Cold anaesthesia decreases foraging recruitment in the New World bumblebee, Bombus occidentalis

Cold narcosis is commonly used for immobilizing bees and has been found to have no effect on mortality and fecundity in honeybees. We present the first study examining the effect of cold narcosis on recruitment and foraging in bumblebees. In a controlled laboratory setting, we observed that the number of foraging Bombus occidentalis, a New World bumblebee, increased after the focal forager returned to the nest with rich 2.5 M sucrose solution. However, cold narcosis (~4° C, ~5 min) significantly reduced the ability of B. occidentalis foragers to incite nestmates to forage in a flight arena: 22% fewer total foragers and 56% fewer new recruits were present in the flight arena 10 min after the return of a cold-treated bee compared to the numbers present after the return of an unmanipulated bee. These results demonstrate unanticipated effects of cold anaesthesia on bumblebee foraging behaviour, suggesting that the use of cold anaesthesia should be treated with caution in bumblebee foraging studies.