Individual study: Increases in densities of the citrus red mite, Panonychus citri (Acarina: Tetranychidae), in association with the Argentine ant, Iridomyrmex humilis (Hymenoptera: Formicidae), in southern California citrus
Haney P.B., Luck R.F. & Moreno D.S. (1987) Increases in densities of the citrus red mite, Panonychus citri (Acarina: Tetranychidae), in association with the Argentine ant, Iridomyrmex humilis (Hymenoptera: Formicidae), in southern California citrus. Entomophaga, 32, 49-57
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Exclude ants that protect pests
A randomised, replicated, controlled study in 1984-1985 in California, USA (Haney et al. 1987) found fewer spider mite destroyers Stethorus picipes in navel orange Citrus sinensis trees with insecticide barriers to exclude ants (0.2-0.8 destroyers/sticky card) vs. control trees (15-32 destroyers) in autumn, but no difference in summer and winter. The same effect was found in grapefruit Citrus paradisi, but not in Valencia oranges. Predatory mite Euseius tularensis numbers were similar between treatments. Fewer citrus red mites Panonychus citri occurred in trees with vs. without ant barriers (2-65 vs. 17-173 mites/tree, respectively) in orange orchards during peak numbers in late summer and the same effect was found in a grapefruit orchard during an autumn peak (approximately 75 vs. 200 mites/tree). Argentine ants Linepithema humile were successfully excluded from orange trees with insecticide barriers (0 ants/minute/tree with barriers applied vs. 14-158 in control trees) but a limonene citrus oil barrier had no effect (19-219 ants/minute/tree). Plots of orange trees (in two orchards) were assigned to insecticide (90 ml of 1% chlorpyrifos applied at the base of trees), citrus oil (135 ml of 15% limonene) or no-barrier treatments. Plots of grapefruit (in one orchard) were assigned to insecticide or no-barrier treatments only.