5 7 2 0.78 15 8 1 0.89 20 9 1 0.90 25 7 0 1.00 3o 11 7 0.61 +. G = 7.78 (4d.f.) not signif5lar,t • = 9.488 'X0.0510.05[4]

Larix leptolepis • o Pupation site proportion in Temperature c Litter Foliage in litter. (p) 5 7 12 0.37 15 12 1- 0.95 set 2/ set 1 20 18 2 . 0.90 25 20 0 '1.00 30 13 5 0.72 G = 31.48 (4d.f.) *** (G for overall heterogeneity) 2 = 14.86 X0.005 1.4j 1 = 2.876 not significant (G for heterogeneity computed from set 1 in Table)

2 = 9.488 -1.0.05 [4] G2 = 4.683 not significant (G for heterogeneity computed from set 2 in Table)

+ Test of independence using the 0 7 test (Sakai and Rohlf, 1969) 210

estimates were obtained; branch samples and sticky trap catches (Figure 39) show that 10.6% of the. total healthy larvae remain in their feeding sites. Using core auger samples of litter and 'soilyand branch samples for'a single tree it was estimated that 2.5% of the pupae will be..located.in the faTiage: A tenflancy to avoid leaving the tree will be of considerable adaptive significance.to-a. population . . which:incurs. regular and high losses of pre-pupae and. pupae in wet litter conditions '(Section2..5.5).. ..These. advantages hast,.ine.volutionary terms, be offset against the disadvantages of intolerable temperature conditions above ground level and the possibilities of predation by birds during the 3 week pupal period. No clear conclusion may be drawn without.further information on the vertical distribution oT pupae and their mortality rates.

'1* 211 2.5. Thr Population Budgets The successive population estimates, adjusted to standard sample sizes are given in-Table 41. Age specific mortalities given within these population budgets are -discussed below under their separate categories.. _2.5.1.: Eggs_ Unfortunately the nature of the sampling programme at Hope Forest did not: permit the separate estimation of egg mortality and some variations in natality under field conditions is obtained from the' live,eggs present at eclosion. Together these values'are' amongst. the highest Mortalities (and.largeet k-values) tor both the 1970-71 and 1971-72 generations where they represent 63 and 53% of the population respectively. Of course there is no way of knowing what proportion of these figures is and attributable to knat. keggs. Far greater detail on egg mo-rtality---is--f-orthc-amin-g-____ at Langdale where egg mortality represented 60% of the population in 1970-71 and 70% in 1971-72. Four identifiable mortality components are present which take — their effects prior to the date. of egg sampling in October and these will be discussed in turn.

(a) Eggs laid in frass The term frass commonly, but inaccurately used to denote the faeces of insects (Southwood, 1966) is coined here as a collective description for the defaecatorY products, the damaged parts of needles and male cones, and the exuviae which are generally attached to the host plant by larval silk. A proportion of the frass remains on the tree during the time fecund females are searching for suitable oviposition sites; indeed, a significant proportion of the total eggs laid seems to be deposited amongst the fra,2s- (25% 1970-71, 13% 1971-72) (see Plate 14).

Table 41 Langdale 1970-71 Population budget

x lx dx dx F I k age or developmental nos. alive per number dying cause of mortality .log161xi- log10 h1.0 stage of population sample unit during age interval eggs (post-oviposition) 375 96 eggs laid in "frase H' 0.1284 eggs 279 28 Trichogramma evanescens 0.0459 eggs (post-parasitism) 251 41.8 predators 0.0798 eggs (post-predation) 209.2 17.2 late summen'abiotic 0.0368 mortality eggs 192.0 41.0 ' residual (additional' 0.1043 mortality overwinter) eggs (at eclosion) 151.0a 125.1 i loss of early instar ' 0.7657 larvae 3rd and 4th instar ' 25.9 larvae 4.5; loss of late instar 0.0829 larvae larvae (pre-pupation) 21.4 .

1. "frass" : excreta, exuviae, silk, damaged needles etc. lost from tree overwinter.. a. corrected for efficiency of trapping. Langdale 1971 Population budget

x lx dx (13i age or developmental nos. alive per number dying cause of mortality - • log 0. 1x.- i log. IK stage of populations sample unit during age interval 10 i+1 3.7 larval parasitoids 010824 (various Species) Larvae (post-parabitism, 17.70 various) 3.75 Meteorus ictericus .0.1034 Larvae 13.95 7.19 Phytodietus griseanae 0.3146 Larvae 6.76 0.44 Virus diSease 0.0292 pupating larvae 6.32 3.32 pupal mortality 0.3236 adults 3.00 Langdale 1971-72 Population budget

x lx dx dx F. age or developmental nos. alive per number dying cause of.mortality 1°g101;c1.+1 stage of population sample unit during age interval

eggs (max. potential natality) adults x prop. females 329 x max. fertility x prop. fertilized 160.7 failure to achieve' - 0.2924 max. natality • eggs (estimated 167.8 ' realized natality) . . 36.3 other variations, • 0.1059 in natality and . error eggs, (post-oviposition) 131.5 16.8 eggs laid- in "frass".. 0.0594 and lost overwinter eggs 114.7 29.1 Trichogl'amma evanescens . 0.1270 eggs (post-parasitism) 85.61 3.3 predators 0.0171 eggs (post-predation) 82.3 '19.0 late summer abiotic -0.1140 mortality eggs 63.3 23.5 residual (additional ,0.2015 mortality overwinter). eggs (at eclosion) 39.8a

a. adjusted for efficiency bf trapping Langdale 1972 Population budget

x lx dx .dx F k cause of-mortality log lx age or developmental nos. alive per number dying 10 i7 log10lxi+1 stage of population sample unit during age interval

1st instar larvae 45.9 (39.8)e 3rd and 4th instar 41.1 larvae 28.10 loss of late instar 0.4999 larvae . 5th instar larvae 13.0 and pupae ri 0.50 larval parasitoids 0.0170 (various) Larvae (post-parasitism) 12.5 - various 1.49 Meteorus ic.tericus• 0.0551 Larvae 11.01.. . • 7.40 Phytodietus griseanae o.46og- Larvae 3.81 0.50 virus disease. . Pupating larvae 303 e. previous stage estimate

Hope 1970 Population budget •

x lx dx dx..F • k

age or developmental nos. alive per number dying cause of mortality lx.- log ix. , stage of population sample unit during age interval •log10 . i 10 1-1-]

eggs (ateclosion) 1.09a 0 0

3rd and 4th instar 1.80 larvae 0.08 loss 0.0198 4th and 5th instar 1.72 larvae

0.53 parasitoids • 0.1600 4th and 5th instar 1.19 . larvae 0.60 loss 0.3047 bc pupae (in litter 0.59 and branch) 0.22 . pupae dying. in litter 0.2027. - 13 adults emerging from 0.37 pupae 0.17 adults lost on emergence 0.2672

adults emerging from litter 0.20 (and branches)

a. corrected for efficiency of trapping b. litter samples corrected for estimated population pupating in branches and c, those already parasitized. Hope 1970-71 Population budget x lx dx dx 1-1 * age or developmental nos. alive per number dying cause ofmortality logiolxi - log lxi+1 stage of population sample unit during age interval 10 eggs (maximum) potential natality) adults x proportion females x max. fertility) 23.89 13.33 failure to achieve Max. • 0.3546 natality eggs (estimated 10.56 - realised natality) 6.69 other variations in 0.4360 natality and egg — mortality - : eggs (at eclosion) 3.87a 0.79 loss 0.0992 3rd and 4th instar 3,08 . larvae N,• 0.37 loss 0.0556• 2.71 4th and 5th instar , • larvae 0.28 •parasitoids' . H0.0474 - 4th and 5th instar 2.43 1 larvae 1 • 0.66 loss ' 0.1376 • pupating larvae 1.77 1.26 pupae dying in litter • 10.5404 • and on emergenc-e. . b • 9 • adults emerging from 0.51 • litter and branches a. corrected for efficiency of trapping b. corrected for 6% pupating in :branches

Hope 1971-72 Population budget dx dx F • k

age• or developmental nos. alive per number dying cause of mortality stage of population sample unit during age interval logiolxi- 1°g101xi+1

eggs (max. potential 46.16 natality) 25.76 failure to achieve 0.3546 max. fertility, eggs (estimated d• 20.40 realised natality) 10.7, other variations in , 0.3269 natality and. egg mortality eggs (at eclosion) 9.61a 0 4th and 5th instar 13.38 larvae 0.54 parasitoids and i.0.0178. virus r I . 4th and 5th instar 12.84 :. larvae

a. corrected for efficiency of trapping d. max. fertility (181 eggs / + ) and mean fertility (80 eggs / ) estimates.s'aMe.as for,1970-71 . . 219

Because the connection to the host plant is tenuous, most if not all eggs laid here are lost during windy and stormy weather while they diapause fox the winter. On the assumption that eggs on the ground produce caterpillars which are unable tolocate a- neW:- pine shoot in the spring, this represents an Unavoidable mortality. An interesting dynamic' interaction between . the numbers of eggs laid in frass (Ef) and-the quantity of frass(ordamage), (F) is likely, At low le'vels'Of. larval density- Ef. will .probably be proportional to F . or to the tctal number of eggs laid,-Et. :When larval damage is severe, however, female moths will tend to avoid those shoots with few fresh needles (see Benz, 1969) and Ef will be inversely proportional.to F. (b) Parasites A considerable a,ifount of attenticn has been paid in the literature to egg parasitoid, of the genus Trichogramma (Hymenoptera: Trichogrammatidae) which have been seen as potential agents of biological control for many crop pests in agricultural'gituations (Scepetil nikova, 1970). The taxonomy of the Mid European species is reviewed by Hochmut and Martirek (1963) and Scepetil nikova (1970) points to the existance of many ecotypes and sub-specific races of the common species. Both authors indicate that at least three species cacoeciae pini ; T. cacoeciae nallida and T. embryophagum) are commonly parasites within coniferous forest habitats where there is often a preferred 220

searching stratum for each species (also Flanders, 1937a). Curiously, none of these are known to _parasitize the eggs of Z. diniana and at Langdale it is T. evanescens Westw. which is found on Lodgepole Pine; 'in Continental Europe, according to Hochmut and Martinek (1963),.this IS more commonly associated with "field

zootopes". ".Eggs parasitized by TrichograMma ara easy to recognise. A colour change occurs in the vitelline 'Membrane 'of the host and is due to minute dark granules deposited during the 'preiapal stage of the parasite (Clausen, 1962); this is illustrated in Plate 14. The chorion is translucent and the dark colour which remains after the emergence of the adult parasitoid, is easily seen. From Norway comes an odd description of Z. diniana eggs (Bakke, 1969) which from their colour- must surely have been hosting parasites although none were reared. Baltensweiler (1958) names T. evanescens as an egg •parasite of Z. diniana on Alpine Larch and Graf (1974) notes the same species on the Swiss platea area and again in the Upper Engadin: From Graf's work apparent rates of parasitism were:— Lenzburg 1970 . 0.8% 1971 2.0% U. Engadin 1969 0.6% 1971 3.8% Eggs used for these estimations were generated by laboratory populations and placed in natural field 221

situations but (possibly) at artificial densities. This may have jeopardized the reliability of the data gained since the proportion parasitized is closely related to egg density in samples within the same area; Figure 35 -(and - Appendix 11)- illustrates- this-paint'for • the 1971 Langdale egg population. At.the egg batch.' level of density (see Section 2.4.1)- this relati.onShip is no longer statiSticadly zignificant-(Figure 36 and Appendix 12). . The explanation fo/, thiP will beilf.the aggrega-. -tion of searching parasites in areas.of'high'host density. Lewis et al. (1972) have recently demonstrated that scales left by ovipositing moths are the source of a host- seeking stimulant in T. evanescens. The active material is hexane soluble, seems to be widely distributed among Lepidopterous species Lnd may with further research emerge as a universal attractant foa. this parasite. Egg-laying moths deposit liberal quantities of scales in areas where . they are ovipositing (eg. Figure 35), but will not necessarily ICeave more scale's where More eggs are laid in a batch (eg. Figure 36). The population budgets show that rates of parasitism for.eggs at Langdale were much higher than previously recorded for Z. diniana:- 1970-71 10.0% 1971-72 25.3% There were no significant differences between rates of parasitism in different oviposition sites. Aside from the 222 Figures 35 and 36. Parasitism by Trichogramma evanescens in egg samples (eggs per 6-branch unit) and in egg batches at Langdale, 1971.

