Why do untreated varroa mite infestations often destroy honeybee colonies?

Untreated varroa mite infestations destroy western honeybee colonies primarily through a combination of direct physical harm and the transmission of debilitating diseases.12

The damage occurs in several ways:

• Direct Parasitism: Female mites attach to both adult bees and developing brood, feeding on them and leaving the bees in a weakened or underweight state.12
• Viral Transmission: Mites act as vectors for various harmful viruses, such as the deformed wing virus and black queen cell virus. These pathogens cause severe malformations in the bees' wings, bodies, and legs, often inflicting more damage than the mites' feeding alone.12
• Immune Suppression: The stress caused by these parasites, potentially exacerbated by exposure to pesticides like neonicotinoids, can suppress the bees' immune systems, making the colony increasingly vulnerable to further infection and collapse.12

Because western honeybees lack the natural defenses found in the mite's native hosts, unmanaged colonies typically perish within two to three years, while severe infestations can wipe out a colony in only a few months.12