Toxicological and Biological Effects of Abamectin, Malathion and Three Plant Oils Singly and in Combination on Cowpea Weevil, Callosobruchus maculatus (F.).

The toxicological and biological effects of abamectin, malathion and three plant oils (olive oil, peanut oil and linseed oil) singly and in three mixture ratios (5:95, 10:90 and 15:85) of the oils and insecticides, were evaluated on cowpea beetle, Callosobruchus maculatus (F.) infested cowpea seeds. Abamectin showed synergistic activity when combined with olive oil and peanut oil at the three mixing ratios recording co- toxicity coefficient values, (128.90, 276.08 and 371.55) and (110.85, 135.96 and 205.72), respectively. Malathion exhibited high synergistic activity with linseed oil at the three mixing ratios recording co toxicity coefficient values 174.56, 307.42 and 472.73, respectively. Also, malathion and peanut oil showed synergistic activity at 90:10 and 85:15 mixing ratios recording co toxicity coefficient value 114.95 and 163.80, respectively. The activity of abamectin and malathion singly or in mixtures with the three oils were significantly increased, particularly at the higher concentrations. Malathion combinations with olive oil and linseed oil were more effective than those with abamectin in reducing number of laid eggs. Abamectin in combination with olive or linseed oils was more effective than those of malathion in suppressing egg hatchability. It was reported that abamectin mixtures with the three tested oils were more effective than those with malathion in decreasing the number of emerged adults. A complete protection of treated seeds was achieved with the mixture of   olive oil: abamectin at 10: 90 mixing ratio, peanut oil: abamectin at 5:95 & 10:90 mixing ratio, at the concentrations of 500 and 1000 ppm, respectively. It could be concluded that the use of plant oils combined with pesticides increase the mortality of the cowpea beetle stages, as well as decrease the use of the chemicals to save the environment from pesticide pollution.