The impact of individual ladybirds (Coccinella septempunctata, Coleoptera : Coccinellidae) cell aphid colonies

Pea aphids (Acrythosiphon pisum) have been reported to produce winged offsp ring in the presence of predatory ladybirds. These offspring may leave host plants by flight after they have developed into winged adults. The inter-g enerational nature of his response raises the question about the chances of survival of aphids developing in attacked colonies. We studied the behavio ur of predatory ladybirds on host plants by releasing adult 7-spot ladybird s (Coccinella septempunctata) on bean plants hosting either no prey individ uals or colonies of 10 or 30 pea aphids. Interactions between predator and prey were recorded until the ladybird Ief the plant. Ladybird patch residen ce time increased with the number of aphids present on a plant but beetles generally left a plant before all aphids were eaten. The time budget of the ladybirds revealed a high proportion of time not spent in feeding activiti es. Predation rate was about one aphid killed per 10 min residence time in both treatments with aphid-infested plants. Aphids that survived an attack by the predator or that were alarmed when a conspecific was attacked often emigrated from the host plant, and their number was of the same magnitude a s the number of aphids killed by the predator. On average, pea aphid number s at the end of an experiment were reduced to less than a third of the init ial value. The results of the experiment show that attack by single ladybir ds does on average not cause immediate extinction of small aphid colonies. The short patch residence times of on average less than two hours show that a predator individual that induces winged-offspring production in an aphid colony will not any longer be present in the colony when the induced offsp ring mature. To understand the adaptiveness of predator-induced wing develo pment in pea aphids the probabilities of subsequent attacks on an aphid col ony need to be investigated.