We are carrying out a multiyear bee-breeding project as part of an effort to reduce the need for mite treatments in honeybee colonies. This short post is specifically directed towards our fellow beekeepers. We hope to 1) give you a summary of the study we’re carrying out and 2) tell you about the precautions we’re taking to protect our fellow beekeepers. We hope that regardless of your own beekeeping practices and experience, we can all agree that the best possible thing for the long-term survival and thriving of the honeybee is tolerance to mites without the need for chemical treatments. Even the most staunch advocate for treatment would prefer to have a bee that didn’t need such intervention.
No one wants to treat honeybees against Varroa destructor, but commercial, side-line, and hobbyist beekeepers spend considerable time and money to prevent high mite levels through chemical and behavioral means. The solution is a European honeybee that does not need treatment to survive with mites but will still produce a viable amount of daughter colonies and honey. Creating such a bee is not the problem—it has been done independently in at least three locations outside of North America. The two impediments to wide-scale implementation are lack of knowledge and/or concerns about financial feasibility. This study plans to 1) replicate and document the method to breed mite-tolerant bees in North America and 2) develop and share resources for beekeepers of all scales to adopt this system.
Beekeepers find themselves on a “treatment treadmill” that locks them into repeated applications of mildly to fairly toxic miticides and the use of behavioral methods to increase their winter survival rates. V. destructor quickly spread from its first occurrence in the US in 1987 to every state, and beekeepers scrambled to find a solution to their high rate of winter losses. The answer came in the form of chemical treatments, but the well-worn observation that it is “hard to kill a bug on another bug” is proving prescient. The first chemicals interfered with mite (and to a lesser extent bee) nerve function but left residues in wax and honey. Later, organic acids and other less-toxic compounds were introduced. Additionally, beekeepers began to employ behavioral methods to control mites (e.g., culling brood comb, brood breaks, small-cell comb, and screened bottom boards). Regardless of treatment method, however, the symptoms are addressed, not the root cause. Beekeepers must continue to use chemicals and/or behavioral methods to treat their colonies because the bees are not allowed to develop tolerance, and prophylactic treatment masks any naturally occurring resistance.
In Asia, Apis cerena has developed behavioral tolerance to V. destructor (which originated in this region) and similar adaptations have occurred in isolated Apis mellifera populations. When Varroa emerged over a century ago in Asia, the local beekeepers had no treatments available and the local bees went through a genetic bottleneck, allowing only bees with mite-tolerant behavior to survive. More recently, researchers in Wales, Sweden, and Germany have been recreating this process through selective breeding of A. mellifera. Others have noticed feral honeybees that have developed mite tolerance in France and Africa. In all of these instances, bees have been artificially or naturally selected for mite tolerance by letting the nontolerant colonies die.
The process is counterintuitive: stop treating for mites to breed mite-tolerant bees. Without treatment, most colonies succumb to mite loads in a season or two, but a few will survive. Queens are raised from the strongest surviving colonies. Because queens mate with fifteen to twenty drones, genetic segregation can be challenging. By using many colonies and isolating them, the local gene pool will be flooded by the survivors’ genes. Previous studies suggest an initial heavy die off and gradual improvement of winter survival until a new, stable population of mite-tolerant bees has been established. This study will demonstrate whether or not this breeding strategy is successful in a North American context. Importantly, the project will use simple beekeeping techniques available to every beekeeper to carry out the task. Finally, a series of resources will be produced to assist other beekeepers in converting their treated colonies into mite-tolerant ones.
The first scientific case study of this method was carried out on the island of Gotlund in the Baltic Sea (Fries et al. 2006). A hundred and fifty colonies with low-level Varroa infestations were established on this island. The colonies were left untreated and allowed to swarm. Initial winter mortality was high (76 and 57 percent in years three and four), but quickly stabilized at a low level (13 and 19 percent in years five and six). Mite infestations fell from 40 mites per 100 bees to about half of that during this time. The researchers found a decreased winter mortality rate, increased swarming rate, and constant but low level of mite infestation (Fries et al. 2006: 568).
The West Wales Breeding Project was established in 2011 and continues to move regional beekeepers towards colonies with greater survivorship. After suffering unusually high losses, beekeepers began to repopulate their apiaries with walk-away splits rather than buying in colonies or queens to replace dead outs (Williams 2013: 20–22; description here). This effort is ongoing and producing positive results with anecdotal suggestions of increased grooming behavior (Dylan Elen, personal communication 2019).
In Tunisia, resistant colonies were identified and their queens helped impart some benefit to European hives when exported (Ritter 1990). Anecdotally it has been noted that African beekeepers who did not have araricides available to them for logistical or financial reasons inadvertently selected for mite resistance and tolerance in their surviving colonies after mites reached the continent.
In the US, one study (Kefuss et al. 2016) has carried out a commercial-scale breeding study similar to the one proposed here with positive results. Seely (2007) has noted feral colonies surviving in the Arnot Forest, and Villa and colleagues (2008) report self-selected survivorship in feral colonies in Louisiana. Our study seeks to recreate these, and other international projects focused on a simple selection process available to every scale of beekeeper as well as to create materials to help others implement and test this strategy.
Concern for Our Fellow Beekeepers
Although the project’s method may sound radical to those who treat prophylactically and depend on their bees for their livelihood, it is based in successful projects from Sweden, Wales, and Africa. The first few years are admittedly the most precarious part, as the initial die-off may be severe, but this is simply a reflection of the weakness in our honeybee population that is masked by the availability of chemical treatments. Using natural and artificial selection on our bees, we are applying a well-known process from other animal husbandries.
What about “Mite Bombs”?
It is a commonly held belief that an untreated hive that collapses due to mite infestation will carry high mite loads to nearby colonies. Recent work has suggested that this is not a scientifically observed phenomenon (see Conrad 2018 generally and Peck and Seeley 2019 suggesting this largely happens because of robbing). Even still, we want to avoid harming our neighbors if this belief is later borne out by evidence. As such, we will be conducting this study in an isolated location. We are in contact with our only identified neighbor with bees in a 2-mile radius and will be working with him to monitor his mite loads in the fall to see whether or not he sees a mite spike.
Throughout the course of the project, we will be measuring the mite loads and other data from the colonies. We will also monitor for other signs of disease and distress. When needed, samples will be sent to the University of Maryland and/or USDA labs. By keeping a close eye on our hives, we will be better bee “neighbors.” If we have the resources available, we will also share queens (and potentially more) with our neighbors to help keep our genetic lines as isolated as possible.
The whole goal of this project is to improve bees for our fellow beekeepers, both through the breeding of mite-tolerant bees and the recording and explication of the method we used, if successful. While we understand that those of you who treat “every hive, every year, no exceptions” may not jump to try out our methods in their own apiaries, we hope that they will recognize that we’re trying to help the bees select their best genes for creating colonies that can survive without mite treatment, as has been done in other parts of the mite-infested world.
We’d welcome your feedback in the comments below or by email.