Strong negative reinforcement interferes with visual learning in a solitary pollinator

Visual learning in insects can be strongly influenced by the underlying context and conditions. Improved colour learning has been demonstrated using differential conditioning with reward-aversion paradigms in eusocial insects like wasps, bumblebees, and honeybees, where substances that induce strong aversion, such as quinine, enable more accurate discrimination. Although learning outcomes are closely tied to the strength of target association during conditioning, few studies have compared the role of negative reinforcements in shaping these associations, and their relevance across insect groups with different life histories. In our study, we compare the effects of aversive substances for learning in the hummingbird hawkmoth (Macroglossum stellatarum)- a solitary pollinator that relies on vision for foraging. Linking to previous learning studies in insects, we paired a sugar-rewarded target with a distractor that was paired with either quinine, salt, citric acid, water, or was presented with no aversive substance. Learning outcomes were compared by inverting a strong colour preference between perceptually close or distant colour pairs, to provide tasks with disparate challenges. Contrary to results from other insect species, we found that moths trained with quinine were worse at switching preferences between similar colours compared to training with citric acid and appetitive-only differential conditioning. We also show that quinine interferes with sucrose perception, potentially impairing target acquisition during training. Additionally, we link differences in learning to the impact of negative reinforcements on exploration during foraging. Our results showcase the role of experience in modulating behaviour and highlight the role of foraging dynamics in influencing learning in a solitary forager.