A gel bait-resistant Blattella germanica (L.) strain (Cincy) was collected in Cincinnati, OH, in 2003. This strain exhibited strong behavioral resistance to Avert (0.05% abamectin), Maxforce FC (0.01% fipronil), and Pre-Empt (2.15% imidacloprid) gel baits. Reciprocal mass crosses and back crosses between the Cincy strain and a susceptible strain (Jwax) were made and tested for their inheritance of resistance to Avert, Maxforce FC, and Pre-Empt gel baits. Topical assays comparing the parental and reciprocal-heterozygous strains indicated the resistance to fipronil was incompletely recessive. LD50 and LD90 values of the Jwax♂ × Cincy♀ strain were not significantly different from the Jwax♀ × Cincy♂ strain, suggesting no sex linkage in physiological fipronil resistance. Feeding assays revealed that F1 reciprocal crosses were significantly less responsive to blank Avert and Maxforce FC baits (without active ingredients) than the susceptible strain. The Jwax♀ × Cincy♂ strain did not display significantly greater consumption of blank Avert and Maxforce FC baits relative to the Jwax♂ × Cincy♀ strain. In feeding assays with agar containing d-fructose, d-galactose, d-glucose, d-lactose, d-maltose, and d-sucrose, the crosses showed an intermediate feeding response to glucose compared with the Cincy and Jwax strains, and a similar response to other sugars compared with the Jwax strain. The Jwax♂ × Cincy♀ strain was significantly less responsive to glucose than the Jwax♀ × Cincy♂ strain. Mortality induced by Avert, Maxforce FC, and Pre-Empt gel baits against the F6 Jwax♂ × Cincy♀ strain was 44.2 ± 6.8, 92.9 ± 2.1, and 78.7 ± 5.2%, respectively, indicating the resistance to Avert and Pre-Empt gel baits inherited by Cincy females was extremely stable. The F6 Jwax♂ × Cincy♀ strain was significantly more resistant to Avert, Maxforce FC, and Pre-Empt than the F6 Jwax♀ × Cincy♂ strain. These findings suggest that behavioral resistance to gel baits has weak sex-linkage, with a greater degree of the resistance trait being inherited by female cockroaches. Alternatively, physiological resistance to fipronil has no sex-linkage, but it is nonetheless important to the complete resistance phenotype.
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Vol. 99 • No. 5