.F:G 35

100 300 500 EGGS PER SAMPLE • SM TI SI FIG. 36

PARA O

- 0 R =0.31

1 5 10 EGGS PER BATCH Figure 37. Histograms for the numbers of adult Trichoerammaevanescens trapped from branch. samples (Langdale).

10- 1971 TS ADUL ED PP n TRA 1972 OF 10-1

CY EN FREQU

1 5 10 15 20 25 MAY

t DATE AT WHICH 50°/o OF THE HOST EGGS HAVE HATCHED 224 density of host eggs, probably the greatest contributory factor inducing high levels of parasitism is the provision of alternative hOste for summer and perhaps late autumn parasite generations., There is no indication which hosts T. evanescens might be using at Langdale although multivoltinism•of parasites reared from sampled eggs seems Oertain. The' dates of.emergence of adult T. evanescens from. the photoeciector traps are given in Figure 37. This,implies'that alternative host species will be sought after'this spring emergence for an unknown number of parasite generations. Budmoth eggs will be available once more from the late summer but, by then, parasite population density will have been determined by the abundance of other, principally Lepidopterous, eggs. . (c) Predators The only detailed study of biotic mortality factors in field populations of Z. diniana eggs, (Graf, 1974) gives predators a prominent place in the population budget. At Lenzburg 70% (1970/71) and 87% (1971/72) of the eggs were eaten in successive years by predators, chiefly'the Mirid, Deraecoris annulipes H.S. and Neuropteran larvae. At Langdale the predation rates of eggs' ("after" the effects of parasitism) were:-

1970-71 16.7% 1971-72 3.9% No predators were identified here, although the common earwig Forficula auricularia abundant in the branches during the autumn, will certainly eat budmoth eggs in 225

the laboratory. It is interesting that Graf (1974) •shows that by far the greatest proportion of total . predation takes place before the early Autumn and in 1971 78% of the eggs are eaten before the end of • August. The later overall phenology of Z. diniana on pine may well assist in lowering predation rates. (d) Abiotic mortality. It, was possible to'estimate mortality caused by abiotic factors .up to the time of sampling by incubating, •, the sampled eggs for aai optimal 180 days at +2°C and realising the proportion 'cif eggs failing to develop subsequently. Including collapsed.(but fertile and unpredated) eggs in this category the mortalities at Langdale were:- 1970 8.2% 1971 23.1% • Considering that a small percentage will probably die even under optimal laboratory incubation conditions, . these proportions are relatively small. Graf (1974) finds about 10% mortality, for eggs experiencing normal temperature conditions in the field (an average for 3 years) and very little of this is due to summer/autumn • deaths. In Section 1.6.2. the resistance of eggs to high pre-diapause temperature was found to be good so that for these two years at least, autumn mortality remains minimal. A further 21% (1970-71) and 37% (1971-72) egg mortality includes sampling error and other egg mortalities from October until April. These values are essentially residual differences between egg counts and photoeclector catches and may comprise error terms for both sets of samples. 226

2.5.2. Loss of larval stages from the population The disappearance of larvae from the population seems to be of major importance. At Langdale reductions in the size of the population between samples constituted the largest k—values for both year of—iriVest-igati-o-n: and — at Hope a single loss is the largest k—value for 1970: losses may take place at. any time between the: first and fifth larval stage. ,In.1970 at Hope and 1972 at Langdale .zero.losSes in the first and seeend.instars are folloWed by large losses in th later larval stages (Hope k=0.09) during the later stages. There are likely. to be • losses of quite different kinds during the larval stages; the disappearance of first instar larvae may be .through an inability to establish feeding sites on new foliage (Sections 1.1.2 and 1.'L..6)- or mortality induced by mutual interference. and effected though increased motor activity and dispersal from host plants. The latter may also apply to the larger caterpillars which in turn may be the subject of predation by birds. Birds are mentioned as predators of Lepidoptera in pinewoods by Tinbergen (1960) and Gage et al. (1970) describe the predation of the black—headed budworm in Canada. In addition, spiders commonly predate populations of Spruce budworm (Loughton et al., 1963; Renault and Miller, 1972). A large number of predators are known to take Z. diniana although most accounts of their activities relate to high budmoth population

Figure

k-VALUESFOR LARVAL LOSSES/ 38. 0.7 - 0.5 - 0.5- 0.3- 0.3- 0.1- 0.1 - k-values forlarvallossesplottedagainstthelogpopulationdensities onwhichtheseact.

0 LATE INSTARDISAPPEARANCE LOG. LARVAL POPULATION DENSITY d5 EARLY INSTARDISAPPEARANCE G5 0

0 r 1:0 1.0 r

,,,1 r • 1:5 1.5

I •

PER FOLIAGE UNIT 20 0 HOPE • LANGDALE • 228

densities. Of particular note is predation by birds .(Pfeffer, 1930: Florov, 1942; Bovey, 1956; Escherich, -1931) and - ants (Thomann, 1929; Bovey 1966), whereas numerous other authors indicate the importance of Staphylinids, Carabids, Coccinellids and Syrphids in reducing the host population. It would indeed by surprising if larval losses due to mutual interference and. predators were not density dependent particularly in the higher ranges of larval density. In Figure 38-the k-values for. early and late larval loss are plotted against the log population densities on which they act. The limited data (which are from different habitats at Hope and Langdale) give no conclusive evidence of density - dependence although the trend at Langdale suggests this. The coincidence problems of first instar larvae, discussed more fully in previous sections, will tend to impose themselves as density independent mortalities •and may obscure biotic mortalities at lower population levels. In fact the low k-values for early instar disappearance at Hope in all three years_seem to indicate that larval coincidence with the flushing needles of Larch was good enough (c.f. Section 1..2.6) although one is reminded of how much more critical mortalities may be in an unusual year at Hope than in the sub alpine regions of Europe or even on the Swiss plateau (Graf , 1974). 229

2.5.3. Larval parasitoids In common with the parasitoids of many . other economically important insects, the,parasitoids.of Z. diniana have received mention in the - literature disproportionate to their rank among the mortality processes collectively responsible for. generation' mortality aid perhaps. also to their Status as' agencies' of regulation. Lists of parasites from.throughout Europe- are given by Prell (1930), Pfeffer.(1930), Florov (1942),-ThOmpson.(1947), - Jahn (1958).and. Rohzkov (1960. while an extensive treatise on -the parasitoid complex in Switzerland is given by Baltensweiler (1958). Taxonomic works include those of Graham (1959), Kerrich (1962),. Aubert (1966), Askew (1968) and Aeschlimann (1969), who also reviews some aspects of the e..-:ology of the Eulophids; Gerig (1960) describes the immature stage'', of a number of parasitoid species. Auer (1968) points to the larval parasitoid complex of the strongly oscillating alpine populations as a key factor (sensu Morris 1963). generating population change. Using their own analysis, Varley and Gradwell (1970) show that parasitoids are not chiefly responsible for changes in generation mortality; instead they appear to act in a delayed density • dependent manner and this appearance is in part the result of the cyclic nature of the key factor (when the conventional tests, Varley and Gradwell 1968,

Figure 39. The fate of larvae in samples at Langdale, 1971. Sampling data is from foliage samples (FOLIAGE), litter samples (LITTER) and sticky traps (TRAPS). FOLIAGE LEGEND: 25.86 JMETEORUSI 12.241 3.75 METEORUS - Meteorus ictericus PARAS. 1.75 4.14 PHYTODIETUS - Phytodietus griseanae IPHYTODIETUSI-10.501 7.19 PARAS. - other parasitoids. [HEALTHYI 21.37 16.331 V VIRUS - Virus disease. 'LOST HEALTHY - not affected by above.

RDUAGE 4.45 121 41]

LITTER

PHYTODIETUSI

PHYTODIETUSI 15.64

Figure 40. The fate of larvae in samples at Langdale, 1972. Legend as for Figure 39. FOLIAGE 41.1

1-179S-71- 117.55

M ETEORUS I 39 PARAS. 11.401 TRAPS FOLIAGE 3.82 119.73 PHYTODIETUSI 9.45 HEALTHY 7.50 PHYTODIETU 2.18 LOST

'HEALTHY' 11. 64 1Q55

TRAPS FOLIAGE 1.45 7.73

PHYTODI ETUSH 0.77 -H HEALTHY 0.681 0.50

HEALTHY 1.83

PARA S.+ 0.491 ME TEORUS 0.50 PARAS. Table 42 Parasitoids of Zeiraphera diniana larval and pupal stages in Britain

Z. diniana identified as a host . -a Britain Hope Forest Langdale Forest Burford pre-1969 197,0- 1971- 1970- Ichneumonidae Pimplinae Ephialtes ( =Scambus) eucosmidarum P. * Scambus linearis, Ratz. N Ratz.atz. species Pimpla turionellae L. Pimplopterus species * 11, Itoplectis alternans Gray. var. kplthoffi Auriv. maculator Fabr. Ichneumoninae Phaeogenes osculator Thb. species :•■ Tryphoninae Phytodietus griseanae Kerr. Banchinae Lissonota transversa Bridg. Table 42 continued.

Metopiinae Triclistus * -codagricus Gray. Hemitelinae Thysiotorus N thom-csoni Kerr. Ophioninae N Blaptocampus nigricornis Wesm. ND Campoplex N faunus Gray. tumidulus Gray. species A * species B Nythobia species , -*+

Braconidae Apanteles jucundus Marshall * lineipes Wesm. r-- Eubadizon extensor (L.) Meteorus ictericus (Nees.) *N pallidipes Wesm. *7 Oncophanes minutus Wesm. Table 42 continued.

Eulophidae Cirrospilus pictus Nees Elachertus isadas Walker

Pteromalidae Habrocytus semotus (Walker)

a from Kirkland and Paramonov (1957), and Bevaiii (1968, pers. comm.) b and c population samples on Larch (b) and Pine!(c) d larval samples only

N a new host record

also a parasite of Spilonota lariciana (Lepihoptera:Tortricidae) x also a parasite of Rhyacionia buoliana Schifr. (LeP.:Tortricidae) '

* present

numerous 235

are used). B,altensweiler (1958) describes the biology of seven of the most important parasites (all .'HYmenoptera excentina T.ypha dubia Fall., a Tachinid fly) and has shown that a."gradolological sequence" of abundance occurs throughout a single host population cycle. The most important single parasitoid, Phytodietus griseanae Kerr. (Kerrich, 1962) is abundant early in the "regression Phase whereas the Eulo- phids:(Aeschlimann, 1969)-become.increasingly abundant subsequently. A complete account.ofihe parasites reared to maturity from sampled larvae and pupae at Langdale and •Hope is given in Appendices 13 to 15. From the respective larval populations the following- percentages were to be consumed by parasitoids:— Hope 30% (1970) 11% (1971) 3% (1972) ' Langdale 57% (1971) 22% (1972) The k—values for parasites are given in the Topulation budgets where the greatest single contribution from a' parasitoid is that of Phytodietus griseanae Kerr. This has not previously been identified from Z. diniana populations but was almost certainly the Ichneumonid so prevalent at Hope in 1957 (Crooke and Bevan, 1958). Very few were found at Hope from 1969-1972 (low host population densities) but large numbers parasitized hosts at Langdale from 1971-72 (higher densities) in accord with the aforementioned gradological sequence and the knowledge the P. griseanae is a monophagous 236 Figure 41. The dispersion of Phytodietus griseanae Kerr. on larval hosts with 1, 2 or 3 eggs per host. The area of black discs is proportional to the % frequency of eggs in those positions for each category of superparasitism.

