1. In the absence of aphids, adult females of Adalia bipunctata (L.) showed a greater reluctance to eat eggs than males.2. Eggs and young larvae were more vulnerable to cannibalism than older larvae and starved larvae were more vulnerable than well-fed larvae.3. Both egg and larval cannibalism is inversely related to the abundance of aphids. 4.Eggs are a better food, in terms of larval growth and survival, than aphids. 5. In the absence of aphids interspecific predation occurred, but not equally, between the coccinellids A. bipunctata, A. decempunctata (L.), Coccinella septempunctata L. and C. undecempunctata L.6. Larvae and adults of A . bipunctata and C.septempunctata were reluctant to eat conspecific eggs painted with a water extract of the other species' eggs and larvae of Cseptempunctata were more likely to die after eating a few eggs of A . bipunctata than vice versa. 7. These results indicate that cannibalism occurs mainly when aphid prey is scarce and is adaptive in that it improves the chances of survival, and coccinellids, to varying degrees, are defended against interspecific predation.

Predator-mediated plasticity in the morphology, life history and behaviour of prey organisms has been widely reported in freshwater ecosystems. Although clearly adaptive, similar responses have only recently been reported for terrestrial organisms. This is surprising as aphids are polyphenic and develop very rapidly compared with their predators and often produce very large colonies, which are attractive to predators. Therefore, one might expect terrestrial organisms like aphids to show a facultative change in their development in response to the presence of predators and other results have con¢rmed this. The results presented below indicate that the pea aphid responded to the tracks left by ladybird larvae by producing a greater proportion of winged o¡spring, which avoid the impending increased risk of predation by dispersing. Associated with this was a short-term increase in activity and reduction in fecundity. The black bean and vetch aphids, which are a¡orded some protection from ladybirds because they are ant attended and/or unpalatable, did not respond in this way to the presence of ladybird larvae.

No abstract

Abstract. 1. In insects, the age schedules of fecundity tend to be triangular and this has been attributed more to temporal patterns of mortality than to fecundity. The objective of the work reported here was to test the assumption that senescence shapes the fecundity function in ladybird beetles, and in particular that the production function declines with age.2. The results of a laboratory study on three species of predatory ladybird beetle indicated that the efficiency with which these insects acquire and process food declined with age. Although supplied with the same amount of food each day, after the onset of reproduction, these beetles ate less and less with increasing age. Egg production mirrored the decline in aphid consumption. Associated with this was a decline in fertility, assimilation, and speed of locomotion with age.3. This study indicates that production declined with age and that this shaped the fecundity schedules in these ladybird beetles. In addition, the results indicated that ladybirds are income breeders and, as predicted, the reproductive effort of the small species was greater than that of the large species used in this study.

There are several examples of intraguild interactions among insect predators of aphids, but little is known regarding the effects of interactions on feeding and oviposition of individual competitors in a guild. In the laboratory, we determined the feeding and oviposition responses of a ladybird predator to its conspecific and heterospecific competitors in an aphidophagous guild. Gravid females of Menochilus sexmaculatus (Fabricius) (Coleoptera, Coccinellidae) reduced oviposition, but not feeding, when exposed to immobilised conspecific or Coccinella transversalis (Fabricius) (Coleoptera, Coccinellidae) individuals in the short-term (3 h) and long-term (24 h). Feeding and oviposition responses were not affected when M . sexmaculatus females were exposed to larvae or adults of Scymnus pyrocheilus Mulsant (Coleoptera, Coccinellidae) beetles or larvae of the syrphid fly Ischiodon scutellaris (Fabricius) (Diptera: Syrphidae). The ratio of eggs laid to numbers of aphids consumed by M . sexmaculatus females was also affected by the presence of conspecific or C . transversalis larvae. The results suggest that fecundity of this predator may be affected by both conspecific and heterospecific competitors in a patchy resource.