Field studies of exterior-only applications with fipronil (Termidor SC) for the post-construction control of interior populations of subterranean termites (Isoptera: Rhinotermitidae)

Abstract

Thirty-two privately owned structures were treated with a 0.06% exterior and interior, 0.06% exterior-only, or 0.125% exterior-only application of fipronil (Termidor SC®) in order to compare their efficacies in the post-construction control of interior populations of Reticulitermes spp. (Holmgren). The concentration of fipronil in the soils from the structures was measured pre-treatment and at 1 week, 3, 6, 9, 12, and 18 months post-treatment. Bioassays conducted with fipronil-treated soils from five locations in Texas determined the minimum effective concentration (minimum concentration necessary to stop termites from breeching a 50 mm column of treated soil) was < 1.0 ppm. Lethal concentration (LC50) values ranged from 0.19 to 0.60 ppm for Reticulitermes flavipes (Kollar). All structures receiving a 0.06% fipronil exterior and interior or 0.125% exterior-only application showed full control of interior termite populations within 6 months. In contrast, 36% of the structures that received a 0.06% fipronil exterior-only application still had termites 6 months post-treatment. When taking the point of termite entry into account, it was shown that only structures treated with fipronil at the point of entry into the structure by termites showed full control within 6 months. This indicated that the placement of the termiticide at the point of subterranean termite entry, and not the rate at which it was applied, was the most important factor that predicted whether a post-construction application of fipronil provided full control of an interior infestation. Results also indicated that Termidor SC® was effective when used according to the current product label, which calls for a thorough application including exterior and interior applications for post-construction termite control. Soil monitoring data for fipronil indicated that the technical material provided by the manufacturer of Termidor SC® was labeled appropriately in terms of concentration. Tank mix samples, while variable, were between 83 - 96% of the labeled concentrations. Post-treatment soil samples and bioassays with treated soil showed that fipronil concentrations were adequate to effectively control termites through the first 18 months.