Could biorational insecticides be used in the management of aflatoxigenic Aspergillus spp. and their insect vectors in stored wheat?

Insect pests in stored wheat cause significant losses and play an important role in the dispersal of viable fungal spores of various species including aflatoxin producing Aspergillus spp. The problems of insecticide resistance in stored insects and environmental hazards associated with fumigants and conventional grain protectants underscore the need to explore reduced risk insecticides to control stored insects and the ultimate effect on fungal infection inhibition. The purpose of this study was to investigate the insecticidal potential of four biorational insecticides: spinosad, thiamethoxam, imidacloprid and indoxacarb on wheat against Rhyzopertha dominica and Sitophilus oryzae and the subsequent effect of insects’ mortality on Aspergillus flavus and A. parasiticus infection in grains. Spinosad and thiamethoxam were the most effective insecticides against R. dominica compared to S. oryzae followed by imidacloprid. Spinosad applied at 0.25, 0.5 and 1ppm and thiamethoxam at 2 and 4ppm concentrations resulted in complete mortality of R. dominica and >90% infection inhibition of A. flavus and A. parasiticus. However, indoxacarb was more toxic against S. oryzae compared to R. dominica. The mortality of R. dominica was directly related to the percent infection inhibition of A. flavus and A. parasiticus in all the treatments. Whereas, mortality of S. oryzae was only related to the percent infection inhibition of A. parasiticus in all the treatments. The results show that although both spinosad and thiamethoxam can provide protection against R. dominica and fungal infections in stored grains, more potent reduced risk insecticides and/or their combinations would be needed than either of these to provide broad spectrum protection of stored grains. In conclusion, the results of the present study provide baseline data for the management of aflatoxigenic fungi by controlling stored insects using biorational insecticides .