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, 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 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 active ingredients tested are viable candidates for P.
alluaudi 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 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.