The Occurrence of Some Coleoptera in Grass Tussocks, with Special Reference to Michocli1jatic Conditions

THE OCCURRENCE OF SOME COLEOPTERA IN GRASS TUSSOCKS, WITH SPECIAL REFERENCE TO MICHOCLI1JATIC CONDITIONS.

M.L.Luff, B.Sc., A.R.C.S.

October, 1964. Imperial College Field Station, Silwood Park, Sunninghill, Ascot, Berkshire. 2

ABSTRACT

In this thesis the beetle fauna of grass tussocks is investigated, and the possible importance of the tussocks to the beetles studied. The first section describes the microbabitat in which the beetles live. The occurrence of grass tussocks at Silwood is outlined, and the morphology and growth of Dactylis glomerate L. is described. The micro - climate, especially temperature, in tussocks throughout the year is studied, and compared with that in the intervening grass. The second section deals with the beetle fauna of tussocks. The numbers and species of beetles found both in and between the tussocks throughout the year are studied, and the species which are regular inhabitants of tussocks are listed. An account of the biology of four of these common species is given, with particular reference to the importance of the tussocks in their biology, and to the stage of the life cycle at which this microhabitat is selected. In the third section, possible effects of the tussocks on the fauna are considered. The behaviour of three common species is investigated with reference to the responses which keep them in tussocks during winter.

Some aspects of their movement in and out of tussocks are investigated. The resistance of the three species to cold is studied, and related to the temperatures in the grass in winter. The precipitin test is used to investigate predation by Carabidae outside the tussocks in summer. 3 CONTENTS Pare I. INTRODUCTION 7 II.THE HABITAT. 14 SOIL 14 A. 1. General Sampling. 14 2. North Gravel. 16

B. VEGETATION. 18 1. Introduction 18 22 2. Occurrence of tussocks at Silwood Park. 3. Description of selected areas. 25 a. Cascade Marsh. 25 b. Rush Meadow. 27 c. North Gravel. 28 i. History. 28 28

11=turigentaotftltylis glomerate L. 31 d. Nursery Field 42 4. Morphology and growth of Dactylis glomerate L. 44 a. Introduction. 44 b. Net annual productivity. 46 c. Changes in morphology due to growth and ageing. 54 C. MICROCLIMATE. 63 1. Introduction. 63 2. Methods. 70 a. Temperature. 70 b. Humidity. 75 c. Other factors. 76 3. Results. 78 a. Temperature. 78 i. Dry summer conditions. 78 ii.Effects of cloud cover. 82 iii.Effects of rain. 82 iv.Effects of 86 v. Dry winter conditions. 88 vi.Effects of snow cover. 94 vii.Comparison of the total subzero temperatures in Holcus.and wdi Dactylis during the winter, 99 1962-3. viii.Conclusions. 104 b. Humidity. 105 c. Light. 111 4. Comparison of micro— and macroclimatic data 114 III. THE FAUNA. 116 A. INTRODUCTION AND METHODS USED. 116 B. TOTAL :IITHROPOD F,UNA. 120 C. TOTAL COLEOPTEROUS FAUNA OF TUSSOCKS. 122 1. Methods. 122 2. Number of species found.. 125 3. Annual changes in the beetle fauna. 127 4

Page, 4. Comparison of the fauna of Dactylis and Deschamps ia. 132 5. Relative numbers of common and rare species. 136 6. Details of common tussock-inhabiting species. 141 7. Conclusions. 149 D. COLEOPTEROUS FAUNA BETWEEN TUSSOCKS. 150 1. Total fauna obtained in pitfall traps. 150 2. Predatory Onrabidae in pitfall traps. 153 3. Sampling of grass between tussocks. 158 4. Conclusions. 161 E. SELECTED COMMON SPECIES. 162 1. Choice of species. 162 2. Stenus clavicornis (Scopoli) 164 a. Introduction. 164 b. Adults. 165 i. Occurrence in tussocks. 165 ii.Occurrence in pitfall traps. 171 iii.Flight and wing dimorphism. 173 iv.Feeding habits. 178 v. Sex ratio. 179 vi.Seasonal changes in reproductive organs. 181 vii.Parasites. 186 c. Immature stages. 187 i. Eggs. 187 ii.Larvae. 188 iii.Pupae. 196 d. Conclusions. 197 3. Stenus impressus Germar. 199 a. Introduction. 199 b. Taxonomy. 199 c. Biology. 206 d. Conclusions. 212 4. Dronius melanoceohalus De jean. 213 a. Introduction. 213 b. Adults. 214 i, Occurrence in tussocks. 214 ii. Occurrence outside tussocks. 218 iii.Feeding habits. 219 iv.Sex ratio. 220 v. Seasonal changes in reproductive organs. 222 c. Immature stages. 223 i. Eggs. 223 ii.Larvae 224 iii.Pupae. 230 d. Conclusions. 230 5. Dromius linenris (Oliver). 231 a. Introduction. 231 b. Adults. 232 i. Occurrence in tussocks. 232 ii.Occurrence outside tussocks. 233 iii.Wing dimorphism 234 iv.Feeding habits. 235 v. Sex ratio 236 vi.Seasonal changes in reproductive organs. 238 5 Pave c. Immature stages . 239 i. Eggs. 239 ii. Larvae. 239 iii.Pupae. 245 d. Conclusions. 246 6. Couoarison of the selected species. 247 IV. POSSIBLE EFFECTS OF THE HABIT .T ON THE FLULT.L. 250 L. BEILLVIOURil EFFECTS. 250 1. Movement into tussocks. 250 a. Methods. 250 b. Results. 251 2. Behaviour of beetles in tussocks. 255 a. Methods. 255 b. Results. 259 1. Temperature. 259 ii. Relative humidity. 261 iii.Light. 265 iv. Tactile stimuli. 266 v. Olfactory stimuli. 267 c. Conclusions. 268 3. Movement out of tussocks. 270 a. Methods. 270 b. Results. 271 B. EFFECTS or SURVIVLL. 274 1. Effects of low temperatures. 274 a. Introduction and methods. 274 b. Results. 280 i. Undercooling point determinations. 280 ii. Laboratory survival experiments. 284 iii.Field survival experiments. 286 c. Conclusions. 288 2. Protection from predators. 290 a. Methods. 290 b. Results. 291 V. DISCUSSION. 293 VI. SUMilLRY. 304 VII.LCIaTOWLEDGE1ENTS. 308 VIII.REFERENCES. 309 IX. 1,PPEND IX TLBLES. 322 7

I. INTRODUCTION.

The occurrence of Coleoptora in grass tussocks has been well known

to beetle collectors for many years, and tussocks as habitats are

mentioned in many standard works on beetles (e.g. Joy, 1932; Walsh and

Dibb, 1954). Pearce (1948) was the first to suggest that the intert-

&orate fauna of grass tussocks might be an interesting ecological study.

He gave examples of the number of invertebrates that could occur in a

tussock, pointing out that the Coleoptara were one of the best represented

orders of insects. As the numbers were highest in the winter, he also

suggested that the tussocks might provide shelter from extreme cold, an

idea which had been put forward earlier by Hancock (1923) and Holmquist

(1926). The possibility of shelter from drought in the summer was also

mentioned. Pearce listed the grasses yielding the best results, which

were Deschampsia, Dactylis, Cynosurus, Malice, Bromus, Holcus, Molinia,

Agrostis and Arrhenatherum. Tussocks of sedge (Juncus species) also

contained arthropods, but he considered their fauna to be somewhat different from those of the grasses.

Little quantitative work has been done on the fauna of tussocks as

such. Richards (1926), in his survey of the fauna of Oxshott Heath, lists

nine species of insect which hibernate in Molinia tufts in winter. Ford

(1937, 1938) studied the Collembola of Bromus tussocks near Oxford, and

listed other insects which occurred commonly in the sem© habitat.

Macfadyen (1952) investigated the Collembola and mites of a Berkshire

Molinia fen, containing tussocks of Molinia, Deschampsia and Juncus, and compared the faunas of these three plant species. Duffey (1962), in a paper on the spiders of Wytham Wood, mentions finding a positive correlation

between the numbers of litter spiders and tussocks of Nardus at Malham,

but omits all details. Data on the Coleoptera of grassland containing tussocks are restricted to surveys of the fauna of the vegetation of

arable land, in which no distinction is drawn between the fauna of tuss-

ocks and that of the intervening vegetation, or to surveys of soil fauna

in which the base of the vegetation was also sampled. A study of the first

type was carried out by Cameron (1917) in two meadows in Cheshire; he

tried to correlate the insects occurring on and under the surface of the

soil with the vegetation, but on too large a scale to give data on indiv-

idual tussocks. Ford (1935) listed the invertebrates of a meadow near

Oxford, but did not distinguish between the faunas of different plant

species. The beetles of a Danish meadow community containing several

tussock-forming grasses were sampled by Schj/tz-Christensen (1954), but

samples were taken in summer only, and again the vegetation of each

sample was not described. Boyd (1960) compared the faunas of grazed prA

ungrazod grassland in Argyll, one of the effects of grazing being the

prevention of tussock formation. In contrast to the previous surveys,

collecting was by pitfall traps, so that species remaining inactive were

not collected, and a comparison of the two total faunas was not obtained.

Examples of soil surveys which include some of the fauna of the surface

vegetation are those of Cameron (1913) near Manchester, Morris (1920) and

Buckle (1921) in Cheshire, Morris (1922, 1927) at Rothamsted, Edwards

(1929) at Aberystwyth and Salt et. al. (1948) at Cambridge.

At the beginning of this study it was decided, therefore, to obtain

quantitative data on the species and numbers of beetles occurring in 9 grass tussocks at Silwood Park throughout the year. In order to compare the importance of the plant species to the beetles, three species of tussock wore chosen initially. Those were Dactylis Paomerata L.,

Deschampsia caespitosa (L.), and Juncus effusus L.; after one month

Juncus was omitted, and the two remaining species sampled for a further eight months, after which the study was restricted to Dactylis glomerate L.

Most of the data in this thesis relate to this species.

The possible shelter from climatic extremes given by tussocks has also received little attention. Ford (1937) made brief measurements of temperature and humidity in Bromus tussocks and suggested that their high humidity was of vital importance to their fauna. Protection from drought was demonstrated by Clark (1947) in New South Wales, where tussocks provide essential shelter for the Australian plague locust, and by Coulson (1962) who concluded that Juncus effusus tussocks provided Tipula species with protection from warm and dry day time conditions. Clo:udsley—Thompson

(1956, 4 included a grass tuft among various habitats in Tunisia in whloh he measured microclimatic conditions, showing that arthropods could obtain shelter there from the extreme daytime conditions of the desert. Van

Hecrdt and Mlorzor Bruyns (1960), working on the arthropods of send dunes in Holland, measured the temperature and relative humidity in an

Ammophila tussock to see whether it provided shelter from drDught, although the necessity for such shelter was not demonstrted. Madge (1953) implied that Dactylis tussocks could prevent a high summer mortality, caused by drought, of the larvae of the moth Oncopera, although no numerical data were published; he did show, however, that the same tussocks prevented mortality by drowning when the soil was waterlogged in winter. 10

The question of whether tussocks might provide shelter from extremes of temperature in winter has not been investigated. Winter temperatures have been measured in other hibornacula by various workers. Examples are in soil (Weil, 1930, 1932), in dead leaves and under bark (Holmquist, 1931), under bark (Miller, 1931), in soil under snow cover (Fox, 1935), in logs and fallen leaves (Hodson, 1937), in wrack beds (Backlund, 1945) and on branches with varying amounts of snow cover (Wellington, 1950). Only

Miller (1931) and Hodson (1937) attempted to correlate the field temperatures with the ranges of survival of the insects concerned. More conclusive work along this line was carried out by Mail and Salt (1933) on the

Colorado Beetle, Leptinotarsa, and by Patton end Mail (1935) on the Grain

Bug, Chlorochroa. Both these insects hibernate in the soil, and the authors were able to show that the soil temperatures above a certain lat- itude, or without snow cover in more southerly latitudes, were fatal to the insects.

It was hoped to investigate this aspect with selected species of beetles occurring in tussocks, in order to determine the amount and importance of any shelter given by the tussocks in winter. This was carried out as part of a larger study of the microclimatic conditions in the tussocks throughout the year, comparable with microclimatic studies of other biologists, such as by Lindroth (1949) in chalk vegetation, by

Milne (1950) in Nordus grassland, by Delaney (1953) in Calluna heath, and by Landin (1961) in dung.

It became apparent, however, that microclimatic factors formed only some of the various possible effects of the tussocks on the beetles living 11 in them, and the investigation was widened into an attempted outecologicel study of four selected species. These are Stenus clavicornis (Stop.),

Stenus imdressus Germ. (Staphylinidae), Dromius melanocephalus Dej. and

Dromius linearis (01.) (Carabidae). It was hoped to study both the effects of the tussocks on the survival of the species, and the behaviour of the beetles which might load to the selection of the tussocks as a habitat.

Many similar studies have been curried out to try and correlate the behaviour of animals in the laboratory with their habitats in the field. The usual aim has been to determine the factors which lead to the selection of the habitat, although the time of year, and stage in the life cycle, at which the selection is made, have not always been made clear.

Lindroth (1949) showed that the temperature differences above different rock types influenced the ranges of distribution of Carabidae of chalk grassland. Pertunnen (1951) investigated the humidity preferences of

Carabidae of wet and dry habitats, and showed that those living in wet habitats were the most strongly hygrophilous. Various Dutch workers (e.g.

Van Heerdt, 1950; Theodorides and Van ileerdt, 1952; Van Heerdt et. al.,

1956; Van Heerdt and A0rzer Bruyns, 1960) have studied the temperature and humidity preferences of Coleoptera from various habitats, and correlated these with the places whore they live, although the significance of such correlations remains a little uncertain in the absence of microclimatic measurements from the habitats. Duffey (1962) concluded that a combination of vegetational and microclimatic factors lad to the choice of habitat by spiders in limestone grassland, although microclimatic measurements were not made. Thiele (1964) studied the factors which restricted Carabidae 12

from various habitats to those particular sites, and found humidity and light to be the most important; temperature affected only a few species.

Other workers have tested experimentally whether behaviour leads to protection from unfavourable conditions. Thus, Chapman et. al. (1926) and Krogerus (1932), both working on the arthropods of sand dunes, showed that resistance to desiccation was negatively correlated with the relative humidity of the habitat selected by various species. Todd (1949) carried out both desiccation and heat death point studies on harvestmen from various habitats. There was a correlation between humidity preference and their stratification in oak woodland. Landin (1961) studied both the behaviour leading to habitat selection and the resistance to microclimatic extremes of Aphodiine dung beetles in Sweden. Except for Landin (1961), however, the term 'habitat' has been used to cover a relatively wide area, such as woodland, grassland, the exposed or sheltered side of a dune system, etc. This approach leads to inconclusive results, as the microclimatic studies already referred to show that biologically significant differences in conditions usually occur between adjacent situations in the same major habitat. Thus to understand the real significance of the behaviour of the animals in habitat selection, the exact situation in which it lives, or I'microhabitatill must be studied. Grass tussocks form such a microhabitat in the general habitat of grassland, and as they have an insect fauna distinct from that in the intervening grass (at least at some times of year) they form a suitable subject for such a study.

The work described in this thesis is thus divided into three parts.

In the first, the habitat is described, in terms of its geology, vegetation 13 and microclimate. The second part contains quantitative data, i.e. the numbers of beetles which occur both in and between the tussocks, together with en account of the habits of the four species of beetles already listed as having been selected for a more detailed study. Finally an attempt is made to correlate the behaviour of these four beetles with their choice of microhabitat, and to study the possible roles which the microhabitat plays in their survival. 14

II. THE HABITAT.

A. SOIL.

1) General Sampling.

Silwood Park is situated on the Eocene Bagshot Sands and Bracklesham

beds. In places these are covered by river deposited gravels from the terraces of the Thames, with resulting flints and flint pebbles (Sherlock,

1947).

The soil is sandy, but there is little podsolisation (Greenslade,

1961), although similar soils in other areas of the Bagshot Beds show well developed podsols (Tansley, 1953). Thus the pH is not very low except around the lake (c.f. map, fig. 1) where acid peat has been formed. Fig shows the areas of Silwood Park where ecological work was carried out; soils from four areas containing grass tussocks were examined. These were

North Gravel (1, fig. 1), a level area with many terrace pebbles toccther

With-biick and other fragments from huts demolished in 1951; Cascade Marsh

(2, fig. 1) and Rush I‘Ladow (3, fig. 1) on the southern :aid northern sides of the lck. r.Jp ctivaly; MursJry Fi_ld (4, fig, 1) Ldjacnt to Rush M:dow, but higher, sloping down to the South and West.

A sample three inches in diameter and nine inches deep was taken from each site in May 1964, and the soil type classified by the subjective method of Sankey (1958). The pH was measured with a Pyo portable pH meter.

The moisture content was determined by weighing the freshly sampled soil, then drying it in en oven at 60°C until constant weight was reached. The results are given in table 1. 15

Table 1. Characteristics of soils from different parts of Silwood Park.

Sampling Site Soil Type pH Moisture Content (%) North Gravel Sand 6.8 12.15 Cascade Marsh Silty loam 4.8 29.63 Rush Meadow Silt loam 6.1 27.45 Nursery field Fine sand 5.4 4.76

Both the presence of the lake, which leads to acid conditions, and the influence of man, es on the North Gravel where the pH is almost neutral due to previous treatment, result in a wide range of soil conditions.

This enables a greater number of tussock—forming grasses to occur within the relatively small area of Silwood Perk than if the soil were uniform. 16

2) North Gravel This area was chosen for most of the ecological work, and the soil was examined in more detail because of its possible influence on the distribution of tussocks within the area. A small section was mapped for detailed study in October 1,61 (21ot 1, fig. 4) and three pairs of soil 9 samples wore taken from this plot; fig. 5 shows the positions of the samples within the plot. The soil particles wore graded by the method of

mechanical analysis of Blyth (1943). Table 2 shows the composition of the two samples from each site, the figures being the percentage of the total dry weight of the samples.

Table 2. Mechanical analysis of soil from North Gravel. e A Site B Site C Total 1 2 Mean 1 2 Mean imuregmarn Gravel & stones>1.25mm 38.6 41.0 39.8 33.8 38.4 36.1 18.4 23.7 21.1 32.33 Coarse sand 1.25-0.6mm 9.1 8.3 8.7 10.2 1.4 10.8 13.4 15.8 14.6 11.37 Medium sand 0.6-0.25mm 32.6 33.0 31.9 37.2 4.2 35.7 47.0 8.9 43.5 37.03 Fine sand 0.25-0.1mm Coarse silt 0.1-0.04mm 17.0 15.2 16.1 16.8 4.6 15.7 7.3 8.4 17.9 16.57 Fine silt 0.04-0.01mm 0.7 0.6 0.65 0.4 0.2 0.3 0.9 0.2 0.55 0.50 Clay < 0.01mm 0.1 0.2 t.15 0.1 0.1 0.1 0.1 0.1 0.1 0.12

The data show the soil to be a sand, but with a high proportion of gravel and stones. The percentage of gravel and stones decreases towards the eastern, tree-lined boundary of the plot, with a corresponding increase in the percentage of medium sand, which makes up 37% of the soil on average. The soil pH was measured in three places on North Gravel in March,

1964; three readings were taken from each sample. The readings obtained are shown in table 3. Table 3. Hoosurements of soil pH, North Gravel.

pH Locality 1 2 3 Mean West edge of N. Gravel 7.1 7.15 7.1 7.12 Centre of N. Gravel 6.7 7.0 6.9 6.87 Between centre and eastern tree-border 6.3 6.3 6.2 6.27 of N. Gravel.

They show a gradient from slightly acid near the trees on the eastern ,dargin to neutral on the west side, and suggest, as do the data on the composition of the soil, that there is a change in soil typo from east to west across the area. 18

13. VEGETATION.

1) Introduction.

Although, as already mentioned, many Coleo:tore have bean listed as living in grass tussocks, the definition of a tussock has not been given.

The list of tussock-forming grasses given by Poort'e (1948) includes species of various habits, the important feature being that they all form "a closely knit entity acting both as a conserver of moisture, and as a protection from extremes of temperature". In his introduction, Pearce states that in order to contain a large fauna, the plants should be "well defined from the adjacent and contiguous herbage, closely knit and well formed, and at a slight elevation above low lying swampy ground". These characters could perhaps be used to define a tussock, but there is the added complic- ation that Pearce also uses the word irtuft" as synonymous with tussock, implying that the two words have the same moaning. The shorter Oxford

English Dictionary gives the following definitions of the two words.

"Tuft. A cluster of short-stalked leaves or flowers growing from a common point, of stems growing from a common root, etc.

"Tussock. A tuft, ,:lump or mattcd growth, forming a small hillock, of grass, sedge, or the like".

From this, the essential feature of a tussock would seem to be that it is raised into a small hillock, whereas a tuft need not be.

A similar distinction was made by Smith and Craiapton (1914), who distinguish between five main types of grassland. Three are relevant to this discussion : i) Meadow types, which have a dominance of taller horloge, including 19

grasses of both tufted and creeping habit, and which depend on floods,

snow or cattle for removal of hay or old herbage.

ii) Tussock types, which have coarse, hard or wiry grasses which tend

to accumulate soil by means of stools or tussocks of dead shoots, and usually carry their dead leafage throughout the resting season.

iii) Stooled meadow types, which are exaggerated forms of the tussock type, in which the stooled habit is assumed as an adaptation to frequent

gentle flooding and silting, or to standing water, rather than to scour

by wind and rain.

Thus, although they do not define the terms, Smith and Crampton imply that tufts are not raised, and that their dead leaf material is removed by

various agencies, whereas in the case of tussocks, the- dead 'herbage remains, and accumulates soil or silt to form a stool beneath the growing grass.

This classification emphasises effects of the geology and climate of the habitat on the habit of the grass plants. At Silwood Park this is shown by Deschampsia caespitosa (L), which occurs commonly around the lake, where the larger plants accumulate soil basally, and develop towards the stooled meadow type of tussock. It also grows more occasionally in rough grass— land away from the lake; in this case the plants are similarly tufted, but do not become elevated as they grow. Dactylis J2lomerato L. is found both in fields which are grazed, where its habit, although often tufted, is open, with no accumulation of dead leaves, and also on rough grassland where the habit is more erect, the dead herbage remains and a certain amount of elevation of the plant base sometimes occurs in the oldest plants. The difference in habit of Deschamosia in the two areas mentioned is slight, and to call one a tuft and the other a tussock does not seem to 20

be a valid distinction. The plants near the lake become elevated at varying ages according to their distance from the water, giving a range of elevation in plants of the same size. In the case of Dactylis all the plants arc tufted, with a group of leaves and starts issuing from a common root mass, but the accumulation of dead material leads to a completely different appearance. Although the base of the plant does not become raised, the leaves and stems become taller in order to grow above the dead herbage surrounding the base of the plant. This results in a different typo of 'tussock', in which the elevation of the leaves above the surrounding grass is due not to elevation of the base of the plant, but to the presence of dead material surrounding the bases of the living shoots.

In this thesis the term 'tussock' includes this type of plant as well as those which are raised on stools of soil. The following characters are taken as defining a tussock. The plant is easily distinguished from the surrounding herbage by the closeness of its leaves and stems, which form a dense tuft, and also either by the accumulation of dead herbage round it, which separates it from the adjacent grass, or by its being elevated on stool of dead vegetable matter in which soil or silt has accumulated.

This definition does not include those typos of grassland in which a grass is broken up into alternate raised hillocks and hollows, without any increase in the density of leaves or stems on the hillocks. Grass mounds formed by ants' nests are also not included, as again the grass is not exceptionally dense or tufted on the mounds. In the case of Dactylis, the type of plant filling the definition given here is similar to the 'tussock' 21 ecotype described by Stapledon (1923) in a daper on the ecotypes of

Dactylis glom-Grata, and which is referred to in wore detail later (Section 4(c)). 22

2) Occurrence of Tussocks at Silwood Park.

Groenslade (1961) has given a summary of the main types of vegetation

occurring at Silwood Park. The basic types are grass heath, oakwood and

beochwood. The woodland areas seldom contain tussocks, although grass-

land along the edges of woods often has abundant tussocks. Most of the

potential grass heath areas are, or have been, used for arable purposes,

and it is these areas which contain most tussocks. In addition, the veg-

etation around the lake is more characteristic of wet areas, and contains

many tussocks.

Fig. 1 shows the areas of Silwood Park which contain abundant grass

tussocks. Three species of grass are shown : firrhenathenthielatius (L.)

Deschampsia caespitosa (L.) and Dactylis glomerate L, and one sedge,

Juncus effusus L.

Arrhonatheruin is found mainly on rough waste grassland north of the

main buildings and west of North Gravel. Because of its height it is vary

distinct from the surrounding grasses Holcus and Actrostis), and

its broad leaves and numerous flowering stems result in plants with quite

dense bases.

Deschamasio is most numerous in Oascade Marsh on the south side of

the lake, and in the wetter (southern) part of the Water Meadow, where it

forms large and often somewhat elevated tussocks. It also occurs occasion-

ally in other rough grassland areas, usually whore Deetylis tussocks are

present. Examples are in Merton's Acres, on Rookery Slope, at the edge of Four Acre Field, and in Nursery Field.

Dactylis is the commonest tussock-forming grass at Silwood, 23

Wood land

Fig. 1. Map of Silwood Park, showing areas containing tussocks.

Lrrhenatherum C, Deschampsia ; D, Dactylis ; J, Juncus. 3. Rush Meadow 1. North Gravel 2. Cascade arsh 5. Pound Hill Field 6. Water Meadow 4. Nursery Field Merten's Acres Nash's Field 8. Pond Field 9. 7. 11. Heron's Brook Field 12. Gunness Hill 10. Church Field 15. Four Acre Field 13. Rookery Slnpe 14- Silwood Bottom 24 occurring almost invariably where there is rough grassland, or waste ground of any sort. It is found in a wide belt up the oast side of the

Park, including North Gravel, and extending up to Huron's Brook Field.

This field is cultivated, but Dactylis tussocks are common in the grass margins of the field; in the same way it is found at the edges of other fields such as Pond Field, Four Acre Field, and Pound Hill Field. A second belt of Dactylis extends down between the central woodland strip and Silwood Bottom, covering Elm Slope and Rookery Slope. Dactylis also forms tussocks in Nursery Field and in the northern part of the Water

Meadow, but its preference for dryer conditions is shown by its absence from the southern, lower lying parts of the Water Meadow.

Juncus is restricted to damp aras of the field station, and is most numerous in Rush Meadow, north of the lake, where it forms a belt of tussocks around the edge of the field, with occasional patches in the centre as well. It is also found in a few dense patches at the wooded edges of

Church Field and Nash's Field, and in the wetter part of Pond Field. This may have led to its occurrence in the adjacent dryer Morton's Acres, which is the only locality whore Dactylis, Deschamosia and Juncus all occur. 25

3) Description of Selected Areas

Three areas were chosen with the intention of comparing the faunas

of different species of tussock. Two were sampled for a short time only,

and only brief details are given here. Those were Cascade Marsh and Rush

Meadow. The third, North Gravel, was studied in more detail, and its

tussocks were sampled for more than two years. A fourth area, Nursery

Field, was included later for comparison with North Gravel; the differences

and similarities between the two areas are discussed in the section on

Nursery Field.

(a) Cascade Harsh

This is an area of grass and young trees, sloping down slightly

from Church Field to the south border of the lake. Fig. 2A shows the

appearance of the vegetation, looking towards the lake, which is hidden by

Salix scrub.

The common grass species are

Holcus lanatus L.

Deschamcsia caesoitosa (L.)

Alopecuuus oretensis L.

with some Anthoxanthum odoratum L.

Fostuca rubra L.

The predominant Holcus often forms hummocks, but these are lower than the

Deschamps is tussocks, which are often somewhat raised in the lower, more

marshy parts. Festuca is mainly confined to the higher and dryer zone.

Other common plant species are

Urtica dioica L.

Campanula rotundifolia L. •••.''ir t‘r:',

' • :'sk• . •,•,;• ,1„irV"rier,; •

'kr :114

*44,354r%

. :=•• ;A*

-74‘, 1,„* • - • • +.(x .-4„,..

•

Fiji. 2. A. Cascade Mush. B. Hash Meadow, 27

Anthriscus sylvertris (L.)

Rubus fructicosus egg.

Cirsium arvense (L.)

Epilobium hirsutum L.

The trees are Quercus robur L.

Salix alba L.

Crataimeus monogyna Jacq.

Quercus is core goner away from the lako, Salix near the lake.

(b) Rush Meadow.

This borders the northern shore of the lake., and slopes up steeply

on its northern boundary to Nursery Field and Pound Hill. It was sown

with barley in 1952 and 1953, then with Loliun orenne L. in 1954. From

1955 until 1963 it was grazed by cattle during each summer, which has

kept the vegetation short, but the Juncus tussocks stand out from the shor

grass throughout the winter. Fig. 2B shows the vegetation looking

towards the lake. Juncus occurs along the southern edge of the meadow,

and in shallow depressions at the foot of the slopes on the northern and

eastern edges.

The dominant grasses are

Anthoxanthum odoratum L.

Holcus lanatus L.

Other common plant species ero

Ranunculus repons L.

Cirsium arvense (L.)

Rumex crispus L.

Ulex euroocous L. 28 Ranunculus occurs in the wetter areas with juncus; Cirsium and Rumex are commonost in the dryer centre of the meadow. Ulex is confined to the north-oast edge adjacent to the road.

(i) History.

This level area of rough grassland, about 750 feet long and 250 feet across, was the site of Army huts until 1951. Most of the huts were then cleared, although several re.icin on the western side. In spring 1952 the area was sown with the following seed mixture :

Lolium perenne 70%

Festuca rubra 10%

Agrostis tenuis 10%

Cynosurus cristatus 5%

Trifolium sp. 5% It was grazed by pigs in 1952, 1953 and 1954, and then loft to beco-le waste.

(ii) Present Vegetation.

The present appearance of North Gravel is shown in Fig. 3A, which wa,,- taken in April 1964, looking north. Unfortunately a strip of grass along the western and northern edge between 50 and 100 feet across was cut early in 1963, and plants occurring there are not included in the species listed below. The following grass species now occur throughout the area :

Dactylis 7lomorata L.

Fostuca rubra L.

Agrostis tenuis Sibth.

A. gigantea Roth.

„•.

- •1,W' ° '4i•e;:;.4 ' ••••••

_410254:r At4c4.41

•

Pig. 3. A. North Gravel. B. Nursery field. 30

Holcus mollis L.

H. lanatus L. Poa trivialis L. P. pratensis L. On the western edge near the buildings, the following are found :

Phleum bertolonii DC. P. matense L.

Lolium orenne L. Agrostis stolonifera L. Alattaarcb.1p,A odoratum L. Bromus mollis agg.

At the northern end, Arrhenatherum elatius (L.)occurs. Other common plant species are

Urtica dioica L. Cirsium arvense (L.)

Plantcgo lanceolate L. Ranunculus acris L.

Taraxacum officinale Weber

Rue acetosella agg.

R. cris-Dus L. R. acetosa L.

Veronica chamaedrys L.

Trifolium spp.

Vic i:.; Cerstium vulgatum Anthriscus sylvestris (L.) 31

In places there are bushes of Ulex, Rubus and Sqrothqmnus, usually adjacent to the wooded border.

Dactylis, Festuca and Agrostis tennis are the most common of the grasses, and each is locally dominant in different parts of the area. Of the grasses sown in 1952, Agrostis and Festuca are widespread, Lolium

2erenne is restricted to the western margin, and Cynosurus cristatus has disappeared.

(iii) Distribution of Dactylis glomerate L.

Dactylis is the most successful of the grasses that have invaded the area since it was sown, and it would appear to be a common invader of arable land that has been left waste. Brenchley and Adam (1915) studied two fields at Rothamsted for twenty years after they ware abandoned, and in each case Dactylis became common. In the first it was scarce four years after the field was abandoned, but increased until after ten years it was the dominant species, comprising 35% of the herbage. After twenty years it was less common, but still moderately abundant. In the second, a wetter field, it also reached a peak abundance after ten years, although it was only moderately abundant then, decreasing to frequent after a further ten years.

Fig. 4 shows the relative abundance of Dactylis throughout the North

Gravel. The terms used are :

i) Domin'art , when Dactylis plants are seldom more than two feet apart, and are the most obvious ground vegetation, often growing adjacent to one another with no intervening other grass species.

Dactyls glomerata L.

•. • • •• •• • • • • • . .• • • • • • • 0 • • • • •

10...•••••• •••••• ••• Dominant

Frequent

Occasional

North Gravel , Plan.

r. Plomer2—a L. on North. Gravel. 33

ii) Frequent, when Dactylis plants occur fairly regularly, but seldom less than two feet apart, except for occasional small groups of plants.

iii) Occasional, when Dactylis plants are scarce, not closer than ten feat from one another, and not in groups of more than one plant.

These groups are obviously only approximate, but they serve to show the general distribution of Dact,ylis throughout the area. The map shows a general concentration of Dactxlis between 25 and 30 feet from the trees, with several extensions westwards from this belt, and other isolated local concentrations throughout the area.

The distribution of individual tussocks in a plot 66 feet X 36 feet

(Plot 1, fig. 4) was investigated in October 1961. The plot was divided up into transects, three feet wide, the Dactylis tussocks in each were measured, and their positions marked on a map. Fig. 5 shows the distribution of tussocks with a diameter of more than 254; where several plants of Dactylis were growing close together they were marked as an irregular large patch, although subsequent examination showed that the individual plants could usually be distinguished if the bases were examined.

There is a concentration of small tussocks under the shade of the trees at the eastern end of the plot; this was true of the entire tree lined border of North Gravel. Fig. 6A shows the appearance of this region in April 1964; there is a belt of small tussocks in the centre of the picture and than a strip of shorter grasses before the Rubus scrub under the trees. The remainder of the mapped plot contains tussocks of various sizes, although there is a strip almost devoid of tussocks about

25 foot from the western end, and a belt containing many smaller tussocks

34 N.Gravel. Area 1. 1961

n o O + o + 0 0 0 0 0 + o O 0 0 ° o T 0 0 0 0+ 0 0 0 0° 0 0 oo 0+ 0 0 0 o 0 o + 0 AA O0 + 0 0 0 + 0 °Qc2 0 0 0 o 0 0a ▪ 0 0 0 0 0 000 0 0 0 0 0° , 0 0 0 0 0 0 0 0 \_, 0 o 0+ 0 0 0 . 0 0 0 0 000 0 0 + 0 0 0 0 1\ 5 0 0 O (N 0 10 • B O ° Q=D Feet

0 0+ + 0 on 15 0 0 0 0 0 00 0 0 20 0 ▪ \✓ + 0 0 0 0 00 0 0 0 0 00 (Th 00 0 0 — o , o 0 o 0 00 0 00 0 0 0 0 0 0 00 0 0 00 0 0 0 0 0 0 o o o 0 0 o 0 ,0, _ -0

o 0 0 0 0 0 0 0 o 0 0 0 0 Tre es . • o o ,3 0 0 0 % o o 0 0 0 o , 0 o 0 o 0 o o o 0 -t- 0 o ,-, 00 0 0 0 '' 0 0 0 0 o + o + o o o+ 0 o 0 00 •

Key. 0 DactyliA Tussock. + Pitfall Traps . A Soil Sample .

Fig. 5. •

)

••••,:$41": • ••., , •°•,.•.. 4 4..•, , •'04,„ c,,„ ,.

;,••• 1 • . • 1411

• t • '-'4", k, • • • .' .r, .• ''' ri,•':. v ( e: ,iiii" ,;•",.."

te • , 36 as well as larger ones, to the west of this. The large scale reap shows these to be local features, not extending along parallel to the trees.

Fig. 6B shows the appearance of the western end of the plot in April

1964, with many large tussocks as well as smaller 21ants.

The numbers of tussocks of different sizes were calculated, and are shown in Fig. 7. From relatively few of 3H diameter (smaller plants were not counted), there was a peak Oa 4H diameter. The numbers then fell steadily as the diameter increased up to 711; there were few tussocks larger than this, only three having a diameter of 10" or more. Fig. 7 also shows the numbers of tussocks of different sizes in the same area in May 1964. The plot was mapped again, and Fig. 6 is the corresponding map for 1964. Tussocks that had been removed in the 1561-62 sampling programme wore marked on the map in their positions before samplings plaS. are indicated by shading. The increase in the numbers of tussocks is evident. Table 4 shows the numbers of tussocks in 1561 and 1964 in the whole plot, and in each of the three zones into which it is divided in

Fig. 8. The 1561 numbers include an approximation of the number of plants in each of the irregular large patches of Dactylic shown in Fig. 52 as well as tussocks of 2" diameter; these inclusions result in a greater total number of tussocks than that given for 1961 in Fig. 7.

Table 4. Numbers of tussocks in naeeed area of North Gravel in 1 1 & 1 9 19a__ _i26...„4._ No. of Density Increase < No. ussocks (per sq.yd.) Density in increase Numbers East 93 1.30 128 1.79 35 37.6 Midd1 90 0.94 141 1.47 51 56.7 West 129 1.34 199 2.07 70 54.3

Total 312 1.18 468 1.77 156 50.0 110-

100-

90- Oct . May 1961 1964 80-

70-

60- Total NumberI 204 396 Number of 50- Mean Diameter 5.13" 4.67" Tussocks

40-

30-

20-

• • • 10- • 0.0.0. • • • • • e ::...• .011 •..... : .•:•...... ••• •.•••• •••••• • • • • • • • • • _•• 3 4 5 6 7 8 9 10+ Diameter of Tussock (Inches)

38 N .Gravel . Area 1 . 1964

acv® 0 0 O 0 0 0 0 0 ,3(2) (00 0 0 0 0 0 0 0 uo oo o o 0 0 o 0 0 ° g) 0 0 moo 0000 e 0 0 0 ,Ye 0 0 0 0 0 o 0 0 a) e 00 0 0 0 0 0 0 0 a. 0 0 o e o o no 0 0 0 ---0 0 0 000 00 0 0 ° 0 0 0 0 ° 0 00 ° Q 00 0 0 00 0 0 0 0 0 0 0 A U 00 0 0 0 0 n ® 0 0 0 o 0 0 0o - 0 e 00 000 oo 0 0 000 S3 0 0 n 0 5 0 0 .., 0 0 o 0 0 0 0 0

0 °00 °0 °C °C Feet 1 o c 000 0 0 0 0 0 0C:0000 07)0 0 00 0 0 1 5 00 0° 0 0 C ° 0 0 0 0 0 20 0 0. 0 0 00 0 0 0 0 jy0 0 0 0 0 O0 0 0000 0 °00®000 0 0 ® P 0 0 0 0 00 ° 0 0° °f 00 C5:82 0 () 0,,, 0 (%0 0 0 0® 0 ki 0 0 0 00 0 ® 0 0 ciD_ . 0 0 _ 0_ ,._.% i)i . 0 0 0 •0 0 0 50E) 0' o 0 0 0 0 0 A 0 0 (Th o 0 ,..., e e 0 0 o o 0 - - - , o 0 - t) 0 O. . 00 0 0 _ 0 e_ , - -0 o 0 00 0 .2774 , 0 0 0 0 ° 0 :' %• •'0— 0 CS) 0 0 (1g, 0 0 eo o u o 63 ® 0 00 e% o 0 0 0 0 0 0 0c9 ° o 0 o o o 00 oo 0o ° 0 0 0 o o 000 0 0 0 0 0 0 0 0 0 o o 0

Key. O Dactylis Tussock present 6) Tussock sampled ,1961-2

Fig. 8. 39

The increase was least under the trees, and greatest in the middle zone

where the initial density was least. The histograms of size distributionin

Fig. 7 show incroc!sed numbers of tussocks of all sizes. The increases are proportional to the numbers present in 1961, except in the case of the 3"

diameter tussocks, which ware relatively scarce in 1961, but which were

the most numerous of all sizes in 1964. This is .possibly because the

1961 measurements were made in October, after a growing season, and the

1964 ones in May, at the beginning of a growing season. Thus the diff-

erence shows the increase in size of young tussocks throughout the summer,

which leads to a greater proportion of 4" than 3" tussocks at the end of

each season. Alternatively, the greater relative numbers of smaller

tussocks may be because, as is shown later in Section 4(b), the size of

tussocks is universoly proportional to the distances between them; the

greater numbers of tussocks in 1964 reduce the mean distances between

tussocks, end this may reduce the mean tussock diameter. In fact the

greater proportion of 3" diameter tussocks reduced the mean diameter from

5.132" in 1961 to 4.667" in 1964.

Using the 1964 map, the fraction of the plot which was covered by

Dactylis was worked out. Examination showed that the growth of other

vegetation within four inches (on average) of the edge of each tussock

was prevented by the dead Dactylis leaves which surrounded each tussock.

For the calculations, therefore, the diameter of each Dactylis tussock

Was increased by eight inches, in order to include all the soil covered by the tussock and its dead leaves. The 396 tussocks present in the 1964

map covered 50,3B8.5 square inches, or almost 350 square feet. The total 40 area of the mapped plot was 36 X 66 = 2376 square feet. Thus the vegetation other than Dactylis covered 2376 - 350 = 2026 square feet. Tho relative percentages covered were 14.7% by Dactylic tussocks, and 85.3% by other vegetation.

Each of the three zones of Fig. 8 was analysed to find out whether there was any significant departure of the arrangement of tussocks from a random distribution throughout each area. This was done by the ',nearest neighbour', technique described by Clark and Evans (1954). In each zone the distance of each tussock from its nearest neighbour was measured, and the moan of these distances calculated. This was then compared with the moan expected if the arrangement of tussocks was random, which was calculated from the formula

E =j0.2500

is the expected mean distance from nearest neighbours, and m is where rE the density of tussocks in the area, measured in the same units as the distances between tussocks. This formula is a modification by Blackith

(unpublished) of that given by Clark and Evans. Tussocks which were nearer to the edge of the area than to the nearest tussock inside the area were not measured. The obsorved, 6, and expected, ;El mean distances were then compared. An observed mean lower than that expected indicates that the tussocks are clumped together; an observed mean higher than expected indicates that they are overdispersed, and tend towards a hex- agonal arrangement, in which they are equidistant from one another. The significance of the differences between 7'2 and ;0 was obtained by calculating the standard error, C, assuming a normal distribution, from the formula 41

(ro - iE)(N.m) C 0.2614

are the observed and expected mean distances from nearest Whore ro and rE neighbours, N is the number of tussocks measured; and m is the density

of tussocks in the area.

Table 5 shows the data obtained from each area, and the values calcul-

ated for the various statistics. R is the ratio of observed to expected

mean distances between tussocks. P is the probability of observing a difference between r greater than that obtained, assuming a random o andrE distribution. All dimensions are in units of feet) or square feet.

Table Results of "nearest neighbour" anaLuos of tussocks in the mapped area of North Gravel, 1964. Zone East Middle West Area 648 864 864 Total number of tussocks 128 141 199 m 0.199 0.163 0.230

7!.E 1.119 1.238 1.043 N 120 1) 182 r 1.135 o 1.150 1.173 R 1.028 0.947 1.088 c 0.579 1.128 2.279 P .57 .26 .03

The table shows that the only significant non-random distribution

was in the western area, where R was >1, indicating that the tussocks

wore overdispersed, tending towards equidistance from one another. This 42

non-random distribution was significant at the 3% level. The slight

amounts of overdispersion in the eastern zone, and of clumping in the

middle zone, were not significant.

(d) Nursery Field

This field slopes down towards the south and oast, joining Rush

Meadow on its south-eastern margin. When it became part of the field

Station in 1952, it supported Lolium perenne L., Dact:lis glomerate L.

and Medicago sativa L; the relative proportions of the three species were

not recorded. It was grazed by cattle in 1953, 1954 and 1955, and then loft to become waste.

The present dominant vegetation differs according to the level of the ground, but most of the common species occur throughout the field, in

varying relative abundancies. Fig. 3B shows the vegetation looking east along the border with Rush Meadow.

The commonest grass species are

gropyron ropens (L.)

Holcus lanatus L.

Ajrostis tonuis Sibth.

Festuca rubre L.

Alopecurus matonsis L.

Dactvlis glomerate L.

Of those, Agropvon is by far the most extensive dounating at least 50 of the field. Holcus and .1 grostis are common in the remaining areas.

Dactylis is restricted to scattered single plants except in the north of the area, whore it is dom:Lnent over a small patch. There are also occasional Doschampsie caospitosa (L.) plants. 43

Other common plant species aro

11cidicago sativa L.

Trifolium spp.

Urtica dioica L.

Cirsium arvense (L.)

Rumex acetosella egg.

R. orispus L.

Veronica chaoaeedrys - L.

linthriscus sylvestris (L.)

Rubus fructicosus egg.

Urtica and Anthriscus occur together, mainly in a patch on the southern border. The remaining plants Listed are found throughout the field.

The interest of this area in com)arison with the North Gravel is due to the fact that most of the Dactylis tussocks ore old, isolated plants and Dactylic is decreasing in abundance throughout the area, except for the small patch at the northern edge. This is in complete contrast to the North Gravel where tho number of old, decaying plants is still small, there aro many small tussocks, and the number of Dactylic plants is still increasing. 44 4) Morphology and vrowth of Dactylis c-lomerata L.

(a) Introduction

Beddows (1959) summarises tho morphology and ecology of Dactylis,

and reviews previous work on the species. It is a course, tussock-

forming, perennial grass, with the culms erect or spreading, and the veg-

otativo shoots considerably flattened. It has neither rhizonos nor

stolons, so that vegetative propagation does not normally occur. This

results in the plants remaining distinct from ono another, although Jonas

(1933) mentions that the lower nodes of the stem may develop tillers

which root and set up clonal individuals a short distance away from the

parent plant. Each flowering shoot is probably annual, since it dies

beck after producing an inflorescence. The plant itself survives because

of now tillers which develop from buds at the base of each shoot. Tho

leafy shoots can survive the winter, so that there is no real dead period,

and new leaves grow away from among the previous season's dead herbage.

Beddows points out that it is a very variable species, and that many

ecotypes have been described. Staplodon (1920 divides the varieties into

six ecotypes as follows :

i) Lax hay. Tall and erect plants with a height to diameter ratio of

more than unity; long leaves, with the lower internodes of the shoots

relatively long, giving a 'loafed up' appearance; few barren tiller;;

early flowering.

ii) Dense hay. Plants similar to Lox Hay, but with many barren tillers

which are produced at the same time as the p',nicle tillers , and which result in much denser plants; late flowering.

iii) Tussocks. Dense, erect plants, usually less high than hay, but

with a height to diameter ratio still greater than unity; leaves long, 45 but less 'leafed up'; very many barren tillers' with the panicles in tiers; flowering over a long period, iv) Cups. Plants with the panicle tillers widely inclined from the vortical, giving a height to diameter ratio of loss than unity; fewer barren tillers than tussocks, but can be lax or dense. v) and vi) Spreading and Dense Pasture types. Short, with short loaves; height to diameter ratio usually greater than unity; plants often dense, but the panicle tillers are very short°

Most of the Dactylic plants on the North Gravel resemble the tussock ecotype of this classification, but some, especially ricer and under the trees, have spreading leaves and stems, resulting in plants similar to the cup ecotype. Where several plants grow close together they sometimes become taller and less dense, and resemble the dense hay typo more than tussoc s. Stapiodon found that tussocks were the only one of the six ecotypes that did net breed true, and concluded that they wore possibl: always hybrid phenotypes. This would explain the occurrence of other typos on the North Grovel as well as the tussocks.

