Host‐finding behavior, host acceptance, and host suitability of the parasite <i>Xanthopimpla stemmator</i>

Abstract

Abstract Xanthopimpla stemmator (Thunberg)(Hymenoptera: Ichneumonidae), a solitary endoparasite of pupae of Old World lepidopteran stalkborers, was recently imported into Texas as a candidate for biological control of New World stalkborers. Information on host acceptability, host suitability and cues responsible for host finding were necessary to gain an insight into parasite/host interactions, because of the absence of a coevolutionary history. Xanthopimpla stemmator females were exposed to laboratory‐reared one‐to six‐day‐old Diatraea saccharalis (F.) pupae. An average of 62% of host pupae were accepted and all ages of pupae were equally acceptable. Host suitability decreased with host age. One‐to five‐day‐old host pupae averaged 31–37% suitability, whereas only 19% of 6‐day‐old pupae were suitable. Successful parasitization, defined as the product of the proportion accepted and the proportion suitable, decreased from 22–23% for 1‐, 2‐ and 3‐day‐old pupae to 13% for 6‐day‐old pupae. Sex ratio (female:male) of the parasite progeny increased with host age. Females comprised 47% of total parasite progeny of 1‐day‐old and 84% of 6‐day‐old pupae. The increase in percent females was a result of a similar number of females in all age classes, coupled with a decrease in the number of males from older hosts. Xanthopimpla stemmator superparasitized 61% of accepted D. saccharalis pupae in the laboratory. On dissection, 73% of host pupae with multiple probe wounds were found to contain parasite eggs or larvae; these hosts contained up to 10 eggs or 7 first‐instar larvae. Increased numbers of probes by the parasites were associated with an increase in successful parasitization. Host seeking activity in X. stemmator was stimulated by the presence of larval frass, host odor and movement of host pupae. Results suggest that X. stemmator is a good candidate for biological control of D. saccharalis and possibly other factitious stalkborer hosts.