California scientists discovered hybrid honeybees that may naturally repel one of the deadliest parasites threatening pollinators.
Southern California is home to an unusual type of honeybee that may help researchers better understand how to protect struggling pollinators. Across the United States, commercial honeybee colonies are collapsing under pressure from deadly parasites, but this locally adapted hybrid bee population appears far better at surviving the threat.
Beekeepers in the U.S. reported losing up to 62% of their managed honeybee colonies in 2025, a trend that could have major consequences for agriculture and food production. Several factors are contributing to the losses, including pesticides, climate stress, shrinking habitats, and parasites. Among the most dangerous is the Varroa mite.
How Varroa Mites Harm Honeybees
Varroa mites attack honeybees by feeding on their fat body tissue, which plays a critical role in immune defense, energy storage, and overall health. If you were comparing it to human biology, the organ functions somewhat like a combination of the liver, pancreas, and immune system. Bees weakened by the mites often lose body weight, become more vulnerable to disease, and die sooner.
The mites also spread harmful viruses, including Deformed Wing Virus and Acute Bee Paralysis Virus. They pass these infections directly into a bee’s bloodstream. To control infestations, beekeepers often depend on chemical treatments, though those methods can become less effective over time.
A new UC Riverside study published in Scientific Reports found that a naturally adapted population of Californian honeybees can consistently keep mite levels lower without eliminating them completely.
“We kept hearing anecdotally that these Californian honeybees were surviving with way fewer treatments. I wanted to test them rigorously and understand the driving force behind what the beekeepers were seeing,” said Genesis Chong-Echavez, a UCR graduate student and lead author of the study.
Study Tracks 236 Honeybee Colonies
Working with researchers from UCR’s Center for Integrative Bee Research (CIBER), Chong-Echavez monitored 236 honeybee colonies between 2019 and 2022.
The hybrid Californian bees were not fully resistant to the mites. However, colonies led by locally raised hybrid queens averaged about 68% fewer mites than colonies headed by commercial honeybee queens. They were also more than five times less likely to reach infestation levels that required chemical treatment.
The bees involved in the research are not part of a commercial strain. Instead, they belong to a genetically diverse population that has become established in Southern California, often from feral colonies living in trees. Previous studies found that these bees trace their ancestry to at least four honeybee lineages, including African, Eastern European, Middle Eastern, and Western European bees.
Honeybee Larvae Show Early Defense Against Parasites
Researchers also carried out laboratory experiments on developing honeybee larvae to better understand why the bees appeared more resistant. Varroa mites reproduce by entering brood cells, so the scientists tested whether the parasites were equally attracted to larvae from commercial colonies and Californian hybrid colonies.
They were not.
The mites were less attracted to larvae from the Californian hybrid bees, especially when the larvae were seven days old, which is normally the stage when mites are most likely to invade. The results suggest the bees’ defenses may begin very early in development, before adult worker bee behavior becomes a factor.
“What surprised me most was the differences showed up even at the larval stage,” Chong-Echavez said. “This suggests the resistance mechanism may go deeper than some kind of behavior and may be genetically built into the bees themselves.”
Hope for Future Honeybee Health
The findings may have implications far beyond Southern California. Honeybees pollinate crops worth billions of dollars, yet they continue to face mounting environmental pressures worldwide. The research suggests that naturally occurring biological traits could play an important role in improving honeybee survival.
Boris Baer, a UCR entomology professor and co-author of the study, said the project also demonstrates the importance of listening to beekeepers who observe these colonies firsthand.
“This question did not start in the lab. It started in conversations with beekeepers,” Baer said. “They were not just observers; they helped shape the questions behind this research.”
The researchers emphasized that the Californian hybrid bees are not completely free of mites, and they are not recommending that beekeepers abandon current treatment practices. Instead, the team hopes to identify the traits that help these bees maintain lower mite levels and determine whether those traits could be used in future breeding programs or reduce reliance on chemical controls.
The next phase of the research will focus on the genetic, behavioral, and chemical factors that may make the larvae less appealing to mites.
“At a time when pollinators are facing global decline, this work offers a hopeful message: solutions may already be emerging in the field, and we just need to understand them,” Chong-Echavez said.
Reference: “Varroa mite resistance in a hybrid honey bee (Apis mellifera) population in Southern California” by Genesis Chong-Echavez, and Boris Baer, 27 March 2026, Scientific Reports.
DOI: 10.1038/s41598-026-45759-9
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