A review of past studies on floral resource competition between managed honey bees (Apis mellifera, left) and wild bees, such as the common eastern bumble bee (Bombus impatiens, right) shows gaps in our knowledge about such interactions and calls for further research to better inform decisions on honey bee management and pollinator protection. (Photo credit, both images: David Cappaert, Bugwood.org)

By Andrew Porterfield

Just in time for World Bee Day on May 20, the United Nations Food and Agriculture Organization issued a call to protect bees, citing a need to control pesticide and fertilizer use to reduce threats to pollinator populations.

Andrew Porterfield

The FAO call left out one potential threat to bees native to the United States: Apis mellifera, the European honeybee.

Pollinators are essential to food production—almost all of the world’s most common crops depend on pollinators to reproduce. Of those pollinators, bees are the most important. About 22.6 percent of developing world agriculture and 14.7 percent of developed world farming is connected to bee behavior.

There are at least 25,000 species of bees worldwide, but the key bee for managed agriculture is A. mellifera, which is native to Europe but was introduced to the United States. While much attention has been paid to a variety of threats to A. mellifera populations, including chemical pesticides, habitat alteration, varroa mites, and beekeeping hygiene, relatively little attention has been paid to the effects the European import may have on the 4,000 species of wild American bees, which also play important roles in pollination. In fact, wild pollinators are often more efficient at their tasks than managed honeybees and can contribute the majority of pollination to up to 86 percent of crops that depend on pollinators. Thus, the impacts of honeybee management on wild bees can have a significant effect on agriculture.

Victoria Wojcik, Ph.D., research director Pollinator Partnership, and a team of entomologists at the San Francisco-based nonprofit, which conducts research and engages in educational and conservation efforts to protect populations of bees and other pollinators, reviewed published literature to identify studies that focused on the relationships between A. mellifera and native bees. The review, published this month in the journal Environmental Entomology, revealed a yawning gap of knowledge surrounding this relationship between honey bees and wild bees.

Working back through literature that appeared in searches conducted between April 2013 and August 2017, Wojcik and her team identified 19 papers that addressed A. mellifera versus wild bees. Of those papers, 14 were experiments in which density of honeybees or wild bees was manipulated, and five were observations of managed honeybees and wild insects. Seven studies looked at reproductive output in wild bees. Most of the studies were very short-term, and none were conducted in areas of current concerns over competition (western U.S. forests, southeast and northeast U.S. conservation areas, and open space in central California).

Even with this low volume of published research, the team did find common threads on bee behavior:

• Foraging patterns by bumble bees decreased with increases in A. mellifera foraging. Increasing honeybee colonies in natural areas appeared to “push” bumble bee foragers to flowers that weren’t used by A. mellifera.
• Bumble bees were not as likely to visit a foraging site a second time if they had encountered a competing honeybee.
• Only seven studies examined reproductive impacts of bee competition, but six of those found exploitative competition and a negative developmental or reproductive effect on native bees when confronted with honey bees. A 1991 study showed that honey bee presence reduced larvae number, size, and reduced pollen carrying among Exoneura asimillima, a social wild bee.

Interference competition, in which organisms fight or otherwise contact each other, did occur but not as frequently as another form of competition. Instead, exploitative competition, in which resources are depleted by one species at the expense of another, was observed as far more common.

The review, the researchers emphasize, shows that “maintaining honey bee colony health for pollination services while causing minimal impact to already threatened communities of native bees should be considered when putting honey bees in floral-rich areas.”

“Trends in rural landscape development … have dramatically changed honey bee forage ability within agricultural landscapes,” the researchers write. “Where beekeepers once had ample forage in managed agricultural lands, today many more seek access to alternative lands, such as natural areas, to make up deficits.”

And there they run directly into habits of wild bees. “Decisions in these cases have largely been based on opinion rather than on scientific evidence,” they write.

Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.