Chlorpyrifos and Diazinon as Barriers to Argentine Ant (Hymenoptera: Formicidae) Foraging on Citrus Trees1

Abstract

Argentine ant, Iridomyrmex humilis (Mayr), was effectively excluded from foraging in citrus trees by removing foliage from tree canopy (skirt-pruning) within 60 cm of the ground and by applying 2% (AI) liquid chlorpyrifos 4 emulsifiable concentrate to the basal 15 cm of the trunk, or by placing a ring of 13 g (AI) diazinon 14 granular (G) on the ground adjacent to and around the trunk. These treatments were effective for 8 and 3 months, respectively. Applications of limonene to the basal trunk area of skirt-pruned trees, or uniform distribution of 32 g (AI) diazinon 14 G beneath the canopy of unpruned trees did not prevent ants from foraging in the trees. Data suggest that in the absence of ants, populations of honeydew-producing citrus mealybug, Planococcus citri (Risso), and woolly whitefly, Aleurothrixus floccosus(Maskell), and nonhoneydew-producing California red scale, Aonidiella aurantii (Maskell), were effectively reduced by their respective natural enemies. Populations of honeydew-producing species declined sooner than populations of California red scale.