PARASITOID r EGGS PER LARVA 1 2 3

0 1 2 3 4 EGGS 289 156 38 10 3 FREQUENCY OF HOSTS

N.B. Eggs are recorded in each of 4 positions for a segment. These are dorsal, ventral left and right; the latter two are averaged and only the right side shown above. 237

.parasitoid of the budmoth on Larch and Pine (Baltensweiler, 1958). The extent of superparasitisrn and the position of eggs of P..griseanae on hosts at Langdale (1971) was chebked for all routine late instar samples. The results are displayed in Figure 41. Each host body segment is regarded, for the purpbses of recording, as a,cylinder Whose. surface may be divided into four equal areas, dorsal ventral, left and right. The positions of all parasites on each .host. caterpillar Were noted in . this way. In Figure 41 only the right side of each segment is represented since the results are not significantly different from the left, and eggs in each position are shown as a proportion of the total. Baltensweiler and Moreau (1957) have shown that localization of eggs to the first 3 (thoracic) segments ' is characteristic of the genus Phytodietus and that P. griseanae (= their sp. A) usually restricts oviposition_ to the dorsal (rather--than the ventral) half of segments II and III. Results from Figure 41 indicate that 64% of eggs on uniparacitized hosts are laid on either the left or right side of segment II and 20% are laid in similar positions on segment III. With the results of Baltensweiler and Moreau (1957) in mind it may be said. more exactly that a large majority of eggs are localized on the dorso—lateral margins of"these two

segmen ts. Superparasitized hosts show egg distributions with far greater posterior displacement (2 and 3 eggs. 238

Per host) to the first two abdominal segments (Figure 41). Many Hymenopterous parasitoids are able to prevent superparasitism altogether by avoiding already parasitized hosts. If it is assumed that P. griseanae lays no more than a.single egg per encounter with a caterpillar and. tends to avoid superparasitism the frequency distribution for numbers.of parasite eggs per hOst should:differ significantly from a Poisson distribution. A goodness of fit test, for this. data • fails to show a statistically significant difference

from a PoiSson distribution. ( (3d.f.) = 3.66) . and it may be assumed that.female parasitoids are laying their eggs randomly throughout the cater: pillar population. Since an ovipositing female can obviously detect an egg previously laid and only'a single parasitoid can complete its de-velopment on the Z. diniana larva, this would appear to be an odd phenomenon. If, however, A female lays more than one egg per host at a single encounter and yet avoids superparasitism if hers is. not the first egg, an apparently random distribution of parasites among hosts may arise. ThiS seems unlikely when only two eggs per day are laid in laboratory culture (Baltensweiler, 1958). A second possibility has greater credence. If a proportion of the host population remains unavailable to Phytodietus through better defensive behaviour, concealment or by virtue 239,

of population age distribution heterogeneity (Section 1.3) which affects coincidence with the parasite, a similar distribution will result. The second most prolific parasitoid at Langdale and most important at Hope was the Braconid, Meteorus icteTicus (Nees). This highly polyphagous species (Hezlett, 1974) has been previously recorded from Z. diniana at Hope (Table 42) but is not mentioned from this host elsewhere in Europe. Few Braconids are featured in the Swiss Alpine parasite'.complex (Baltensweiler, 1958) and no species1' occupies a primary position amongst those which are the most important natural enemies of the Larch budmoth. Perhaps because of its polyphagy it remains effective in low density host populations, destroying 15% of the ■■. caterpillars present at Hope in June 1970; at higher host population densities (Langdale 1971; 1972) it is less effective than P. griseanae destroying relatively fewer hosts (21% and 12% respectively). At Langdale M. ictericus was subject to hyperparasitism by at least one Pteromalid, identified as Habrocytus chrysos (Walker). A complete list of all parasites recorded-in Britain from 1969 is given in Table 42, Broadly speak- ing this forms a unique complex for British habitats and contrasts particularly with that of the Alpine populationc3; 6 of the Langdale species and 13 of the

1. with the exception of Eubadizon extensor which is commoner in the lowland Swiss area (Graf, 1974) 240

Hope species are absent from the Upper Engadin. New to Z. dinia,„a are four Hymenoptera, Scambus nucum Ratz., Thysiotorus thompsoni Kerr.; Blaptocampus nigricornis Wesm. and Camponlex faunus Gray. which are all Ichneumonids and none is abundant. A notable absehtee from British Zeiraphera is the Tachinid, Lypha dubia. Fall. An important Alpine Eulophid parasite, Dicladocerus westwoodii Westw. (Aeschlimann, 1969) .Was absent from Zeiraphera but was nevertheless found frequenting larch and was reared. frem.a Pandemis sp. at Hope (1970). Baltensweiler (1958) records separately parasites of the "pineform" and "larchform" caterpillars in the Engadin although few seem to be similarly exclusive in Britain, ie. only Eubadizon ext-en-s=-L. (B-rac-onidae--)- is exclusive to Larch at Hope and in the Engadin whereas no species is exclusive to pine in both the Engadin and at Langdale. However, a characteristic parasite 2° at Langdale, Pimpla turionellae L. is more commonly. found on pineform larvae in .Switzerland. _ In conclusion it seems, therefore, that the parasite complex is more strongly influenced by geographical considerations than by host race characteristics or by similarities in habitat type. The parasite complexes in Britain are less diverse than in the Alps and Prell (1930) finding a similar situation in Saxony attributes this to the maintenance of polyphagous parasite species on the

2. P. turionellae I. is also recorded from other pine Lepidoptera, particularly R. buoiianae Schiff. (Morley and Rait-Smith, 1955) 241

varied alpine flora. Jagsch (1973) working in Austria on the larch needle miner, Coleophora laricella Hbn., which shares many of its parasitoid species•wit'h Z. d:iniana, finds parasite diversity higher,in the

• Alps than elsewhere in Europe. In fact is is difficult not to believe that, in• Britain, lower- arasite•specieS •. • diversity i-s partially due to lower host.density and sporadic geographical distribution: 242

2.5.4. Virus disease' The impact of a pathogenic granuloisiS virus on Z. diniana larval stages is well known'(Martignoni, 1957; Martignoni_and Schmid, 1961; Benz, 1962; Schmid 1974). Some quantitative relationships between the virus and its host have' been revealed by Benz. (1964)' and its consequences for the cyclicly fluctuating alpine populations are Indicated by Auer (1968). ' The proce6s of infection may take' place.in several ways; virus may be transmitted from adult to- progeny or_•an infected host may die contaminating the food of healthy hosts. In addition, hymenopterous parasites may transmit virus by means of the ovipositor (Stairs, 1968). The fate of susceptible larvae is described -by .Martignoni (1957);' when it- dies the insect is fragile'and the body wall easily ruptures to sjread the viral contents over the food plant. Adults and pupae may of course contract the virus and die' as a result of it although detection of individuals affected at these stages may be more difficult in the field (Stairs, 1968). In Switzerland the virus disease acts as a delayed density dependent mortality process and is of less numerical importance than insect parasitoids. Its incidence is less_ widespread and it is less lethal during some population cycles than others (Baltensweiler, 1968) and there is some notable geographical variation in resistance to the disease (Benz, 1962, 1964). Undoubtedly some of these features of its biology are 243

due to the different physiological condition of hosts which is mediated by intraTspecific competition for food at high densities. Thus, reports- of viral infed7 tion come almost exclusively from areas where there. . have been extremely high larval populations causing. partial defoliation of the host plant (eg. Jahn,' 1958; + Plorov, 1942; Crooke and Bevan,_1958 )...

At Langdale in 1971 and 19 7.2 virus disease accounted for only. very spallproportiOnd'of the • total larval deaths (Table 41 and Figures 39.and 4 ) in foliage samples. Its presence at.Langdale, and probably also at Hope Forest (Crooke and Bevan, 1958), suggests that it may be partially responsible for bringing ,to an end economically important budmoth outbreaks while normally it remainE enzootic.

+ cited as a "bacterial disease". 244

2.5.5. Pupal mortality Until recently the pupal stage of Z. diniana had received very little attention in population studies. Sampling at Hope and Langdale revealsthatmany pupae ' will succumb to parasitoids while being parasitized in the earlier larval stages and even Triclistus podagricus, the most universally abUndant parasitoid of - the pupae, lays its eggs on- the larger larvae; -Predators are ' frequently said.to,take pupae from their cocooning -

sites in . the litter (e. ants: tscherich,.1931). The most potentially interesting mortality, however, is

investigated by Graf (1974) who estimates the mortality of pre—pupal and pupal stages to be 62% (mean for. 4 years) in the field and only 26%o in the. laboratory (18°c/800.H.). This is partly duc to the negative influence of heavy rainfall on eclosion rate in "wet"

• areas and the increased activity of predators in "dry" areas. A better eclosion rate of adults is experienced in cool, humid conditions than after rainfall according to Graf's results at Lenzburg. Pupal mortality at Hope and Langdale seems to be important. Estimates exclude parasitized pupae (larval mortality) and constitute the second highest k—value for the Langdale population in 1971. At Hope, pupal mortality is the third highest mortality in 1970 (40% of pupating larvae die) and the highest in 1971 (71% of pupating larvae die). The only indication of the cause of these pupal mortalities is given by the . 245

1970 estimates at Hope (Appendix 14) where about 40% of the pupating larvae simply fail to hatch' as adults. 'No 'parrallel studies to those of Graf (1974) have been done to investigate the possible microclimatological implications for pupal survival although once again,, high rainfall and temperature may be involved. The similar levels of pupal mortality in Britain and at the "sub-optimal" Ienzburg site are extremely interesting and particularly worthy of further study are the effects of high temperature on pupal survival; the. suggestion in Section 1.6.6 (Table 22) that lower than average August temperature favours population increase may well be important in relation to the pupal stage. 246

5.6. Variations in natality ► ,Failure.to achieve maximum possible natality in field populations is a. significant process in many insects and Zeiraphera diniana is no exception, The components . of natality are hazardous to estimate in the field and population changes at this stage are deduced - partly:here from laboratory reared adults. The number of eggs laid by mated females reared in optimal laboratory conditions (Benz,'71969, Meyer 1969) ' from pupae of more. or less maximum size is representative of maximum population natality'end deviatiOns from this in the field may be considered as belonging to several categories. Mating The most critical influence on the production of a fertile complement of eggs is the introduction of a spermatophore into the bursa copulatrix of a female moth. Furthermore, oogenesis is stimulated by this; although the number of active spermatozoa is unimportant to egg production (Benz, 1969). A'guide to the rate _of mating in the field (at Langdale 1971), provided by dissected .samples of females, was found to be relatively high throughout the adult flight period (Figure 42)0 Mating was infrequent in the field cages (10 out of 20 cages contained females which failed to mate) but this was thought to be a result of the caging technique rather than a real reflection of field mating activity. Failure to mate was not considered further 247 Figure 42. Some changes in the status of the adult population during August and September, 19711 (Langdale) and variations in some weather parameters.

• TREE / MOTHS ULT AD to PROPORTION OF MATED

1 99 80-

50- E MOTHS AL 20- FEM /0 0

10 15 20 1 5 10 E 1 601 FEMAL

0 0 EGGS!

