LARVICIDAL EFFICACY OF SOME PLANT EXTRACTS AGAINST RED FLOUR BEETLE, TRIBOLIUM CASTANEUM (HERBST) (COLEOPTERA: TENEBRIONIDAE)

Abstract

An investigation was carried to find out the larvicidal efficacy of four plant extracts namely, custard apple (Annona reticulata), neem (Azadirachta indica), castor (Ricinus communis) and thorn apple (Datura stramonium) against the larvae of red flour beetle, Tribolium castaneum (Herbst) in the laboratory of the Department of Entomology, HSTU, Dinajpur during the period of February to July 2016. Different doses were made with methanol solvent for different larval instars (3rd, 4th, 5th and 6th) and were applied at different time interval. The result showed that all the four plants extracts were effective in checking insect infestation and had different toxic effects against the larvae of red flour beetle. Average mortality indicated that castor plant extract showed the highest toxic effect in all the larval instar (3 rd, 4th., 5th and 6th) of red flour beetle (average mortality 47.60%, 47.75%, 45.77% and 57.78% respectively). Whereas the lowest toxicity was found in the thorn apple leaf extracts on 3 rd and 5th instar larvae (average mortality 20.14% and 25.14%, respectively) and neem leaf extracts at 4th and 6th instar larvae (average mortality 30.26% and 27.46%, respectively). The larval mortality was significantly differed among all the concentrations of the plant extracts applied. The highest mortality (52.26, 59.48, 55.00 and 60.75%) was recorded in maximum concentration (1.77, 3.54, 7.07 and 10.61 mg/cm 2 , respectively) at different larval instar (3 rd, 4th , 5 th and 6th). Mortality percentage was also observed directly proportional to the level of concentrations of plant extracts and to the exposure period. Probit analysis of larval mortality also revealed that the castor plant extract maintained its highest toxicity at different time interval among all the plant extracts applied.