Possible Limitations in the Management of a Small Ant Pest Species (Plagiolepis alluaudi) Using Gel Baits

Alluaud's little yellow ant, Plagiolepis alluaudi Emery 1894, (Hymenoptera: Formicidae), is an emerging nuisance species in floriculture and residential areas around the globe. Originally described from Madagascar, it ranks among the smallest widespread formicine pests. To date, no evaluations of management protocols for this species have been reported. In ants, feeding preference is related to ant body size and viscosity and nutritional content of the food source. Optimizing these factors could lead to improved bait performance. To assess population management implications of various bait parameters on a small pest ant species, four commercial ant baits of varying viscosities, active ingredient (AI) group and concentration, and nutritional content were evaluated in laboratory and field assays against P. alluaudi. All four products negatively affected P. alluaudi survival compared to the untreated control, and all products were associated with greater visitation compared to the control, suggesting all AIs tested are viable candidates for P. alluaudi management. However, their direct use for population management in the field may be limited, as feeding cessation was eventually observed on all four baits. When baits were diluted with water, viscosity was reduced and survival was initially higher compared to with undiluted baits. However, similarly low levels of survival were maintained over time. Most importantly, we found in a 2-year observational field study involving sustained baiting within an infested structure that only the bait formulation with the lowest overall viscosity was able to alleviate P. alluaudi nuisance indoors. Our results suggest that diluting baits may be a viable strategy for targeting very small pest ant species, and the greater time to lethality of diluted baits, resulting from reduced toxicant concentration, may be a reasonable trade-off allowing smaller ant species to continue feeding for a sufficient duration on a bait formulation.