Insecticidal effect of fenitrothion, diatomaceous earth and Beauveria bassianaagainst Coleopteran pests of stored grain

Abstract: Pest insects of stored grains can cause losses in weigth, quality, commercial value andseed germination. Toxicity and protectant potential of a chemical and two biological insecticidesagainst two major stored-grain beetle species: Tribolium castaneum (Herbst) and Rhyzoperthadominica (F.) were investigated in the laboratory. The organophosphate fenitrothion at 100% and50% of the labelled rate, and two biological insecticides: diatomaceous earth (DE) at 3000ppmand the entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin (Hyphomycete) at1ml/kg grain of water suspension (1 x 108 conidia/ml), were applied both or combined on hardwheat grain. For grains bioassayed after 14 days of storage following chemical treatment at least98% mortality was obtained in T. castaneum and R. dominica even with the lowest dose. For bothinsect species DE powder + B. bassiana formulations showed a mortality significantly higherthan each biological insecticide alone. When T. castaneum and R. dominica were exposed to B.bassiana or DE, the mortality means were 2% and 45% respectively, but when the weevils weretreated with both the fungus and DE, there were 20% mortality for T. castaneum and 54% for R.dominica. The results suggest that additive effect was evident for the fungus-diatomaceous earthcombination and the application of B. bassiana and DE may be a way to overcome some of theconstraints of virulence on fungal entomopathogens as biocontrol agents against stored-productinsect species.