Effect of Fipronil on Bait Formulation-Based Aversion in the German Cockroach (Dictyoptera: Blattellidae)

We examined the effects of 3 active ingredients in baits containing glucose on a behaviorally resistant (glucose-averse, T-164) strain of Blattella germanica L. Baits with glucose and hydramethylnon or chlorpyrifos killed few T-164 individuals; however, fipronil–glucose baits killed 60% of the cockroaches by day 14. Although ingestion levels were low, fipronil–glucose baits were consumed more than hydramethylnon or chlorpyrifos glucose baits by T-164 cockroaches. Fipronil bait was 17 and 29 times more toxic to the T-164 strain than hydramethylnon and chlorpyrifos, respectively. Despite aversion to a key bait component, low-level bait consumption of a highly active toxicant such as fipronil may to some degree override bait inert-based behavioral resistance mechanisms.