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(Lepidoptera : Geometridae). by Olive Wall, B.Sc

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(Lepidoptera : Geometridae). by Olive Wall, B.Sc The biology and egg development of two species of Chesias Treitschk (Lepidoptera : Geometridae). by Olive Wall, B.Sc. (Loud.), A.R.C.S. Thesis submitted for the Degree of Doctor of Philosophy. July 1970 Imperial College of Science and Technology, Silwood Park, Sunninghill, ASCOT, Berkshire. -1- ABSTRACT The biology, and in particular the embryonic develop- ment, of two species of Chesias (Lepidoptera: Geometridae) are described and compared. Some aspects of the general biology of these species are examined, and these include the time of occurrence of the different stages of the life cycle, the behaviour (particularly during oviposition) of the adults, and the parasites attacking the larvae. The morphology of the developing embryo is described in detail, and comparisons between the two species are made. Morphogenesis is divided into a number of arbitrary stages, and the relative duration of the different stages is compared. The temperature relations of the developing embryo are examined in detail in both species. In particular, the changing temperature requirements of the embryo of C. leqatella, which diapauses at an early stag- ,are determined by the exam- ination of large samples of eggs killed at different times during embryonic development. The existence of parental effects on the embryonic development of the progeny is also investigated, and certain aspects are discussed. -2- TABLE OF CONTENTS Page ABSTRACT 1 TABLE OF CONTENTS 2 GENERAL INTRODUCTION 6 GENERAL MATERIALS AND METHODS 7 (i) Collecting 7 (ii) Rearing 10 1. BIOLOGY 16 (i) Introduction and Review of Literature 16 (ii) Habitat and Distribution 16 (iii) Life Histories 17 (a) Life History of C. legatella 18 (i) Adults 18 (ii) Oviposition 23 (iii) Egs 27 (iv) Larvae 28 (v) Pupae 31 (vi) Parasites 33 (b) Life History of C. rufata 37 (i) Adults 37 (ii) Oviposition 42 (iii) Eggs 43 (iv) Larvae -3- Page (v) Pupae 46 (vi) Parasites 46 (iv) Discussion 50 (v) Summary 53 (a) C. legatella 53 (b) C. rufata 54 2. EGG DEVELOPMENT 56 (i) Introduction and Review of Literature 56 (ii) Experimental Methods 74 (a) Handling of Eggs 74 (b) Sterilisation of Eggs 74 (c) Containers for Eggs 74 (d) Incubators 78 (e) Fixation, Preparation and Examination 81 of eggs (iii) The External Morphogenesis of the Etbryos 86 of C. legatella and C. rufata (a) The Stages of -Embryonic Development 86 in C. legatella (b) The Stages of Embryonic Development 101 in C. rufata (iv) The Egg Development of C. rufata 116 (a) The Duration of Development in an 116 Outdoor Insectary (b) The Duration of Development at Two 121 Constant Temperatures (0) Tmbryogenesis at 20°C. 124 (i) Timetable of Embryonic Development 124 Page (ii) Variability in Rate Development 130 (d) The Effect of Temperature on 138 Embryonic Development (i) The Effect of Temperature on 138 the Rate of Development (ii) The Effect of Temperature on 140 Variability in Developmental Rate (iii) The Effect of Temperature on 141 the Proportion of Eggs Hatching (e) Parental Effects on Embryonic 141 Development (i) The Effect of Maternal Age on 143 the Rate of Embryonic Development (ii) The Effect of Maternal Age when 145 mated on the Proportion of Infertile Eggs produced (iii) The Effect of Maternal Age on 145 the Proportion of Eggs Hatching (f) Summary 147 (v) The Egg Development of C. legatella 149 (a) Duration of Development under 149 Natural Conditions (b) Duration of Development in an 152 Outdoor Insectary (c) Etbryogenesis in an Outdoor Insectary 154 Summary of (a), (b) and (c) 165 (d) 'embryonic Development under 165 Controlled Conditions (i) The Effects of Three Constant 187 Temperatures on Egg Development (ii) The Effect of a Low Temperature 192 Regimeon Subsequent Development at 20C. -5-- Page (iii) The Effect of High Initial 193 Temperatures on Embryonic Development (iv) The Effects of 20°C. and 9°C./3°C. 198 on Embryonic Development after Blastokinesis (v) The effects of Dif7erent 199 Temperature RegiEes with a common mean of 6 C. (e) Further Aspects of Embryonic Develop- 203 ment under Natural and Insectary Conditions (i) The Effect of Temperature early 203 in Development on the Dispersion of the Emergence Curve (ii) The Effect of Temperature on 210 Eclosion (f) Parental Effects on Egg Development 215 (i) Parental Effect on Duration of 215 Development (ii) Parental Effect on Egg weight 218 (iii) The Effect of Maternal Age on 219 Egg Viability (iv) The Influence of Egg Weight and 223 Time of Oviposition on the Duration of Development (g) Summary 225 (vi) Discussion 229 SUMMARY 256 ACKNOWLEDGEMENTS 258 REFERENCES 260 STATISTICAL APPENDICES 272 -6- GENERAL INTRODUCTION The genus Chesias Treitschke is represented in this country by two species, Chesias legatella Schiffermiiller and Chesias rufata Fabricius. These