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Harbo Assay, Varroa Sensitive Hygiene Testing

Posted October 17, 2024

From Wild Hives

More than likely you could simply Google “Harbo Assay” and get all you ever wanted to read on this topic, but my hope is that the organized extracts below might take you from “knowing” about this topic to actually getting involved. Yes, you as a backyard beekeeper can participate. Commercial breeders located far away from you, no matter how great they say their queens are, will never be the long-term solution. A local solution, even if it seems to take years, will be what helps the bees come to a natural balance with this evolutionarily new pest and its vectored pathogens. This will take all of us in our own locations and with our own local bees to make a true impact. This is a great topic to bring up to your bee club, maybe organize a club run VSH testing apiary, or simply handout directions that club members can follow in their own backyard such as these from Harbo Bees or an alternate method from Westerham Beekeeping, UK.

Starting is only one step away.

History of Harbo Assay

Varroa Sensitive Hygiene (VSH) is neither a line nor a breed of bee. Rather, it is identified as a “trait.” It’s suggested that the trait involves a small group of genes, perhaps only two. While the VSH trait was first identified in honeybees in the U.S., current research supports the theory that the VSH alleles (alternate forms of genes) may occur in bee populations worldwide. Moreover, the VSH alleles can be bred into any honeybee population to produce VSH-based resistance

In 1992, as varroa mites were becoming widespread in the United States, Dr. John Harbo at the USDA’s Honey Bee Laboratory in Baton Rouge was assigned the task of breeding bees for resistance to varroa. In 1995 he and Dr. Roger Hoopingarner at Michigan State University discovered the VSH trait. During the next ten years Dr. Harbo led USDA research to understand how this trait works and to evaluate its effectiveness in field colonies. The VSH trait was released to the beekeeping industry in 2001.

A valuable feature of VSH is that bees will express a high level of mite resistance when a colony contains as little as 50% of the alleles for VSH. A simple way to produce such a colony is to raise daughter queens from a VSH breeder and allow the daughters to naturally mate. This is good news for queen producers. They can rear VSH queens, mate them to any drones, and those queens will produce colonies that require no chemical control for varroa. Another benefit is that beekeepers can have mite resistant colonies without destroying their existing bee populations –populations which may be well adapted to certain locales or have desirable beekeeping qualities.

VSH Details

VSH is not the same as freeze-kill or pin-kill hygiene and cannot be measured with those methods.
Bees with the VSH trait express mite resistance by disrupting mite reproduction in worker brood that is aged 4-6 days post-capping. Mites on adult bees and mites in younger and older stages of worker brood are not affected.
Very useful in measuring VSH is the fact that VSH bees do not disturb a varroa-infested cell if the mite is not producing progeny. In a typical varroa-susceptible colony non-reproducing mites commonly occupy about 5-15 percent of the varroa infested cells. When one finds a higher proportion of infested cells with non-reproducing mites, that colony has some VSH alleles. If the only varroa infested cells in a sample contain non-reproducing mites, the bees are 100% VSH.
The VSH trait is expressed only by adult worker bees that are at least one week old. Therefore, when a VSH queen is introduced to a varroa-susceptible colony of bees, the mite population will continue to grow for the next 35 days.
It takes about 20 days for all of the mites to pass through this three-day vulnerable period in their reproduction. Therefore, it will take at least 55 days following the introduction of a VSH queen for her progeny to fully control a mite population.
VSH does not result in poor brood pattern unless one introduces a VSH queen to a colony with a high rate of varroa infestation. In that case, one may notice 3 weeks of spotty brood that begins about 7 weeks after a VSH queen is introduced. After the 10^thweek, VSH bees will have reduced the mite population and brood removal will move into maintenance mode with minimal removal. If a VSH queen produces a poor brood pattern in her first month, the issue is not caused by VSH.
VSH is not a pedigreed stock. The VSH trait represents only a tiny fraction of a bee’s genome, so bees with VSH can be as diverse as any existing bee population and the trait can be added to any stock.

Heritability and Genes

Genomic and transcriptome (messenger RNA molecules) studies have shown that genes associated with visual and olfactory perception, development and functioning of the nervous system (learning and memory formation) play the main role in Varroa sensitive hygiene behavior but are these genes heritable. Heritability (h2) has been measured on many characteristics of bees. Heritability is the proportion of the observed variance (among a group of bee colonies) for which differences in heredity are responsible. If a characteristic has an h2 close to 1, then the characteristic can be changed rapidly with selective breeding. If h2 = 0, selective breeding will fail. As a general rule, selective breeding can proceed if h2 is >0.25.

Four characteristics impacting the growth of mite populations had heritability (h2 ) of >0.25. These were mite reproduction (varying over time), proportion of mites in brood (h2 = 1.24), hygienic behavior (h2 = 0.65), and the duration of the capped period. Therefore, one should be able to intensify the expression of those characteristics through selective breeding.

Drone Health and Natural Mating

The benefit of natural mating is its role in healthy drone selection. It’s estimated that fewer than 1% of the drones successfully mate with a queen, and those that do are probably those which (1) are not diseased, (2) are not parasitized by varroa during their development, (3) have strong and well-functioning bodies, (4) come from successful colonies, and probably most importantly (5) are competing in all of those challenges with only 1 set of chromosomes. When successful in mating, a drone transfers identical copies of his winning gamete (a reproductive cell having a single set of unpaired chromosomes) to a queen bee. Thus, natural mating maintains the quality of our bee populations and may also support varroa resistance as long as the drone source colonies are not treated to control mites.

What’s Next

If all beekeepers —novices included—are able to measure VSH, both bees and beekeepers will benefit. By measuring varroa resistance, one can know whether or not a queen is producing varroa resistant workers long before there is a varroa crisis. Now this all may seem limited to the world of scientists and laboratory experiments, but they really aren’t doing anything that you couldn’t do.

So, what should a beekeeper do?

At least review the two documents linked at the very beginning of the blog.
During inspections keep a close eye on your colonies and log your findings.
Test and identify colonies that have steady/stabilized mite counts throughout the year.
Split only from the colonies that show resistance and are growing and productive.
Don’t hesitate to cull poor colonies.
Resist treating and feeding colonies which simply dilutes your understanding of the true quality of the colony.
Only include local swarms into your apiary.

Reference Materials

Robbing Stress

Mold, should I be concerned?

Spreading Varroa Resistant Traits

STOP PRETENDING.

START BEE-TENDING.

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