30- 0 0 0 o ° MATURE

25-

--20- cc ou 15- w cc

CL 10- W

5- <7( 0 VERY WET DAYS >10mm RAINFALL FINNINGLEY( MAXIMA AND MINIMA)

11111111111 TTT 1 1 lll r 10 T 15 20 25 310 1 I 10 15 20 T 25 AUGUST SEPTEMBER 248

as an important Mortality process. Nutrition 'Larval (or pupal) weight, a direct consequence . of nutrition, has been correlated with subsequent adult fecundity on numerous occasions in species of Lepidoptera. Iflomp (1968) for example shows that a shortfall in pupal weight of 2/3 maximum results in a similar fraction of maximal fecundity for Pine Looper Moths. Variations in pupal weight May be considerable (Section 1.4) according- tothe larval feeding regiMe, and sexual differences in weight may be eliminated on'a poor food base. Altwegg (1971) reared female pupae to a sizeable 47.4 ±1.1 mg; Gerig (1966) records them at 32-35 mg on a similar diet and Benz (1969) used pupae between 27-37 mg fog -hi-s-experimen.ts._ Weights of female pupae reared in the experiments of Section 1.4 were between means. of 24.3 mg (Hope/JL) and 30.0 mg (Langdale/EL). Reductions in pupal weight (and hence fecundity) may be attributed, therefore, to the feeding caterpillars themselves and to the host plant in the case of Pinus contorta. Ful..6hermore Table 43 records the numbers of eggs laid by.laboratory populations of adults which were collected in the field as 5th instar larvae and pupae. To be compared with these ar•e the results of the oviposition experiments in which laboratory reared insects were used. Evidently the potential fecundity of field populations is reduced and by as much as 35%. 249

Table 43

Eggs laid 13.,-7 laboratory populations of adults reared from field collected 5t11 instar larvae and pupae and laboratory reared larvae

eggs laid per female - FIELD LAB (from Table 20) mean s.e. maximum mean s.e. • Langdale 117.1 • ± 18.94 219. 129.4 :± 14.20 Hope 78.8 ± 11.53 .181. 123.0 ± 7.46 250

for those at Hope Forest. Field nutrition of larvae, therefore, probably plays an important part in reducing natality. Other investigations alsa suggest that-the means in Table 41 are rather low; Benz (1969), gives a mean of 155 (max. 200), Altwegg (1971) 129. and Meyer an unusually low 601.. Field results by BaltenSweiIer . (1968) and Graf (1974) show estimatiOns'of. 169 and 150 respectively for years of maximum egg ,production•and in poor .year reductions of 68 and 65% are-expeDiended. These are comparable with'the percentage reductions from maximum numbers of eggs laid• in Table 41 of 47% (Langdale) and 56% (Hope). Inadequate nutrition in female moths may also reduce egg production Benz (1969) fund evidence that egg production would Tall by 42% in the absence of "adequate space and nutrition" and Graf (1974) has demonstrated a 50% Deduction for moths given water in place of 10% sucrose' solution. This is difficult to account for in a natural population and it should be borne in mind that natality estimates here are derived from fully fed adults. Failure to lay all eggs matured A comparison, between the number of eggs laid by laboratory reared populations (Table 41) and those laid by adults in field cages (both of which were derived from 5th instar larvae and pupae collected in the field

1. Meyer's results varied from 0-252 eggs. 251

and should therefore have excluded larval nutritional differences) would have been possible if normal longevity and mating success, had been assured. In fact only 5 (out of 20) cages at Langdale retained mated females which lived long enough to lay eggs.. An average of '26 ± 4.6 eggs were laid — an estimate proved unreliable through the inadequancy of the experiment. A .similar result was obtained.from field cages at Hope Forest. • Environmental conditions in the field, for example rainfall and temperature, may preVent moths from laying their potential complement of eggs. Maximum and minimum temperatures equivalent 'to those experienced at Langdale in August and September 1971 are given in Figure 42. and are,___Qn_the able for oviposition. The number of eggs matured in the female ovaries on a series of sampling occasions does not seem particularly high and encourages the view that environmental conditions are not inhibiting egg laying at this time (Figure 42) Although the high reductions in natality shown in the po,ulation budgets (Table 41) have not been fully accounted for, one of the largest components would seem to have been a failure to achieve maximum fecundity through an inadequate larval nutrition. For this reason a low natality is experienced particularly at Hope on Japanese larch. 252

Conclusions The life tables constructed at, Hope Forest for a population on Japanese Larch and at Langdale for a

. population on_Lodgepoleyine have revealed important information on the processes responsible for intragener- ation change. There is not enough infortation, however, to be sure.of how these processes might behave throughout a longer series of generations;' this, may be .investigated with a Varley and Gradwell key factor analysis only over a sequence of at least five generations. Nevertheless certain comparisons are possible, but it should be borne in mind that both populations differ from each other in two important respects; the host plants have been indirectly responsible for selecting populations which have differing ecological characte-ristics-and-gin- - the population at Hope was increasing in size during the three years it was studied while the Langdale populatiOn was decreasing and had probably been at its maximum one generation before studies were commenced.1 At Hope Forest consistantly high k values are attributable to pupal mortality in the litter, and to variations in natality resulting from low fecundity. Other large mortalities include the loss of larvae and adults and there may be contributions from egg mortality although sampling did not facilitate their identification. If pupal mortality is due to high temoerature or humidity as suspected then it will act in a denSity independent

1 N.B. R (Hope 1969 70) = 9.69 R o(Langdale 1970 71)= IC (Hope 1970 71) = 1.93 0.)5 253

manner and by varying with climate as well as weather will be among those factors determining the range for this insect in Britain. FUrthermore, this will be • additive -to--the mortalities experienced by temperature . sensitive eggs in years with above average August' temperatures (1.6). In both egg and .pupal mortality, populations in Britain probably differ from those in the Alpine.regions.of Central Europe. Pupal mortality of "a similar magnitude has been recorded by. Graf (1974) but .from the loweraltitude Ienzburg Site in Switzerland, and Baltensweiler et al (1971). discuss the influence of egg mortality in sub optimum areas. Because experimentally determined egg mortalities are lower than expected (1.6.1) there is also the intriguing possibility that eggs in Britain have been selected for- fh-6E-f-teiripatut --- resistance. In any case variation rates of egg and pupal mortality due to climatic influences, represent disturbing processes which, in locations where they are periodically effective, will prevent the prolonged increase of .populations and may extinguish some.- The Hope Forest outbreak in 1357 was concentrated on the Snake Pass plantations (366m above sea level) but a certain amount of daidge to Sitka Spruce and Larch was experienced lower down the valley on the Ladybower Reservoir plantation (183m.a.8.1.). During the co-arse of this study Larch and Spruce were examined at many. points along the valley and on no occasion was Z. diniana found at the 254

lower altitudes. Whether or not the 1957 Ladybower infestation. was the result of immigration from an original higher altitude population (as in the case of immigration at Lenzburg and other low altitude sites, 73altensweiler and Von Sails,' 1975) it is difficult to ascertain; it is evident that if local. extinction is related to altitude and/or.latitude then climatic events are most likely to be resTionsible and it is on' the egg and pupal stages, that these are demonstr.Oly effective. ' — ... -Low fecundity (2.5:6) ,:particularly. at Hope Forest, has been attributed to poor larval nutrition which results in low pupal weight. Larvae reared on optimally sized needle shoots (1.4) produced heavier — pupae. Graf (1974) _attributes a similar drop in fecundity to physical differences in early flushing • Larch needles. In 1.2.6 a disparity - between early needle flush and larval emergence was discussed with the emphasis on asynchrony but, of course, if mortality is not experienced in the early instars, the food quality during later development may well be sufficiently poor to subsequently reduce natality. Thus, Larch which flushes early in relation to egg hatch in Britain either prevents establishment (early larval mortality) or provides a sufficiently poor nutritional base so that later instars will die (late larval loss) or allows survival of caterpillers of lower than normal weight which as adults produce fewer than 255

normal eggs. Th€= life tables at Hope, in fact, indicate that early larval mortality has been minimised during the three study years. All these mortalities. are density independent becauSe weather determines . the insect and plant phenologies, but certain circumstances may induce density related larval loses. In the event of any nutritional "stress" there will ,be. greater survival rates among.typical pine form. individuals. (1.4)'or'among .intermediate :type ..(Day and Baltensweiler, 1972) which happen to be.-OnLarch. The problem for - British populations on'all host conifers is that selection for a specific hatching phenology (ie. rate of post diapause development) is from two directions; early hatching larvae will run the risk of exposing their egL3 to high summer temperatures whereas late hatching larvae will risk poor nutritional conditions throughout their. development. The co—existence of forms with widely variable rates of post diapau:e development on the same host plant is facilitated by this sitvation, and the kind of introgressive hybridization discussed at the end of Section 1 is therefore of survival value to Zeiraphera populations experiencing a hazardous and variable environment. Genetic heterogeneity;.as Birch (1970) argues, tends to reduce the chances of extinction in marginal populations and probably also the chances of synchronous outbreaks in contrast with 256

widespread synchrony in the Alps (Baltensweiler, 1966). The circumstances under which la-rval loss may become density_ related are apparent during the first. larval instar. The experiments with Lodgepole pine a buds (1.2.1) show that in most. cases, "crowding first instar larvae leads to a greater proportional mortality even in the absenca-of.arecognisabla food. shortage. ThiS. density dependence may well be real under field conditionS;. it is Omphasised'in.particular, by the st/ong tendency for eggs to be . clumped (2.4.4) among branch samples and sample units smaller than this. There may frequently be occasions when many hatched larvae are competing within' the same bud groups and some will p-r.c,bably be f6rced to disperse or die. The loss of larvae is an important mortality at Langdale but only for one year is it aarge.for first instars. It may include density dependent mortality from larval.competition which may in turn be superimposed upon a mortality clue to nutritional stress. In support of this it is Shown that density dependence is more noticable on older and less acceptible buds (1.2.1), but the effect of nutritional stress may be altered in the field by the presence of male flowers on Lodgepole pine (1.2.4). It is the interesting s,;ggestion of Klomp (1966) that the evolution of mutual interference among cryp- 257

tic caterpillars of the pine looper moth may be the result of an anti-predator behaviour; predators finding caterpillars in groups will be encouraged to • search in the vicinity of- the first -capture-whiIe'a - . • more regular dispersal of caterpillars increases their individual chances of survival. The converse • is true of aposematic insects which, .are gregariOus.or. insects which feed in groups and are cryptic but possess, good•defensive Mechanism's (Knerer,and Atwood,' 1972).• Mutual interference among. Z. diniaria.caterpillars could be in this category of anti-predator behaviour; predation of the larval stages has not been demonstrated although it may be included in larval losses (2.5.2) and in addition such behaviour might equally well reduce parasitism. Body colour is only cryptic in the last instar (Plates 19 and 20) when caterpillars will feed openly among the foliage rather than between shoots (Plate 2). The colourforms on Pine (Langdale) are fairly typical-bf those described from Cembran pine (and other species) in Alpine Switzerland (Bovey, 1966), and on Japanese Larch (Hope) the population colour composition (see Baltensweiler, 1970) is similar to that at Lenzburg (sub-optimal Swiss site) but includes rather more light types (1970, 30%; 1971, 25% 1972, 20%) in addition to a predominance of intermediate forms. Nutritional stress, as it has already been pointed out, is one 258

of the factors which will kill proportionally more dark types. The later phenology of typical pineform populations, by largely avoiding Mortalities associated ' with high_ summer temperatures; will confer•distinct• • advantages to these populations on their-appropriate host plants, over population& committed to feeding on Larch. - Apart from larval losses at Langdale, other. . important mOrtalitieS include the death .of pupae and • variations in natality; which although:only:demonstrated for a single generation may have. similar origins to the same mortalities at Hope. A detailed account of egg mortalities at hangdale show four main, components, none of which is liable to regulate population growth very efficiently. Parasitism and predation will not readily respond ,to host density -. because both parasites and predators will be polyphagous. There May be a feedback-mortality from the damage causing larva:, stages to the,eggs laid in the following generation in larval frass (2.5.1) but the dynamics of this are uncertain. Temperature mortality of eggs will be one of the truly density independant processes although once again it is difficult to say how much this may contribute to generation mortality in unfavourable years. During the two study years it remained rather low. harval parasites together may be expected to act in a delayed density dependent 259

way. In 1972 parasitism affected 71% of the available larvae, an of magnitude similar to that caused by parasitoids 2 years after a population peak in the Swissklps.--The presence and increasing importance of the Monophagous Phytodietus griseanae reinforces the similarity, but marked oscillations are not expected in the parasite population. These are only present in the. Alps because the key factor is also 'delayed density dependent. To conclude, may be said that the British populations of Z. diniana are characterised by low amplitude fluctuations and periodic extinction in certain areas. The result is a "patchiness" in the distribution of populations which is reinforced by ------the co-existance of populations on more than one host tree and is analogous to the theoretical contention of Gillespie (1974) that increasing the numbers of patches in a population,system makes genetic polymorphism more likely. Weather; acting on both the food plant and the insect, permits the maintenance of permanent populations in restricted areas only but will allow increase and the expression of regulatory processes in some years. In this way British populations are marginal and may be compared with the cyclic alpine populations which are considered to exist under optimal environmental conditions for this species, despite the apparent ecosystem immaturity 260

noted by Watt (1970). Similar distinctions in the effects of salubrious and hazardoud environments are . made by Whittaker (1971) for Spittlebug'populations. In the'optimum regions regulatory procesSes are operative ,although for populations of Zeiraphera there is a characteriStic time delay Iefore they are effective. - Benz: (1974) has suggested.that the resource recovery time (changes in conifer physiology which are a direct result of defoliation) may be. equivalent, to several budmoth generations and it. can be argued in the manner of May et al (1974) that where the return time (their Tp) for the population is exceeded by the time delay, a simple and stable cyclic behaviour can result° 261

Acknowledgements This work was completed during the tenure of a N.E.R.C. grant which assisted particularly by the . provision of transport facilities. Thanks are due especially to Professor T.R.E. Southwood and Dr. W. Baltensweiler for valuable di.scussion and encouragement throughout and to members of staff in. the Entomology' Division of the Forestry, Commission at Alice Holt for guidance and essential background information in the early stages of the investigation. am grateful to staff at the Darncombe Forestry Office for assistance with some field measurements and to the Department of Silviculture at Alice Holt for kindly providing young conifers for experimental purposes. For bearing the burden of typing the manuscript thanks are due to my wife, Jenny. 262

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Appendix 1 Lodgepole Pine bud elongation at Langdale.' •Bud length is given as a percentage of final (mid-June) length and means presented below.

