Abstract
BACKGROUND: Bait formulations are considered to be the most effective method for reducing German cockroach (Blattella germanica) infestations. An important property of some bait formulations is secondary kill, whereby active ingredient (AI) is translocated in insect-produced residues throughout the cockroach population, especially affecting relatively sedentary early-instar nymphs. RESULTS: B. germanica was collected from a location where baits containing hydramethylnon, fipronil or indoxacarb had become ineffective, and these AIs were topically applied to adult males. Results revealed the first evidence for hydramethylnon resistance, moderate resistance to fipronil and extremely high resistance to indoxacarb. Insecticide residues excreted by field-collected males that had ingested commercial baits effectively killed nymphs of an insecticide-susceptible laboratory strain of B. germanica but failed to kill most nymphs of the field-collected strain. CONCLUSIONS: We report three novel findings: (1) the first evidence for hydramethylnon resistance in any insect; (2) extremely high levels of indoxacarb resistance in a field population; (3) reduced secondary mortality in an insecticide-resistant field-collected strain of B. germanica. We suggest that, while secondary mortality is considered to be advantageous in cockroach interventions, the ingestion of sublethal doses of AI by nymphs may select for high insecticide resistance by increasing the frequency of AI resistance alleles within the population. © 2015 Society of Chemical Industry.