1 THE OCCURRENCE OF SOME COLEOPTERA IN GRASS TUSSOCKS, WITH SPECIAL REFERENCE TO MICHOCLI1JATIC CONDITIONS. By 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 imp- ortance 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 diff- erent 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.