While testing how well commercial bumblebees pollinate early spring crops, Cornell University researchers made a surprising discovery: dead wild bumblebee queens in the hives, an average of 10 per nest box.
A new study finds that nest boxes of commercial eastern common bumblebees (Bombus impatiens) lead to the deaths of wild queens who are attracted to the brightly-colored hives.
The boxes draw wild B. impatiens queens (and those of other species) engaged in usurpation, a natural behavior in which a queen who has yet to establish her own nest takes over another queen’s nest for a potential advantage. These usurping wild queens are killed by workers upon entry, as commercial hives have many more workers than natural nests.
An existing technology called an excluder, which narrows the nest box doorway, was 100% effective at keeping the resident queen in and usurpers out, according to the study.
“Every one of those queens that is killed will now not found her own nest somewhere else on that farm, which would then contribute worker bees later in the season to pollinate those crops,” said Heather Grab, senior lecturer in the School of Integrative Plant Science and senior author of the study.
The finding potentially adds to the list of human practices that contribute to the decline of wild bee populations. While wild eastern bumblebee populations are not a species of conservation concern, the researchers did find dead queens of other species, such as the declining Bombus perplexus (called the confusing bumblebee), inside the commercial hives.
Researchers hypothesized that the dead queens in commercial hives could be due to poorly understood usurping behavior. In addition, the bright colors and smells of the nest boxes may serve as hyper-attractive cues to nest-searching queens.
To test the hypothesis, they placed commercial bumblebee colonies in early spring on apple orchards in eight sites around the Finger Lakes area of New York. Commercial colonies were set up side by side, half of them with queen excluders in the open doorways, and half with no excluder. They also marked each hive’s original queens. The nests were then checked every few days over a two-week period. Nests without excluders included more dead usurpers, including one nest which had 19 dead queens in it.
“If you are a commercial grower, and you want to manage bumblebees, especially if you are bringing them in early in the season, you may actually be reducing your overall pollination services by investing in these commercial bumblebee colonies, unless you are taking some risk-mitigation strategies like putting in a queen excluder,” Grab said.
For additional information, see this Cornell Chronicle story.