Development of commercial-scale hydrogel-based management systems for Formica aerata (Hymenoptera: Formicidae) in...

The mealybug, Planococcus ficus (Signoret), is a direct pest of grapevines in California. It causes damage by feeding on plant sap, vectoring viral pathogens, and contaminating table grape clusters before harvest. Natural control of this mealybug by parasitoids and predators is disrupted by the presence of sugar-feeding ants, including Formica aerata Francoeur, which defend mealybugs from these natural enemies. We developed a system to manage F. aerata using ultra-low concentrations of toxicants in a 1:4 sucrose: water solution, imbibed into polyacrylamide hydrogels. We began with a series of field trials to identify toxicant concentrations and application rates that were effective for 6 active ingredients (abamectin, boric acid, pyriproxyfen, pyrethrins, spinosad, and thiamethoxam). This work culminated in replicated, commercial-scale trials (>1,000 vines/plot), that evaluated the season-long effectiveness of the 2 most promising active ingredients: spinosad at a concentration of 0.011% and thiamethoxam at a concentration of 0.0015%. Two spring applications of the spinosad or thiamethoxam formulations, applied at a rate of 93.5 l/ha, reduced the density of foraging F. aerata by 97.4% and 83.0%, respectively, for periods exceeding 4.5 months. Economic analysis showed that the materials and labor costs for each application were $93.04 to $96.18/ha, which is less than half the cost of a traditional insecticide applied for vineyard mealybugs. Adoption of hydrogel-based management programs for F. aerata has the potential to decrease ant populations, and thereby improve biological control, decrease mealybug damage, and contribute to the overall sustainability of grape production systems.