Two aspects of the development of the plants, which might be of importance to the insects in them, were considered. The first was tho production of dry matter throughout the year, or Nat Annual Productivity of the plants. Together with information on the length of life of individual loaves, this gives en idea of the relative abundance of dead and living loaf material throughout the year, and of annual changes in total leaf matter, both living and dead, of the plant. Secondly, the morphology of plants of different sizes was observed over a period of almost three years. This made it possible to gain an idea of the ages of tussocks of varying sizes, and to study changes in morphology as the plants grew older. 46

(b) Not annual productivity.

It has already boon mentioned that loaf production in Dactylis is

almost continuous, being slowed down or halted only by cold weather in

winter. Each leaf has a life of only a few months (Webster, 1956), so

that there is a continual accumulation of dead Loaf material. Roppo

(1963) measured the growth rote of various species of gross, including

Dactylis alomerata, throughout the year. Leaf production started towards

the and of arch (although there was considerable variation in the date

due to temperature), and continued until mid-November. The growth curve

was bimodal, with a main peak at about the 20th. June, and a second,

smaller, maximum around 20th. September. Knight (1960, 1961) showed that

the total amount of green material increased throughout each growing season,

and then decresed throughout the winter, when the summer and autumn

loaves died without being replaced byfrosh growth.

From those papers the following possible sequence of events can be

worked out. The amount of green leafage increases abruptly each year from

April till June or July, and then, as the spring leaves begin to die more

gradually till about October, when the dying loaves outnumber the new ones still being produced. The amount of dead material begins to rise some two months after the peak loaf production end continues to increase until mid winter, when all the previous seasons leaves have died. The ratio of dead to living material is high in the spring, but falls during the summer duo to the fresh crop of loaves. It then rises again from

Late autumn onwards as the dying leaves outnumber those produced. In winter there aro few green leaves, and these are dormant, but a proportion 47

of the dead leafage is removed by rotting in wet weather. In oath sub-

sequent year the initial amount of dead material is greater, giving a

higher ratio of dead to living material at the beginning of each growing

season.

During sampling of Dactylic tussocks for their fauna between December

1561 and December 1962, measurements wore made of the basal area, density,

and ratio of dead to living leaves of all tussocks sampled. The density

and dead to living ratio were calculated by removing both dead and living

material between the heights of kis and 6", and separating the dead and

living leaves which were then dried and weighed.

The total dry weight per square inch of the area of the base of the

tussock was termed the density of the tussock, and the dry weight of dead

leaves divided by that of living loaves gave the dead to living ratio. The

mean distance in feet of each sample from the two nearest neighbour tussocks

was also calculated, and two co-ordinates worked out for the position of

the sample in the plot. One corresponded to its position on the east-west

axis of the plot, measured in foot from the east end, end the other to its

north-south position, measured in feet from the south side.

Table 6 summarises the data obtained. The mean area of 23.72 sq.

inches corresponds to a diameter of 5.5 inches. The mean tussock diameter calculated from the data on tussock sizes already given in Section 3(o)(iii)

and shown in Fig. 7 is 5.1 inches. The mean of the tussocks sampled

is larger because the samples were chosen so as to contain approximately equal numbers of tussocks in the three size groups 3v4", 5,6" and 7-10",

whereas in fact there were fewer tussocks in the 7 — 10" group than in the

3-4" group. This resulted in a greater proportion of the larger tussocks being sampled, so that the moan diameter is correspondingly higher. 48

Table 6. suididary of characteristics of tussocks sampled, December, 1961 - Docember,_1962.

Standard Characteristic Minimum i\aiXiLlUld Moan eviction Area (sq. irk) 4.0 78.6 23.72 12.68 Density (gu . per 3.86 1.589 sq. in.) 0.69 0.598 Dead/living ratio 0.70 15.40 2.715 2.207 East-West position 2.5 67.4 36.95 19.24 North-South position 0 36.0 17.15 11.37 Distance from 0.6 neighbours 6.0 2.36 1.09

The density varies relatively little, from 0.69 to 3.36 grams dry

weight per sq. inch. The density of loaf material of other common grasses

on the North Gravel was investigt_Ited briefly for comparison. Table 7

shows the density of various grasses: in each case a six-inch diameter

circle of turf was removed, and the grass between the heights of and

611 cut off, dried and weighed as before.

Table 7. Density of various North Gravel grasses

Dominant Other grasses present Density grass in tho sap (gus. I-Jor. sq.in. Agrostis - 0.52 ii - 0.56 ti Holcus 0.44 ii Fostuca 0.46 Festuca - 0.89 II - 0.38 it Agrostis 0.33 it ii 0.51 Holcus - 0.47 tt - 0.50

Mean density 0.507 gus. per sq. in. The mean valuo of 0.507 is loss than a third that of Dactylis 49

The dead to living ratio of the Dactylis samples is much more

variable than the density, varying by a factor of 22 from loss than 1 in

a young tussock to 15.4 in a tussock which was almost completely dead.

The position data merely show that tussocks were sampled from all

parts of the 33 X 66 foot plot; slightly greater numbers were sampled

from the western end, which resulted in the moan position being 36.95

foot from the eastern end, almost four feet from the centre of the plot.

There was hardly any bias in the north—south direction.

The figures on the distance of each tussock from its neighbours

show a range of from just over six inches to six feet: these figures were

obtained from the map after the tussocks had been sam)led, rather than from the field at the time of sampling, and are therefore probably not

very accurate, although sufficient to give en indication of the, relative distances apart of the tussocks which were sampled.

In order to try and determine the effects of those factors on the

beetle fauna of the tussocks, these data, together with data on the

beetle fauna and date of each sample were analysed by Pegasus computer at the Forestry Commission Research Station, Alice Reit Lodge, Surrey. The date was calculated as the number of days since the beginning of the year, to try and show up any cumulative changes taking place throughout the year.

A multiple correlation and regression was carried out using the programme described by Jeffers (1959). The effects of the tussock characteristics on the beetle fauna are given later, but the correlation coefficients between the various tussock characteristics are given in Table 8 below. 50 Tablo 8. Multiple regression coefficients of characteristics of tussocks sampled between December 1961 and December 1962 First Analysis

Area -.049 Density .218xx -.138 D/L ratio .2373E* .170 -.037 East-West Position .164 -.118 -.002 -.098 North-South Position .217xx —.035 -.015 -.034 .081 Neighbour distance ** .060 .175 -.328, -.125 -.058 .063 Date

Degrees of Significance : 10% * 5% 2% 1%

The significant correlations ore as follows. i) Between area, and dead to living ratio. This is duo to the progressive increase in both size and dead leaf content as the plant ages. ii) Between area and oast-west position: the size increases towards the west of the area. iii) Between area and distance from adjacent tussocks: the more isolated the tussock, the larger it is. Knight (1960, 1561) investigated the difference in growth of Dactvlis grown under spaced plant and sward conditions, and showed that sward conditions, when there are many plants close together, result in smaller plants as fewer tillers are produced. He suggested that the amount of light that each plant received might be the factor influencing its growth rate, and that isolated plants, which got more light, became larger than sward plants of similar age. This is supported by the significant correlation between basal area and distance from 51 adjacent tussocks. The significant correlation between area and east-

west position also supports the idea, as the tussocks at the eastern end

are shown to be smaller, and it is at this end of the plot that the light

is reduced by the trees.

iv) The ratio of dead to living leaf matter is inversely proportional

to the date. As the date was recorded in days since the beginning of the

year, this confirms the decrease in dead to living ratio throughout the

greater port of the year as the new growth is produced. The relatively $10,- don increase in deed to. living ratio that .lust occur at the end of the year

when all leaf growth has ceased evidently does not greatly affect the

significance of the correlation during the year as a whole.

A second analysis was carried out with additional data on the numbers

of dead flowering stems of each tussock sampled (the first ton samples lacked this information, and were omitted), and with the sampling dates re numbered so as to show the number of days away from the nearest end of the year. This was in order to investigate both whether the flowering

stems had any effect on the fauna, and possible cyclical changes throughout the year of both fauna or tussock characteristics. Any cyclical change with a maximum in summer should give a positive correlation, and with a

maximum in winter a negative one. The multiple regression coefficients are shown in Table 9.

The correlations between area of tussock and ratio of dead to living leaves, east-west position and distance from adjacent tussock show up as before. In addition the following coefficients, which were not significant in the first analysis, are significant at the 10% level or below. 52 Table 9. regression coefficients of characteristics of tussocks salTpled between Deck3aber 161 and Docoilbr lam. Second Analysis.

Area -.062 Density .219k -.268*x- D/L ratio .099 East-West .219k 2o s it ion .163 -.137 -.186 -.037 North-South Position -.051 .015 -.030 .063 Neighbour distance -X** .35i:! No.of .453, .170 .183 .026 .212* Stews -.133 .266** -.184 .174 -.023 -.020 .079 Date

Degrees of significance 10% ;, **

i) Between density and dead to living ratio. This is a negative coeff-

iciont, indicating that as the dead to living ratio decreases during the

growing season, the density increases, duo in both cases to the new

growth of young leaves.

ii) Between density and east-west position. This suggests that at the

western end of the plot the tussocks are denser us well as bigger than

at the eastern and.

iii) Between density and date. As the date in this analysis was given

as the nuaer of days free the nearest end of the year, this correlation

indicates a peak density in the surlier. This agroes with the theoretical sequence in that the density wilt obviously rise during the growing season. The fact that it correlates significantly with the date in this 53

analysis but not in the previous one suggests that there is a consider-

able drop in density in the winter, presumably due to the rotting of the

previous season1 s dead leaves.

iv) Between the number of flowering stems end. area. This shows that the number of panicles produced each year increases as the plant grows,

which is to be expected. Thera is evidence (cf. Section 4(c)) that in

very old tussocks the number of panicles produced decreases, but there

mere few tussocks of this age in the plot, and probably only one or two

at the most were sampled. v) Between the numbers of flowering stems and east-west position. The tussocks at the western end of the plot arc thus shown to be more vigorous in panicle production as well as in size and density. vi) Between the numbers of flowering stems and distance from adjacent tussocks. As in the case of the increased size of isolated tussocks already demonstrated, this is probably clue to the increased light available to the isolated tussocks.

The fact that both area and number of panicles are correlated with both distance from other tussocks and distance from the trees, whereas density is correlated only with distance from the trees suggests that some factor other than the increased light causes the increased density of the tussocks at the western end of the plot, but there is no evidence as to what this is. The dead to living ratio shows a negative correlation with the date as previously, but it is not quite significant at the 10% level. The decreased level of significance in the second analysis could either mean that there is little cyclical fluctuation in the ratio, or that the period from December 1961 to February 1962, whose samples were 54

not included in the second analysis, was the tineo when the ratio in-

creased again as the loaves died. It is possible that in a multiple

correlation with a fairly high number of sets of date, as In this caw))

significance levels greater than 10'1. can be taken to be 'meaningful; oven

considering only those which are significant at the 10 level or below, however, these analyses support the sequence of leaf production and decay

outlined previously.

The Dactylis plants on the North Gravel range in size from young

plants about one inch in diameter up to tussocks with a diameter of ten to twelve inches. Little information is available on the length of life of Dactylis plants, or the time taken to reach any given size. This is

probably because work on Dactylis has concentrated on pasture and hay types which are of economic importance, and the tussock ecotype, with its accumulation of dead loaves, has received little attention.

Beddows (1959) mentions that somo Dactylis plants at the Welsh Plant

Breeding Station at Aberystwyth wore known to have survived for eleven years, but does not mention the type or size of the plants.

The question of how long each plant lives was considered important when discussing the permanence of the habitat formed by the tussocks.

Kershaw (1960) bias described. a cyclical change in vigour over a period of twenty years in Alchemilla aloina.; the plant vigour, as indicated by loaf diameter, increased to a la Leu.i after about ton years, and then fell as the plants aged. An attempt was made to discover whether any similar cyclical change occurred in Dactylis: if so, it would give en indication of the size of plants at their maturity, size being taken as 55

proportional to ago.

Twenty basal leaves wore sampled from each of 240 tussocks varying

in dinueter fron 3" to 12N. The leaves were driod and weighed, and the

weight plottad against the tussock diameter, which was taken as en indic—

ation of the age of the tussocks. The variation in the weights of leaves

of tussocks of all diameters was so groat, however, that no association

could he seen, and the curve obtained by plotting the weight of 20 leaves

against tussock diameter did not differ significantly froei linearity,

using the test given by Snedocor (1956, p. 455). There are various possible reasons for this inconclusivo result.

Rappo (1963) mentions that the leaves produced at different times of year

in the same plant were of different sizes: as different plants probably

vary in the time of their peak leaf production, this mill increase the

variation in leaf sizo of a number of tussocks at any one time. Samples

of more then 20 loaves might have reduced this variation, but the work

involved would have boon excessive. Also the tussock diameter is not a

true indication of the ago of the tussock, as other factors, especially

distance from other tussocks influence the size of any tussock; thus if

there is a cyclical change in vigour with ego it might net have shown up

when compared with size of the tussocks.

The morphology of tussocks of varying sizes was considered next. Duo

to the effects of proximity of other tussocks on tussock size, well isoL

eted tussocks away from the trees were chosen. Figs. 9 and 10 show 4 tussocks of varying ages. The photographs were taken in Ape i1 1964,

when the growth of new leaves had just begun (although it had started late); the flowering stems visible in some of the tussocks are all dead • -

•;I' .;-• • *1: *n.•• -c,, • ;7

( *a, • , - i•• tift4itt ,

• ak*„ , - To v. diii,2.-Lts.•-. • — itO •(/' .

4040.11!:' • .1•1 • Ais 4;:

- ' 4‘.s. ' • .11F, I. ‘7

• •••

AO 3" Diameter nimmaiure tueseciu

;]4 6" Diameter "mature" tuasook.

-. 4 ''' : '..-... ' r ° le; ,z' ,o• -.."-:-.;7410,-., ::- ''''il?...`,:::,,-4-'.. '15•til ' IAA ''' 'fl'"•' .-','• -. ' ' r.. 4 A.y: ,':4,,:•`;'..-..-- ,41 - f *.,,,t:E.P::';'- ,. '-':' 1:\ -„.. i,: ::!): 2 :, :.,_ ;E•r - , . -Y.' • ' ' iil' . .,/ ; _.. .,4. :r.iii. ', ' • ' .'•-• _.- - - : •:', ,t, 1 -4-4,4.,.. Ji.,---. ".. -" . _ . ;' .g.-_=7, "V,' ,,,,...:::-... Mil ' • -' iciki I iy

** fk.

, • 1.44,1.11"1%•"-‘,' ' •••:- jeplry • ; • •

I I I I I t j • t

Fla. 10. A. 10" diameter tussock, be&ilinilig to decay. B. 12" diamei,er decaying tussock. C. Movement of an old tussock in three yaars. 8 50 8) 64000 co C2o° 000 0 0 0 A 0

oocao B Qicf

-o

-1 Inches -2 0 °QC O 0 -3 0 000 00o 00 0 CD °co or-cf_o 4 00 Oc'gc? Ouo i0.1 40(o1 oodoo 00 -5 0 0 DO og OR° 1 0000 0 ,3 0 0 0 0 00

1?ig. 11. Piagrammatic cross sections of tussocks, to show arrangement of tiller bases.

A. Young, 2" diameter tussock. B. Dature, 5" diameter tussock. C. Old, 8" diameter tussock. 59

remains from the previous year.

Fig. 9A shows a plant which must have started growth the previous

year. The base is about 2n in diameter, and the remains of one flowering

stom taro visiblo at the base of the plant, so that it must have flowered

during 1963. In Fig. 11A a diagrammatic cross-section of this tussock

at ground level is shown. Zech ring shows the base of a tiller. No .

distinction is mode between dead tillers and those with a live shoot at

the centre. In general the larger and older tillers are mainly made up

of concentric layers of deed loaves, usually with a live shoot in the

centre at this young stage of the plant. The smaller tillers consist

of a live shoot surrounded by one or two dead leaves at the most. The

tillers in this young plant are nearly all small (a quarter inch or loss

in diameter) and only about half of them are touching adjacent tillers;

the others are scattered, so that the overall density of the plant at

this stage is small.

Fig. 9B shows a fairly small tussock, about 5" in diameter. There

are several flowering stems still standing, which indicates that a con-

siderable number of panicles were produced in 1963. Already the central

upright loaves are surrounded by aI Skirt' of dead loaves whichfoul fo a

fallen mess around the outside of the plant, and isolate the tussock

from the adjacent grass. Fig. 11D shows the cross-section of this tussock

at base level. The number of tillers is greatly increased compared with

the si:oller tussock of Fig. 11A, and in this case the tillers tend to lie

in two aLitost isolated groups, a fairly frequent phenomenon in medium sized tussocks. This may be the result of a tiller having rooted, and set up a clonal individual next to the original plant. In older plants the division is not usually evident, probably because each plant spreads into 60 the intervening space. In the tussock of Figs 9B and 11B the tillers

era mostly still small, but lie close together in each group, giving a

dense, young growth.

Fig. 10A shows a large tussock, with a basal diameter of 8". Host of

the leaves showing are dead ones which have fallen down, with relatively

few new, erect, green leav,s emerging from the centre of the plant. The

dead leaves aro thickest on the side of the tussock downwind from the pre-

vailing winter winds, which are from the south-west. In Fig. 11C the

arrangement of tillers at the base of this tussock is shown. The arrow

indicates the prevailing wind direction. Most of the smaller, newer till-

ers arc in the portion of the tussock facing the wind. The downwind portion

has hardly any tillers except for a ring of dead ones around the edge of

the tussock. This is because the dead leaves, most of which are blown over

to the north-east stifle any tiller growth in that section of the tussock,

and the dead herbage at their base decays completely, leaving the area

devoid of loaf base remains. Young tillers develop among the older tillers

on the upwind side of the tussock, resulting in a zone of high density. In the middle of the tussock there) is a region with only largo tillers whose

bases have not yet decayed, and some of which contain live shoots; behind this is the decoyed area.

Fig. 10B shows a tussock in which this process has gone a stage further, and is evident from the external appearance of the tussock. This tussock was ono of the largest on the North Gravel, and therefore presumably one of the oldest. Nearly all the plant is a mass of dead leaves, and only on the left in the photograph, which is the upwind side, is there any new growth. In effect, the growing zone of each tussock moves upwind when the plant becomes old, 61

and choked by its own dead loaves. This was confirmed by ommination

of tussocks which had been used for thermocouple measurements in Autumn

1961. Fig. 100 shows one of these tussocks: the stake urrowed in the

photograph was inserted into the centre of the tussock in Novomber 1961.

When the photograph was taken in March 1964, the stake was almost six

inches from the centre of the growing zone of the tussock.

Similar observations mado on various tussocks at the beginning and end of the 2i•- year period of study indicate the following stages in the growth of Dactylis tussocks. Tho sizes given refer to isolated tussocks.

i) nIumaturell tussocks. From the first growth of the seed to a diameter of three to four inches takes 2 or 3 seasons. The plant alroady shown

in Fig. 9A shows the amount of growth that can occur in the first year.

Plants of this size in 1961 had a diameter of about four inches in 1964, after two further growing seasons, giving en age of 3 years.

ii) 'ligature', tussocks. These are from four to seven inches in diameter approximately., and the tussock shown in Fig. 9B is a young example.

Production of panicles is high, so the tussocks usually have a crown of dead flowering stems throughout the winter. Dead loafage accumulates at the base of the tussock, but not markedly asymmetrically. This stage seems to last for about three years, and continues till the stage shown by the tussock of Fig. 10A. iii) Decaying tussocks. This covers tussocks such as thoso shown in Figs.,

10B and 10G, in which most of the tussock consists of dead loaves, and the new growth is restricted to a small area on the upwind side of the plant. The number of both now leaves and panicles is loss than in mature plants. The tussock of Fig. 10A is just ontoring this stage, as 62 the 1964 season's growth would hove been concentrated in the upwind section, and there are few remains of flowering stems. Again, it appeared that the degeneration from a large mature tussock to that of advanced decay such as in Fig. 10B tokos at least three years.

From these estimates, the age of such a large and decaying tussock can can be worked out as 0 or 9 years at least; the number of years during which a decaying tussock will continua to produce new growth before dying completely is not known. It is reasonable to suppose that the oldest Dactylis plants on the North Gravel began to grow when grazing of the area ceased in 1954. This givos the oldest tussocks, such as that of

Fig. 10B, an ago of 92 years in March 1964, which agrees with the estimate based on observations on morphological changes.

The work of Brenchloy and Adam (1915) already referred toy showing that Dactylis was commonest about ton years after introduction onto waste land may correlate with this. If the ageing is assumed to be as worked out on the North Gravel, all the tussocks increase in vigour during tho first or 8 years, and there is ra rapid colonisation of the area. From this time onwards, however, an increasing number of tussocks decay, with reduced panicle production, and probably reduced competitive ability.

This enables other plants to invade, so that the percentage of cover of

Dactylis decreases after about 9 or 10 years. Possibly this has happ- ened in Nursery Field, where Dactylis was Jresont as ono of the dominant grasses in 1952, but whore by 1964 only a few old and decayed Dactylis plants remained, and Agropyron repens L. had dominated over half of the field. 63 C. MICROCLE‘LATE.

1) Introduction.

Investigations of microclimntes have been made by both meteorologists and biologists; their different requirements hove led to variations, both in the meanings of terms, and in their methods of study. In all cases, microclimate is token to mean variations in climate either more localised, or at a lower level, than those obtained by instruments at standard meteorological stations usually tens of miles apart, the measurements from which are indicative of the macroclimate. The exact meaning of microclimate varies considerably, however. Brunt (1945) defines microclimatology as "the study of variations of climatic conditions over distances which, at most, amount to a few miles". In fact, many of the differences that he gives are on a smaller scale than this, so that the effects of soil type, plant cover, water and snow on air temperature are all considered.

'Geiger (1950) gives "climate in the least space" as the best definition of microclimate; in practice he includes all studies on the air layers less than two metros above the ground, which rather exceed the limits of his definition. He mentions the suggestion of Scnettn (1935) that a further term, "mesoclimate", should be used for climate on a scale intermediate between "the least space" and the macroclimate, but does not use the word. Many meteorologists hove since used microclimate to cover all climates more localised than the macroclimate (e.g. Brooks and

Kelly, 1951; Sutton, 1953); this includes a range of conditions from

"the gradient above a transpiring leaf to observed variations of temperature among hill and valley stations" (Wellington, 1950). 64

This is obviously too wide n range for entomological work, and has

led to other definitions being put forward by biologists; Uvarov (1931)

stressed the importance of the climate in the insectts habitat, when

considering the effects of climate on insects. lie distinguished between

two terms :

(i)"Ecoclimote", which is the climate in any major habitat type, such

as a wood, marsh, sand-dune, etc..

(ii) qiicroclimate", which is the climate in the actual medium or position

where the insect is living, such as under bark, in soil, in plant stems,

under stones, etc..

These terms correspond to the meso- end microclimato respectively of

previous workers. Kirkpatrick (1935) used the term ItecociLlate" to cover the conditions in all animal habitats, and did not use microclimate. He considered that the distinction between eco- and microclimate was not always clear, e.g. when studying relatively large and mobile animals such as birds, whose microclimate was in fact the ecoclimate of the vegetation type in which they were living. Because of this, he preferred to use "ecoclimate", even for the conditions in the restricted microhabitats of many insects. But this also leads to confusion. For example, if an entomologistclls the climate under the bark of a tree an ecoclimate, because his animals live there, what is he to call the climate between the trees in the forest, which the ornithologist has already celled an ecoclimate, because it is the habitat of the birds 'no is studying? It is • probably simpler to retain Uvarov's two definitions, and accept that larger animals may live in an ecoclimate, and are not subject to a microclimate in the restricted sense, which applies only to insects and other animals living in restricted places. 65

Thus the distinction between coo- and microclimate can be a

useful entomologic,: 1 one, and the restricted definition of microclimate

has since been used by Wellington (1950), Delaney (1953)end Landin (1961),

among others. Linargth (1949) defined microclimate as "the climate of end

within square metres", and introduced the term "lecoalimate" as "the climate of hundreds of square metres". This is on a larger scale than the ococlimato of Uvarov, but it has since been expanded by Landin (1961) to include "all the climatic conditions which constitute the transition

zone between the macreali-ate and the microclimate". Thus it becomes

synonymous with mesoclimate, and does not seem to be a necessary addit-

ional word. It is therefore not used in this thesis. Smith (1954) has summarised the literature on terminology, and distinguishes between three scales of climate below the macroclimate:

(i) Variations of climate in an area perhaps two or three miles in extent

(topoclimote, microclimate, e.g. Drunt (1945), mesoolimete, local climate).

(ii) Variations due to large local features (ecoclimate, lococlimete, e.g. Lindroth (',949).

(iii) Microclimate in the restricted sense of Uvarov (1931).

In this thesis, microclimate is used in the restricted sense, and is taken to be the climate of the air spaces between the stems and leaves of grasses of various species. This covers both the microhnbitAs of insects living between the loaves, and the conditions immediately surrounding those that live within leaves or stems.

The types of measurements usually made in the investigations of microclimatos by meteorologists and biologists also differ. Meteorolog- ists generally attempt to find an explanation for the phenomena which 66 they are measuring. The climate is explained in terms of its physics, such as by measuring heat end moisture transfer throughout the area studied, and often by expressing the results in mathematical relationships and formulae. This has been celled the dynamic or physical approach by Van Wijk and do Wilde (1962). The alternative, which they call the static or descriptive approach, is the description of the microclimate in terms of its tomporaturo, humidity, wind, radiation, etc., with only the minimum of explanation of the changes and value's of the factors measured. Such explanations are not mathematical, and cannot be used to predict the effects of other combinations of conditions. The physical approach is important for the study of the, influence of the environment on living or inanimate objects in that environment. The local temperature generated by the animal itself is the important quantity in many physical studies by biologists, and it is the transfer equations and the heat and moisture balance which determine the body temperature. Van Wijk and de

Wilde consider, however, that as insects are small, the microclimate of a location is not disturbed by a limited number of them, and the physical approach is therefore not as important as it is with bigger objects. The descriptive approach is considered quite satisfactory to answer questions such as whether conditions are favourable for insect development or survival.

This distinction is also discussed by Wellington (1957). He considers that the physical approach leads entomologists into excessive complexity, with respect to the factors to be measured, numbers of ob- servat ions to be made, and methods of presentat ion. Smith (1954) emphasises that the data collected, and the methods used, by biologists 67 should be designed to relate clearly to the ecology of the organisms.

He says "We should study insects and their microhnbitnts, and not micro-

climates without reference to their contained organisms". Certainly the description of the microclimate by measuring selected factors gives the essential information on the conditions encountered by the insects,

and enables experimental work to be based on a knowledge of the field conditions. There is no guarantee, however, that two apparently similar

microhnbitnts will have identical microclimates, as they may vary in shape or position. Thus some understanding of the effects of these

variations on the microclimate is helpful. A limited explanation of the

microclimatic phenomena makes these effects understanablo, and is a

quicker alternative than the description of conditions in many microhabitats which differ only in minor structural or positional characters.

Wellington (1960) also considers the frequency with which records need to be taken. For a dynamic understanding of the microclimate, continuous records are needed in order to give a complete picture of what takes place: this loads to extensive and complex analyses of the data.

Wellington considers this to be unnecessary for most entomological work, and advocates taking extensive readings on selected days only. Those days should be chosen in order to show extremes of weather conditions, as indicated by macroclimatic measurements. He also suggests that the microclimatic data should be related to a synoptic description of the macroweather; the type of weather should be described in terms of the air masses or frontal systems present, and their origins. Tha advantages of this system would be in the ease of comparison between measurements made at different times in different localities. The British climate is 68 influenced by both continental and oceanic air masses (Tansley, 1957), but the characteristics of these air masses arc often altered in the depressions which pass over the area (Sutcliffe, 1940). In this thesis, therefore, it was not attempted tc classify the types of air.

Continuous readings were made, although a physical explanation of the climatic processes which occur in the micro environment was also not intended. From the continuous records, certain days were than selected to'illustrate the extent to which the microclimate is affected by the macroweather. Humidity measurements were made on selected days to give a similar picture. The main intention throughout was to gain an idea of the conditions experienced by insects in the grass, with particular reference to extremes; the information then provides a valid basis for experiments on behaviour and survival in relation to climatic factors.

The microclimate in an even stand of Dactylis glomerate at Silwood was measured by Hughes (1954, 1955), in order to determine which macroclimatic factors affected the microclimato. Other studies have boon made in various types of low vegetation, but the results are not always directly comparable. Geiger (1950) and Chauvin and d'Aguilar (1946) summarise much previous research, mostly German, and carried out from a physical point of view, but all showing similar effects. There is a tendency at ground level for low vegetational cover to reduce fluctuations of temperature by raising the level at which most radiation is absorbed and radiated (the llouter effective surface', (Geiger, 1950)). Tho diurnal variation in temperature is greatest at this level, and is reduced below this. Roussakov (1925) obtained similar results in cereal crops in

Russia. Champnass (1950) showed that as seedlings of Timothy Grass 69

(Phloum) grew, the outer effective surface was raised because of the

increased height and density of the plants. Similar results have since

been obtained by Broadbent (1950) in a potato crop, and by Penman and

Long (1960) in wheat. Itinterheuse (1950, 1955) showed that the stratif-

ication of temperature in grass is dependant on the height, density and

mode of growth of the plants, and also on the solar altitude. Delaney

(1953) studied the microclimate of Callum henthland, where the reduced height and different nature of the vegetation gave rather different results from those in grass and cereal crops. As already mentioned in

Section I, brief investigations of conditions inside grass tussocks of various species have boon made by Ford (1937), Clark (1947), ClOadsloy

Thompson (1956) van Roordt and 110rzer Bruyns (1960) and Coulson (1962).

All these authors took measurements in summer only, and data on the microclimate in low vegetation in winter are lacking. To remedy this, measurements of temperature were taken throughout the year in tussocks.

This gave both summer data for comparison with other grasses, and winter data for comparison with summer conditions in the tussocks. It also served as a basis for ecological experiments on the insects inhabiting the tussocks. rleasurements of other factors wore only made when their importance to the behaviour or survival of the insects was suspected; thus light and humidity were briefly investigated. 70

2) Methods

(a) Temperature.

Initially, attempts were made to use thermistors for measurements of temperature in tussocks. Stantol thermistors, type F 23, ware used, connected to a motor in a Wheatstone bridge potentiometer circuit. This circuit was designed so that a correction could be made for the different resistance (and resulting different calibration) of each thermistor. In operation several thermistors were switched sequentially into the bridge circuit, the control was adjusted for the appropriate resistance of each thermistor at 20°C (which was determined previously in the laboratory), and the standard calibration scale of the potentiometer used to rend the temperature of the thermistor in circuit. This removed the need for a separate calibration chart for ach thermistor, which is one of the usual disadvantages of thermistors (Wellington, 1957). The relative cost and delicacy of thermistors, compared with thermocouples, prevented their being loft out in the field for long periods, and to re-insert them into the grass each time that measurements were taken was inprocticable. This was because the temperature inside the tussocks was disturbed by the introduction of the thermistors, so that time had to be allowed for acclimatisation to take place, and also because of damage to the plant through continued insertion and removal of the thermistors.

Because of these disadvantages, thermocouples wore used for nearly all the measurements. From December 1961, until August 1962, readings were made at selected times using 18 thermocouples made of 29 s.w.g. copper and constantan. The ends of each pair of wires were soldered together, and the resulting thermocouples arranged in sets on throe thin 71

stakes so as to give three sets of readings at varying heights up each

stake. The stakes were inserted into various types of grass in order

to measure the vertical temperature gradients, or toimoorature profiles,

in the grasses. Two stakes were inserted into Dactylis tussocks: one

was in an old mature tussock, 8" in diameter, with thermocouples at

intervals from 21 to ground level, and the other in a rather short

tussock, 6" in diameter, with thermocouples from 11 to ground level.

The third set was in Fostuca about 6" high, and also had thermocouples

from 11 to ground level. each stake was held upright by a retort stand

and clamp about 12" from the stake, and the thermocouple lends were

carried upwards clear of the grass before being led over and down to a o junction box. From this, common wires load to a reference junction at

(in molting ice), and to a Doran "Mini" Potentiometer, with which readings

were taken. Measurements were made about three times each day, usually

in the morning, afternoon end evening. On occasions further readings

ware taken during the night.

Various authors (e.g. Vao."Lja, 1949; Wellington, 1950) have

recommended that thermocouples be shielded with a polished materiel to

reduce error duo to absorption of radiation, which would raise the temp—

erature of the thermocouples above that of the air. If readings of the

ambient temperature are required this is a necessary precaution, but the

ambient temperature is not always what is needed. As insects have no

protecting shield, they absorb radiation to which they are subjected,

and their body temperature is raised accordingly: thus if the body temp— erature of insects in a particular habitat is required, unshielded thermo— couples will probably give more relevant readings (Wellington, 1949). 72

In this study the temperatures to which the insects are subjected was the

important factor; as radiation affects this, unshielded thermocouples

wore used for all measurements.

In August 1562 it was decided that continuous records of temperature,

although possibly giving a lot of superfluous data, would aid in understanding the variations of temperature in the tussocks, especially by showing the times of minima and .Anxima at various levels. A Sunvic

Recording Potentiometer, Type R.S.2.M., which could give automatic recordings of up to 16 thermocouples, was available. The instrument was situated on Observatory Ridge, north of the North Gravel, and the only

Dactylis tussocks within reach of the thermocouples wore some rather isolated ones on the west-facing slope of the ridge. In order to determine whether continuous measurements made in these tussocks would be comparable with the profiles from North Gravel, thormistors, and the bridge circuit already described, were used to measure temperatures in similar tussocks at each site, within as short a time as possible of one another. As each site two sets of readings were taken in five tussocks, at heights of 3", IP and ground level. The sots of readings were compared using Studentts"tn test to show any significant differences. Table

10 summarises the results.

At ground level, the differences between the two sites ware never significant. At litt they were on one occasion, and at 311 on two, one in the morning and the other in the evening, when the western aspect of the tussocks on observatory ridge might have been responsible. It was concluded that any differences in results from those obtained on the

North Gravel would be slight, and the Sunvic Potentiometer could therefore 73 be used.

Table 10. Students "t" test of differences between temperatures in tussocks on North Gravelt_and Observatory Ridge.

"t" Date Time Weather Ground 3" level 12tlevel Le v el 27.6.62 1330 - 1420 icioud, windy, dry 0.5829 0.8622 0.1982 29.8.62 1725 - 1800 I cloud, calm, dry 3.0514* 2.0260 2.6012 3.9.62 0920 - 0950 i cloud, brooze,dry 2.9020* 3.769 0.1437 7.9.62 0850 - 0910 Total cloud, breeze 0.1858 0.4309 1.3659 rain just stopped 7.9.62 1930 - 1955 Clear, breeze, dry 0.6360 2.0839 0.1850

Significance levels : ** 1Y! * 5°;

Six ther,kcouples worn installed, using commercial plastic insulated

thermocouple wire, with the ends bared, soldered together, and then

dipped in wax to prevent wat.r entering between the wires and the

insulation. The thermocouples were installed in two sets of three, at

heights of 3", 1?f"- and ground level; one set was put in an old Dactylis tussock, 10" in diameter, and the other in Holcus about 5" high. The common "cold junction" lead was taken to a thermostatically controlled reference junction, maintained at 45.5°C. The instrument was in operation

between 21st. September 1962 and 6th. September 1963, but the record was not continuous, due to numerous breakdowns, especially during the coldest of the winter weather, when the teupereture in the hut housing the instrument fell below freezing, despite electric heating. Fig. 12 shows, in the form of a chart, the days of each month when the recorder was

10 recorded

Sept. Jill I Lit P 81 eri Oct. IIIIIIIIIIIIIIIIIII 1. 1IIII 99 od

1962 Nov. I ilt IIIIIIMIIIIIIIIIIIIIIMI III 81 of

Dec. lli 11.11 III MIIII I! 1111i I u 72 se Jan. IMIII. I ili ,IIIIIII II , I, . I UM I I. 70 of

S Feb I I I I I I I I I I I I I I I I I III i ill , III I 97 unvi Month Mar. 1 Ms III I IMAM' I I I I IIIIIIII I 88

c R Apr. IIIIIIIIIIIII I 1 I I I I I mill I Mil 91

e I cordi I I I iiiiiii May IIIIIII I II I I I I I I I 98 1963 June III It i I iiii IIIIIIIIIII II iiiii I 95 n g P July 111111 IIIIIIIIIIIIIIIIIIIIIMIIIIIII 91

ot II tit III I I Aug. B. I ...... 1. I 84 e nti Sept. 79 omet

er 5 10 15 20 25 30 . Day of month AMIE = Recorder not working 75

not working. The worst month was January 1963, when only 70% of the time was recorded; the best was October 1962, with a 99$ complete record. The total proportion of the year recorded was 87.5%. The calibration was checked at intervals using the 44.5°C reference junction, together with a thermocouple in melting ice at 0°C. Froa September 1962 until 14th. January 1963, the range was from 45°C to -5C; it was then o altered to cover from 47°C to -20 CI in order to record the low temp- eraturos being experienced at that time.

(b) Humidity.

Humidity was measured by papers impregnated with cobalt thiocyanate, which were compared with coloured standards as described by Solomon (1957).

The papers were exposed to field conditions in long pieces of glass tubing, of an internal diameter, hold vertically in sets of three, with their upper ends at heights of 31?, 1:111 and ground level reepoctively.Pieces

of cobalt thiocyannte paper X 2:t1 mere inserted into the tubes from above, until the top of the paper was level with the top of the tube, and left for 12 to 2 hours to allow for the time taken to roach equilibrium in the narrow tubes. The papers ware than removed, placed in liquid paraffin, and taken back to the laboratory for comparison with the standards.

This rather crude method was adopted after various more complex types of humidity measuring apparatus had been tried unsuccessfully. A

Gregory hygrometer was available, and was used for a few readings, but the element was rather large, and had to be moved from place to place for each reading, so that the time required for acclimatisation in any one position prevented a quick series of readings being taken in adjacent 76

microhabitats. An attempt was made to use anodised aluminium elements

which function as a capacitance-resistance hygrometer (Cutting et. el.,

1955), but the calibration of the instrument was not reliable, and it

WS considered impracticable without further research being done on it.

Various typos of thermocouple psychrometors have been described (e.g.

by Powell, 1936; Bcleire and Anderson, 1951; Unger, 1953), but their use

in the field is limited by the effoct of evaporation from the wet "bulb",

which raises the humidity in any confined space where humidity is being

measured. Trials wore made using twin thermocouples, ono dry, the other

coated with a "bulb" of plaster of Paris, which was saturated with water

before use. It was possible to obtain readings accurate to about 2%

in the laboratory, but in the field the results were indeterminate, and

it was probably loss accurate than the cobalt thyocyanate papers, which

were used instead.

(e) Other factors.

Light was measured with an E.E.L. Ilightmasterl photometer, with a

sensitive area of 15.2 square centimetres, and a sensitivity of from

0-10,000 foot candles. In practice it was inserted horizontally into

the vegetation at various heights, to discover at which levels, and to

what extent, light was absorbed in the various types of grass. In the

absence of a suitable radiometer, it was assumed that the total radiation

was absorbed at similar levels, as Hughes (1955) showed that the readings of a multi-directional radiometer in Dactvlis wore directly proportional to those of a photometer measuring only the vertical component of light

intensity, similar to that used in this work. 77

R3cords of the wind speed at different 'levels in the grass wore not :Lied° during this work. Where an indication of tho wind speed near tho ground was needed for comparison of different days, records wore available, in the summer months only, from a wind spend and direction recorder at a height of three foot over mown grass, which was situated in Silwood Bottom, about 200 yards south west of Observatory Ridge. 78 3.) Results.

(a) Temperature.

The data from the continuous recorder on Observatory Ridge, and the

readings at intervals from the Doran Potentiometer on North Gravel were

examined together, to SOG how differing ,ncreclimrtes affected the micro-

climate at various heights. The micreclimat - during oxtrome weather

conditions of various typos was studied to discover whether biologically

significant differences occurred between the tussocks and the intervening

gross. The examples which follow are illustrations of variations of temp-

erature in the different typos of weather.

( ) Dry summer conditions.

The daily courses of temperature in the 10n diameter old Dactylis

tussock, and in adjacent Holcus on a clear hot day (26th. May 1963) cre

shown in Fig. 13. The temperature profiles on a similar day (17th. June

1962) aro shown in Fig. 14, with the difference that the intervening

grass was Festuca. Appendix Table 1 summarises the uacroclimatic data for each day for comparison: those data, together with other macroclimatic

measurements presented in the same table, were measured in front of the

main building at Silwood.

The day on which the profiles wore measured land :core sunshine duo to the later time of year, with resulting higher ambient temperatures, but

in other respects the two CoTs were similar.

Fig. 13 shows the temperatures at ground level and at 349 in the

Dactylis and Holcus on the 26th. May 1963. The tussock is shown to give a considerable reduction in variation of temperature at the 3n level: in

Holcus the range was from -1°C to 40°C, whereas in the tussock it was from 5°C to 20°C. At ground level the ranges wore from 6°C to 17°C, and

*.IGTIVe0,71

. 1 . g Fi . D . 3 ail y t y em perat s s yli ct a D . n i res H. u II H 0 0 C1 9 ( c) T )

0 C 20 30 40 0200 04000600 0800 10001200140016001800 200022002400 ••• ------3 3" levelinHolcus 11 levelintussock Time 26 May1963

------.

Soil levelinHolcus Soil levelintussock

1 1 1 081

V 7 June 1962 ll

'ae 2' T e m pe 0900 1100 1300 rat Height ure

1' 1P pr ofil

6" O. e s i 3" n 0 D 0 10 20 30 a ct yli 2'

s T and 1500 2130

F Height e st

u 0 c 1' 9 a

6" 4°. H. I • • o o 10 20 30 10 20 30 • 10 20 30 0C

10" d lam. tussock ° 'O 'Slalom. tussock • -II 5* high Festuca 81

from7°C to 13.5°C, respectively. The peak temperature was reached at

1230 in the Holcus at 3", at 1400 in the Holcus at ground level and in

the tussock at 3", and at about 1500 in the tussock at ground level,

although the peak was greatly smoothed out at the base of the tussock.

The minimum temperatures occurred just before dawn, at 0400 at the 3"

level in the Holcus, at 0430 at this level in the tussock, end between

0500 and 0600 at ground level in both situations. The temperatures at the 1:? level were intermediate between those at 3" and ground level in

both cases.

The profiles of Fig. 14 show that the reduced fluctuations in

temperature are a result of the lower level at which the thinner grass is

heated as the day warels up. Lt 0900 the profiles wore similar in both

tussocks and in Festuca, although the latter was warmer. By 1100, the

shorter grass had warmed up, with the peak temperature, corresponding to

the level at which most radiation was absorbed, at 3". The tussocks,

however, absorbed the radiation at a higher level, so that they ware

warmest at the 21 level, below which height the temperature decreased.

At night the gradients wore reversed, so that by 2130 the Fostuca was coolest between 6" and 3", the region from which it loses most radiation,

whereas the tussocks wore still relatively warm at this level, but cooler

at the 1' level. The nocturnal gradients were always less stoop than those occurring during the day, so that the differences in temperature between the tussocks and the intervening grass were less.

Thus the temperatures in the tussocks are much lass extreme, especially during the day, and the peak temperatures occur later in the day, than in the intervening grass. 82 (ii) Effects of cloud cover.

The effects of cloud cover are best shown by comparing the

temperatures shown in Fig. 13 with those of Fig. 151,. The two days

whose temperatures are graphed in Fig. 15 were both overcast, but

whereas on 16th. Juno, shown in Fig. 151,, there was no rain, on the

6th. July 1563, shown in Fig. 15B, it rained for ton hours. Fig. 15B

is discussed later, but Appendix Table 1 gives the macroclimatic d,tn for both days.

The obvious effect of cloud cover is to reduce the differences

in temperature between the different points. The 3" level in Holcus had a range of only 15°C, from 12°C to 27°C, and at ground level the range was from 11.5°C to 16°C. The points in the tussock showed oven less variation: at midday the 311 high point was only 1.5°C warmer than at ground level. The fall in temperature in the evening was slight, and there was no nocturnal temperature inversion, so that the 3" level in Holcus remained the war:Jest point measured (except at the start of tyre period shown, when cloud hod not formod).

(iii) Effects of rain.

The graph for the 6th. Juno 1963, shown in Fig. 15B, shows clearly the effect of continuous rain. Between 0900 and 1900 rain foil almost continuously, with a total of 21.6 mu. falling over a period of 9.9 hours.

The temperature at the 311 level in Holcus decreased to about 2°C above those of the other points, and fluctuated about that level until after dark, when a break in the cloud cover at 2230 resulted in sudden cooling.

The temperature at the 3" level in the tussock fell from about 1200 onwards, and became the coolest of the points measured: this contrasted

- -•- - -•-Sf level in tussock Soil level in tussock 3"level in Holcus Soil level in Holcus R

IJ 30-

°G, 16 June 1963 A sq- cic O J 0 20-:. 0 Q.,

10-

0 cdoo oiioo orobo oebo lobo 121)0 1400 1600 1800 2000 22b0 2100 O'g 307 20-6 mm. Rain CD 6 July 1963 CD 0C B 0 4 CD CD 20-

Cl-

CD ------_ ------' • CO •.;.•;.; '' ' ''''''''''' ------• • ' ------107

0200 0400 0600 0600 1000 1200 1400 1600 1000 2000 2200 2400 Time 84 with the dry overcast conditions shown in Fig. 15A, whore this point

reuained warmer than either of the ground level temperatures. The points

at ground level were not noticeably affected by the rain. The falls in

temperature at 399 wore probably a result of the warmer gross being cooled on contact with the rain, rather than cooling by evaporation,

because they occurred during the rain, and not afterwards as the grass dried. This is shown more clearly in Fig. 16 in which the temperatures of the same points as in Figs. 13 and 15 are shown during showery weather.

In Fig. 16A, the effects of a very heavy shower from 1255 to 1350 on

28th. Juno 1963 are shown. During the period of loss than one hour,

15.6 al. of rain fell. The La-edict-6 drop in the tuperature at 399 in the Holcus is quite dramatic; at tho soma time the temperatures of the

399 point in the tussock, and ground level in Holcus, fell to the same level, so that by 1330, the ground level in the tussock was the warmest point. From 1330 onwards this fell as well, which suggests the rain took over half on hour to penetrate to the base of the tussock. After the rain ceased, the 311 point in Holcus warmed up immediately, although there was a second drop at 1530 due to light rain (0.2 mm.). The other points continued to cool, reaching a minimum at 1415, with the 399 level in the tussock 100 colder than the other two points. If the continued cooling was due to evaporation, it is difficult to see why the 391 level in

Holcus, the most exposed of the points, was not also cooled, unless heating as a result of incoming radiation was sufficient to overcome cooling by evaporation at this point only. This sort of question would be answered by the physical approach to microcli-atic .leasuroments discussed in Section 1, but for a knowledge of conditions in the grass, the data of Fig. 15A are adequate. 85

15.6 mm. 28 June 1963 A 30- - level in tussock 3" level in Holcus Soil level in tussock Soil level in Holcus 25- °c

10 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 , 3.8mm. 0.6mm. 1.3mm. 27 August 1963

25- B

20- °c

15-

...

