Three Posted Articles are Included in This Tab:

 

(1) Finding and Retaining Varroa-Resistant Bees

Our downloadable 23 page manual contains graphs, photos, and instructions to enable you to measure and score the level of VSH in a colony and how to record scores in a mother-father-daughter format.   Click here  

 

 

(2) Establishing Quality Standards and Expanding the Availability of Varrora Resistant Bees 

Our bee industry is now positioned to evaluate, produce and distribute high quality VSH. Therefore, it is important to set standards to ensure that we are producing queens with the highest score, a score of 4. Queen producers want to produce the best product, but queens are scored indirectly, and variation exists. I will explain why this variation exists and how to minimize the problem.

Improve the accuracy of VSH scoring

Producers of VSH queens will have a VSH score for their queens because they need to graft from a colony that has been scored for VSH. When a colony is scored, only worker bees are scored, but the score of those workers also applies to all the past and future queens that are produced from that colony. Therefore, if we graft from a colony that has been scored for VSH, the queens already have a score, whether they are larvae, newly emerged queens, or mated queens. In every case, the queen score should be disclosed.

A colony may express a high level of varroa resistance even if some of the workers do not express VSH. That’s good news, but this poses a problem for bee breeding. For example, if 30% of the workers in a high scoring colony are missing one or more of the VSH alleles, then 30% of the queens produced from that colony will also be missing one or more of the VSH alleles. 

This problem is minimized by grafting from a high scoring colony that has a queen inseminated with a single drone. In such a colony, all workers and queens produced in that colony share the same gamete from their father and are very very closely related. When workers are genetically very uniform and highly resistant to varroa, all of their sister queens will have the same genetic uniformity. If one is able to inseminate queens, single drone inseminations provide the simplest way to find VSH (step 1) and produce a breeder colony (step 2).

Below is a way to divide a score of 4 into confidence grades. Confidence refers to the likelihood that a queen has all of the VSH alleles and therefore has a true score of 4. 

4.4 is the highest grade. These queens are the daughters of a queen inseminated with a single drone. It doesn’t matter where you collect the drone. If a single drone inseminated colony scores a 4, the drone was a winner and you have a dependable VSH breeder.

4.3 is second best. These queens are the daughters of a queen mated to multiple drones. Those drones were kept in a way that ensured that they were produced from a high scoring queen (such as, drones caged or marked when newly emerged or stored in a confined area).

4.2 These queens are the daughters of a queen that was inseminated with semen from multiple drones that were collected from VSH colonies when at the entrance or when free inside. Flying drones drift, so errors are likely.

4.1 These queens are the daughters of a free mated queen.

 

 Use these four grades to justify value

Listed below is a guide to pricing virgin queens with different confidence grades. “Base” is the seller’s price for a virgin queen that is not scored or one which has a score below 4. Don’t sell a virgin with a score below 4.

 4.4 has 85% confidence* and valued at base + $15

 4.3 has 80% confidence* and valued at base + $15

 4.2 has 70% confidence* and valued at base + $10

 4.1 has 50% confidence* and valued at base + $5

* Confidence percentages are hypothetical; my best guesses. They represent the likelihood that a queen in that grade has all of the alleles for VSH and would therefore deserve a score of 4. For example, if I could know the true score of 100 queens at grade 4.4, 15 of them would not have all of the alleles for VSH. The good news is that if a queen does not deserve a score of 4, she is probably a 3, and that is still good.

If a score of 3 is good, why not sell queens with a score of 3? Because a group of queens with a score of 3 is also subject to a confidence error that would give some of them a true score of 2 or lower, and that is unacceptable. Note that with scores below 4, scoring errors include queens whose true score is higher as well as queens whose true score is lower.

Every person receiving a VSH queen can score her progeny for VSH to confirm the presence or absence of the trait. Although we examine brood, keep in mind that we are measuring the behavior of the adult bees. Brood does not express the VSH trait. In fact, it is equally valid to insert varroa infested brood from another colony and check it exactly 7 or 8 days later and get a score. Therefore, the scoring must be done when a queen has been laying in a colony for at least 7 weeks. This ensures that her workers are old enough to express varroa sensitive hygiene.

