Toxicity and oviposition inhibitory effect of extract and powder of Momordica charantia leaf against Callosobruchus maculatus Fab. (Coleoptera: Chrysomelidae) on stored cowpea seed

The pulse beetles, Callosobruchus maculatus is a principal field-to store pest of cowpea in the tropics and at present synthetic insecticides constitute a major means of control. The insecticidal effect of ethanolic extracts and powders of Momordica charantia leaf against the cowpea beetle, Callosobruchus maculatus Fab. were carried out in the laboratory. The efficacy of powder and ethanolic extract of M. charantia leaf as toxicants against C. maculatus were investigated using contact toxicity and oviposition deterrence. The powders and extracts were applied at various dosages of 0.2, 0.4, 0.6, and 0.8 g and 0.2, 0.4, 0.6 and 0.8 ml per 20 g of cowpea seeds. Beetle mortality was monitored for 96 h. The mortality of the insect increased with increase in dosage and period of exposure. Within 24 h post treatment, 0.8 g dosage of the plant powder recorded the highest beetle mortality of 35% but its effect was not significantly (p>0.05) different from that of 0.4 and 0.6 ml. At 96 h of post-treatment, all the dosages of the plant powders recorded above 75% insect mortality with 0.8 g of the powder achieving the highest insect mortality of 85% and its effect was not significantly (p<0.05) different from 0.2, 0.4 and 0.6 g. At 96 h post treatment, 0.8 ml of the extract achieved the highest mortality of 95% which was not significantly (p<0.05) different from that of 0.6 ml. All dosages of the extract recorded up to 80% bruchid mortality within 96 h post treatment. At all treatment levels, insect mortality was significantly (p<0.05) different from the control. It was observed that oviposition was reduced in both powder and extract treatments when compared to the control. The results show that both powder and extract of M. charantia were effective in controlling C. maculatus and could serve as alternative to over-dependence on synthetic insecticide for preservation of stored cowpea seeds against C. maculatus