Chronic acetamiprid exposure moderately affects the foraging behaviour of buff-tailed bumblebees (Bombus terrestris)

Bumblebees are important pollinators in both natural and agricultural ecosystems, but their survival and pollination service are threatened by extensive pesticide use. Due to regulation changes, acetamiprid has become the only neonicotinoid substance that can be used without restrictions and in open-field cultivations in the European Union. Yet, we know little about how this active ingredient affects bumblebees' foraging behaviour and if such effects are similarly detrimental to those of other neonicotinoids. Here we investigated how a 14-day-long (chronic) exposure to low (5 ppb) and high (2500 ppb) concentrations of acetamiprid in syrup affected different aspects of foraging behaviour in buff-tailed bumblebees (Bombus terrestris, Linnaeus). We recorded individual foraging at artificial food patches during one-hour-long trials and then compared several foraging-related measures between differently dosed individuals. We found that 75.12% of the total syrup consumption occurred at the first-exploited patch, but individuals did not exhibit any bias toward pesticide-treated food patches. Chronic exposure to acetamiprid had little effect on individual foraging decisions at the first-exploited food patch but significantly affected the time to the first feeding and the number of feedings at the second-exploited patch in interaction with body mass. The duration of the first feeding was affected only by foragers' body mass. Our finding indicates that chronic exposure to a high but field-realistic concentration of acetamiprid may alter some aspects of bumblebees' foraging behaviour. If such behavioural changes accumulate during consecutive foraging bouts, chronic exposure to this pesticide might lead to a reduction of daily resource collection, ultimately jeopardising colony fitness or plant (crop) pollination.