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Individuals are different, but they can work together to perform adaptive collective behaviours. Despite emerging evidence that individual variation strongly affects group performance, it is less clear to what extent individual variation is modulated by participation in collective behaviour. We examined light avoidance (negative phototaxis) in the gregarious cockroach Blaberus discoidalis, in both solitary and group contexts. Cockroaches in groups exhibit idiosyncratic light-avoidance performance that persists across days, with some individual cockroaches avoiding a light stimulus 75% of the time, and others avoiding the light just above chance (i.e. ~50% of the time). These individual differences are robust to group composition. Surprisingly, these differences do not persist when individuals are tested in isolation, but return when testing is once again done with groups. During the solo testing phase cockroaches exhibited individually consistent light-avoidance tendencies, but these differences were uncorrelated with performance in any group context. Therefore, we have observed not only that individual variation affects group-level performance, but also that whether or not a task is performed collectively can have a significant, predictable effect on how an individual behaves. That individual behavioural variation is modulated by whether a task is performed collectively has major implications for understanding variation in behaviours that are facultatively social, and it is essential that ethologists consider social context when evaluating individual behavioural differences.

Background Animal pollinators provide vital ecosystem services that sustain biodiversity and support agricultural yields. Declining pollinator populations threaten to affect human health outcomes by decreasing crop yields and human nutrient intake, and there is a well-recognised need to understand how environmental stressors such as pesticides affect bees, the most important animal pollinators. Neonicotinoid pesticides in particular, the most widely used class of insecticide globally, pose a major threat to bees. While there is now strong evidence that neonicotinoids can affect bee behaviour and colony growth, major knowledge gaps remain in understanding how these pesticides affect pollinator health. First, the specific mechanisms by which neonicotinoid exposure affect bee colonies are not well understood, limiting the ability to predict their effects. Second, it is unclear how pesticide exposure interacts with other environmental stressors, which could either amplify or attenuate the effects of neonicotinoids. Methods We describe the development of an automated, robotic system aimed at helping to fill these gaps in knowledge. Specifically, this system harnesses advances in computer vision to track the behaviour of hundreds of individual bees across dozens of colonies simultaneously. Specifically, this system uses a computer-controlled, motorised camera array to collect video data from up to a dozen bumblebee colonies in parallel. We then use computer vision-based techniques to automatically measure key aspects of behaviour (eg, activity level, task performance, and social interactions) for individually tagged bees before and after exposure to neonicotinoid pesticides. Findings Using a preliminary version of this system, we have found that exposure to field-realistic levels of a common neonicotinoid pesticide (imidacloprid) affects key aspects of social behaviour in bumblebees ( Bombus impatiens ). These effects include reduced rates of nursing (27% reduction; p Interpretation This automated, parallel system is ideal for studying the effects of multiple environmental stressors, and we are currently extending it to investigate simultaneous exposure to neonicotinoids, thermal stress, and nutritional deficiency on the behaviour and health of bee colonies. This system can provide efficient screening of agrochemicals at low cost, and could provide an important instrument for policymakers and other shareholders to assess the risk of agrochemicals to the health of both bee and human populations. Funding Winslow Foundation, Rockefeller Foundation.