1971 Date 22/4 25/4 28/4 1/5 4/5 7/5 10/5* 13/5 'mean 19.2 19.9 21.4 23.8 25.3 28.2 32.2 36.9 s.d. 5.0 4.8 5.1 6.1 6.8', 5.6 5.1 4.8

date 16/5 19/5 22/5. 25/5 28/5 31/5. 3/6 6/6 'mean 41.3 46.7 61.0 .66.0 71.1 76.8 82.8 88.6 s.d. 5.3 6.3 6.4 5.3 4.4 4.1 3.6 2.6 final length 138mm,n (buds) = 20 s.d. 44.3

1972 Date 19/4 28/4 4/5 11/5 18/5 23/5 30/5 mean 29.6 32.8 39.7 46.8 55.7 65.8 71.7 s.d. 14.3 13.7 12.8 13.2 10.4 8.3 •5.0 final length 108mm,n (buds) = 21 s.d. 28.57 283

Appendix 2: Bud classes, presence of male flowers and number of first

instar larvae on bud group samples from Langdale.

Bud groups are numbered 1 - 155. •

1 2 -3 4 -5 6 7- -8- -9 10 _11_12' 13. 14 15

•+ • A + + B 1 2 2 1 C 1 2 1 2 D 2 1 1 2 2 2 -4 2 2 1 1 . 2. 2

16 17 18 19 20 21 22 23 24 25 .26 27 28 29. 30 -

A B . C 1 1 D 5 3 2. 2 2 2 3• 2

31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

A + + + + .+ B 1 C 1 D 6 3 2 1 3 1. 4 3 1 2 1 2 2 3 2

46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

A + + + + B 1 1 • 1 C 1 2 1 D 3 2 2 2 2 • • 3 2 3 2 3 6 2 3 4

61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 .

A + + + + B C 1 D 2 2 4 3 2 1 3 2 6 4 3 2 1 2 3

76 77 78 79 8d 81 82 83 84 85 86 87 88 89 90

A + + + + + + + + B 1 1 3. C 1 1 D 2 3 4 3 3 4 4 6 3 2 2 6 3 3 2

A presence (+) of male flowers B larvae in flowers C larvae in buds D bud developmental stage 1-6. 284

Appendix 2 (continued)

88 89 90. , , 76 77 78 79 . 80 81 82 83 84 85 86 87 + • +. + A + 4. B 1 1 .3 C 1 2 3 D 2 3 4 3 3 4 4 6 3 2

102 103 104 105 91 92 93 94 95 96 97 98 99 100 101

+ + + A ' + + + + + + + 1 B C. 1 2 2 2 2 2 . . 6 D 2 3 2 2 2 2

118 119, .120 106 107 108 109 110 111 112 113. 114 115. 116 117

A B C 2 5 ,3 2 1 D 2 2 3 6 2 3 3 4 4 3

132 133 134 135 121 122 123 124 125 126 127 128 129 130 131

A + + + + B 2 1 1 C 2 3 4 2 1 D 3 2 3 3 1 . 2 2 2

147 148 149 150 136 137 138 139 - 140 141 142 143 144 145 146 ' + A + + + + + 2 1 B 2 1 C 1 2 2 1 3 2 D 2 -2 2 2 2 1 6 2 1 2

151 152 153 154 155

A B C D 3 2 1 2 2 Appendix 3: Deviations of monthly mean temperatures from 47 year means (°C), Buxton.

• Jan. Feb. Mar. Apr. May June Jul. Aug. Sept. Oct. Nov. Dec. Long-term mean 2.1 2.0 3.9 6.3 9.3 12.4 14.0 13.8 11.8 8.5 5.0 2.9 Year 19 30 0.8 1.2 1.0 0.1 - 0.7 1.0 - 0.8 0.0 0.0 0.1 - 0.2 0.0 1931 0.2 0.0 2.1 - 0.7 0.3 - 0.1 - 0.4 - 1.5 1.8 - 1.1 1.4 1.0 1932 2.8 0.1 0.7 - 1.7 - 1.0 - 0.5 0.2 1.3 - 0.8' - 1.5 0.1 1.3 1933 1.1 0.4 1.5 1.0 1.0 1.0 1.9 1.6 1.3 - 0.1 - 0.6 - 2.2 1934 0.8 1.0 0.9 - 0.3 0.0 0.6 2.2 - 0.7 0.8 0.1 - 0.1 3.4 1935 1.0 1.9 1.1 - 0.2 - 1.1 1.0 1.2 1.3 0.2 - 0.8 0.4 - 1.8 1936 0.4 1.8 1.0 - 1.9 0.1 0.4 - 0.7 0.5 1.0 - 0.5 - 0.5 1.0 1937 1.1 1.2 2.9 0.7 0.9 - o.3 - 0.2 1.2 - 0.4 0.1 - 1.2 - 1.5 1938 2.0 1.3 3.8 - 0.6 - 0.4 - 0.2 - 0.8 0.4 0.4 0.4 2.5 - 0.1 19 39 0.0 1.6 0.1 0.3 0.3 - 0.2 - 0.4 0.9 0.5 - 2..1 1.7 - 0.4 1940 0.6 1.9 0.4 0.1 1.4 2.3 - 1.0 - 0.5 - 1.3* - 0.7 0.1 0.7 1941 0.9 0.9 0.8 - 1.8 - 1.8 0.8 1.8 - 0.9 0.9 0.3 - 0.3 1.4 1942 2.6 3.7 0.9 0.8 - 0.1 0.3 - 0.6 0.8 - 0.2 0.2 .- 0.7 2.3 1943 0.6 2.4 '.2 2.1 0.4 0.1 - 2.5 0.0 - 0.6 0.5 0.2 -7. 0.5 1944 2.3 0.2 0.2 ‘ 2:0 - 0.1 - 1.3 0.3 0.9 1.1 1.1 - 0.6 - 0.4 1945 3.3 3.6 2.4 1.9 0.6 ' 0.2 1.1 0.4 0.5 2..0 .1.0 , 0.5 1946 3.0 2.0 0.5 1.8 - 0.9 - 1.1 0.4 - 1.0 - oA' - 0.8 1.6 1-'14 1947 1.8 5.8 2.9 0.3 2.3 1.4' 1.3 2.6 -.0.8 0.7: 0.6 . 1.0 1948 1.4 0.6 2.9 0.7 - 0.2 - 1.1 - 0.1 .- 0.7 -'0.1 : - 0.2 . 1.0 1.0 1949 1.6 2.1 1.1 1.8 - 0.2 0.7 1.0 1.0 2.4' 1.1 '- 0.1 i'1.0 1950 0.7 1.3 1.8 - 0.7 - 0.4 1.7 - 0.3 - 0.2 - 0.6 - 0.6 - 1.0 i 3.6 1953 0.5 1.0 1.8 - 1.2 0.8 0.2 - 0.2 0.6 0.4 - 0.4 2.2 1 2.5 19 54 0.8 1.6 0.3 - 0.5 0.2 - 1.0 2.1 - 1.3 - 0.9 1.6 - 1.4 H 2.O 1955 0.1 2.8 2.5 1.4 - 1.9 - 1.1 1.9 2.2 0.5 . - 0.6 0:4 1 0.9 1956 0.1 3.6 0.2 - 1.7 0.8 - 1.3 0.0 - 2.2 0.3 '- 0.6 1'1.3 1957 1.8 1.4 3.2 0.4 - 0.9 0.5. 0.0 - 0.5 -1.4 •0.4 0.1 -0.2 Appendix 3: Deviations of monthly mean temperatures from 47 year means (°C), Buxton. - (continued),, •

Jan. Feb. Mar. Apr. May June Jul. Aug. Sept. . Oct. Nov. Dec.. Long-term mean 2.1 2.0 3.9 6.3 9.3 12.4 14.0 13.8 ' 11.8 8.5 5.0 2.9 Year 1961 - 0.5 3.1 3.3 1.5 - 0.5 0.0 - 1.2 - 0.4 1.1 0.2 - 0.5 2.4 1962 0.6 0.6 - 3.3 - 0.5 - 1.2 - 0.9 - 1.3 - 1.4 - 0.5 0.0- - 1.1 Z.0 1963 - 4.9 - 4.7 0.0 0.2 - 0.7 0.8 - 0.5 - 1.0 0.4 0.7 1.3 - 1.3 1964 0.0 - 0.1 - 2.1 0.8 2.2 - 0.5 0.0 -'0.4 0.1 - 1.6 0.9 1.0 1965 - 0.3 - 0.4 - 0.8 - 0.1 0.5 0.5 - 2.3 - 0.8 - 1.0 -1.1 - 2.3 0.2 1966 - 1.0 1.4 0.8 - 1.4 0.0 1.3 - 1.1 - 1.0 0.1 - 0.3 - 0.8 0.7 287

Appendix 4: Sampling equivalents obtained from field measurements.

, . Langdale Hope

P. contorta L. leptolepisl P. sitchensis 2 2 Sample plot area 156,250m 1,700m

Total number of 74,448 54, 241 trees . , 1 • 2 2 Folige area • Incomplete 470m 1230m • canopy cover • • 2 Ground area per 2.10m. ,- .8.70m ' 5.10m2 tree •

Branches per tree: total 29.4+ 0.71 21.7+ 2.74 15.14 +1.11 Crown upper level 14.7+_ 0.41 7.78+1.10 4.76 +0.41.. middle level - 7.78T1.00 5.67 70.39 lower level 14.7+. 0.46 6.1140.97 4.71 TO.55

2 lm ground area 2.33 0.99 2.51 equivalent (6-branch (1-branch (1-branch samples samples samples

Branch sample 1335+ 58.77 1604 1517 Fresh weight (gm) 1654 Crown upper level - 1153 + 72.6 + 1274+_ 225 middle level - 1712 T152.0 lower level - . 1947 + 119.0 1760+ 431

Terminal bud groups per branch: - - Crown upper level 12.33+ 1.41 . lower level 37.00 -1- 6.01 Per 6-branch sample (from above) (a) 148 *(b) 119

Buds per terminal 1.99+ 0.05 - - bud group

* Derived from Appendix 7. See Appendix 5 for analysis of variance between levels.

Appendix 5: Branch weights (gin) in Upper (U) and lower (L) levels of the Larch canopy at Hope Forest.

L . U Tree L U 72ree L U Tree L U Tree

1275 1914 31 . 1382 807 1 1344 750 11 1559 797 21 22 1082 758 32 1341 595 2 5231 716 12 1438 954

23 2635 1143 33 1305 560 3 1845 2209 13 504 1210

24 1862 854 34 1570 413 4 2933 1657 14 1135 1043 i 25 1125 1281 35 1394 424 5 2864 1242 15 824 954 26 1062 523 6 1143 1258 16 1760 954 27 2833 1557 7 1646 1425 •17 4059 1902

28' 1043 1158. 8 2184 1790 18 2870 669 .

29 2084 1690' 9 6012 1450 19 1479 1368

1138 30 1082 690 • • 10 1182 790 20 1417 I 289

Appendix 5 .(continued).

