Relative Susceptibility of Confused and Red Flour Beetles1 to Twelve Organophosphorus Insecticides, with Notes on Adequacy of the Test Method2

Abstract

The comparative susceptibility of the confused flour beetle, Tribolium confusum Jacquelin duVal, and the red flour beetle, T. castaneum (Herbst), to 12 organophosphorus insecticides was determined by direct application of spray solutions to adult insects with a Potter laboratory spray tower. The order in effectiveness of insecticides against the confused flour beetle at LC95, with an indication of the significance of differences shown by 95% confidence limits, was: fenthion ≽ Gardona® (2- chloro-1- (2,4,5 - trichlorophenyl) vinyl dimethyl phosphate) ≽ fenitrothion (O,O -dimethyl O -4-nitro- m -tolyl phosphorothioate) > Bay 77488 (O,O -diethyl phosphorothioate O -ester with phenylglyoxylonitrile oxime) ≽ Dursban>® (O,O -diethyl O -3,5,6-trichloro-2-pyridyl phosphorothioate) ≽ Bay 78182 (O,O -diethyl phosphorothioate O -ester with (o -chlorophenyl) glyoxylonitrile oxime) ≽dichlorvos ≽ C-9491 ( O - (2,5-dichloro -4-iodophenyl) O,O -dimethyl phosphorothioate) ≽malathion > Abate® (O,O -dimethyl phosphorothioate O,O -diester with 4,4'- thiodiphenol) > dicapthon > diazinon. The order and an indication of the significance of differences in effec- tiveness of insecticides against the red flour beetle at LC96was: fenthion ≽ fenitrothion ≽ Bay 77488 ≽ Durs- ban ≽ Bay 78182 ≽ malathion ≽ Gardona ≽ Abate ≽ dicl1lorvos ≽ dicaplhon ≽ diazinon ≽ C-9491. On the basis of 1 being assigned to the LC95 value obtained with fenthion, the ratio of differences in effec- tiveness of insecticides ranged up to 10.2 X with diazinon against the confused flour beetle and up to 4.4 X with C-9491 against the red flour beetle. At LC95 and LC50, C-9491 and Gardona were more toxic to confused than to red flour beetles. All other insecticides were more toxic to the red flour beetle than to the confused flour beetle. The magnitude of differences between species in susceptibility to cacll insecticide ranged from 1.14 X for Gardona to 3.27 X for diazinon at LC60 and from 1.27 X for dichlorvos to 3.53 X for diazinon at LC95. It was concluded that the Potter laboratory spray tower was adequate for use as a standard method of application to assess the direct-contact toxicity of insecticides on a comparative basis.