Residual toxicity of Spinetoram against to bean weevil, Acanthocelides obtectus Say. (Coleoptera: Bruchidae) on bean

Abstract

In present study, residual contact toxicity of spinetoram suspension applied to bean against Acanthocelides obtectus Say. (Coleoptera: Bruchidae) adults was investigated under laboratory conditions. In laboratory bioassays, A. obtectus adults were exposed to bean sprayed with spinetoram suspension at 0.1, 0.25, 0.5 and 1 ppm (mg active ingredient/kg commodity) at 26 +/- 1 degrees C temperature, 65 +/- 5 % relative humidity and completely dark condition. Paralysis and mortality of the adults were recorded after 1, 3, 5 and 7 day of exposure and 40 day later the bean was examined for progeny production. Based on the results obtained from the biological tests, concentration of spinetoram suspension and the exposure period had a significant effect on paralysis and mortality rate of A. obtectus adults on bean. Spinetoram treatments at all concentrations after 1 day of exposure resulted in low mortality of A. obtectus adults. Mortality of A. obtectus adults increased after 1 day of exposure period. Spinetoram treatments at low concentrations (0.1 and 0.25 ppm), resulted in low mortality of paralysis or mortality of A. obtectus adults at all exposure times. However, spinetoram treatment at higher concentrations (0.5 and 1 ppm) after 3 day of exposure resulted in almost 100 % paralysis or mortality of A. obtectus adults. These results indicated that 1 ppm concentration of spinetoram is enough to obtain the complete mortality of A. obtectus for 3 day of exposure. Spinetoram treatments at 0.25, 0.5 and 1 ppm completely hindered its progeny production. In conclusion, based on mortality and progeny production results spinetoram would be potential to be used for control of A. obtectus on stored beans as an alternative protectant to the conventional insecticides.