Analysis of variance

Source of variation df SS MS

between crown levels 1 11057257 11057257 16.54*A*

between trees • 34 32601069 958855 1.43n.s.

Remainder 34 22716439 668425

Total ' 69'' 66384765

F = 1.84 F = 13.3 0.05 30,30 0.001 1,30

Due to the rather close canopy and poor growth conditions of the

forest stand at Hope the nature of branches at different levels within the

canopy was evidently quite variable. In a fairly open canopy the amount

of available foliage could be expected to be (approximately) proportional to

•the fresh weight of the branch irrespective of canopy level. This was

clearly not so at Hope and if population intensity was expressed as numbers/

unit weight of branch then the resulting estimates would have been less

biologically meaningful. An analysis of variance between crown levels is given

here to clarify the weight differences. The amount of fresh foliage per

branch is probably much more similar between crown levels (although

estimates of this are not available). It was therefore decided to

express sample results as numbers per branch and to sample branches equally

from canopy levels. Appendix 6. The regression of Lodgepole pine branch weight on length (Langdale).

2000 - E cn I-- 0 LT - 3 1 6fx 1000- u_ i 0 Z _ g m

I I I I I I 1 1 1 1000 2000 3000 4000 TOTAL BRANCH LENGTH cm * P=0.05 Appendix 7. The regression of Lodgepole pine branch weight on the number of terminal bud groups per branch (Langdale).

600-

E cy) I— 400-

LTJ

V) cr LL 200- U 2r cr on

10 20 30 40 501 NUMBER OF TERMINAL BUD GROUPS PER BRANCH

P=0.05

Appendix 8 The distribution of Zeiraphera diniana in population samples

developmental sample sample quantity source sample variance. Goodness2of fit test location stage date unit mean ,distri- signi- 2. (negative bution -xd.f. ficance binomial)

Hope eggs 3.70 branch 18 U/L4' 0.50 1.44 P n.s. (1970) N n.s. 0.35 middle 20.5.70 branch 15 U/L 1.80 4.31 P larval instars N n.s. 0.99 18 U/L ' No instars 24.6.70 branch 1.72 2.65 P. 171!E - ! h.s. QD 4 and 5 . N , 0.60 4 n.s. 3.19 N) pupae 8.70 0.42m2 9 litter 1.44 4.78 ' P 1.50 1 n.s. N 2.06 2 n.s. 1.04 ** Hope eggs 3.71 branch 27 U/L/M3' 1.78 3.95 P 12.30 3 (1971) - N 9.38 4 n.s. 1.07 3-branch 9 3 per 5.33 9.00 ' . P.' 8.08 7 n.s. tree N , 4.91 - 6 n.s. 10.48 Middle larval 23.5.71 branch 12 U/L ' 3.08 8.45 P 14.72 5 * instars N , 2.58 4 n.s. 1.42 instars 12.6.71 branch 14 1 per 2.71 8.84 . P - 12.52 4 * 4 and 5 tree N 5.20 4 n.s. 1.22 pupating 7.8.71 0.42m2 19 sticky 0.47 0.49 • .P 0.19 .1 n.s. larvae trans 0 N 0.18 1 n.s. 58.94 Hope eggs 3.72 branch 19 U/L 4.42 24.80 P 119.10 7 * (1972) N . 3.29 5 n.s. 0.96 *** instars 19.6.72 branch 13 13:38 48.42 P r 416.30 6 6. 4 and 5 - N - (D=0.12 n=13) n.s. 5.11 Appendix 8 continued.

developmental sample sample quantity source sample variance 'Goodness of fit test k location stage date unit mean distrf- .x•2 . d.f. signi- (negative bUtion ficance binomial) Langdale eggs 10.70 18cm 437 19 2.57 62.53 P 4345.78 7 ' * * * (1970/71) branch single . N . 30.24 12 ** lengths branches eggs 3.71 6-branch 23 tree 69.48 6040.44 • groups . mid-ins tar 24. 6.71 6-branch 21 tree 25.86 461.83' larvae groups Pupating 14. 7.71 0.42m29 24 sticky 10.67 73.28. 2718.50 14 * * * larvae traps 17.32 11 n.s. 2.00 Langdale eggs 10.71 18cm 1435 7. 0.64 P 1756.51 3 * * * (1971/72) branch N 41.32 15 . * * (0.03) lengths eggs 3.72 2-branch 60 6-branch 6.10 138.36 88.06 7 * * * samples - 13.24 8 n.s. 0.27 6-branch 20 tree 18.30 450.22 (D.0.31 n=19)6! *** groups . 2.61 - 2 n.s. 0.78 instar 1 24. 5.72 terminal 155 1 per 0.31 0.38 P 7.23 1 . ** bud group tree N 2.59 1 n.s. 1.01 mid-instar 22. 6.72 terminal • 360 5 per 0.28 0.31 P 1.92 . 1 n.s. larvae bud group tree 0.09 1 n.s. 2.50 5-terminal 72 3 trees 1.39 2.95 P 15.72 3 * * bud groups per group . N 5.28 4 n.s. 1.27 15 terminal 24 24. 4.17 10.32 P 11.12 6 n.s. bud groups • 3.65 8 n.s. 2.82

Appendix 8 continued.

developmental sample sample quantity source sample variance Goodness of fit test location stage date unit mean distri- X2 signi- (negative bution ficance binomial)

Langdale instars 21.7.72 terminal 270 5 per 0.14 0.15 P ' 0.05 1 1 n.s. ( 4 and 5 bud group tree N 0.47 1 n.s. 2.23 5 terminal 54 3 trees 0.67 0.91 P 0.15 1 n.s. bud groups per N 0.55 2 n.s. 2.59 group ND 15 terminal 18 18 • 2.00 3.65 - P • 1.82 3 n.s. LSD bud groups trees . V.. 0.45 4 n.s. 2.63 .-P- pupating 21.7.72 0.42m2 ' 22 sticky 3.82 13.49.: ,P 37.50 6 ..* larvae traps N 5.25 7 n.-s. 1.51 13.8.72 1.29 4.41 . P ., 6.93 2 * N . 2.04 4 n.s. 0:53

1. N negative binomial P poisson 2. Significance at probability level P 0.05 * P 0.01** ,P 0.001*** n.s. not significant 3. k estimated from the iterative solution N (1+ ) = (Ax ) where N=total number of samples, In .Napierian logs, ik+x 3E= mean, Ax= the sum of all frequencies of sampling unl_ts containing more than. x individuals.Southwood (1966) 4. U/L Upper and Lower canopy levels 1 5. U/L/M Upper, Lower and Mid canopy levels. 6. Kolmogorov-Smirnoff test 7. 7 six-branch samples and 9 single branch. samples Appendix 9. The relationship between the number of eggs per 100g branch weight and the total branch fresh weight (Langdale 1971).

i U z 4 cc 0040 40- Li_w 0 Ecr) 0 0 ixw 20- a_ (r) 0 - w

I 100 200 300 FRESH WEIGHT OF BRANCH gm Appendix 10. The relationship between the number of eggs per 100g branch weight and the total branch fresh weight (Langdale, 1970).

• 200- 2 U z

0 E 100- 0 • 0 • • • • • tf) • • • • • • • • • • • I I 100 200 300 400 FRESH WEIGHT OF BRANCH gm 297

Appendix 11 Percentage parasitism of eggs within branch samples by T. evanescens on P. contorta (Langdale 1971),

Sample Eggs per .6-branch _Total parasitized' %. parasitism sample unit

1 66 • 11 :16i7. 2 . 19 . • 2 . - 10.5* •

3 212 . . - 45 . .- .2142:- .. . • 4 119. 22 • 18.5._ . . 5. 95 • .. • 11 . :11.6 • • • . 6 • 1.24 . . • 29.-• : • 23.4 ,.

7 41 5. 12.2 8 0 ' 0 0

9 330 .96 . 29.1 10 180 12 - 6.7 , .11 120 48:. 40.a 12 558 438:. 78.5

13 36 a. 0

14- 18 0 0 15 42 '.0 . - - 0

16 144 72 50.0 • 1 Appendix 12 Parasitism witiiin Z. diniana egg batches by Trichogramma evanescens on P. contorta (Langdale, October 1971)

nos. parasitized unparasitized 1 2 3 4 5 6 8 10 11. 12 proportion eggs per frequency batches parasitized batch 1 151 105 46 0.31

2 71 45 18 8 0.24

3 56 36 6 110 4 0.23

4 24 16 1 1 2 4 0.26 CO

5 14 5 2 3 2 2 0.34 6 13 8 1 1 3, 0.22 7 4 1 1 2 0.43 8 2 1 0.44

9 4 4 0

10 1 0 1' • 0.7 11 0 0

12 3 0 0.361 r

1. where eggs in a batch touch and are cemented to at lust, one other in the. group. '299

Appendix 13 Hymenopterous parasitoids in the Langdale larval samples 1971 (57% of host larval population)

hyperparasites. Phytodietus griseanae Kerrich. ,Meteorus ictericus (Nees.). Habrocytus chrysos (Walker) * Triclistuspodagricus Gray. Campoplex faunus Gray. l*.Pimpia turionellae I. .Itoplectisalternahs GraV. Apanteles lineipes Wesm. Habrocytus. semotus (Walker) Elachertus isadas Walker * Phaeogenes sp. Scambus linearis Ratz. • .-- Nythobia sp. Dibrachys cavus (Walker) 1972 (22% of host larval population) hyperparasites Phytodietus griseanae Kerrich Meteorus ictericus (Nees.) Habrocytus chrysos (Walker) Campolilex faunus Gray. Pimply turionellae L. Lissonota transversa Bridg. Phaeogenes sp.

emerging after pupation of the host 1. primarily a parasite of Rhyacionia buolianae Schiff. 300

Appendix 14 - Mortality of larvae and pupae at Hope, 1970 Parasitism in the larval samples, 30% (total larvae, 40) externally iepding iprasitoids. Eubadizon extensor (L.) + Thysiotorus thompsoni Kerrich internal parasitoids Meteorus ictericus ,(Nees.) approx. 15% iIissonota transversa Bridg. Itoplectis alternans , Gray. • *. Oncephanes minutus Wesm. parasitoids frequently Blaptocampus nigricornis emerging from host pupae We sin. .+ Itoplectis alternans Gray. +Itoplectis maculator Fab r. * .exhibits multiparasitism + also parasitoids of Spilonota lariciana .

Fate of pupae in litter samples

% of total % of remainder healthy pupae parasitized dying in litter and emerged adults per sample unit

61.7 ± 13.7 39.1 ± 18.6 0.3362 65

1. exit holes in pupa, or containing dead or live pharate parasites. 301

Appendix 15 Mortality of larvae at Hope, 1971 and 1972 •

1971 Parasitism in the larval stages 10.5% (total larvae' 38) Lissonota transversa Bridg. Eubadizon extensor (L.) Itoplectis- alternans Gray.

1972 Parasitism in the larval stages 2.9% (t.otai larvae )74) Lissonota transversa Bridg.

Virus disease 1.2%

4 302

PLATES. Plate 1. Lodgepole Pine bud developmental classes 1 — 6 used in the determination of larval survival rates. Male flowers (FL) are also shown at the base of one developing shoot.

Plate 2. Three terminal shoots of Lodgepole Pine which are bound together by silk produced during the larval stages. On the right, separation of the shoots reveals a feeding larva, (arrowed).

304 Plate 3. An experimental=bi.anch on Lodgepole Pine frOm whibh larval emergence is monitored. Eggs are. • located at the nodes and hatching larvae are trapped on the sticky tapes.

Plate 4. Designs for cages in which a choice of oviposition sites is given to female moths. Artificial sites include green blotting paper spirally bound to dowelling rod (left) and paper strips fixed to the sides of the cages (2nd from right).

306 Plate 5. The sample plot at Hope Forest seen from the opposite.side of_the_valley_in Japanese Larch are light brown and Sitka Spruce remain dark, green..;

Plate 6. The valley at Hope.Forest froti.the side of the sample plot.

308 Plate 7. Sitka Spruce (left) and Japanese Larch (right of centre) at Hope proximity of trees and close canopy cover are noticeable features of.this habitat.

