Suitability of lepidopteran stemborers for parasitization by novel-association endoparasitoids

Extensive study of insect immune systems has yielded a better understanding of the mechanisms used by insects to defend against invaders. This knowledge can be used to predict how natural enemies utilize potential hosts, which will aid in the planning of biological control programs. Our experimental system consists of novel host-parasitoid associations, with two New World pyralid stalk borers, Diatraea saccharalis and D. grandiosella; one Old World crambid borer, Ostrinia nubilalis; and three Old World microgastrine braconid parasitoids, Cotesia chilonis, C. sesamiae, and C. flavipes. Experiments on host suitability indicate that parasitoids that are taxonomically, behaviorally and ecologically very similar may differ in their ability to utilize a host of the same species. Likewise, utilization of related hosts can produce different outcomes for a given parasitoid species. D. saccharalis is a suitable host for all three parasitoid species, whereas D. grandiosella often encapsulates C. sesamiae and C. flavipes. O. nubilalis is an unsuitable host for all three species. Different species of parasitoids may use different factors at different times after parasitization to counter the host's immune response. This study suggests that the physiological host range of these parasitoids will be narrow, thus limiting effects on non-target species. However, the lack of consistent patterns also shows that explicit testing will be needed to determine host ranges.