Evaluation of volatile constituents of neem (Azadirachta indica A. Juss.) leaf extracts against Callosobruchus maculatus (F.)

Abstract

The effect of neem (Azadirachta indica A. Juss.) leaf volatiles was investigated against the cowpea bruchid, Callosobruchus maculatus (F.) to test fumigant toxicity, contact toxicity and repellency using olfactometcr and choice chamber bioassays. Callosobruchus maculatus is more susceptible to contact toxicity than to fumigant toxicity. During fumigant and contact toxicity bioassays, the percentage mortality increased, while oviposition and the number of F1 adults that emerged were significantly inhibited by neem leaf volatiles at concentrations higher than 23.0 g/l and 3.8 g/l respectively at 3 days after treatment. The LC50 values for contact and fumigant toxicity were 1.14 g/l and 8.45 g/l respectively. The results for the toxicity bioassays revealed that the contact effect of leaf volatiles on bruchids is higher than the fumigant effect. Choice chamber and olfactometer bioassays demonstrated the repellent effect of neem leaf volatiles against cowpea bruchids. At a dose of 160 mg, the mean number of bruchids that responded in the olfactometer and choice bioassuys were 3.83 and 0.20 respectively. These findings indicate the suitability of neem loaf volatiles as a botanical insecticide and a repellent in the control of cowpea bruchids. Further studies on the active compounds in the volatiles und their effect on bruchids need to be investigated before recommending neem leaf volatiles as a suitable commercial product.