Bee Scientifics

Resistance vs Tolerance

The USDA-ARS Honey Bee Breeding lab is world renowned for bee research attracting collaborations from United States and international organisations. During my visit at the lab, Dr. Jiri Danihlik from Palacky_University in Olomouc Czechia spent a few weeks working on a project started by a student of his studying oxidative stress in bees. Dr. Juri specialises on bee immunity, but is also a skilled and experienced beekeeper and queen producer.

A few of us were having a chat in Bob’s lab (Bob Danka) where I was explaining to Juri the complexities of trying to prepare Australian stocks for living with Varroa and about the goals of my fellowship to better understand Varroa tolerance selection techniques. During my explaination, I was gently corrected by my friend and mentor Mike Simone-Finstrom that I was not looking for traits that conferred Varroa tolerance but rather Varroa resistance.

Up until that point, I through of resistance and tolerance as interchangeable words meaning the same thing: bees that lived with Varroa. However, after deeper consideration, we don’t want bees that tolerate Varroa just as we wouldn’t want a housemate that tolerates a dirty kitchen. Tolerance is about living with something and accepting it. Varroa tolerance becomes tricky to achieve because high mite levels usually means high virus loads and high virus loads are difficult to defend against and often lethal for colonies. So unless bees are tolerant of Varroa AND resistant to viruses, colonies will still die. In fact, we want traits that confer Varroa suppression and Varroa resistance, not Varroa tolerance.

Traits under selection providing protection from Varroa mites, must keep hive mite numbers and consequently keep virus loads at levels the bees’ immune systems (social and innate) can handle. Varroa resistant bee populations have been developed through both selective breeding programs and through good old fashion natural selection. The exact mechanisms providing resistance are not fully understood, and likely a combination of genetic and environmental influences. The end result, however, is the same: colonies keep Varroa from reproducing, keep virus levels low, and remain healthy without chemical intervention.

This article in Science Mag published in 2019 is quite a good read explaining “where we are at” with respect to breeding and arriving at Varroa resistant bees. It highlights work on marker assisted selection, the golden ticket in bee breeding, and describes some of the main reasons why uptake of Varroa resistance stock isn’t greater in commercialised beekeeping operations.

In the coming weeks, I will expand on some of the issues and projects mentioned in the article based on experiences from this fellowship.

Thank you to the International Specialised Skills Institute and the Victorian Honey Bee Compensation fund for making this possible.

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