Laboratory and field evaluation of the repellency of six preservatives to red imported fire ants (Hymenoptera: Formicidae)

Abstract Baiting is widely applied for the detection and control of the red imported fire ants, Solenopsis invicta Buren. Adding preservatives into baits would prevent microbial contamination during production and storage, and might extend period of bait attractiveness in the field. However, it is not known if preservatives are repellent to S. invicta . In the present study, potential effects of six commonly used preservatives (potassium sorbate, sodium benzoate, sodium diacetate, sodium dehydroacetate, calcium propionate, and nisin) on the foraging behaviors of S. invicta foragers were evaluated under laboratory and field conditions. Four-choice tests (laboratory study) showed that the number of foraging ants on the preservative-treated (immersed in 2000-, 5000-, or 10,000-ppm solution for 30 min) and control (immersed in distilled water for 30 min) food was similar, with an exception of sodium dehydroacetate, which significantly decreased the number of foraging ants at the three tested concentrations. Interestingly, 46%, 58% and 71% of the food items treated with 2000-, 5000- and 10,000-ppm solutions of sodium dehydroacetate were buried with soil particles, respectively, whereas only 17% of the control food was similarly buried. Multiple-choice tests (field study) showed that food treated with the 5000- or 10,000-ppm solution of sodium dehydroacetate attracted significantly fewer S. invicta workers compared to other preservatives and the controls. Our study showed that the use of sodium dehydroacetate should be avoided during the production of aqueous-based or liquid baits against S. invicta .