Monitoring the effects of granular insecticides for Argentine ant control in nursery settings

The effects of broadcast granular insecticide formulations on Argentine ant , Linepithema humile (Mayr), foraging rates were measured in two types of n ursery settings. In an artificial nursery setting, colonies of Argentine an ts were collected and introduced into the soil of potted oleander plants (N erium oleander L.). Plants were relocated into 12 field plots that were sub sequently treated with granular formulations of fipronil or bifenthrin, or left untreated. Two or three days after treatment of artificial nurseries, the number of foraging ants was reduced 80% or more in all treated plots co mpared with controls. Ant foraging rates in fipronil treated plots were red uced for about 3 wk after treatments and began to recover by week 4. Bifent hrin treatments almost eliminated foraging ants for the duration of the tri al. The number of ants in control plots increased in the first three days a fter treatment, suggesting ants may have initially moved from treated plots to untreated areas. In commercial nursery settings, similar sized plots co ntained plants naturally infested with L. humile of varying size colonies. Plots were treated with a granular formulation of fipronil, or left untreat ed. Foraging rates were measured in each plot. Trials in commercial nurseri es showed a similar response in to fipronil treatments compared to the arti ficial nursery. Fipronil granules were effective in significantly reducing ant foraging rates, but did not completely eliminate them from treated plot s. In both types of studies, it was difficult to space plots far enough apa rt so that treatments did not interfere with each other. Fluctuations in co ntrol foraging rates indicated that ants were probably moving from plot to plot during the course of the study.