STRATEGIES INVOLVED IN THE LOCATION OF HOSTS BY THE PARASITOID APHIDIUS-ERVI HALIDAY (HYMENOPTERA, BRACONIDAE, APHIDIINAE)

The parasitoid Aphidius ervi Haliday uses both semiochemical and physi cal cues to locate and recognize its main host, the pea aphid Acyrthos iphon pisum (Harris). In wind tunnel studies, it was demonstrated that plant volatiles, particularly those induced by aphid feeding, are imp ortant long-range cues in the initial stages of host location. Further more, A. ervi distinguished between plants damaged by Ac. pisum and th ose damaged by the nonhost aphid Aphis fabae (Scop.). Host-induced vol atiles were emitted by young broad bean plants (Vicia faba) in suffici ent quantities to elicit a flight response from female parasitoids aft er 40 aphids had been feeding for 72 h. Aphids confined to a single le af caused systemic production of herbivore-induced volatiles throughou t the plant. Previous experiences with hosts or host-related cues heig htened parasitoid responses to host-induced volatiles and also trigger ed responses to other plant volatiles. This learning ability provides the parasitoid with behavioral plasticity to adapt its responses to su it prevailing foraging opportunities. A. ervi females also responded t o synthetic aphid sex pheromones in wind tunnel experiments, and attem pts are being made to manipulate field populations using host pheromon e lures. Contact kairomones in the host cuticle and cornicle secretion appear to be involved in host recognition and acceptance by A. ervi f emales. In addition, visual cues play a role in host location and reco gnition, with color being an important short-range cue. Color alone st imulated attack responses; A. ervi females attacked green aphids in pr eference to brown aphids and showed attack responses toward yellow pai nt pigments enclosed in glass capillary tips. (C) 1998 Academic Press.