Using Microscopy to Assess Chorion Structural Integrity and Parasitoid Oviposition Sites on Stink Bug (Hemiptera: Pentatomidae) Eggs

Previous efficacy studies found that many insecticides used by growers could be having an adverse effect on egg parasitoids (Telenomus podisi) developing in the eggs of the brown stink bug (Euschistus servus), while unhatched stink bugs experienced lower levels of mortality. One plausible explanation for this was that insecticides might enter parasitized eggs more readily via oviposition wounds. Parasitized E. servus eggs, as well as nonparasitized stink bug (Acrosternum hilare, E. servus, Murgantia histrionica, and Podisus macoliventris) eggs, were examined using electron microscopy. Egg response to perforation by a tungsten probe served as a control. Microscopy images depicted the chorion surface as characterized by a matrix of ridges and micropylar processes in a ring around the margin of the operculum. Observations of oviposition sites showed a "scab" formed where the ovipositor penetrated the chorion, and at sites penetrated by the probe. These formations appeared to be the result of fluids from inside the egg leaking out, drying, and hardening after oviposition or probe perforation, suggesting that the response was not due to substances secreted by the parasitoid. Further, no open wounds or holes were seen to increase the possibility of insecticides entering parasitized eggs.