Horizontal Transfer of Insecticides in Laboratory Colonies of the Argentine Ant (Hymenoptera: Formicidae)

Abstract

Five insecticides used by urban pest management professionals for ant control and three experimental insecticides were tested to determine whether these insecticides were horizontally transferred among individuals in colonies of Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae). Ants were exposed to insecticide-treated sand for 1 min and then placed in a colony of untreated ants. Ants exposed to 20 and 40 ppm fipronil readily transferred the insecticide to other individuals in the colony, resulting in high mortality. Most of the transfer and subsequent mortality occurred within 4 d after exposure to treated ants. The other insecticides were not transferred, and ants exhibited mortality rates similar to that of the controls. Experiments in large foraging arenas demonstrated that necrophoresis was an important behavior facilitating the horizontal transfer of fipronil. When ants contacted contaminated corpses in the process of removing them to refuse piles, they received a lethal dose of fipronil and subsequently died. Fipronil-contaminated dead ants that were placed in the vicinity of the nest resulted in significantly higher mortality than did corpses placed in a distant foraging arena (30 cm away). Most of the dead ants accumulated in the vicinity of the nest rather than in the foraging arena, workers retrieving dead ants to refuse piles from the foraging arena. The position effect of insecticide-contaminated corpses relative to the nest and its implication for Argentine ant control are discussed.

Activity of Bifenthrin, Chlorfenapyr, Fipronil, and Thiamethoxam Against Argentine Ants (Hymenoptera: Formicidae)

“…Of the chemicals we tested, chlorfenapyr had the lowest horizontal toxicity to Argentine ants. Other results presented here suggest that this may be due to low contact toxicity rather than an aversion to handling the treated corpses, because removal rates of chlorfenapyr-treated corpses was 94% after 1 h. Using brief exposure of live donor ants to treated sand, Choe and Rust (2008) found that Þpronil was the only one of eight insecticides tested that exhibited horizontal activity against Argentine ants. As in our study, Soeprono and Rust (2004b) found that treatment with Þpronil caused the highest rate of horizontal mortality.…”

“…However, only the 40 ppm treatment continued to cause signiÞcant mortality through the remainder of the 7 d study. A difference in dose and donor location may account for differences between our results and those of Choe and Rust (2008). In our study, all donor ants were placed near the nest and received comparatively high insecticide doses, administered topically.…”

“…When the goal is to provide a reduction in ant numbers both around the structure and in the surrounding yard, strategically placed spot treatments of a slow-acting toxicant such as Þpronil can eliminate the need for perimeter treatments. Choe and Rust (2008) found higher mortality when Þpronil-treated donors were placed close to the nest than in the foraging arena. Spot treatments close to nests would result in more corpses in the nest area and a greater potential for horizontal transfer due to necrophoresis.…”

“…Horizontal activity of toxicants can play a more important role in warmer weather when populations are more diffuse, increasing the difÞculty of locating all nests for treatment. Choe and Rust (2008) demonstrated the importance of dose on sustaining horizontal toxicity over Each replicate (n ϭ 10) contained a total of 300 ants. Numbers do not total 300 because some ants did not cross either bridge.…”

Ecological impacts on native ant and ground-dwelling animal communities through Argentine ant (Linepithema humile) (Hymenoptera: Formicidae) management in Japan

“…Due to the relatively small size of these infestations, a control program commenced soon after detection to attempt eradication. In this program, we used the slowacting insecticide fipronil, which produces substantial mortality rates in workers and queens of L. humile (Costa and Rust 1999;Hooper-Bui and Rust 2000;Klotz et al 2007;Wiltz et al 2009) by horizontal transfer among live workers (Soeprono and Rust 2004), even though ants had contact with corpses contaminated with fipronil (Choe and Rust 2008). Importantly, our control program took an "adaptive management" approach, whereby on-ground actions would be influenced by the information gained from the monitoring efforts.…”