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

Abstract

A consumption bioassay was used to evaluate hydramethylnon tolerance among 14 insecticide-resistant and 1 insecticide-susceptible strain of the German cockroach, Blattella germanica (L.). The feeding bioassay provided the ability to assess physiological changes in hydramethylnon tolerance while simultaneously 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 in 2 groups. The 1st group was bioassayed by the dose-response method and the 2nd group was assayed with a single diagnostic dose. None of the strains evaluated by the dose-response consumption bioassay method were more tolerant of hydramethylnon than the Orlando laboratory strain. Although the dose-response data did not indicate physiological resistance among these strains, behavioral resistance (avoidance) was implicated in the Union 511 and Malo strains. In a 2nd group of insecticide-resistant strains, physiological as well as behavioral resistance to hydramethylnon was implicated when cockroaches were challenged with a diagnostic dose of hydramethylnon in Siege bait matrix. At the Orlando LD99 (3.5 μg of hydramethylnon per cockroach), only 80 and 75% of the NASJAX and HydSel adult males consumed the bait, respectively. These data indicate that avoidance behavior may be developing in these strains. Furthermore, physiological resistance was indicated only in the strain selected with hydramethylnon (HydSel) because only 89% was killed at the LD99 Orlando dose.