•••......

10-

1100 1200 1300 1400 1500 1600 17.00 1800 1900 2000 2100

Fig. 16. Temperatures in Dactylis and Holcus in showery weather. 86 Fig. 16B shows the temperatures on a day when there were several showers, separated by dry intervals, with occasional patches of sunshine.

Each of the three showers during the afternoon was marked by an immed- iate docr_ase in temperature at the 3" level as before, and a slight, delayed fall in temperature at the base of the Holcus; the base of the tussock was not affected by the smaller quantities of rain in these showers. Thus the only ef2ect of moderate rain fall is to reduce the temperature in the lower part of the grass between the tussocks. Cond- it ions at ground level, and within the tussocks, ore only affected by exceptionally heavy rainfall.

(iv) Effects of wind.

Wind records at 31 were only available for the period from May to

August, 1963, when there were no strong winds. Hughes (1954, 1955) showed that minor fluctuations in wind speed, above a critical level of about 3.4 m.p.h., resulted in minute to minute variations of the temperatures in the upper part of the grass, but had relatively little effect on the daily variations in temperature, which wore more dependant on air temperature and radiation. The data which were available did not record such minor variations in wind speed, and thus few of the effects of wind on the temperatures in the gra ss could be demonstrated.. Most of the more windy days during the recorded period were overcast, so that the differences in temperature between various points in the grass wore slight in any case. However, Fig. 17 shows the graphs of temperature from 1100 until 1400 on three successive hot days when the wind was stronger on each day than on the one before. The temperature at the tin level in the Holcus is included as well as the 3" and ground level 2 June 1963 31 May 1 June 40-

3" in Holcus 30- 1 in Holcus co

co Temp. oc 3" in Dactyl is 0"in Holcus 20- 0 1-3 co 0" in DacAylis_

c+ 10-

(1) 1100 1200 1300 1400 1100 1200 1300 1400 1100 1200 1300 1400 CD Time sv 0] 11

40 10 20 30 40 10 20 30 40 _ 10 20 30 0---• 1:14:111_,qkal °C Profiles at 1300 0---0 DCISIYILI tussock

88 temperatures in bath grasses. Appendix Table 1 gives the macroclimatic data for the three days, which were Ihy 31st, and Juno 1st. and 2nd, 1963.

The three days showed a gradual decrease in ambient temperature with an

increase in the wind speed at mid-day. The microclimatio ne-suroments

indicated that the t mperatures throughout the tussock, and above the

1P level in Holcus, were lowered, whereas at ground level and 1:1-1t in

Holcus there was no drop in temperature. The reasons for this are not clear, but it does suggest, at least, that the effect of wind may be to reduce the temperatures in the upper parts of the more open grass; below

12" the wind speed was probably reduced sufficiently to have little effect. Correspondingly, the Holcus profiles bcoame more erect on each successive day, but the tussock profile was similar on each day. The. effects of wind speed on the low level inhabited by the insects in the tussocks are probably slight, in any case, as a dense tussock must form an almost complete wind brook.

(v) Dry Winter conditions.

The minimum temperatures reached in winter were of great interest, as previous microclimotic studies in grassland did not include winter measurements, and it was hoped to investigate the possible importance of the grass tussocks as shelters from temperature minima. Fig. 18A shows the range of temperttures, end Fig. 18B selected profiles, on two comparable dry clear days without snow in late winter. The two dates were the 2nd. March 1963 (Fig. 18A) and the 13th. March 1962 (Fig. 18B).

Appendix Table 1 gives the mocrocliaatic data for the two clays.

The graph of Fig. 181, is similar to that of Fig 13, which showed the temperatures on a clear summer day; the greatest fluctuation was shown

• 2 March 1963 A 10- G ra 0 ss t C em pe r at ure - - -3- level in tussock Soil level in tussock

s i -10- Sieve! in Holcus Soil level in Holcus n

cl 02'00 0400 0600 0800 1000 1200 1400 1600 1600 2000 22b0 2400 ea

r 13 March 1962 wi B

nt 0930 1730 2230 er

cond Height i ti o ns

. cji

0 10 15 0 oC 10"d jam. tussock a -6 5"high Festuca 0 0 ediam.tussock 90

by the points at the 3" Leval, and the Holcus temperature fluctuated

more than that in the tussock. The fluctuations were generally less then

in summer. There was a nocturnal temperature inversion as in summer,

but it lasted for longer, in this case for 14 hours. The coldest time

was just before dawn, although there was little change in the temperatures during the night. The temperatures at ground level wore rcuarkably

steady, and never varied by more than 1°C from the freezing point; the differences in temperature between the two points at ground level were negligible.

The profiles from a similar day shown in Fig. 1CD also resemble those of the summer, as shown in Fig. 14. Lt 1930 the warming up process had started, and the, Festuca was warmer than tine tussocks, which still showed a negative gradient of temperature with increasing height up to

6". By 1400 typicrl incoming radiation profiles were shown, with the

Fcstuce, warmer than the tussocks at 3" 1)3cr,uso its outer effective surface was lower. At this time of year the Fostuca was warmest 6" above the soil, compared with at the 3" level in su,imer. This was because of the reduced altitude of the sun in winter, so that thc incoming radiation

Was at a more acute angle to the ground, and did not penetrate so deeply into the grass. The tussocks, on the other hand, were lower in height, in winter than in sum....,r, as most of the leaves ware dead, end were blown over by March. Thus they heated up nt the same level as in summer, because the reduced penetration of the sun's rays was offset by the reduced height and density of the tussocks. This explains the reduction in differences in temperatures at the 3" levels in Dactylis and Holcus shown in Fig. 18.1,1 when compared with Fig. I3 . The _)rofile at 1730 shows 91

that all temperatures wore similar, during the change from diurnal to

nocturnal conditions. The cooling appeared to take place earlier than

in the grass measured in Fig. 181, possibly because the graphed measure-

ments were taken on a west-facing slope, whereas the North Gravel, on

which the profiles wore measured, is level, and has huts on its western

edge, which cut off the sun's radiation shortly before it sets. The

2230 profile shows a temperature inversion similar to that on clear

summer nights; the gradients appear steeper when compared with the 2130

profile in Fig. 15, but this is because of the different scales in the

two figures. Both Fastuca and Dactylis showed minimum temperatures at

the 6" level in clear nights, with similar gradients below this, and

little difference in temperature between the two grasses: the Festucc

was 3.5°C colder than one tussock, and 100 colder than the other, at the 3" level.

These differences seemed to be typical of cold clear nights, as is shown in Table 11. This gives the temperatures at 3" in Festuco and

Dactylis during all such nights in the winter of 1961-2 on which readings wore taken. Readings taken in the morning after a cold night are included if the temperatures were still below freezing, and are bracketed with the readings of the preceding night. The moan difference was 1.55°C which suggests that the protection given by the tussocks was relatively slight.

Fig. 19h shows the temperature minima at 3" on clear nights in

Doctylis and Holcus throughout the period of almost a year during which continuous records were taken. In this year the minima wore lowest in

March, after the snow had melted: had there been no snow, this might have occurred earlier. 92

3" Min. Temp. °C

Mean Temp. 4- •-• difference °C 3.

S 0 N DIJ I F I M I A I M I J 1 Jy l A i S 1962 1963

Fig. 19. A. Minimum temperatures at 3" level in grass on clear nights throughout the year. B. Differences between minima in Dactylis and Holcus. 93

Table 11. Comparison of nir,ht temperatures at " in Festuca end Dectylis during winter 1961 - 2.

Tc:Aperaturc at 3" (°0) Date Time 811 diameter Difference Dectylis tussook Festuca 05" high

6.12.61 2145 0.8 -0.3 1.1 7.12.61 0915 -1.8 -4.7 2.9 7.12.61 2245 0.2 -1.1 1.3 14.12.61 2215 1.6 0.8 0.8 15.12.61 0930 0.8 -0.3 1.1 18.12.61 2230 -2.7 -4.2 1.5 19.12.61 0930 -1.7 -2.0 0.3 19.12.61 1730 -1.0 -2.6 1.6 29.1.62 2300 0 -0.5 0.5 13.3.62 2230 0.7 -0.6 1.3 4.3.62 2215 0 -2.7 2.7 21.3.62 2230 0.3 -3.2 3.5

Fig. 19B shows the differences between the niniuuu temperatures at 3" in the two typos of grass on each pccasion. The monthly moan differences are also shown, as a dotted line. The differences aro least in winter, and rise to a peak in May. This could be caused by the increase in height and density of the tussocks in sur.uor, as already suggested. Also, according to the Stefan-Boltzmann law, the amount of heat radiated by a body is proportional to the fourth power of its absolute temperature. This means that as the ambient temperature decreases, so does the c_Junt of cooling due to radiation at night, and thus _differences of temperature between the two grasses, which are duo to greater radiation from the Holcus covered ground are also reduced. The reduced radiation also enables light winds to disrupt the radiation pattern below about -12°C. 94 (Wellington, 1950); although the temperatures wore not as low as this

except when snow cover was present, this indicates that wind could be

another factor reducing the differences in temperature between Holcus

and Dactylic in winter.

Thus the temperature stratificatiln in clear winter conditions is

similar to that in fine summer weather; the differences between the

tussocks and the intervening grass are loss, both in the day, when there

is loss heating by the sun, end at night, when outgoing radiation is

reduced by tho lower ambient temperature. Nocturnal differences between

the tussocks and the intervening grass are negligible at ground level,

and are seldom more than 3°C at the 3" level.

(vi) Effects of snow cover.

The winter of 1961 - 2, when the measurements of temperature pro-

files wore made on the North Gravel, had relatively little snow. During

the following winter of 1962 - 3, however, the ground, was snow covered

from 27th. December 1962, until 26th. February 1963, so that a long

series of records was _made. The continuity of these records suffered

because of the frequent faults in the record ng potentiometer in January,

but the increased reliability in February allowed e, suitable nnount of data to be recorded.

Fig. 20 shows the data obtained on the North Grovel during a period of snow which lasted from January 1st. to 5th., 1962. The graphs show the temperature at 3" in Dactylic (en 8u tussock) and Fostuca, and also the depth of snow. When the snow was 1211 deep, the temperature in the tussock was low, and similar to that in cold weather without snow, as the tussock protruded through the snow layer. The temperature in the shorter 95

3 2- ,e,

0 • -•, C 0 -1- ° 3" level in tussock -2- ♦ • 3" level in Festuca -3-

4 1 1 2 3 4 5

12- Snow Dept h 8: (Inches) 4-

0 1 1 1 2 3 4 5 Date (January 1962)

Height

0 5 0 5 Prof i les at 1600 )1----x 10.cliam.tussock -•5"high Festuca

Pig. 20. Temperatures in Dactylis and Festuca under melting snow. 96 Fostuca was higher, and did not fall below -1°C in any of the readings

taken. As the snow pelted, the teuporature in the tussock rose ziero than

that in the Festuca, and the two had changed their relative positions by

the evening of January 5th., when the snow was only 1H deep. The profiles,

ueasured at 1400 on each day show that when the snow was 12H deep, its

surface above the 69 high Fostuca was colder than the tussock at this

level, but below this th:, tussock warliod up relatively little, whereas

the Fostuca under the snow was warmer because of the insulating properties

of the snow cover above it. As the snow welted, the te..iperatures rose,

and the gradients booamo less steep as the reduced snow level

led to norual teuperature profiles within the vegetation.

Graphs of the tepperAure at 3" and ground level in Holcus and

Dactylis during various nights of the cold 1962 - 3 winter are shown

in Fig. 21. Appendix Table 1 gives relevant klicrocLii.iptic datu for the

days following each night graphed; these include the relevant mininum air

and grass temperatures, as those occur just befJre dawn on the preceding

night.

During the night of January 25th. - 26th. (Fig. 21A) there was about

69 of snow still lying on the ground; this covered uost of the sharter

grass, incluing the Holcus in which readings were token, but left the

tussocks uncovered. The first half of the night was clear, and the

graph shows that while the tcuperatures in the Holaus renamed just above freezing, because of the insulation given by the snow, the tussock teLiperatures wore as 1,uch as 5:)C colder at soil level, and 6°C at 3H, reaching -4°C and -5°C respectively. This agrees with the data given in

Fig. 20. After 0200 on January 26th., the sky clouded over, and this allowed the to..aperatures in the tussocks to rise to just below freezing, 97

25-26 Jan

0- ...... A -10

13 -14 Feb B

-10

Temp. °C

Off

o -

1-2 March

10 5-6 March 10-

... 0— E 1600 1800 2600 2200 2400 0200 0400 0600 odoo 1000 3.. Holcus: 0- Time Tussock: • -•- 3-,

Fig. 21. Grass temperatures on selected winter nights. 98 and also raised the 311 temperatures above those at soil level in each

grass.

The night of February 13th. - 14th. (Fig. 21B) was an example of

overcast weather, with some sli7ht thawing each day, but with 3" of snow

still lying on the ground. The temperatures in the Holcus were still

above those in the tussock, but not as much as in Fig. 21A, because of

the reduced depth of snow. There were no temperature inversions, and the

relative positions of all the four points graphed did not alter at dusk

or dawn. These conditions were typical of a large part of the winter,

when there was snow on the ground, with overcast and fairly cold weather.

The Holcus temperatures under the snow at ground level always remained

above freezing, usually at about 1°C., throughout the winter; the reason for this is unknown. The calibration of the recorder was checked on

several occasions, and found to be correct, so that it appears that the soil surface temperature under the snow was above freezing even on the coldest nights, although in the tussocks the temperature at ground level was much lower.

This condition was shown on the night of February 24th. - 25th.,

(Fig. 21C), which was one of the coldest nights of the winter. Only about

1,1 of snow remained, as was shown by the fall in temperature of the 3" point in Holcus, which was no longer snow covered. It reached a minimum of -7.5°C, compared with -5.5 C at 3" in the tussock. The ground level temperatures fell to -1.0°C in the tussock and almost to 0°C in the shorter grass. The reason why the ground level in the tussock remained near the freezing point, when it had fallen to -4°C on the 25th. - 26th. January, when the night was less cold, with snow between the tussocks only, is not 99 known. It suggests that the presence of snow on the ground between the tussocks reAuces the temperature in the snow-free tussock, possibly as a result of contact with the temperature minima occurring at the surface of the snow.

The night of March 1st. - 2nd. (Fig. 21D) is included for comparison with Fig. 21C. It was also a clear night, although not so cold, and with no snow on the ground. The graphs are similar, except that on the 1st. -

2nd. March, the soil level temperature in Holcus fell below zero, which suggests that its previous steady temperature of about 1°C was in fact due to insulation provided by the snow.

The night of March 5th. - 6th. (Fig. 21E) shows the temperatures that prevailed when the weather warmed up after the cold spell. There was a steep temperature gradient, with the temperatures at 3" about 8°C in

Holcus, and 5°0 in Dactylis, warmer than those at soil level, which were still near freezing. The sky was overcast throughout the night, so that the relative positions of points measured did not change, As the warmer weather continued, the soil level temperatures rose until they were similar to those at 3" in dull weather, as in summer (Fig. 151'.).

Thus when the ground is snow covered, the temperatures in the intervening grass are not as low as in the tussocks, because the snow is deeper, and therefore provides more insulation, between the tussocks.

(vii) Comparison of the total subzero temperatures in Holcus and Dactylis durlazthe winters 1_962 - 3.

During the investigation of the temperatures experienced by insects in tussocks during winter, it was considered important to know the total times spent at various temperatures below freezing, as well as the 100 extremes reached, in each location. The times spent at various subzero temperatures wore therefore calculated for the 11" high and ground level points in both Holcus and Dactylis, by examining the continuous records produced by the Sunvic Potentiometer. The period covered was from

October 21st. 1962, until May 3rd. 1963, which wore the dates of the first and last frosts respectively, in the ress. The poor reliability of the machine resulted in only 80% of the time being recorded, but the data have not been adjusted to compensate for this, as the coriods when records wore missing were not distributed evenly throughout the winter.

The graphs already shown indicate that the differences in temperature between Dactylis and Holcus varied according to the presence or absence of snow; because of this, two sets of totals were calculated, one for the period between 27th. December 1962 and 26th. January 1963, when there was snow on the ground, and the other for the proceeding and following periods of cold weather without snow. Table 12 and Fig. 22A show the total number of hours spent in each half degree range below zero at each point during the snow free periods.

Table 12. Total times at subzero temperatures in snow free conditions, Winter 1962 - 63.

Temperature 10n diameter Dactylis tussock 21 .high Holcus Range (°C) le level Ground level 1-1e level Ground level 0 1 r

1 L. .r - - 0 to -0.5 36 108 , 13 < r— 1 1 -0.5 to -1.0 24 38 6 cr cm ) -1.0 to - ,

1.5 c 0 30 3 ( V o

-1.5 to -2.0 19 0 C' 0 . . t. i -2.0 to -2.5 6 0 Cr

0- 0 \ C

-2.5 to -3.0 1 0 0 0 . .o V C . -3,0 to -3,5 0 0 . 0 . .o V

-3.5 to -4.0 0 0 . 0 r- . .o 1 -4.0 to -4.5 0 0 0 c \ -4.5 to -5.0 0 0 0

Totals 116 149 303 19 101

100 No snow A

-2 - 5 °C Snow on ground B

100 o -0 Soil level in Holcus x------x Soil level in tussock

Hours o 1 1/2 level in Holcus x x 1 1/2 level in tussock 50

0 -1 -3 200 x, Totals 150

100

-5°C

Fig. 22. Total times spent at subzero temperatures during winter 1962-3. A. Without snow. B. With snow. C. Entire winter. 102 A comparison of the 1-k" level totals shows that the Holcus had more extreme conditions, with temperatures of down to -5.0°C, and more time than in the tussock at all temperatures below -1.0°C. At ground level Holcus had less extreme conditions, but in neither grass did the temp- ernture fall below -1.5°C, which was considered later to have little effect on insects. Table 13 and Fig. 22B give the equivalent totals

for the period with snow cover. Table 13. Total times at subzero temperatures with snow on the ground, Winter:, 1962 - 63.

--- Temperature 10" diameter Doctylis tussock 5" high Holcus Range CC) li-u level Ground level ly Level Ground level

0 to -0.5 124 124 130 0 -0.5 to -1.0 62 144 50 0 -1.0 to -1.5 76 142 3 0 -1.5 to -2.0 36 50 5 0 -2.0 to -2.5 29 20 3 0 -2.5 to -3.0 20 9 2 0 -3.0 to -3.5 9 4 0 0 -3.5 to -4.0 4 0 0 0 -4,0 to -4.5 6 0 0 0

Totals 366 493 193 0

The presence of snow cover reversed the positions; the 1k" level in the tussock experienced more extreme conditions than the same level in

Holcus. However, neither the temperature minima reached, nor the amounts

of time at temperatures below -2°C were as great as in the Holcus at this level in the absence of snow. This reduction in extremes indicates that

the tussocks have better insulating properties than the Holcus, although

the reduced times at lower temperatures could partly be a result of the longer period of time without snow cover.

The total times at each temperature for the entire winter wore then

calculated, and are shown in Table 14 and Fig. 22C. 103 Table 14. Total times at subzero temperatures. Winter 19627 61.

Temperature 10" diameter Dactylis tussock 5" high Holcus Range (°C) irn high Ground level 1 lvA.. Ground level

0 to -0.5 160 232 187 13 -0.5 to -1.0 86 182 97 6 -1.0 to -1.5 106 145 36 0 -1.5 to -2.0 55 50 33 0 -2.0 to -2.5 35 20 37 0 -2.5 to -3.0 21 9 35 0 -3.0 to -3.5 9 4 26 0 -3.5 to -4.0 4 0 26 0 -4.0 to -4.5 6 0 16 0 -4.5 to -5.0 0 0 3 0 Totals 482 642 496 19

"Coldness 66o 12.5 Factor", 0. 706.5 785.5

The Table shows that the level in Holcus had longer periods at all temperatures below -2.0°C than all the other points, although the ground level in Holcus was by far the least cold point. In the tussocks, considerable time was experienced at 1 or 2°C below freezing at both levels, but there was relatively little time below those temperatures. To compare the different points, taking into account both the extremes reachc1, and the times spent at each temperature, a "coldness factor" was calculated, giving the number of degree-hours below zero experienced at each point.

The factor was calculated using the expression

c = (t.nt) where c = the "coldness factor", and nt = the number of hours spent at each temperature t°C below zero. This takes into account both the )(quantity" and "intensity" factors of cold, as distinuished by Payne

(1927 ). 104

The 1 11 level in Holcus, which had only slightly more hours below

00C than the same level in Doctylis, hod a considerably higher cs because

of the increased time that this point spent at tem,)eraturos below -3.00C

in comparison. The ground level point in the tussock had considerably

more hours below zero than the 1.?-f.41 level, but the coldness factor of the

two levels do not differ so greatly, because the tem eratures at the

base of the tussock were loss extreme that those at 1?. Thus in

general these data show that in the winter of 1962 -3, with a long

period of snow cover, the protection given by the tussocks was distinct

at the 11t1 level, but not at soil level.

(viii) Conclusions.

The following conclusions suwariso the differences in temperature

between the tussocks and the intervening grasses in different types of weather.

In fine summer conditions, the diurnal range of temperature at

31t above soil level is greatly reduced in the tussocks; this range is greatest at the 31t level in the more open grass, but at highar levels in the tussocks. At ground level the range is reduced in all situations, but is still greatest outside the tussocks. The maxima and minima in temperature are later in the tussocks than in betme::n them.

Cloudy conditions greatly reduce the diurnal fluctuations, both by limiting the amount of solar heating in the day, and by preventing out going longwave radiation at Night, so that temperature inversions do not occur. Under such conditions, there are only slight differences between the different typos of grass. 105

Rain affects the temperature only outside the tussocks, where cooling of the upper layers occurs, unless it is exceptionally heavy, when all the temperatures ere lowered to the same level.

Winds probably have little effect below the 3" level, but may reduce thermal stratification in the more omen grass above this height.

In clear winter conditions, the temperature stratification is similar to that in fine summer weather, but the diurnal range of temperature fluctuation is loss. At night the differences between the tussocks and the intervening grass are slight at ground level, but the tussocks may be as much as 3 or 490 warmer at the 3" level.

Snow provides more insulation over the shorter intervening grass, whore it is deeper, than over the tussocks, where it melts fast. Thus the coldest temperatures occur in the tussocks when the ground is snow covered. The minima under those conditions, however, are not as low as those in the intervening grass in the absence of snow.

Examination of all the periods when the temperatures in the grass were below freezing during the cold winter of 1962 - 3, when the around was usually snow covered, shows that there was no greet difference in total coldness between the tussocks and the intervening grass at ground level, but that the tussocks were distinctly loss cold at the lin level and above.

(b) Humidity

Humidity measurements were made usually in fine summer weather, as those were the only conditions in which it was considered that differences

in humidity between the tussocks and the intervening grass might be biologically significant. This assumption was made because in winter 106 all the grass was almost invariably moist at the levels at which insects were found, and also because, at the lower temperatures experienced in winter, low humidities do not lower the saturation deficit so much as at summer temperatures. Thus a relative humidity of 25% at 500 has a saturation deficit of only 5 gms./cu.m., which is loss thin that at

80% relative humidity and 30°C. As the saturation deficit is a measure of the "drying power" of the air, and the2'efore of its ability to harm insects by desiccation (Mellanby, 1935), low humidities at low temper— atures are insignificant compared with relatively high humidities at the temperatures experienced in the grass in sumer. The work of Webster

(1956) also indicated that the humidity was always high in tussocks in winter.

Measurements were first made by placing pieces of cobalt thiocynnate paper in tubes in various situations in the crass on July 29th., 1963, a fine sunny day. The papers were put in position at 1330, and removed at 1445 G.N.T.. The positions of the tubes era listed below; Fig. 234 shows their positions in the crass diagrammatically, together with the relative humidity at each position.

Tubes 1, 2 and 3; on the surface of the litter layer in Festuca,

Tube 4; at the base of the litter layer in Festua,

Tube 5; at soil 1—vel between the Festuca litter and the dead

leav©s surrounding a DactyLis tussock,

Tube 6; at soil level bencath the the edge of the

tussock.

Tube 7; 311 above soil level, one third of the way into the centre

of the tussock.

Tube 8; 2" above soil level, in the centre of the tussock. 107

A athiL§ tussock Height

Dead leaves

Festuca

Litter I I

% R.N. 35 25 70 20 45 65 5070

0/0 B Sat C R.H. Def., 0- - - - 3" level Festuca gm/cu-m. o 3" level, Dactyl is 20 •- - - - -*Soil level, Festuca 25 -o, •----•Soil level, Dactylis 30 .0 5' 40 • 20 0 5' 5' 5' 15 60 5' 0 5' 70 10 5' 80 -•-- 0

90 _ -• ------e___

100 0 1200 1400 1600 1800 1200 1400 1600 1800 Time.

Fig. 23. A. Relative humidities in grass in summer, measured with a Gregory hygrometer. B. & C. Relative humidities and saturation deficits in Dactylis anet Festuca in fine summer weather. 108 !t ground level the humidity was high except in the space between the Fostuca litter and the dead loaves at the edge of the tussock, whore it

was only 45%. At the surface of the Fostuc,] litter, which was about 171 deep, the humidity was low, ranging from 20 to 35%. In the tussock, however, it was 70% two inches above ground level, and 50% one inch above this, but nearer the edge of the tussock.

To find out how those humidities compared with those at higher levels, profiles were measured on the same afternoon between 1435 and 1535

G.M.T., and at heights between 11 9" and soil level, in both Dactylis and Fostuca, using a Gregory hygrometer. The results obtained ore shown in Table 15, in which the saturation deficits at each level have also been calculated (Temperature was measured with a thermistor attached to the hygrometer element).

Table 15. Humidity_ profiles measured with a Gregory Hyr!rometer, 1435-1535 G.M.T., July 29th., 422.

Dactyls Festuca t l 'igh Relative Temperature Saturation Relative Saturation humidity (o0 Deficit Humidity Temeraturepo c) Deficit (%) (gms/cu.m) (Y.) ( (gms/cu.m)

1'9" 40 31.1 19.0 35 29.2 18.5 110" 39 30.8 19.0 35 29.6 19.0 9" 41 30.6 18.1 35 30.3 19.6 6" 41 31.1 18.7 35.5 31.7 21.2 5" 39 29.4 17.6 35 32.8 23.0 4" 43 30.3 17.3 36 34.4 24.3 3" 39 30.8 19.0 37 33.9 23.2 2" 43 30.6 17.5 37 35.0 24.5 1" 51 30.0 14.6 41 33.9 22.0 109

The tussocks had a lower saturation deficit than the Festuca at all levels below 9", but the humidities measured in tha tussock wore much lower then by the cobalt thipcy ,n to papers. This was thought to be caused by the disturbance of the habitat by the hygrometer element, and the instrument was not used subsequently.

In 1964 measurements were made using sets of cobalt thiocyanete papers nt the 3P, and soil levels, as explained previously (p.75).

The humidities on an overcast dry day in spring are shown in Table 16; the saturation deficits are calculated from humidity measurements made on April 7th., 1964, and from temperature measurements made by the Sunvic recordings potentiometer on April 8th., 1963, a day with similar weather conditions.

Table 16. Humidities in Festuca and Dactylis on an overcast spring day. Dactylt.s Festuca Height Time Relative Temp. Saturation. Relative TcAmp. Saturation (t) deficit (ins.) (G.M.T.) humidity (°o) deficit humidity(o0) (zinjcu.m) (Rmiallla/-- 3 1100 85 10.0 1.4 65 20.0 6.0 II 1300 80 10.5 1.9 55 20.0 7.6 It 1445 75 12.0 2.6 60 19.0 6.4 il 16 45 80 12.0 2.1 70 16.0 4.0 ti 1945 80 9.5 1.8 72.5 10.0 2.5 1.:'f 1100 85 9.0 1.3 90 14.5 1.2 II 1300 85 10.0 1.4 85 14.0 1.8 It 1445 SO 10.5 1.9 85 14.5 1.9 ii 1645 82.5 10.5 1.6 85 12.5 1.6 It 1945 80 9.5 1.8 85 7.5 1.2 0 1100 95 6.o 0.3 82.5 8.0 1.4 li 1300 90 '7.0 0.8 85 8.5 1.2 tt 1445 87.5 7.5 1.0 82.5 9.0 1.5 il 16 45 90 8.0 0.8 77.5 8.5 1.9 If 1945 80 7.5 1.6 82.5 6.5 1.3

At the 3" level the shorter grass was distinctly less humid than the tussock until the evening, but below this height there was little 110 difference, and conditions wore humid throughout the day.

On May 15th., however, which was a clear and sunny day, very different results were obtained. At this time of year there was considerable loaf growth in the tussocks, but little in the intervening grass, so that the normal differences between the two grass types were exaggerated. The data are given in Table 17, together with temperature measurements made in Festuca on Juno 17th., 1962 with the Doran potentiometer.

Table 17. Humidities in Fostuca and Dactylis on a fine summer day.

Dactyls Festuca ioight Time (ins.) (G.M.T.) Relative Ton Saturation Rcaative Tom Saturation humidity /o,1 1)" deficit humidity focr deficit 0) 1/4 u (gms/cu.m) (A (gmsjcu.m) 3 1200 68 19.2 5.2 25 33.0 26.5 It 1400 50 20.8 8.9 10 28.7 25.0 it 1600 60 20.1 6.8 30 28.9 19.6 1, 1830 69 17.8 4.6 65 21.2 6.4

1-1.- 1200 80 15.9 2.7 35 29.3 18.7 1, 1400 69 17.3 4.5 30 26.8 17.5 II 1600 73 16.9 3.8 45 25.9 13.1 il 1830 75 15.9 3.4 70 20.6 5.3 0 1200 90 11..5 1.0 87 17.8 1.9 II 1400 89 12.8 1.2 78 18.2 3.3 II 1600 89 13.0 1.3 80 17.9 3.0 11 1830 87 13.9 1.5 83 16.4 2.2

Tho relative humidities and saturation deficits at the ground and 3ft levels are also shown in Figs. 23B and C. The tussock was more humid than the Fostuca at all levels, and only at the soil level ware the differences always slight, and the saturation deficits low. The maximum heating of the Fastuca at the 311 level combines with the low humidity to give a saturation deficit at midday which is much greater than that at the 311 level in the tussock, as is shown in Fig. 23C. 111 Readings which were token later in the sumuer showed that conditions in the tussock were similar, but the extent of drying out in the intervening grass was not as groat as in May because the now leafage was more extensive. Thus the risk of desiccation to insects outside the tussocks is greatest in fine weather in early summer. In those conditions the tussocks remain humid, but only the soil level in the intervening grass is not dried out. Long dry spells later in the year probably also constitute a risk but suitable weather for measurements of those conditions did not occur. (c)

The intensity of light at various heights in both Doctylis and Festuca was measured on August 9th., 1964, a sunny day with some cumulus cloud. Readings wore taken between 1100 and 1200 Table 18 shows the values found at each level in two situations in each gross; each column gives the mean in log. foot-candles of three profiles within one foot of ono another.

Table 18. Light readings in 12g. foot-candles in Dactylic and Fostuca, 1200 G.M.T. August 9th., 1964.

Dactylic Festuca --..- Height A B Mean A B Mean

2'6" 3.80 3.80 3.80 3.87 3.83 3.85 2' 3.68 3.68 3.68 3.87 3.83 3.85 1' 3.48 2.98 3.23 3.64 3.80 3.72 9" 2.98 2.94 2.96 3.54 3.80 3.67 6" 2.55 2.55 2.55 3.43 3.73 3.58 3" 1.53 2.13 1.83 3.21 3.54 3.37 2" 1.16 1.89 1.52 3.10 3.10 3.10 1" 0.98 1.53 1.26 2.90 2.83 ' 2.86 Ground level 0.89 1.29 1.09 2.49 2.46 2.47 112

Tho means in each gross are shown graphically in Fig. 24A. The tussocks absorb light evenly from above 2' high down to ono foot above the ground.

Between the 1' and 3" levels, nearly all the remaining light is absorbed, end below this there is little decrese. The gradual absorption in the upper part of the tussock shows that there is no distinct "outer effective surface" at which most of the radiation is absorbed, but tho zone between

1' and 6" probably approaches this most closely.

In Festuca, only a small proportion of the light is absorbed above

9", but between this level and the ground the light is greatly reduced.

At ground level there is about 20 times as much light as in the tussocks.

The absorption is greatest between the two clnd three inch levels, which thus form the "outer effective surface" of the grass between the tussocks.

This agrees with the observations already mode showing that t4is level hosts up more than any other in sunshine.

Thus the tussocks and intervening grass differ both in the levels at which radiation is absorbed, and in the intensity of the light which reaches soil level.

113 A B I Field max. 3" level in Holcus i 0 o Dactyl is i temp.(t) ---•-•-•- 34 level in tussock 1 50.-. i Soil level in Holcus

Soil level in tussock 40-

Summer

10 15 20 25 Max. air temp. (*c)

1.0 2.0 3.0 4.0 10 - Light intensity (Log ft-candles) D

10- 5- •::••••;. Field Field min, - min. - temp. • temp.. (°C) (°C) 5- 0

Summer Winter

0 5 0 5 10 15 -10 0 10 "Grass minimum" temp (°C)

Fig. 24. A. Light intensity profiles in Dactylis and Festuca. B. Regressions of maximum temperatures in grass on maximum air temperature C.& D. It " minimum It it t I " grass- minimum temperature in summer and winter. 114

4). Comparison of macroclimatic and micraclimatic measurements.

The mocroclimatic factors which determine the microclimote in the

;Tess have boon summarised in the results already given; the conclusions reached agree with those of Hughes (1954, 1955), who made measurements in an oven Dactylis stand in summer. Ho did not attempt, however, to predict the conditions in the.grass from macroclimatic data. The need for such predictions varies with the type of investigation. Thus Kirk- patrick (1935) gave values for the probable differences in conditions in coffee bushes and in a Stevenson screen in various common typos of weather in Tanganyika, as part of a comprehensive study of the microclimate of coffee plantations. Such detailed figures are not always needed; thus

Richards and Walo.ff (1961) showed that the mean temperature of 16 points on broom bushes did not differ substantially from that in a Stevenson screen except on clear days, and even then the daily moans were almost identical. As the microclimatic data used by Richards and Waloff were moan values from points which were chosen to represent different parts of the bushes, differences between the different points were obscured. The variations between the different levels and grasses wore important in this study, however, and thus the same method could not be used. The extremes of temperature were considered to be of greatest interest when considering the survival of insects in the grass, and these were compared with macroclimatic data from the Silwood meteorological site.

The regressions of the daily maximum temperature in the grass on the maximum air temperature in summer, and of the daily minimum temperature in the grass on the standard "grass minimum" temperature in both summer and winter, were calculated.. The data which were used were those of November and December 1962 (winter), and of Mhy and June 1963

115

(summer), from the 3" and ground level points in Dactylis and Holcus. The results of the calculations aro given in Table 19, in which a and b are the factors in the regression equation + bx and s is the standard error of the dependent variable, y, after the portion of the total variation of y attributable to the regression has boon removed. The standard error of the regression coefficient, b, is

also given. Table 19. Calculated regression statistics of temperature extremes in press on "grass minimum" and 2it maximum temperatures.

Level a b s Dependant variable Grass inches) Maximum temperature, 8.268 1.396 + 0.149 4.740 in summer Holcus 3 U II 0 0.964 0.871 + 0.048 1.509 If Dactylis 3 -1.462 1.077 + 0.039 1.226 n n 0 0.664 0.726 + 0.045 1.415 /--- Minimum temperature Holcus 0.979 1.071 + 0.060 1.448 in summer 3 n ft 0 6.675 0.528 + 0.029 0.710 It Dactylis 3 5.603 0.705 + 0.051 1.261 n n 0 6.412 0.529 + 0.052 1.287 Minimum temperature in winter Holcus 3 2.807 0.781 + 0.058 1.675 it " 0 5.234 0.315 + 0.045 1.299 n Dectylis 3 3.785 0.495 + 0.056 1.625 if sr 0 4.606 0.346 + 0.062 1.790

All the regression coefficients were significant below the 10-6 level. The three sets of regression linos are graphed in Figs. 24B, C and D; from those graphs, and from the date in Table 19, the probable

value of the extreme temperatures in and between the tussocks can be cal-

culated, if records of daily "grass minimum" and air maximum temperatures

aro available. The graphs also show the com)arative extent of the protection from oxtromos given in each position, and how this varies with macroclimatic extremes, as already summarised (p. 104). 116 III THE FAUNA.

A. INTRODUCTION AND ''ilETIIODS

As mentioned in Section I, little work has been done on the fauna

of tussocks, and elaborate methods for sampling their fauna have not

been devised. Pearce (1948) recommended that the entire tussock should

be removed from the soil with a sharp knife or saw, inverted, and shaken

over a tray or sheet to extract the fauna. After shaking, the tussock

should be torn up and examined for specimens which have resisted the

shaking process. Ford (1937) sampled the Collembola of Bromus tussocks,

initially by removing all the tussock vegetation, and extracting the

animals from it in a Derlese funnel; subsequently he extracted the

animals from small samples of the basal vegetation, again in Derlese

funnels. 'iacfadyen (1952) took samples of plant bases, litter and soil

extending from 0.5 ems. above to 5.0 ems. below the litter surface, and

extracted the fauna in Tullgren funnels.

The methods used by Ford and Macfadyen, in which each sample con-

sisted of only a part of the tussock, were considered to be unsuitable

for the sampling of relatively large insects such as Coleoptera. This

was because the numbers of individuals were smaller than those of the

Collembola and Acarina studied by Ford and Macfadyen. Also the variation

of structure within a large tussock results in increased variation between

samples, if only a part of each tussock is sampled. The extraction of the fauna from entire tussocks has the disadvantage that if many samples

are to be taken, the area under study may become significantly depleted.

A vacuum sampling device (Johnson et. al., 1955, 1957) was tested to find out whether it could extract the insects from the dense vegetation of grass tussocks, but was found to be unsuitable. Entire tussocks were 117

therefore removed to estimate the numbers of insects in them. In practice,

the spread and increase of Dactylis on North Gravel compensated for the

numbers of plants removed from the area during the sampling period.

The other areas from which samples were taken were not studied enough to

affect the numbers of tussocks to any great extent. When tussock-

inhabiting insects were required for experimental purposes, they were

obtained from tussocks in areas situated well away from North Gravel,

Cascade Marsh and Nursery Field, in which samples were taken regularly

for quantitative data.

The details of the sampling method used varied at differing stages

in the work, but the essentials were as follows.

The dead leaves surrounding each tussock sampled were separated

from the soil and litter on which they were Lying, and, together with

the upright living leaves and stems, cut off at a height of six inches

from the ground, leaving only the basal vegetation of the tussock. The

fibrous base of the tussock, together with this lower six inches of

vegetation, was then cut away from the underlying soil with a saw-

toothed knife, and transferred to a polythene bag, in which it could

be taken back to the laboratory. Here the majority of the larger insects

such as beetles were extracted by vigorous shaking over a tray, by

placing the inverted tussock in a Tuligren funnel, or by both methods in

succession. The details of the method used in each part of the work

are given in the relevant sections. In some cases, selected parts of each tussock, such as the rotting dead leaves, or the flowering stems, were removed in the field, and treated in Tullgren funnels separately from the base of the tussock. 118 During the first year of sampling, all Coleoptera found in tussocks wore recorded, so as to obtain an idea of the relative importance of tussocks, either as a winter refuge, or as a permanent habitat, and to find out the extent to which various groups of beetles of differing habitats occurred in tussocks. Four species were then selected, and sampling was continued for a further year to obtain information on their life histories and biology. These species were :

Stenus clavicornis (Scopoli) ) ) Staphylinidao S. improssu.3 Gamer

Dromius 111219E22apthpluE Dejoan) ) Carabidae D. linearis (Olivier) )

It was hoped that once the outlines of the biology of these species were known, they could be used for experiments on the methods of selection of, and advantages of living in, tussocks.

In addition to the data on Colooptera, a feu preliminary counts were made of the total arthropod fauna of the tussocks and intervening grass at different times of year.

At the same time as data were being collected on the beetles in tussocks, pitfall traps were used to obtain an idea of the numbers of species of tussock-inhabiting beetles which were also active outside the tussocks. One pound jam jars wore tried, but the problem of predation by larger animals in the traps, hientioned by Mitchell (1963) and Greenslade

(1964), meant that a preservative had to be used in the jars. Formalin was used for this purpose, but the practical difficulties of sorting a large number of one pound jam jars half full of diluted formalin, led to the use of 3n x 1" specimen tubes as pitfall traps. These could be exchanged rapidly for clean tubes, and the full tubes taken back to the 119 laboratory for examination. It was not possible to do this easily with jam jars, because changing the jars disturbed the soil above the over- hanging lip of the jar; this soil then fell into the hole as the jar was removed. Specimen tubes, being both smaller in diameter, and parallel sided, slid in and out of their holes easily, without disturbing the surrounding soil. Further advantages of the smaller size of the traps are that small mammals cannot fall into them and that predation of the trap contents (a problem mentioned by Briggs (1561)) is impossible. To keep rain out of the traps, 2-? x 1. -" covers of cellulose acetate were had about one inch above the tram pierced by 4" nails inserted into the soil close to the traps. These covers also made the traps readily visible from above, and each trap could be separately numbered.

The beetle and total arthropod fauna of the grass between the tussocks was also sampled by methods similar to those already dosoribod for the tussocks, namely cutting up, followed by shaking or treatment in a Tullgren funnel. The suction sampler was also more efficient in obtaining the beetles from the more open grass between the tussoc, and was used on occasions. 120 B. TOTAL ARTHROPOD F,'1UNL.

The total fauna of tussocks was investigated very briefly in order to find out the approximate numbers of smaller arthropods that might be available to the larger predatory forms as food at various times of year.

Also, a comparison could bo made with the data of Ford (1937) and Pearce

(1948), who also give the total faunas of various types of tussocks.

Samples of Dactvlis tussocks wore taken in FolTuary and June 1964, from North Gravel, and the fauna in winter and summer was compared. The tussocks selected wore removed from the soil as usual, but none of the loaves wore cut off. The entire tussocks were then inverted in Tullgron funnels, and the animals collected in tubes containing l formalin solution. Simultaneously, two samples of turf conta.ning other grasses wore removed and treated in the same way.

Table 20 shows the numbers of arthropods in each sample: the insects have been classified into orders. The most numerous groups in all samples were the Acnrina and Collembola which, although more numerous in the tussocks, were always present in large numbers. In winter the other groups which were characteristic of the tussocks wore the Isopoda,

Homiptora, Thysanoptera,dipterous larvae, Hymenoptera, Coleoptera and

Arenoida. Of these, only the Thysenoptora, dipterous larvae, and

Aranoida were present in any numbers outside the tussocks in winter.

In summer, the tussock sampled contained more Myriepoda, dipterous larvae and adults, coloopterous larvae, ,)nd Phalangida then in winter. The other groups were loss numerous in tussocks in summer than in winter. In gunerall the differences in numbers between Dactylis and other grasses were less in summer, as more arthropods occurred outside the tussocks. 121

Table 20. Total numbers of arthropods in Dactylis and other grasses.

Date 17th. February 13th. June Holcus+ Grass pact lis Festuca Dactylis Festuca ostis Fostuca --- Sample area (sq.ins 0.8 27.0 22.5 38.4 227 41.2. Isopoda 59 2 0 91 4 4 Myriapoda 7 6 0 30 13 3 Collombola 165 623 87 1,790 864 922 Dictyoptora 5 0 0 0 0 0 Psocoptere 0 1 0 0 0 0 Hemiptera 37 4 1 16 9 4 Thysanoptera 147 25 4 10 0 3 Lepidoptera (adults) 0 0 0 0 0 0 fl (larvae) 14 19 3 1 0 0 Diptera (adults) 4 0 1 19 4 1 " (larvae) 131 38 15 175 4 8 Hymenoptera 44 1 0 5 1 4 Coleoptera (adults) 111 10 3 15 9 8 n (larvae) 6 1 2 78 8 3 Phalangida 0 0 0 23 0 0 Aranoida 59 30 12 28 11 11 Acarina ; 545 1,711 805 3,672 1,989 1,387

Total Arthropoda ,334 21 471 933 5,953 2,916 2,358

The large numbers of beetle larvae in the tussocks in summer indicate that they may servo as a habitat for the larvae of many species at this time of year, with few larva() in the intervening grass.

Thus those few samples show that the density of the arthropod fauna of Dactylis tussocks was more than twice that of the intervening grasses.

Large numbers of small arthropods, especially Acarina and Collembola, were always present in the tussocks. 122 C. TOTAL COLEOPTEROUS FAUNA OF TUSSOCKS.

1) Methods.

Between September 5th., 1961,and December 11th., 1962, all the beetles found in tussocks were counted and identified. This included both preliminary sampling of Dactylis, Deschampsia and Juncus tussocks in various parts of Silwood Park between September 5th. and October 2nd.,

1961 and subsequent regular sampling of Dactylis on North Gravel until

December 1962, and of Deschampsia in Cascade Marsh, until the end of may, 1962.

The tussocks were cut up as already described, and the beetles obtained by thorough shaking over a sheet in the laboratory. Normally the tussocks were not treated further, but initially some were broken up and examined in detail to find out the proportion of beetles which were obtained by shaking. Table 21 shows the numbers of beetles obtained from the tussocks which were both shaken and broken up. Table 21. Comparison of the numbers of beetles obtained by shaking and subsequent breaking-up of tussocks.

Number of beetles obtained _% of total Grass Shaking Breakin. u. Total Shakin Breakint u. 0 N c r ‘ Dactylis 20 50 60 40 ,- -/

It x 6 23 26

r 74 1 -4 it 1

C 18 83.5 16.5 c\ 3 O tt j 10 38 26

U 0 C\ 74 It N 6 56 11

Crs 89 I ON

tt t 10 42 76 24 it r-i

\ 6 25 76 24 1--1 D

vs 64 36 L 9 25 n escham sia ) 26 91 72 28 Total 272 96 368 73.9 26.1

The mean percentage of beetles obtained by shaking alone was 73.9%. As the breaking up of tussocks was a long and laborious process, shaking alone 123

Was considered to be a suitable sampling method, provided. that it was

remembered that it yielded only about 75% of the beetles actually present.

There was little evidence of any species being especially resistant to

extracting by shaking, with the exception of Xantholinus linoaris (01.),

and the two very small species, ..Laischa snails (Gray.) and Sipalie

circellaris (Gray.). These species ware usually obtained in greater

numbers by breaking up the tussock base than by shaking, so that the

numbers recorded in samples throughout the year may be less than 50% of

those present, .and are certainly less than the 7517 assumed for the remain-

ing species.

