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Title: Activity of Bifenthrin, Chlorfenapyr, Fipronil, and Thiamethoxam against Red Imported Fire Ants (Hymenoptera: Formicidae)

Author
item Wiltz, Beverly
item SUITER, D - University Of Georgia
item GARDNER, W - University Of Georgia

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2010
Publication Date: 12/1/2009
Citation: Wiltz, B.A., Suiter, D.R., Gardner, W.A. Activity of Bifenthrin, Chlorfenapyr, Fipronil, and Thiamethoxam against Red Imported Fire Ants (Hymenoptera: Formicidae). Journal of Economic Entomology 103(3): 754-761. 2010.

Interpretive Summary: The most effective control strategies for pest ants often combine multiple treatment techniques that may include nest treatments, perimeter treatments, and baits. Different control strategies require toxicants with different sets of properties, such as topical and contact toxicity, transferability to untreated individuals, and repellency. The purpose of this study was to evaluate the contact insecticides bifenthrin, chlorfenapyr, fipronil, and thiamethoxam for topical toxicity, knockdown rate, horizontal toxicity, contact toxicity, and barrier effects against the Argentine ant. We found that bifenthrin has properties best suited for use as a barrier treatment against Argentine ants. It was the fastest acting of the four chemicals in contact toxicity assays was the only chemical that was effective as a barrier to ant movement. Chlorfenapyr was most effective when applied topically. However, both contact and horizontal toxicities were less than those of other chemicals tested. Topical toxicity of fipronil was delayed relative to the other chemicals. Horizontal toxicity from topical or contact exposure was the greatest of the four chemicals. Thiamethoxam also resulted in significant mortality due to contact with topically or contact exposed ants. Like fipronil, thiamethoxam acted slowly enough to allow exposed ants to return to the nest and transfer toxicant to nestmates.

Technical Abstract: Bifenthrin, chlorfenapyr, fipronil, and thiamethoxam were evaluated for activity against the Argentine ant, Linepithema humile (Mayr). Mobility impairment and lethal times were determined following topical treatments. Ants were immobilized most quickly by bifenthrin, followed by chlorfenapyr and thiamethoxam. After 2 h, the number of fipronil-treated ants unable to walk out of test arenas did not differ from control ants. Median lethal time (LT50) following topical treatment was lowest in the bifenthrin treatment, followed by thiamethoxam, chlorfenapyr, then fipronil. Mortality due to horizontal exposure was evaluated at 10, 20, or 30°C, with topically treated ant corpses serving as donors. There was low to moderate horizontal activity in bifenthrin and chlorfenapyr treatments, with no temperature effect in bifenthrin treatments and a positive temperature effect in chlorfenapyr treatments. Mortality in the fipronil treatments was highest and was positively correlated with temperature. Thiamethoxam treatments did not differ from controls at 10°C, but mortality increased with temperature. To evaluate contact activity, either all of 20% of the ants in a cohort were exposed to insecticide treated pine needles. In both tests, mortality was highest in fipronil and bifenthrin treatments, followed by thiamethoxam, with lowest mortality in chlorfenapyr treatments. Effectiveness as a barrier was evaluated by providing a choice between bridges treated with insecticide or water. While bifenthrin did not provide an impenetrable barrier, it was the only treatment having fewer ants than its paired control. Mortality data suggest that lack of recruitment rather than repellency account for this result.