TOXICITY OF THREE INDIGENOUS PLANT EXTRACTS AGAINST CALLOSOBRUCHUS CHINENSIS L. (BRUCHIDAE: COLEOPTERA)

Abstract

The study was conducted to evaluated the efficacy of three indigenous plant extracts namely, neem (Azadirachta indica L.), custard apple (Annona reticulata L.), and eucalyptus (Eucalyptus camaldulensis L.) in acetone and methanol solvent for their toxicity and residual effects against the pulse beetle, Callosobruchus chinensis L. (Bruchidae: Coleoptera) in the laboratory conditions of the Department of Entomology, HSTU, during February to May 2017. The 5 concentrations (5.0, 2.50, 1.25, 0.625, and 0.3125%) along with a control of the botanical plant extracts were applied in bioassay. The results of the present study indicated that all the plant extracts had toxic and residual effects for controlling pulse beetle in storage but neem extract was more toxic. Different plant extracts and doses with hour after treatments against the pulse beetle mortality and residual effects were statistically different. Among the plant extracts, neem extract provided the highest mortality (36.78%) whereas eucalyptus extract possessed the lowest mortality (22.75%) effect. The order of the toxicity of three plant extracts were found neem > custard apple > eucalyptus. Mortality percentages were also found directly proportional to the hour after treatments. The highest mortality was found in the highest time and the lowest mortality was found in the lowest time. Between two solvents, acetone solvent possessed the highest toxicity effect (32.95%) and methanol solvent possessed the lowest toxicity (30.56 %). The residual toxicity was evaluated by considering egg laid, adult emergence, seed infestation and weight loss caused by the insect. Among the plant extracts with two solvents (acetone and methanol), the highest residual toxicity was found in neem and custard apple extract with acetone and methanol solvent respectively. On the contrary the lowest residual toxicity was found in eucalyptus extract with acetone and methanol solvents. Toxic and residual effects of two different solvents, neem extract with acetone solvent and custard apple extract with methanol solvent were the highest effective against pulse beetle among all the plant extracts applied.