THE STRUCTURE OF BRUCHID EGGS MAY EXPLAIN THE OVICIDAL EFFECT OF OILS

Bruchid eggs have very rarely been studied and yet oils, many of local, vegetable origin, having an ovicidal effect, are one of the commonest means of controlling infestations by subsistence farmers. This study incorporates a description of the external and sectional appearance of the eggs of four species of Callosobruchus and of Zabrotes subfasciatus (Boh.) (Coleoptera: Bruchidae) and comparable published data on the eggs of other major pest species. Callosobruchus eggs each have a large space enclosed between the egg and the testa of the seed to which it is attached. Uniquely among those eggs adequately described, this space is connected with the exterior by a short funnel at the posterior end of the egg. It is suggested that the differences in egg structure between genera may explain the traditional use of oils for Callosobruchus control but lesser use for control of other genera. The hypothesis is presented that occlusion of the funnel by some oils is the reason for their ovicidal and perhaps their 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.