Invasive ant learning is not affected by seven potential neuroactive chemicals

Abstract

Nectar-feeding insects are often the victims of psychoactive manipulation, with plants lacing their nectar with secondary metabolites such as alkaloids and non-protein amino acids which often boost learning, foraging, or recruitment. However, the effect of neuroactive chemicals has seldomly been explored in ants. Argentine ants (Linepithema humile) are one of the most damaging invasive alien species worldwide. Enhancing or disrupting cognitive abilities, such as learning, has the potential to improve management efforts, for example by increasing preference for a bait, or improving ants ability to learn its characteristics or location. Here, we test the effects of seven potential neuroactive chemicals - two alkaloids: caffeine and nicotine; two biogenic amines: dopamine and octopamine, and three non-protein amino acids: {beta}-alanine, GABA and taurine - on the cognitive abilities of invasive L. humile using bifurcation mazes. Our results confirm that these ants are strong associative learners, requiring as little as one experience to develop an association. However, we show no short-term effect of any of the chemicals tested on spatial learning, and in addition no effect of caffeine on short-term olfactory learning. This lack of effect is surprising, given the extensive reports of the tested chemicals affecting learning and foraging in bees. This mismatch could be due to the heavy bias towards bees in the literature, a positive result publication bias, or differences in methodology. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=129 SRC="FIGDIR/small/514620v1_ufig1.gif" ALT="Figure 1"> View larger version (17K): org.highwire.dtl.DTLVardef@10a971org.highwire.dtl.DTLVardef@1e4701dorg.highwire.dtl.DTLVardef@7cb741org.highwire.dtl.DTLVardef@1e33eea_HPS_FORMAT_FIGEXP M_FIG C_FIG