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. Recent research shows that when animals can compare a test food containing a bitterant with another option, they are much better at detecting the bitterant and thus rejecting the test food. Here, we deploy a newly developed comparative evaluation methodology to examine the palatability to L. humile workers of three toxicants commonly used in invasive ant control: fipronil, spinosad, and imidacloprid. Additionally, we tested egg-white protein in sucrose solutions to assess its impact on bait acceptance. Ants showed no significant preference between pure sucrose and sucrose-toxicant solutions, indicating that they either cannot detect the toxicants or do not find them distasteful. Survival tests confirmed that the toxicant concentrations used, fipronil at 0.0001% and 0.001%, spinosad at 0.015% and 0.15%, and imidacloprid at 0.005%, were lethal, with a survival rate of 50% or below after 72 h. However, ants found egg protein additive unpalatable, significantly preferring pure sucrose to a sucrose egg-white 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 alone 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.