Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2005
Publication Date: 4/1/2006
Citation: Chen, J., Allen, M. L. 2006. Significance of Digging Behavior to Mortality of Red Imported Fire Ant Workers, Solenopsis invicta Buren, in Fipronil Treated Sand. Journal of Economic Entomology. 99: 476-482. Interpretive Summary: Residential households in the United States spend $3.4 billion/year in controlling fire ants. Repeated applications of contact insecticides are a common practice for controlling fire ants near the home, which increases the level of insecticides in the environment. Fire ant digging effort was found to increase insecticide effectiveness. Exploiting fire ant digging behavior will allow us to improve insecticide effectiveness without increasing the dose of insecticide and to make applications of contact insecticides more environmentally friendly.
Technical Abstract: The effect of fipronil treated sand on digging behavior and mortalities of red imported fire ant workers, Solenopsis invicta Buren, was examined in the laboratory. No-choice digging bioassays where fipronil treated sand was the only available digging substrate, were conducted on two colonies at fipronil concentrations of 0.00, 0.05, 0.10, 0.50, 1.00, 1.50, and 2.00 ppm. Workers dug into the fipronil treated sand in all cases, even at 2.0 ppm level which caused 100% mortalities in acute toxicity tests for both colonies. At 1.5 and 2.0 ppm, workers from the less sensitive colony had significantly higher mortalities than those from the more sensitive colony, which might be explained by the significantly higher digging activity of the less sensitive colony. In two-choice digging bioassays where untreated sand was also available, workers dug into the fipronil treated sand in 29 of 30 cases, even at 10.0 ppm level. At 1.0 and 10.0 ppm, mortalities were positively correlated to digging effort in treated sand; however, such correlation was significant only at 1.0 ppm level. This indicates that digging did affect mortality; however, such effect is concentration dependent.