Native bee species face extinction due to honey bee competition

European honey bees, celebrated for their industrious nature, may be pushing Australia’s native bees to the brink.

Research from Curtin University reveals how these introduced bees could be reducing the reproductive success of native cavity-nesting bees.

The findings hint at a deeper problem – one that could disrupt ecosystems and challenge biodiversity in ways that few expect.

Native bee reproductive struggles

Dr. Kit Prendergast, a researcher at Curtin’s School of Molecular and Life Sciences, didn’t just set up bee hotels to provide shelter. She turned them into research stations.

“Bee hotels are more than just a way to give bees a place to nest – they’re powerful research tools that let us measure how well native bees are surviving and reproducing in different environments,” Dr. Prendergast said.

For two spring-to-summer seasons, Dr. Prendergast and her team studied 1000 native bee nests in 14 urban bushland and garden sites.

The findings? In areas swarming with honey bees, native bees faced trouble. They produced fewer female offspring. Their offspring had higher mortality rates. And the males that survived were noticeably smaller.

Honey bees outcompete native bees

Honey bees collected pollen from many types of plants, including both local and non-native ones. Native bees, however, focused on a smaller number of specific plants.

This difference in foraging behavior made it harder for native bees to find enough food, as honey bees took pollen from a wider range of sources.

During the first year, honey bees collected pollen from 10.3 different species on average, while native bees gathered from just 4.3. In the second year, honey bees still maintained their wide range, collecting from 8.1 species. Native bees, however, only managed 2.8.

That’s a lot of overlap. Too much. In areas with high pollen overlap, native bees provisioned fewer cells for their offspring. Less food meant fewer babies. And fewer babies meant a population under pressure.

Urban gardens intensify pollen competition

Gardens may look like paradises for bees, but they can also be battlegrounds.

Honey bees, with their broad pollen preferences, took full advantage of exotic plants. They outcompeted native bees in residential gardens, where floral diversity was often lower and more fragmented.

Dr. Prendergast pointed out that in these urban gardens, the impact of honey bee densities became more pronounced. Parasitism rates among native bees increased, suggesting that honey bee competition might make them more vulnerable to parasites.

Honey bees affect native bee sex ratios

Honey bees didn’t just take pollen. They also affected the sex ratio of native bees. Female bees need more resources to develop, and when those resources get scarce, fewer females emerge.

“In some conditions, greater overlap in pollen use was associated with lower offspring numbers in native bees,” Dr. Prendergast noted.

And the offspring that did emerge? More males than females. This male-biased sex ratio could destabilize native bee populations over time, making it harder for them to recover.

Competition reduces reproduction

Pollen is essential for bees. They collect it, eat it, and use it to feed their young. The study found that honey bees gathered pollen from more plant types than native bees.

In the first year, honey bees collected pollen from 58 plant species, but native bees only collected from 41. The next year, honey bees still foraged from 41 species, while native bees dropped to 24.

This difference matters. When honey bees take pollen from many plants, they leave less for native bees.

With less pollen available, native bees have less food to feed their young. This leads to fewer offspring, smaller young, and fewer females, which can weaken native bee populations over time.

The urban vs. bushland divide

Urban gardens didn’t just have more honey bees. They had more floral competition and higher parasitism rates.

Native bees in bushland remnants fared slightly better, surrounded by more native flora and fewer honey bees. But even in these relatively protected areas, the pressure was still on.

The competition in gardens was particularly intense, with honey bees exploiting exotic plants that native bees couldn’t use as effectively. As a result, native bees had to work harder, forage longer, and ultimately, face greater risks from parasites.

Honey bees increase native bee mortality

Mortality rates for native bee offspring spiked in the first year of the study. Urban gardens with high honey bee densities saw the most significant increases. Fewer provisioned cells. More dead larvae. And for the males that did survive? They were smaller than usual.

“This shows that honey bees are not as benign as some might think – they can negatively impact local ecosystems and potentially contribute to declines in native bee populations,” Dr. Prendergast explained.

And those smaller males? They’re less likely to find mates, further straining the population.

Honey bees collect more pollen

Pollen analysis revealed a stark picture. Honey bees collected over twice as many pollen species as native bees. They didn’t just stick to native plants – they also targeted exotics, increasing the overlap and making it harder for native bees to find enough food.

The most common pollen species for honey bees included Eucalyptus marginata, Corymbia calophylla, and Melaleuca sp. For native bees, it was the same lineup.

This shared preference intensified the competition, with honey bees taking more than their share, leaving native bees with less.

Strategies to protect native bees

What can be done to protect native bees? Dr. Prendergast suggests increasing native plant diversity in urban areas. By planting more species that native bees prefer – and that honey bees don’t – we can reduce competition.

Managing honey bee populations in urban gardens could also help. Fewer managed hives, fewer feral colonies. But it’s not that simple. Honey bees are valuable pollinators, and their removal isn’t always practical.

Future research directions

Dr. Prendergast’s work is just the beginning. The study, funded by the City of Stirling, the Australian Wildlife Society, Hesperia, and the Forrest Research Foundation, points to a need for more targeted research.

Future studies could focus on long-term monitoring, examining how native bee populations fare over several years in areas with varying honey bee densities.

Understanding how pollen overlap affects native bee fitness in different habitats could also provide clues for more effective conservation strategies. Because in this hidden battle, the stakes are high.

For native bees, survival may depend on more than just flowers – it may depend on the flowers they can still call their own.

The study is published in the journal Frontiers in Bee Science.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–