>Is it true that honey bees will sometimes displace native pollinators?
>

This is one of those questions that will be debated on and on. Researchers have observed foraging bees, calculated nectar depletion of plants, weighed pollen accumulation in the hive, used radar to track foraging locations, identified pollen sources, but as yet I don't think there is a conclusive answer. And there probably never will be. The big problem with studies is that since the honey bee arrived in North America, it has spread to just about every spot on the continent. There is no way to measure what it was like before the honey bee arrived. Without any baseline data it is very difficult to gauge what the impacts are.

Competition can occur in two ways, for forage resources and for nest sites.

Forage resources is the most likely way in which honey bees and native bees compete. Certainly, a hive of honey bees has the capacity to collect large amounts of nectar and pollen in a relatively short period of time. The question is whether or not this depletion of resources deprives native bees. As I said, there is no conclusive evidence one way or the other.

There is little competition for nest sites between honey bees and native bees. Honey bees need a cavity and the great majority of the 4,000 native species are solitary nesting bees that dig narrow tunnels into bare ground or occupy abandoned beetle tunnels in snag. Bumble bees are the only native bees that require cavities, so there is some chance of competition. However, most bumble bees nest in old rodent holes in the ground and I suspect most honey bee colonies will be established in rot holes in trees, reducing the direct pressure on bumble bee nest sites. (I have read that honey bees can be effective competition for other rot hole users, such as woodpeckers.)

As a foot note, there is evidence that native bees will displace honey bees, at least while foraging on sunflower crops. It seems the presence of native bees makes honey bees move on more quickly, which mixes the pollen between rows more effectively, resulting in better pollination.

Matthew
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The Xerces Society for Invertebrate Conservation
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Matthew Shepherd
Director, Pollinator Conservation Program
4828 SE Hawthorne Boulevard, Portland, OR 97215, USA
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