More than 100 strains of Tribolium castaneum (Herbst), Rhyzopertha dominica (F.), Sitophilus spp., Cryptolestes spp., and Oryzaephilus spp., were collected from grain bins on farms in 14 grain-producing states. These were screened for resistance to malathion by the discriminating dose technique, using impregnated filter papers. Measurable tolerance occurred in 31 of 36 strains of Tribolium 11 of 13 strains of Rhyzopertha, 7 of 22 strains of Sitophilus, 5 of 42 strains of Cryptolestes, and none of 13 strains of Oryzaephilus. Resistance was widespread and severe only in Tribolium castaneum. Fifteen of the T. castaneum strains were tested further, and all achieved resistance levels of >20-fold after a single selection. Resistance in this species was largely or completely suppressed by triphenylphosphate in all 13 strains tested.
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Haliscak et al. (1983) studied this question.