The bees were selectively bred to strengthen a trait in which they expell infested larvae from the hive, killing larvae and mite
Many beekeepers face a challenging spring as they cope with massive honeybee losses.
Those range from 40 percent across the Prairies to 60 percent in Quebec. Some honey producers have lost as much as 90 percent of their bees due in large part to the parasitic mite varroa destructor mite.
In addition, some farmers are facing problems securing replacement stock due to supply lines disruptions.
Now, a new breed of honeybee has shown major advances in the fight against the varroa mite.
In a study by researchers at the University of Exeter in the United Kingdom, the University of Louisiana and the U.S. Department of Agriculture’s Agricultural Research Service “Pol-line” bees have been bred for resistance to the mite in a rigorous breeding program.
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“In the case of Pol-line bees, it had been observed that some colonies naturally displayed the behaviour of uncapping and removing infested brood,” said Thomas O’Shea-Wheller with the University of Exeter’s Environment and Sustainability Institute.
“(It is) termed varroa sensitive hygiene (VSH). But the expression of this trait was relatively low, thus a selection program was initiated.”
Varroa mites feed on bees’ fat bodies and reproduce in the cells of bee larvae. They originated in Asia but since honeybees in North America are of European origin, they lack effective resistance.
In addition, managed bees cannot develop resistance as they would in wild settings. However, it was discovered in 2005 that managed honeybees responded to the mite by expelling infested larvae from the hive, killing both the larvae and the mite at the same time.
Selectively breeding to strengthen this trait could lead to colonies programmed to automatically protect themselves from infestation while maintaining healthy population sizes, pollination services, and honey production.
“The great thing about this particular trait is that we’ve learned honeybees 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,” said Michael Simone-Finstrom, research molecular biologist with the ARS.
The Pol-line bred bees were tested in Mississippi, North Dakota and California, where beekeepers move thousands of colonies annually to provide pollination services. The trials, which began in March 2017 and concluded in March 2018, were conducted alongside a standard variety of bees in a large-scale pollination operation. The mite-resistant bees — those that identify and remove mites from their colonies — showed they were more than twice as likely to survive the winter at a ratio of 60 percent survival compared to 26 percent survival in standard honeybees.
“While this is the first large-scale trial, continued breeding and use of these bees has shown consistently promising results,” said O’Shea-Wheller. “New methods to control the mites and the diseases they carry have had limited success and the mites are becoming increasingly resistant to chemical treatments. It’s a ticking time-bomb. This kind of resistance provides a natural and sustainable solution and does not rely on chemicals or human intervention.”
He said the locations for the trials were chosen partly because they comprised a range of climates and environments. These are key areas in the migratory pollination route with the Dakotas being important for honey production, and California for almond pollination. They underscored the applicability of the chosen sites and the logistical support needed to carry out the study.
O’Shea-Wheller said that commercial bee farmers in the U.K. do move colonies to provide pollination services, but those operations comprise less than one percent of all colonies and are usually related to producing higher-value honey. British agricultural lands generally consist of patchworks of smaller fields interspersed with hedgerows and natural areas so, in many cases, additional pollination services are not required.
While the selectively bred bees in the Pol-line have been available and sold to a few bee breeders, the genetic development of varroa-resistant bees is still a work in progress.
“It remains challenging to get the correct genetics in mass-produced bees because of the need to control the mating of free-flying queens and drones,” said O’Shea-Wheller. “The latest attempt at breeding using high-quality Pol-line genetics and distributing properly mated queens on a commercial scale is the Hilo Bee project. This public-private partnership continues to field test bees in commercial U.S. beekeeping operations and has begun to distribute queens to early adopters.”
The Hilo Bee Project is an affiliation between the USDA, the Hawaii Island Honey Company, and the non-profit Project Apis m organization, which provides research funding for science-based solutions to honeybee challenges. Project Apis m’s name comes from Apis mellifera, the scientific name for the honeybee.
“One interesting aspect (in our research) is that we are not yet sure whether the varroa-resistant bees are responding to varroa per se or more generally to the damaged or diseased brood,” said O’Shea-Wheller. “European honeybees usually express the behaviour to some level, thus it is quite likely to have additional benefits even in the absence of varroa. The recent advance has been the consistent selection for VSH to amplify the trait to a point that significantly disrupts Varroa reproduction.”
He said their commercial collaborators have been happy with Pol-line bees and have started to incorporate them into their own operations. In addition, and of great value, is that the resistant bees have also shown lower levels of other diseases such as deformed wing virus and chronic bee paralysis virus.
While chemical agents used to kill mites and other varroa-focused treatments provide a solution, they are not necessarily sustainable in the long run. Bee breeding takes time and money and can only offer solutions several years down the line.
He said that a lot of research is focused on the viruses with perhaps not enough focus on the mites themselves.
“The key take-away is that it is important to support multi-year breeding efforts with clear goals and long-term delivery as these will bear fruit in the future. The viruses are clearly important, but we need to take a step back and be rigorous in delivering the best practical outcomes. If you control the mites, you automatically control for the viruses they transmit.”
The study was published in the journal Scientific Reports.
