ORAL TOXICITY OF CHLORDANE, HYDRAMETHYLNON, AND IMIDACLOPRID TO FREE-FORAGING WORKERS OF CAMPONOTUS-PENNSYLVANICUS (HYMENOPTERA, FORMICIDAE)

The oral toxicity of the delayed-action insecticide hydramethylnon, in contrast to the acute toxins chlordane and imidacloprid, was evaluated in free-foraging workers of the black carpenter ant, Camponotus pennsylvanicus (DeGeer), gathering insecticide-laced, sugar-milk baits. Hydramethylnon was slower acting than either chlordane or imidacloprid. When workers fed upon 500-ppm baits, hydramethylnon killed ants significantly more slowly (LT50[95% CL] = 12.7 [12.5-12.9] d) than did chlordane (1.3 [1.1-1.4] d) or imidacloprid (0.3 [0.1-0.5] d). All toxicants were transferred via trophallaxis (i.e., indirect exposure). In ants exposed to a single forager that fed upon a 500-ppm bait (i.e., the donor ant), hydramethylnon caused death significantly more slowly (LT50[95% CL] = 12.2 [11.9-12.4] d) than did chlordane (4.1[3.8-4.4] d) or imidacloprid (0.9 [0.8-1.0] d). In both direct and indirect exposures, significant concentration-dependent time delays before mortality were observed with each toxin. Donor ants in indirect exposures survived after gathering and transferring sugar-milk bait laced with chlordane or hydramethylnon but did not survive their exposure to imidacloprid. On the basis of these and other analyses, we identify delayed-action toxins suitable for carpenter ant baits.