Argentine ants are a majorly invasive tramp species in natural, urban, and agricultural settings all over the world. Practical and effective control strategies for their control in agricultural settings are still being sought out as the predominant form of control, chlorpyrifos, continues to be phased out in the United States. This research develops our understanding of boric acid hydrogel bait as a potential solution for Argentine ant, Linepithema humile (Mayr) control. Laboratory studies revealed 1) that this bait with a representative preservative, potassium sorbate, is effective in causing Argentine ant mortality 2) that bait is best used fresh and 3) that prior to mortality, Argentine ants exhibit a clumping behavior in response to bait consumption. A large-scale and continuous method of manufacture of the hydrogel beads was devised, allowing for large-scale field applications of the bait in a citrus grove operated by UCR Agricultural Operations. The bait proved effective in reducing ant numbers by up to 80%. If the levels of control prove to be sufficient, then boric acid hydrogel bait utilizing calcium alginate can be considered an effective, practical, sustainable, and environmentally friendly means of Argentine ant control in citrus groves.

Argentine ants are a major pest in California. In this study, a biodegradable calcium alginate hydrogel with an aqueous boric acid bait was tested against Argentine ant populations in a citrus orchard and a vineyard. A new continuous method was developed to produce large quantities of hydrogel bait for the field test. Foraging activity levels of ants were compared between baited and untreated zones. For both study sites, four to five monthly bait applications throughout summer provided a greater than 80% reduction in ant activity. Based on spatial analyses by distance indices, the baited areas were characterized by gaps (areas with lower ant counts) and the untreated control zones were characterized by patches (areas with higher ant counts). This indicated area-wide suppression of Argentine ants. For the citrus orchard, post-baiting panel trap monitoring showed reductions of both ants and Asian citrus psyllid in the baited zone compared to the control. For the vineyard, mid-season soil analyses indicated that the impact of boric acid baiting on soil boron concentration was negligible. In sum, the calcium alginate hydrogel bait with boric acid as an active ingredient may provide a promising solution for Argentine ant baiting.