Females of Cotesia vestalis, a parasitoid of diamondback moth larvae, learn to recognise cues from aphid-infested plants to exploit honeydew

1. To maximise their reproductive success, the females of most parasitoids must not only forage for hosts but must also find suitable food sources. These may be nectar and pollen from plants, heamolymph from hosts and/or honeydew from homopterous insects such as aphids. 2. Under laboratory conditions, females of Cotesia vestalis, a larval parasitoid of the diamondback moth (Plutella xylostella) which does not feed on host blood, survived significantly longer when held with cruciferous plants infested with non-host green peach aphids (Myzus persicae) than when held with only uninfested plants. 3. Naive parasitoids exhibited no preference between aphid-infested and uninfested plants in a dual-choice test, but those that had been previously fed aphid honeydew significantly preferred aphid-infested plants to uninfested ones. 4. These results suggest that parasitoids that do not use aphids as hosts have the potential ability to learn cues from aphid-infested plants when foraging for food. This flexible foraging behaviour could allow them to increase their lifetime reproductive success.