Efficacy of artificial seeds in the delivery of bioactive compounds to the seed dwelling larvae of Callosobruchus maculatus (Coleoptera: Bruchidae)

Abstract

Artificial seeds offer an important method to assay the bioactivity of natural and synthetic compounds against insect larvae that develop within the cotyledons of seeds. Here, the efficacy of artificial seeds as a mechanism to deliver bioactive compounds to larvae of the bruchid beetle, Callosobruchus maculatus, was compared to that of black-eyed beans that had been imbibed with the same bioactive compounds: malachite green or the methanolic extract of neem (Azadirachta indica). Females laid an equivalent number of eggs on control artificial seeds in comparison with black-eyed beans, although egg-to-adult survival on artificial seeds was reduced. Manipulation of the hardness of artificial seeds influenced female oviposition decisions, with more eggs laid on the harder seeds, although seed hardness had no effect on egg-to-adult survival. Incorporation of neem extract or malachite green into the artificial seeds resulted in 100 % larval mortality, while larval mortality on seeds imbibed with neem extract or malachite green was between 50 and 70 %. This suggests incorporation of toxins into artificial seeds, produces a more sensitive assay of compound toxicity in comparison with the method of imbibing seeds and offers a useful method to study of seed–arthropod interactions.