ARS | Publication request: Varroa destructor resistance of honey bees in Hawaii, USA, that express various levels of Varroa sensitive hygiene (VSH)

Submitted to: Journal of Apicultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 15, 2012
Publication Date: July 2, 2012
Citation: Danka, R.G., Harris, J.W., Villalobos, E. 2012. Varroa destructor resistance of honey bees in Hawaii, USA, that express various levels of Varroa sensitive hygiene (VSH). Journal of Apicultural Research. 51(3):288-290.

Interpretive Summary: There is a large industry for production of honey bee queens in Hawaii, USA, that now is threatened by Varroa mites. The few miticides that commonly are used to manage mites can interfere with queen rearing and sperm production, and so can be problematic for queen production operations. We determined the usefulness of mite-resistant bees for managing mites. The bees were bred for a resistance trait known as Varroa sensitive hygiene (VSH). A commercial queen breeder established 30 colonies that had either 0%, 50% or 75% of the genetics for VSH. We sampled the colonies every two months to monitor the density of Varroa mites and to measure the population of brood. Individual colonies that reached a threshold density of mites (10 mites per 100 bees) were removed from the experiment and treated with a miticide. We found that Varroa mites were significantly suppressed only in the group of colonies with 75% VSH. Six months after colonies were formed, all 0% and 50% VSH colonies required treatment. In the 75% VSH colonies, average mite densities increased to 5 mites per 100 bees at 4 months and then decreased to 0.5 mites per 100 bees at 8 months. Brood populations were smaller in the 75% VSH colonies than in the other groups. This information provides initial guidance for using genetically resistant bees to manage Varroa mites in the tropical conditions of Hawaii. More than half of the genetics for VSH are necessary to significantly suppress mites, and further breeding to retain large colonies is required.

Technical Abstract: The Big Island of Hawaii, USA, supports an important honey bee (Apis mellifera) queen rearing industry that has been threatened by Varroa destructor since 2008. Miticides widely used to manage mites are known to interfere with queen rearing and sperm production. We investigated whether bees bred for resistance to mites via the trait Varroa sensitive hygiene (VSH) can confer useful resistance in Hawaii. A cooperating queen breeder established 30 colonies that were assigned to one of three treatment groups. Instrumentally inseminated queens were added to each colony; these queens were created so that their workers had either 0%, 50% or 75% of the genetics for VSH. Beginning in September (two months after colonies were established), we sampled the colonies every two months to monitor the density of Varroa mites and to measure the population of brood. Individual colonies that reached a threshold density of 10 mites per 100 bees were removed from the experiment and treated with a miticide. Populations of Varroa mites were suppressed only in the group with the highest level of VSH. By January all 0% and 50% VSH colonies required treatment. In the 75% VSH colonies, average mite densities increased to 5 mites per 100 bees at 4 months (January) and then decreased to 0.5 mites per 100 bees at 8 months. Only one of the 75% VSH colonies needed treatment (at four months) through the 8-month test. Brood populations were smaller in the 75% VSH colonies than in the other groups. The data show that, unlike on the mainland, more than half of the genetics for VSH are necessary to suppress Varroa population growth in Hawaii. Furthermore, breeding appears to be needed to restore full fitness in highly resistant colonies.