The structure of bruchid eggs may explain the ovicidal effect of oils.
Bruchid eggs have very rarely been studied. However, many oils of local, vegetable origin which have an ovicidal effect are one of the commonest means of controlling infestations by subsistence farmers. A description of the external and sectional appearance of the eggs of the bruchids Callosobruchus maculatus, C. chinensis, C. analis, C. rhodesianus and Zabrotes subfasciatus with published data on the eggs of other major pest species is given. Callosobruchus eggs each had a large space enclosed between the egg and the testa of the seed to which it was attached. Uniquely among those eggs adequately described in the literature, this space was connected with the exterior by a short funnel at the posterior end of the egg. It is suggested that differences in egg structure between genera may explain the traditional use of oils for Callosobruchus control, but their lesser use for control of pests in other genera. The hypothesis is presented that occlusion of the funnel by some oils is the reason for their ovicidal and perhaps larvicidal effects. It is further proposed that changes could be made to the physical characteristics of oils, in the light of the funnel dimensions, to enhance their effects.