Toxicity, Uptake, and Transfer Efficiency of Fipronil in Western Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract

The potential horizontal transfer ofnonrepellent termiticides has become an important paradigm to control termites in recent years. In this study, 14C-radiolabeled fipronil was used in a series of laboratory experiments to demonstrate the extent and ability of termites to transfer lethal amounts of fipronil to unexposed nestmates. Fipronil is an active and nonrepellent termiticide against western subterranean termites, Reticulitermes hesperus Banks, on sand at relevant doses. It exhibited delayed toxicity with the lowest LD50 approximately 0.2 ng/termite expressed between day 4 and 7. Both continuous and brief exposures to fipronil-treated sand seriously impaired the termite's ability to move and respond to a dodecatrienol trail, limiting potential horizontal transfer. In tunneling studies, fipronil prevented termite tunneling at concentrations as low as 0.5 ppm and was nonrepellent even at 500 ppm. Greater than 90% mortality was recorded by day 7 with concentrations ranging from 0.5 to 500 ppm. There was a linear relationship between the time of exposure and uptake of [14C]fipronil when termites were continuously exposed to 0.5, 1.0, and 5.0 ppm for 24 h. However, uptake discontinued when the termites were immobilized. Maximum transfer of fipronil from donors to recipients occurred within the first 24 h. Fipronil was transferred by body contact and trophallaxis did not play a major role in horizontal transfer. In successive transfer studies, there was not enough fipronil on recipients for them to serve as secondary donors and kill other termites. In a linear arena study, there was an inverse relationship between the amount offipronil on dead termites and their distance from the treated zone. Maximum mortality was observed within 1.5 m from the treated zone. Results in our laboratory studies suggest that horizontal transfer was not a major factor contributing to the efficacy of fipronil in the field.

Factors Affecting Performance of Soil Termiticides

“…Bifenthrin was also found to have the highest activity against Reticulitermes hesperus when compared with other pyrethroids (Smith & Rust, 1990). Saran and Rust (2007) found that R. hesperus tunneled through untreated sand and stopped near the interface of fipronil treated sand. There was little tunneling in the treated sand, but termites tunneled close enough to obtain a lethal dose of fipronil.…”

“…Delayed toxicity can provide opportunity for horizontal transfer of the active ingredient, potentially reducing termite activity (Remmen & Su, 2005;Shelton & Grace, 2003). While there is some evidence of colony suppression or elimination following perimeter treatments with imidacloprid (Parman & Vargo, 2010), other studies have shown that a reduction in activity occurs over only a small portion of a colony's foraging range, making it unlikely that soil treatments affect the overall termite population (Osbrink et al, 2005;Rust & Saran, 2006;Saran & Rust, 2007;Su, 2005). This limited potential for transfer emphasizes the importance of bioavailability of termiticides in soil over an extended period of time.…”

Effect of Sub Lethal Concentrations on Population Size of Termites Odontotermes Obesus (Rambur) and Coptotermes Heimi (Wasmann) Under Laboratory and Field Conditions

“…Saran and Rust [26] found that Reticulitermes flavipes tunneled through untreated sand and stopped near the interface of fipronil treated sand. There was little tunneling in the treated sand, but termites tunneled close enough to obtain a lethal dose of fipronil.…”

“…Non-repellent insecticides often maintain the property of nonrepellency even at high concentrations (up to 500 part per million in Reticulitermes flavipes Saran and Rust [26]. Fipronil is more toxic to insects than people and pets because it is more likely to bind to insect nerve endings through contact toxicity.…”

“…This also suggesting that even longer exposure to low insecticide concentrations might lead to greater incidence of lethal transfer, so long as sufficient no of termites remained alive for better transfer of lethality. Osbrink et al [38] did not find significant differences in LT50 values among workers from different colonies exposed to fipronil.The transfer of fipronil among termites can be caused by body contract, mutual grooming and trophallaxis Song and Hu [39], Saran and Rust [26].…”