Comparison of commercial bait formulations for efficacy against bait averse German cockroaches (Blattella germanica) (Dictyoptera: Blattellidae)

Abstract:
Commercial gel bait formulations, including two new formulations of indoxacarb (0.6% AI; RG2V3 and DPX411), were evaluated for efficacy against a "bait averse" strain of German cockroaches (Saginaw strain). Bait consumption and subsequent mortality of the Saginaw cockroaches were compared with that of the VPI, susceptible strain. Both cockroach strains were exposed to bait formulations in choice tests where dry dog food was the alternative food resource. Feeding indices were calculated for each bait formulation. Feeding indices were positive for all bait products offered to the VPI susceptible strain. Negative feeding indices were calculated for MaxForce FC (0.01% fipronil), MaxForce (2.15% hydramethylnon) and Avert Formula 3 (0.05% abamectin B1) when these baits were offered to the bait averse Saginaw strain. However, feeding indices for the indoxacarb bait formulations were positive, indicating that the bait averse cockroaches preferred both of the indoxacarb baits to dog food. Mortality due to bait exposure was also significantly different between the susceptible and bait averse strains. In bioassays evaluating the VPI strain, all of the baits produced 100% mortality within the 7 d test period. The indoxacarb RG2V3 formulation produced the most rapid results with 100% mortality recorded within 24h. In bioassays evaluating the bait averse strain, mortality was dependent on the bait formulation offered. After 7d only 5% mortality was recorded for the Saginaw cockroaches exposed to fipronil bait. Hydramethylnon bait produced < 50% mortality during the same period. Mortality in the abamectin and indoxacarb DPX411 bioassays was 75% and 88.8%, respectively, in 7 d. However, the greatest efficacy for control of bait averse cockroaches was observed in bioassays evaluating indoxacarb RG2V3, where 100% mortality was achieved within 3 d.