Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2006
Publication Date: 6/1/2006
Citation: Chen, J. 2006. Digging behavior of Solenopsis invicta workers when exposed to contact insecticides. Journal of Economic Entomology. 99:634-640. Interpretive Summary: Since its introduction to the United States, red imported fire ants have become a major agricultural and urban pest throughout the southeastern states. Contact insecticides are frequently used in controlling fire ants, and this practice has resulted in increased amounts of insecticides in the environment. Fire ant digging behavior increases the chance for fire ants to contact insecticide. Therefore,the effectiveness of insecticide can be increased by exploiting fire ant digging behavior. This will enable us to improve effectiveness of insecticide without increasing the dose, which will benefit the environment.
Technical Abstract: Contact between ants and an insecticide is a prerequisite for contact insecticides to be effective in the control of red imported fire ants, Solenopsis invicta Buren. Typically, passive contact occurs in the insecticide application process, but ants may also actively contact insecticides by digging treated soil. Laboratory experiments were conducted to determine whether fire ant workers would dig sand treated with contact insecticides. Eight insecticides which are currently registered in the United States for imported fire ant control were tested. They include acephate, bifenthrin, carbaryl, cyfluthrin, deltamethrin, ?-cyhalothrin, permethrin, and pyrethrin. Workers dug the treated sand for every insecticide tested, even at concentration up to 10 times of the lowest lethal concentration (LLC) which caused 100% mortality in a toxicity bioassay. However, in most cases, insecticides significantly reduced the digging effort, even at the concentration which did not cause any significant mortality in the toxicity bioassay. In no-choice digging bioassays where insecticide-treated sand was the only available digging substrate, only 2.00% to 28.40% mortalities were achieved for eight insecticides at LLC and 12.00% to 100.00% mortalities at concentrations of 10 times of LLC (LLC×10). Only acephate, carbaryl, and deltamethrin at LLC×10 achieved 100% mortality. The majority of dead workers were found outside the treated sand, so were the living ants if any. In two-choice digging bioassays where non-toxicant sand was also available for digging, only 5.20% to 47.40 % mortalities were achieved at LLC×10 and the difference on the digging effort between treated and untreated sand was significant for all insecticides except acephate. Most dead workers were found outside the treated sand, whereas most of surviving ants were found in the untreated sand.