A hybrid population of honeybees in Southern California demonstrates natural resistance to Varroa mites, a major threat to bee colonies. Researchers at UC Riverside found these bees carry 68% fewer mites and require far less chemical treatment. The discovery, detailed in a new study, suggests early-life defenses in larvae may hold the key.
Southern California hosts a unique hybrid honeybee population that thrives despite heavy losses elsewhere. U.S. beekeepers reported losing up to 62% of their managed colonies in 2025, largely due to Varroa mites, pesticides, climate stress, and habitat loss. These mites feed on bees' fat body tissue, weakening immunity and spreading viruses like Deformed Wing Virus. Beekeepers often turn to chemical treatments, which can lose effectiveness over time. Genesis Chong-Echavez, a UC Riverside graduate student and lead author of a study published in Scientific Reports, tracked 236 colonies from 2019 to 2022. Colonies with locally raised hybrid queens averaged 68% fewer mites than those with commercial queens and were more than five times less likely to need intervention. These bees blend lineages from African, Eastern European, Middle Eastern, and Western European stocks, often tracing to feral colonies. Lab tests revealed Varroa mites show less attraction to their larvae, particularly at seven days old when most vulnerable. Chong-Echavez noted, 'What surprised me most was the differences showed up even at the larval stage. This suggests the resistance mechanism may go deeper than some kind of behavior and may be genetically built into the bees themselves.' Co-author Boris Baer, a UCR entomology professor, credited beekeepers for sparking the research: 'This question did not start in the lab. It started in conversations with beekeepers.' Researchers caution these bees are not mite-free and stress continued management. Future work aims to pinpoint genetic and behavioral traits for broader breeding applications, offering hope amid global pollinator declines.