Insecticidal Compound from Himatanthus drasticus Latex against Cowpea Infestation by Callosobruchus maculatus (Coleoptera: Chrysomelidae)

Vigna unguiculata is an important source of proteins and energy for humans and animals. However, postharvest losses caused by Callosobruchus maculatus can reach from 20 to 100% of stored seeds. In this study, the insecticide potential of compounds extracted from Himatanthus drasticus latex was assessed. The latex was extracted with ethanol (70%) and then partitioned through sequential use of hexane and chloroform. These fractions were investigated by chromatography to determine their chemical composition. Plumieride, identified in a hydroalcoholic subfraction, was tested for insecticidal activity against C. maculatus. The ethanolic fraction (LC50 = 0.109; LC90 = 0.106%) and the plumieride (LC50 = 0.166; LC90 = 0.167%) were lethal to larvae. Plumieride (0.25%) delayed larval development, and mortality reached 100%. Its inhibitory action on intestinal alpha-amylase from larvae was higher (89.12%) than that of acarbose (63.82%). Plumieride (0.1%) inhibited the enzyme alpha-amylase in vivo in the larval intestine. This result was confirmed by a zymogram test performed by SDS-PAGE when the enzyme electrophoresed on gel copolymerized with starch. When spread on seeds, the hydroalcoholic fraction (1.0%) reduced infestation. The loss of seed mass was 5.26% compared to the control (44.97%). The results confirm the effect of latex compounds in protecting stored seeds against weevil infestation.

Automated summary

This study assessed the insecticide potential of compounds extracted from Himatanthus drasticus latex against Callosobruchus maculatus. The results showed that plumieride from the latex had lethal effects on the larvae and inhibited enzyme activity in vivo. Additionally, the application of the hydroalcoholic fraction on seeds reduced infestation effectively.