Comparison of toxicity and residual effectiveness of Actara® (Thiamethoxam®) with three pyrethroid insecticides against five Coleopteran species infesting stored – products.

Abstract

The purpose of this research is to present results from laboratory experiments designed to compare the toxicity and residual effectiveness of the neonicotinoide Actera (25%WG) to five coleopteran species pests of stored products with those of the three pyrethroid insecticides Copex (20%EC), Decis (2.5%EC) Vapcocidine (20%EC) using 24hr vial bioassays. One – day old adults of Callosobruchus maculatus Fab., Trogaderma granarium Everts. and 4 weeks old adults of Sitophilus oryzae L., Tribolium costaneum Herbst and Tribolium confusum J du val. were used throughout the tests.The relative toxities (LC50 values) of the four insecticides to the five insect species were determined by exposing the adults to an insecticide deposit in glass vials (2.7*7.5cm) immediately (zero - time) after treating the vials. The results showed Actara to be the most toxic one followed in desending order of toxicity by Decis, Vapcocidin and Coopex. The susceptibilities of the five species to the four insecticides were in the order of C.maculatus > T.granarium >> S.oryzee >T.costaneum and T.confusem. The results from residual test designed to evaluate the relative efficacies of the four insecticides 1 and 2- weeks after treating the vials showed Actara to be a little more effective than Decis and much more effective than Vapcociden and Coopex . The results also showed that the three pyrethroid msecticides, in general, lost activity against the five insect species faster than Actara, indicating that Actara is relatively more persistant than the three pyrethroids tested.