Entomology PhD student Abdulla Ali’s dissertation project, “Captive Rearing and Semiochemical Ecology of Trichogramma papilionis (Hymenoptera: Trichogrammatidae),” was mischaracterized in the May 4 story “Fighting Insects With Insects.” CTAHR Notes apologizes for the error.
A Tiny Stingless Wasp
Abdulla’s project is on T. papilionis, a tiny stingless wasp that is an egg parasitoid. The insect lays its eggs in other insects’ eggs, keeping them from hatching, Abdullah addressed aspects of the mass rearing of T. papilionis, including the effects of varied colony founder size on wasp fitness and factors allowing the wasps locate egg hosts in which to lay their eggs.
First, Abdulla looked at what happens when a colony of wasps is started with just a single breeding female. This inbreeding didn’t change the amount of eggs laid per female over 10 generations, suggesting the imposed bottleneck didn’t result in reduced female fecundity. However, the number of founders of a colony did affect the emergence rate and sex ratio.
During the study, it was discovered that T. papilionis searched poorly in corn, the target crop for biocontrol. So Abdulla shifted to looking at their searching behavior in terms of chemical cues. He hypothesized the wasps are attracted to volatile chemicals put out by the host’s eggs or by the plant the host feeds on.
He discovered that captive-reared wasps actively prefer odors from corn earworm (Helicoverpa zea) eggs, with only a neutral response to eggs of the Mediterranean flour moth (Ephestia kuehniella). Further, the wasps were attracted to volatile emissions from sunn hemp (Crotalaria juncea) over maize (Zea mays), as long as both plants were infested with H. zea eggs. No preference was observed for plants not infested with H. zea eggs.
Abdulla’s findings underscore the importance of interactions between natural enemies, herbivores, and host plants in influencing insect behavior, and how variable environments impact parasitoid wasps. His results may help improve the efficacy of natural enemies of pests in augmentative and conservation biocontrol.
Since semiochemical cues can positively or negatively affect the response of parasitic wasps, this may provide an understanding of ecology that could help growers to achieve field parasitism and better pest management.