Selective breeding protects honeybees from Varroa mites – The result of a new study at the University of Exeter has shown that a new breed of honeybees could be the solution for the global fight against varroa mites, the public enemy number one for honeybees.
Background – Varroa Mites
The tiny, reddish brown Varroa mites that originated in Asia quickly spread around the world. European honeybees (Apis Mellifera) have not evolved alongside the Asian bees and therefore lack effective resistance against the mites. The mites mainly feed on the fat of developing brood and reproduce. As a result, they cause malformation and weakening of the honeybees. Furthermore they transmit a number of other viruses. Varroa mites are currently the biggest threat to honeybees.
Managed bees cannot develop resistance like they might in the wild. However, they occasionally respond by killing the varroa mite infested larvae. This is known as Varroa-sensitive hygiene (VSH). For the last 20 years, the USDA Bee Breeding Lab has bred VSH honeybees. These so called ¨Pol-line bees¨ are resistant to varroa mites. In light of the breeding program the USDA managed to successfully breed honeybees that automatically protect themselves from infestation. Furthermore, they can maintain large colony sizes and sufficient honey production.
Dr Michael Simone-Finstrom a molecular biologist from the USDA Agricultural Research Service, said,
“The great thing about this particular trait is that we’ve learned honey bees of all types express it at some level, so we know that with the right tools, it can be promoted and selected for in everyone’s bees.”
The research by the universities of Louisiana and Exeter together with the USDA (Agricultural Research Service of the US Department of Agriculture) trialled these Pol-line bees together with ´normal´ honeybees. The trial was done in a large-scale pollination operation across three US states (Mississippi, California, and North Dakota).
They found ¨Pol-line¨ bees to be twice more likely to survive the winter compared to standard honeybees, with a survival rate of 60% compared to 25% of standard honeybees. The researchers also found that unless they used extensive chemical miticide treatments, the standard honeybees suffered high losses.
Dr Thomas O’Shea-Wheller, of the Environment and Sustainability Institute at Exeter’s Penryn Campus in Cornwall commented,
“The Varroa mite is the greatest threat to managed honey bee colonies globally. So far, new methods to control the mites — and the diseases that they carry — have had limited success, and the mites are becoming increasingly resistant to chemical treatments. It’s a ticking time-bomb.
By selectively breeding bees that identify and remove mites from their colonies, our study found a significant reduction in mite numbers, and crucially, a two-fold increase in colony survival. While this is the first large-scale trial, continued breeding and use of these bees has shown consistently promising results.
This kind of resistance provides a natural and sustainable solution to the threat posed by Varroa mites, and does not rely on chemicals or human intervention.”
The researchers also examined bee colonies for viruses linked to Varroa mites. They found that colonies with Varroa resistance had lower levels of three major viruses (DWV-A, DWV-B, and CBPV). Surprisingly, these viruses were not the main reason for colony losses. This was discovered when they examined the bees separately from levels of mite infestation.
Dr O’Shea-Wheller concluded,
“A lot of research is focussed on the viruses, with perhaps not enough focus on the mites themselves… The viruses are clearly important, but we need to take a step back and be rigorous in delivering the best practical outcomes, because if you control the mites, you automatically control for the viruses that they transmit.”
Thomas A. O’Shea-Wheller, Frank D. Rinkevich, Robert G. Danka, Michael Simone-Finstrom, Philip G. Tokarz, Kristen B. Healy. A derived honey bee stock confers resistance to Varroa destructor and associated viral transmission. Scientific Reports, 2022; 12 (1) DOI: 10.1038/s41598-022-08643-w
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University of Exeter. "Selective breeding sustainably protects honey bees from Varroa mite." ScienceDaily. ScienceDaily, 7 April 2022. <www.sciencedaily.com/releases/2022/04/220407101021.htm>.