The Presence of Flour Affects the Efficacy of Aerosolized Insecticides used to Treat the Red Flour Beetle,Tribolium castaneum

Experiments were conducted in tightly sealed pilot scale warehouses to assess the efficacy of common aerosolized insecticides on all life stages of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) when exposed in dishes containing 0 to 2 g of wheat flour either under pallets or out in the open. Petri dishes containing 00.11or 2 g of flour were prepared with 25 eggs 3rd instarspupaeor adults and then immediately treated with aerosolized solventpyrethrinsor esfenvalerate. Twenty-four h after insecticide exposurethe dishes were brought to the laboratory and placed in a growth chamber and held for a 3 day moribund (knockdown) assessment and a 21 day mortality assessment. Mortality in untreated controls was generally less than 10%with the exception of the 21 day counts of adults and eggs. Solvent-treated replications followed similar trendsexcept that additional mortality was observed in exposed larvae and pupae. In the insecticide-treated dishesmortality of T. castaneum provisioned with flour generally showed a linear decrease with increasing flour deposits. Regardless of life stagemortality did not exceed 60% when individuals were exposed in petri dishes containing 2 g of flour. Exposure location also made a significant difference in observed mortality. While mortality never exceeded 75% in dishes positioned under palletsthere was never less than 80% mortality in dishes exposed in the open. Although there was a perceptible increase in mortality with esfenvalerate compared to pyrethrinsthese differences were considerably less than the variation observed among flour deposits. The study suggests that sanitation and preparation prior to aerosol insecticide treatments were more important than choice of a particular insecticide.