Effects of liquid insecticide baits on Argentine ants in California's coastal vineyards

Liquid ant baits were evaluated for control of Argentine ants, Linepithema humile (Mayr), and associated mealybug pests (Pseudococcus species) in commercial vineyards. In all trials, liquid baits were an insecticide dissolved in 25% sugar water. In 2000, two liquid baits—crystalline boric acid and imidacloprid—were deployed in ground-based dispensers at rates of 85 (site 1) and 175 (site 2) dispensers per ha. Season-long ant densities were significantly lower than a no-insecticide control in only the boric acid treatments, and at only 1 of 2 sites. In 2001, four liquid baits—imidacloprid, fipronil, and thiamethoxam, each mixed at 0.0001% (A.I.)—were delivered in ground-based dispensers at a rate of 120 dispensers per ha. There was no treatment impact on ant or mealybug densities. In 2002, a liquid bait—thiamethoxam, mixed at 0.0001% (A.I.)—was delivered in ground-based (site 1) and canopy-based (site 2 and 3) dispensers that were recharged every 2 wk and cleaned every 4 wk, and deployed at rates of 160 (sites 1 and 2) and 620 (site 3) dispensers per ha. There was a significant reduction of season-long ant densities in liquid bait treatments at all sites, and of mealybug densities at 2 of 3 sites; crop damage was significantly lower in the liquid bait treatment at all sites. The results are discussed with respect to the methodologies used to deploy liquid baits and the development of a viable commercial program.