The 1.5mm Godzilla
Varroa destructor Mites and Their Attack on Bee Colonies
Background
The organismal name Varroa destructor is ominous, inducing mental images of a ferocious Godzilla-like creature with blood dripping from its fangs towering over a city, ready to attack at any moment. This name has the power to strike fear into the hearts of those who hear it spoken, and more specifically, the hearts of beekeepers, for while Varroa destructor is, in fact, a rather Godzilla-like monster, it is but a mite that is a mere 1.5 cubic mm in size. Though small, this arachnid is mighty, and possesses the power to utterly destroy entire honey bee colonies, just as Godzilla destroys complete cities. The female mites enter the hive on the backs of foraging bees and then seek out the hive’s newly-laid brood, on which they reproduce and feed, usually transmitting pathogenic viruses to their hosts. When the infected larvae grow into adult bees and emerge from their brood cell to join the colony, they will have a compromised immune system and a severely shortened lifespan. Not to mention, the young bees serve as a taxi for the original female mite and her offspring allowing them to find a new brood to feed on, which furthers the spread of Varroa throughout the hive. This exponential growth and spread has resulted in the Varroa destructor mite rightfully earning the title of “most damaging parasite of the western honey bee,” as it wreaks havoc on most every hive it enters.
Varroa destructor is endemic, meaning that the mites are widespread and most honey bee colonies are subject to infestation if left untreated. Currently, the most popular method of treatment among beekeepers is the use of synthetic chemical miticides to help control the populations of Varroa within their hives. Over time, however, the mites develop resistance to the chemical compounds, which then will no longer prove effective at destroying the destructive arachnids. This study investigated the plausibility of developing Varroa-resistant honey bees as a method of controlling mite populations.
Summary: Breeding For Resistance
The underlying methodology behind this study is the specific selection and breeding of low and high rates of Varroa destructor population growth traits among honey bees, as denoted by LVG(low) and HVG(high), respectively. To accomplish this, honey bee Generation 0 was selected from more than 300 colonies with genetically different queens. Mite counts of each colony were taken in both mid-spring and late-summer, and the six colonies with the highest proportional mite increase were selected as HVG colonies and the six colonies with the lowest increase were chosen as the LVG colonies. The following spring, three of the six of each HVG and LVG hives were used to produce approximately 150 queens per colony, which represent each possible genotype for the high and low Varroa growth traits. These queens were then permitted to openly mate in a specifically designated yard kept separate from other apiaries. To help ensure similar starting mite levels and apiary conditions in each hive, pre-established colonies were split in two and an HVG queen was added to one half and a LVG queen was added to the other half. These colonies were then allowed to naturally grow and reproduce to create honey bee Generation 1 the following year. Mite counts were taken mid-spring and late-summer, and winter mortality rates were measured. This procedure was repeated the following year using Generation 1 bees to produce Generation 2.
Over the two generations, this breeding program has seen significant differences in mite infestation between the LVG and HVG genotypes. In the LVG colonies, V. destructor populations increased by a factor of 1.7 between generations, while the HVG colonies saw an increase by a factor of 9.6, and the HVG hives had notably higher overall mite infestation rates when compared with the LVG groups. Future work must be done to determine specific molecular mechanisms which account for the genotypic differences, but overall, this study has exciting possibilities for the beekeeping world! The breeding and production of genetically resistant honey bees for beekeepers to purchase and house in their apiaries is a powerful and effective step towards taking down the 1.5 mm3 Godzilla known as Varroa destructor.
