No second chances for pollen-laden queens?

Abstract

Bumble bees are eusocial, yet queens are solitary for much of their lives. Little is known about the stages in the solitary phase of queens, including the factors that influence successful initiation of nests. One anecdotal recommendation suggests that wild-caught queens are less likely to initiate nests if they are captured while carrying pollen loads. Queens that are collecting pollen have already chosen a nest site and are either preparing to lay their first clutch of eggs, have already begun oviposition, or are provisioning developing brood. Although there is a conservation-based argument for leaving these queens to their own devices, we were interested in the biological aspect of this: if a queen has already initiated a nest in the wild, will she initiate another one in captivity? In 2016 and 2017, 960 queens of five species were captured, and the presence or absence of corbicular loads of pollen was noted. Each queen was then placed in an artificial nest and provided with unlimited food for 21 days. Nests were monitored for brood presence daily, and rates of nest initiation (brood production) were compared between queens captured with and without pollen loads. Nest initiation rates varied among species, as did the influence of pollen-collecting behavior at the time of capture. Pollen-laden Bombus occidentalis queens were less likely to lay eggs, yet B. bifarius and B. vosnesenskii queens with pollen had a greater chance of initiating a captive nest. These results should inform both commercial and conservation efforts.