Toxicity, Repellency, and Laboratory Performance of Consumer Bait Products for German Cockroach (Blattodea: Ectobiidae) Management

Toxicity, repellency, and laboratory performance of consumer bait formulations were evaluated for control of 7 insecticide-resistant, field-collected strains of the German cockroach, Blattella germanica (L.) (Blattodea: Ectobiidae) in continuous exposure and Ebeling choice box assays. Solid and gel baits contained avermectin, dinotefuran, fipronil, or hydramethylnon as active ingredients, and were active for control of all German cockroach strains. However, the laboratory susceptible strain was generally more sensitive (lower median lethal times or LT50 values) than the field-collected strains. Resistance ratios in continuous exposure tests ranged from 0.37 for 0.01% fipronil (strain H) to 14.23 for 0.05% dinotefuran (strain DCC2). The LT50 values for most baits and strains generally were greater when tested in Ebeling choice boxes compared with continuous exposure tests. Resistance ratios ranged as high as 98.43 for 0.05% dinotefuran for control of strain DCC2. All strains had resistance to 0.05% dinotefuran bait, and the resistance ratios were greatest when tested in Ebeling choice boxes. All bait formulations had some repellency to most strains; however, repellency was never greater than 70% for any treatment-strain combination. Combining Ebeling choice box mortality and repellency data, maximum estimated performance index values (PIMax) reached 100, i.e., no repellency and complete mortality, for most treatments. There was not complete mortality of the majority of strains exposed to 0.05% dinotefuran bait and therefore the PIMax value did not reach 100. The rate of increase in performance index value over time or tPImax/2 ranged 0.26 and 7.85 d. Our results indicate that although all baits were toxic to multi-resistant strains of German cockroaches, there was significant resistance or tolerance to many formulations that would likely negatively impact field control.