Responses of aphids to semiochemicals released from ladybirds

Abstract: Predatory ladybirds, as natural enemies of aphids, can influence their prey in various ways, for example by consuming them or making the aphids drop off from their host plants. In this study, I have examined whether aphids can respond to the semiochemicals released from ladybirds. The tritrophic system chosen for my study will be barley plant (Hordeum vulgare L) - aphid (Rhopalosiphum padi L.) and an aphid predator, the seven-spotted ladybird (Coccinella septempunctata L.). In the laboratory experiments, a significant reduction of aphid host acceptance was observed on plant with previously presented ladybirds in comparison with control plants (without ladybirds). Aphid host acceptance was studied using a no-choice settling test. Aphids could respond to tracks left by ladybirds, showing avoidance responses in the choice test. In the olfactory experiments, aphid avoidance responses to volatiles released from ladybird adults and their track were correlated to the number of ladybirds that had previously been present on the plant. Volatiles released from both ladybird sexes may induce aphid response but aphids responded more intensively to female ladybirds than male. The results from these experiments indicate that aphids can discover the previous presence of ladybirds. Aphids, like parasitoids or competing female ladybirds, can recognize chemical components in the volatiles exuded by ladybirds and show avoidance responses to the places with former presence of predatory ladybirds. Aphid host plant acceptance and aphid settling on the plants were significantly affected by the previous presence of ladybird adults, both sexes. From an applied point of view, it would be very interesting to identify semiochemical components from ladybird tracks and potentially utilize them to reduce aphid population development in the field. This might lead to better biological aphid control and a remarkable reduction in the pesticide use.