Pldte 8. Lodgepole Pine at Langdale iii November. In the middleground are trees damaged • by Zeiraphera in successive years. 309 310 Plate 9. The sample plot at Langdale.

Plate 10. The relationships of the sample plot area (approximately arrowed) to surrounding. topography. 311 312 , . . Plate 11. Sticky/emergence traps. The wire netting cover prevents predation of the catch birds while allowing insect access. *A-L the bottom right of the - rap .is. a collecting tube.

Plate 12. A sleeve cage for field trials of fecundity.. 313 314 Plate. 13. A node of Lodgepole. Pine at which' eggs —.are typically located. The tightly ' packed scales provide ideal sites,

Plate14. Eggs on a current years'iodgepole Pine shoot. A: on larval faeces and silk ("frass"). B: eggs parasitized by Trichorramma in the same position. C: a batch of 6 eggs laid under a bud scale.

316 Plate 15. Adult Z. diniana

Plate 16. 5th instar larvae illustrating the black larval colourform (1111). Larch, Hope.

318 Plate 17. Larval colourform 1121. Larch, Tope.:

Plate 18. Larval colourform 7432. Larch, Hope.

320 Plate 19. Larval colourform 2224. Larch, Hope.

Plate'20. Larval colourform 4343, Pine, Langdale.

Ent. exp. & appl. 15 (1972) 287-298. N. Holl. Uitg. Mij Amsterdam

CHANGE IN PROPORTION OF LARVAL COLOURTYPES OF THE LARCHFORM ZEIRAPHERA DINIANA WHEN REARED ON TWO MEDIA BY K. R. DAY1) and W. BALTENSWEILER Department of Entomology, Swiss Federal Institute of Technology, Zurich, Switzerland

In the course of a population cycle of the Grey Larch Bud Moth it was observed that the proportions of larval colourtypes change. This was believed to be attributable to density induced changes in the food quality of the host plant during the cycle. Seected representatives of naturally occurring larval populations were reared in controlled laboratory conditions on freshly cut larch shoots and on a semi-synthetic food medium. Larval mortality on the laboratory culture media was shown to be different and the proportions of colour forms in the resultant and corresponding groups also differed. These experiments suggest higher mortality of early-instar larvae of the dark colourtype under food-stress conditions and a resulting change in colourtype composition of the next generation. Further to this there is an indication that effective true-breeding is more likely under food-stress conditions. The results support the hypothesis for a changing population fitness with regard to food-stress conditions throughout a gradation cycle.

Zeiraphera diniana Gn. has been known for a long time as the cause of periodic defoliation in alpine larch stands (Baltensweiler, 1964). The understanding of this cyclic fluctuation type relies on a knowledge of the relative importance of the various mortality factors acting on each bud moth generation in the course of a cycle. Without doubt life-table information could provide the most suitable basis for an understanding of this life system, but such information is not readily available. An alternative is a combination of descriptive and experimentally derived information to gain further insight into the regulating processes of the bud moth cycle; this approach is used here. In relation to the larval census in the 4th and 5th larval instar (Auer, 1961) various population criteria, such as apparent mortality due to parasitism and unknown causes, fecundity, sex ratio and proportions of larval morphotypes were determined (Baltensweiler, 1968). The results for parasitism together with information on disease, damage to needles and temperature were used in a deterministic population model to explain the fluctuation (Auer, 1969). His conclusions, however, were questioned by Varley & Gradwell (1970), using a key-factor analysis, which suggested that a large unknown residual mortality was the biggest component of generation mortality. From local census work during the larval stage it is known that heavy larval mortality shifts in the course of a cycle from 4th- and

1) Present address: Imperial College Field Station, Silwood Park, Ascot, Berks., England.

288 K. R. DAY AND W. BALTENSWEILER

5th-instar larvae during population increase to young larvae in the declining phase of the cycle (Auer, 1961). Since a corresponding change in proportions of larval morphotypes from dark to intermediate colourphases (Baltensweiler, in press) was found, it seemed worth- while to determine its ecological implications. Larval mortality is commonly connected with the state of the host plant as a nutritional medium and as a physical environment. In the case of the bud moth causing periodic defoliation, it seems obvious to postulate a change in food quality, either nutritional or physical, in response to larval densities; a postulate which is implicitly expressed by the defoliation index in Auer's model. A preliminary clue to such an effect is provided by the corresponding fluctuations of annual ring increment in larch, which amounts to about 300/o of its total width (Badoux, 1952). Long-term studies intended to define the real nature of this change in the nutritional quality of the larch needles are in progress (Benz, unpublished). The present experiment is directed at demonstrating the comparative mortality of various colourtypes of the bud moth larvae on two laboratory nutritive media. Neither of these media can be fairly said to represent actual nutritional conditions in the field. But from a comparative standpoint it is possible to discern different responses to each medium in various ecotypes of the bud moth population on larch and, thus, to some extent, clarify the qualitative differences which are believed to exist (Baltensweiler, 1968).

METHODS

Eggs were hibernated and hatched under standardized laboratory conditions and the larvae reared through to the pupal stage in equal proportions on the two media. Numerical mortality was noted at each instar and those larvae which survived to the fifth instar were typed according to a standard system of morphological criteria (Baltensweiler, in preparation). The media selected for a nutritional comparison were needles of freshly cut young larch branches and an artificial medium (Altwegg, 1971). Physically if not nutritionally, the media presented quite different feeding environments. The choice was partially based on the fact that larval mortality is consistently greater on the artificial medium than on fresh cut larch, particularly in the first instar. Larch needles not less than 3 mm long and not greater than 10 mm were cut from fresh branches and placed in glass tubes 31 x 7 mm. First-instar larvae were introduced, one per tube, immediately after hatching or within one day after hatching. When the larvae reached later instars they were transferred to tubes 40 x 20 mm and fed larch until reaching the pupal stage. During the feeding stages, fresh larch was introduced at regular intervals and as far as possible all larvae handled in this experiment were given the same amount of fresh larch needles. The artificial medium was kept under deep-freeze conditions until ready for COLOURTYPES OF ZEIRAPHERA DINIANA 289 use. After thawing, the medium was cut into small pieces and excess moisture removed with a warm air current. The small pieces were then shredded and each tube (31 X 7 mm) was half-filled with the shreds. It was necessary to take extra precautions concerning the moisture content and to test for water condensation on glass under the microscope before using as larval food. Colourtypes: Each larva which survived to the fifth instar was typified according to a system which accounts for a range in colour variation in four distinct morphological features — the head capsule (KK), thoracic shield (NS), anal plate (AS) and body (K). The 4 criteria were divided into 7 (KK), 4 (NS), 4 (AS), and 7 (K) colour classes, ranging from black (1) to light orange (4) or yellow (7). Thus the individuals of the extreme colour phases were characterized by the symbols IIII and 7447 respectively. This scheme was derived from knowledge of the extreme dark-and-light colour forms of the bud moth, confined either to larch (Larix decidua Miller) or the cembran pine (Pinus cembra L.) (Bovey & Maksymov, 1959). For the larvae of the larch form the classes range from 1 to 4 in all morphocharacters, but for an easier distinction larvae exhibiting colour classes 1 and 2 only are called dark and those showing numbers 3 and 4 intermediate. Dealing with the larch form only, the fourth morphocharacter, body colour, is for the entire experimental population black (1), this criterion therefore is omitted from all subsequent discussion. Size and origin of bud moth experimental populations: Adults were selected from larvae collected from larch all over the Upper Engadin in June 1968. They were mated to give crossings, homogeneous according to colourtype. Eggs used were produced by the parents listed and divided at random into two groups to be reared on the two media (Table I).

TABLE I

Parental colourtypes

Family Colourtypes Number of first-instar larvae hatched and reared on 2' 9 8 Larch artificial medium

I 1111 2111 21 23 Dark 2 2211 2211 76 70 parents 3 2111 2111 79 77 524 4 2211 2211 88 90

5 3211 3211 20 21 41

Inter- 6 2231 3231 65 61 mediate 7 3241 4331 39 40 589 parents 8 3331 3331 114 119 9 3331 3431 75 76

577 577 1154 290 K. R. DAY AND W. BALTENSWEILER

HEAD CAPSULE THORACIC SHIELD ANAL PLATE K K NS AS R STA IN

H LARCH

270 SURVIVED THE FIFT

TO G N VIVI

SUR 100_ RVAE LA F O

MBERS 50 - NU ART. MEDIUM

179 SURVIVED

< DARK LIGHT> COLOUR TYPES FOR EACH MORPHOCHARACTER Fig. 1. Numbers of larvae surviving to the 5th instar in relation to the three criteria of morphocharacter with four classes each. COLOURTYPES OF ZEIRAPHERA DINIANA 291

RESULTS

Larval instar mortality on each medium was recorded at each instar. Total larval mortality is greater on the artificial medium (70.00/o) than on larch (62.5°/o) and is in most part due to greater mortality in the first larval instar (91.00/o and 70.50/o respectively), significant at P = 0.01 (Table III). The comparative survival of colourtypes on each medium: Since an equal number of freshly hatched larvae derived from each parental crossing were divided randomly between the two rearing media at the outset of the experiment the results were analyzed in two ways: (1) the larvae which survived to the fifth instar were tabulated according to colourtype and relative differences in survival of each colourtype were indicated by the value of chi-squared in a 2 X 4 contingency table. (2) The percentage of larvae which survived in each family (a family here is defined by the single parental crossing in the previous generation) on each medium is given in a 2 X 9 contingency table and relative differences in survival in each family were again indicated by the value of chi-squared. Survival and larval colourtype: Table II and Fig. 1 show the extent to which differences in larval survival are in some way linked with each of the three morphocharacters (KK, NS, AS).

TABLE II Numbers of larvae with various colour characters surviving to 5th instar on two media

criterion: head capsule (KK)

Food 1 2 3 4 and 5 totals Larch 33 93 101 43 270 Art. Med. 6 64 76 33 179 Totals 39 157 177 76 449 For KK: x2 = 13.88. Differences in survival between media significant at P = 0.01** criterion: thoracic shield (NS)

Food 1 2 3 4 totals Larch 162 81 24 3 270 Art. Med. 49 70 49 11 179 Totals 211 151 73 14 449 For NS: x2 = 58.41 P = 0.001*" criterion: anal plate (AS) Food 1 2 3 4 totals Larch 130 28 100 12 270 Art. Med. 66 20 88 5 179 Totals 196 48 188 17 449 For AS: x2 = 7.76 not significant

In effect this gives no absolute percentage survival for larvae possessing particular morphocharacters since the latter are not known in the first instar when maximum mortality occurs. However, for comparative purposes between media the figures for surviving larvae are informative owing to an equal and more or TABLE III

Percentage survival per family on Larch and Artificial Medium with relative survival values on (2) in relation to (1) Group DARK INTERMEDIATE

Family 1 2 3 4 5 6 7 8 9 TOTAL

9 x S (types) 111x211 221x221 211x211 221x221 321x321 223x323 324x433 333x333 333x343 Number Li 21 76 79 88 20 65 39 114 75 hatched 577

Number L5 8 49 46 45 9 23 20 50 26 276 survived 1-1 t:$ %/family 38.1 64.5 58.2 51.1 45.0 35.4 51.3 43.9 34.7 47.8 422.2 %/group (52.97)2 56.051 (41.32) 40.64 Number Li 23 70 77 90 21 61 40 119 76 577 a.) hatched Number L5 U 6 26 37 19 3 20 11 54 14 190 • survived %/family 26.1 37.1 48.1 21.1 14.3 32.8 27.5 45.4 18.4 32.9 270.8 1-1 %/group (33.10) 33.85 (31.02) 33.45

1154 Totals 64.2 101.6 106.3 72.2 59.3 68.2 78.8 89.3 53.1 693.0 466

% Relative survival on 1. weighted 68.5 57.5 82.6 41.3 31.8 92.7 53.6 103.4 53.0 art. medium mean/family arithmetic 2. arith. 62.5 75.7 mean/group mean/family

For the 2 x 8 contingency table, involving % survival/family on larch and art. medium, X2(8c1f) = 18.66**. Tabulated values for P 0.05 = 15.51 P 0.01 = 20.09 COLOURTYPES OF ZElRAPHERA DIN lANA 293

