Voracious honey bees threaten the food supply of native pollinators

(Press-News.org) The majority of the earth’s plant species, including our crop plants, rely on the services of animal pollinators in order to reproduce. Honey bees and other pollinating insects annually contribute billions of dollars to the U.S. economy, and are responsible for nearly a third of the food that ends up on our tables. Our modern agricultural industry is so reliant on honey bees that humans have introduced them worldwide, and in many cases, they have escaped human management and risen to prominence in natural ecosystems as non-native, feral populations. And, like any other non-native organism, feral honey bees may perturb native ecosystems when they become sufficiently abundant.

Feral honey bees have greatly proliferated in Southern California, along with the rest of the Southwestern United States. A new study by University of California San Diego biologists Dillon Travis, Joshua Kohn, David Holway and Keng-Lou James Hung is calling attention to the threat posed by non-native honey bees to the diverse native pollinators of the San Diego and broader Southern California region. These researchers previously estimated that honey bees comprise up to 90 percent of all bees visiting flowers of multiple native plant species in the region.

The new study, published in the journal Insect Conservation and Diversity, a Royal Entomological Society journal, estimates the impact honey bees may be having on populations of native bees in this important global hotspot of native pollinator biodiversity. The researchers found that honey bees remove about 80 percent of pollen during the first day that a flower opens. This finding is important because all bees in the region — and the vast majority of bee species worldwide — use pollen to raise their offspring. The amount of pollen removed daily by honey bees from just one hectare (2.5 acres) of native vegetation is enough to provision thousands of native bees per day during the peak bloom of native shrubs, the researchers found.

Because honey bees are larger than most native bee species in Southern California, the new study calculated that honey bees now comprise 98% of all bee biomass in this ecosystem. If the pollen and nectar used to create honey bee biomass were instead converted to native bees, populations of native bees would be expected to be roughly 50 times larger than they are currently. 

“Although honey bees are rightly considered an indispensable asset to humans, they can also pose a serious ecological threat to natural ecosystems where they are not native,” said Hung, who earned his PhD from UC San Diego and is now an assistant professor at the University of Oklahoma. “The plight of the honey bee is an issue of animal husbandry and livestock management, whereas when it comes to conservation issues here in North America, honey bees are likelier to be part of the problem, not a solution or a target for conservation.”

In another cause for concern, a study published in 2023 by Travis and Kohn showed that plants pollinated by honey bees produce lower-quality offspring compared with offspring from native pollinators.

While bees in general are being threatened by habitat loss, climate change and chemical pollution, the researchers say that such a level of honey bee pollen exploitation is not well documented, and could well pose an additional and important threat to native bee populations in places where honey bees have become abundant. Even as the number of managed honey bee colonies is increasing worldwide due to the commercial beekeeping industry, many species of native pollinators are declining. “Public concern for honey bees often fails to consider their potential negative effects on native pollinators,” the authors note in their report.

“Honey bees are incredibly effective at extracting resources like pollen and nectar,” said Travis, who earned his PhD at UC San Diego in 2023. “Unlike the vast majority of native bee species in the region, honey bees can communicate to their nestmates the locations of rewarding plants and quickly remove most of the pollen, often early in the morning before native bees begin searching for food.”

The new study used pollen-removal experiments to estimate the amount of pollen extracted by honey bees using three common native plants (black sage, white sage and distant phacelia — also known as distant scorpion weed) as targeted pollen sources. The researchers found that just two visits by honey bees removed more than 60 percent of the available pollen from flowers of all three species. Such prodigious rates of pollen exploitation leave scant pollen for the more than 700 species of native bees in the region.

“The most surprising finding was the extraordinarily small number of individual native bees observed that were as large or larger than honey bees,” said Professor Emeritus Kohn of the Department of Ecology, Behavior and Evolution.  “Particularly rare were bumble bees, which made up only 0.1% of all bees we observed.”

With the new study shedding light on the steep honey bee/native bee imbalance in San Diego and Southern California, the researchers say resource consumption by honey bees should receive greater attention as a potential factor in pollinator declines. One step to address the situation could be increased guidance on whether and where large-scale contract beekeepers are allowed to keep their hives on public lands after crops have bloomed, to limit opportunities for honey bees to outcompete native species for scarce resources provided by native vegetation.

“In areas with threatened bee species, natural preserve managers may also want to consider systematic removals or relocations of non-native honey bee colonies to provide wild bees a fighting chance,” said Hung.

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