Resistance to grain protectants in field populations of the sawtoothed grain beetle in southern Queensland

Abstract

Resistance of field strains of Oryzaephilus surinamensis L. (sawtoothed grain beetle) to grain protectants was assessed using commercial dose rates of protectant in treated grain bioassays. Grain protectants tested were: chlorpyrifos- methyl, 5 and 10 mg/kg grain; methacriphos, 10 and 18 mg/kg; pirimiphos-methyl 4 mg/kg; fenitrothion, 12 mg/kg, plus carbaryl, 8 mg/kg; fenitrothion, 12 mg/kg, plus bioresmethrin, 1 mg/kg, plus piperonyl butoxide, 8 mg/ kg; pyrethrins, 3 mg/kg, plus piperonyl butoxide, 24 mg/kg. About 10% of farms surveyed and about 42% of merchant premises were infested. Most of the insects originating from farms were effectively controlled by all grain protectants. However, some strains showed less than 100% adult mortality and some progeny production when treated with: chloropyrifos-methyl at 5 mg/kg; pirimiphos-methyl; and pyrethrins plus piperonyl butoxide. In contrast, for all strains obtained from the premises of grain merchants, none of the grain protectants, except methacrifos at 18 mg/kg, caused complete adult mortality whilst fenitrothion, chlorpyrifos-methyl at 5 mg/kg and pyrethrins plus piperonyl butoxide failed to completely suppress progeny production in some strains. A composite strain showed no mortality with fenitrothion at 12 mg/kg after five generations of laboratory selection.