In the preliminary sampling throughout Silwood, the different species

of tussock were sampled indiscriminately, but after the first month,

alternate samples of three Dactylis and Deschampsia tussocks wore usually

taken at approximately two week intervals. After liay 1962, only Dactylis

samples were taken. The number of replicates on each sampling date should

preferably have been more than three, but as there were only a limited

number of tussock in each sampling area, it was consided that the

removal of more tussocks might significantly affect the ecology of the

area. In practice, the samples taken were enough to show changes in

numbers in the total beetle population and of several common species, as

well as giving a good idea of the total numbers of species of beetles

found in tussocks. The tussocks were taken from mapped areas of the North

Gravel and Cascade liarsh, in which they were divided into three size

grades of 511, 5 to 7'1 and 711 diameter respectively. The tussocks in

each grade were numbered, and on each sampling date, one of each grade

was selected using random number tables.

Table 22 shows the numbers sampled during each month. 124

Table 22. Numbers of tussocks sampled. September 1961 to December 1962.

Month Dactylis Deschampsia Juncus Total

1961, Sept. 14 2 3 19 Oct. 6 8 0 14 Nov. 0 0 0 0 Dec. 3 3 0 6 1962, Jan. 3 3 0 6 Feb. 6 3 0 9 Mar. 3 6 0 9 Apr. 6 0 0 6 May 12 11 0 23 June 6 0 0 6 July 12 0 0 12 Aug. 9 0 0 9 Sept. 9 0 0 9 Oct. 6 0 0 6 Nov. 6 o 0 6 Dec. 3 0 0 3 Totals 107 36 3 146 125

2) Numbers of species found.

The species of beetles found in those samples are listed in

Appendix Table 2. The species of grass tussock in which each beetle species was found are shown, together with the months of occurrence, and total number of individuals found, of each species. Where a species was found in Dactylis tussocks, but did not occur on North Gravel, the relevant cross is shown in brackets.

The family classification used in the list is that of Crowson (1956).

The specific nomenclature follows .loot and Hincks (1945), except for the

Carabidae, whore the list of Moore (1957) has boon used, and the following groups where the appropriate parts of the "Handbooks for the Identification of British Insects" were used :

Histeridae

Staphylinidae; Metopsiinne

Omaliinae

Oxytolinaa ateninao

Pselaphidao

Scarabeeidae

Phalacridao Coccinellidac

A total of 198 species were recorded from 23 families. This is a little over 10Z of the total numbers of Coleopters recorded from Windsor

Forest (of which Silwood was part) by Donisthorpe (1939). The numbers in each family are considered later when the relative numbers of common and rare species are discussed, but the two best represented families, the Carabidae and Staphylinidaa, wore represented by 17.7% and 12.6% of 126 the species listed by Donisthorpe.

Certain genera wore not identified to species level, because of the difficulties involved. Those were Acrotrichis, Philonthus and

Gabrius. Acrotrichis was certainly represented by more than one species;

Philonthus and Gabriue may have only yielded one species each. Stanus aceris Steph. and S. imoressus Germ. are listed separately, but were not counted individually in the samples. The taxonomy of those two species is considered later. In the some way) all the species of Apion were counted as one in the samples .nd a selection of mounted specimens from tussocks was identified: the species listed are those which occurred in the mounted material, and more species may have been present in the samples.

The total givoh is therefore an underestimate, and the true number of species of beetles obtained from the tussocks was probably over 200.

127 3) Annual chant;es in the beetlp fauna. The list of beetles found was examined to find out whether changes in either the numbers of individuals, or of species, took place during the year. Initially, the data from both Dactylis and Deschampsia tussocks were considered together. Table 23 shows the total numbers of beetles obtained from the tussocks sampled in each ionth, and the resulting monthly averages are graphed in Fig. 25A, in which the autumn results of two years have been combined. Table 23. Numbers of beetles found in tussocks sampled, September 161 to November 1 2.

Month Tussock No. of No. of beetles _ sam- les Average *opt. 1961 Dactylis 14 38, 26, 47, 36, 13, 50, 23, q1.7) 18, 38, 56, 42, 25, 7, 25. ' )31.5 It Deschampsia 2 14, 43 28.5) sot. 1961 Dactylis 6 39, 52, 21, 7, 25, 82. 37.7) II Deschampsia 8 36, 91, 78, 21, 51, 22, )41.3 24, 29. 44.0) ) moo. 1961 Dactylis 3 53, 44, 38. 4 .0)43.0 It Deschampsia 3 116, 3, 4. 41.0)) an. 1962 Dactylic 3 92, 42, 74. 69.3)48.5 n Deschampsia 3 41, 20, 22. 27.7) eb. 1962 Dactylic 6 14, 6, 49, 61, 9, 6. 24.2)25.9 it Deschampsia 3 20, 49, 19. 29.3) Dactylis 'far. 1962 3 40, 12, 22. 24.7)25.0 II Deschampsia 6 32, 42, 25, 20, 18, 14. 25.1) 'pr. 1962 Dactylis 16 39, 14, 9, 26, 18, 5. 18.5 i4ay 1962 it 12 9, 13, 6, 27, 5, 10, 14, 4, 7, 46, 28, 16 15.4) nDcschampsia 11 7,7,3,40,6,22,15,7,38,12,13 15.5p.5.4 une 1962 Dactylis 6 19, 11,6, 9,6,8. 9.8 July 1962 II 12 17,17,1130,10,5130121,9,33, 10,13. 16.3 Aug. 1962 II 9 7,2,4,11,33,7,28,4,2. 10.9 opt. 1962 II 9 15,3,26,46,35,15,39,37,5. 24.6 Oct. 1962 d 6 36,21,7,9,13,12. 16.3 Nov. 1962. u 6 58,11,22,34,29,21. 29.2

128

In ) 1 • d le amp

0 s ks c o s s f tu o o.

0 n ( Log

C 0 L „2 0 .11' 0 0 0 0 . 0 O 0 . CO N 8 in q CV) (Ni Z• (mu 0

4 >,

- 0 X

0 O 0 O c;) cv -0 .5 -s 8 0 N 0 3 44 Cc 2 -8 CIifi' .4"41' 3

Fig. 25. A., B. & C. Numbers of beetles found in tussocks throughout the year. D. Increase in the number of species found with the number of tussocks sampled. 129 Thcm wns a pock from October until January, after which tho numbers

fell until Juno, and then tended co rise again. To see whether the

increase in winter resulted from the presence of more species in the

tussocks, or merely of increased numbers of the species already present,

the number of species occurring each month was exam.,ned.

Comparison of the months was complicated by the different numbers

of tussocks which wore sampled in each. The number of species now to

tussocks falls off exponentially as the number of tussocz.s sampled in

any period increases. Thus a simple linear correction to calculate the

number of species in a standard number of tussocks cannot be used.

Williams (1944) has shown that the number of species in a sample of a

populat_on is proportional to the log of the area of the sample. kn

increase in the number of tussocks sampled in any month is equivalent

to increasing the area of the total sample taken. Thus a graph of the

number of species obtained against the log of the number of tussocks

sampled should give a straight lino. This has been done using the data

from May 1962, when 24 tussocks wore sampled; the result is shown in

Fig. 25D. The steepness of the line increases as the number of samples

becomes larger: this is probably because of an overall change in the

composition of the tussock fauna during the month, as the samples are

plotted in the order in which they are taken. Gleason (1922), plotting

number of species against log of the area sampled, found a similar

effect when the samples were plotted in their geographical order, because

of grouping of species together in different regions of cho area sampled.

Using Fig. 26D, the number of species found in each month was then

corrected to the number which would be expected in ten tussocks, biased

on the indicated rote of increese in species with nymber of tussocks.

130

Thus, in May 1962, ten tussocks should have contained 48.4 species.

If another month yielded x species from y tussocks, the corrected number

was calculated by first measuring upwards from y on the horizontal scale to the line, and then horizontally to cut the vertical scale at a number

of species, xi. This is the number of species that ten tussocks would

give in the unknown month is given then by

48.4x x = 10 Xn

where xio is the required theoretical number of species expected in ten tussocks. Table 24 shows the actual number of species obtained in each

month, and the corrected figures using the above method.

Table 24. Calculationof the numbers of species of beetles j,n ten tussocks in each month of the ,Year.

Actual no. No. of Theoretical number Month of species tussocks of species in found sampled ten tussocks

Jan. 52 6 63.68 Fdb. 41 9 43.13 Mar. 48 9 50.49 Apr. 33 6 43.39 May 73 24 48.40 June 26 6 34.19 July 3 9 12 36.04 Aug. 30 9 31.56 Sept. 93 30 59.52 Oct. 84 19 63.50 Nov. 50 8 56.55 Dec. 55 9 57.86

Fig. 25C shows the calculated numbers of species in each month in graph

form. The number of species was highest in early winter, rising in Sept—

ember, and falling from January onwards: the minimum was in August. From

Figs. 25A and C, the resulting graph of average numbers of individuals can

be calculated: this is shown in Fig. 25B. This also shows a winter peek, 131 and summer minimum. Thus the increase in numbers of individuals in tussocks in winter is caused both by e greater number of species being present, and by an increase in the average number of individuals of the species present. 132

4). Comparison of the fauna of Dactylis and Deschampsia.

Table 23, in which the total numbers of beetles were given, also

shows the monthly average numbers in Dactylis and Deschampsia tussocks

separately, during the months in which Deschampsia tussocks were

sampled. Fig. 26A shows the graphs of the two sets of averages from

September 1961 until nay 1962. The winter peak in Deschamosie was more

spread out, by comparison with the sharp January peak in Dactylis. Over

the entire period, however, there was very little difference in the

average numbers: the overall averages were 28.35 beetles per tussock in

Dactylis, and 28.44 in Deschampsia tussocks.

The numbers of species of beetles in the two types of tussock were

plotted against the log of the number of tussocks sampled. Fig. 26B

shows the resulting graphs. In order to remove effects of changes in the

composition of the fauna during the sampling period, the numbered samples

were plotted in a randomised order. The Dactylic tussocks used for the

graph were the first 36 sampled on the North Gravel. After the first

ten tussocks, the number of species in the Deschampsia tussocks was

greater than that in the Dactylis, and increased at a greater rate.

The final numbers of species from 36 tussocks were 80 in Dactylis and

91 in Deschumsia, corresponding to 80.1 and 71.2 species par 1000 square

inches respectively. Thus although the number of species was greater

in Deschampsia, their density was less.

The species found in the tussocks on which Fig. 26B was based were

examined to sea how many were either common to both, or alternatively,

confined to orc, or othc.r of th:.: grass specie;. It was not considered

necessary to give a full list of the numbers of individuals of species 133

70-

60-

50- Number of beetles per tussock

30-

20-

10 S 0 D I J F M A M 1961 1962 . Deschampsia 90

Number of 80 B Dactyl is species found 70 O 60 - • • 50 -

40-

10 O

Log (no. of tussocks sampled +1) 0 • I I 0 0-5 1.0 1.5

Fig. 26. Comparison of the numbers of beetles in Dactylis and Deschampsia tussocks. 134 common to both types of tussock, as many were represented by a few individuals only, so that the apparent preferences of the individual species would have little significance. The total distribution, however, is of interest, and is summarised in Table 25, in which. only the presence

Or absence of each species in each sample was used, when calculating the relative frequencies of the species common to both grasses.

Table 25. Distribution of species between Dactylis and Doschampsio tussocks.

Species restricted to Dactylis 31

More fro9uent in Dactylis 26 clually common in both Species common to both grasses 1 45 grasses 9 More frequent in Deschampsia 10

Species restricted to Deschamosia 44

Tho figures show that Deschampsia has a more isolated beetle fauna than

Dactylis. The number of species restricted to Deschampsia is greeter than that restricted to Dactylis, and most of the species common to both grasses are commoner in Dactylis. Examination of the species present suggests that the differences are caused by the different areas from which the tussocks ware removed, rather than a result of any properties of the grass species themselves.

The Deschampsia tussocks came from Cascade Marsh, which has already been described as predominantly damp, whereas North Gravel is higher, with a dryer, sandy soil, and different surrounding vegetation. Many of the species which were found to be restricted to Deschampsia, tussocks are known to prefer ma7'shy areas. Examples are : 135

Loistus rufescons (F.)

Pterostichus stronuus (Panz.)

Ac,onum obscurum (Herbst.)

Arfonum fuliginosum (Panz.)

Cercyon haemorrhoidalis (F.)

Stenus flavines Steph.

Tachy,porus scutellaris Rye

Bryaxis spp.

Hydrothassa aucta (F.)

Chnetoonama subcoorulea huts.

Cassida floveola Thunb.

Liosoma deflexum (Panz.)

The slope of Cascade Marsh probably results in sufficiently dry conditions at the southern edge for species usually found in dryer situations to occur, whereas North Gr':vel has no wetter areas in which damp- preferring species might live.

136

5). Relative numbers of common and r3re species.

Examination of the list of species given in Appendix Table 2, shows

that many species worn represented by one or two individuals only, with

relatively few having large numbers of individuals. The commoner species

are also restricted to a few families. Table 26 summarises the numbers

of species in each family. The speciL,s are divided into three groups,

according to whether there were less than 10, between 10 and 50, or more

than 50 individuals found in the year's samples. The percentage of

species in each of these groups is also given for each family.

Table 26. Numbers of soocios of various families found in tussocks, grouped according_to numbers of individuals present.

S ecios Family (10 individuals 10-50 individuals >50 individuals No. P No.

Carabidae 17 65.5 6 23.0 3 11.5 26 Hydrophilidao 0 3 75.0 1 25.0 4 0 Histeridae 2 100 0 2 Ptiliidae 100 0 0 2 2 S ilphidae 0 1 100 0 1 Anisotomidao 7 100 0 0 7 Scydmaenidae 2 100 0 0 2 Staphylinidee 42 65.5 13 22.0 8 12.5 64 Pselaphidao 4 100 0 0 4 Scarabaeidao 1 100 0 0 1 Clambidae 1 100 0 0 1 Elateridao 2 100 0 0 2 Cantharidae 2 100 0 0 2 Phloiophilidao 1 100 0 0 1 Phalacridae 2 100 0 0 2 Cryptophagidae 2 50.0 2 50.0 0 4 Coccinellidae 7 78.0 1 11.0 1 11.0 9 Lathridiidao 5 62.5 2 25.0 1 12.5 8 Corylophidae 1 100 0 0 1 Bruchidae 1 100 0 0 1 Chrysomelidao 9 50.0 1 10.0 0 11 pionidae Identification of all individuals not attempted. urculionidae 31 93.8 2 6.2 0 33

Total 16.8 13 7.1 198 137 The Table shows that, out of the 23 families represented, only four, the Carabidae, Staphylinidael Lathridiidao and Coccinellidael contained species which were represented by more than 50 individuals. The percentages of species in each of the three groups were vary similar in the first three of these families. Thus they all had about 65% of the species represented by less than 10 individuals, 23% by 10 - 50 indiv-

iduals, and 12% by more than 50 individuals.

In comparison, the Chrysomelidae and Curculionidee also had 10 or more species, but 900 or more of these had loss than 10 individuals, and the remainder nil had less than 50 individuals. The remaining families all had less than eight species each, nearly all of which wore represented by less than 10 individuals.

This shows that the beetle population of tussocks consists largely of species represented by a few individuals only, and which may be temporary inhabitants. In addition there are relatively few species which are well represented, and which are probably permanent inhabitants.

Mathematical methods can be used to give a quantitative measure of the relative numbers of occasional and commonly occurring species. One such measure of the distribution of abundance of species within a population is the nequitabilityn component of species diversity, proposed by Lloyd and Ghelardi (1964); this was applied to the data from tussocks. As a basis, a hypothetical distribution of individuals among species based on a mathematical model is used. This is considered to represent the most Isequitablen or Heveno possible distribution of individuals among the species present, and has an "equitability” component,

El of unity. The actual distribution of commonness and rarity among the species of the observed population is then compared with this 138 hypothetical distribution. If the rare species are rarer, end the common

ones more common, than in the model, the value of S decreases. Thus in

the tussocks, which were suspected of having many species with a few

individuals, and a few with many individuals, the equitability was

expected to be low as a result of this rather distinct division into

common and rare specie' s .

The comparison of the observed and theoretical distributions is

carried out as follows. Lloyd and aaelardi give a table of the diversity

of abundance of various numbers of species, calculated according to the

mathematical model. The observed diversity is then calculated and

compared with the table to determine the number of species that would

be needed to produce a similar diversity according to the equitable

distribution of the model. The ratio of this hypothetical number of 1 species, termed S , to the actual number of species, S, in the observed

population or sample, gives a measure of the equitability of the distrib-

ution of individuals among the species. Thus, in the sample of litter

arthropods given by Lloyd and Gilalordly there wore 44 species. The

common species were commoner, and the rare ones rarer, then in the hypo-

thetical model. The calculated diversity was 4.16, which corresponded

to the equitable diversity of 26 species. The equitability of their

sample was thus 26/44 :•-• 0.59. The validity or otherwise of the math-

ematical model used as a basis for these calculations does not prevent

their being used as a basis for comparisons of the equitability of different populat ions.

As a comparison with the litter arthropods of the example given,

the equitability, 5, of the 1 5 species of beetles obtained from tussocks 139 was calculated (14 species whose identification was not taken to species level for all individuals wore omitted). The calculating formula is

-logionr} H (s) = 3.321928 log10N whore H(s) is the observed species diversity.

N is the total number of individuals

n is the number of individuals of the r-th species. r

From this formula, H(s) was 5.189. Using the table already referred to, this corresponds to the hypothetical equtable diversity of 55 species.

As the actual number of species was 185, the equitability, E, was given by 1 S 0.298. S m- 185

The equitability was calculated in the same way for the species of

Carabidso and Stephylinidea separately, and for the beetles of the remaining families together. The results, together with those for the total beetle population, are given in Table 27.

Table 27. Calculation of Itecuitabilityn comeonent of soccios diversity of beetles from tussocks, 1961-2.

H Sample material S (S) S1 E

Carabidae 26. 2.822 9.8 0.377 Stephylinidee 64 3.843 21 0.328 Remaining beetles 97 4.757 40 0.412 Total beetles 185 5.139 55 0.298

The beetles of the families other than Carabidae and Staphylinidae have the highest equitability as they are mostly species with few individuals.

The relatively low equitability of the Carabidae l Staphylinidac, and the entire beetle population is duo to their being made up of a few excessively common species, together with many excessively rare ones. The total 140 booties give a lower equitability than any of their constituent parts.

This could be caused, in part, by the reduced sample size of the sub- divisions, which gives an upward bias to E. But it also indicates that the division of the beetles into the two families which contain most of the common species, on the one hand, and the remaining families with many occasionally occurring species is a justifiable one As each group has a more equitable distribution of common and rare species than the resulting population when the groups arc combined. It is worth noting, however, that all the values of E obtained are lower than that of the leaf litter example mentioned. If that example is typical of many permanent populations, it shows that ail the groups found in tussocks have a relatively low equitability, because of an excess number of species represented by few individuals. The method should be applied to more field populations before this can be proved, however. 141

6). Details of common tussock—inhebitiEgspecies

The commoner species, of which 50 or more individuals wore found, were the following :

Garabidne : Trechus obtusus Er.

Bredycellus harpftlinus (Ser.)

Agonum obscurum (Herbst.)

Dromius melanocophalus Dej.

Stophylinidao Stenus clavicornis (Scope)

S. flavipes Steph.

S. impressus Germ.

Tachyporus nit idulus (F.)

T. chrysomolinus (L.) T. hypnorum (F.)

4J.a0114 annlis (Gray.) Atheta (Acrotonn)funPi (Gray.)

Goccinellidao Rhizobiellus litura (L.)

Lathriciiidae Enicmus transvorsus (01.)

Corticeria imoressa (01.)

Data on Dromius melanocahalus Doj., Storms clavicornus (Seep.) and

Stenes improssus Germ. are given in Section IIIE, as those more three of the four species chosen for more detailed study. The relative numbers of the remaining species throughout the year are shown in Figs. 27 and

28. The histograms show the calculated numbers in six tussocks of

Dactylis and Deschompsia each month. As no Descham'esia tussocks wore sampled in April, Juno, July and August, only Dactylis records are available for those months. In most cases the periods of occurrence and tussock preference of each species c:m be seen. 142

Trechus obtusus Er.

30- 20- Bradycellus harpolinus(Se0 10. 0

Agonum obscurum (Hbst.)

0 40 30 20 Stenus flavipes Steph. 10 0

Tachyporus nitidulus (F.)

5 40 30 2 Tachyporus chrysomel inus(L.)i

F M A M J Jy A S O N D

Fig. 27. Calculated numbers of common species in six tussocks throughout the year. Black ; Deschampsia : Stipple ; Dactylis . 143

Trechus obtusus r. shows a rnthor indistinct increase in numbers in winter, with a secondary peak in July. Tha numbers per month were the lowest of the common species, but wore compensated for by its occurrence throughout almost all the year. It was more common in

Dactylis than Deschamosia, although probably occurring regularly in both grass species.

Bradycellus harpnlinus (Ser.) had a distinct peak in September, occurring only in small numbers during the rest of the year. As it was almost absent in Dactylis tusocks, which wore the only ones sampled in

Juno, July and August, none wore recorded during these months. The high numbers in September indicate that the species would probably have been present in Deschampsia in August as wall, had samples been taken. Thus it is probably ono of the few species of tussock booties which have the greatest numbers of adults present in late summer and early autumn.

AP:onum obscurum (Herbst.) was restricted to Deschampsia tussocks, where it occurred in large numbers in late autumn and early winter only; it was almost absent during the rest of the year.

Stenus floviees Staph. was also restricted to Doscham-Qsia, except for a single specimen which was found in Dactylis in September. It was found throughout the winter months from September until March, with a peak in February.

Tachyoorus nitidulus (F.) had two peaks in numbers; one in November, and the second in May. This could indicate that there arc two gener— ations a year in tussocks, although the numbers obtained were too small to confirm this. It was found minty in Dactylic, although some, specimens were obtained from Deschamosia tussocks as well. 144 30- Tachyporus hypnorum (020-

Amischa analis (Gray.)

Atheta spp., mainly A. (Acrotona) fungi (Gray.)

Rhizobiellus litura (L.)

10 Enicmus transversus (01.) -

Corticaria impressa (01.) 10-

FMAMJJyA S 0 N D

Fig. 28. Calculated numbers of common species in six tussocks throughout the year. Black ; Deschampsia : Stipple ; Dactylis. 145 TachyporT4 chrysomelinus (L.) occurred throughout the winter from

September to April, with a pock in November. It was more common in

Deschamosin than Dactylis, although it occurred regularly in both grasses.

Tachyporus hypnorum (F.) had similar annual fluctuations in numbers to T. chrysomolinus . It also was found commonly in both grasses, but the numbers in Deschampsia were distinctly fewer, and in Dactylis slightly more, than those of T. chrysomelinus, resulting in a slight preference for Dactylis tussocks. Numerous larvae of Tachyporus spp. were found in the bases of Dactylis tussocks in the summer months. This shows that at least one (and probably several) of the Tachvorus spp. found in the tussock in winter, pass through their life cycle in the tussocks.

Amischa analis (Grey.) was another species which occurred in greatest numbers in winter. The peak in numbers was in January. It was found in both grasses but was slightly commoner in Deschamosia. As mentioned previously, this was one of the species in which the samples yielded

Probably not more then 50 of the specimens present.

Athota spp., mainly A. (Acrotona) fungl. (Gray.), were in— cluded although more than one species was present in the material. Most of the specimens examined were A. fungi, and because of the largo numbers which wore found, it was considered worth while to include it in the list of common species. Again the numbers wore highest in winter, although the poak in December was a gradual one, with considerable numbers present in all months except Juno, July and August. As it wes more numerous in

Deschampsia than in Dactylis, this probably caused the low numbers in these months, when only Dactylis was sampled. 146

Rhizobiellus litura (L.) was found throughout the yoL;r, mainly in

Dactylis tussocks. The numbers were greatest in autumn, with a second small peak in April end May; there may be two generations each year.

Larvae which later pupated and emerged as Rhizobiellus adults wore found in the dead flowering stems of Dactylis, feeding on mites. Thus this species can pass through its life cycle in the tussocks.

Enicmus transversus (01.) also occurred throughout the year. The apparent peaks in March and September ore due to the increased numbers found in Descheapsie tussocks in those months. The numbers in Dactylis did not show any definite annual fluctuations.

Corticaria impress° (01.) was found in greatest numbers in late winter and spring. It occurred in both s:JE.,,cies of tussock, regularly in

Dactylis, and less frequently, although in largo numbers, in Doschglmpia.

Thus, out of these 12 common tussock booties, eight showed a definite increase in numbers in winter, two (Agonum and Rhizobiollus) had a peak in autumn, one (Bradycellus) had a peak probably in late summer and one

(Eniamus) did not show any distinct annual fluctuations. The data also suggested that two species (Rhizobiellus and Tachyporus nitidulus) might havo more than one generation par year in the tussocks.

None of these species were restricted to Dactylis, although two

(Agonum and Stenus flavipas)were found only on Deschamipsia, and several

(e.g. Bradycellus, Tachyporus chrysouelinus, Atheta) were commonest in

Dc.,,schanosia, in contrast to the general trend shown by the whole beetle population. Thus the Deschamosia contained more common species than

Dactylis.

It is interesting to note that none of the common tussock-inhabiting beetles are restricted to a plant diet. Their ibeding habits can be 147 divided into three typos (although exact details are lacking in many cases).

i) mainly or entirely predatory. Trc,chus altaaas Er.

Agonum obscurum (Herbst.)

Stenos spp.

Rhizobiellug litura (L.)

(ii) omnivorous or saprophagous.

Bradycollus harpalinus

Tachyeorus spp.

Amischa analis (Grave)

Athota fungi (Gray.)

iii) Mycetophagous.

Eniciaus transvorsus (01.)

Corticaria iraprosse (01.)

Food for all these typos is available in the tussocks at all times of year. The data already given on the total fauna of tussocks show that there is no shortage of small animals available as food for the larger predators throughout the year. There is also a resulting continual supply of dead animal material, as well as dead vegetation such as the rotting grass leaves, for the saprophytes. The rotting loves and stems also support fungi (Webster, 1956), which provide food for the mycetophagous forms. Thus these types of feeders are able to live in the tussocks as a permanent habitat.

In contrast, the species which are entirely phytophagous are usually represented by small numbers in tussocks. Thus the Ohrysix.ielidae 148 and Curculionidee, although well represented in tussocks, have no species with more than 50 individuals, end loss than 10'1 with more than 10 individuals. There do not appear to be any beetles which feed specifically on these grasses, and which might be oxpoctod to occur in large nulAbers as a result. All the phytophagous species present have other host plants, and therefore must occur in the tussocks only temporarily, when they arc not feeding. 149

7). Conclusions.

Although the number of sample's taken was not wry large, the following preliminary conclusions can be made concerning the total beetle population found in the tussocks sampled.

a) The beetles form a permanent part of the insect fauna of tussocks,

and are represented by a largo and varied selection of species. The best—represented families are the Corabidae, Staphylinidao. and

Curculionidae.

b) The number of species, and a verc,.zo number of individuals per species, are greatest in winter and least in summer. These two factors combined result in a marked increase in the numbers of individuals during winter.

) The numbers of individuals found in Dactylis and Deschampsis tussocks wore similar, but the Deschamesia tussocks had a more isolated beetle fauna, sharing fewer species with Dactylis than vice versa. This w-as probably because of differences between the two areas from which the samples wore taken, rather than between the two species of grass.

d) The beetle population of tussocks comprises a large number of species which occur relatively rarely, which are represented by a few individuals only, and a few species which are common, and found in very large numbers by comparison. This results in a low equitability component of species divers it y in the beetle population.

o) The commoner species are all either predatory, omnivorous, saprophogous or mycetophagous. Phytophagous species are not represented by many individuals in tussocks, although many such species occur in small numbers. 150 D. C0LE02TZROUS FLJNA DETI,TESN TUSSOCKS.

1) Total fauna obtained in oitfall traps.

Pitfall traps wore used to collect beetlosin between the tussocks on

North Gravel frola July 1562 until March 1964. Sixty two 3" x 1" specinon

tubes were installed in pairs in the napped plot. The tubes of each pair

wore about 3" apart, and the pairs were separated froze one another by

about three foot in each direction. This spacing would have resulted in

a grid containing 8 x 4 = 32 pairs of traps, but the area in which the

therLdocouples had bon installed was left undisturbed, so that only 31

pairs were set up. Fig. 5 shows the positions of the pairs of traps.

The tubes were half-filled with forna1in solution, and changed at

intervals which varied iron one to 14 days, according to the tine of year,

and nuiabor of insects which ware caught in then. The average tine between

changes was throe days. During the sunner of 1563 live cerebid booties were needed for experildental work: in order to obtain those, one tube of each

pair was filled with water instead of for..ialin, fron 13th. Juno onwards.

As is described later, this affected the nuldbers of beetles which wore

caught in the traps.

All the beetles caught in the traps between 9th. July 1962 and 6th.

larch 1964 were identified (to the generic level only, as specific ident-

ification of the large opeunt of naterial would have taken too long).

Adccndix Table 3 lists the genera obtained, and gives the total nunbers of

individuals caught, as well as the nonths of occurrence of each genus.

Genera which were found in Dactylis tussocks on North Gravel are also

indicated.

97 genera were found in the pitfall traps, of which 65 (67A also occurred in tussocks on North Gravel. Thus a considerable proportion of 151 the beetles which were active on the ground in the plot were shown to go into the tussocks at some tine. Of the 95 genera which occurred in the tussocks on North Gr,.vel, 65 (63.4A were found in the pitfalls. This cannot moan that those which did not occur never leave the tussocks, but suggests that some species may move between the tussocks in such a way as to ovoid the traps; e.g. by moving in the higher grass above ground level, or by flying.

A comparison of the calaonest Species in the tussocks end in the

eitfall traps shows that only a few occurred commonly in both. Table 28 lists the com_ionest genera in tussocks and pitf-lls, uith the total numbers found during the 15 months sampling of tussocks, and the 20 months of

pitfall trapping.

Table 28. Comparison of the commonest species of beetle in tussocks and in pitfall trees.

Number of individuals Genus in tussocks In pitfalls

a)Commonest tussock genera Stenus 458 103 Drouius 284 2 Tachyporus 223 58 Athota 201 326 Rhizobiollus 107 7 Aaischa 97 110 Enicuus 70 45 Trechus 63 724 Ilon 35 32

b)Commonest pitfall genera 2terostichus 2 6,101 Trochus 63 1,724 Abax 1 681 Calathus 5 543 Cetops 1 381 Athete 201 326 Sitona 13 320 Staplglinus 0 307 Megasternura 21 304 152 All of the commoner tussock-inhabiting beetles wore found in the

pitfall traps, but only two genera, Athota and Trechus, were among the

commonest of the beetles caught in the traps. Dromius and Rhizobiollus,

although common in tussocks, occurred only very occasionally in pitfalls.

The remaining five species wore found fairly regularly in pitfalls,

although not in sufficient numbers to be among the commoner pitfall

genera listed in the second. half of the Table.

Several genera commpn in pitfalls wore rare or absent from tussocks,

e.g. Pterostichus, AbE.lx„ Calathus, Catoos and Staphylinup. Trechus and

Atheta, as already mentioned, were among the commonest genera in both.

The remaining three species occurred in tussocks fairly commonly, but

wore not among the commonest nine genera listed in tussocks.

Thus only two gcnora wore really common both in and between the tussocks, which shows a distinction between the beetle fauna in the tussocks and that in the surrounding veget,,,ition. This supports the idea that the commoner beetle species found in Dactzlis are permanent inhab-

itants of the tussocks, and that many of the species which wore found

in small numbers in tussocks occur there only temporarily.

The numbers of genera obtained from the pitfalls each month, and given at the foot of Appendix Table 3, show a peak in summer, in contrast to the winter peck which occurs in the tussocks. An increase in indiv-

iduals trapped is to be expected in summer, as activity increases with temperature. However, the increase in numbers of genera may also show that species which era absent from the intervening grass in winter, and which racy ovcrwintoring in the tussocks, aro active outside the tussocks in summer. 153 2) Predatory Oarabidae in pitfall traps.

The four most common genera of beetles taken in pitfalls wore

Ptorostichus, Trochus, Abax and Calathus. These arc all predatory beetles; Pterostichus and Abax era especially large and active. It was therefore decided to investigate whether they fed on any of the species of tussock inhabiting beetles selected for further study. The details of this work aro given in Section IV, but the numbers of Pterostichus and Abaz caught in the traps are considered in this section.

Abax was represented by the solo British species, A. perallelaQepidus

(Pill and Mitt.), 681 individuals being caught during the trapping period. Three large species of Ptorostichus wore present

P. madidus (F.), 5819 individuals caught

P. niger (Scholl.), 142

P. nolanerius (Ill.) 118 it sr

The numbers of these species caught in different times of the year are shown in Fig. 29. The Ptorostichus species wore contionest in August, but Abax was most numerous in July, although the first specimens wore not caught until'later than those of P. madidus. After mid-June, 1963, one tube of each pair of traps was filled with water instead of formalin, so as to obtain living predators for experimental purposes. A comparison of the catches in the water and formalin-filled tubes shows that the numbers in the water traps were lower than in those with formalin.

Table 29 shows the numbers of P. madidus caught in the two types of traps during the half-monthly periods from 16th. July until 30th.

September, 1963. 1.54

A 0--01962 pmadidus 0-4, 1963

0- - - - -o 1962 Abax 41- - - —41 1963

100 50

5 % \ N. ON NO \ \ \ \ \ \ \ \ \

0-----01962 •—•1963 B

0 o 1962 P melanarius • •1963

Fig. 29. A. Pitfall catches of P. madidus and Abax. t I 11 B. " P. niger and P. melanarius. 155

Table 29. Comparison of the numbers of P. madidus caught in traps containing water and formalin.

Formalin Period Water Number caught c,.7 , Number cauqht June 16-30 25 43 33 57 July 1-15 82 36 143 64 July 16-31 65 17 311 83 Aug. 1-15 206 29 484 71 Aug. 16-31 92 26 259 74 Sept. 1-15 18 30 41 70 Sept. 16-30 5 12 37 88

Total 493 27.4 1,308 72.6

The number caught in the water-filled traps was less than half of that in those with formalin, so that the total catch must have been reduced by about a quarter during the period that water traps were used. This may partially account for the reduced numbers of these species caught in

1963, compared with 1962, and also the drop in numbers of P. madidus from May to June 1963. The beetles could not climb out of the water filled tubes, so that the greater numbers in formalin show that this liquid acts as an attractant.

The distribution of P. madidus and Abax throughout the area differed.

Fig. 30 shows the numbers of each species caught in each trap between

9th. July, 1962, when trapping was started, and 17th. December, when the last specimens of the year were recorded. The plot is shown diagrammatically, divided up into 32 squares, in 31 of which there was a pair of traps (the remaining one contained thermocouples, as already explained).

The number of beetles in each pair of traps is given as the percentage of the maximum number caught in any pair, and is shown as a histogram in each square of the plot. P. madidus occurred throughout the plot, and was more numerous at the east and west ends than in the centre: there was

156

A P madidus

West East

B Abax

West East

Fig. 30. Relative abundance of P. madidus and Abax in pitfall traps throughout the mapped plot. 157 little difference between the two ends. The increased numbers caught at each end of the plot might have been caused by immigrating individuals, which were trapped as they entered the area. Abax, in contrast, was commoner at the eastern, tree bordered end of the plot, and few were caught at the other end. Greenslade (1961) studied the ecology of both species, and showed that P. madidus was primarily an inhabitant of grassland, whereas Abax was essentially a species of scrub and the edge of woodland. This explains the occurrence of P. madidus throughout the rough grass plot, and the concentration of Abax at the wooded end. 158 3) Saroli/T of grass between tussocks.

Although pitfall traps catch the species that occur between the tussocks, they do not give an idea of their density, as the sample obtained

is a measure of both activity and population density. To find out how the numbers of beetles in tussocks compared with the numbers in areas of the

intervening grasses, samples of turf containing other grasses were taken.

These were either dug up, and the fauna extracted by shaking or in a

Tullgren funnel, or the vacuum sampler was used to extract the fauna without digging up the sample. The number of samples taken was small, but they give an idea of the numbers of beetles present; these are shown in Table 30.

Table 30. Numbers of beetles obtained from samples of the grass between Dactylis tussocks.

Date Diameter of sample (ins.1 Grass Sampling Method Number of beetles 21.9.61 8 Festuca Proken up 3 12.12.61 6 II Shaken & broken up 3 II 6 II 9 it it 4 18.1.62 6 Ayrostis tt tt II 0 it 6 II II II II 6 II 6 Festuca II If 9 1 17.2.64 6 Holcus & Tullgren funnel 10 Festuca II 5.5 Festuca II Il 3

16.5.62 •samples of Not record Vacuum sampler 5,4,1,1,2,2. 61! —ed

31.5.62 12 samples of ti II II 3,2,0,1,1,0, 61, 2,2,0,3,2,0. 7.6.62 12 samples of II it it 1,2,0,0,1,0, 611 0,0,0,1,1,1. 28.6.64 6.75 Festuca Tullgren funnel 9 11 7.25 Agrostis it It 8 159 The Tullgren funnel samples are a bettor comparison with tussocks than

samples taken with the vacuum sampler, as they include the beetles in the top half inch of soil, which was also seieplod in the tussocks. Table 32 shows that although beetles are obviously regular inhabitants of .the gross in between the tussocks, the density of individuals is much

lower than that in the tussocks in winter. In summer, however, the densities of adults in all grasses are probably similar, although the data on the total fauna of tussocks show that beetle larvae are concen-

trated in the tussocks in summer.

From the relative areas covered by Dactylis and the remaining vegetation, and from the densities of beetles in and between the tussocks, the total populations of beetles in Dactylis and the intervening grasses can be calculated. This was done for the winter months, when the density of beetles in tussocks was highest. Thus, between October 1561 and March

1962, the average number of beetles per tussock was 37.54, and the number present in 396 tussocks is thus 14,886. But as the samples wore only shaken, this figure can be assumed to be only 74% of all the beetles in tussocks. The total population thus becomes 20,116. The average number of beetles present in the intervening grass samples during the winter months was 3.75 in an average sample area of 30 square inches; this is a density of 18 per square foot. Thus, in the 2026 square foot of grasses other than Dactylis, there were 2026 x 18 or 36,468 beetles. This indicates that, out of the total beetle population of 56,584, the tussocks contained 35.6%, and the remaining grass 64.4%. The densities of beetles per acre were 784.080 in the grass between tussocks, and 1,037,381 in the whole plot. 160 No great accuracy can be claimed for those figures, as approximations have been made in almost every stage of the calculations, and the number of beetles per square foot outside the tussocks is based only on a few samples. But they do show that although the density of beetles is much greater in the tussocks than elsewhere, they probably always contain less than half of the total beetle population in the experimental plot, since they cover only a small proportion of the area. All the samples outside the tussocks were taken in the day, so that the possibility of their consisting, entirely or in part, of beetles which had left the tussocks temporarily, and which would return when the temperature dropped at night, cannot be ruled out. However, when tussocks were sampled at night, there was no evidence of any inorease in beetle numbers. 161 4) Conclusions.

The following conclusions can be made from these data.

a) The numbor of genera of beetles caught by pitfall traps between tussocks was similar to the number found in the tussocks.

b) The commonest species in pitfalls were usually not those which were found commally in tussocks, and vice versa. This indicates that the faunas inside and outside the tussocks differ considerably.

c) The commonest species found in pitfalls wore large carabid beetles. Those are predatory, and occur in greatest numbers in July and August.

d) The density of beetles between the tussocks is low throughout the year, and is probably similar to that in the tussocks in summer, when the number of adult beetles there is lowest. But since the tussocks cover only a small 2art of the grassland, they contain loss than half of the total beetle population in the field, even in the winter :.1onths.- 162 E. SELECTED COMM S2ECIES.

1). Choice of Species.

The only species which were considered for detailed study at first were those which wore represented by more than 200 specimens during the first year of sampling of tussocks. These were Dromius melanocephalus

Dej., Stenus clavicornis (Seep.), Tachyporus chmsomelinus (L.), Amischa analis (Gray.) and Atheta (Acrotona) fungi (Gray.). Of these five species, A. fungi was the commonest; however Atheta species are small, and very difficult to identify quickly. Rapid separation of A. funf/i from the other species which also occur in tussocks would be almost impossible, and as easy identification in the field was considered to be an essential feature of the chosen species, A. fungi was not used.

Amischa analis was not considered further for similar reasons. Tacliyporus chrysomelinus was the least common of the three remaining species, and was therefore abandoned in favour of Dromius melanocephalus and Stenus clavicornis, as both were very common, and could be easily recognised in the field.

Both Dromius and Stenus were represented by more than one species in tussocks, and a second species of each was included for the purpose of comparison. The only other species of Dromius present was D. linearis

(01.), which was only moderately common on North Gravel, but which was later found to be one of the commonest beetles in Dactylis tussocks in

Nursery Field. The second species of Stenus which was chosen was

S. impressus Germ.. This was selected both because it was the second- commonest Stenus species, and also because it was the only Stenus (and one of the few species of tussock beetles) which was more common in the summer months than in winter. Unfortunately, little ecological work 163 could be done on this species, as it was found to be confused with the

loss common but closely allied species, S. aceris Steph., and the taxonomy of the two species had to be studied. A satisfactory moans of separating the two species was found, but identification in the field was not practicable. 164 2) Stenus clavicornis (Scopoli)

(a) Introduction.

Stenus species are primarily inhabitants of wet situations, living on river banks, in marshes and in similar moist habitats (Renkonen, 1950).

Soma species prefer dry habitats, however, and Renkonen (1934) divided the

Finnish species into 41 which occurred near water, 16 which were characteristic of wet heaths, 11 which ware found in woods and dry heathland, and nine which were typical of grassland and arable regions.

He recorded S. clavicornis from sandy river banks, woodland, dry heaths and alluvial pastures, but considered it to be primarily a species of woodland or dry heathland. It has been recorded from various habitats by other authors, e.g., from grassland in Cheshire (Cameron, 1917), near Oxford (Ford, 1935) and in Denmark (Schjotz-Chistensen, 1954); from sand dunes (Van Heerdt and ilii.rzer Bruyns, 1560); from wrack beds

(Backlund, 1945) and from woodland litter (Thiele, 1964,b). Regional surveys of beetles, such as Fowler (1307-1913), Donisthorpe (1939) and

West (1940-41) agree that it is commonest in damp places in woods and fields, such as at grass roots, in haystack and vegetable refuse, and in litter. Thus it would seem to be found in a wide range of habitats, most of which are moist, although not necessarily close to water. Such situations are frequent in woodland litter, and among the bases of close- growing grasses, such as those that form tussocks. It is a widely distributed species, occurring throughout Europe (but not Iceland), and its range extends eastwards through the Caucasus and Siberia to Nongolia

(Strand, 1944).

Biological and autecological studies on Stenus are almost entirely lacking. 1,1embers of the genus are generally believed to feed on 165

Collembola, although Renkonen (1950) describes them as "rather poly-

phagous predators", without giving details of the range of food taken

by any of the species. iInclagan (1932) reoorted that S. clavicornis

was known to feed on Smynthurus, but did not say whether this was based

on field observations or laboratory experiments. The larvae of a few

species only have been described, and their feeding habits are unknown.

When two species of Stenus were chosen for special study, it was

realised that the lack of biological information on the genus probably

reflected the difficulty that previous workers had had when studying

them. The large num7:ers of S. clavicornis made its choice an obvious

one, however, and it was hoped that its commonness would reduce the

difficulty of finding specimens of the immature stages, and investigating

choir biology, as well as that of the adults.

(b) Adults.

(i) Occurrence in tussocks.

The tussock sampling methods used during the first year have already

been described (p.117). After December 11th. 1962, until 14th. April

1964, only tussocks of more than six inches diameter were sampled, in

order to confirm the annual fluctuations of the selected species in the

more favourable tussocks. After shaking out most of the fauna as before,

the tussock bases, dead leaves and dead flowering stems were treated

separately in Tullgren funnels. In order to compare the number of

beetles present in an area containing older Dactylis tussoks, samples

wore also taken from Nursery Field between January 30th. 1963 and

February 20th. 1964, and treated in the same way. The numbers of S. clavicornis found in each tussock are listed in Appendix Table 4. For 166 each date the arithmetic and geometric means have been calculated.

Williams (1937) has shown that the geometric mean often gives a truer representation of the numbers present when there are many samples with few individuals, and one or two with very large numbers. In such cases, the arithmetic mean is given en excessive upward bias by the few large

samples, and the samples with few individuals ere ',swamped". As this was

often the case with the tussock means, the geometric means were used, and

Fig. 31 shows the geometric m:ans on each sampling data throughout the whole period. The numbers of S. clavicornis in both areas rose each winter and fell abruptly in April. After the minima in May, a few individuals were found throughout the summer until the numbers rose in the autumn. The date of the increase in numbers varied from year to year; in 1961 and 1963 S. clavicornis was numerous in the tussocks by November, but in 1962 the increase did not occur until after December. Possible reasons for these variations are considered later (p. 197).

Both the numbers and the times of fluctuations wore similar in the tussocks from North Gravel and Nursery Field. The graph appears to show that the numbers were lower in the Nursery Field tussocks during February to April 1963, but this was because no samples were taken during the time that the numbers were highest. The number of samples taken from

Nursery Field during the winter of 1962 - 3 was a result of the severe weather, which made sampling difficult.

It has already been mentioned that tussocks obtained from other parts of Silwood were sampled so as to obtain insects for experiments. There were thus some data on the numbers of S. clavicornis in other parts of

Silwood at various times of year. These are given in Table 31. In each n . N Geometric mean no. of umb $.clavicorni* per tussock. ers 0 o North Gravel of 25- •- . Nursery Field

. 20- cl 15- avi co 10- rni s i n t 5- us . . ,i 4 so , ‘‘ i ck s .

0 V 1 D I J I F I M I A M J I Jy ' A 1 S 1 0 I N I D 1 J I F I M A M J Jy A S I O I N I DIJ I F I M ' A 1961 1962 1963 1964 Date 168 case the arithmetic moan of beetles per tussock has been calculated, end divided by the corresponding mean from North Gravel to give a ratio of commonness in the two areas. All the tussocks samplod wore Dactylis glomerate, as S. clavicornis was not found in Doschamdsia.

Table 31. Co.aarison of the numbers of S. clavicornis in Dactylic tussocks from North Gravel and other areas of Silwood Park

Total Corresponding Number Number Area Date of Mean North Gravel Ratio of Mean Samples S. clavicornis Rookery Slope 8-11.10.62 31 26 0.84 1.17 0.72 Pond Field 18.10.63 20 7 0.35 1.7 0.21 North, Gunness 21.10.63 30 56 1.87 1.7 1.10 Hill i1idd1e, 23-30.10.63 47 888 18.89 4.5 4.20 Gunness Hill Slm Slope 1.11.63 2 5 2.5 5.2 0.48 Morton's Acres 1.11.63 9 10 1.11 5.2 0.21 i 1idd1e, 15-17.12.63 64 974 15.22 20.7 0.74 Gunness Hill

On Rookery Slope, south of the path between Silwood and Ashurst Lodge, the grassland was similar to that on North Gravel, although the area slopes down to a stream on its western margin. The number of S. clavicornis found was slightly lower than on North Gravel.

