Possible limitations in the management of a small ant pest species (Plagiolepis alluaudi) using gel baits

<p>Alluaud’s little yellow ant, <em>Plagiolepis alluaudi </em>Emery 1894<em>, </em>(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, management protocols for this species have not been reported. In ants, feeding preference is partly correlated with body size and viscosity of the food source, and small ants may not be able to feed on formulated baits of relatively high viscosity. To assess population management implications of bait viscosity on a small pest ant species, four commercial ant baits of varying viscosities were evaluated in laboratory and field assays against <em>P. alluaudi</em>. All four products negatively affected <em>P. alluaudi </em>survival compared to the untreated control and all products were associated with greater visitation compared to the control, suggesting all active ingredients tested are viable candidates for <em>P. alluaudi </em>management. However, their direct use for population management in the field may be limited, as ants eventually displayed feeding cessation on all four baits. When baits were diluted with water, viscosity was reduced and ant 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 two-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 <em>P. alluaudi </em>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.</p>