A hybrid honeybee population in Southern California was studied over a 4 year period, and was found to have lower mite infestation rates than colonies with queens from commercial stock. Varroa mites feed on the fat body tissue of honeybees, which weakens their immune system and ultimately shortens their lives. The California hybrid honeybees were not completely immune, they were found to have about 68% fewer Varroa mites on average. The differences showed even at the larval stage, suggesting the resistance must be more than learned behavior, but genetically built into the bees. One explanation for the difference between the hybrid honeybees and the managed honeybees they were compared to, is that continued chemical treatments in managed honeybee populations reduces natural selection for host resistance.
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