The tussocks which were sampled from the edge of Pond Field were mainly small, and surrounded an isolated oak tree. They contained fewer

S. clavicornis than those on North Gravel.

Tho North End of Gunness Hill had previously boon planted with

Dactylis, which formed an almost continuous stand, although the individual plants were still distinct enough to be sampled. The numbers of S. clavicornis were similar to those on North Gravel. To the south of this sown area, isolated Dactylis tussocks surrounded an oak tree. These 169 tussocks contained large numbers of S. clavicornis when they were

sampled between October 23rd. and 30th., 1963, and more than four times

as many per tussock wore found as on North Grovel. When tussocks from

the same area were sampled in mid December, the average number of S.

clavicornis was slightly lower, and less than that on North Gravel.

Thus the higher number in October probably shows that the beetles wore

present in the tussocks earlier in the Gunness Hill area, although by

mid-winter the numbers in both areas wore similar.

The two remaining areas sampled, Elm Slope and 'erten's Acres, both

had only a few, widely distributed Dactylis tussocks, and the numbers of

S. clavicornis in both were less than on North Gravel.

Thus the numbers of S. clavicornis present in the tussocks on North

Gravel are probably typical of the densities reached in more favourable areas. However, in autumn the numbers may rise earlier in some areas than in others, which complicates the comparison of different sites at that time of year.

In Section lin, reference was made to a multiple correlation and regression analysis, which was carried out to find out how various characteristics of the tussocks affected the numbers of beetles found in them. The correlation and regression coefficients between the tussock characteristics and the numbers of S. clavicornis are shown in Table 32.

The degrees of significance of the Student's ”t" tests of the regression coefficients and their standard errors are given first from the tests including all the coefficients, and then from the tests carried out when the variation resulting from non significant factors had bean incorporated into the residual variation.

170

Table )2. MUlt:;.mie correlation and rearession analysis of numbpr of S. clayicornis in tussocks.. and tussock characteristics.

Final • Initial Characteristic Corrolatio Regressio Standar Student's Signif- Signift Coefficient Coefficient error fltH icance is ranee level level

Area 0.251 .06674 .05344 1.25 30% ••• Density -0.142 1.075 .045 -1.03 40% Dead/living 0.450 ' ratio 1.058 S.3017 3.51 0.1% 0.1% East-West position 0.218** .06332 .03393 1.87 10% 5% North-South position -0.027 -.02443 .05448 -0.45 80% Distance from neighbours -0.013 -.2011 .5642 -0.36 90% Date -0.264** -.007111 .007330 -0.97 40%

Degrees of significance of corrolation coefficients : 5% , ** 0.1% ***** Number of samples, n = 83, D.F. = 75.

Four factors, namely the tussock area, dead to living ratio, east-west position and date, had correlation coefficients which Ifere significant below the 10% level. However, only two of these, dead to living ratio and east-west position had signifient regression coefficients. The regression of the numhors of S. clovicornis on the ratio of dead to living

material was the most significant: this shows a strong tendency for tho

beetles to occur in the tussocks with the most dead loaf material. Tho

numbers of S. clevicornis were also signifie-ntly greater in the western

end of the plot. As the obvious differences between the tussocks at each

end (i.e., the smaller sizes and inter tussock distances at the eastern 171 end) wore also included in the analysis, the preference of S. clavicornis for the western end must be a result of some other unknown factor. (ii) Occurrence in )itfall traps.

S. clavicornis was found in pitfall traps on North Gravel from April until October. Table 33 shows the numbers obtained each month in the 62 traps. The traps were not used before July in 1962.

Table 22. Numbers of S. clavicornis taut in oitfall_traPs.

Numbers of S. clavicornis Month 1962 1963

april — 7 Ilay — 24 Juno — 18 July 19 9 ugust 5 1 eptembor 7 1 October 1 I

Tho mean numbers in each month are graphed in Fig. 32. The first spoci— mans wore caught in April, when the numbers in the tussocks fell, and most were trapped in May, when no specimens wore found in the tussocks.

Thus adults of S. clavicornis left the tussaaks in April and May, and were active in the intervening grass during those months.

The numbers of S. clavicornis caught in each )air of traps aro shown in Table 34.

Examination of the map of the plot giving the positions of the

pitfall traps (Fig. 5), shows that there is no obvious correlation between the numbers of S. clavicornis caught in any pair of traps, and the numbers, or proximity, of the tussocks adjacent to the traps. All that is shown by Table 34 is that many more specimens were caught in the western half of the plot, and that there was a distinct gradient CD

• 251 J. Total numbers S. clavicornis 0 in pitfalls

JI 20

0 Jy 173 from South to North; the traps in the most northerly row caught more than twice as many S. clavicornis as those in the most southerly one.

Table 34. Distribution of S. clavicornis caught in pitfall traos.

West 4- Fast-West -->Sast row total North 12 4 2 7 4 3 1 2 35 8 5 No 5 2 1 0 2 23 traps 4 0 2 6 2 3 2 21 South 3 6 1 2 0 0 4 0 16 North-South totals 27 15 5 20 8 7 7 6 95 --- The east-west differences agree with the results of the multiple regression analysis, which showed that more S. clavicornis were present in the tussocks at the western end of the plot. The analysis did not show any significant differences between the numbers of beetles in the north and south parts of the plot. Thus the greater numbers in the northern pitfalls may be caused entirely by the greater numbers of tussocks in this area, or by some other unknown factor.

(iii) Flight and wing dimorphism.

The capture of S. clavicornis in pitfall traps between the tussocks indicates trivial movements at ground level from one tussock to another.

1igratory movement from one area of grassland containing suitable tussocks to another can be distinguished from these small scab movements, and is probably usually by flight. Southwood (1962) has suggested that the level of migratory movement of any species is correlated with the degree of impermanence of its habitat. The tussocks in any one area form a semi- permanent habitat which probably lasts from 10 to 15 years at least. Thus the need for migration caused by impermanence of the habitat is probably 174

slight, although other factors, such as overcrowding, may make migration

essential. The maximum possible level of migratory movement can be

tassessed in S. clavicornis, as the species shows wing dimorphism, and

relatively few individuals are capable of flight from one eras to another.

The wings of the two forms differ only in size, and are well devel-

oped in all individuals. Figs. 33A and B show typical wings of the

macropterous and brachypterous- forms. The difference in length of wings

between the two forms is small compared with that seen in many-wing-di-

morphic beetles (e.g. as shown by Jackson, 1928), but still results in a

considerable difference in their areas. The wing of Fig. 32A has 1.77

times the area of that of Fig. 33B, although it is only 1.28 times as

long as the smaller wing. Thus the differences in value as organs of

flight could be considerable. The flight ability of the macropterous

forms is proved by their occurrence in suction traps, discussed later,

and also, on a few occasions, by personal observations in the field. Wing

muscles wore present in the few macroptorous specimens that wore dissected.

None of the raicropterous specimens which were dissected had noticeable

wing muscles at any time of the year and the mesa- and meta-thorax were usually filled with conspicuous orange fatty globules.

Although the variation in size of individuals resulted in ell intermediate sizes of wings, the existence of two distinct forms is clear from the relative frequencies of the various sizes. Measurements of wing lengths were made of specimens used for experiments or those which died in attempted cultures throughout the three winters of 1961 to 1964. The results obtained in each year are shown separately for each sox in Table 35, and the totals for each sex are shown in Fig. 33C. 175 A

1 mm.

No. of beetles C

2-o 2.5 3-0 3.5 40 Wing length (mm.)

Fig. 33. A. & B. Facro and micro wings of S. clavicornis. C. Abundance of diffe-rent ming lengths. 176 Table. Wing lengths of S. clavicornis.

Wing Females Males length(rm.) 1961-2 1962-3 1963-4 Total 1961-2 1962-3 1963-4 Total I o 1 1 2 2 i—l • 1 1 2 2 1 3 cv • 1 6 1 8 5 4 9 N cr \s 5 12 21 38 3 17 8 28 zti

14 44 30 88 6 30 13 54 i 4 r N

‘Dc- 19 76 40 135 5 50 32 87 4 18 87 50 155 4 47 31 82 4

14 71 45 130 46 21 72 t 5 oON • 7 41 28 76 4 18 13 35 • 3 27 14 44 1 12 9 22 0 • 1 4 2 7 1 1 ,--i ••• 1 1 cvcr 2 1 3

\I 1 1 1 1 ••••• - 3 1 1

4- 3 . 1 4 . 3 2 2 7 3 .0 2 4 1 7 1 1 N 2 5 2 1 t 1 2 3 o cr •• s 1 1 0 1 i

Macro- 6.8 3.4 2.1 3.4 0 3.2 pterous 3.4 3.5

The distribution of wing lengths is clearly bimodal, with peaks at 2.5 • to 2.6 mm., and at 3.5 to 3.6 mm., which represent the brachyptorous and macroptcrous forms respectively. In each sex there is one length not represented betwoon the two forms; 3.2 Lim. in the females and 3.1 mm. in the males. Because of the smaller average wing length of the males, the two forms overlap and all sizes are found, whon the wing lengths of both sexes arc combined. In both sexes the proportion of raacroptorous individuals was small, and averaged just over three per cent. The differences between the sexes in the throe years are not significant, as the number of fully winged individuals present was small. 177

Although migration in inso ts often takes place early in adult life, and frequently before maturation (Johnson, 1960), there was no evidence

.,hat flight was limited to this period in S. clavicornis, although this was the time when the adults wore active in the grass between the tussocks. Several suction traps of the typo devised by Johnson and

Taylor (1955) wore operated in Silwood Bottom, Midway between North

Gravel and Elm Slope, both of which contained Dactylis tussocks. The catches of some of thoA3 trees in 1961, 1962 and 1963 wore examined to ascertain the time of flight of S. clavicornis. All those traps wore of the propeller type, with a diameter of 18 inches, and a throughput of

2510 cubic foot of air per minute. Only a few specimens of S. clavicornis were found, but they occurred throughout the summer from May until Sept- ember. Table 36 gives the details of the trapped specimens.

Table 36. S. clavicornis caught in suction traps. 1961-3.

Trap Period S.clavicornis Year Height above Ground Number ground (ft.) Vegetation examined caught

1961 II 4.5 Grass 21.4-10.10 1 14.5..61 It 11 It 11 9 1 18.6.61 It II II II II 1 21.6.61 1962 II 4.5 Dare ground 1.5-31.7 1 11.5.62 1962 V 4.5 Grass 1.5-10.9 1 11.6.62 n it 11 11 11 1 2.9.62 1963 II 4.5 Grass 19.3-31.1 None 1963 IV 30.0 Grass 19.4-31.1 None 1963 VI 4.5 Bare ;round 3.5-31.10 None

Thus flight had little effect on the, populations of S. clavicornis which ware studied. Only a small proportion of the individuals were. caoablo of flight, and insufficient specimens wore caught in suction traps to show whether or not there was a distinct post-hibernation migratory flight.

(iv) Feeding habits. 178 It has already boon mentioned that the exact feeding habits of

Stenus species are not well known, although it is generally considered

that they food as predators on CoIlembola and other small orthroaods.

Their specialised mouthparts with the protusible labium (Schmitz, 1943)

support this idea, but give no clues as to the exact food of any particular

species of Stenus. It has already boon shown that Gollembola and Acarina

were numerous both in and between the tussocks, so that the possibility of

food shortage in either type of vegetation does not socm likely. Because

of this, attempts wore not mado to determine the exact food of S. clavicornis

in the field. In the laboratory, it fed readily on Folsoinie cavicola Del., a collombelon which was available from cultures at Silwood, and also on

several of the smaller Colloiabola from tussocks. When feeding, the prey

was not all ingestod, but was held by the labial palps, while the body

contents wore apparently sucked out. The skin of the prey was then dis-

carded. This method of feeding made it impossible to try and identify

the exact pray of S. clavicornis by the examination of the gut contents,

as solid remains were not present.

Specimens were dissocted throughout the year and the state of the

reproductive organs was examined; in some cases (although relatively

rarely), the gut was found to contain liquid food. The aEounts -present

were graded, and Table 37 shows the numbers in each grade in various

months. In the months omitted from the Table, the gut contents of the

specimens chssected were not noted. The numbers of specimens with no

food in the gut are not included.

Most of the specimens had empty guts in all months. This may have

boon a result of the delay bdtwoon obtaining the specimens, and killing

them, which was usually at least half an hour; (South 1959) mentions 179 that no trace of food was visible in the gut of S. similis (Herbst.),

30 minutes after it was soon to food on Entomobrya. However there was evidence that feeding took place throughout the year. It was probably reduced in winter, as only moderate amounts of food were found in the gut

in the winter months.

Table 37. Amount of food in alts of S. clavicornis dissected.

Amount of food in:ut Month Hodorato Trace much (somewhat (very distended) (flo distention) distended) February 1 7 3 March 1 0 0 April 8 5 7 July 1 1 4 November 3 1 0 December 7 18 2

(v) Sex ratio.

The sexes of S. clavicornis can easily be distinguished by the secondary sexual characters on the ventral surface of the abdomen, which are described by Fowler (1887-1913). Figs. 34A and B show the ventral surface of the abdomen, meta- and mese-thorax of the male and female respectively. In addition to the omarginations of the 6th. and 7th. visible abdominal sternites, which are mentioned by Fowler, the male has the motasternum and posterior part of the mesosternum clothed with long, dense, white, semi-erect pubescence; in the female, the pubescence is scanty, very fine, and similar to that found on the whole of the ventral surface. This character is easily seen in the males, and it enables living and active specimens to be sexed quite easily. B

1 rnm

C Vas defe rens Test is Lateral accessory glands Aedeagus Median

Ejaculatory duc7 1m m.

34. . Tnt-uc,1 mf.1,0- and Irlet:2.-tiorax of ,nd 9 S. Plaoornis. rop-Y•oduc-tivc syE-tem. 181 The sex ratio of the population in tussocks was determined each winter by examining the specimens which were obtained for experiments, or for attempted br ading and culture. The sex ratio of the specimens which wore caught in pitfall traps was also calculated in 1962 and 1963.

The results are shown in Table 38.

Table 38. Sex ratio of S. clavicornis.

Source of specimens Number of males Number of females 1211194 Males

Tussocks, winter 1561-2 28 88 3.15 11 II 1962-3 235 383 1.63 II it 1963-4 145 238 1.64

Total from tussocks 408 709 1.64

Pitfalls, 1562 4 16 4.00 11 , 1963 18 43 2.39

Total from pitfalls 22 59 2.68

The tussock population contained more females than males, in the ratio

of 1.64 to 1. In pitfalls, however, the proportion of females was higher

still. This shows that the females were more active than the males in the grass between the tussocks.

(vi) Seasonal chanries in reproductive organs

Fig. 34C shows the structure of the ,lule reproductive system. The testes lie laterally in the anterior half of the abdomen. From the

posterior end of each testis, a slender vas deferens leads forwards and

inwards, and the two meet at the posterior end of the four elongated

white accessory glands, which extend forwards as far as the motathorax.

The median pair of accessory glands lie close together, and their anterior halves era fused together. From the junction of these glands

and the vase deferentia, a thin ejaculatory duct loads back to the 182 eadoagus. The maturation of males was not studied in detail, but from

the size of the testes, it appeared that they matured after emergence in

autumn, and specimens dissected during the winter worn presumed to bo

mature, although histological examinations of the testes ware not made.

The anatomy of the female reproductive system of Stenus has not

been described in detail, but Jenkins (1953) figures the anatomy of the

rolatou species, Diapos coorulescons Gyll., and claims that the structures

shown are similar in the Stonus species which he has examined. The

female reproductive system of S. clavicornis is shown in Fig. 35A. The

arrangement of ovariolos is basically the same as that found in Dianous,

but the two ovarioles are not fused medially, and there are nine to 11

ovariolos in each ovary.

The development of the ovaries was studied by dissections of female

specimens caught in the tussocks in winter, and in pitfalls in summer.

Various stages in the development of the acrotrophic ovariolos are ill-

ustrated in Figs 35B to E. Fig. 35B shows en imeaturo ovariolo in which

oocytc for has not begun. In Fig. 35C the oocyte wall is forming,

but is not yet complete. By the stage shown in Fig. 35D, the oocyte wall

is complete, but the deposition of yolk has not begun. In Fig. 355, yolk

is accumulating in the first oocyte, and a second oocyte wall is forming.

These stages wore designated one to four, respectively, and the specimens

which were dissected wore classified according to the stage of the most

developed ovariole. In the fifth stage, ripe eggs wore present; these

often filled the body cavity, apparently rupturing the bases of the ovariolos. The numbers of ripe eggs in the gravid females varied from two to 16; the average was 6.4. There was no evidence that the second oocyte in any ovariole developed further than the stage shown in Fig. 35E: it A 1mm.

•

• ,'D) •

0 Ovary H N• CD Lateral oviduct c!-

U.' 1$ 0 Common o o oviduct o ct

• (1) H. o Ue Rectum CD C.):, (cut) Pygidial ct- a, 0 glands C- •

CD Vagina H c+

01 mm. 184 in specimens which were full of eggs, the number of eggs was always

less than the number of ovarioles, and the size of the egg prevented

any further development of the oocytes until they had been laid.

Whether repeated maturation occurs is not clear from the limited data

obtained. However the maximum possible size of each egg "batch" would

seem to be about 18 - 22 eggs per female, which is a low number for the

Coleoptera (Dick, 1937). The presence of ten ovarioles per ovary may

partly compensate for the low numbers, as S. clavicornis is almost the

only species of the genus which is known to have more than six ovarioles in

in each ovary (Welch, 1964); an exception is S. similes (Hbst.), which has nine (Stein, 1847).

The stages of the ovarioles of females dissected each month and the

numbers containing ripe eggs are shown in Table 39, and in Fig. 36

(which also shows the monthly numbers of larvae and callow adults).

Table. Ovariole development of S. clavicornis.

Ovariole stage Month J F M A M J Jy A S 0 N 1 3 5 9 1 - 1 2 - 4 8 5 2 - 1 4 - - - 2 - 1 - - 3 - - 4 1 - - 1 3 1 - - 4 - - 1 6 1 1 - 2 - - - Gravid females - - - 9 9 12 2 - - - -

In the winter the ovaries were immature, but development took place rapidly from April onwards, so that gravid females were present by May;

in June and July nearly all the females examined were gravid. The first

callow individuals appeared in July, and there was evidence that these

specimens started to mature in the late summer and autumn. Thus in

September, all the specimens dissected were at stages 3 or 4 (oocytes 0 0

8 0

8 8 0 8 0 •• •• it • • • • • • • • • • • • 0 • • • 0 • • 0

• • •

u) (v) 1Ct 4) %-- NM 0 -J .-1 _J 4.1 0 t 4; -o 4- 4) 0 0 0 ( > 5 7 E. 3 5 o cr)4) : o CI 0 2 -J -i3 4, > 0 u) 0 U

Fig. 36. Ponthly occurrence of ovariole stages and larvae of S. clavicornis. 186

formed, with or without yolk deposition). However no gravid females

were found subsequently, and all the specimens dissected during the

winter had no oocytes formed, so that any development in the autumn must

be resorbed at the onset of winter. In spring, several specimens had

small clear spots below the developing oocytes; these may be the sign of

abortive oocyte development during the previous autumn, or corpora lutoa,

indicating that the species lives for more than one year.

(vii) Parasites.

The information obtained on parasitism of S. clavicornis is incom-

plete, es no eggs or pupae were found in the field, and thus any para-

sites that may have emerged from these stages remain unknown. However,

a number of adult S. clavicornis were found to be parasitised by nem-

atodes of the family Allantonematidae. In this group, the adult, gravid females are found in the body cavity of the host, often singly. The eggs,

which are usually vary numerous, start to develop in the host, and escape as first or second stage larvae via the anus or the female genital aperture of the host. The gravid females found in the host are greatly enlarged in size, and consist almost entirely of the distended uterus full of eggs or developing larvae (Steinhaus, 1949).

The nematodes in S. clavicornis ware not identified to species; this can only be done with certainty by breeding mature male nematodes from the larvae in the host, which could not be done successfully.

However, Professor B.G. Peters considered that the parasite belonged to the genus Parasitylenchoides. A species of this genus, P. steni:Wachek, has been recorded from five other species of Stepus (Tilachek, 1955). It

is possible, therefore that this was the species found in S. clavicornis.

According to Wachek, fertilised females of P. steni infect Stenus pupae 187 in the field, and the females enlarge in the body cavity of the resulting adults. HG recorded between one and 16 parasites in each host, and found a maximum level of parasitism of 6%; the parasites did not kill the hosts, but affected them only by depleting their metabolic reserves.

Although Steinhaus (1949) claims that allantonematid parasites very often cause host sterility, Wochek found that P. steni never caused sterility of the host beetle.

Dissections of parasitised S. clavicornis at Silwood showed that although the male reproductive organs were apparently not affected (only two parasitised males were dissected), all the parasitised females had greatly reduced or vestigial ovaries, with no oocyte development. Thus sterility of females was caused by the nematode parasite. The percentage of parasitism was calculated separately in the 1962 - 3 and 1963 - 4 generations of S. clavicornis. Of the 1962 - 3 generation, 79 specimens ware dissected, out of which 13 (16.5%) ware parasitised. In 1963 - 4, only 42 specimens were dissected; 13 of these (31%) contained nematodes.

Thus, it is obvious that the level of parasitism was quite high, and must have cc used a significant decrease in the total fecundity of the Stenus populat

(1) ERIKS.

These were never found in the field, and the actual oviposition site is unknown. As the first inster larvae were found in the bases of tussocks, oviposition probably takes pltle in the same situation.

Attempts were made to induce S. clavicornis to breed and oviposit in the laboratory, but these were unsuccessful. Thus the appearance of the 188 eggs is based entirely on that in the body cavity of gravid females.

They are oval, opaque and pale yellow, with a smooth and shining surface,

but with a finely granular appearance inside. The length varies between

0.56 and 0.74 mm, and the maximum diameter from 0.21 to 0.36 mm. The

moan dimensions were 0.65 mm x 0.29 mm. Js already mentioned, up to 16

eggs were found in the body cavities of female S. clavicornis, and gravid

females were found from May until August (Fig. 36).

(ii) Larvae.

The first description of any Stenus larvae was that by Schiodto

(1861 — 1883), who figured the larva of S. biguttatus (L.). Boving and

Craighead (1931) give a figure of a Stenus larva, but do not say which

species it is. Both these larvae have extremely long antennae, palpi

and carol. Larsson and Gigja (1959) give brief descriptions of the

characteristic features of the larvae of S. canaliculntus G5;11., and

S. carbonarius Gyll.. Both these larvae have much shorter appendages

than those previously described, and Larsson and Gigja consider that

th y are the more normal typo of larva of the genus. This might help

to explain the scarcity of data on Stanus larvae, as the species with

shorter antennae and pelpi may not have been recognised. The only other

references to Stenus larvae are by Blair (1917), who found a larva of

S. similis (Herbst.) on vegetation, and by Cameron (1917), who mentioned

that Stanus larvae occurred on decaying tubers in the soil. Neither of

these authors gave any description or figures of the larvae.

As S. clavicornis adults occurred in large numbers in tussocks, it

was hoped that it would be possible to find the larvae in similar

quantities. When tussocks were sampled in 1963, the soil beneath ooh tussock, the tussock base, the surrounding dead vegetation and the dead

189 flowering stems were all examined separately in the hope of finding

Stanus la rya°. On Juno 6th., those wore found for the first time, in the basal material of the tussocks, and further specimens wore found regularly in this part of the tussocks until the end of August. The months of occurrence, and numbers of each inster found, are shown in

Table 40, and in Fig. 36.

Table 40. Numbers of S. clavicornis larvae found in tussock bases, 19634

Date Number of Instar tussocks 1 2

June 6th. 3 17 0 0 July 3rd. 3 8 0 0 July 19th. 3 4 1 1 August 1st. 3 3 2 0 August 15th. 3 2 2 1 Sept. 25th. 3 1 0 0

The first instar larvae appeared at the beginning of Juno in considerable numbers, and their numbers gradually decreased during the Jeriod in which larvae wore found. Only five second instar larvae were found, end only two third instar. It is possible that the first inster larvae migrate to another pert of the habitat, but no larvae were found in any of the other parts of the tussock, or of the surrounding vegetation and soil which were searched. Thus the habits of the older larvae remain unknown.

Many attempts were made to food the larvae which wore obtained from the tussock bases, but none was successful. They were kept in 2' x 1" plastic boxes, with a layer of moistened plaster of Paris in the base. Possible foods which were tried included many typos of small arthropods, e.g. mites, Collemboln, Thysanoptora and aphids (both dead and alive); living and dead vegetable material from the tussocks (including various fungi which wore growing on the rotting loaves); pieces of dead blowfly larvae 190 and worms. In no case was any reaction to the food observed than oh

initial avoiding one. The first instar larvae usually died within one

or two days, even when kept at outdoor temperatures in an insectary. The second and third instars lived for a week or more in some cases, but still

could not be made to feed, and died eventually. Although their mandibles

suggest predatory habits, their movements in captivity were always

sluggish and deliberate.

Because no eggs of S. clavicornis were obtained in the field or in

the laboratory, and it proved impossible to breed the larvae which were

found in the field, it was not shown conclusively that the larvae were

those of S. clavicornis. However their identification is based on

the following indirect evidence.

a) Their long antennae and palpi, end two groups of six ocelli, dist-

inguish them immediately as the larvae of a Stenus species.

b) Their occurrence in the tussocks in June correlates with the occurr-

ence of gravid S. clavicornis from May onwards.

.) Only S. clavicornis adults wore sufficiently numerous in Dactylis

tussocks to account for the numbers of first instar larvae subsequently

found there.

Table, 41 gives the head dimensions and the "size factors" of the

larvae. The factors are those used by Van Emden (1942) for Cerabid larvae,

and era as follows

a) Head width of second instar divided by that of first instar.

b) Head width of third instar divided by that of second instar.

c) Adult length divided by held width of first instar.

d) Adult length divided by head width of second instar.

e) Adult length divided by head width of third instar.

191 These factors are included because they often enable the approximate

size of the adult of allied, unidentified larvae to be calculated, or

alternatively, the instnr of the larvae of known allied species can be

determined. The average adult length of S. clavicornis was 4.565 mm.

Table 41. Head dimensions and size factors of S. clavicornis larvae.

1st. Instor 2nd. Instar

0.250 0.307 0.431 0.262 0.349 0.449 0.274 0.375 0.482

Min. 0.304 0.438 0.470 Head length Moan 0.329 0.475 0.521 Mox. 0.351 0.534 0.543 Head length Mean Head width 1.26 1.36

Size factors: a 1.33 b 1.29 c 17.42 d 13.08 o 10.17

The following is a description of the third instal-. larva (Fig. 37A).

Head rounded, slightly elongate, sides broadened between ocelli. Frons

transverse, nasal° almost straight. Six ocelli present on each side.

Antennae (Fig. 38A) very long, almost twice as long as head; first

segment broad and transverse; second segment thin and very elongate,

slightly shorter than the third, which has two small setae at apex;

fourth segment thinner and very small, with four minute apical setae.

Mandibles (Fig. 37B) thin and evenly curved, apicel half of inner edge

with fine tooth, apex fine and pointed.

Maxillae (Fig. 37D) swollen and conical; cardo small, transverse;

stripes conical with a single prominent seta near base of the inner 192

O.5 mm.

Fig. 37. A. S. clavicornis, L.3, dorsal view. B. /: ) head, ventral view with left maxilla removed. C. , L.1, dorsal view. 193 A

0.5rnm

0.5mm. I

Fig. 38. S. clavicornis. A, B & C. Left antennae of L3, 2 & 1. D, E & F. Hight maxillary palpi of L3, 2 & 1. G, H & I. Left hind legs of L.3, 2 & 1. 194 margin; male only moderately produced, with three distinct setae near apex; pelpiger small and v ry transverse.

Maxillary palpi (Fig. 38D) very elongate, as long as head.; first segment four times as long as broad; second segment as broad as first, but longer; third segment as long as first and second together, tapering gradually to the apex, which is finely pointed.

Gula (Fig. 37B) large, elongate, evenly narrowed posteriorly, posterior margin smoothly rounded; mentum strongly tramsv rsc; prementum as broad as mentum, slightly transverse; ligula consisting of two small conical membranoous' projef!tions. Labial palpi as long as prementum, first segment broader than and twice as long as the second.

Pronotum almost as broad as head, quadrate, almost rectangular, but narrowed slightly anteriorly. Prothoracio spiracles situated on conical lateral projections visible between pronotum and mesonotum. Meso- and metanota transverse, broader than pronotum.

Legs (Fig. 36G) all similar in length; coxa conical, strongly transverse; trochanter slightly shorter than coxa; femur elongate, shorter than the tapering tibiotarsus; tibiotarsus with several small setae, and single simple apical claw.

Abdominal tergitos strongly transverse increasing in width until the fourth, and then decreasing in width towards the posterior end of the abdomen. Ninth tergite almost quadrate; cerci long and very thin, second segment longer than the first, tapering to a fine point. Anal tuba as long as ninth tergite.

Pubescence fairly sparse but very long and erect, especially on thorax and Sides of abdomen. Frons with a pair of short setae between antennel bases. Head with four pairs of setae on dorsal surface 195 between ocolli. Pronotum with one pair of setae on anterior margin, two pairs on lateral margins and one pair on posterior margin. iieso- and meta-note also with four pairs of setae, but with the anterior pairs situated nearer the centres of the torgites. First, second and eighth abdominal tergitos with two pairs on the posterior margins; third to seventh tergitos with three pairs, the outer two adjacent to one another.

The second instnr is similar, but can be distinguished by its smaller size. The antennae (Fig. 38B) are longer relative to the head, and the second joint is distinctly shorter than the third; the maxillary palpi (Fig. 38E) have the second joint longer relative to the first; the pronotum is more markedly transverse; tho logs (Fig. 38H) have longer setae, and the tibiotersus is slightly longer relative to the femur.

The first instar (Fig. 370) has the following distinguishing characters. The antennae (Fig. 380) are distinctly more than twice as long as the head, with the second segment only half as long as the third, and the fourth segment longer than in both the later insters. The first segment of the maxillary palpi (Fig. 38F) is almost as long as the second. The pronotum is distinctly transverse. The legs (Fig. 38 I) have the tibio- taraus distinctly longer than the femur, and the setae on the tibiotersus are longer than in the other stages. None of the abdominal tergites have a third pair of setae on the hind margin. The first instar larva shown

in Fig. 370 appears more elongate than the third instar specimen of Fig.

37A, but this was Largely because the third instar specimen was starved, whereas the first instal, was freshly killed from the field, with a distended abdomen.

The larva of S. clavicornis resembles that of S. biauttatus (L.) and the unknown species figured by Boving and Craighead (1931) more than those 196 of S. canaliculatus Gyll. and S. carbonarius Gyll., because of its long antennae and palpi. The numbers of Stonus larvae known are -erobably too small to prove or disprove the claim of Larsson and Gigja (1959) that the short antennal type is the normal within the genus, and that long antennae era only found in n few species. The S. clavicornis larva can be distinguished from that of S. biguttatus (L.) as the letter has longer antennae

(almost three times as long as the head in the third instar), maxillary palpi, logs and cerci. The larva figured by Boving and Craighead resembles

S. clavicornis more closely, but it has a larger frons, slightly longer antennae, more projecting male and longer carol.

(iii) Zuee.

No Stenus pupae have been described in detail or figured. Blair

(1917) found two silken" cocoons containing pupae which developed into

S. similis (Herbst.). They were found attached to the underside of leaves.

Pupae of S. clavicornis were searched for after the end of August,

1963, when no furthe: third roster larvae were being found. As the larvae were found in the bases of the tussocks, these were searched thoroughly by tearing up each base, and examining the fragments under a binocular microscope. The soil beneath the tussocks was also examined down to a depth of six inches, but no pupae were over found. The search for remains of pupae or their cocoons was continued into the winter when S. clavicornis adults were present in the tussocks, but none were found. As an extreme case, the base of a tussock which contained '108 adult S. clavicornis was completely diieected and examined, but no trace of pupae was found. Thus the pupation site is still a mystery. As no larvae were found migrating away from the tussocks, there was no evidence that they pupated outside them, yet no trace of pupae was found inside the tussocks. Despite this, 197 however, the first callow adults were found in the tussocks at the end

of July, and they occurred regularly from August until October.

Probably the method of searching was at fault, and the pupae were

either overlooked in the dense vegetation of the tussocks, or destroyed

in the breaking up of the tussock base; pupation probably takes place in

the tussocks, as the movement of callow adults into the tussocks would

almost certainly have resulted in increased pitfall catches of S. clavicornis

in late summer, which was not the case.

(d) Conclusions.

Although there are still many gaps in the knowledge of the biology

of S. clavicornis, the following outline of its life history and biology

can be constructed.

S. clavicornis eggs are probably laid in the bases of tussocks from

May until August. The choice of oviposition site by the mature females determines the winter habitat of the subsequent generation of adults. The

larvae develop in the tussocks, although their food is unknown. Pupation takes place, probably in the tussocks, in late summer and autumn, and the

new generation of adults are found from autumn onwards.

It was mentioned previously that the time of increase in numbers of

adult S clavicornis in tussocks varied from year to year; thus it Was relatively early in 1961 and 1963, but lato in 1962. There was no obvious association between the time of increase in numbers and the weather conditions at that time, but the temperatures throughout the summer and autumn, when development takes place, may affect the time taken for the adults to emerge. In support of this, the mean temperature was higher

in 1963 than in 1962 in every month of the summer and autumn except

August. In summer the difference was almost 2.5°C., which may have 198 significantly affected the pupation time.

The newly emerged males mature during the autumn and winter.. The females which emerge in late summer probably start to develop, but no eggs are produced, and all the overwintering females arc immature. They mature in kril and May, when all the S. clavicornis leave the tussocks, and are active in the intervening grass.

S. clavicornis is predatory, probably feeding on many species of small arthropods. It feeds throughout the year, but feeding is restricted

in winter.

Only a small proportion of the population can fly, and there is no evidence of a spring migratory flight away from the tussocks.

Insect parasites were not found, but a nematode parasite causes sterility in a considerable percentage of the females. 199 3) Stenus impressus Gerniar.

(a) Introduction.

S. impressus was considered by Renkonen (1934) to be a species which is characteristic of woodland, and which is only found occasionally in dry heathland and moorland. It occurs throughout the British Isles

(Fowler, 1857 — 1913) and, like S. clavicornis, can be found in various damp habitats such as moss and leaf litter. It has also been found by sweeping vegetation in the evening (Donisthorpe, 1939). Its geographical distribution does not extend as far east as that of S. clavicornis, only reaching the Caucasus, but it has been found as far south as Algeria, and as far north as arctic Norway (Strand, 1944).

Soon after sampling of the beetles in tussocks began, some difficulty was experienced in deciding whether all the specimens which were obtained were S. impressus, or the closely allied S. aceris Steph. Specimens were collected for a year so as to obtain enough material to try and determine which species were present. In fact, both species were found, but their separation using the existing keys was not always possible. Even when a reliable method of identification was worked out, this could only be done by care2u1 measurements, or by dissections of genitalia in the laboratory; identification in the field was not possible. Thus the material of S. impressus on which the biological conclusions of this section are based contained a small proportion of S. aceris as well. For this reason S. impressus was not used for any experimental work and only brief biological data are given.

(b) Taxonomy.

The synonomy of S. imressus and S. sceris is as follows. S. improssus Gamer, 1824 200 proboscideus Germar, 1831

subrugosus Stephens, 1832

tenuicornis Stephens, 1832

aceris : Boiduval and Lacordaire, 1835, nec

Stephens, 1832

Agustulus Heer, 1839

annulipes Hoer, 1839

carinifrons Motschulsky, 1857

ailvipes Motschulsky, 1857

S. aceris Stephens, 1832

aerosus Erichson, 1840

elegans Fairmaire, 1860

onnulatus Crotch, 1866.

The two species are usually sperated by the length of the elytra, which are longer in S. aceris than in typical S. imressus. It has previously been assumed that this difference indicates that S. aceris is winged, and

S. impressus is not; thus Crotch and Sharp (1866), when describing

S. annulatus (a synonym of S. aceris) thought that it might possibly be a winged form of S. impressus. Other differences given by Fowler (1887 —

1913) are that S. aceris often has the posterior knees ringed with black, and both the first segment of the antennae and the apical segment of the palpi, darkened; the puncturation of S. aceris is also claimed to be closer than that of S. impressus. The aedeagi of both species are figured by Wusthoff (1934) and by Tottenham (1954), but in both cases the more important differences aro not emphasised, and only the general facies are shown. 201

Identification of the specimens from tussocks was attempted

initially on the basis of elytral length and the shape of the aedeagus

using the figures of Tottenham (1954). It became apparent that forms

with intermediate elytral lengths occurred, and that the drawings of the

aedengi were insufficiently detailed to be of use. The characters used

to separate the two species were therefore investigated in more detail, using material from the field at Silwood, from the collection of Mr. W.O.

Steel, and from the Sharp and Cameron collections in the British Museum

(Natural History).

The nedeagi were examined first to ascertain that there was a

genuine difference between the two species, and that the males at least

could be identified using this character. Both species can be sexed

externally by the differences in the last two dpdominal sternites (Figs.

39A and B). The sixth visible sternite is more distinctly and closely

rugoso in the male, and the seventh has a sinuate posterior margin

(although this is almost hidden by pubescence). These characters were'

similar in the two species. The differences in aedeogal structure were

found to be slight, but constant. Figs. 39B and C show the apical half

of the aedeagus and right paramere of S. imiresslig and S. aceris, respect—

ively. In S. imJressus the median lobe is more abruptly contracted with

a larger apical swelling. The striae arc deeper, and more numerous at

their bases than near the tip of the aedongus. The parameres show the

most useful characters; in S. imaressus they are broader, and extend

almost to the Level of the narrowest part of the median lobe; their

apical setae are longer, and are all directed obliquely. In S. aceris

202 B 0 5mm.

o o • A o • _ . 3 0 o o • 0 . 0 .0 02 0 . .j. 0 0 0 0 . ,. , .. 0 0 0 0 C5 ..' 41 1.1.‘' ...... ,,...., 0 1:::, ... 0 0 O 170 \ ' ''.1----.%.,"'... ,...--' ‘)0 0 0 o C 1/4" " 7•J ,- 1- .--- "7° o0 .s. 0 y 0 0 0 0° ° 0 00 (IC (4 ...-'._3. 0 0 0 Y 0 0 0 0 0 .... u0 0 0 0 ° 0 C. ';1 0 .4 e0 °0 420 CZ 0 0 0 o0 .0 0 0 0 0 0 o 0 o 0a.. . 0 . 0 o oo 0 o 0 0 o ° 0 0

C D mm.

E F

• 1 mm.

Fig. 39. A & B. Ventral view of end of abdomen of d and 9 S. impressus. C & D. Apex of aedeagus and left paramere of S. impressus and S. aceris. E. & F. Vacro and micro wings of S. impressus. 203 the median lobe of the aedoagus is more gradually contracted, with a smaller, more abrupt, swelling at the tip. The striae are more numerous at the neck of the apical swelling than basally. The parameres are more slender, and distinctly shorter than those of S. imeressus; their apical setae are shorter, and are directed uoro ni5ically. The length of the parameres, and the size and direction of their setae, enable the two aedoagi to be distinguished at once; the other characteas mentioned are less obvious, and require very good illumination to be soon clearly. The figures of Tottenham (1954) show the differences between the parameres somewhat diagrammatically, but no mention is made of them in the text.

The general shapes of the aedeogi are unreliable in dried specimens, which often shrink or distort when drying; in microscope preparations the shape can usually be relied on if the organ is not squashed by the cover slip. Little difference was found between the two aedoagi in either shape or external structure.

Having establis-ed that two species were present, the elytrol length of each specimen was compared with that of the pronotum, using an eyepiece micrometer, and the specimens ware examined to see whether the lenth of the olytra was correlated with the length of the wings. The elytral length was measured along the suture from the tip of the scutellum to the posterior margin. The results are shown in Fig. 40A. Of the 40 males which wore dissected and identified by their aedeagi, 32 were S. imeressus and eight were S. aceris. In the specimens of S. impressus, the length of the elytre divided by that of the pronotum ranged from 0.95 to 1.12 whereas in S. aceris it was from 1.15 to 1.24. Thus there is a small gap between the two ratios, and S. aceris con just be distinguished by

204 • • • 0 • • • • •

•

s • 1 us • .2- • ro

rou - te

, te P

hy _C rop

E ac s 0 C Mac

su E B r

res 0 0

imp 0 O00 00 • 0 0 0 • 0000 000 00 • 0 0 0 00 0 00 • 0 0 0 0 0 0 _0 00 000 Ln O00 000 0 000 00 0 • 00 00 0 0 0 -o 0 0 0 0 tn o o < E 7:3 u. 2 O

Fig. 40. A. 'Distribution of elytra/pronotum ratios of S. impressus and S. aceris. B—F. Pronotum and elytra of specimens with various ratios. 205

its longer elytra relative to the pronotum. The measurements of females resulted in two similar groups of ratios, which can be assumed to be

S. imurassus and S. aceris. However, it is almost impossible to judge the ratio of elytral and pronotal length by eye without considerable experience and a long series of specimens. Figs. 40 B F show the pronotum and elytra of selected measured specimens, whose olytra to pronotum length ratios vary from 0.95 to 1.24. The variations in size of the specimens, and in the breadth of the elytra, make their comparison very difficult, and it is evident that the elytral length can only be used to separate the two species when an accurate method of measurement is available.

Fig. 40A also shows whether or not the s_ecimens which were measured were fully winged. Two forms of wings were found, and these are ill— ustrated in Figs. 39E and F. The macroptorous forms were similar to those of S. clavicornis, but the reduced wings wore smaller than in that

species, and were usually only about one millimetre long. Only five out of the 68 S. improssus which were examined were macropterous: thus this species is similar to S. clavicornis in showing wing dimorphism, with only a small proportion of macropterous forms. The presence of large wings did not appear to affect the length of the elytra. S. accris, in comparison, was always fully winged. Thus the absence of large wings will distinguish most specimens of S. imoressus from a. aceris, and the fully winged specimens of S. im)ressus can be separated by the lengths of the olytra and pronotum, or by the aedeagus.

None of the remaining characters mentioned by Fowler (1887 — 1913) 206 were found to be reliable. The colour of the legs and antennae varies considerably with both the maturity of the animal (in freshly killed specimens), and age of the specimen (in museum material); there is also

individual variation. No consistent differences in puncturation could be seen on any pert of the body.

The following key summarises the reliable characters which can be used to separate the two species. The aedeagal characters are the most conclusive.

1. Elytra shorter, less than 1.13 times as long as the pronotum; nearly always micropterous; aedeagus with parameres longer, their setae longer and directed inwards S 1m-2n:sous Gamer.

2. Elytra longer, more than 1.14 times as long as the pronotum;

macropterous, aedeagus with parameres shorter, their setae shorter and not directed inwards S. seal-is Stephens.

The parcenta,7e of S. oceris in the material of the two species obtained from tussocks and pitfall traps at Silwood was 10A, although not all the specimens found during the throe years ware measured or dissected, so that this percentage may not have been true of all years.

S. imerossus was found in Dactylis tussocks both on North Gravel and in Nursery Field, and also in Deschampsia tussocks in Cascade ilarsh.

The numbers found in samples each month are shown in Appendix Table 5,

and the means are graphed in Fig. 41.

As relatively small numbers were present in the tussocks, only the arithmetic moans were calculated. The numbers were lowest in the •

Mean no. of S.impressus per tussock

40-

H 3.5-

cn • 3.0- dmT

2.5- .Ussaa s

uT 20' ssnq oo s3l

1.0-

0 0 N D IJ FMAMJJYAS SONO NDIJF D I J F M AMJJYASONDJA M J Jy A SOND J F 1961 1962 1963 1964 r\, Date 0 208

first half of each winter, and rose in the early spring. Moderate numbers wore present in the tussocks throughout the summer until October. The sudden increase in numbers in July 1962, which was one of the reasons why S. imiressus was chosen for study, did not occur in 1963, and the numbers remained fairly low, averaging loss than two specimens per

tussock throughout the summer. Both the Doschampsia tussocks, and the Dactylis in Nursery Field, contained more S. imarossus than the Dactylis

on lorth Gravel, in all the months when more than one area was sampled. However, the difference between the two areas with Dactylis tussocks was slight.

The data on the numbers of S. impressus in tussocks on North

Gravel was included in the multiple correlation and regression analysis previously referred to. Table 42 shows the correlation and regression coefficients.

Table 42. Multiple correlation and regression coefficients of the numbers of S. imoressus in tussocks, and tussock characteristics.

Initial Sig.level Tussock Correlation Regression Standard Students signif- with non- Characteristic Coefficient Coefficient Error "t11 icance signific- level ant coeff icionts elminld Area 0.116** .03054 .01926 1.59 20% - Density 0.290 1.168 0.3766 3.10 1% 1% Dead/living _ ratio -0.038 -.09540 .1087 -0.88 40% East-West position -0.038 -.01884 .01223 -1.54 20% _ North-South position -0.128 -.03032 .01963 -1.54 20% - Distance from neighbours 0,232** -.429S 0.2033 2.11 5% 5% Date -0.030 -.004086 -.002641 -1.55 20% -

Degrees of signfficsnce of correlation coefficients: 5% , 1% **** Number of samples, n = 83. D.F. = 75. 209 The numbers of S. impressus in tussocks were positively associated with the density of th_ tussocks, and their distance from neighbouring tussocks. Thus they wore most numerous in dense, isolated tussocks.

Very few S. impressus were caught in the pitfall traps on North

Gravel. The traps wore in use between July 9th., 1962 and April 17th.,

1964, but the only specimens caught wore two females on October 1st.,

1962, one male on October 22nd., 1962, one male on October 17th., 1963, and one male on April 17th., 1964. Unlike S. clavicornis, S. imarossus can climb glass easily, and specimens may have escaped from the pitfalls after falling into them, as formalin does not immobilise them very rapidly. However, relevant data are available from work done by Prof.

O.W. Richards and Dr. N. Waloff on the occurrence of insects on broom at Silwood Perk. S. impressus was found by boating the broom bushes, and Table 43 shows the numbers per sampling date in each month from

April to October in 1956, 1957 and 1958. Dactylis plants were common both among and adjacent to the broom plants which were sampled.

Table 41. Occurronce of S. im.)ressus on Broom at Silwood.

Month Mean Numbers er set of samples 1956 1957 1%258 Mean April 0 0 1.0 0.17 May .0 3.0 1.0 1.33 June 0 0 0 0 July 0 0 0 0 August 0 0.67 4.0 1.64 September 3.0 12.33 14.83 10.61 October 12.25 Not samp- 0 9.80 lad 210

The Table shows that S. impressus is active mainly in September and Oct—

ober, but that some activity also occurs in April and May. The pitfall

captures, which ware all in October, except for ono specimen in April,

confirm these periods of activity. The activity in autumn followed the

decrease in numbers in tussocks, from which it was concluded that S.

impressus leaves the tussocks at this time of year, and is active on the

surrounding vegetation.

No specimens of S. impressus macropterous forms or of S. aceris,

were found in the suction trap catches which were examined, so it is not

known when they fly, or even whether they fly at all. However, the flight

muscles appeared to be well developed in the macropterous specimens which

were dissected.

S. impressus has been shown to feed on Collembola by South (1959)

and by Delaney (1960), who also found that it rejected mites. Specimens

kept at Silwood fed readily on Folsomia cavicola Del., so the species does

not appear to be specific in its choice of prey. Thus a plentiful food

supply is available throughout the year both in and outside the tussdlcks.

