Factors affecting secondary kill of the German cockroach (Dictyoptera: Blattellidae) by gel baits.

Abstract Secondary kill of the German cockroach, Blattella germanica (L)., by baits was reported to increase the overall control efficacy of bait products. However, most studies have been based on laboratory strains and small nymphs. We compared the secondary kill of four cockroach gel baits against various developmental stages of a laboratory (Jwax) and a field (Dorie) strain B. germanica. The four baits were: 0.35 % acetamiprid (Transport), 0.01 % fipronil (Maxforce FC), 2.15 % hydramethylnon (Maxforce), and 0.6 % indoxacarb (Advion). In addition, the secondary kill by acetamiprid, hydramethylnon, and indoxacarb was evaluated against mixed-stage cockroach populations. All baits exhibited secondary kill against various developmental stages of B. germanica. The levels of secondary mortality decreased from 100 % in the first instars to as low as 12.1 % in adult males. The field strain was much less susceptible than the laboratory strain, with only 9.2-16.6 % secondary mortality among the 3rd-4th instars. Acetamiprid caused significantly lower secondary mortality of the laboratory strain first instars than fipronil, hydramethylnon, and indoxacarb. In an experiment evaluating direct and secondary kill against mixed-stage populations (100 total per experimental arena), the direct kill by acetamiprid, hydramethylnon, and indoxacarb was 40.0, 74.0, and 98.5%, respectively. Only indoxacarb caused significant secondary kill at 0.985 donor/recipient ratio. Acetamiprid and hydramethylnon did not cause detectable secondary kill at donor/recipient ratios of 0.40 and 0.74, respectively. We conclude the level of secondary kill by baits was highly influenced by cockroach developmental stage, strain, and donor/recipient ratio. Key Words Blattella germanica, gel bait, secondary kill, toxicant transfer