Certain ants in almond orchards can be a problem, causing economic loss for growers. Pest ants feed on almond nuts during harvest while they are on the orchard floor. California has approximately 245 native and 25 introduced ant species, yet very few of them are an economic threat to agricultural crops. The majority of ant damage is caused by three ant species: southern fire ant, thief ant, and pavement ant.

Area IPM Advisor Kris Tollerup is raising awareness about the importance of knowing if the ants in almond orchards are pest ants in order to prevent unnecessary pesticide applications. Nonpest ants that often occur in almond orchards are the native gray ant, pyramid ant, and California harvester ant. “A common understanding among growers and pest control advisers is that ants are ants, and when ants are observed in an almond orchard an insecticide bait must be applied,” says Tollerup. “Moreover, too often monitoring is a foregone conclusion and an insecticide bait is applied as cheap insurance.”

In addition to differences in how the ant looks, foraging activity and behavior, nest location, and ant mound structure provide useful information for identification. Tollerup has been gathering this information, including photos, to help growers and pest control advisers learn to quickly recognize pest ants while in the field.

For instance, during hot daytime temperatures, the foraging activity of the pest southern fire ant and pavement ant diminishes considerably, while that of the nonpest native gray ant and California harvester ant remains high. Both the pest Southern fire ant and nonpest native gray ant construct their nests in shaded areas with multiple entrances. The Southern fire ant entrance holes are smaller than the larger native gray ant entrance holes. Southern fire ant entrance mounds are hillier and made with finer grains of soil compared to the flatter mounds made with larger grains of dirt or no mounds at all by the native gray ant.

Tollerup anticipates an increase in the ability to identify pest from nonpest ants. He is training growers and pest control advisers to increase their knowledge about IPM and to monitor and identify before applying an insecticide. Tollerup’s work could potentially reduce insecticide applications for ants.