Barrier sprays to control Argentine ants (Hymenoptera: Formicidae)

Abstract

Insecticide was applied to the perimeter of homes and adjacent areas likely to be visited by Argentine ants, Iridomyrmex humilis (Mayr). Treatment configuration consisted of a 1.8- to 2.4-m-wide band of spray around the exterior of the structure. Margins of sidewalks and pathways and around stepping stones, buses of trees, potted plants, and garbage cans were sprayed with 1.2- to 1.8-m-wide bands. Based on monitoring with traps, significant and relevant control was achieved when the number of ants trapped posttreatment declined at least 80%. Barrier sprays of 237 mg (AI)/m2 chlorpyrifos, 14.5 mg (AI)/m2 cyfluthrin and 67.2 mg (AI)/m2 cypermethrin provided >80% reductions in the number of ants trapped at 7 d. Chlorpyrifos provided >82% reductions for at least 30 d. The combination of cyfluthrin spray + granules provided >85% reduction in ant trap counts at day 7. Only the combination treatment provided >80% reductions at 60 d. Cypermethrin and permethrin sprays failed to provide >80% reductions for 30 d. Factors that likely contribute to decreased performance of barrier sprays against ants include heavy irrigation, dense ground cover, exposure to direct sunlight, alkaline nature of the stucco and concrete surfaces, and extremely high temperatures.