Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2006
Publication Date: 10/12/2006
Citation: Oi, D.H., Oi, F.M. 2006. Speed of efficacy and delayed toxicity characteristics of fast-acting fire ant (Hymenoptera: Formicidae) baits. Journal of Economic Entomology. 99(5):1739-1748. Interpretive Summary: The red imported fire ant is an invasive, stinging ant that infests over 320 million acres in 14 states and causes an estimated $6.5 billion annually in damage, control, and medical expenditures. Insecticidal baits can be a very effective method of fire ant control because they utilize the food-sharing behavior of ants to distribute toxicant throughout a colony. Depending on the toxicant, fire ant baits have typically required weeks to months to significantly reduce ant populations. Faster acting, effective baits are desirable, especially in sensitive areas such as playgrounds. Scientists with the USDA-ARS Center for Medical, Agricultural, and Veterinary Entomology and the University of Florida Entomology and Nematology Department confirmed that a new fire ant bait containing the active ingredient indoxacarb can kill fire ant colonies significantly faster than standard baits. The indoxacarb bait killed over 85% of the fire ant colonies within 3 days and 100% of the colonies were dead by the sixth day in laboratory tests. In contrast, a standard bait containing hydramethylnon resulted in death of 60% of the colonies in 9 days. Under field conditions, the indoxacarb bait gave comparable control almost 4 times quicker than standard bait. The development of fast-acting fire ant baits is of significant benefit to the inhabitants of fire ant infested areas because hazardous fire ant colonies can be eliminated more quickly and/or efficiently than traditional fire ant control methods.
Technical Abstract: Efficacy and speed of action of fire ant baits that claimed fast control of colonies were compared to a standard bait. Over 85% of red imported fire ant, Solenopsis invicta Buren, laboratory colonies provided bait containing the active ingredient indoxacarb died within 3 d, and all colonies were dead in 6 d. The standard bait containing hydramethylnon resulted in death of 60% of the colonies by the ninth day. Another bait containing spinosad did not cause colony death. Under field conditions, half of the areas treated with the indoxacarb bait did not have any active fire ant nests within 3 days while 11 days were needed to reach the same level of control with the hydramethylnon bait. The delay in death of S. invicta adults with the indoxacarb and spinosad baits was shorter than the standard hydramethylnon bait which had mortality similar to the traditional delayed toxicity criterion of <15% mortality within 24 h. Indoxacarb caused 57% mortality at 24 h, however, visual symptoms of toxicity were not readily observed for at least 8 h before the abrupt increase in death. Spinosad caused 96% mortality by 24 h, and initial mortality became apparent at 4 h. The time required for death of 15% of a treated population (LT15) of spinosad, indoxacarb, and hydramethylnon were 3, 9, and 16 h, respectively. These laboratory and field results suggested that the traditional criterion for delayed toxicity can be shortened for the development of baits that control fire ant colonies faster.