Physiological factors determining host suitability of lepidopteran stemborers for parasitization by Cotesia flavipes-complex parasitoids (Braconidae: Hymenoptera)

Determining the host range of a biological control agent is crucial to the success and safety of a biological control program. I studied some of the physiological factors that determine the host range of Cotesia flavipes-complex endoparasitoids, and the determinants of host suitability of pyralid (Diatraea saccharalis and D. grandiosella ) and crambid (Ostrinia nubilalis) stemborers for the development of these parasitoids. I found that closely related parasitoids that are taxonomically, behaviorally and ecologically very similar differ in their ability to utilize a host of the same species. Similarly, utilization of related hosts can produce different outcomes for a given parasitoid species. In addition, suitability studies using two different strains of the same parasitoid species showed different results between the two strains.; The main component of the host's immune response is the encapsulation of the parasitoid progeny by the host's hemocytes. The chronology of encapsulation varies for different host-parasitoid combinations and was not correlated with the changes in total hemocyte levels within the host. Different species of parasitoids may use different factors at different times after parasitization to counter the host's immune response. I looked at two factors specifically. First, there were no differences in gross egg surface ultrastructure observed while the egg develops in a unsuitable host compared to when it develops in a suitable host. The second factor studied were the teratocytes which appear when in some host-parasitoid combinations the encapsulation process ensues. During the course of parasitization the teratocytes grow larger but decrease in number. In less optimally suitable hosts the teratocytes actually grow larger. There is little difference in overall growth between unparasitized and parasitized Diatraea larvae. No differences in hemolymph protein profiles for the different host-parasitoid combinations were seen.; The physiological host range of C. flavipes-complex parasitoids will likely be narrow, but exact host range will be difficult to predict. It is the hope that basic biological studies, such as those presented here, will help in the design of host range tests while also providing better understanding of the mechanisms used by insects to defend against invaders.