The ability to learn plant volatiles in Cotesia kariyai females was examined by wind tunnel bioassays. Searching experience on a host‐infested corn plant increased subsequent flight responses of females to the infested plant. Females experiencing host by‐products together with the volatiles extracted from infested leaves one time showed an increased response. However, such behavioral changes were not observed in females which experienced only the host by‐products or the volatiles. Thus, the increased response is considered to be preference learning. Multiple experiences of C. kariyai with host by‐products together with the volatiles did not increase their flight response to the volatiles. Furthermore, this learned response gradually decreased within 2 days. These behavioral modifications based on experience would be advantageous for C. kariyai to locate their polyphagous hosts efficiently.

Responses of the tachinid fly Exorista japonica Townsend to odors from corn plants infested with the fly's host, the larvae of the noctuid moth Mythimna separata (Walker), were examined in a wind tunnel. Naïve female flies showed a higher rate of landing on M. separata-infested corn plants from which the host larvae had been removed than on artificially damaged or intact corn plants. When paper impregnated with a solution of headspace volatiles collected from host-infested plants was attached to intact plants, females landed on the plants at a high rate. Females also responded to intact plants to which had been attached with paper impregnated with a synthetic blend of nine chemicals identified previously in host-infested plants. There was an optimum concentration of the synthetic blend for the females' landing. Of the nine chemicals identified previously, four [(E)-4,8-dimethyl-1,3,7-nonatriene, indole, 3-hydroxy-2-butanone, and 2-methyl-1-propanol] released only by host-infested plants were classified as a host-induced blend. The other five [(Z)-3-hexen-1-yl acetate, (E)-2-hexenal, hexanal, (Z)-3-hexen-1-ol, and linalool] were classified as a non-specific blend released not only by infested plants but also by artificially damaged or intact plants. In the wind tunnel, E. japonica females did not respond to intact plants to which paper containing a solution of non-specific blend or host-induced blend was attached. However, they showed a high level of response to a mixture of the non-specific and host-induced blends. These results indicate that naïve E. japonica use a combination of non-specific and host-induced blends as an olfactory cue for locating host-infested plants.

No abstract

The influence of host pupal age on host preference and host suitability in Brachymeria lasus (Walker) was examined. Rice armyworm, Mythimna separata (Walker), pupae of different ages, i.e., 0-1, 2-3, 4-5, 6-7 and 8-9 d old were used as hosts. The females accepted the host pupae equally for oviposition among 5 age groups, suggesting that female B. lasus does not discriminate hosts of different ages. However, the rate of progeny emergence was lower in old (6 to 9 d old) hosts. The adult parasitoid progeny produced from young (0 to 5 d old) hosts were heavier in body weight than those from old hosts. The developmental time of the immature stages of progeny was not significantly affected by host pupal age. Adult progeny with heavier body weight emerged earlier than lighter ones when reared on 0-to 5-d-old hosts. However, there was no correlation between the progeny body weight and developmental time of the immature stages when reared on 6-to 9-d-old hosts. Most of the progeny were females and no effect of host age was found on progeny sex ratio, which may be due to the low oviposition rate they experienced.