Relatively few female S. impressus were dissected to examine the state

of the reproductive organs, but from those which were looked at, en idea

of he possible timing of the life cycle can be obtained. The structure

of the female reproductive system is similar to that of S. clavicornis,

except that there are only six ovarioles in each ovary; the same stages

of oocyte development could be distinguished. Table 44 shows the numbers

of specimens which had reached each stage of development, and also the numbers of callow specimens found. No dissections were made between

December and March, when very few adults were found. 211 Table 44. Ovariole development of S. iinpressus.

Stage of oocyto Month A M J Jy A S 1 2 - 3 1 1 - - 2 - 1 1 - - - - 3 1 ------4 ------Gravid - - - 4 1 2 -

Callows 4 ------L Callow specimens occurred in the tussocks in April, after which

various stages were found throughout the summer, until by August females containing ripe eggs were found. Gravid specimens were found until

October. Thus oviposition must take place in autumn, which is the time

when S. imoressus is active outside the tussocks: oviposition may therefore

be outside the tussocks. The larvae must develop in the winter, and

pupate before the spring, to produce the newly emerged adults found in

April. Possibly the small amount of activity found outside the tussocks in April was caused by the migration of these specimens into the tussocks, whore they spend the summer.

A few Stenus larvae were found in pitfall traps during the -winter.

These may be the larvae of S. im)ressus or S. aceris, if those are the only species in the area which ovorwintor as larvae. If the eggs are in fact laid outside the tussocks either the larvae before pupation, or the immature adults must move into the tussocks before the summer. The larvae found (which were third instar specimens) aro similar to those of S. clavicornis, but the antennae are slightly shorter, being only about times as long as the heed, the thoracic torgitos are shaped differently, and the thoracic and abdominal setae are noticeably thicker and more 212 spine—like. Detailed descriptions and drawings have not been made, because of the doubt as to the correct Identification of the larvae. The gut of eno specimen contained large quantities of dark material. This was examined microscopically, and found to consist largely of algal or fungal remains: the material was, however, too fragmentary to allow oven a provisional identification of the typo of plant.

(d) Conclusions.

The data suggest the following outline of the biology of S. imarossus at Silwood. The eggs are laid, probably outside the tussocks, in autumn, and the larvae develop during the winter. They may either move into the tussocks to pupate in the late winter, or pupate outside the tussocks, moving into them after emergence as adults. In either case, callow adults occur in the tussocks in April, and the numbers in the tussocks are relatively high throughout the summer. During this time they probably food on Collembola in the tussocks. There is no evidence that flight takes place. The oocytos develop during the summer, and by September the gravid adults leave the tussocks and are active outside the tussocks throutzhout the next two months. The stage at which the tussocks aro selected as the adult habitat is thus uncert-jm: it may either be the larvae which are about to pupate in winter, or the newly emerged adults in spring. 213 4) Dromius melanocephalus De jean.

(a) Introduction.

Although more ecological work has been done on the Carabidee than on most other families of beetles, Dromius species have received little attention, probably on account of their small size, and the subcortical habits of most of them. The habitats and life cycle of D. molanoceehalus have boon summarised in several faunistic works on Carabidee (Blunck at: al., 1925; Burmeister, 1939; Larsson, 1939; Lindroth, 1945-9). It is found in a varlet:7 of habitats such as in moss, leaf litter and grasses, as well as less commonly under stones and bark. It has boon recorded in

Elymus and Ammoehila tussocks by Van Heordt and Morzer-Bruyns (1960).

In horthern Europe it overwinters in the adult stage; reproduction is believed to take place in the spring, and immature adults are found in autumn (Larsson, 1939). In Central Europe, however, pupae have been found in the spring, and there are two generations per year (Burmeister,

1939). The larvae have been recorded in old wood (Blunck et. al., 1925), but this is based on on incorrect record, which is referred to later.

The wide range of adult habitats probably results in the larvae occurring in a variety of situations as wall. Dromius species are predatory (Davies,

1953), but the food of D. malanoce2halus has not been recorded. Although the works referred to above mention the times of occurrence of the larvae, drawings and descriptions of the immature stages have not bean published.

Thus there is a lack of detailed information on the habits of the species, despite its widespread occurrence in a variety of habitats.

It is found throughout 'Western Europa and the Mediterr nean region; it also occurs in North Africa. The variety uniformis Reittor is found 214

in the Caucasus. It is not found in areas with cold climates, however,

and is absent from Norway and Sweden. It is common throughout the

British Isles, except the extreme north of Scotland.

(b) Adults.

(i) Occurrence in tussocks.

The numbers of D. melenocophalus wore recorded from the same tussocks from which data on Stenus species have already been given. Appendix

Table 6 shows the numbers which wore caught in samples in the three chief areas studied, and the monthly means in each area are graphed in Fig. 42.

There were considerable differences between the three winters, but the numbers were relatively high in each winter, and fell to a minimum in

midsummer; they then rose again in late summer and autumn. The numbers ware higher in January and February 1963 than at any time in the other winters. There were fewer D. maLanocephalus in Deschamosia tussocks than in Dactylis on North Gravel, but the Dactylis tussocks in Nursery Field consistently had higher numbers. The fluctuations ware similar in all throe areas, however.

Table 45 shows the numbers of D. melanoccohalus found in tussocks from other parts of Silwood from which specimens were obtained for experiments.

Thera were more D. melanoccohalus than in North Gravelx in all areas except the middle of Gunnoss Hill in December 1963, when there was little difference. None of the areas contained as many D. melanoceohalus as Nursery Field, however. The only areas in which the tussocks contained more Stenus clavicornis than D. melanoceohalus were the middle of Gunnoss

Hill and Elm Slope. Thus North Gravel and Nursery Fioil both of which also contained more Stenus than Dromius, were not typical of most of the • Mean no. of D.melanocephalu_s per tussock 20- o o 0acty I is, North Gravel • • Dactylis,

Nursery Field V 18 •-•Deschampsia, Cascade Marsh wnx

aaq 16 s o J

Q 14- mel an

o 12- ce 'I• ph • / I al 10- ,

us i , ,.• ..., I Jr n t 8 usso

ck 6 s . 4 • 2

0 . . 0 N D FMAMJJyASONDIJ F MA I:4 ,1 Jy A S 0 A D' Ij F. 1961 1962 1963 1964 \)_, Date k.), 216

areas which contained Dactylis tussocks.

Table 45. Coiaoarison of the numbers of D. molano2t2halus in Dactylis tussocks from North Gravel and from other areas of Silwood

Number of Number of Mean North Ratio Area Date samples specimens number Gravel of means moans South of path, 4.76 Rookery Slope 8-11.10.62 35 305 8.71 1.83 South Gravel 11.10.62 7 39 5.57 1.83 3.04 Water Meadow 16.9.63 6 12 2.00 1.67 1.20 dge of path, 18.10.63 Pond Field 20 101 5.05 1.33 3.80 North of 21.10.63 3.14 Gunnoss Hill 30 125 4.17 1.33 Middle of Gunness Hill 23-30.10.63 47 407 8.66 1.33 6.51 1 lm Slope 1.11.63 2 5 2.50 1.67 1.50 Merton's Acres 1.11.63 9 48 5.33 1.67 3.19 Middle of 2.46 0.73 Gunness Hill 15-17.12.63 64 123 1.92

Significant associations between D. melanocechalus and two of the

tussock characteristics were shown by the multiple correlation end

regression analysis. The coefficients are given in Table 46.

This Table shows that the presence of D. melanocephalus was strongly

and positively correlated with both the area and density of tussocks.

The correlation coefficients with East-West position and date (days since

the beginning of the year) were also significant at a low level, but the

regression coefficients of those characteristics wore not.

217

Table 46. Multiple correlation and regression analysis of the numbers of D. molanoccohalus in tussocks and the tussock characteristics

Tussock Correlation Regression Standard Student's Initial Final characteristic coefficient coefficient error "t" signif- lovas icance tkiE. Area 0.432Ft .08540 .02196 3,89 0.1% 0.1% Density 0.350 1.480 0.4294 3.45 1% 0.1% Dead/living ratio 0.071 .09025 0.1239 0.73 50% - East-West -X* position 0.221 .01110 .01394 0.80 50% - North-South position -.063 -.01795 .02239 -0.80 50% - Distance from neighbours 0.113 .08352 0.2318 0.36 80% - Date 0.193 .004002 .003012 1.33 20% -

Degrees of significance of correlation coefficients 10% * 570 ** 1% -*** 0.1% ***X- Nuiaber of samples, n = 83. D.F. = 75. 218

(ii) Occurrence outside tussocks.

Very few D. melanoca2halus were caught on North Gravel outside the tussocks, and the means and time of dispersal remain somewhat obscure.

The only specimen which was caught in pitfall traps was a male on

January lst.,1964. Thus it appears that D. molanoceohalus is not active at ground level between the tussocks. Data were available on the numbers of Dromius species (mainly D. melonocephalus, with some D. 11,nearis (01.)) on broom bushes recorded by Prof. O.U. Richards end Dr. N. Waloff.

These era given in Table 47.

Table 47. Occurrence of Dromius (mainly D. molenocophalus) on broom at Silwood.

Numbers or set of samDles Month • -. 1956 1957 1958 Mean Lpril 0 0 1 0.17 May 0 0.25 0 0.08 June 0 0 0 0 July 0 0.5 2.0 0.87 August 0 3.0 1.25 1.18 September 9.5 2.7 5.5 6.08 October 4.5 - 7.0 5.00

Like Stenus impressus, Dromius molanoceohalus was active on broom from

August onwards. The vegetation on North Gravel was swept on various occasions between May and August, 1963, to see if D. molanoceohelus was active on the plants there as well. The only specimen which was caught was a female et 2230 G.M.T. on August 6th.. This is within the period of activity observed on broom, but doe's not provide evidence of much similar activity on North Gravel.

D. melanocelphalus is always fully winged, but there is no evidence that the seacios can or over does fly. Lindroth (1945-9) says that it 219

is probably capable of flight, although this has never been recorded.

The specimens which were dissected at Silwood possessed apparent flight

muscles, but these were not very well developed: no individuals could

be induced to fly, or were ever seen to attempt to fly in the field. Nona

wore found in the suction trap catches which were exa,ained. Thus, if flight tae es place, it probably only consists of short flights between

plants during late summer and autumn, when the individuals are active.

(iii) Feeding habits.

South (1959) examined the gut contents of 41 specimens of D.

melanoco-ohalus to find out whether they were predators of Collombola,

especially Entomobrys. He found no traces of Collembola, but did not

mention what other material, if any, was present in the guts. D.

molanocoehalus from both tussocks and broom bushes wore therefore dissected to find out the food material. In all cases whore recognisable

fragments wore found, these wore of mites. A wide variety of tyzos of

fragment was found, and it seems unlikely that the species is specific

in its feeding habits. :Aites were the most numerous arthropods both in

and between the tussocks, so there is probably never any food shortage.

The state of the gut was not recorded in dissections which were made before

July, 1963, but Table 48 shows the amount of food in the guts of beetles

which were dissected between July 1963 and February 1964. 220

Table 48. Amounts of food in the guts of D. melanocephalus dissected.

Amount of food in gut Month Moderate Kone Trace Much •uantit 1963 July 1 August 1 September 1 1 1 October 2 1 November 1 3 2 December 1 1 2 1964 January 1 February 2 1 3

Food was found in the gut in all months in which dissections were mado,

including several winter months, so that feeding takes place throughout

the year.

(iv) Sex ratio

It is almost impossible to separate the sexes of D. molanocephalus

using only external characters. Figs. 43A and B illustrate the

ventral views of the end of the abdomen of male and female specimens.

The posterior sternites are more transverse in the female, but this is

difficult to distinguish without comparing both sexes simultaneously.

Both sexes have four setae on the posterior margin of the last (7th.)

visible stornite, and two on the sixth. However, when a bright light

is used, the outline of the aedeagus can be seen in the male, as an oval

structure extending from the end of the abdomen forwards through the

three posterior segments. In the female the outline of the sclerotised

parts of the eighth sternitos can usually be seen beneath the seventh,

and the tips of the styles often protrude slightly from the and of the

abdomen.

Table 49 shows the-numbers of each sex caught during the winter of

1962-3, and throughout 1964. C

F0' aut

0 'et u

p) po a N•

CD N• 0 1 mm. Or rn 0 •

CD 5 (D • 0 Ovary o

e J Spermathecal gland er Common oviduct uop et

u Spermatheca

0 Spermathecal duct }-1)

Vagina go

• Rectum (cut) Tergite 8 222 Table 49. Sex ratio of D. melanocephalus.

Males Sourao of specimens Number of males Number of females Females

orth Gravel tussocks, 93 53 1.75 1962-3 Gravel Torth tussocks, 42 1.40 1963-4 30 Field Nursery tussocks, 108 2.05 1963-4 221 Total 1963-4 263 138 1.91 Total, 1962-4 356 191 1.86

Males were always more common than females, in en average ratio of

1.86 to one; in Nursery Field in 1963-4 they were more than twice as numerous as females.

(v) Seasonal changes in reproductive organs.

The structure of the reproductive system of an almost completely immature female is shown in Fig. 430. There are three polytrophic ovariolos in each ovary; the ovaries lie vontro-laterally in the abdomen, and ere twisted anteriorly so that the outside ovariole lies above the other two in each ovary. Three or four oocytas usually start to develop at once in each ovary, but when yolk formation begins, one or two in each develop before the others, so th 't not more than three or four eggs were over found ripe at once. However, in gravid females, yolk begins to fora in the oocytos behind the eggs. The development was divided into five stages.

(i) Complete immaturity;

(ii)Oocytes starting to enlarge (Fig. 340);

(iii)Much yolk in oocytes;

(iv) Ripe eggs present; 223

(v) Ovariolo bases swollen but empty after oviposition; more oecytes developing behind these.

The numbers of females at each stage which wore dissected each month are shown in Table 50.

Table 50. Ovariole development of D. molanoceohalus.

Month Stage of development J FMA'M -J JyASOND 1 (immature) 1 3 10 6 3 1 3 2 2 1 3 3 1 3 1 2 1 1 4 (gravid) 1 3 1 2 5 3

In July all the females which wore dissected wore iamature. Development took place between October and January, and ripe eggs were present from

January until May, although females which had laid eggs were not found until June.

(i) 4Fgs. Female D. melanocephalus never ovipositod in captivity, but a single egg was obtained from a tussock base in a Tullgren funnel on April 30th.,

1963, and hatched into a D. melanocephalus larva in the laboratory.

Its appearance was similar to that of the ripe eggs which were found previously in gravid females.

The eggs are ovoid with very rounded ends, opaque and almost white, with a smooth, shining surface. The length varied between 0.68 2,nd 0.80 rim., and the maximum diameter between 0.40 and 0.49 mm.. The mean dimensions were 0.72 x 0.44 mm.. 224 (ii) Larvae.

Schiodte (1861-83) described and gave figures of the larva of

D. ailis (F.), with comparative notes on that of D. quadrimaculatus (L.).

Van Emden (1942) illustrated an unidentified smaller Dromius lerva

separated the larvae of Dromius from the remainder of the Lobiini by the

presence of toothed claws, and by the cerci; which are either vary short or absent. Perris (1862) described the larva of D. quadrinotatus (Danz.);

however, this larva has long coral., and was probably misidentified, as the

identification was based only on finding adults of D. quadrinotatus in the habitat from which the larvae had previously been recorded. Xambou

(1903) described the larva of ilDronisus melanocephalus De jean", which

is probably a misprint for Dromius molanoceehalus. However this larva also is not that of a Droraius, as the coral are Long; the larva of

D. melanoceohnlus was found at Silwood, and did not resemble x&mballs description.

Although larvae wor,:, searched for after the beginning of 1963, and ripe eggs wore found in adult females from January onwards, the first larvae were not found until nay 16th., when four first instar specimens ware extracted from the base of a tussock. lAirther specimens were found, both in the bases and among the dead leaves of tussocks, in June, July and

August. The numbers of specimens of each Laster found in each month are shown in Table 51.

Development took place in the tussocks between May and August, and the new generation of immature adults was found in the tussocks from

August onwards. 225

Table 51. Numbers of D. me anocenhalus larvae found in tussocks.

Instar 2 May 4 0 June 4 2 2 July 2 3 5 August 0 1 0

The larval food in the field is unknown, but they are obviously predacious. In the laboratory they fed readily on dead Lucille larvae and 3upae. Complete rearing from the first instar was not achieved, as all the larvae, died at the first moult, but one second instar larva was successfully reared through to the adult stage, thus confirming the identity of the larvae.

The dimensions of the head capsule, and the size factors of the larvae arc given in Table 52.

Table 52. Head diuensions and size factors of D. melanocephalus larvae.

1st. instar 2nd. inter 3rd. instal/.

Min. 0.37 0.41 0.49 Head -width Akan 0.378 0.432 0.511 (uu.) Max. 0.39 0.46 0.53

Min. 0.35 0.42 0.52 cad length Nean 0.373 0.445 0.547 Gan.) Max. 0.38 0.47 0.58

Head length Moan 0.99 1.03 1.07 ' Head width

Size factors: a 1.14 b 1.18 c 7.94 ) d 6.94 ) Adult length = 3.0 m..i. o 5.87 ) 226

The following is a description of a third instar larva (Fig. 44A).

Head (Fig. 44B) depressed, only slightly longer than broad, sides

almost parallel, barely rounded. Frons (Fig. 44C) 171- tines as long as

broad; nosale with two tooth, which extend as far forwards as the

adnasalia; the outer margin of each tooth sou times with a small projection.

Antennae short, not more than two thirds of the length of the mandibles; first segint very short, twice as broad as long; second

segment subqundrate; third segment as long as first two together,

tines as long as broad, widened apically; fourth segment as long as third,

thin and parallel sided, four tines as long as broad, without long setae

at apex.

Mandibles fairly strongly broadened basally; retinaculum slightly

nearer base than apex of mandible, curved backwards slightly into a hook

shape.

Maxillae (Fig. 45A) with stripes quadrate, one third as long as the

entire maxilla, eight setae on or near inner margin, throe near outer

margin; galea extending as far as apex of first segment of palp, first

segment quadrate, second segment elongate, twice as long as first segment

and four tiiaus as long as broad; palpiger strongly bronsvorsovalp with

first segment quadrate, second and third elongate, subequal in length.

Labium (Fig. 45B) narrow, mentum quadrate with six long setae

(including those of the ligula) on its apical half; palpi with first

segment broad, quadrate, slightly shorter than the second which is

elongate, 2 times as long as broad.

Thoracic torgitcs only slightly sclerotised; pronotum elongate, as

long as the head, sides rounded; mese- and uetanota slightly transverse. 227

0-5mm.

7ig. AA, D. melanoceThalus, larva. A.. L3, dorsal view. B. L3, head, dorsal view. C-! Wrons of L3, 2 1.

228

O1mm.

Fig. 45. 1). melanooepbalus, L3. A. Left maxilla. B. Labium. C. Apex or left hind leg. 1). of abdomen, dorsal view. 229

Legs short, tarsal claws rather long, with two small teeth on each in

addition to the apical tooth (Fig. 45C).

Abdominal tergites transverse; ninth tergite (Fig. 45D) without

trace of cerci; tenth segment without anal crotchets.

Pubescence generally rather sparse; dorsal surface of head with

only four large setae on each side of the frons; pronotum with only three

setae on or near each lateral margin; meso- and metanotn with only one

large auirginal seta; all thoracic tergites with few dorsal setae; abdom-

inal tergites with setae almost restricted to the posterior half of each

segment (Fig. 45D), without microtrichia between the larger setae.

The earlier instars can be distinguished by the size of the head

capsule, and by the shape of the frons.

Second instar with frons (Fig. 44D) similar in shape to that of the

third instar, but smaller and with the anterior half of the lateral

margins more rounded.

First instar with frons (Fig. 44E) as broad as that of the second

roster, but shorter, with the posterior margin abruptly truncate; four

simple egg bursters present, all of similar size and situated in the

posterior half of the frons.

This species resembles the Dromius larva illustrated by Van L'mden

(1942), which also hes no cerci or anal crotchets; it is not the same

species, however, as the frons is differently shaped and the relative

lengths of the antennal segments are not the same. Details of the differences between the Dromius larvae which have been described are given after the larva of D. Lineeris has been described (p 245). 230 (iii) Pupae.

Pupae were not found in the field, but pupation con be assumed to

take place in the bases of the tussocks where the larvae are found. The

only pupa soon was that of the larva which was reared through to the

adult stage to confirm the identification of the larvae. Detailed draw-

ings were not made in case the light harmed the pupa, but it was similar

in appearance (although less elongate) to the pupa of D. linearis (Fig. 48E).

(d) Conclusions.

The following is an outline of the life history and biology of

D. melanocenhalus in tussocks at Silwood.

The eggs are laid in the bases of the tussocks in early summer) and

the predatory larvae develop in the same habitat, and also in the dead

leaves surrounding the tussocks. The new generation of adults is found from midsummer onwards, and they are active on vegetation outside the tussocks in the autumn, feeding on mites. Although the adults are

winged, no evidence of either migratory or trivial flight was found.

The selection of the winter habitat is made by the immature adults in

autumn) and feeding continues in the tussocks in winter. Ovariolo devel-

opment takes place from November onwards, and ripe eggs are present in the females in late winter and early spring; however) there was no evidence that they mere laid before late spring. 231

5) Dromius linearis (Olivia - .

(a) Introduction.

Like D. melanocephalus, this species occurs in a variety of habitats.

It has a greater preference for dry habitats, however, and thus is common on dunes, both coastal (Van Haerdt and rzer Druyns, 1960) and inland (Lindroth, 1945-9), where it lives in tussocks of xerophilous grasses such as Elymus and Ammophiln (Larsson, 1939; Kryger and Sonderup,

1952). It is also found in dry fiolds with a sandy or gravelly soil, when it occurs on vegetation, under stones, in moss and litter, etc.

(Burmeister, 1939). It is gemrs14 believed to ovorwintor in the adult stage, and to reproduce in the spring, with the larvae developing in summer; however some overwintering larvae may also occur, and Larsson

(1939) concluded that all stgas could be found at 011 times of the year, although the larvae were commonest in summer.

Det21ls of the biology of D. linecris have not been published, except by Xambau (1903), who recorded copulation, and oviposition at the bases of stems of herbs and shrubs. Ho did not mention the time of year at which this took place, and gave no description or details of the biology of the larvae. Both adults and larvae are believed to be predatory, but no details of their food are available.

It is a western palaearctic species. It does not occur in Scandinavia elmopt in Southern Sweden, and its range extends eastwards throughout southern Europe to the Urals; it is also found in North Africa. It is widespread throughout the Lritish Isles except in Scotland, where it is restricted to the South West. 232

(b) Adults.

(i) Occurrence in tussocks.

D. linearis was not one of the commonest beetles in Dactylis tussocks on North Gravel, or in Deschamosia in Cascade Marsh. Although it was found in most months of the year, only 45 specimens wore found during the first year's sampling in these areas. 40 of these were from

Dactylis, and only five from Deschamosial which emphasises the preference of the species for dryer habitats. It was common, however, in Dactylis tussocks in Nursery Field, and the numbers in samples from that area are shown in Table 53.

Table 53. Numbers of D. linearis found in Dactylis tussocks in Nursery Field, 1963-4.

Arithmetic

Month Numbers in each sample mean 1963 January 42,14 28.0 February No samples taken March It April 2 2.0 May 0,3,0 1.0 June 4,0,2 2.0 July 2,2,2 2.0 August 1,0,0 0.33 September 6,4,11 7.0 October No samples taken November 0,0,27 9.0 December 10,1,12 7.67 1964 January No samples taken February 0,1,1,5,23,9,6,2,0,2,20,2,5,2,0,1,4,2,2,6,8, 4.30 1,0,2,2,0,1,5,1,7,14,6

Although few samples wore taken in most months, the numbers of adults show a regular fluctua tion. i^iany specimens were found in the winter of

1962-3, but bad weather prevented extensive samling. By May only small numbers were_)resent; in September they rose again, and were greatest in the first half of the winter. 233

None of the tussocks which were sampled in other 'Darts of Silwood yielded large numbers of D. linearis. As only a few specimens were found on North Gravel, the multiple regression and correlation analysis did not show any significant associations between the numbers of D. linearis and the characteristics of the tussocks.

(ii) Occurrence outside tussocks.

D. linearis„ again like the preceding species, was not commonly found in pitfall traps on North Gravel, although in view of the smeller numbers present in the area, this was less surprising. The only specimen which was caught was a female on August 18th., 1963. Data have already been given on the numbers of Dromius species recorded on Broom at Silwood; the specimens, which included a small proportion of D. linearis, were most common in September and October. On North Gravel, D. linearis was found outside the tussocks on fine nights, when it could be swept off the upper parts of the vegetation, especially the Dactylis flowering stems and inflorescences. Table 54 lists the numbers which were found on various dates. On each occasion, three sets of 25 sweeps at waist height were made. Table 54. Numbers of D. linearis cau9:ht by sweeping North Gravel.

Date Time (G.M.T. Number caught 9.5.63 1600 0 2000 2 21.7.63 1930 1 U 2130 5 u 2230 7 22.7.63 2330 1 25.7.63 2300 4 27.7.63 2400 0 29.7.63 2230 7 6.8.63 2230 2 8.8.63 2130 1 11.8.63 2230 3 234 These beetles were found from May until August; they appeared to be most numerous at about 2230 G.M.T., and were absent after 2330.

(iii) Wing dimorphism.

D. linearis is generally wing dimorphic, most of the individuals being macroptorous (Lindroth, 194579). The difference in wing size of the two forms is extreme, as shown by Figs 46A and B, and no intermediate forms wore over found. Reduction of the wings to rudiments is carman in

Carabidne (Darlington, 1936), but no completely apterous species have ever been found. The numbers of macropterous and brachypterous forms collected at various times are shown in Table 55.

Table 55. Numbers of Macrooterous and brachy2terous D. lineeris caught.

Source of Males Females specimens Macrooterous Brachynterous Macro rows Brachyoterou, North Gravel tussocks 6 10 1 15 1961-2 North Gravel tussocks 2 10 1 14 1962-4 Sweeping North Gravel 2 11 4 15 Pitfall, North Gravel 0 0 0 1 Total, North Gravel 10 31 6 45 Nursery Field 0 127 1 54 tussocks, 1962-4 Total 10 158 7 99

The specimens from North Gravel contained about 20% of fully winged forms, but only one macropterous individual was fund among the 182 specimens examined from Nursery Field. Lindroth (1945-9) considers that wing size in Carabidee is usually' genetically determined, the brachypterous form being dominant over macropterous; recently colonised areas have a higher percentage of winged forms of dimorphic species than areas in which the species have boon established longer. Although he only applies this idea to the relatively large scale distribution of 235 macropterous end brochyptorous forms, it may also be valid on a smeller scale; this is supported by the lower proportion of fully winged forms in the older tussocks in Nursery Field than in the relatively recently introduced Dectylis on North Gravel.

(iv) Feeding habits.

D. linearis was another of the species which mere examined by South

(1959), end found not to contain Collembolan remains in the gut, but again the actual food was not specified. Specimens which were caught by sweeping end in tussocks wore examined to find out their food material.

Those which wore swept off the grass stems and flowers in summer wore found to be feeding on Thysanoptera, and many of the fragments could be identified as Chirothrips manicatus Hal. by the charactoristic process on the second antennal segment of this species. This thrips is found regularly on Dectylis (Beddows, 1959); it was found on the influorescences throughout the summer, but is usually commonest between. May and July (Morison,

1947-9). In winter it was found inside the tussocks in moderate numbers, and nearly all the Thysanoptora listed in the total arthropod fauna of tussocks (Table 20) were of this species. Recognisable fragments of the food of D. linoaris in winter consisted both of Chirothrips, and, in a few cases, of mites. Thus although thrips are its chief food, mites are also eaten, (but probably not Collembola). Table 56 gives the amounts of food in the guts of specimens which were dissected after July 1963.

Specimens with full guts were present in all months in which dissections were made, both in winter and in summer, indicating that this species feeds throughout the year. 236

Table 56. Amounts of food in the guts of D. linearis dissected.

Amount of food Month Moderate ,such None Trace uant it 1963 July 1 1 3 1 August 1 1 1 Saytember 1 1 November 1 1 December 2 1 3 1964 February 2 1

(v) Sex ratio.

The sexes of D. linearis can be distinguished by the shape of the

seventh abdominal stornito (Figs. 460 and D). In the male, the sternite

is less transverse, and has a distinct invagination in the posterior

margin, from -which the tip of the aedeagus often protrudes. The female

stornito is broader, with an almost evenly curved posterior margin. Tho

male has 6 setae on the posterior margin of the sixth starnito, but only

four on the seventh, whereas the female has 6 on the margins of both stornites.

The numbers of each sex caught in tussocks and by sweeping ore given in :able 57. Table 57. Sox ratio of D. linearis.

Source of specimens Number of males Number of ---Mnlos- females Females7 North Gravel tussocks,1961-2 16 16 1.0 'I ti ii ,1962-4 9 14 0.64 Sweeping, North Gravel 16 20 0.8 Total, North Gravel 41 50 0.82 Nursery Field tussocks, 1963-4 145 57 2.54 Total 186 107 1.74 237

A B

1 mm.

E C

1 mm.

Ovary

Spermathecal D gland Common oviduct Spermatheca Spermathecal duct Bursa copulatrix

Vagina

0 5mm. Rectum (cut) Tergite 8

Fig. 46. D. linearis. A & B. Eacro and micro wings. C & D. Ventral view of end of abdomen of o and o. E. 4 reproductive system. 238

Although the relatively small population on North Gravel contained

ap)roximately equal numbers of each sex, the samples taken from the denser

population in Nursery Field contained :core than twice as many males as

females. The difference in sex ratio between the two populations, together

with the different frequencies of macropterous individuals, emphasises

their isolation from one another.

(vi) Seasonal changes in reproductive organs.

The structure of the female reproductive system (Fig. 46E) is very

sifailcir to that of D. molanocephalus, but the ovarioles are longer, the

spermathoca is more complex, and the bursa copulatrix is distinctly

swollen. The same stages in oocyte development could bo recognised, and

the numbers of females of each stage which were dissected in each month

are shown in Table 58, together with the numbers of callow individuals

found of both sexes.

Tablo 58. Ovariolo development of D. linearis.

Stage of Month development FMAMJJyASO N D 1 (immature) 3 1 11 2 1 5 1 1 3 3 2 3 2 2 1 2 4 (gravid) 1 11 4 Callow specimens 1 3 2 3

Gravid females wore found between y and august, and females at inter-

sta&,s of ovariolo development wore found throughout the year.

Callow specimens wore also found both in summer and winter, so that this species may have more than one generation n year; certainly there does not appear to be any set period for maturation. 239 (c) Immature stages.

(i)Eggs.

No eggs were found in the field, but measurements were made of ripe

eggs found in gravid females. Those wore similar in appearance to those

of D. molanoce-ehalus, although slightly loss elongate. Their length

varied between 0.86 mm. and 1.01 mm., and their maximum dicta ter between

0.57 and 0.71 mm.; the mean dimensions were 0.90 x 0.64 am.. The remains

of three eggs from which larvae had emerged wore found in a dead Dectylis

panicle stem. From their appearance and size, and as D. linearis larvae

were later found in similar stems, they were probably the eggs of this

species. Xambeu (1903) recorded that D. linearis lays its eggs at the

abases of plants, close to the neck of the roots", and this is in agree-

ment with oviposition at the base of the panicle stems in Dactylis tussocks.

(ii) Larvae.

All stages of the larvae of D. linearis were found oxclusivoly in the deed panicle stems of the tussocks. Those stems are quite woody, and rot internally during their first winter, becoming hollow. In this condition they may stand for one or two years until their bases rot com-

pletely, and they are blown down. The larvae are predatory, and fed readily on various decd invcrtibrates in the laboratory. Their exact food in the field was not determined, but other possible organisms which war:., found commonly in the stems included dipterous and lepidopterous larvae, nites and nabid eggs. The numbers of each instar found each month are listed in Table 59. 240 Table 59. Numbers of D. linearis larvae found in dead Dactylis 2nicle stems.

Instar Month 2 April 1 1 May 2 Juno 2 July 2 2 2 August 1 1 September 1 1 2 October 1 November 1 December 1

The data support the idea that D. linearis can overwinter either in the adult or the larval stage, s first instar larvae were found in November and and December. However, most of the larvae were found in summer, although no definite period of emergence and development was evident. Thus the suggestion of Larsson (1939) that all stages can be found throughout the year may be corr,ct. The identity of the larvae was confirmed by rearing third instar spool:Jona in the laboratory, and also by finding third roster and JuDal exuvi,-e together with freshly emerged adults in stems on several oc, salons.

The dimensions of the head capsule, and size factors of the larvae are given in Table 60. Table 60. Head dimensions and size factors of D. linearis larvae.

Instar 1 2 Head Min. 0.32 0.41 0.60 width Mean 0.35 0.47 0.66 mm4.1 Max. 0.38 0.40 0..1 70. Heed Min. 0.40 0.49 0.77 length Mean 0.42 0.57 0.80 (rem.) Max. 0.9 0.61 0.8 moan Head length Head width 1.20 1.21 1.2.1 241

Size factors a 1.34 b 1.40 c 14.3 ) d 10.6 ) Adult length = 5.0 mm. e 7.6 )

The following is a description of the third instar larva (Fig. 47A).

Head (Fig. 47B) depressed, distinctly longer than broad, slightly broadened )osteriorly, sides slightly rounded; epicranial suture with two or three sinuations. Frons (Fig. 47C) almost twice as long as broad, nasale with two simple teeth which do not extend as far fowards as the adnasalia, which have an outwardly projecting tooth on each. Antennae

almost as long as mandibles; first and second segments quadrate; third segment shorter than the first two together, twice as long as broad, widened apicdlly with the apex very obliquely truncate; fourth segment shorter than the third, thin and parallel sided, 2 times as long as broad, apex with three long setae.

Mandibles only moderately broadened basally; retimaculum distinctly nearor npox of unndiblo than base, net unrkodly aurvod IvaltwIrds.

Maxillae (Fig. 48h) with stipos elongate, almost twice as long us broad, almost half as long as the entire maxilla, with ten setae on or near the inner margin, four near outer margin; gales extending as far as apex of first segment of palp, segments elongate, the first 12 times as long as broad, the second only very slightly longer than the first, but narrower, five times as long as broad; palpiger strongly transverse; palp with segments elongate, the first and third subequal in length, slightly longer than the second.

Labium (Fig. 48B) fairly broad, mentum slightly transverse, with eight long setae (including those on the ligula) on its apical half; 242

0.5mm.

Fig. 47. D. linearis, larva. A. L3, dorsal view. B. L3, head, dorsal view. C-E. irons of L3, 2 & 1.

243

01mm.

1 mm.

Fig. A8. D. linearis. A. L3, left maxilla C. L3, apex of left hind leg. B. L3, labium. D. L3, end of abdomen, dorsal view. E. Pupa, lateral view. 244

palpi with segments elongate, subequol in length, the second segment five times as long as broad.

Pronotum moderately sclerotised, quadrate, shorter than the head, sides straight; mesa- and metenota less sclerotised, transverse, aides rounded. Legs short, tarsal claws (Fig. 4S0) moderately long, with two distinct sharp teeth in addition to the apical tooth.

Abdominal segments transverse; abdomen sometimes broader than head

and thorax in fully fed specimens; ninth tergite (Fig. 48D) with a pair of single segmented, blunt cerci, which are as long as the tergite; tenth segment with a group of five or six distinct and sclerotised anal crotchets on each side of the anal tube.

Pubescence fairly thick; dorsal surface of head with eight to 12 large setae on oach side of the frons; pronotum with more than six setae on or near the lateral margins; meso-and metanota with three or four marginal setae; dorsal setse fairly numerous on all thoracic tergites; abdominal tergites (Fig. 48D) with setae present in two transverse bands, one along the posterior part, and the other slightly in front of the middle of each segment; microtrichie present on the central portion of each tergite between the longer setae.

The earlier instars can be separted by size, and by the shape of the frons, as follows.

Second instar with frons (Fig. 47D) similar in shape to that of the third instar, but less elongate, and less contracted and pointed at the posterior end.

First instar with frons (Fig. 47E) more elongate than that of the second instar, with the posterior margin abruptly truncate; four simple 245

egg bursters present, two small ones at the posterior angles, and two

larger on the anterior half of the frons.

This species resembles the two species described by Schiodte (1861-

83), with both anal crotchets and cerci. It differs from these species,

however, in the number of anal crotchets. The following key can be used

to separate the species.

Key to the described larvae of the European species of Dromius.

1. Cerci and anal crotchets present 2,

- Cerci and anal crotchets absent 4.

2. Five or six anal crotchets in each group D. linearis (01.)

- Nine or more anal crotchets in each group 3.

3. Kasale not protruding forwards beyond the adnesalie, its median

indentation as large as its tooth D. Dallis (F.).

- Nasal° protruding in front of the adnasalia, its median indentation

smaller than its teeth D. cuadrimaculatus (L.).

4. Fourth antennal segment as long as third; maxillary palpi shorter

than antennae, first segment quadrate D. melanoceaplus Dej.

- Fourth antennal segment shorter than third; maxillary pelpi as

long as antennae, first segment elongate Dromius sp. indet.

(Von Emden, 1S42).

(iii) ?twee.

Live pupae were not found in Dactylis stems, but several pupal oxuviae were found, from which it was clear that the larvae pupate in the stems in which they live. A pupa of a third instcr larva which had pupated in the laboratory was killed and fixed, and is shown in lateral view in Fig. 48E. It is white, rather elongate, with conspicuous long 246 setae on the abdominal torgites and head, but with shorter pubescence on the thoracic tergitos. The time spent in the pupal stage in the laboratory, at a temperature of about 20°C, varied between eight and

11 days.

(d) Conclusions.

Unlike the other throe chosen species, maturation, oviposition and larval development of D. linearis are not restricted to limited times of the your. Eggs aro laid throughout the summer, and larvae can be found throughout the year. All the immature stages are spent inside the dead panicle stems of Dactylis. The adults feed nocturnally in summer on

Thysanoptera in the Dactylis inflorosooncoa, and on Thysanoptera end mites in the tussocks in winter. They are wing dimorphic, with only a small proportion of macropterous forms, which were not observed to fly. The tussocks in Nursery Field contained many more D. linearis, with a higher proportion of males, and fewer fully winged individuals than those on

North Gravel.. The stage at which the choice of the tussocks as a winter habitat is made varies. The choice of oviposition site by the parent generation determines the winter habitat of overwintering larvae, and of overwintoring adults which have emerged in late autumn, and remain in the tussocks until spring. Adults which have emerged earlier in the year, however, are active in the summer and autumn, and choose their own winter habitat. 247

6) Comparison of the selected species.

The details of the biology of the four species are still incomplete, and many of the onclusions that hove been reached era based on the examination of only small numbers of specimens. A comprehensive study of the biology of at least one of the species would have been of interest, but the amount of work involved would have limited the scope of the rest of the investigation into tussocks. As the plan of the study was initially a broad ono, a great degree of concentration on any single aspect or species was not intended, and the conclusions based on these four species could be used as a basis for a more restricted study in the future. From the information already obtained, interesting similarities and differences between the species appeared.

All four are carnivorous, and food on microarthropods which are numerous throughout the year in all parts of the grassland. Thus the tussocks do not provide food which is unobtainable elsewhere, and both

S. clavicornis in May, and D. linearis in July, were seen to leave the tussocks to feed. Activity outside the tussocks on North Gravel was limited, and only S. clavicornis showed a definite period of activity at ground level in the intervening grass. Flight was not common, as D. melanoceohalus, the only species which was always fully winged, was not seen to fly, and only the small proportion of S. clavicornis which were macropterous showed evidence of flight. This may reflect the stability of the tussocks as a habitat, as they last for several years. It also indicates that the amount of food and shelter available are probably seldom so limited as to cause overcrowding among the beetles, when the ability to fly to new areas would be en advantage, as random dispersal by movement at ground level is slow (Skallam, 1951). 248

Although threo or tho spacies overwintered as adults in the tussocks, their life histQt"'ies woro not identical. Thus 2- clavicornis larvae develop in tho tussoc~\:s in middle and late summer, and tho resulting edults remain immature in the tussocks until tho follovJing spring. Q. mtlanocepholu8 mature during the winter, and the eggs are laid earlier, so that tho new gener8tion of adults is pres8nt from midsummer onvwrds, ond thoy are aetive outside the tussocks beforo the winter. !2. lin0Qri~, unlike thu provious sp0cios, docs not have its life cycle so strictly synchronised with the time of yeelr; egc;s arG 10 id throughout tho sUlTh-ner, and dovolopmont tokes plncG to the adult stage in the same sooson, unless they are laid in the autumn, whsu the lnrvt)o over1~inter bofore cont .... inuing the ir development in the following yeor. Thus, cons idering those throo specios, thQ choico of the tussocks as a wint~r h8bitat is msdo in

§. ~J8vic0t..~s by tho ovipositing felnElles, in!2.. }!o].0U9£9..2halus by the immature adults, and in £. ].i,no

.Q.lavicornis is only found commonly in 1vin~er, VJhen all tho specimens are immature, ~nd they l08vo tho tussooks before maturing. Gravid females aro found in relatively small numbers, becnuso they are widely dispersed throughout tho intervoning gross, and insufficient material can be obtained for oxtensivG behaviour experiments on this stage.

Adults of the fourth spuc ios, §.. impresslls, 'Were found in tho tussooks in summer, Dnd the stDgG at which they entered thorn was not certain. Larvae which were probably of this species were found both 249 outside and inside Dactylis in winter, so it is also not clear whether the tussocks form an essential winter habitat for the species.

The data do show that all the species are present in the tussocks, not only in winter, but also in summer, three of them being represented by larvae during this period. Colcopterous larvae were as numerous in the tussocks in summer as were the adults in winter, and thus the habitat

may provide essential shelter for the animals in this period of the year.

As the larvae are particularly susceptible to desiccation, shelter from low humidities may be important. The differences in humidity among the typos of grass have already bean given (13016 ), but there was insufficient time and material to carry out experiments on the resistance of the larvae to desiccation. 250 IV. POSSIBLE EFFECTS OF THE HABITAT ON THE FAUNA.

A. BEHLVIOURAL EFFECTS.

1). Movement into tussocks.

(a) Methods.

The beetles varied in the stages in their life cycles at which they chose the tussocks as their habitat, and these stages were usually not obtainable in large numbers. Thus it was not feasable to carry out experiments to determine directly the factors which led the insects to choose their microhabitat. Indirect evidence on the characteristics of tussocks which were most favourable was obtained from the multiple correlation and regression analysis, already referred to (Tables 32, 42 and

46). In addition, experiments were designed in which tussocks were altered in various ways in the summer, before the numbers of adult beetles in them increased, and the effects on their fauna in the following winter were then observed. The tussocks were altered in the following three ways :-

1) All the leaves and stems above the 9u level were removed, leaving the dead leaves surrounding the tussock.

ii) All the loaves and stems above the 1" level were removed, including the dead leaves surrounding the tussock.

iii) The dead loaves surrounding the tussock were removed, leaving the erect living and dead vegetation.

Six tussocks were altered in each way on July 12th. 1963, and their fauna was sampled on December 2nd., together with that of six unaltered tussocks as controls.

To find out whether beetles outside the tussocks in winter would 251

move into them, a simple experiment was done by releasing marked beetles

between the tussocks, and observing whether they entered them. S.

clavicornis was used, marked on the pronotum with a spot of quick drying

white lacquer. They wore released during a spell of mild winter weather,

and the tussocks adjacent to the release point were sampled four days

later.

(b) Results.

The significant results of the multiple regression analysis have

already been listed separately for each of the beetle species. Table 61

combines those separate results, and shows the characteristics of the

tussocks which wore significantly associated with the presence of each

of the throe species chosen for separate analysis, and also with the

remaining beetle fauna.

Table 61. Significance levels of significant multiple correlation and refYression coefficients for selected species and remaining beetles.

Tussock S. clavicornis S. impressus D. meleno- Remaining beetles Characteristic co halus R 0 R C R • Area 5% 0.1% 0.1% 0.1% 0.1% Density 1% 1% % 1% Dead/living ratio 0.1% 0.1% 1 East-West position 57. 5% 5% North-South 5% 10% position Distance from neighbours 5% 5' Date 5% 10%

C = Correlation coefficient. R = Regression coefficient.

Those data give an idea of the types of tussocks that are selected

by the beetles, but do not indicate the factors in the tussocks to which the beetles are responding. 252

The experiments in which tussocks were altered in July, end their fauna sampled in December, gave similar indications. The numbers of each species found in the six tussocks of each type are given in Table 62.

Table 62. Results of alteration of tussocks experiment, Julx to December, 1963.

Number of beetles Treatment S. S. D. D. clavicornis am ressus molanoce halus linearis Total ut down to 9" high 2 1 0 3 6 ut down to ln high 0 0 1 0 1 urrounding dead 8 1 12 leaves removed 2 1 Controls 19 1 10 2 32

The numbers of S. impressus and D. linearis were too low for any

conclusions to be drawn, and the following comments apply only to the

remaining two species.

Reducing the height of the tussocks to 9" leads to conditions of

temperature and humidity more similar to those in the intervening grass,

although their density is still greater than that of the other grass

species. This alone, however, did not load to an increase in their

beetle fauna: this could be because the altered conditions either killed

the larvae of species such as S. clavicornis, which were already present

when the tussocks were altered, or prevented selection of these tussocks

by the adults of species such as D. melanocephalus, which select in

autumn. Removal of all the vegetation above the 111 level gave similar,

but more extreme, results.

The removal of only the surrounding dead leaves reduced the number

of S. clavicornis adults, but had little offeCt on D. melanocenhalus.

This agrees with the significant regression coefficient of the numbers 253 of S. clavicornis on the dead to living ratio of tussocks, and suggests that the dead leaves are in some way necessary for tha species.

Thus these two sets of data show that different species select tussocks with different characteristics; the presence of S. clavicornis, in particular, is associated with the quantity of dead leaves surrounding the tussocks. D. melanoceehalus does not select tussocks purely for their increased density, despite its significant correlation and regression coefficients with tussock density, and humidity and temperature are probably also important.

Tho marking and recapture experiment was not intended to be quantitative, but only to find out whether the beetles would move into tussocks if released outside them in winter. 63 marked specimens of S. clavicornis were released in Fostuce inside a ring of four Dactylis tussocks on January 25th., 1962. The tussocks surrounding the area wore sampled on J, nuary 29th., and the Festuca was searched for any beetles that might not have moved out of the area. The results are shown in

Table 63. Table 6. Results of marking and recapture exeeriment, Januar,y. 1962. c Details of tussocks Igo. of S. clavicornis present

Mean diameter Distance from Marked Unmarked in. release .oint in. 3.25 3 15 4 7.75 4 0 36 3.0 7 0 13 5.0 10 1 6

Almost 25 of the marked specimens moved into the nearest tussock, although it was only a small one, with few S. clavicornis already present. Only one marked beetle was found in the larger tussocks, and 254 this was in the most distant one, which contained the smallest number of unmarked specimens. Of the 47 marked specimens still unaccounted for, five were found near the release point betmeon the tussocks, and the remainder had apparently left the area. Thus S. clavicornis will move into tussocks in winter, although the tussocks which are chosen are not those in which the highest numbers are already present. 255 2) Behaviour of booties in tussocks.

