Could biorational insecticides be used in the management of aflatoxigenicAspergillus parasiticusand its insect vectors in stored wheat?

Abstract

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 producingAspergillus parasiticus. The problem 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 with the ultimate effect on aflatoxin production. The purpose of this study was to investigate the insecticidal potential of four biorational insecticides: spinosad, thiamethoxam, imidacloprid and indoxacarb, on wheat grains artificially infested withRhyzopertha dominica/Sitophilus oryzaeand/orA. parasiticusspores, and the subsequent effect on aflatoxin production. Spinosad and thiamethoxam were the most effective insecticides againstR. dominicacompared toS. oryzaefollowed by imidacloprid. Spinosad applied at 0.25–1 ppm and thiamethoxam at 2 and 4 ppm concentrations resulted in complete mortality ofR. dominica. However, indoxacarb was more toxic againstS. oryzaecompared toR. dominica. Wheat grains inoculated withR. dominica/S. oryzae+spores elicited higher aflatoxin levels than wheat grains inoculated with or without insecticide+spores. In all the treatment combinations containing insects, aflatoxin production was dependent on insects’ survival rate. In addition, thiamethoxam and imidacloprid had also a significant direct effect on reducing aflatoxin production. Aflatoxin levels were lower in the treatment combinations with any concentration of thiamethoxam/imidacloprid+spores as compared to wheat grains inoculated with spores only. Correlation analyses revealed highly significant and positive association between moisture contents/insect survival rate and production of aflatoxin levels, and insect survival rate and moisture contents of the wheat grains. In conclusion, the results of the present study provide baseline data on the use of biorational insecticides againstR. dominicaandS. oryzaeand subsequent effect on aflatoxin production.