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SPECIFICITY IN PREDATOR—PREY RELATIONSHIPS seilcoAL WITH PARILIQULAR REFERENCE TO THE APHIDOPHAGOUS COCCINELLIDAE R. L. Blackman B.Sc. A thesis submitted for the Degree of Doctor of Philosophy of the University of London Imperial College of Science and Technology, Field Station, Silwood Park, Sunninghill, ASCOT, Berkshire. October, 1965. 2. ABSTRACT In the first section of the thesis an attempt is made to present a picture of the nature and extent of specificity as it occurs in the food relations of certain groups of predacious insects, in so far as the present state of our knowledge permits. The experimental work described in the second section of the thesis was done on two species of aphidophagous Coccinellid, Adalia bipunctata L. and Coccinella septem- punctata L. The effects of different aphid species on the rate of development and mortality of the larvae and the size and fecundity of the adults are compared. The relative unsuitability of certain aphids, especially Aphis fabae as food for Adalia bipunctata, is discussed. A comparison is made of the feeding behaviour of the two Coccinellids on four species of aphid. Experiments are described in which the ability of larvae and adults to select a suitable aphid or avoid an unsuitable one was investigated. The ecological significance of the results is considered, and the potential value of such predators in pest control, given a better knowledge of their prey relations and specificity, is briefly discussed. CONTENTS SECTION 1. INTRODUCTION AND REVIEW OF THE LITERATURE. INTRODUCTION 6 SPECIFICITY IN PREDATOR-PREY RELATIONSHIPS 10 1. Insects which are predatory in the larval stage only 10 2. Insects which are predatory in the adult stage only 18 3.Insects which are predatory in both feeding stages a) Adults and larvae with different feeding habits 22 b) Adults and larvae with similar feeding habits 27 SPECIFICITY IN THE COCCINELLIDAE 39 SECTION 2. THE SUITABILITY OF DIFFERENT APHIDS AS FOOD FOR ADALIA BIPUNCTATA L. & COCCINELLA 7-PUNCTATA L. INTRODUCTION 61 REARING TECHNIQUES AND GENERAL PROCEDURE 62 THE EFFECT OF DIFFERENT APHID FOODS ON THE DEVELOPMENT OF THE LARVAL PREDATOR 68 (A) Adalia bipunctata: 1) Rate of Development 68 4. 2)Weight of Food Eaten 72 3)Mortality during Larval Development 77 4)Weight of Adult at Emergence 79 (B) Coccinella 7-punctata 82 THE EFFECTS OF DIFFERENT APHID FOODS ON THE FECUNDITY OF THE ADULT PREDATOR. 87 (A)Adalia bipunctata 87 (B)Coccinella 7-punctata 92 APHIS FABAE AS FOOD FOR ADALIA BIPUNCTATA 97 A COMPARATIVE STUDY OF THE FEEDING BEHAVIOUR OF LARVAE OF A. BIPUNCTATA & C. 7-PUNCTATA ON FOUR APHID SPECIES. 107 SELECTION BEHAVIOUR BY THE LARVAL PREDATOR 120 (A)Adalia bipunctata • 120 (B)Coccinella 7-punctata 131 SELECTION BEHAVIOUR BY THE ADULT PREDATOR 136 EXAMINATION OF THE GUT CONTENTS OF FIELD COLLECTED ADULTS 145 DISCUSSION 150 SUMMARY 161 ACKNOWLEDGEMENTS 165 BIBLIOGRAPHY 166 5. SECTION 1 INTRODUCTION AND REVIEW OF THE LITERATURE. 6. INTRODUCTION The predatory habit has been developed many times independently in insects. Some members of every major insect order are predacious. As a result predacious insects considered as a group are an extremely diverse assembly, incorporating a wide range of structure, feeding habits and choice of food. The situation is further complicated by the fact that an insect may be predacious in both larval and adult stages, in the larval stage only, or in the adult stage only. Accounts of the occurrence of predatism among insects have been given by Sweetman (1936), Clausen (1940), Balduf (1936,1939) and Brues (1946). It is somewhat surprising that Balduf (1942) is the only writer to attempt any sort of classification of the types of predator-prey relationship occurring in insects. He uses three main divisions; (1) Hyphenic relations, in which he places all 'occasional predators', irrespective of whether they meet the rest of their food requirements as phytophags, scavengers, or parasites; (2) Absolute predatism, characterised by the fact that 7. the food taken by one or both feeding stages "consists exclusively of insect prey", and (3) Opportunistic feeders, insects which accept any food that comes their way, exemplified by the feeding habits of most Tric ioptera. As an example of an 'occasional predator' in group (1), Balduf cites the Anthomyid fly Hylemya cilicrura Rond, of which the larva, although a major pest of various crops throughout the world, is essentially a general feeder and has been recorded feeding on living and dead animal matter, particularly the eggs of locusts. He also includes in this group Lycaenid caterpillars which feed on plants in the earlier instars but complete their development by devouring the brood in the subterranean nests of ants. The change of diet is here brought about by the production from the second instar onwards of an ant- attractirv; secretion by the caterpillar, as a result of which it is tolerated in and may even be carried