Improving resistance to Varroa mites in honey bee colonies via cultural brood mixing
Date
2024
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Publisher
University of Delaware
Abstract
Honey bee, Apis mellifera, colonies are susceptible to failure due to the novel parasitic mite Varroa destructor. Genetic diversity has been shown to be vital to colony health, productivity, and resistance to mites. Genetic diversity can be augmented within a colony via artificial insemination, which mimics the derived polyandrous state of all members of the genus Apis. Alternatively, brood mixing is a manual method of transferring immature bees between colonies, thereby providing a non-technical method of increasing colony genetic diversity. To evaluate the effectiveness of brood mixing for improvement of colony strength and resistance to Varroa mites via augmented genetic diversity, I conducted two field experiments over two seasons. In the first season (2021), honey bee colonies were established with one of four types of queens from distinct geographic breeding regions in the continental US: Florida, Georgia, and 2 queen types from California. These queens did not have distinct selected resistance traits against Varroa mites and there were only minimal effects of brood mixing and queen source on colony productivity and mite levels. In the second field trial (2022), I investigated the mixing effect between only two types of colonies: those with the highly selected Varroa-sensitive hygienic (VSH) trait and wildtype colonies (WT) that lacked the trait. Mixed colonies were observed to investigate the possibility of trait sharing between colonies via repeated brood mixing and resulted in colonies with intermediate adult bee populations and intermediate mite levels, with WT-control colonies having the highest mite levels and VSH-control colonies having the lowest mite levels. Finally, I conducted a thorough pathogen screen using relative quantification of honey bee viruses, and microsporidian and bacterial parasites using real-time qPCR at 3 time points in the 2021 field trial to assess the risk of pathogen and disease spread between brood mixed colonies. Brood mixing did not affect pathogen prevalence nor relative quantities, however, general increases in Deformed Wing Virus and decreases in Black Queen Cell Virus and Sacbrood Virus were observed over the season.
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Keywords
Varroa destructor, Varroa-sensitive hygienic, Wildtype colonies, Apis mellifera