species are of no economic importance, but are of interest because their larvae feed on the same host plant, Sarothamnus scoparius (L.) Wimmer, and yet they differ in many features of their biology. This thesis seeks to provide information on the biology of C. legatella and C. rufata and of their parasites (mainly Braconidae in the genera Ap.nteles nrster and Microplitis nrster), and provides a detailed comparative account of the embryonic development of both species. The effects of various factors on the development of the embryo are examined in several ways. A detailed investigation has been made of the morpho- genesis of both species, and of the variation in its rate under different conditions. Studies of this kind, involving the use of large samples of eggs, previously have been con- fined almost entirely to Orthopterat and this is probably the first attempt of its kind within the Lepidoptera. GENERAL kATERIALS AND THODS (i) Collecting The abundant broom at Silwood Park provided a moderate supply of C. lesatella. The overwintering eggs, which are laid on the younger stems, were collected by the close examination of branches gathered from the field. They can be recognised by their bright orange colour, even though many are hidden in the stem axils. Larvae were obtained at all developmental stages by beating broom bushes onto a white boating tray; the larger ones were picked up individually, whilst the younger instars were taken up in an aspirator. The adults of this species we-'e collected by beating bushes of broom, and in two light traps. The beating method sometimes yielded reasonable numbers of both sexes, particularly during the latter part of a warm sunny afternoon; the moths would fly when disturbed, and could be caught in a net. The light traps were placed in an area of broom bushes; trap No.i (Plate 1 0 fig. a) was a standard Rothamsted trap fitted with a 200 w. tungsten lamp Oilliams, 1948); trap No.2 was a portable version with a 125 w. Phillips U.V. lamp, collapsible legs, and "Perspex" panels replacing the glass. In both traps the conventional killing jar was replaced by a large polythene bag filled with egg packing, and attached at the top by a strong elastic band; moths entering the bag settled quietly under the packing, and the whole bag could be removed the following morning and its contents sorted in the laboratory. The traps were operated by a time switch, which switched them on one hour after sunset and off one hour before sunrise. Large numbers of C. legatella were caught with these traps, but females were in the minority. Considerable difficulty was experienced in locating a plentiful supply of C. rufata. This moth is only present in very small numbers at Silwood Park. Areas of broom were beaten in the following localities at various times during the summer of 1967, in the hope of disturbing adult moths: National Locality Grid Reference Disused Gravel Pit, Easthampstead, Berks. ... SU 873659 Bisley Camp, Surrey. ... SU 94.4579 Blackwater, Hants. ... SU 846597 Ascot Heath, Berks. ... SU 924.693 Farnham By—Pass, Surrey. ... SU 833460 Romsey, Hants. ... SU 343201 This proved unsuccessful, and it was not until A.L. Goodson a. :iothamsteM. Light . trap b. Sleeved broom plant c. Mating Cage Plate 1. Collecting and Rearing Apparatus. -10— (personal communication) recommended Barnes Common, London, 8.7.13 (Nat, Grid. Ref. TQ 225759), that larvae were located in large numbers, and collected in September of that year. Subsequent collecting during the adult season showed that, even when present in large numbers, this moth is very reluctant to fly when disturbed during the daytime. Consequently this species may be present at some of the localities mentioned above; however, a plentiful supply from Barnes Common made the verification of this unnecessary. At dusk, moths of this species suddenly become very active, and may then be collected with the aid of a net and torch as they fly between the broom bushes. During this time females can be seen vibrating their wings on the top of broom bushes, and may be collected in specimen tubes. The small size of the eggs, and the dense foliage of the broom plants, made the collection of eggs of this species quite impractical. (ii) Rearing Rearing for experimental purposes took place in an outdoor insectary, thus providing all stages of the life cycle of each species with conditions comparable with those in the field. The result of this was that only one generation was reared in each species in any one year, -11— since both have an obligate diapause in each generation. When any one stage in the life cycle was subjected to experimental conditions, neither the later stages of that generation nor subsequent generations bred from that material were used in further experiments. (a) Larvae were reared in a variety of ways. When individual rearing was necessary, each larva was kept in a 7.6 x 2.5 ems.
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