into the ant-nest. The change of diet is thus the result of a special adaptation on the part of the Lycaenid, which becomes an obligatory predator for the rest of its larval life. 8., Thus Balduf's 'hyphenic relations' may be obligatory, or facultative on the part of the predator entering into them. It would seem more logical to make a basic distinction between facultative and obligatory predation. Facultative predators may resort to predation in certain circumstances, perhaps even more often than not, but adoption of the predatory habit is not essential to them. Obligatory predators do not necessarily feed exclusively by predation, and in fact many predators use other food sources when their prey becomes scarce, but the predatory habit is essential to their survival and development at one or more stages in the life-cycle. Further consideration of the types of facultative predation occurring in insects would be outside the scope of this thesis. The discussion of specificity in prey relationships of obligatory predators depends on an understanding of the different types of relationship occurring between predators and their prey. It is important to distinguish between insects in which only the larvae are predatory, insects in which only the adult stage is predatory, and insects which are predatory in both feeding stages. In the 9. last of these groups, which is much the largest, it is necessary to make a distinction between insects where the larvae and adults are markedly dissimilar in their feeding habits, and insects where both feeding stages have similar food and habitat. The following consideration of specificity in predator-prey relation- ships is based upon this scheme. Only the more important groups of terrestrial insect predators will be considered, and as mentioned already discussion will be restricted to obligatory predators. 10. SPECIFICITY IN PREDATOR-PREY RELATIQNSAIP (1) Insects which are predatory in the larval stage only. Balduf (1938, 1939) has given a very complete account of the occurrence and development of the predatory habit in the Lepidoptera, and this forms a convenient and interesting starting point for the review. Entomophagy in larvae of Lepidoptera was first reviewed by Clark (1926). Eight families of Lepidoptera contain members with predacious larvae, yet with very few exceptions in all these families Coccids are the only prey. Balduf's theories as to the origin of entomo- phagous habits in Lepidoptera attempt to explain this almost exclusive coccidophagy. In the Lycaenidae, larvae of some species eat lichens and algae on the bark of trees, whereas other species in genera of the same sub-family prey on scale-insects in the same sort of situation. A change of feeding habit from eating lichens to eating Coccids is not difficult to envisage, and Balduf proposes that such a change has come about many times in different families of Lepidoptera. Feniseca tarquinius Fabr., the first caterpillar known to be entomophagous (Edwards 1886), is an exception to the general rule of coccidophagy. This species feeds on several species of aphids, but all are woolly aphids, sessile insects similar to Coccids in that they would not involve a significant change in feeding behaviour from a lichen-feeding habit. Other minority foods of predacious caterpillars include ant larvae(Liphyra Lycaena spp., Cyclotorna) and Jassid and Membracid guests in ants' nests (Megalopalpus, Lachnocnema); both these habits having arisen according to Balduf's theories from the entrance of ants into the lives of the caterpillars. The ants either build the caterpillar into their nest incidental to sheltering the Coccids on which it is feeding, or guide or transport the caterpillar to their nest because it yields an attractive secretion. In the latter case the Lepidopteran may be deprived of its original food and resort to other food-sources, such as the ant-brood and ant-guests. The egg-laying habits of the adults of coccido- phagous Lepidoptera are imperfectly known, but in general the eggs seem to be deposited in close association 12. with the larval food, and are often inserted in between or laid on the backs of individual Coccids. The range of species preyed upon clearly depends on the degree of specificity shown by the adult in its oviposition behaviour. There is some evidence of specificity, in the relationship between Eublemma amabilis Moore and lac scales (Laccifer spp.) for example (Misra, 'Negi and Gupta, 1930), but other species show little sign of any preference in their choice of Coccid as larval food, and prey records are too inadequate for any definite conclusions. It seems possible that the adult butterfly is attracted by the Coccid honeydew, and this is another way in which the caterpillar- Coccid association could have arisen. Two other groups in which larvae only are predacious will be considered. These are members of two families of Diptera, the Syrphidae and the Cecidomyidae.

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