Sub-lethal doses of imidacloprid alter food selection in the invasive garden ant Lasius neglectus

Abstract

Despite several restrictions to their use, neonicotinoid insecticides are still widely employed worldwide. Residual sub-lethal amounts of these chemicals can have detrimental effects on the behavior of non-target insects. Toxic effects on economically important species such as bees have been widely documented, but less is known about their toxic action on other social insects, such as ants. In this study, we assessed the effect of different sub-lethal doses of the neonicotinoid imidacloprid on the ability of colonies of the invasive ant Lasius neglectus to select the most profitable resource. We used Y-shaped mazes having an imidacloprid-polluted or an unpolluted sucrose solution on the two branches. Two sucrose (0.1 M, 0.5 M) and two imidacloprid (1 μg/ml, 10 μg/ml) concentrations were used. In parallel, we evaluated the marking activity of foragers who fed on the same solutions. We found that the 0.1 M sugar solution polluted with 1 μg/ml imidacloprid was significantly more frequently selected in binary choices experiments than the unpolluted resource. Moreover, the ingestion of the same combination of sugar and imidacloprid significantly increased the marking rate of foragers. The higher concentration of the pollutant had lower effects, probably because of the hormesis phenomenon. Results suggest that the lower sub-lethal dose of imidacloprid can lead ants to select again the polluted resource. This “active” selection of the pollutant may magnify the negative effects on the colonies. Due to their ecological role, any impairment of ant survival or behavior may have detrimental cascade effects on the whole ecosystem.

Invasive ant learning is not affected by seven potential neuroactive chemicals

“…Even though none of the chemicals tested showed an effect on learning and memory, we cannot exclude the possibility that these might interfere with foraging motivation through preference manipulation. Recently, sub-lethal doses of the neonicotinoid imidacloprid were shown to shift colony-level preference in the invasive ant Lasius neglectus ( Frizzi et al 2022 ). At the individual-level, orally administered serotonin decreases the amount of food ingested by treated ants ( Falibene et al 2012 ) whilst its antagonist, ketanserin, increases consumption ( Josens et al 2021 ).…”

Invasive ants fed spinosad collectively recruit to known food faster yet individually abandon food earlier

“…Nevertheless, a recent study showed GABA promoting flower fidelity, suggesting its effects are complex (Calderai et al ., 2023). Interestingly, sub-lethal doses of the neonicotinoid imidacloprid, also an antagonist of nicotinic acetylcholine receptors, were shown to shift colony-level preference in the invasive ant Lasius neglectus towards toxicant-laced solutions (Frizzi et al ., 2022), even though imidacloprid has been shown to impair olfactory learning and memory in honeybees (Yang et al ., 2012; Williamson & Wright, 2013). However, were this the case, control attempts using spinosad as the toxicant would likely have been more successful, unless such effects are lost at high doses, as they are for caffeine and imidacloprid (Frizzi et al ., 2022; Galante et al ., 2024).…”