While investigating how well commercial bumblebees (Bombus impatiens) pollinate early spring crops, a team of scientists led by Cornell University has made a surprising and worrisome discovery: a series of dead wild bumblebee queens in the hives (an average of ten dead queens in each nest box). According to the experts, the brightly-colored hives play a significant role in attracting the queens, which are afterwards killed by worker bees from those hives.
Bumblebee queens frequently engage in a behavior called “usurpation,” in which a queen who has yet to establish her own nest takes over by force another queen’s nest. However, as commercial hives have many more workers than natural nests, these usurping wild queens are often killed by workers upon entry. Fortunately, the scientists found that an existing technology called an “excluder,” which narrows the nest box doorway, is fully effective at keeping the resident queen in and the usurpers out.
The researchers placed commercial bumblebee colonies in early spring on apple orchards in eight sites around the Fingers Lakes area of New York. The colonies were set up side by side, half of them with excluders on their doorways, and half without. After marking each hive’s original queens, the experts checked the nests every few days during a period of two weeks. The investigation revealed that nests without excluders included more dead usurpers, one of them containing a staggering 19 dead queens.
These findings add yet another item on the list of human practices which contribute to the decline of wild bee populations. Although wild eastern bumblebee populations are fortunately not a species of conservation concern, the scientists did find dead queens of other species too – such as the rapidly declining Bombus perplexus (known as the “confusing bumblebee”) – inside commercial hives.
“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,” concluded senior author Heather Grab, an expert in Integrative Plant Sciences at Cornell.
The study is published in the Journal of Applied Ecology.
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