VSH-Based Resistance to Varroa


Varroa Sensitive Hygiene, identified and researched at the USDA Bee Lab in Baton Rouge, is neither a line nor a breed of bee.  Rather, it is identified as a “trait.” Backcrossing suggests 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 honey bee 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.

 Six Important Points

1. Varroa Sensitive Hygiene (VSH) is not the same as freeze-kill or pin-kill hygiene and cannot be measured with those methods.

2. With VSH resistance, varroa mites are controlled by adult worker bees beginning when worker bees are about 10 days old. When a VSH queen is introduced to a colony, the mite population will continue to grow until her worker bees begin to take control about day 35.

3. Worker bees with VSH trait control varroa by disrupting mite reproduction (uncapping mite-infested cells and pulling out pupal bees from worker brood) when brood is 4-6 days postcapping. That is their only method and their only window of control. 

4. It takes about 20 days for all or most of the mites in a colony to pass through this 3-day vulnerable period. Therefore, it is necessary to wait at least 55 days for the workers of a newly-introduced VSH queen to fully control the mite population. If the VSH queen has been introduced into a highly infested colony, there will appear to be a "spotty brood" pattern. This pattern may well be the result of VSH workers removing mite-infested bee pupae (disrupting mite reproduction). It does not necessarily mean the queen is laying poorly but that her workers are busy cleaning out mite-infested cells. 

5. The VSH trait does not seem to control mites in drone brood.

6. VSH is not a pedigreed stock. VSH represents only a tiny fraction of a bee's genome so VSH resistance can be added to any bee population.


A Valuable Feature

 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. Click here to download How to Measure VSH.