The effect of water on the attractiveness and efficacy of a fast-acting ant bait

Abstract Invasive ants are some of the most important environmental and economic pests globally, with granular corn-grit based baits being a common method of control. One of the limitations of these baits is their perceived ineffectiveness after rainfall or heavy dew, with control programs frequently suspending treatment due to these conditions. Empirical research to support or refute these restrictions, however, is lacking, and has not delineated the effects of water on the attractiveness of baits to ants and the effectiveness of baits in controlling colony activity. Here, we compare the number of ants interacting with baits (attractiveness) and the activity levels of colonies after baiting (efficacy) across wet and dry baits in the field, using S. invicta colonies in Queensland, Australia. Dry baits were removed by ants at a greater rate than wet baits, but more ants were observed interacting with wet than with dry baits. Dry baits outperformed control baits (with no active ingredient), but not wet baits, in supressing colony activity. These results suggest that the complete suspension of baiting during wet conditions may place unnecessary restrictions on management.