Varroa Mite Genetic Secret Revealed: How Parasites Maintain High Resistance
An international study led by University of Haifa researchers reveals that male Varroa destructor mites carry and express both copies of their mother's genome, slowing genetic loss and explaining their high pesticide resistance.
An international study led by the University of Haifa and the Shamir Research Institute, published in Nature Communications, has revealed that the Varroa destructor mite—a major threat to honeybees—reproduces in a manner previously unthought of for decades. While the scientific community traditionally held that male mites carry only a single copy of each chromosome, researchers discovered they carry and express both copies of their mother's genome, making each male a genetic clone of its mother.
"Varroa mites reproduce mainly between siblings, and new populations start from a small number of mites," said Dr. Nurit Eliash from the University of Haifa and the Shamir Research Institute, who led the research. "Therefore, we would expect it to rapidly lose its genetic diversity. The way genes pass from generation to generation, as we discovered in this study, slows down this process and may explain how the parasite maintains high adaptability and resistance to pesticides."
Methodology and Findings
The research team—including colleagues from the Okinawa Institute of Science and Technology in Japan, the University of Texas, the Australian National University, the University of Maryland, and the University of Arizona—tracked 30 mite families over three generations, examining a total of 223 mites. They sequenced genomes and analyzed RNA expression to observe how genes pass from mothers to sons and from males to daughters.
The results showed that in 97% of the genomic points tested, males carried both genetic versions found in the mother, and both versions were active. Mathematical models demonstrated that this reproductive mechanism significantly slows down the loss of genetic diversity compared to previous assumptions, helping the parasite adapt to new bee populations and chemical treatments.
"Until today, models examining how the Varroa mite responds to pesticides and breeding programs relied on the assumption that males carry only a single genetic copy," Dr. Eliash concluded. "It is now clear that this starting point needs to be updated. While the study does not offer a new treatment, it may help predict more accurately how resistance develops in the future."