(a) Methods.

A series of behaviour experiments was carried out on S. clavicornis,

D. melanocemhalus and D. linoaris, using material from tussocks in winter

and early spring, to see whether their behaviour showed any preference for

the conditions in the tussocks. The beetles used in these experiments

were either taken straight from the field, or kept in a refrigerator at

2.5°01 100% R.H., and no light.

The physical factors which were studied were temperature, relative

humidity and light, as wall as the reactions of the booties to tactile

and olfactory stimuli.

The apparatus used in temperature preference experiments was a

gradient apparatus, previously used by Bishara (1963). It consisted of a rectangular aluminium trough, 2t long, 2" wide and 111 deep. One end was

heated by a thermostatically controlled element to about 33°C, and the

other was attached to a solid metal cylinder which was immersed in a container of ice, reducing the cold end of the trough to about 12°C. The

perspex lid of the trough was divided into six sections, and the temperature of the floor of the trough in each section was measured by a thermocouple inserted through the lid. Experiments were carried out at room humidity (40 - 60%) using both the bare metal floor of the trough and a lining of dry filter paper, and at high humidities using a lining of moist filter paper which was kept saturated by a wick immersed in water. Madge

(1961) has pointed out that this method results in a humidity gradient as well as a temperature gradient in the apparatus, but the humidity is always higher than when a dry floor is used, and the gradient is slight 256 if the floor is kept saturated. The insects were inserted through holes in the lid of each section, and their numbers in each section wore noted at five minute intervals for 50 minutes, by which time there was usually little movement.

The apparatus used for humidity experiments was intended to function either as a choice chamber or as a gradient apparatus. Syrjamaki (1962) has reviewed the typos of humidity preference apparatus which have been used by other workers; most of them are either circular choice chambers, or ring gradients. Some linear gradient crones have boon described, however, and the type used was similar in principle to that of Green (1954).

It was constructed of -PI thick perspex, and is shown in lateral pro-

jection and plan views in Figs. 50A and B. There ware two main parts: the lower one was a shallow, partitioned box, 61; long, 2" wide and --11 deep, divided into six sections into which liquids could be placed to control the humidity. The box was surrounded by a flange, into which fitted a false floor of perforated zinc, beneath a rectangular arena with a muslin floor. The lid of this arena had six -" diameter holes corresponding to the six suctions of the base of the apparatus; each hole was normally kept covered with a oo square of perspex held in position with vasoline. Potassium hydroxide solutions of various strengths (Solomon,

1951) were used to control the humidity in the arena. It was soon found that all the species tested aggregated at the ends of the apparatus, which was too short for a gradient to be sot up only in the centre, and thus it was used only as a choice chamber, with solutions giving different humidities in the end sections. The solutions were chosen to give relative humidities of 100, 70, 40 and 20%, as checked using cobalt thiocranate papers. All the experiments were carried out at 2000, and 257 under artificial illumination of 60 foot candles. To cancel out any effects of uneven illumination, each apparatus was rotated through 180° halfway through each experiment. The beetles wore inserted through the holes in the lid of each arena, and the numbers in each half counted at five minute intervals for 50 minutes. The relative numbers of beetles which aggregated at each end wore used to calculate an index of the humidity reaction from the formula first used by Gunn and Cosway (1938):

100 (W — D) Index of reaction - (W + D) where W and D are the total numbers of insects in the 'wet' and 'dry' halves of the apparatus.

The response of the beetles to light was investigated using simple choice chambers of 3*" diameter plastic potri dishes, lined with moistened white filter paper. The top and side of half of the lid of each dish was lined with black paper, and the set of five such dishes was illuminated artificially from above. The illumination could be altered to give a choice of between 20 and 1.2, or of between 90 and 2.4 foot candles in the centre of each half of the dishes. These levels of illumination are low, but similar to those found near the bases of the grass. All the experiments were carried out at about 20°C, and the humidity was kept high by the moistened paper in the baso of each dish. The beetles were placed in the contra of each dish, and the numbers in each half counted at five minute intervals for 20 minutes; the lid of each dish was then rotated through 180°, so that the dark half became illuminated, and the experiment was then continued as before for a further 20 minutes to see if the abrupt change in illumination caused the beetles to alter their positions again. 258

An index of reaction towards the dark side was then calculated in the same way as that used to express the humidity results.

The responses to tactile stimuli were investigated because it was considered that the increased density of stems and leaves in the tussocks might bo of importance. Choice cheiabers wore made in 3111 diameter plastic dishes; those were filled to a depth of 0.5 ems. with polyester wax, which was then covered with filter paper. Headless entomological pins, long and .022" diameter (24 s.w.g.) were then stuck into the wax in regular patterns, using different densities of pins in each half of the dishes.

The densities used wore 0,4, 3 and 16 pins per sq. cm., with six chambers containing all the possible combinations. Most of the experiments wore carried out at 20°C with the filter paper moist, and with artificial illumination of 20 foot candles, but in a few cases dry filter paper, no light or low temperatures were used. The experiments lasted for 20 or

30 minutes, according to the species used, end the positions of the beetles wore noted every five minutes.

To investigate the reactions of the beetles to olfactory stimuli, the perspox choice chambers already described in connection with the humidity experiments were used; the only modification was the insertion of a semicircular clear plastic partition at each end of the arena to round off the corners, and thus reduce the thigmotectic end effects.

Three olfactory substances were usedg crushed green Dectylis loaves, crushed dead Dactylis loaves, and mixed grosses, mainly Festuca from between the tussocks. Activated charcoal was included as a control substance. Six choice chambers were used to obtain all combinations of the four substances, which were placed in the end sections of the base of 259 each chamber, with water in the adjacent sections to keep the humidity

high. The experiments wore conducted at 20°C, in darkness except when

the positions of the beetles were noted, which was done every five minutes for 20 minutes.

(b) Results.

(i) Temperature.

Experiments wore carried out on all three species, with the apparatus

with a bare metal floor, and also lined with both dry and moist filter

paper. The results ore shown in Fig. 49, in which the percentage in each

section of the total number of beetles, n, is plotted against the corres-

ponding moan temperature in that section for each experiment.

S. clavicornis was almost confined to the coldest end when the

humidity was low; it was more common at temperatures up to 25°C, however,

when the humidity was high, although it still avoided temperatures above

2500.0 ,end the greatest numbers were still found at the cold end. The

mechanism of aggregation at the cold end was orthokinesis, the beetles

becoming less active as the temperature decreased. The hot end was

avoided by a klinokinetic reaction, as the beetles not only moved more rapidly, but changed direction frequently in en apparently random manner until they moved into cooler regions. At high humidities the avoiding reaction was loss extreme, as the beetles were loss active, and tended to move through all positions except the vary hottest, unless reduced to

immobility at the cold end.

Host specimens of D. melanocephalus aggregated at the cold end, but there was a distinct second peak between 20 and 27°C when the humidity was low, which was extended up to 30°C when moist filter paper was used. °A of S.clavicornis p. melanocephalus D. I inearis beetles Surface 70 R e 60 sult 50 metal s 40 of t 30 em 20 per 10 at 0 ure 70

pref dry 60 Paper e 50 ren 40 ce 30 e x

pe 20 ri 10 moist m

e paper

nt 0 s 40 . 30 20 10 0 10 15 20 25 30 10 15 20 25 30 30 Temperature (°C ) 261

In this species also, the individuals which aggregated at the cold end

were simply "trapped" by their reduced speed of movement, but the pref-

erence for the warmer region was distinct. They were active between 20 and 27°C, but only short runs wore made, with apparent klinokinotic responses both above and below this region. As with S. clavicornis, the

preference was less restricted when the humidity was high.

A similar concentration of beetles at higher temperatures was shown by D. linearis; only about 20% of the beetles aggregated at the cold end in dry conditions, and there was a definite "preference" for the 24 - o 27 zone. When the humidity was raised, however, over 30% of the beetles wore found at the cold end, and the distribution at higher temperatures was much more even. The mechanism of aggregation in this species was similar to that in D. melanoceohalus, but in this case humid conditions reduced the klinokinetic reaction above and below the "preferred" zone, so that more beetles either moved down and were trapped at the cold end, or moved to the hot end where they were injured by the heat, so that their movements became uncoordinated.

The significance of these results to the field conditions in winter is that all three species will tend to concentrate in colder regions, once the temperature is below their "preferred" active range. In winter the night temperatures are too low for the beetles to be active, and in the day the tussocks are cooler than the intervening grass, so that the

"preferred" range is not reached.

(ii) Rotative humidity.

Humidity preference experiments were only carried out on S. clavicornis and D. melanocophalus. The results of a single set of experiments on S. clavicornis, with ton beetles in each, are shown in Table 64, 262

which gives the humidities in each hat', and the resulting index of

reaction, in each choice chamber.

Table 64. Humidity reactions of S. clavicornis.

High Alternative humidities 100 100 100 70 70 40 Low 70 40 20 4D 20 20

Index of reaction +0.54 +0.64 +0.33 +0.24 +0.30 +0.38

In every case, most of the beetles aggregated at the more humid end of the

apparatus, showing that the species is hygrophilous. This reaction would tend to keep S. clavicornis in the tussocks if the grass between the tussocks dried out to any extent.

D. melmocephalus showed an initial reaction towards the less humid ends of the chambers, which conflicted with its occurrence in one of the most humid parts of the habitat. Perttunen (1951) showed that some carabid beetles had an initial response towards low humidities, which changed to a hygrophilous reaction after they had been exposed to dry air for varying lengths of time. This was tested with D. molanocgphalus by keeping six sets of 10 beetles at 70% R.H. and 10°C, and testing their humidity reaction at intervals. The beetles were also weighed before each set of experiments to soc what loss of weight by dessic0tion was needed to reverse the humidity reaction. The results aro given in Table 65.

The mean index of reaction, and percentage loss in weight of each set of experiments are plotted against the total time spent at 70% R.II., in Fig. 50C. There was a steady change from a 'dry' reaction to almoistl ono until after 140 hours, when there was no further increase in the hygrophilous reaction, although water loss was still taking place.

263

5 cm.

B 0 ot 0 0 0

Mean intensity of loss reaction " of weight C

-0-5 • s. -30

+1-0 . 0 50 100 150 Hours at 70% R.H.

Fig. 50. A. Humidity reaction apparatus, side view. 13. tt ti plan. C. Change in humidity reaction of D. melanocephalus after desiccation at 70. R.H. 264

Table_61. Humidity reaction of D. melanocenhalus kept at 70% relative humidity.

Alternative Hours at 70 R.H. humidities 28 70 100 140 100 100-70 -0.66 -0.44 +0.32 -0.36 -0.28 -0.25 100-40 -0.84 -0.44 -0.16 +0.52 +0.56 +0.95 100-20 -0.74 -0.36 +0.24 +0.52 +0.72 +0.69 70-40 -o.60 -0.80 -0.12 -0.16 +0.68 +0.03 70-20 -0.38 -0.12 -0.24 +0.08 +0.32 +0.24 40-20 -0.16 +0.04 -0.12 -0.12 +0.36 +0.56

mean index of -0. +0.39 reaction 56 -0.35 -0.01 4.0.08 +0.37 % loss in 0 26.6 weight 2.4 10.5 15.3 20.3

The mean index of reaction changed from negative to positive after the

booties had been kept for 70 hours at 70% R.H., and had lost just over 10% of their original weight. In the early experiments the intensity of

the 'dry' reaction was not evidently correlated with either the steepness

of the gradient or the maximum humidity available. After 190 hours all the booties were hygrophilous except those in the 100 - 70% R.H. choice

chamber, where a 'dry' reaction was still recorded. The importance of this behaviour to D. melanocephalus is not certain.

Of the three species of Carabidee which Perttunen (1951) found to show a

similar reversal of reaction, two (Harpalus) normally live. in dry

habitats, and only move. into moist situations when strongly desiccated. The third (Odacantha) lives at the bases of :slants in damp situations, but climbs the vegetation to feed. It was suggested that the initial dry reaction allowed this species to climb up the stens where the humidity was lower, until it was sufficiently desio.cated to become hygrophilous, and move down again. Such en explanation night apply to D. nelanocephalus,

but its habits outside tussocks are still not clear. 265 (iii) Light.

ExporLionts on light reactions were only carried out on S. clavicornis, except fora single experLient with D. uolanocoehalus. Five choice chaLabers were used, with 10 beetles in each; one sot of oxperileents was done at each of the light intensities already given. The results of each sot of experiuents aro shown in Table 66.

Table )(). Light reaction experieents. using S. clavicornis.

Duration of 10 45 50 exporieent 15 20 25 30 35 40 (Ans.) tornative light °1 20-1.2 intensities (foot= +.20 +.40 +.68 +.64 +.44 -.08 -.08 +.28 +.28 +.12 candles) 90-2.4 +.12 +.28 +.44 +.52 +.40 +.20 +.30 +.52 +.72 +.76

/1' lid rotated through 180°

The initial reaction was towards the dark side of the chaJbors in both sots of oxporiuents. When the lighting conditions in the two halves wore reversed, the redistribution was rather slow in the loss extreue gradient, but rapid in the experLionts where a brighter light was used. The two halves of each experident show the difference in reaction between disturbed beetles which are finding their own resting sites, and stationary beetles which arc subjected to a change in light intensity; only in the latter case does the intensity of the light influence the index of reaction. The single experLient which was carried out using D.

CCTJhnlus showed that it was also negatively phototactic; the indices of reaction were 0.93 and 0.20 in the two halves of the exporLient, with alternative light intensities of 20 and 1.2 foot candles.

As the light intensity is always lower in the tussocks than in the intervening grass, these reactions would tend to keep the beetles in the tussocks. 266 (iv) Tactile Stimuli.

The results from the choice chambers containing different densities of pins are shown in Table 67. All three species were used, and details of the numbers of beetles and experiments are included in the Table.

Table 67. Results of experiments on reactions to tactile stimuli.

D, melano- Beetle species S. clavicornis rephaTis D. linearis Temperature (°C) 20 6 20 20 20 State of substrate Moist Moist Dry Moist Moist Light intensity (foot- candles) 0 0 0 20 10 No. of beetles per expt. 15 15 10 10 10 No. of sets of expts. 6 6 4 6 5 Alternative pin densities (no. per sq-cm.) 16 - 8 -0.15 -0.17 +0.17 +0.33 +0.44 16 - 4 +0.05 +0.28 +0.38 +0.56 +0.69 16 - 0 +0.54 +0.50 +0.52 +0.84 +0.97 8 - 4 +0.17 +0.40 +0.19 +0.29 +0.37 8 - 0 +0.38 +0.54 +0.15 +0.73 +0.62 4 - 0 +0.50 +0.19 -0.02 +0.81 +0.74

The indices of reaction are positive when the reaction is towards the denser half of the dish, and vice versa. Under humid conditions,

S. clavicornis always aggregated in the denser part of each dish, except in the one containing the two highest densities, where the numbers of beetles were slightly gre;Aer in the side containing eight pins per sq. cm.. The index of reaction was greatest when the choice was between 0 and 16 pins per sq. cm.. There were no consistent differences between the results obtained in moist conditions at 20 and 6°C. Under dry conditions at 20°C, however, a positive reaction was shown between the two highest densities, but there was no distinction between the two halves of the chamber with 0 and 4 pins par sq. cm.. Thus the lowest densities were not distinguished at low humidities, and the highest at high humidities. This is probably a result of the decreased activity under 267

humid conditions. The mechanism of aggregation in the dense pins was a

reduction in movement when in contact with an obstacle. In high humidit-

ies all activity is stopped by a density of S pins per sq. cm., and thus

there is no difference at higher densities than this. At low humidities

the activity at 8 pins per sq. cm. is higher and leads to aggregation at

densities higher than this, whereas a density of 4 pins per sq. em. is

insufficient to stop the beetles for long enough to give any significant

difference from no dins at all.

Both species of Dro:lius were more strongly positively thigmotactic

than S. clavicornis; the intensity of the reaction was greatest when

half of the dish contained no pins, but otherwise was proportional to the

ratio of the densities in the two halves. The specimens of D. melanocemh-

alus had not been desiccated, and were therefore active at high humidity,

and able to discriminate between the two highest pin densities.

Thus all three species show a strong tendency to aggregate where

the density of obstacles is highest; as the tussoc.Ks are very dense

compared with the intervening grass, this would tend to keep the beetles in the tussocks.

(v) Olfactory stimuli.

All three species were tested in the olfactory choice chambers. Six sets of six experiments were carried out with S. clavicornis and three with each of the species of Dromius, with 50 beetles in each experiment.

The results are given in Table 68. Each index of reaction is profixod by a letter which indicates the direction of the reaction, as follows :

charcoal.

Dl = Live Dactylic leaves.

Dd 2 Dead Dactylis leaves.

Festuca loaves. 268

Two sets of four control experiments with similar substances at each end of the choice chambers wore also done on each species, and the 95% confidence limits of Students 'V are given for the mean control index of reaction for each species. Tho experimental indices which lie outside these limits are marked with an asterisk, and are significant below the

level.

Table 68. Results of olfactory choice operiments.

Alternative substances Species S. clavicornis D. molanoce halus D. linearis C - D1 Di 0.59* 0 0.64 * C 0.49 * C - Dd Dd 0.64* C 0.43 C 0.24 C - F F 0.57k C 0.47 * C 0.57 * D1 - Dd Dd 0.26 0 Dd 0.13 D1 - F F 0.63* Dl 0.05 F 0.19 Dd - F F 0.6 * F 0.03 Dd 0.04 95% confidence limits of control indices 0 - 0.409 0 - 0.441 0 - 0.448

S. clavicornis was significantly attracted to all of the crushed leaves in preference to charcoal, and preferred Festuca to Dactylis leaves either living or dead, between which it showed no preference. In contrast, both species of Dromius preferred the charcoal to all of the olfactory substances, and did not show any significant preferences between the types of crushed leaves.

kiparently the only preference which might be of importance in the field was that of S. clavicornis for Festuca, which would oppose its occurrence in the tussocks.

The following is a summary of the possible significance of tho results presented in this section, taking each factor separately. In the 269 field the beetles are subjected to all these factors simultaneously, but few of their interactions have been studied. Many of the factors support one another, however, in keeping the beetles in the tussocks.

Tho temperature reaction of all three species tends to keep them in the tussocks at the temperatures experienced there in winter. The hygro-

philous behaviour of S. clavicornis traps this species in the tussocks, although the initial 'dry' reaction of D. melanocephalus acts in the opposite direction. The negative reaction to light of the two species tested mckes the tussocks more preferable to them in the day. The thigmotactic responses of all three species also keep them in the tussocks. The

Dromius species were more strongly thigmotactic than S. clavicornis, and this may explain why D. melanoceehalus, but not S. clavicornis showed a strong positive association with tussock density (c.f. multiple regression analysis). S. clavicornis was attracted to the smell of crushed Festuca from between tussocks. It is not known whether this odour is present in the field, but if so it would tend to attract the beetles out of the tussocks. The Dromius species did not show any significant olfectory reactions.

Thus nearly all the reactions of these three species that were tested tend to trap them in the tussocks: the only exceptions are the initial humidity reaction of D. molanoc22halus, and the olfactory reaction of S. clavicornis. 270 3) Movement out of tussocks.

(a) Methods.

Largo numbers of beetles were never available when they were actually leaving the tussocks, and the only experiments which were carried out wore designed to find out whether e definite period of emigration took place, and whether this could be affected by altering the tussocks.

To see whether there was a distinct period of emergence from tussocks, which was suggested by the abrupt fall in numbers of S. clavicornis in April 1962, a 10" diameter tussock was surrounded by 20 pitfall traps made of 2" x 1" specimen tubes, which were situated beneath the dead leaves around the tussock; and spaced 2" apart from one another.

Fifty individuals of S. clavicornis were marked with white lacquer as before, and put into the centre of the tussock at dusk on April 19th.,

1963. The numbers of beetles, both marked and unmarked, in the pitfall traps were then observed daily until May 13th.

The following year, sets of 10 tussocks were altered in various ways as in the autumn experiment previously referred to (p.250), but this was done at the beginning of January, when they contained large numbers of beetles. In mid-April, before general sampling showed that the beetles had loft unaltered tussocks throughout the area, the altered tussocks and ton unaltered controls were sampled to detect the effects of alterations on the fauna.

To see whether the reductions in height of the tussocks lead to rapid emigration of the beetles, pitfall traps were installed around the

bases of two tussocks which had been cut down to 6" and 1-P1 high 271

respectively, and around an unaltered control tussock. These pitfalls

wore examined at frequent intervals between January 23rd. and May 10th.

(b) Results.

The numbers of beetles which were caught in the pitfalls around the

tussock containing marked S. clavicornis are shown in Fig. 51A. 1ithin

five days from the start of the experiment, throe marked and two un-

marked S. clavicornis were caught, together with several specimens of

Dromius. After this, no more marked individuals wore found, but unmarked

S. clavicornis occurred until May 5th. From this it was concluded that

the numbers caught were probably high initially because the beetles were

active after being disturbed by the introduction of the pitfalls, and

that the extended period of capture of S. clavicornis probably indicated that there was no definite period of emigration.

Pitfall traps around tussocks were examined over a much longer

period in 1964, and the results are given in Fig. 51B. All three sots of traps showed that S. clavicornis was active throughout the whole period.

The numbers caught tended to be highest soon after the traps were installed, but may have boon significantly reduced later by the loss of the beetles removed from the traps. Thus S. clavicornis (and probably also Dromius, of which a few were caught) is active under the dead leaves surrounding the tussocks throughout the winter when the temperature is high enough for activity. In April and 1,lay the beetles probably continuo to move away rather than return to the tussocks, as the numbers in the tussocks decrease, and specimens are found in pitfalls some distance from tussocks.

The results obtained by sampling in April the tussocks which wore altered in January are shown in Table 69. A

Marked x S. clavicornis o D. I inearis • D. melanocephalus Unmarked

April May 1963

1 1/2" high XX x

6" high x L x x xX

Unaltered XXXI •x XX X X control

in 111 111 I I 1 I Ja . Feb. Mar. April May 1964

7ig. 51. 3 B. Beetles caught in pitfall traps surrounding tussocks, 1963 and 1964, 273

Table 69. Results of alteration of tussocks experiment, January to April, 1964.

Number of beetles Treatment S. S. D. melan- D. clavicornis imoressus oce.halu linearis Total Cut down to 1" high 1 0 1 0 2 Cut down to 6" high 8 0 8 0 16 Cut down to 12" high 26 7 9 1 43 Surrounding dead 12 0 50 levos removed 35 3

Controls 31 5 10 0 46

Cutting the vegetation of the tussocks down to the 1" and 61t levels were the only treatments which significantly reduced the numbers of beetles. It is interesting that removal of the surrounding dead leaves, which prevented the numbers of S. clavicornis from increasing in autumn, hod no effect in this case, showing that the leaves are not important to the booties at this time of year.

As the beetles have been shown to move outside the tussocks into the adjacent dead leaves throughout the winter even inumattered tussocks, any emigration beyond this region would probably not be shown by pitfall captures close to the altered tussocks. Slightly more beetles yore caught around the 6" high tussock than around the control, but very few emerged from the 1" high tussock. This may indicate that the beetles cmcrLed from the 6" high tussock, but were killed by the extreme conditions in the shorter one. No valid conclusions can be drawn at this stage, however) as to -whether the reduction in the numbers in the shortened tussocks was caused by emigration, or by mortality resulting from the altered conditions in the tussocks. 274

B. EFFECTS ON SURVIVAL

1) Effects of low teneeratures.

(c,) Introduction and Methods.

Cold resistance in insects has been given various neanings by differ-

ent authors. Backlund (1945) doternined the tenpernturo at which various

species became. inactive, and used this as a measure of cold resistance,

but this is only the "chill-cona temperature" (Mollanby, 1939), or Sower

notility limit" (Landin, 1961), and is distinct fron the "cold-death point",

below which exposure is lethal. Only the cold-death point was investigated

in this work, to find out whether the temperature which the insocts exper-

ience either in or between the tussocks in winter are low enough to cause

death. Cold-death in nost insects is caused by freezing of the body

fluids, as few species are known which can survive freezing. Most species can supercool below tho true freezing point of their body fluids, and death occurs when they freeze at a toupernture known as the mundorcooling point"

(Salt, 1936). Thus the ability to supercool is a direct ucasuro of an

insect's cold-hardiness (Salt, 1956b); this can be altered by various factors such as the prosonoo of food in the gut (Salt, 1953) and the

insect's noisturo contont (Salt, 1956c), both of which raise the undercooling point. Conditioning at moderately low tomperr,turcs is known to decre-sc the chill-coma te:Iperaturc (Mollonby, 1939), but its effects on the uortality at sub-zero temperatures vary with the species tested. Thus acclimatisation was demonstrated by Payne (1926b) and by Mellonby (1939), but Salt (1956a) and Atwal (1960) found sone insects which did not show it.

Although the undercooling point of any species is the lowest temperature that it can survive, cold-death can also take place on freezing 275 at any temperature between this lowor limit, and the true freezing temeerature. of the body fluids (Salt, 1950). Freezing at these inter- medlato temperatures can be either endogenous, commencing with the formation of on ico crystal nucleus in the body fluids, or exogenous, when the body fluids arc inoculated by contact with ice outside the body of the insect. These two ty)es of freezing have been termed "nucleative" and "inoculative" by Salt (1963). The probability of occurrence of both typos is determined both by the temperatur9 and the time spent at that temperature, which correspond to the intensity and quantity factors of cold, described by Payne (1927), so that the lower the temperature, the shorter the time required to freeze any given proportion of the population. The probability of inoculative freezing is also dependant on the ox-ont of the surface of the insect which is in contact with ice, and on the properties of the insect's cuticle.

In this study, undercooling point determinations were carried out to find the temperatures which were instantaneously fatal to the beetles.

Specimens wore also kept for longer periods in contact with moist surfaces at sub-zero temperatures above their undercooling points to investigate the mortality caused by inoculative freezing at these temperatures, both in the laboratory and in the field.

Previous methods of determining the undercooling Joints of insects have been based on measuring the body temperature thereto--electrically while the insect was cooled in a container, usually by immersion into alcohol which was kept cold either by a cooling coil (Salt, 1936) or by adding solid carbon dioxide (Way, 1960; Sullivan and Green, 1964). The insect should not be pierced by the thermocouple as this results in inoculation. The method used in this work differed in that the indiv- 276 idual insects in a holder wore cooled by contact with a thermoelectrical device known as a "Frigistoru. This is a block of semiconductor material with the property that when a direct current of about 10 c„-Lps is passed through it, a temperature differential is developed between its faces. If the "hot" surface is kept cool artificially, the "cold" surface con be cooled as low as -20°C. A second frigistor with its hot face placed on the cold surface of the first, will have a cold face correspondingly colder, and in practice two wore used in this way to give temperatures of down to -350C on the surface of the upper frigistor.

Details of the construction of the apparatus are shown in Fig. 52A.

The two frigistors wore joined together only by a coating of sealing wax at the sides, as they were required for individual use in the future.

The lower frigistor was stack with "Araldite" to a metal block through which cooling water could pass via a system of tubes (shown in simplified form). The water circulation was by gravity from a tank above the apparatus to another on the floor, and could be controlled with the tap below the apparatus. The two frigistors were wired in series electrically, end connected to a variable voltage power supply whioh gevo up to 15 o:aps at about 1.5 volts D.C.; for the lowest tomporatures, about 12 amps were required. A semicircular tunnel of copper foil was attaahcd with adhesive tape to the cold surface of the upper frigistor, and the insects were inserted into this tunnel in a cylindrical probe. The frigistors and cooling block were enclosed in a close fitting box of expanded poly- styrene (omitted from Fig. 52A) to provide insulation from the high ambient temperature in the laboratory. 277

A Copper tunnel Probe containing beetle

Probe To frigistor 4-Z r4 Cfli thermocouple power supply Frigistor thermocouple Upper frigistor —Lower frigistor Cooling water inlet Metal block

Cooling water outlet

B Glass tube Plastic collar Thermocouple

Sealing wax Plastic tube containing 1 cm. beetle C D.C. amplifier Thermocouples : and recorder 4 1 B A 1. Probe Calibrating potentiometer 2. Ice (zero check)

D 3. Frigistor surface

Frigistor and 4. Cooling water water temp. microammeter 5. Ice (reference junction)

Fig. 52. Undercooling point determination apparatus. A. Details of arrangement of frigistors. B. Section of end of probe containing beetle. C. Circuit diagram of control box. 278

The end of the probe in which the beetles were inserted into the

apparatus is shown in cross section in Fig. 52B. Tho probe itself was

made of glass tubing, 5 mm. o.d., drawn out at the tip, over which was

fitted a plastic collar. Two thermocouple wires lead down the inside of

tho glass tube, and wore extended by very fine -wires (45 s.w.g.) for 8

mm. beyond the end of the glass. The wires were held in place by sealing

wax which was melted in the tip of the glass tube and allowed to set around

the junction of the two thicknesses of wire. Each beetle was placed in

a single ended plastic tube, 13 mm. long and 1.5 nun. i.d., with a pin

hole at the closed end to enable the beetles to be poked out after

freezing. TAThan the tube was placed on the end of the probe, the beetle

was held between the side of the tube and the thermocouple. As the

beetle was cooled, its temperature was recorded on a chart by a Fielden

"Servograph", via a control panel and a D.C. amplifier. The circuit of the control panel is shown in Fig. 52C. Four thermocouples wero used,

with their constanten wires (thick linos on diugram)connected to a reference junction in melting ice at 0°C. The probe thermocouple (No. 1)

was connected by switch B to either the amplifier and Servograph, or to

a "-Doran" thermocouple potentiometer for calibration purposes; switch A

could be used to connect either of these instruments to thermocouple 2, which was also in melting ice, to give a zero calibration point. Thermo- couples 3 and 4 measured the temperatures of the frigistor surface and the cooling water; either could be connected to a microamLL:ter by switch C. Switch D was included as a protective device to short circuit the delicate microallunoter movement when it was not in use.

The operating procedure for the apparatus was as follows. The

D.C. :amplifier and Servograph were switched on, and allowed to warm up for 279

at least 15 minutes. The frigistors were then switched on, and the upper

surface temperature adjusted to the correct figure (usually -30°0). The

empty probe was then inserted into position above the frigistors, and its

temperature measured using the Doran potentiometer. It was then connected

to the Sorvograph, which was calibrated from the potentiometer reading,

and the zero thermocouple. Once this calibration was completed, the under cooling point determinations could be started. Each beetle was

inserted into a separate dry tuba on the end of the probe, to avoid

inoculation by water which condensed on the used tubes when they wore withdrawn from the apparatus. The falling temperature was recorded on the Servograph, and when freezing took place there was a sudden rise in temperature as the latent heat of freezing was released. Theoretically, the temperature should rise to the true freezing point, but in practice cooling takes place again too rapidly, so that the body temperature rises a few degrees at the most, and then falls again. Fig. 53A shows a typical trace; the point at which the body temperature suddenly rises is the undercooling point. Only about 30 seconds were taken to reach -10°0 from room temperature, but the rate of cooling does not affect the undercooling point if it is f,L ter than about one degree per minute (Salt,

1961). The beetles used in both those and later cold resistance experiments were usually obtained from the field on the day that the experiment was started, and were Kept at 2 to 3°0 in a refrigerator for a few hours at the most before being used, in order not to remove any cold hardiness that they might have acquired in the field.

To find out the effects of loss extreme temperatures experienced for longer periods of time, beetles wore placed in a deep freeze cabinet 280 in plastic petri dishes lined with moist filter paper. It was found that there was a temperature gradient in the cabinet from -4°C at the top to

-13°C at a depth of 12", and a series of dishes was placed at levels corresponding to temperatures of -4.5, -7, -9.5 and -13°C. A fifth dish was kept in a refrigerator ice box at -2.5°C. Thermocouples were attached to the bases of all the dishes to chock their temperatures. Fifty beetles were put into each dish, and their mortality examined each day by warming them up to room temperature for one hour; specimens which wore still not capable of co-ordinated movement after this time were classed as dead.

This alternate warming and cooling probably resembled field conditions more closely than continuous periods below zero, and meant that one set of beetles could be used to estimate the mortality after varying lengths of time, instead of using a different sot at each exposure time.

To cogere this mortality with that under field conditions, beetles were gut into similar lined plastic petri dishes, which wore loft in the field on cold winter nights. Dishes were placed either in the open, under about 6" high thin Festuca, or under 12" high dense Festuca and Arrhen- athorum, which resembled the conditions in tussocks more closely. The dishes were too large to insert into Dactylis tussocks without altering the dense nature of the tussocks. Several replicates were usually planed in each position, and the temperature on the floor of one of each was measured by a thermocouple connected to the Sunvic recording potentiometer.

(b) Results.

(i) Undercooling point determinations.

S. clavicorniql D. molanocophalus and D. linearis brought from the field wore tested on five occasions between November 1963 and April 1964. 281 One sot of determinations was also made on beetles which had been kept at 1000 for three weeks, to sea if this treatment reduced their cold hard i- mass. In all the experiments the insects wore kept dry, so that freezing was nucloativo. In the field contact moisture is usually present, and a sot of determinations was carried out with the beetles placed in contact with both living and dead Dactylis leaves in the end of the probe, to see if these altered the under000ling points. Freezing always killed the insects, although specimens of S. clavicornis which wore supercooled below -15°C without freezing, and then warmed to room temperature, shoved no ill effects. The results of the dry undercooling point dcteruinations ::re shown in Table 70, and the aoan undorcooling points of S. clavicornis on each date ore graphed in Fig. 53D. Table 70. Dry undercoolinrr point determinations. ---- No. Undercooling_point (°C) Date caught Species of - specimens Mean Range 1.11.63 S. clavicornis 10 -14.72 -10.8 to -18.0 (kept at 10°C D. melanoceph- 6 -13.90 -11.0 to -15.7 for 3 'weeks) alus D. linoaris 4 -11.12 - 7.6 to -15.7 25.11.63 S. clavicornis 15 -13.58 - 7.3 to -20.0 D. molanocoph- -11.36 - 9.2 to -13.9 alus 5 D. linoaris 1 -11.1 - 9.12.63 S. clavicornis 16 -15.58 - 8.3 to -19.2 D. molonoceph- -9.83 - 6.0 to -13.9 alus 12 D. linearis 9 -11.09 - 5.4 to -15.2 30.12.63 S. clavicornis 15 -14.91 - 9.5 to -1L,9 D. mel. 4 - 6.5 - 2.5 to -11.1 D. linearis 5 -11.2 - 8.6 to -13.6 3.2.64 S. clavicornis 10 -13.86 - 7.3 to -20.2 D. mel. 6 -12.35 - 7.6 to -16.1 D. linearis -14,12 - 9.8 to -19.8 7.4.64 S. clavicornis 13 - 7.67 - 2.7 to .10,1 D. linonris 1 - q.2 282

0 963 1 U C o OJ L 0 01 I -10 0

L 12 Dec

of C 0 0 2 U L -o C

: is

CO n or ic v la c S.

01 C

= C 0 7, ) 0 a-

L tes 41 73

C inu 4:t

------(m I ime T

Fig. 53. A. Theoretical undercooling curve. B. Dry undercooling point of S. clavicornis throughout the winter. C. Effect of contact with leaves on the undercooling point. 283

S. clavicornis was the most cold resistant of the three species, and its undercooling point was lowest in December, rising gradually until April.

This seasonal variation in cold hardiness hap been found in other species

(Payne, 1926a, 1926b) and may be partly caused by reduction in water content, and emptying of the gut before hibernation. It has already been shown that S. clavicornis is active at intervals throughout the winter and probably feeds during this period, so that food in the gut during the winter must remove any cold hardiness caused by emptying of the gut. In practice, all the specimens were dissected after freezing, but no correlation could be found between the amounts of food in the gut and the undercooling point in any of the species. D. melanoceehalus males showed slightly less cold resistance than females, but the difference was not statistically significant; there were no differences between the sexes of the other two species. The results obtained from the beetles which had been kept at 1000 for three weeks showed that the temperature to which the beetles were subjected before testing did not affect their undercooling point; this is confirmed by the lack of any correlation between the undercooling points of specimens from the field, and the temperatures of the preceding days. Thus the factors which lead to the loss of cold resistance in the spring are not clear; it was thought that maturation of the ovaries might be involved, but this had not started in the specimens supercooled on

April 7th., which had lost most of their cold resistance.

D. 11pearis was slightly less resistant than S. clavicornis, and

D. molanocephalus was considerably so, although the resistance of D. melanoceohalus varied from date to date. The variations in undercooling point of all three species on any date was considerable, but the means were often very consistent from day to day. 284

S. clavicornis was the only species whose undercooling point was determined in contact with leaves. The results of five determinations in contact with dry and wet leaves, and succulent living leaf bases are shown in Fig. 53C. Contact with dry dead leaves did not significantly alter the undercooling point, but moist leaves raised it to between -4.5 and -9.0°C, showing that inoculation was taking place. With living leaves, there was extreme variation, from -4.5 to -16.7°C, so that inoculation took place in some beetles but not in others. As conditions in the tussocks are moist in winter, these results show that some mortality occurs as soon as a temperature of -4.5°C is reached, but some of the beetles that are sheltering among the bases of the living shoots may not be killed by short cold spells unless a temperature of -17°C is reached.

When cold resistance is lost in spring, this lower limit rises so that, by April, a temperature of -10°C will kill all the specimens, and as the upper limit of the dry undercooling point was only -2.7°C, some mortality probably occurred above this in moist conditions.

The mortality of D. melanocephalus and D. linearis in field conditions cannot be estimated from these data, but is probably greater than that of S. clavicornis, as they are less cold resistant in dry conditions.

(ii) Laboratory 'survival experiments.

The results of keeping S. clavicornis on moist filter paper in the deep freeze at temperatures between -2.5 and -13.0°C for up to 25 days are shown in Fig. 54A, in which the percentage of beetles still alive is plotted against log. time. The mortality increased with decreasing temperature down to -9.5°C, but there was no difference between the mortality at -9.5.and -13'.0°C. Salt (1963) found that the probability of inoculative freezing did not increase when the temperature was decreased below -10°C,

285 A

alive

05 1 2 3 4 5 10 15 20 25 Time (days) B C D.melanocephalus • cIo S. clavicornis Y =15•12x + 40-89. p <.001

Mortality _ „ _ 4 at_

-4 -5 -6 -7 -8 -9 -10 -2 -3 -4 -5 -6 -7 -8 -9 Minimum temperature (°C)

Fig. 54. A. or t;r2li hy of S. C? L:,47 (-to s kept at low temperatures In deep frreze. -13 r C. R('Lvessinns or mortality on minimum temperature during overnight exposure to field conditions. 286 and explained this on physical grounds. The results obtained from S. clavicornis support his theory, and indicate that the freezing in these experiments was inoculative, as the probability of nucleative freezing increases with decreasing temperature.

The mortality after one day was almost half of that after 25 days, so that relatively short exposures had a serious effect on the beetles.

Comparison with the undarcooling point data obtained from beetles in contact with wet leaves shows that the mortalities are less than those expected. When the insects were supercooled, 50% had frozen at -7.50, and all by -9.5°C, but after 24 hours in the deep freeze, there was only

17% mortality at -7.0°C, and 50% at -9.5°C. These figures are nearer to those expected in dry conditions. This suggests that although the insects were on moist filter paper, they were able to resist inoculation in some way, although this conflicts with the conclusion reached in the preceding paragraph.

(iii) Field survival experiments.

Beetles were exposed to low overnight temperatures in the grass on eight nights between December 1963 and February 1964. Only S. clavicornis was used until the end of January, after which all three species were used; ten beetles were put into each dish, with at least two replicates of each species in each height of grass. The results are summarised in

Table 71. Although continuous temperature records were made, only the minima reached on the floors of the dishes in each type of grass are included, as it was found that these were significantly correlated with the mortality, and attempts to take the duration at each temperature into consideration did not increase the significance. The duration of 287 exposure was similar in all the experiments, from 1700 until 1000 the folldwing morning.

Table 71. Mortality of beetles exposed to field conditions on cold nights.

Exposed Under 6'1 grass Under 12" grass Date Min. % Mortality Min. % Mortality Min. % Mortality temp 6-. D. D. temp S. D. D. temp S. D. D. (c1C) clay. mel. 17.n. (°C) clay. mel. lin. (°0) clay. reel. tin. 1--- H 0 22/23.12.63 -8 90 - - 0 - - 23/24.12.63 -6.5 55 - - -4.5 - - - -

16/17.1.64 - - - - -2 0 1 - - -8.5 30 a 000 0 17/18.1.64 -10.5 45 - - -4.5 k_ - - -2.5 - - 3 •

6/7.2.64 -10.5 65 100 100 -6.0 ok. 40 50 -4.0 30 0

7/8.2.64 -6.5 45 100 50 -3.5 0L 0 0 -2.5 0 0 8/9.2.64 -5.0 17 20 20 -2.5 0 0 -2.0 0 0

) 0000 20/21.2.64 -8.5 42 100 100 -4.5 t‘ 00 20 0 -2.5 0 0 Mean -8.0 48.6 80 68 -4.2 12.5 15.0 12.5 -2.61 0 7.5 0

These data also show S. clavicornis to be the most, and D. melanocephalus the least, cold hardy of the three species. With no protection by the grass, there was often considerable mortality of S. clavicornis, and all the Dromius were killed on two occasions; 6" high grass reduced the mortality considerably, and 12" high grass gave complete protection to S. clavicornis and D. linearis.

The regressions of mortality of each species on the minimum temperatures experienced wore calculated, and these data are shown in Figs.

543 and C. The regression for S. clavicornis was not quite significant at the 5% level (P 4. 0.10), but those for the Dromius species were highly sig- nifioent. (P < .001). The regression lines show that at temperatures of about -4°C, the mortality of all three species is similar, but at lower temperatures the mortality of the Dromius species increases more than that of S. clavicornis. The mortality of S. clavicornis was similar 288 to that when it was supercooled in contact with wet leaves; thus 50% mortality occurred at -8.5°C in the field, and half the specimens froze above -8°C in the laboratory. Thua inoculation by contact moisture appeared to take place in these experiments, although possibly not in the deep freeze at similar temperatures.

The following conclusions can be drawn from these experiments. i) Of the three species, S. clavicornis is the most cold hardy, and

D. melanocephalus the most susceptible to low temperatures. ii) The dry undercooling point of S. clavicornis ranged from —9 to -20°0 in December, but rose to between -3 and -10°C in April. The factors influencing cold hardiness, causing both individual and seasonal variations, were not clear. iii) Contact with moist leaves raised the undercooling joint of S. clavicornis to between -5 and -10°C, by causing inoculative freezing. iv) In the deep freeze, the mortality of S. clavicornis on wet filter paper was similar to that expected in dry conditions, which suggested that little inoculation was taking place. v) Then exposed to low temperatures in the field, more died than at similar temperatures in the deep freeze, and inoculative freezing evidently occurred. vi) 6" high grass reduced the mortality in all species, and only a few

D. melanoce3halus died at the base of 120 grass. vii) Hortality of all three species starts at about -4°C, by inocul-

ative freezing, but S. clavicornis can withstand lower temperatures than Dromius because the individuals which are not inoculated have 289 lower undercooling points, and therefore a lower probability of nucleative freezing above this. Thus, all Dromius individuals, but only

50% of S. elavicornis, are usually killed in a night when the temperature falls to —8°C. viii) The regression lines of Fig. 54B can be used to estimate the mortality in the field after known temperature extremes have been experienced.As the rclAtJnships between the temperature minima in the grass and in standard meteorological sites have already been given (p. 115) the theoretical mortality in the grass can be estimated from the standard

"grass minimum" records. 290

2). Protection from predators.

(a) Methods.

The precipitin test was used qualitatively to find out whether pred-

ators outside the tussocks fed on Stenus and Dromius. The suspected

predators were the carabid beetles, Pterostichus spp. and Abax parallel-

opopidus (Pill. and Mitt.) which were common between the tussocks on

North Gravel in summer. This method has been used to find out whether

these carabids feed on pupae of Phytodocta by Dempster, Richards and

Waloff (1960). The test is based on the interaction of Stenus or Dromius

material in the gut of a predator with antibodies in the blood serum

of rabbits which have been injected with an extract of Stonus or Dromius.

The antigen and antiserum were prepared by Dr. Dempster, and full details of the methods used have been given by Dempster (1960), as well as subsequently by Rothschild (1962) and by Watmough (1963). Only details

which differ from the methods of these authors aro given hero.

About seven grams of freshly killed Stenus or Dromius were needed for the injection of one rabbit; this required about 2,500 S. clavicornis, or 4,500 Dromius (with at least 25 of the heavier D. linearis)4 Deetlos

more collected from tussocks in the winters of 1962 - 3 and 1963 - 4, and kept alive until at least a gram at a time was available for the preparation of antigen. Dy the end of January 1964, 3,000 Stenus had been collected, which weighed 0.35 grams, and injections were started. More than three grams of Dromius were collected in the winter of 1962 - 3,

but both D. molanocephalus and D. linoaris wore less common in the following winter, and insufficient material for injection was collected, so that only Stenus antiserum was prepared. 291 A satisfactory antiserum should react with a dilution of between

1:1000 and 1:4000 of the original antigen used for injection. The anti-

Stenus serum, however, had a sensitivity of only 1:400, which was not

increased by subsequent injections. This may have been a result of the

reaction of the rabbit which was used, but insufficient Stenus were

available to inject a second rabbit, and it was decided to use the serum

available. The serum was tested for cross reactions with the following

genera of beetles also commonly found in tussocks; Trechus, Dromius)

Tachypollia, Xantholinus, Conosomus, Acrotona, Amischa and Rhizobiellus,

as well as with Pterostichus and Abax. No cross reactions were found,

however, possibly as the antiserum was already of low sensitivity.

Gut smears were made from 371 Carabidnal collected from pitfall

traps between August 22nd. 1962 and June 17th. 1964, and from 47 which

had been fed with Stenus in the laboratory at various intervals of time

before they were de-gutted. All the Carabidee which were tested fed

readily on Stenus when confined in 311 diameter plastic boxes with a base

of moist plaster of paris. These test meals showed that Stenus was det-

ectable in the gut up to 12 hours after it was eaten by starved carehids

ke2t at 20°C. In the field the rate of digestion is probably slower,

as the beetles are unlikely to have been starved, and the temperature at

ground level is cooler than that in the laboratory; thus Stenus remains

aro certainly detectable after 12 hours, end possibly after longer

periods) in the guts of carabids from the field.

(b) Results.

The numbers of guts of each species which were tested, and the

positive results obtained in each year aro given in Table 72. The total number of beetles tested (T), and the number of positive results (p) 292 are Listed under each species.

Table 72. Results of precipitin tests with anti-Stenus serum.

