Organic citrus growers can use low-toxic ant control measures to rid their groves of pesky Argentine ants, according to a study funded by the UC Exotic/Invasive Pests and Diseases Research Program. After one week of using baits, ants were reduced by about 50 percent and after two weeks, by about 70 percent.

In their study, Les Greenberg, entomology specialist, John Klotz, University of California Cooperative Extension urban entomologist, and Michael Rust, entomologist, all from UC Riverside, demonstrated a reduction in Argentine ants in an organic citrus grove using ant bait stations containing liquid toxicants.

“We used a commercially available liquid bait with a borate toxicant to reduce season-long ant population densities,” says Greenberg. “Our results indicate that small amounts of relatively non-toxic insecticides, delivered in a sugar-bait, can reduce ants.”

Argentine ants are probably the most prevalent of the ant species in California agriculture and urban environments. The small, deep brown insects travel in trails on trees, the ground, or irrigation lines and build their nests underground. Ant populations peak in midsummer and early fall.

The ants feed on honeydew excreted by soft scales, mealybugs, cottony cushion scales, whiteflies and aphids. As part of this relationship, they also protect these insects from their natural enemies, thus interrupting biological control of the honeydew-producing pests.

No effective natural enemies of the Argentine ant are known. Cultural controls, including the use of sticky materials applied to tree trunks, are acceptable for use in organically managed citrus groves.

Greenberg, Klotz and Rust recommend that growers monitor their orchards in spring when honeydew-producing insects, such as aphids, appear. Check the abdomen of ants descending the tree trunks to see if they are swollen and translucent. This identifies them as honeydew-collecting species. Growers should periodically inspect for ants and bark damage under the trunk wraps of several young trees. For the most effective and economical ant control, begin treatments when ants become active in the spring following the winter rains.

The UC EDRP targets research on exotic pests and diseases in California. The program aims not only to improve our knowledge and management of pests that are already here, but also to reduce the potential impact of those pests and diseases that pose a threat to the state. The program is collaboration between the UC Statewide Integrated Pest Management Program and the UC Riverside Center for Invasive Species Research. U.S. Department of Agriculture, Cooperative State Research Education and Extension Service, funds the program.