Oral toxicity of abamectin, dechlorane, and sulfluramid to free-foraging workers of Camponotus pennsylvanicus (Hymenoptera: Formicidae)

Oral toxicities of delayed-action insecticides abamectin, dechlorane, and sulfluramid were characterized in free-foraging Camponotus pennsylvanicus (DeGeer) workers gathering insecticide-laced, sugar-milk baits. Abamectin acted significantly faster than either dechlorane or sulfluramid. When workers fed upon 500-ppm baits, abamectin killed the ants faster (LT50 [95% CL] = 1.06 [0.88-1.23] d) than either dechlorane (5.82 [5.62-6.00] d) or sulfluramid (6.20 [5.76-6.65] d). All toxicants were readily transferred by trophallaxis. In ants that were exposed to a single forager that had fed upon a 500-ppm bait, abamectin caused death more rapidly (LT50 [95% CL] = 2.56 [2.29-2.81] d) than did dechlorane (6.71 [6.35-7.05] d) or sulfluramid (6.96 [6.06-8.42] d). In both direct and indirect exposures, significant concentration-dependent time delays before mortality were observed for all toxins. Based on the effective lethal time for 90% (ELT90) of the exposed workers, the concentration dependence of the time delays for dechlorane and sulfluramid were equivalent, and both were active over a wider range of concentrations than abamectin