Carabid spades Annual Year P. madidus P. niger P. melanarius Abax totals T P T P T P .T P T P 1962 (August) 8 1 8 0 0 0 2 0 18 1 1963(Apr.-Nov.) 201 18 14 1 7 0 18 3 240 22 1964(Jan.-June) 89 4 6 0 2 0 16 0 113 4

Species totals 298 28 28 1 9 0 36 3 371 27

Seven per cent. of all the tests gave positive results, which shows that these predators do feed on Stenus in the field. The differences

between the throe years, and between the various carabid species are not significant, and more tests would be needed to give quantitative data on the mortality caused by these predators. Fifteen of these large carabids were also found in tussocks during the three years of study, so that this microhabitat cannot give complete protection for its fauna. The numbers of carabids outside the tussocks, however, are very much greater, so that the larvae which do not leave the tussocks in summer must be protected from predation by Ptorostichus and Abax to a large extent, whereas the adults which are active between the tussocks are much more likely to be eaten. 293 V. DISCUSSION.

Few previous attempts have been made to study grass tussocks as micro-

habitats in which insects live, and their importance in grassland ecology

has not been considered. As intended in the introduction to this thesis,

data have been obtained on the numbers of beetles both in and between

grass tussocks, and on the microclimatic characteristics of these micro-

habitats. Some investigations have also boon carried out into the effects

of the microhabitat on the behaviour and survival of the beetles. Those

data can now be compared with the work of other authors on similar

subjects, and their significance considered.

It must be remembered that previous grassland surveys have included

the fauna of the upper layers of soil with that of the vegetation, when

comparing their data with those from tussocks. The number of species

of beetles per 1000 square inches in tussocks was 80.1: .comparable figures

which have been calculated from surveys in which the total sample area

was given are 50.3 in a field containing Dactylis (Morris, 1920), 35.4

in arable land (Edwards, 1929), 38.7 in a rough pasture field (Ford,

1935) end 40.3 in Corynephorus grassland (Schjiftz - Chistensen, 1957).

The numbers of species in all these surveys were considerably less than in

Dactylis tussocks, which emphasises the large number of species found in

tussocks.

Elton (1933) considered that not more than 200 species of animals

were likely to be found in any one habitat, As almost 200 species of

beetles alone were found in tussocks, this idea of a limit to the number

of species in a habitat would seem to be invalidated. The large fauna

found in tussocks, however, may result from the extensive sampling over

a long period of time, or from the complexity of the typo of habitat, 294 at the border of arable, heath and wooded land.

The equitability component of species diversity of the tussock beetle fauna was lovi (0.298), which shows that the large number of species contains a high proportion with a few, and a small number with many, individuals. This method has not yet boon applied to other habitats except to the mosofauna of beech litter (Lloyd and Gholardi, 1964), from which a figure of 0.59 was obtained. If it is used more widely, it should enable the relative proportions of common and rare species in different habitats to be compared. The number of species with few individuals in tussocks was greatest in winter, which confirms the suggestion of Pearce (1948) that many species which do not usually inhabit tussocks enter them at that time. The presence of a relatively small number of common species does show, however, that the tussocks may form a permanent habitat of some species.

The density of beetles has already been calculated as 784,080 per acre in the areas between tussocks, and as 1,037,380 per acre when tho tussock fauna was included. Comparable figures from surveys of surface vegetation excluding tussocks are 744,038 per acre in a field with

Dactylic (Morris, 1920), 163,000 per acre in arable land (Morris, 1927),

580,800 par acre in a pasture field (Ford, 1935) and 126,509 per acre in Coryne)horus grassland (Schj/tz Chistensen, 1957). The numbers between the tussocks on North Grovel were similar to those obtained by

Morris (1920) and Ford (1935), but when the fauna of the tussocks was included the total density was considerably higher than that found by these authors. Thus surveys of the insect fauna of grassland which contains tussocks may seriously underestimate the density of booties, unless the fauna of the tussocks is sampled as well as that of the intervening grass. 295

The direct comparison of microclimatic measurements made in various

typos of vegetation is difficult, as roadings are taken on different dates,

and in different weather conditions, and two situations in the same veg-

etation are unlikely to have identical conditions, oven at the same time.

Such data, however, can show how the type of vegetation affects the micro-

climate near the ground, and as the structure of tussocks is now known,

their microclimate can be correlated with this. Geiger (1950), Champness

(1950) and Waterhouse (1955) have all shown that the outer effective

surface is raised as the vegetation becomes taller, so that the temperature

is less variable near the ground. Broadbent (1950) and Penman and Long

(1960) show that increasing the density of plants has a similar effect.

In Dactylis tussocks in hot weather the warmest level is about two feet

above the ground, but it is only eight inches high in more open lax hay

Dactylis (Hughes, 1954), which shows the effect of the greater density

of the tussocks. In the more open intervening grass, about six to nine

inches high, most radiation is absorbed at the three inch level, et the

same height as in shorter but denser Celluna (Delaney, 1953). Thus both

the greater height and density of the tussocks reduce the temperature

fluctuations in the lower part of the vegetation, in comparison with the

conditions in the intervening grass. At ground level, however, the diff-

erences between grasses are always slight, and it is unlikely that the

tussocks provide much essential shelter at this level except in the

hottest conditions, or when they are aeparated by bare ground.

The temperature differences between the types of grass era reduced

in winter. Tho minimum temperatures can be compared with those found by

Holmquist (1931) and Hodson (1937) under bark and dead loaves; when the

air temperature was below -20°C, there was more than 15°C difference 296

between the temperature outside and inside these hibernacula. The amount of protection given by grass at these temperatures would be only 800 at

3" in the short grass, but 14°C at this level in the tussocks, and 18°C at ground level in both typos of grass (calculated from the regressions of the temperatures in the field on grass minimum temperature). Thus the protection at ground level is as great as that in the other hibernacula mentioned, but this protection extends above soil level in the tussocks only, to a level of about 3". In damp areas such as Cascade Marsh, there is a danger of flooding at ground level, so that insects in hibernacula such as tussocks, which give protection from cold above soil level, aro at a distinct advantage. The insulating effects of snow cover aro well known (Mail, 1930, 1932; Wellington, 1950), but the reduced protection given by long grass, which is the first to bo exposed when the snow melts, has not previously been pointed out. This is unlikely to be important to the insects in the tussocks, as they are still protected by as much vegetation as when the snow is absent.

In South-east England, the value of the tussocks as shelter from cold seems to be slight, wherever there is much grass between them. Some mortality of all of the three species studied occurs below -4°C, which is reached above soil level only outside the tussocks; thus the tussocks offer slight protection to insects above sodl level. S. clavicornis, the most cold-hardy of the three, was not completely killed in the coldest conditions of winter 1963-4, and the protection of the grass outside the tussocks was sufficient to prevent any from being killed. The two species of Dromius were less cold-hardy, and the shelter of the tussocks was needed to prevent any mortality in the coldest conditions. 297

When considering the general importance of shelter from cold, various other aspects must be remembered. The vegetation between the tussocks is

not always as tall or as dense as the Festuca and Holcus in which measurements were taken. In one part of North Gravel, for example, the

ground between tussocks was almost bare of vegetation, and in areas such as this the shelter of the tussocks would be essential to Dromius, and advantageous to S. clavicornis.

It is likely that minimum temperatures limit the range of these three species, as the northern and eastern extents of their geographical distributions correspond with their relative cold resistance. Thus S. clavicornis is found in Arctic Norway (Strand, 1944), and occurs eastwards through Russia to Siberia, whore winter conditions are much more severe than in Britain. Neither of the Dromius species are found in Eastern

Europe: and their northern ranges only extend to Scotland, and the southern tip of Scandinavia (Lindroth, 1945-9). At the limits of distribution, shelter from climatic extremes must be very important, and the behaviour of the beetles must be adapted to obtain maximum possible shelter. This behaviour which enables them to survive in such areas probably takes them into unnecessarily protected microhabitats in areas such as Southern England with its less extreme climate.

It has also been pointed out (Barrett, 1382; Uvorov, 1931; Larson,

1949) that in cool temperate climates such as that of Western Europe, long periods of extremely cold winter weather may be less harmful to insects than sudden frosts in autumn and spring, when insects have either not yet acquired, or lost their seasonal cold-hardiness. Thus S. clavicornis loses its cold resistance in April, although ground frosts may occur between tussocks in Nay; in these conditions the shelter of tussocks must 298

be more important. In the same way, shelter may be more vital in a mild,

snow—free winter with sudden cold spells, then in a hard winter when all

the beetles are inactive, and there is often snow on the ground.

There was no evidence of any limit to the number of beetles of any

species that could obtain shelter in a single tussock. Thus increasing

density does not result in greater competition for shelter, with corres—

ponding density dependant mortality from lack of shelter, as suggested by

Smith (1935) and Nicholson (1958). There may, however, be adverse effects

of overcrowding which affect the physiology or behaviour of the beetles,

but this possibility was not investigated.

Other possible advantages of the tussocks as a microhnbitat have boon

less thoroughly studied. The characters of the tussocks which give

shelter from cold in winter, namely height and density, ere also those

which keep the humidity high in summer, when the temperature differences

between the tussocks and the intervening grass are et their greatest.

This suggests that larvae found in the tussocks in summer may obtain

essential shelter from desiccation and heat death. Although this was not

tested experimentally in this study, en investigation into the resistance

to desiccation at various temperatures of the larvae of S. clovicornis

and the two Dromius species would be interesting. Certainly the larvae

are sheltered from predators outside the tussocks, although the numbers of

such predators will very from area to area. The numbers trepped on North

Gravel suggest a population density of P. madidus higher than those found

by Greenslade (1961) in any other part of Silwood. The tussocks do not seem to provide an essential food supply for S. clavicornis and D. melano— cePholus, although the more specialised feeding habits of D. lincaria 299 may tend to restrict it to Doctylis.

It must be remembered that conclusions based on these three species, which arc regular inhabitants of tussocks, may not be applicable to those species which only enter the tussocks to ovcrwinter. Most of the species of beetles which wore found in tussocks wore of this type, but experimental work on them is difficult, because they occur in low nu,abers. The relative rarity of these species in tussocks suggests that, as well as tussocks, they choose other microhabitats as overwintering sites, which have features in common with the tussocks.

The choice of the tussocks as microhabitat must be studied separately for each regular inhabitant, as selection occurs at different stages of the life cycle and times of year. In some species, such as S. clavicornis, it is the oviposition site which determines the microhabitat of both the larvae and the werwintering adults; the choice of oviposition site by insects is often tie result of a set of behaviour responses to different stimuli (Makins, 1956), although olfactory responses may be very important

(Crombie, 1941; Waloff and Richards, 1946). In such cases, suggestions as to why the tussocks era selected cannot be made without experimental work on the species concerned.

The choice of overwintering site, however, may be determined by more simple responses. Hancock (1923), Holmquist (1926) and Hodson (1937) have all shown that many insects are found in places with moist conditions in winter, and Hodson pointed out that the some factors which keep the humidity high in autumn may also give insulation from cold in winter.

Also, the greeter the water content of a hibernation site, the more gradual is its fell in temperature when the air temperature is below 300 freezing point. These advantages probably offset the disadvantage of

reduced supercooling in the presence of free water; by keeping the

temperature above that et which inoculative freezing occurs. Hodson

also showed that many insects; which have a reduced water content during

tho winter, must drink water at the and of hibernation before returning

to their normal activity, and thus are at an advantage in a moist

microhabitat.

If shelter from climatic extremes is important, one would expect

the behaviour of the insects to lead to selection of extreme situations,

such as the moistest or densest microhabitats available, rather than

intermediate conditions such as a particular range of temperature. They

would then be in the most sheltered conditions even when at the edge of

their range of distribution. Thus it is more likely that the density

or humidity, both of which are always highest in the tussocks, Ere the

factors selected by the overwintering species. The density, in part-

icular, is always higher than in the intervening grass, and all the

species which wore tested showed a strong positive thigmotactic response

which kept them in the area with the greatest density of obstacles.

Some insects show a reversal of their normal behaviour patterns

before hibernating, and become negatively phototactic (Park, 1930;

Porttunen, 1958), hygrophilous (Perttunen, 1952) or thigmotactic (Park,

1930). These reactions were all shown by beetles taken from tussocks in

winter, which suggests that even if their habitat is selected by the

previous generation, their behaviour responses will keep them there until the spring. 301

Non specific behaviour of this nature explains why species which

normally live outside tussocks racy choose various other hibernation

sites as well as tussocks, but there is another aspect of habitat selection which is of interest. Even species such as S. clavicornis and

D. linearis, which are apparently restricted to tussocks at Silwood, are known to occur in different micrehabitats in other areas. Thus S. clay-

icornis has been recorded from leaf litter in woodland areas (Thiele,

1964,b), end D. linearis occurs in dry coastal dunes (Lindroth, 1945-9)

as well as in moist situations such as tussocks. On a large scale, Bey-

Bienko (1964) has suggested that insects with wide geographical distributions live in different microhabitats in different parts of their range, so as to experience similar microhabit^,ts in areas with different microclimates. This does not explain relatively small scale changes in the microhabitat of a species in areas in which the climate does not differ appreciably. Probably microhabitats which appear dissimilar have similar features for the insects concerned, and are only separate in space. Thus tussocks may be the preferred habitat of S. clavicornis in grassland, and loaf litter in woodland; the factors which determine whether the species is found in woodland or grassland in any area are not as yet known.

A classification of habitats such as that of Elton and Miller (1954), which classifies terrestrial habitats by their vertical stratification in different types of vegetation, is useful, but does not show which similarities exist between microhabitats in different types of vegetation.

Elton and Miller describe recurrent components of environment containing characteristic groups of species, which they call licentres of action"; some of these, such as dung, carrion, rotting wood and macrofungi are classed 302

together as "general" habitats which can occur in any of their major

habitat systems. In the some way as climate is graded according to its

scale into macro, Geo and microclimate, it would be advisable for ecol-

ogists to classify habitats into corresponding divisions of size. Elton

and Miller's classification divides habitats into major systems (terrest

rial, aquatic, etc.) which can be called the "mocrohabitot", and those are

subdivided into components (e.g. vegetation types and vertical layers)

which can define the intermediate "ecohabitat". Their system does not,

however, delimit the microhabitat. To correspond with the microclimate,

which is the climate found in the actual medium or position in which the

insect is living, the microhabitat must define the actual situation of

the insect as precisely as is possible. It may vary from season to

season according to the needs of the species, and as no two individuals

of the same species can be in exactly the same place, the definition must be broadened to include all the similar places in which the individuals of a species ore typically found at any time. A proposed definition of the microhabitat of a species is "the minimum part of the ocohabitat which supplies the requirements of the species in its physiological state at that time". This does not correspond exactly with a centre of action, as a single centre of action, such as a log, can contain separate microhabitats of species restricted to different parts, such as under the bark, in the dry wood, etc.. It is also distinct from the concept of

"ecological niche", which is generally interpreted as the status of the species in the community in relation to food and enemies as well as to microhabitat (Landin, 1961), and it is also more restricted then the

"habitat niche" of Alice et. al. (1949, p. 232). The study of the beetles 303

Of grass tussocks shows that distinct microhebitats can occur within an ecohnbitct such as the field layer of grassland, and emphasises the nood fora classification of all sizes of habitats. This classification could be based on that of Elton and Miller, modified as suggested by

Delaney (1956) to include other factors such as geology and topography in the descriptions of ocohabitats. From such a classification, if the microhabitat of a species in one ecohabitat was known, its possible preferences in others might be apparent, and the study of the common features of the alternative microhabitats of any species would clarify its method of habitat selection. 304

VI. SER,&iARY.

1. Tussocks are defined as grass plants which are easily distinguished from the surrounding herbage by the closeness of their loaves and stems, which form a dense tuft, and also either by the accumulation of dead

herbage around them, which separates them from the adjacent grass, or by their being elevated on stools of dead vegetable matter, in which soil

or silt accumeulates. They were studied as a microhabitat of several

species of beetles.

2. The commonest tussock-forming grasses at Silwood Park are Dactylis glomerate L. in dry areas, and Doschompsia caespitosa (L.) where the soil is wet. The distribution and morphology of Dactylis tussocks was studied, and their microclimate compared with that of the intervening

gross.

3. Dactylis tussocks have a life of at least nine years, and are most numerous about ten years after the colonisation of abandoned arable land.

4. In clear weather the temperature near the ground in tussocks is loss variable than in shorter grass. In winter the range of diurnal

variation is less than in summer; the nocturnal differences between the tussocks and the intervening grass are slight at ground level, although

greater above this.

5. In cloudy conditions there are only slight differences between the types of grass; wind and rain (unless it is exceptionally heavy), have little effect on tempernturos below the three inch level.

6. Snow provides more insulation over the shorter grass than over tussocks, where it melts first, so that the tussocks protrude through it. 305

7. Light is absorbed at a higher level in tussocks, and the intensity

at soil level is greater, than in more open grass.

8. The variations in relative humidity between the types of grass were

greatest in fine weather in early summer, when there were large differ-

ences in saturation deficit between the tussocks and the intervening grass.

9. The total beetle fauna of tussocks was sampled for over a year. The

beetles are most numerous in winter, but form a permanent part of the

insect fauna of tussocks; 198 species were found, from 127 genera in 23

families. The best represented families are the Carabidae, Staphylinidoe and Curculionidae.

10. Most of the species wore temporary inhabitants which occurred in

small numbers, but a few, which were all either predatory, saprophagous

or mycetophogous, wore common.

11. Dactylis and Deschaarpsia tussocks contain similar numbers of beetles,

but Descheiepsia has a more isolated fauna, probably because of differences

between the areas sampled, and not between the two grasses.

12. The numbers of species found in tussocks and in pitfalls between

tussocks were similar; the commonest species in pitfalls wore large,

predatory carebid beetles, which were found only very occasionally inside tussocks.

13. The density of beetles is higher in tussocks than outidel but

since the tussocks cover only a small proportion of the area studied, they contain less than half of its total beetle population, even in winter.

14. The biology of four common tussock-inhabiting beetles was invest-

igated. Those wore Stonus clavicornis (Seep.), S. impressus Germ.,

Dromius melanoeeehalus Dej. and D. linearis (01.). 306

15. Immature adults of S. clavicornis are common in tussocks throughout the winter until April, when they move into the intervening grass; the mature females subsequently lay eggs in tussocks during summer. The larvae are found at the base of the tussocks until autumn. Only a small proportion of adults are fully winged and capable of flight.

16. S. imoressus is commonest in summer. It was found to be confused with S. accris Steph., and a method of separating the two species in the laboratary was described. Separation in the field was not possible, and this species was not used for experimental work.

17. D. melanoceohalus eggs are laid in tussocks in early summer, and the predatory larvae develop in the same habitat. Immature adults arc found on vegetation outside tussocks in late summer, feeding on mites.

They are winged, but flight was not observed. In autumn they enter the tussocks, and mature during the winter.

18. Both larvae and adults of D. linacris are found throughout the year, although the larvae are commonest in summer. The predatory larvae live in deed Dactylis panicle stems. The adults feed nocturnally on Thysan- optera in the panicles in summer, and on mites in the tussocks in winter.

They are wing dimorphic, but flight was not observed.

19. Tho numbers of S. clavicornis were correlated with the ratio of dead to living leaves, and are, of tussocks; those of S. inprossus with the density and distance from other tussocks, and those of D. melanoccohalus with the tussock area and density.

20. In winter D. molanocephalus showed an initial preference for dry situations, and S. clavicornis was attracted to crushed grass from gut- side tussocks, but the remaining reactions to temperature, humidity, 307 light, tactile and olfactory stiuuli all tend to trap the beetles in the tussocks.

21. S. clavicornis is the most, and D. melanoceohalus the least cold- hardy of the selected species; the factors influencing both individual and seasonal cold-hardiness wore not clear.

22. In moist conditions in the field, all Drouius individuals, but only 50% of S. clavicornis were killed by overnight exposure to the coldest winter tomperatures; a cover of 6/1 high grass reduced the mortality of all species, and only D. melenoceohalus was not completely protected by 121/ high grass.

23. Tho precipitin test was used to show that the Carabidae found between the tussocks do food on Stenus; larvae and adults of this genus which are in the tussocks are almost completelt protected from those predators. 308

VII. ACKNOWLEDGMENTS.

I wish to express my sincere thanks to the following persons for assistance which I received during the course of this work.

To Professor O.W. Richards for granting facilitios at Silwood Park.

To my supervisor, Dr. N. Waloff for valuable guidanco and helpful criticism throughout the work, and in the preparation of this manuscript.

To Dr. R.E. Bleckith for statistical advice, and for making arrange— ments for the computer analyses at the Alice Holt Lodge Research Station.

To Dr. J.R. Dempster for preparation of antigen and serum for the precipitin tests, and for advice on this work.

To Dr. J.N.R. Joffers, Forestry Commission Research Station, Alice

Holt Lodge, for carrying out the multiple correlation and regression analyses.

To Professor B.G. Peters for the identification of the nematodo,

Parasitylonchoides stoni Wachok.

To Mr. J.W. Siddorn for advice on microclimatic measurements, and on the undorcooling point detormination apparatus.

To Mr. W.O. Steel for helpful criticism of the section on the taxonomy of Stenus imeressus Germ.. and S. aceris Stoph., and for advice on the identification of various Colooptera.

This work was carried out while I was the recipient of a Nature

Conservancy Research Studentship, and the generosity of this authority is gratefully acknowledged. 309

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Appendix Table 1. Macroclimatic data for the days on which microclimatic data are given in the text. (Arranp.ed in the order in which they are referred t21.

Date 26. 7. 16. 6. 31. 1. 2. 2.-73. 26. 14. 25. 2. 6. 5. 6. 6. 7. 5. 6. 6. 3. 3. 1. 2. 2. 3. 3. 63. 62. 61. 63. 63. 63. 63. 63. 62. 63. 63. 63. 63. 63. Temp.(Mean 12.8 14.4 13.9 13.3 17.8 17.8 15.6 1.7 1.7 1.1 0.3-2.8 1.7 10.0 ( o0 ) (Max. 20.0 21.4 15.8 15.0 25.8 23.6 21.1 8.9 6.1 4.2 3.1 3.9 8.9 15.0 (Min. 3.9 6.4 12.2 11.7 9.4 12.8 10.6 -4.4 -2.2 -4.2 -2. 9.2 4.4 6.7 Gross ::lin. -0.3 -0.6 7.5 10.3 3.6 6.4 5.8-11.4 -9.4-11.4 -7.5--13.3-11.4 0 (Mean 64 66 76 R.H. 62 86 90 65 66 64 66 65 89 86 78 /0N (Max. 94 94 91 92 92 85 88 92 83 97 92 88 v./ 3 (min. 39 36 76 84 35 39 45 36 36 80 71 41 36 6o Pres-(Mean 1016 1024 1006 1007 1007 1008 1007 1019 1013 1029 992 1020 1019 1008 sure (Max. 1018 1026 1007 1011 1009 1009 1008 1020 1015 1031 1001 1022 1020 1013 (mb.)(Min. 1015 1023 1005 1003 1006 1007 1006 1018 1012 1028 983 103.8 1018 1003 Total Radiatio 401 635 168 138 560 626 465 284 328 97 91 204 284 222 (MwH/cm. ) Sunshine 8.6 5.3 (Hrs.) 13.1 14.3 0 0 14.1 13.2 13.2 8.6 9.0 1.9 0 5.6 Rainfall 0 0.1 21.6 0 0 0 0 0 0 1.1 0 0 (ram.) Rainfall duration 0 0 0.3 9.9 0 0 0 0 0 0 2.5 0 0 0 (Hrs.) Mean wind speed at 2.2 2.3 4.2 2.0 5.0 6.7 7.6 ------3 1 (m.p.h.) Wind dir- E S S SW action N NE SW NE E NE S NE W S Snow depth 6 3 .1 (inches) 0 0 0 0 0 0 0 0 0 0 323

.a.MDI)DC TABLE 2. List of species of beetles found in tussocks.

Tussock species Month

Species Dact- Des- Jun- JFMAMJJyASOND Total vlis cham- cus No. PS is CARABIDAE Leistus rufescens * 1 (Fabricius) * L. ferruginous (Linne.fl'us) * * * 4 Not iophilus mlustris (Duftschmid) 2 Bembidion lunulatum (Geoffroy) (*) * 1 B. lampros (Herbst) (*) * * 7 Trechus obtusus Erichson * * * * ** * ** * * 4:- * * 77 T. quadristriatus (Schrank)* * 1 Panagaeus bipustulatus * * * * * (Fabricus) 5 Badister bipustulatus * * ** * * * * * * * 18 (Fabricius) Bradycellus sharpi Joy * * -x- ** * * 21 B. harpalinus (Serville) * * * * * * * * ** 50 B. collaris (Paykull) * * 1 Amara lunicollis Schiodte * * * * * * 7 Stomis pumicatus (Panzer) * * 1 Pterostichus vernalis 1 (Panzer) P. niger (Schaller) * * 1 P. strenuus (Panzer) * * * * * 10 P. madidus (Fabricius) * * * 2 Abax mrallelopepidus * (Pill. and Mitt.) * 1 Calathus malanocaphalus .yT * * * * (Linnaeus) 5 Agonum obscurum (Herbst) * * * -x- * * * 95 A. fuliginosum (Panzer) * * * 7 Demetrias atricapillus 4:- -,, * * * * * * * * * * 26 (Linnaeus) Dromius 1 inearis (Olivier) * * * * * * * * * * * * * * 45 D. melanocephalus Dejean * * * * * * * * * * * * * w 345 Metoblotus foveatus 9 (Geoffroy) ,` HYDROPHILIDLE Helephorus minutus * * 2 (Fabricius) Coelostoma orbicular° * * 1 (Fabricius) Cercyon haemorrhoidalis * * 1 (Fabricius) 324

Tussock species Month D es- Spocios Dact- _t_____ Jun- JFMAMJJyASOND Total vlis /u/2 cus No. I- sic HYDROPHILEAE (cont.) Megastornum obscurum , (Marsham) * * * * * * * 26 HISTERIDLE Onthophilus striatus * * 1 (Forster) Margarinotus cadavorinus * * 1 (Hoffman) PTILIMDLE Ptenidium fuse icorne 4k• * * * * * * * * 19 Erichson Acrotrichds spp. - * * * * ,.- * * * 32 S ILPH IDLE Phosphuga atrata ., * * * * * * 14 (Linnaeus) LNISOTOMIDLE Nargus velox (Spence) * * 1 Catops nirTicans -' 4 * * 2 (Spence) C. fuliginosus Erichson * * 1 Cholova glauca Britten * * 1 C. fagniezi Jeannol * * 1 Loiodes dubia (Kugelann) * * 1 Ap;athidium marginatum .,L„ 1 Sturm SCYDNLENIDLE Neuraphes angulatus * * * * 2 (T ien.. and "Kunz()) Stonichnus collaris * -,: * * 5 (Muoll. and Kunze) STAPHYLIKID,E Moto.sia clypoata (Mueller)* * ii- * * * * * * * 23 Omelium rivulare (Paykull) * * 1 Lnthobium unicolor * * 1 (Marsham) Olophrum picoum * * * * 6 (Gyllonhal) Lcidota cruontata * 1 (Mannerhoim) Oxvtelus laquoatus * 2 (Marsham) 0. tetracarinatus (Block) * * * 3 Platvstothus arenarius * * 1 (Gooffroy) Stenus juno Fabricius * * 1 325

Tussock species Month Des- Species Dact- Jun- JFIIL MJJyLSOND Total ylis cham- cus No. all a STLPHYLINIDLE (cont.) S. clavicornis (Scopoli) * * * * * * * * -x• * * * * 350 S. rogeri Kreatz * * 1 S. nanus Stephens •(*) * 1 S. brunnipos Stephens (*) * * * 7 S. fulvicornis Stephens * * * * * * * * * ii• 36 S. similis (Herbst) (*) * 1 S. flavipes Stephens * * * * * * * * * 74 S. aceris Stephens . * * * * * * * * * * * * * * 116 S. impressus Germar S. ossium Stephens * -* * -X- 3 S. subaonous Erichson „. * * * * * * * * * * 33 Lstenus gracilis (Paykull) * , * * * 5 Rugilus rufipos (Germar) (*) * 1 R. orichsoni (Feuvel) * * * * 3 Sunius propinquus * * * (Brisont) 5 Lathrobium brunnipes * * * 2 (Fabricius) (*) Xantholinus linearis * * * * * * * * if * (Olivier) 33 X. glabratus (Gravenhorst) * * 1 X. longivontris Hear * * 1 Gyrohvpnus punctulatus (Goeze) 10 G. myrmecophilus -)E• * * * * * * * * (Kiosonwotter) 17 Philonthus spp. * * * 2 Gabrius spp. * -,s * - * 3 Staphylinus siculus 1 Stiorlin (*) Quodius fuliginosus * * 4 (Gravenhorst) . molochinus " 2 (Gravonhorst) 2. nigricops Kraatz * * * 2 Q. rufipos (Gravenhorst) (*) * 2 Q. boops (Gravenhorst) (*) * 1 Habrocorus ea illaricornis * * 1 (Gravonhorst) Mycotoporus brunneus 2 ( orsham) Bolitobius analis * -- * * (Paykull) 3 B. cingulatus (Mannorheim)(*) * 1 Conosomus testacous * * * * * * -x- * 13 (Fabricius) 326

Tussock specios Month Des- Species Jun- Total Dact- chain----- JFMAMJJyASOND ylis cus No. . psis --- STAPHYLINIDLE (cont.) Conosomus immaculatus it- * * * * * * -x- 11 (Stephens) C. pediaularius (Gravenhorst), var. * * * lividus (Erichson) Tachyporus nit idulus -x- * , * * * * * * * 78 (Fabricius) T. pusillus (Gravenhorst) * * * * 20 T. tarsus Erichson * * * * 5 T. chrysomolinus (Linnaeus)* * * * * * * * * * * * -X- * * 252 T. scutellaris Rye ik * * * * iE 36 T. hypnorum (Fabricius) * * * * * * * * * * * * * 185 Tachinus rufipes (DoGeor) * * * * * 4 T. morginellus (Fabricius) * = * it- 2 Hypocatus 2.0ligismnLs * it- * * 'E :E* >E ;.* ;E * 29 (Paykull) Encephalus complicans * * * 4E. * * * it- * 21 Westwood Amischa analis * * * * * * * * * * * * * * * 217 (Gravenhorst) Sipalia circellaris * * * * * * * * * * * 30 ( ravenhorst) Atheta spp. mainly A. (Acrotona) * * 4:- * * * * * * * * * it- * * 445 fungi (Gray.) Drusilla canaliculata * * * (Fabricius) (*) Ocaloa picata (Stephens) * * 1 Oxypoda spoctabilis * -)- Moorkol 1 O. lividiponnis * if 2 Mannerhoim 0. altornans (Gravenhorst) * * 1 Aloochara lanuginosa * -Y: 1 Gravenhorst PSELAPHIDLE aybaxis longlicornis * * 2 (Leach) Bryaxis validus (Aube) * * 2 B. bulbifor (Reichenbach) * * * 3 Iychus niger (Paykull) * * 1 SCARAB/2'0LE Iphodius sphacelatus * 1 (Panzer) 327

Tussock species Month Des- Species D act- Jun- otal cham- JFMA MJJyASOND y1 is ---7- cus No. psla,

CLLMB IDLE C iambus pube scans - * * Rodte nbac he r E LLTER Da Limonius minutus *1 (Linnaeus) * Lthous vittatus * (Fabric ius) C LNT HLR ID LE C anthar is polluc ida * * 1 Fabric ius Rhagonvcha to st acoa * * (Linnaeus) PHLO IC PH IL IDLE Ph10 iophilus edwards ii Stephens (*) PHLILCR IDLE 01 ibrus census (Fabriceus) * * * 2 St 11bus testacous (Panzer) * * * - 3 C RYPT 0 PHL G D LE Crvptophagus a cut angu lus _,. 1 Gyllonha 1 C. lycoperdi (Scopol 1) * -;. 1 Ltomaria fuscata * * * * * * 14 (Schoonherr) A. ruf icornis (Marshcm) * * * * * * 13 COCC INELLDLE C occ idula ruf a (Herbst) (*) * 6 Rhizobiellus litura -x- 141 (Linnaeus) Pallus sutur ails (Thun * 1 (Thunbo rg) Scvmnus front al is * * 1 (Fabric ius ) S. rubromaculatus (Goo ze ) * * 1 Micra spis sexdsc impunct at a 4 * 9 (Linnaous) Ldc1ia decompunctata * -x- 1 (Linnaeus) C occ inolla so ptempunct at a * * * * 5 Linnaeus Thea vigint iduopunct at a * * * * * * * 14 (Linnaeus) 328

Tussock spocids Months Dos- tact- --- Jun- Total Species cham- JFMAMJJy L,SOND y lis cus No. --7-psia

LLTHRID IDLE Lathridius nodifer * * 6 Westwood -)s- * L. bifasciatus Reitter * * * * * * 6 Enicrnus transvorsus * 4:- 120 (Olivier) * * * * * * * * * * * * * Cartodere elongata (Curtis)* * 1 Corticaria lint:Tessa 49 (Olivier) * * .). * * * * * * * * * Corticarina gibbosa (Herb , 2 (Herbst) * C. fuscula (Gyllenhal) * * * * * * * * * * 37 l'etophthnlmus serripennis * 1 (Broun) * CORYLOPHIDLE Soricodorus int/Grails 4 (Gyllenha11) * * * * BRUORIDLE Bruchidius ater (Marsh=) * * * 2 CHRYSOMELIDLE Loma molanopa (Linnaeus) * * * * * 4:- * 8 Chrysolina staphylea * (Linnaeus) * * * * * 6 Rydrothassa aucta * -x- * (Fabricius) * 3 Galeruca tanocoti * * (Linnaeus) * 3 Crepidodera forruginon 1 (Scopoli) * Chaotocnema subcoerulea 1 Kutschera * C. hortonsis (Geoffrey) * * * * * * 5 Sphaoroderma rubidum 1 Graolls * * Cassidy flovcola * * * 4 Thunberg * * C. vittata de Villiers * * * * * * * 15 I APIONIDLE Lpion violaceum Kirby ) A. hydrolapathi (Marsham)) A. curtirostre Gerrnar ) see next page -.' miniatum Gorman ) I,. rubons Stephens ) 329

Tussock species Month Species Des- Total matt- ;17;m_ Jun- JFMAMJJyASOND ylis cus No. .2218 --- APIONIDAE (cont.) A. tenue Kirby ) * * k * * * * * * * * * * * * 60 A. reflexum Gyllenhall ) A. simile Kirby ) • A. dichroum Bedel ) A. aestivum Germar ) A. apricans Herbst ) CURCULIONIDAE Otiorrhynchus singularis * * (Linnaeus) 3 O. ovatus (Linnaeus) * 1 Trachyphloeus scabriculus * * 1 (Linnaeus) Phyllobius pyri (Linnaeus) * 1 P. maculicornis Germar * * * 2 Barypithes araneiformis * * * 2 (Schrank) B. pellucidus (Boheman) * * * * * 5 Strophosomus melanogrammus * * 4E. * * 5 (Forster) S. subrotundus (Marsham) * * 2 Barynotus obscurus * * 1 (Fabric ius) Sitons cambricus Stephens * * 1 S. lineatus (Linnaeus) * * * * * * * * * 12 S. sulcifrons (Thunberg) * * 1 S. hispidulus (Fabricius) * * * 2 Tropiphorus terricola * * 1 (Newman) Notaris acridulus -;i- * 3 (Linnaeus) (*) Miccotrogus picirostris * * -X- ,E* * * * * 26 (Fabricius) Liosoma deflexum (Panzer) * * 1 Phytonomus nigrirostris * * -X- * 5 (Fabricius) Acalles klinoides * * 1 (Marsham) Coeliodos dryados (Gmelin) * * 1 Cidnorrhinus quadrimacul- * * * * 3 atus (Linnaeus) Ceuthorhynchidius trog- * -Y, 2 lodytes (Fabricius) * Ceuthorhynchus chrysanth- * * 1 emi Germar 330

Tussock species Month Des- Species Dact- Jun- Total chain- --- J F M A M J JyASON D No. ylis --7-pals cus CURCULIONIDAE (cont.) teuthorhynchus punctiger ( ) * * 2 Gyllenhal C. erysimi (Fabricius) * * 2 Rhinoncus pericarpius * * 3 (Linnaeus) R. castor (Fabricius) * * 1 Phytobius quadrituber- * 1 culatus (Fabricius) ( ) Gymnetron labile (Herbst) * * * 2 G. pascuorum (Gyllenhal) * * * 2 Miarus campanuli (Linnaeus)* * 2 Rhynchaenus fagi (Linnaeus)* * 1 J Total number of species, 198 331

Append ix Table 3. Genera of beetles found in pitfall traps on North Gra vol .

Occurring Months of occurrence Tot al number of Genus in tussocks in pitfall traps on North ind iv ids . J F MA M J Jy L S 0 N D Gravel caught LRA B IDLE C arabus 32 C vchrus 3 Le istus 45 No br is 16 Not io ph ilus 17 Lor ice ra 2 :omb id ion 2 Trechus 724 Rim 2a ous 2 Bad is t or 6 Ha r pa lu s 31 Br ad yco llus 10 Amara 98 Pt oros t ichus 6,701 Abe x 681 C a 1 at hus 543 Svnuchus 1 Odontonyx 11 Dromius 2 Met abletus * * 2

HYDROPH IL IDLE Mc 7asternum 304 Sphaer id ium 1

PT IL IIDLE Pt on id ium 1 Lcrotr ichis 2

S ILPH IDLE PhosphLwa 2

STLPHYL IN IDLE Micro poRIaz * * 3 Met ops is * * 2 Om° 1 ium 2 Ant hob ium * * * * 12 Lc idot a 1 Oxytelus 1 St e nus * * * * Rig i1us * * * * La throb ium 332

Occurring Monthei of occurrenco Total in pitfall traps number of Genus in tussocks ind iv id s . on North J MJJyASOND Gravel F M eau:tilt Xantholinus * * * * * * * * * * * * * 262 alt- v%-,..ckui.s * * * if- * * -X- * * * * * * 137 Philont bus * * * if * * * * * 43 Staphylinus * * * * * * * * * * -x- * 307 2u.cd ius * * * * * * * * * * * * 159 Mycot oporus * * * * * * * * * 47 C ono s.:imus * * * * * * * * 18 Bol it ob ius * * * * * * 5 T a c }Iyous * * * * * * * * * * * * 58 Tachinus * * * * * * * * * * * * * 120 Hypo c yptus * * * * 3 E nee pha lu s * * * 4 Lra is c ha -x- * * * * * * if * * * * * 110 S Lea 1 ia * * * * * * * * 9 At ho t a „e.. * * * * * * * * * * 326 Oxypod a * * * * * * 17

AN ISOTOMIDLE C atops * * * * * * * * * * * * 381 Choleva * * * * * * * * * * * 52 Le lodes * * * * * * * * * * 57 Pt ornaphagus * * * * 4 S c iodre pa * * 5 Ln is ot ore * 1

SCLRLBLE IDLE Lphod ius * * 1 Se r ic a * * * 35 Hopl is * 13 BYRRH IDLE S iraplocar is * * * * 7 Bvrrhus * * 2 E LATER ma A t hcu s * * 1 Lar iota s * * 10 C LNTHLR ID AE Rhagonycha * 1

DERMESTID:2 An hre nu s * 1

RED OPHLG IDLE MonoLoma * Total Occurring Months of occurrence number of in pitfall traps Genus in tussocks individs. on North JFMLMJJyLSOND caught Gravel PHLLLCRIDLE Olibrus * * 1

CRYPTOPHLGIDLE Cryptoahagus * * * 15 Ltomaria * * 4 COCC/NELLIDLE Rhizobiollus * * * * 7 Scymnus * * * * 6 Coccinolla * * 2 Theo * * 1 LLTHRIDIIDLE Enicmus * * * * * 45 Cartodore * 1 EELLNDRYIX,E. Lbdora * 1

LNTH IC IDLE Lnthicus * 1 MYCETOPHLGIDLE Mycotophagus * 1

CHRYSOiELIDLE Chrysellua * * * * * * 6 Galoruca * * * * * 12 Sormvlassa * * * 4 Longitarsus * * * * 9 Cropidodora * * 1 Chaetocnema * * * -x- * * * 7 Sphaoroderms * * - 3

APIONIDAE Lpion * * * * * * i.;- * * * * 32 CURCULIONIDLE Otiorrhynchus * * * 3 Phyllobius * * * 3 B a rjrp it ho s * * * * n * 52 Strophosomus * * * * * * if * * - * , 263 Barynotus * 1 S it ona * * * * * * * * * * * * = 320 Miccotrogus * * * 3 Phvtonomus * * * * * * - 21 Ceuthorhynchus * * -X- * * * 7 Rhinoncus * 1 Rtnphnonus * * 1 ,Iotal numbers of generaf_ 21 17 28 27 40 V 60 79- 48 43 34 331_ 334 Appendix Table 4. Numbers of S. clavicornis in North Gravel and Nursery field tussocks.

Geometric Month Numbers of S. clavicornis in each sample Arithmeticmean mean 1) North Gravel 1°4.1. sotober 2, 7, 7, 3, 6, 21 7.7 6.0 meoember 17, 18, 11 15.3 15.0 1962 January 21, 17, 20 19.3 19.0 February 5, 0, 9, 35, 1, 0 8.3 3.0 March 6, 5, 12 7.7 7.0 April 19, 5, 0, 4, 1, 0 4.8 2.3 May 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0 0.25 0.2 June 0, 2, 0, 1, 0, 0 0.5 0.35 July 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0 0.4 0.3 August 2, 0, 0, 3, 2, 0, 5, 0, 0 1.3 0.8 September 0, 0, 2, 3, 7, 0, 1, 1, 1, 1.7 1.1 October 3, 1, 1, 0, 0, 2 1.2 0.9 November 4, 1, 1, 2, 1, 1 1.7 1.5 December 7, 1, 0 2.7 1.5 1963 January 10, 2 6.0 4.75 February 6, 10, 30, 21 16.8 14.0 March 6, 29, 14, 17, 12, 2, 13, 5 12.2 9.8 Lpril 19, 9, 14, 13, 1, 2, 3, 2 7.9 5.5 May 0, 0, 0, 0, 0 0 0 Juno 1,0, 0 0.3 0.25 July, 2,0, 1 1.0 1.0 August 1, 0, 3 1.3 1.0 September 0, 0, 0 0 0 October 0, 4, 1 1.7 1.0 November 8, 9, 32 16.3 13.5 December 28, 20, 4, 26, 27, 5, 26, 30, 14, 16, 14 19.1 16.4 114 January 17, 27, 32, 20, 13, 17, 5, 34, 32, 8, 15 20.0 17.5 April 4, 9, 1, 0, 2, 3, 7, 7, 0, 2, 7, 1, 2 3.5 2.5 2) Nursery Field

ary 6, 7 6.5 6.5 w 2.0 April 2 2.0 May 0, Op 0 0 0 June 0, 0, 0 0 0 July 0, 2, 0 0.7 0.5 August 2, 0, 1 1.0 1.0 335

f Geometric Month Numbers of S. clavicornis in each sample Mean mean

•eptember 2, 0, 0 0.7 0.5 November 1, 4, 26 10.3 5.5 mecember 14, 13, 60 29.0 22.5 1064 January 4, 9, 28, 9, 12, 9, 3, 10, 13, 4, 10, 8, 19.3 11.9 12, 74, 84 February 43, 1, 24, 9, 3, 7, 4, 46, 30, 21, 3, 3, 12.0 6.2 3, 3, 1, 1, 2 336 Appendix Table 5. Numbers of S. impressus in tussocks sampled.

Dactylis Descapsialm Month Nursery Arithmetic North Gravel Field Cascade Marsh mean 1961 Oct. 0, 0, 0, 0, 0, 0 0, 0, 0, 1, 0, 0, 0 0.08 Nov. Dec. 0, 0, 0 0, 0, 0 0 1962 Jan. 0, 0, 0 3, 0, 0 0.50 Fob. 0, 0, 0, 1, 0, 0 0, 2, 2 0.56 Mar. 0, 0, 0 3, 0, 1, 2, 2, 0 0.89 4pr. 2, 0, 0, 1, 4, 1 1.34 May 0, 0, 0, 2, 0, 0, 1, 0, 0, 0, 3, 1, 3, 0, 0, 0.61 1, 2, 0, 0, 0, 0, 0 June 1, 0, 0, 1, 0, 4 1.00 July 8, 7, 0, 11, 1, 2, 41 4.09 2, 3, 10, o, 1 Lug. 0, 0, 0, 3, 2, 3, 2 , 1.11 0, 0 Sept. 0, 0, 2, 0, 0, 0, 1 , 0.33 0, 0 Oct. 0, 0, 0, 0, 0, 0 0 Nov. 0, 0, 0, 1, 0, 0 0.17 Doe. 1, 0, 0 0.33 1961 Jan. 1, 0 0, 0 0.25 Feb. 0, 0, 0, 0 0 Mar. 0, 1, 1, 0, 2, 1, 0.75

1, 0

Apr. 0, 2, 0, 0, 1, 0, 0.89 2, 2 May 0, 1, 3, 2, 1, 1 0, 2, 6 1.78 June 2, 2, 1 0, 0, 5 1.66 July 1, 0, 1 1, 3, 0 1.00 Aug. 0, 0, 0 6, 1, 3 1.66 Sept. 0, 2, 0 0, 0, 0 0.33 Oct. 0, 0, 0 0 Nov. 0, 0, 0 0, 1, 0 0.17 Doc. 0, 0, 1 2, 0, 0 0.50 1.6„4. Jan. 0, 0, 0, 0, 0 0 Feb, 0, 1, 1 0.66 337 L000ndix Table 6. Numbers of D. melanoceohalus in tussocks sampled.

Dactylis Deschamps is Lrithmetic Month moans Nursery Cascade 1 2 North Gravel (1) ___rield (2) Marsh (3) 1961. Oct. 11,2,1,3,10 3,1,9,1,0,2 5.4 2.67 Dec. 6,6,0 9,0,0 4.0 3.0 1962. Jan. 6,2,6 0,0,0 4.67 0 Fob. 3,0,3,5,0,1 1,3,0 2.0 1.33 Mar. 1,0,0 7,1,0,2,0,2 0.33 2.0 Lpr. 1,410,0,2,0 1.16 May 1,1, 010,0,0,0,0,0,012o 1,0,1,5,0,0, 0.42 1.0 1 0,1,3,0,0 June 0,1,0,0,0,0 0.16 July 3,4,0,6,1,1,4,3,019,3,0 2.83 Lug. 0,1,0,0,6,0,8,0,o 1.67 Sept. 1,0, 5, 7, 7, 2,6, 5,0 3.66 Oct. 7,1,0,2,1,0 1.83 Nov. 111011, 5, 2, 4 3.84 Dec. 5,0,0 1.67 1963, Jan. 7,23 41,12 15.0 26.5 Fob. 5, 5, 5,10 6.25 Mar. 6,6,2,5,3,0,3,0 3.13 Lpr. 2,2,2,0,10,2,5,14 18 4.64 18.0 May 5010,1,3,1 108, 16 2.16 8.33 June 1,0,1 7,0,20 0.66 9.0 July 1,1,2 ,5,3 1.33 3.0 Aug. 0,0,1 21,1,19 0.33 13.67 Sept. 0, 4,1 7:5,14 1.67 8.67 Oct. 0,2,2 1.33 Nov. 0, 4,1 2,18,14 1.67 11.33 Dec. 4,01 2,311,1,011, 4 5,13 2.46 7.33 8,4,3 ,1964. Jan. 4,5,2,2,1,1,0,2, 2.0 0,2,3 Feb. 13,11,2,14 8.13 5,3,0,17