Developmental Stage- and Gender-Dependent Differential Susceptibility of German Cockroaches (Dictyoptera: Blattellidae) to Various Commercial Baits

The toxicity of five commercial bait formulations (Raid Max, Combat, Maxforce, Avert PT310, and Magnetic Roach Food) against various stages and sexes of JWax-susceptible and Muncie-resistant strains of German cockroaches, Blatella germanica (L.), was investigated in choice and no-choice bioassays. The role of strain, bait, stage, sex, and feeding bioassay main effects on cockroach mortality was determined. The biological toxicity of all five baits differed markedly among the different stages and sexes of both strains in both types of feeding bioassays. The range of LT50s for each bait tested against various life stages in choice bioassays was wider and slower in killing cockroaches than in no-choice bioassays. The LT50s of nymphs differed significantly for each bait tested. Large nymphs were less susceptible to baits than small nymphs. Except for exposure to Maxforce bait, all baits tested affected adult genders differently. Palatability ratio values were highly variable in this study. At the LT50 levels, the values of palatability ratios for all baits tested against most stages and sexes were significantly >1.0. These values may indicate feeding deterrence. The magnitude for certain stages and sexes was small, however, and the values may well be explained purely by random feeding. Palatability of a toxicant bait was different among baits offered to cockroaches with or without a bait station. In the feeding bioassays, the resistance ratios for various commercial baits to different stages and sexes were similar and low (with few exceptions). Factors affecting the susceptibility of various strains, stages, and sexes to baits are discussed.