Abstract
Summary The ability to forage and return home is essential to the success of bees as both foragers and pollinators. Pesticide exposure may cause behavioural changes that interfere with these processes, with consequences for colony persistence and delivery of pollination services.We investigated the impact of chronic exposure (5–43 days) to field‐realistic levels of a neonicotinoid insecticide (2·4 ppb thiamethoxam) on foraging ability, homing success and colony size using radio frequency identification (RFID) technology in free‐flying bumblebee colonies.Individual foragers from pesticide‐exposed colonies carried out longer foraging bouts than untreated controls (68 vs. 55 min). Pesticide‐exposed bees also brought back pollen less frequently than controls indicating reduced foraging performance.A higher proportion of bees from pesticide‐exposed colonies returned when released 1 km from their nests; this is potentially related to increased orientation experience during longer foraging bouts. We measured no impact of pesticide exposure on homing ability for bees released from 2 km, or when data were analysed overall.Despite a trend for control colonies to produce more new workers earlier, we found no overall impacts of pesticide exposure on whole colony size. Synthesis and applications. This study shows that field‐realistic neonicotinoid exposure can have impacts on both foraging ability and homing success of bumblebees, with implications for the success of bumblebee colonies in agricultural landscapes and their ability to deliver crucial pollination services. Pesticide risk assessments should include bee species other than honeybees and assess a range of behaviours to elucidate the impact of sublethal effects. This has relevance for reviews of neonicotinoid risk assessment and usage policy world‐wide.
Highlights
Bumblebees experience their surrounding landscape at large spatial scales (Westphal, Steffan-Dewenter & Tscharntke 2006a) and can navigate back to their nests from long distances
As bumblebees operate at these large spatial scales, navigation and foraging ability are essential to the foraging success of Pesticide effects on bee foraging, homing ability and colony growth 1441 individual bumblebees
Twenty-four individuals were found to drift between colonies, with significantly more drifting from natal control than pesticide colonies (ANOVA: F1,6 = 35Á53, P < 0Á001, Table 1); these individuals were removed from any further analyses of foraging behaviour as they may have been exposed to both treatments
Summary
Bumblebees experience their surrounding landscape at large spatial scales (Westphal, Steffan-Dewenter & Tscharntke 2006a) and can navigate back to their nests from long distances (up to 9Á8 km; Goulson & Stout2001). Bumblebees experience their surrounding landscape at large spatial scales (Westphal, Steffan-Dewenter & Tscharntke 2006a) and can navigate back to their nests from long distances As bumblebees operate at these large spatial scales, navigation and foraging ability are essential to the foraging success of Pesticide effects on bee foraging, homing ability and colony growth 1441 individual bumblebees This ability to locate, forage and navigate over large distances from a central nest site in the environment is a cognitively challenging task, and any increased stress on colonies (such as homing failure of individual bees) might lead to colony failure (Bryden et al 2013). Neonicotinoids have been shown to have a variety of sublethal impacts on honeybees and bumblebees (Godfray et al 2014, 2015), and concern over these sublethal effects has led to a moratorium (Regulation (EU) No 485/2013) on their use on crops attractive to bees in Europe and restrictions in some provinces of Canada
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