Toxicity, Repellency, and Horizontal Transmission of Fipronil in the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract

Toxicity of fipronil was evaluated against field-collected Coptoteres formosanus Shiraki. In topical application assays, fipronil was highly effective against both workers and soldiers at very low doses. Acute toxicity after 24 h was significantly greater in workers than in soldiers. The LD50s were 2.59- and 2.91-fold greater with soldiers than with workers from the two tested colonies. The LD50s of fipronil at 72 h after treatment were <2.0 ng/insect, with no significant differences regarding the tested workers/soldiers or colonies. Treated soldiers placed with untreated workers significantly increased worker mortality. However, there was no significant horizontal transmission of fipronil from treated workers to untreated soldiers. Fipronil at rates of 0.063% or less showed no repellency, whereas sand treatments of 0.125% fipronil were repellent to termite workers.

Evaluation of Efficacy and Nonrepellency of Indoxacarb and Fipronil-Treated Soil at Various Concentrations and Thicknesses Against Two Subterranean Termites (Isoptera: Rhinotermitidae)

“…Despite that large intercolony differences in response to insecticides is common (Su and La Fage 1984), there were incidences where differences in susceptibility between colonies were not detectable. Osbrink et al (2001) and Ibrahim et al (2003) reported similarity among the Formosan subterranean termite colonies in their susceptibility toward Þpronil.…”

“…Ibrahim et al (2003) reported an LD 50 Ͻ 2.0 ng per termite after 72-h treatment of the Formosan subterranean termite. They also reported 100% mortality of termites at 48 h after exposure to 50 g sand treated with 10 ml of Þpronil at rates of 0.01Ð 0.125% in a choice assay.…”

“…Ibrahim et al (2003) reported that Þpronil showed no repellency to the Formosan subterranean termite when exposed to 50 g of sand treated with 10 ml of 0.01 or 0.0625% Þpronil solution [equivalents of 20 and 125 ppm (wt: wt)]. Repellency was observed only at the highest concentration of 0.125% Þpronil-treated sand [equivalent of 250 ppm (wt:wt)] because signiÞcantly lower number of dead termites was found in the treated chambers compared with untreated chambers.…”

“…Osbrink et al (2001) reported Formosan subterranean termite, Coptotermes formosanus Shiraki, susceptibility toward Þpronil by exposing termites to treated Þlter paper. Ibrahim et al (2003) also tested Þpronil toxicity against Formosan subterranean termites by using topical application assays. Termite penetration into Þpronil-treated substrates was only examined at concentrations of Ն20 ppm (Ibrahim et al 2003), or at 5 ppm (Osbrink and Lax 2002).…”

“…Ibrahim et al (2003) also tested Þpronil toxicity against Formosan subterranean termites by using topical application assays. Termite penetration into Þpronil-treated substrates was only examined at concentrations of Ն20 ppm (Ibrahim et al 2003), or at 5 ppm (Osbrink and Lax 2002). Neither of the previous studies examined the Eastern subterranean termite, Reticulitermes flavipes (Kollar), nor have they used formulated Þpronil.…”