Possible relationship between egg morphology of stored-product insect eggs and fumigant efficacy

Eggs of Carpophilus hemipterus (L.) (Coleoptera: Nitidulidae), Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), and Amyelois transitella (Walker) (Lepidoptera: Pyralidae) were imaged using scanning electron microscopy to explore how respiratory openings on the chorion surface may affect relative efficacy of fumigation. C. hemipterus eggs each had two aeropyles and no micropyles, T. castaneum did not have any aeropyles or micropyles, and lepidopterous eggs of A. transitella as well as P. interpunctella had many aeropyles and several micropyles. The cross-sectional area of the chorion for all species was imaged using a transmission electron microscope. C. hemipterus had the thickest chorion relative to other species. Our data suggest that a fumigant or fumigants may differentially diffuse into the eggs of these species, with penetration through aeropyles and micropyles likely occurring to a greater extent in P. interpunctella and A. transitella than in C. hemipterus and T. castaneum. Although measurements of fumigant diffusion into eggs are needed to confirm our findings, these results suggest that species-specific ovicidal efficacies are related, at least in part, to the surface morphology of eggs and that chorionic thickness and respiratory openings may differentially affect fumigant penetration and/or uptake.