Small numbers of mites can infest many honey bees, study suggests – ScienceDaily

Varroa damage is an ectoparasitic mite that can cause European honey bee colonies to collapse by spreading deformed wing virus as they feed. Study published in PLOS pathogens by Zachary Lamas and colleagues at USDA-ARS and the University of Maryland suggest that a relatively small number of mites can contribute to a large number of infected bees.

Arthropod disease vectors transmit pathogens while feeding on susceptible hosts. However, little is known about how the dynamics of Varroa virus feeding propagate in adult honey bees. In order to better understand Varroa mite parasitism on honeybees, the researchers conducted a series of experiments. First, they used fluorescent microspheres to test whether Varroa mites fed on adult bees each time they entered a known feeding position. They next determined whether Varroa microspheres could be transferred to an adult bee by feeding Varroa by allowing Varroa to feed on pupal bees that had been injected with fluorescent microspheres. In the third experiment, the researchers observed mites switching from adult bee host to host. The researchers then observed how a single mite can spread pathogens by feeding on multiple bees and calculated the relative risk of Varroa parasitism to adult workers.

Mites with high levels of virus that mutated frequently contributed to the highest mortality rate among adult honey bees. Varroa are mixed feeders and switch hosts at a high rate. Moths switching hosts with the highest frequency were responsible for nearly three times as many hosts parasitized as their low-switching counterparts. Future studies are needed to better understand the mechanisms that drive moths to switch hosts.

According to the authors, “Our work shows that virus spread is driven by the efficient transfer of Varroa mites from one adult bee to another as they feed. Relatively few of the more active Varroa mites parasitize the majority of bees. The ability to parasitize and infect many adult bees offers the best explanation yet for the maintenance and spread of viruses from host to host among the long-lived worker bees that are common in these crowded and vulnerable colonies.”

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