Influence of experience on the response of Bathyplectes curculionis (Hymenoptera : Ichneumonidae), a nonaphidophagous parasitoid, to aphid odor

Bathyplectes curculionis (Thomson) is an introduced natural enemy of the al falfa weevil in North America. The wasp requires carbohydrate foods as an a dult. Adult wasps have increased longevity and fecundity when provided acce ss to pea aphid, Acyrthosiphon pisum (Harris), honeydew in the laboratory, and adults respond positively to the presence of pea aphids in alfalfa fiel ds. However, it is unknown how these wasps find aphid honeydew in the field . In a series of Y-tube olfactometer experiments, we evaluated the response of naive and experienced adult female B. curculionis to odors from pea aph ids, alfalfa, and pea aphids on alfalfa. Naive adult females did not respon d positively to pea aphid odor even when hungry. But adult females were abl e to learn aphid odor, and the mechanism of learning appears to be associat ive rather than by sensitization. Naive females also showed no preference f or alfalfa odor but learned alfalfa odor through sensitization. The wasps d id not distinguish between alfalfa with aphids and alfalfa without aphids, even after exposure to aphids or alfalfa with aphids, However, they preferr ed pea aphid odor to alfalfa odor after a feeding experience in the presenc e of pea aphid odors. But after exposure to mixed odors of aphids and alfal fa while feeding, B. curculionis females preferred the odor of alfalfa to t he odor of pea aphids. These results suggest that alfalfa odors mask or ove rride aphid odors when aphids are associated with alfalfa (as happens natur ally), thus interfering with the wasp's ability to respond to learned aphid odors. Therefore, although the wasps are capable of learning to find pea a phids and their honeydew in a simplified laboratory setting, it appears unl ikely that they do so in the field. (C) 2000 Academic Press.