HOST DISCRIMINATION BY THE APHID PARASITOID APHELINUS-ASYCHIS (HYMENOPTERA, APHELINIDAE) - WHEN SUPERPARASITISM IS NOT ADAPTIVE

Females of the solitary parasitoid Aphelinus asychis Walker discriminated between unparasitized and parasitized second-instar nymphs of the pea aphid, Acyrthosiphon pisum (Harris). Wasps normally avoided superparasitism, except when they were confined with few hosts for a long time. Parasitoid females did not need previous experience with unparasitized aphids (learning) in order to discriminate. They probed with the ovipositor any aphids encountered, a behaviour suggesting that host acceptance and rejection were determined by internal cues. Prolonged ovipositor insertion (>80 s) was correlated with host acceptance and egg deposition, but short insertion times (∠80 s) generally indicated host rejection. Females tended to reject both self-and conspecific-parasitized aphids when provided with two of each kind. We consider hypotheses that conspecific superparasitism may be adaptive and give examples to show exceptions. We propose that, in egg-limited parasitoid species such as A. asychis, a reproductive strategy based on the regulation of egg production and on oosorption can explain the equal avoidance of self and conspecific superparasitism. © 1990, Entomological Society of Canada. All rights reserved.