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 physical cues to locate and recognize its main host, the pea aphid Acyrthosiphon pisum (Harris). In wind tunnel studies, it was demonstrated that plant volatiles, particularly those induced by aphid feeding, are important long-range cues in the initial stages of host location. Furthermore, A. ervi distinguished between plants damaged by Ac. pisum and those damaged by the nonhost aphid Aphis fabae (Scop.). Host-induced volatiles were emitted by young broad bean plants (Vicia faba) in sufficient quantities to elicit a flight response from female parasitoids after 40 aphids had been feeding for 72 h. Aphids confined to a single leaf caused systemic production of herbivore-induced volatiles throughout the plant. Previous experiences with hosts or host-related cues heightened parasitoid responses to host-induced volatiles and also triggered responses to other plant volatiles. This learning ability provides the parasitoid with behavioral plasticity to adapt its responses to suit prevailing foraging opportunities. A. ervi females also responded to synthetic aphid sex pheromones in wind tunnel experiments, and attempts are being made to manipulate field populations using host pheromone lures. Contact kairomones in the host cuticle and cornicle secretion appear to be involved in host recognition and acceptance by A. ervi females. In addition, visual cues play a role in host location and recognition, with color being an important short-range cue. Color alone stimulated attack responses; A. ervi females attacked green aphids in preference to brown aphids and showed attack responses toward yellow paint pigments enclosed in glass capillary tips. (C) 1998 Academic Press.