Abstract

In spite of the wealth of information about the role of semiochemicals in the behavior of non-parasitized aphids, the olfactory responses of parasitized aphids have not yet been studied. Although parasitoid-induced behavioral changes have been shown in aphids, the cues involved in those behaviors are not well known. We studied the behavior of Sitobion avenae (Fabricius), non-parasitized and parasitized by Aphidius ervi Haliday, towards volatiles of conspecifics and of the hyperparasitoid Alloxysta victrix (Westwood) in an olfactometer. At 120 hours after parasitization, the aphids were significantly attracted by females of the hyperparasitoid, while 160 hours after parasitization the aphids were significantly repelled by conspecifics. Non-parasitized aphids showed neither attraction nor repellence toward either hyperparasitoids or conspecifics. Our results show that volatiles are involved in behavioral differences associated with parasitization. The results are discussed in relation to evolutionary hypotheses to explain the behavioural modifications in parasitized aphids.