Unless a virgin queen mates with drones having VSH alleles, customers should not expect their colonies to have a score of 4. Expect a 2 but hope for a 3 and don’t complain about a 1. Complain about a zero. Customer education and participation greatly benefit efforts to establish varroa resistance nationwide.

Virgin or free-mated VSH queens: both are acceptable

Virgin queens and free-mated VSH queens address the same goal, that of inserting varroa resistance into a bee population. The difference is that virgin queens are mated to drones in your locale rather than from elsewhere.

The sale of VSH virgin queens allows more queen producers to be a part of the selection process for varroa resistance. If a beekeeper can produce queens and has a colony whose progeny score a 4, she or he can sell high scoring virgin queens. When selling virgins, the newly emerged queens need to be marked and examined for size and imperfections, but there’s no need to establish mating nucs and no worries about mating failures, missing a queen cell, or not being able to find a queen in a 3 frame nuc. In short, those who sell virgin queens are selling varroa resistance: the customer is producing the mated queens.

Both virgin and free mated VSH queens produce varroa resistant colonies that will add VSH to the bee population in your locale. They will produce VSH drones that carry all of the VSH alleles and VSH daughters (workers and queens) with 50% VSH (more if the drone population where they mate already has some VSH).

Avoid needless sampling

Unless one is choosing a breeder queen, VSH scores don’t need to be so precise. Save time by limiting your VSH counts to 100 cells; it’s seldom necessary to score all your colonies. If you find 5 cells with reproducing mites before reaching 100, stop counting, the score is zero. However, when choosing a breeder queen, the score needs to be more accurate and should be based on data from at least 200 cells. To choose a breeder colony, count 100 more cells from a few colonies that are potential breeders and then base your decision on samples that now consist of 200 cells per colony. It doesn’t matter if the counts are done days or months apart or all the same day.

--- John Harbo 2025

 

 

(3) A Path to Nationwide Resistance to Varroa

Probably the best thing we can do to establish nationwide varroa resistance is to stop basing our breeding decisions on the number of mites on adult bees. Counting mites on adults selects against varroa sensitive hygiene (VSH).

In his book Parasite Rex, Carl Zimmer describes the progression of many parasite-host relationships. The common theme is that new parasite invasions (as when varroa first entered the USA) are typically very damaging to the host in their earliest encounters. The host responds with high mortality rates. After that rough start, host and parasite gradually develop a mutually acceptable relationship.

Does this sound familiar? Our feral bees were almost non-existent for many years after the introduction of varroa. Feral colonies are back, and from my recent experience, many express VSH. Bees with the VSH trait disrupt mite reproduction in worker brood, while continuing to allow varroa to reproduce in drone brood. That may be a good strategy, because if the VSH trait destroyed all the mites, varroa would be challenged to develop resistance to VSH. Varroa’s history of developing resistance to miticides has shown that they are very capable of genetic adaptation.

VSH creates a situation where bees destroy varroa infested cells, thereby destroying the progeny. The mother mite survives, resulting in an increase in the number of mites residing on adult bees. In 1999, we called this proportion of mites in brood (PMIB), and proved that it was a highly heritable trait. That was before we understood varroa sensitive hygiene in 2005. We now realize that having a high proportion of the mite population on adult bees is caused by varroa sensitive hygiene. PMIB is a piece of the VSH puzzle. Therefore, breeding decisions based on having fewer mites on adult bees will often be selecting against VSH.

I used to think that there may be many mechanisms of varroa resistance. Now I’m not so sure. For example, we don’t know the fate of the mites that are forced out of the brood cells. Maybe the mites are weakened by their experience and become more vulnerable to removal by worker bees. Perhaps VSH, PMIB, and ankle biters are 3 components of a single mechanism of resistance to varroa. For those who like acronyms, we could call it DMR: destruction-migration-removal. That’s only an hypothesis. Prove it wrong.   --- John Harbo 2025