Mites & Diseases – A Deadly Combination for Bees

Tuesday, May 10, 2016
By: Dick Rogers, Principal Scientist/Entomologist of Bee Health and Integrated Apiculture Research
Honey bees together on blue box

I don’t like scare tactics. If someone tries to motivate me on the basis of fear, I usually look the other way, because to me it suggests a lack of sound reasoning. In looking back on my blog post last year ("Expect a Hard Winter for Bees"), I tried to strike the right balance between providing useful information about bee parasites and communicating a genuine sense of concern. 

So with this follow-up blog, my goal remains the same: not to frighten, but to inform.

Beekeepers are coming off one of the worst Varroa mite infestations seen in recent years. Across the country, autumn mite populations in honey bee hives were frequently found at levels that were three-to-four times above what is known to be harmful to colonies. I expect that we will learn of many lost colonies when the Bee Informed Partnership/USDA releases their 2015 report later this month. 

No more colonies lost, colonies replaced…rinse, repeat.

And, as they always do, beekeepers will compensate for these losses by building up their colonies in time to meet the seasonal demands of crops needing bees for pollination purposes, as they did to meet the record number of colonies needed for almond pollination this past February. Unfortunately, we’ve seen this story all too often…colonies lost, colonies replaced…rinse, repeat. 

But we should be talking about Varroa right now and not later in the season, when it’s too late to do much about it. I was reminded of this after reading several new scientific publications that reaffirm the need to better manage the Varroa mite, not only because of the damage it inflicts directly on honey bees, but also because of  indirect and unwanted side-effects as a result of viruses that it transmits.

Varroa mite is more abundant than people appreciated.

The National Honey Bee Disease Survey (NHBDS) recently completed a six-year study that showed the Varroa mite is far more abundant than many people appreciated and is closely linked to several serious viral diseases.  This field survey supports the findings and provides further evidence of other field and lab studies which have linked Varroa to viruses. The survey found that the incidence of the rare chronic bee paralysis virus has skyrocketed since it was first detected in 2010, suggesting that the deadly alliance between parasite and pathogen is evolving. As one researcher explained, the mite acts like “a dirty hypodermic needle.” 

Varroa populations are typically low earlier in the season, but can jump dramatically late in the fall. The study found that migratory colonies tended to have fewer Varroa than stationary ones. Surveys show that 60% of hobby beekeepers do not treat for Varroa, which suggests that these colonies could act as sources of mites that could re-infest even treated colonies. The study concluded that Varroa and viruses go hand-in-hand and that intervention to control escalating infestations must be given top priority.

Varroa Management requires an Integrated Pest Management approach.

Successful Varroa management requires a good understanding of both honey bee and Varroa mite biology and life cycles, as well as an Integrated Pest Management (IPM) approach. Miticides that control Varroa are useful tools in the IPM toolbox, however, there are relatively few products currently available, plus mites can develop resistance to them when they are used too often. And there can be other concerns as well. For example, some scientists from Texas A&M and North Carolina State universities investigated two currently registered varroacides (Apistan and Checkmite+) and found that the reproductive health of queens reared in beeswax containing residues of these products could be compromised. However, strategies such as product use rotation, discovery of resistance breaking compounds and products with new modes of action, and using treatments only when needed based on careful monitoring of Varroa will help prolong the useful life of current products so they will be useful as IPM tools. 

With each new study we learn a little more about how to better manage Varroa. Last year, the Honey Bee Health Coalition published its Varroa Management Guide, which provides beekeepers with practical tips for monitoring and controlling this pest. And Bayer recently released a new Varroa publication that gives a comprehensive overview of the parasite’s biology and life cycle, as it relates to honey bee colony development and hive management. More research is adding to our understanding of how to manage Varroa. Companies like Bayer are committed to exploring new management techniques and treatments to add to the IPM toolbox.  

In the meantime, it’s critical that all beekeepers routinely monitor their hives during the season and take proactive steps to prevent harmful populations of Varroa from building up, or to reduce populations before they get out of control. Also, it is essential to understand the importance of proper hive management so that colonies do not become an unwitting source of infestation to other colonies. 

Communication is key. 

As of this writing, I’m happy to say that we have had more than 7,500 visitors to the Bayer’s North American Bee Care Center, where we’re helping to promote bee health awareness and contribute to solutions that will improve and maintain honey bee colony health so they can survive and be productive for the benefit of all.

It’s been nearly 30 years since the Varroa mite first arrived in the United States. After experiencing substantial losses, beekeepers soon gained access to several acaricides that have helped keep this pest in check. With more research and implementation of improved management practices, I believe the health of honey bee colonies can be improved so they can continue to provide the products and services we all appreciate and need.


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