Palatability of Insecticides and Protein in Sugar Solutions to Argentine Ants

Invasive ant species like Linepithema humile cause significant ecological and economic harm, making effective control strategies essential. Insecticide baits are currently the most effective approach for controlling ants. Therefore, quantifying how palatable or unpalatable baits, bait additives, or toxicants are, is critical for developing effective control methods. It has recently been demonstrated that in the comparative evaluation of foods, animals that are aware of both a test food and a comparator food exhibit greatly increased sensitivity when detecting the unpalatability of liquid baits. Here, we deploy a newly developed comparative evaluation methodology to examine the palatability to L. humile workers of three toxicants used in invasive ant control: Fipronil, spinosad, and imidacloprid, as well as egg white protein. Ants showed no significant preference between pure sucrose and sucrose-toxicant solutions, indicating that they either cannot detect the toxicants or that they do not find them distasteful. Survival tests confirmed that the toxicant concentrations used were lethal, with a survival rate of 50% or below after 72 hours. However, ants found egg protein additive unpalatable, significantly preferring pure sucrose to a sucrose-egg protein mix. These findings confirm that three major toxicants are suitable for use in baits, and that reported abandonment or avoidance of toxic baits is not due to the unpalatability of these toxicants. However, the addition of egg protein to sucrose baits, even at ratios which optimise colony growth, is likely counterproductive. Future research should investigate the relative preference of invasive ants for various bait matrixes over naturally available food, ensuring more effective pest management strategies.