Avignon bees

Le Conte et al. [190] collected 82 colonies that had survived the invasion by Varroa without treatment. They were placed in the region where they had been found: 30 in an apiary near Le Mans, and 52 in an apiary in Avignon. Treated control colonies were placed nearby. The mortality of colonies varied between 9.7 and 16.8% per year. Surviving colonies had only 32.4% of the Varroa infestation rate in control colonies. Honey production by untreated surviving colonies was half of that of the controls. The experiment shows that the collected colonies had some degree of Varroa resistance at the start of the study. The surviving colonies were maintained under artificial selection as is witnessed by this citation: 

“What has happened to these bees since we published those results in 2007? Once every two years, we graft queen larvae from the three best colonies in each apiary (west and south of France) to get 20 colonies. The queens are naturally mated by local drones. About 30–35% of the colonies die within 18 months, but the rest of the colonies are good candidates for surviving to the mite, so the stock still survives efficiently”. Hence, despite continued selection, Varroa resistance has not increased over a 10year period.

The natural and artificial selection for colony survival did not increase the frequency of resistance genes probably because the bees are kept in an open panmictic breeding population. While selection favours colonies with a higher frequency of resistance alleles, panmictic mating in a population with a low frequency of these alleles makes that queens of the selected colonies mate with drones with a low frequency of the resistance alleles, In addition, drones with resistance genes from the untreated colonies disperse into the environment. Thus, the mating structure of the population counteracts local selection for Varroa resistance.

When the Avignon bees were tested outside their native environment in a Europe-wide experiment [197], neither their Varroa infestation rate after one year without treatment nor their survival outperformed that of colonies descending from non-selected genotypes tested at the same locations.

Alphen and Fernhout Zoological Letters (2020) 6:6

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