HEAD CAPSULE THORACIC SHiElD ANAL PLATE 100 KK NS AS DARK III PARENTS 50

LARCH

2 3 4 2 3 4 2 3 4

100

ART. MEDIUM w ~ > 2 3 4 2 3 4 2 3 4 a: ~ -' 100 u. 0 INTERMEDIATE -' PARENTS ~ D > :> a: 50 :::> !J) w (,:J LARCH ....~ z w 2 4 u 2 3 4 2 3 4 3 a: w 0... 100

ART.MEDIUM

234 234 2 3 4

< DARK LIGHT> COLOUR TYPES rOR EACH

MORPHOCHARACTER

Fig. 2. Relative proportions of colour criteria in ft-generation ensuing from dark and inter mediate parents when reared on two different media. 294 K. R. DAY AND W. BALTENSWEILER less random allotment of hatched larvae to either medium at the start of the experiment. From the contingency table x2-values provide a measure of differences in survival between the two media for the range of types involved. Significant differences are found for the head capsule (P < 0.01) and the thoracic shield (P < 0.001), whereas the anal plate criterion just falls short of the 0.05 probability level. Survival and parental colourtype: Table III shows the percentage survival on larch and artificial medium of fifth-instar larvae from individual families. Thus, if, for example, we were to expect larvae originating from dark parents to exhibit high percentage survival on larch then we would expect Table III to show a heterogenous pattern if we could also expect larvae of intermediate origin to show low survival. This heterogeneity within the contingency table is expressed by the x2-value which with 8 degrees of freedom in Table III is significant at P = 0.05. The relative percentages of survival on artificial medium and on larch show the areas in which heterogeneity occurs. However, the heterogeneity is not as consistent as could be hoped, because dark parents do not necessarily give rise to dark larvae only and intermediate parents also give rise to dark offspring. Survival in relation to larval and parental colourtype: In Fig. 2 relative frequencies of colour characters of surviving larvae from either the dark or intermediate group of parents are compared. For all three morphocriteria the greatest contrast in frequencies is found between larvae from dark parents, fed on larch and larvae from intermediate parents, fed on artificial medium. To quantify the extent to which either parental origin and/or medium affects the composition of the fifth-instar colourtypes, the offspring of each family are divided into groups of larvae being alike and unlike the parental morphotypical composition. Since the criterion thoracic shield exhibits the least correlation between parents and offspring it has been neglected for this grouping. Thus the frequencies of the two criteria, head capsule and anal plate, and their 4 classes are expressed as a combination based on the larva as a unit. The results of this analysis are tabulated per family in Table IV whereby the relative mean per family group is calculated as a weighted mean (1) and as the arithmetic mean (2). For a discussion on a population level, the weighted mean is considered to be more appropriate than the arithmetic mean (Tables IV & VI). From the surviving F1-larvae of dark parental origin, only 470/o are like the parental morphotype on both media, whereas 530/0 are of the more intermediate type. The ensuing generation from intermediate parents on larch and artificial medium gives 690/o and 850/o respectively which resembles their parental colourtypes. The paired percentage values (Larch/Art. medium for each family) from Table IV indicate that more individuals reared on the artificial medium and surviving to the fifth larval instar will resemble their parents than when they are reared on larch (Wilcoxon signed rank test, significant at P = 0.05). Therefore we have to eliminate this nutritional influence on F1-colour-composition, when using the same experimental information for a further comparison of parental and offspring TABLE IV

The proportions of the fi-generation which resemble the respective parental morphotype

GROUP DARK INTERMEDIATE

FAMILY 1 2 3 4 5 6 7 8 9 (-)o t- o 9 x a 1111x2111 2211x2211 2111x2111 2211x2211 3211x3211 2231x3231 3241x4331 3331x3331 3331x3431 1... Number-like 7 49 45 43 9 23 20 49 26 ti)trl Number like o 3 41 13 11 2 15 14 41 12 .11 parents Na LI 42.86 83.67 28.89 25.58 22.22 65.22 70.00 83.67 46.15 % .-J x Mean 47.21 (45.2)2 69.41 (66.3)2

Total larvae 3 24 36 17 20 10 54 . 14 il j ium 5: d Number-like z 2 22 11 3 14 8 53 9 ›. Me parents l ia 66.67 91.67 30.56 17.65 70.0 80.0 98.15 64.29 ific t

Ar Mean 47.51 (51.6)2 85.71 (78.11)2

1. weighted mean 2. arithmetic mean

296 K. R. DAY AND W. BALTENSWEILER colourtypes i.e. we have to reduce all values on artificial medium to level comparable with the values on larch. This adjustment was made by using the ratio 0.86 derived from the combined arithmetic means of parent-like proportions Tables 1V and V. However, the Mann-Whitney U test (Table V) does not give a significant result, and we must say that there is no difference between dark and intermediate families for the parent-like proportion in the F1-generation.

TABLE V The percentage of larvae in each family which resemble their parents in colourtype including an adjustment to compensate for the nutritional effect family dark intermediate larch 1 2 3 4 6 7 8 9 adjusted 43 84 29 26 65 70 84 46 art. med. 56 76 28 15 64 73 81 53 Comparing dark and intermediate groups, the Mann-Whitney U test gives a U-value of 13 which is not significant here. DISCUSSION There is evidence that under the nutritional stress of an artificial medium: (1) survival is lower; (2) there is a greater likelihood of effective true-breeding, i.e. more progeny which survive will resemble their parents than under non-stress conditions. Although there is no significant difference in true-breeding between families of dark and intermediate parents, there is a consistent trend of higher proportions of intermediate colourtypes in the F1-generation for any of the experimental groups tested. A combination of the relative survival values and the proportions of colourtypes in the F1-generation gives some insight into the rate of change of the population composition with respect to colourtypes. From Table VI we can see that although relative survival for offspring of dark parents is slightly higher than for those of intermediate parents, the F1-generation shows on both media higher proportions of intermediate colourtypes. On the assumption that the results of this experiment represent a true picture of what would happen in the field, populations under nutritional stress should change faster from one generation to the next to a population of intermediate colourtypes as compared to a population reared on optimal food conditions. In fact such a change from predominant proportions of dark to a predominance of intermediate colourtypes was observed to occur simultaneously with a change from high to low larval densities for the cyclic population in the Engadin (Baltensweiler, in prep.). It is to be expected, however, that under conditions allowing a greater survival to the 5th instar a predominance of dark ecotypes will result, which would then reflect the situation during the progression phase of the population cycle. This experiment then supports the hypothesis for a genetically controlled change in population fitness which might be triggered by a change in food quality. Being

COLOURTYPES OF ZEIRAPHERA DINIANA 297

TABLE VI Rate of change of population structure with respect to colourtype

FOOD LARCH ARTIFICIAL MEDIUM

FAMILY GROUPS DARK (DI INTER. (I) DARK (DI INTER III

100% 100% 100% 100%

SURVIVAL IN F1 GENRN_

IN % ( TABLE XI 56 41 34 33

PROPORTIONS OF F 1

COLOURTYPES PER D47 153 D 31 169 D 47 I53 D15 185

TREATMENT IN %

CALCULATED FREQUENCY

OF COLOURTYPES IN

SURVIVING F1 GENERATION/ 26 30 12 29 16 18 5 28

FAMILY GROUP IN %

TOTAL FREQUENCY OF

F1 COLOURTYPES/POPLN.

ON EACH MEDIUM 38 59

PROPORTIONS OF

COLOURTYPES ON

EACH MEDIUM IN % 39.2 60.8 31.3 68.7

2.19 RATIO 1 1.55 1 genetically fixed, the reduction in population numbers continues for one or two generations after relief of the nutritional stress. It is conceivable that this process does account for part of the residual mortality (kr) in Varley and Gradwell's critical analysis of the population data and may be a function of the defoliation index in Auer's population model. Although not synonymous, then, the three phenomena, i.e. population fitness, defoliation index and reduction in population density, may be closely linked. Contribution No. 45 of the working group, under the direction of Prof. Dr. P. Bovey, on the population dynamics of Zeiraphera diniana; aided by a grant of 298 x. R. DAY AND W. BALTENSWEILER the Swiss National Funds for Scientific Research. The authors thank Imperial College, London and E. T. H. Zurich for an exchange scholarship.

ZUSAMMENFASSUNG VERANDERUNGEN DER ANTEILE LARVALER FARBTYPEN DER LARCHENFORM VON ZEIRAPHERA DINIANA ALS FOLGE VON ZWEI VERSCHIEDENEN FUTTERARTEN Im Verlaufe einer Massenvermehrung des Grauen Larchenwicklers verandem sich die relativen Anteile der larvalen Farbtypen. Es wurde vermutet, daB diese Erscheinung mit der dichtebedingten Schadigung der Wirtspflanze und einer nachfolgenden Anderung der Nahrungsqualitat gekoppelt sei. Zwecks Abklarung dieser Hypothese wahlte man aus Freiland- populationen Individuen bestimmter Farbtypen aus und ziichtete die Fi-Generation auf frischen Kurztrieben der Larche und auf einem semi-synthetischen Nahrmedium. Es konnte gezeigt werden, daB nicht nur die Larval-Mortalitaten auf den beiden Nahrmedien von- einander abweichen, sondern daB auch die Anteile der Farbtypen in den entsprechenden Gruppen verschieden sind. Die Versuche lassen schliel3en, daB unter Nahrungsstress die dunklen Farbtypen wahrend der friihen Larvenstadien eine hohere Monalitat erleiden und somit die Selektion zu einem Wechsel in der Zusammensetzung der Farbtypen der folgenden Generation beitragt. Zusatzlich beobachtet man aber, daB unter Nahrungsstress die Ober- einstimmung zwischen dem elterlichen Farbtyp und jenem der Nachkommen groBer ist. Somit bekraftigen die Resultate die Annahme einer variablen Leistungsfahigkeit der Popula- tion in bezug auf Nahrungsstress wahrend einer Massenvermehrung.

REFERENCES ALTWEGG, P. (1971). Ein semisynthetisches Nahrmedium und Ersatzsubstrate filr die Oviposi- tion zur von der Jahreszeit unabhangigen Zucht des grauen Larchenwicklers Zeiraphera diniana (Gn.) (Lepidoptera: Tortricidae). Z. ang. Ent. (in press). AUER, Ch. (1961). Ergebnisse zwolfjahriger quantitativer Untersuchungen der Populations- bewegung des Grauen Larchenwicklers (Zeiraphera griseana Hb.) im Oberengadin 1949- 1958. Mitt. Schweiz. Anst. 37 : 175-262. — (1969). Erste Ergebnisse einfacher stochastischer Modelluntersuchungen tither die Ursache der Populationsbewegung des Grauen Larchenwicklers, Zeiraphera diniana Gn. (Z. griseana Hb.) im Oberengadin, 1949/66. Z. ang. Ent. 62: 202-235. BADOUX, E. (1952). Notes sur la production du meleze. Mitt. Schweiz. Anst. Versuchsw. 28 : 210-270. BALTENSWEILER, W. (1964). The case of Zeiraphera griseana Hb. (= diniana Gn.) (Lep. Tortricidae) in the European Alps. A contribution to the problem of cycles. Can. Ent. 96 : 790-800. — (1968). The cyclic population dynamics of the Grey Larch Tortrix, Zeiraphera griseana Hb. (= Semasia diniana Gn.). Roy. Ent. Soc. Lond. Symp. on Insect Abundance. 4: 88-97. — (1970). The relevance of changes in the composition of larch bud moth populations for the dynamics of its numbers. "Dynamics of Populations" eds. P. J. DEN BOER & G. R. GRADWELL. Proc. Adv. stud. Inst. (Oosterbeek, 1970). BOVEY, P. & MAKSYMOV, I. K. (1959). Le probleme des races biologiques chez la Tordeuse grise du meleze. Zeiraphera griseana Hb. (Note preliminaire). Vierteljahresschrift Naturf. Ges. Zurich, (Festschrift Steiner) 104: 264-274. VARLEY, G. C. & GRADWELL, G. R. (1970). Recent advances in insect population dynamics. Ann. Rev. Ent. 15 : 1-24.

Received for publication : August 26, 1971.