Variation in hydramethylnon susceptibility among insecticide-resistant German cockroaches (Blattodea : Blattellidae)

A consumption bioassay was used to evaluate hydramethylnon tolerance among 14 insecticide-resistant and 1 insecticide-susceptible strain of the German cockroach, Blattella ger manica (L). The feeding bioassay provided the abi lity to assess physiological changes in hydramethylnon tolerance while simu ltaneously evaluating German cockroach avoidance behavior toward Siege gel bait. Cockroach strains, which had been shown previously to be resistant to pyrethroid, carbamate, and organophosphate insecticides, were bioassayed i n 2 groups. The 1st group was bioassayed by the dose-response method and th e 2nd group was assayed with a single diagnostic dose. None of the strains evaluated by the dose-response consumption bioassay method were more tolera nt of hydramethylnon than the Orlando laboratory strain. Although the dose- response data did not indicate physiological resistance among these strains , behavioral resistance (avoidance) war implicated in the Union 511 and Mal o strains. In a 2nd group of insecticide-resistant strains, physiological a s well as behavioral resistance to hydramethylnon was implicated when cockr oaches were challenged with a diagnostic dose of hydramethylnon in Siege ba it matrix. At the Orlando LD99 (3.5 mu g of hydramethylnon per cockroach), only 80 and 75% of the NASJAX and HydSel adult males consumed the bait, res pectively. These data indicate that avoidance behavior may be developing in these strains. Furthermore, physiological resistance was indicated only in the str ain selected with hydramethylnon (HydSel) because only 89% was kil led at the LD99 Orlando dose.