Impact of controlled neonicotinoid exposure on bumblebees in a realistic field setting

Abstract

1. Pesticide exposure has been implicated as a contributor to insect pollinator declines. In social bees, which are crucial pollination service providers, the effect of low-level chronic exposure is typically non-lethal leading researchers to consider whether exposure induces sub-lethal effects on behaviour and whether such impairment can affect colony development. 2. Studies under laboratory conditions can control levels of pesticide exposure and elucidate causative effects, but are often criticised for being unrealistic. In contrast, field studies can monitor bee responses under a more realistic pesticide exposure landscape; yet typically such findings are limited to correlative results, and can lack true controls or sufficient replication. We attempt to bridge this gap by exposing bumblebees to known amounts of pesticides when colonies are placed in the field. 3. Using 20 bumblebee colonies, we assess the consequences of exposure to the neonicotinoid clothianidin, provided in sucrose at a concentration of five parts per billion, over five weeks. We monitored foraging patterns and pollen collecting performance from 3282 bouts using either a non-invasive photographic assessment, or by extracting the pollen from returning foragers. We also conducted a full colony census at the beginning and end of the experiment. 4. In contrast to studies on other neonicotinoids, showing clear impairment to foraging behaviours, we detected only subtle changes to patterns of foraging activity and pollen foraging during the course of the experiment. However, our colony census measures showed a more pronounced effect of exposure, with fewer adult workers and sexuals in treated colonies after five weeks. 5. Synthesis and applications. Pesticide induced impairments on colony development and foraging could impact on the pollination service that bees provide. Therefore our findings, that bees show subtle changes in foraging behaviour and reductions in colony size after exposure to a common pesticide, has important implications and helps to inform the debate over whether the benefits of systemic pesticide application to flowering crops outweigh the costs. We propose that our methodology is an important advance to previous semi-field methods and should be considered when considering improvements to current ecotoxicological guidelines for pesticide risk assessment

Pesticide exposure affects flight dynamics and reduces flight endurance in bumblebees

“…We made the assumption that spiking the sucrose solution with the neonicotinoid would not deter feeding if given no other option, as supported by pilot observations and previous studies (Arce et al, 2017;Gill et al, 2012;Kessler et al, 2015). Our pilot study also indicated that workers took a mean (±SEM) duration of 50 ± 13 s to commence feeding, defined as prolonged (>2 s) proboscis extension on to the cotton wool, and fed for a mean (±SEM) duration of 213 ± 24 s before stopping, with subsequent feeds being rare, sporadic, and short (<10 s).…”

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 2: impacts on organisms and ecosystems

“…However, control workers learned to handle flowers efficiently after fewer learning visits. Arce et al (2016) placed B. terrestris nests out in an area of parkland for a 5-week period while also supplying them with sugar solution treated with 5 ppb of clothianidin. The volume of sugar solution provided was estimated to be half that which colonies typically consume over the course of the experiment.…”

Quantifying the impact of pesticides on learning and memory in bees

“…There is strong evidence to associate pesticide use with bee population decline (Woodcock et al., ) and consequently with potential losses to pollination services and crop yields (Stanley & Raine, ; Stanley, Garratt, et al., ). At the colony level, pesticide exposure is associated with negative impacts on fitness‐determining traits that include colony initiation, colony growth, and reproductive output (Arce et al., ; Baron, Jansen, Brown, & Raine, ; Baron, Raine, & Brown, , ; Rundlöf et al., ; Tsvetkov et al., ; Whitehorn, O'Connor, Wackers, & Goulson, ; Woodcock et al., ). The mechanisms that underlie these effects remain unclear, but pesticides have been shown to negatively impact key aspects of worker performance including foraging efficiency and navigation ability (Feltham, Park, & Goulson, ; Gill & Raine, ; Gill, Ramos‐Rodriguez, & Raine, ; Henry et al., ; Stanley, Russell, Morrison, Rogers, & Raine, ).…”