Over the past 15 or so years colonies have been identified which appear to tolerate mites better than others. Upon closer inspection the bees are found to be sensitive to varroa and exhibit hygienic traits towards the mites. This bee behavior has gone by several names such as suppressed mite reproduction (SMR) and varroa sensitive hygiene trait (VSH). The common term now used is the VSH trait.
The Varroa destructor mite is a major honey bee pest throughout most of the world. Varroa mites feed on the fat body of adult bees and developing bee larvae and reproduce under capped cells of pupating honey bee stages. Mites can compromise bees’ immune systems, transmit viruses, deform developing bees or kill them outright when multiple mites reproduce in a single brood cell.
While the application of miticides is the most common method of controlling varroa mite populations, it is only one part of the arsenal of techniques beekeepers should use in an integrated pest management (IPM) program. Other aspects of IPM to consider include monitoring mite levels within each hive to optimize timing of chemical treatments, following the dosage on the treatment label, rotating between different types of chemical treatments to prevent mite resistance, baiting mites with drone brood to be removed from the hive before it emerges (if managing few hives), and breeding for traits that result in a degree of mite tolerance (i.e. grooming behavior, varroa sensitive hygiene, mite-biting, etc.).
Queen breeders like Meyer Bees and others, are creating queens that exhibit the varroa sensitive hygiene (VSH) trait as an additional, non-chemical pest control tool. VSH is a behavioral trait of honey bees which gives them some degree of varroa tolerance. VSH trait selection increases bees’ ability to reduce levels of varroa through detection and removal of varroa from capped brood cells. VSH bees have the VSH trait and are highly sensitive to the presence of varroa in/on the pupae. It is now surmised that the pupae give off a chemical cue which signals a varroa incursion.
VSH bees respond to the stressed pupae by uncapping the cells and removing the pupae, which in turn releases the varroa mites. VSH bees are also known to uncap and then recap pupae. This sometimes releases some of the invading varroa. The uncapping response is normally when the pupa is at the white, pink and purple-eyed stage, at which point the varroa mother would have had two to five offspring. The uncapping displaces the mother varroa and her offspring, who are at different stages of maturity.
A displaced varroa may be killed by adult worker bees, may enter a new larval cell where the mother often cannot produce a normal family of offspring or fall from the frame. These ‘nonreproductive’ mites are a key feature resulting from high levels of VSH activity.
In this way, varroa sensitive hygiene bees are able to keep the mite population levels down by interrupting the life cycle of the varroa. VSH is a heritable breeding trait that can be selected and can be used in combination with an Integrated Pest Management Plan. Meyer Bees currently offers a number of options from VSH queens to VSH package bees to choose from.