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Informed Discussion of Beekeeping Issues and Bee Biology

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From:
Matthew Smart <[log in to unmask]>
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Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Date:
Tue, 30 Jun 2015 18:23:02 -0400
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With respect to the question about the bee immune response, like just about everything in science the answer is...it depends. 

For example, Varroa mites (and Nosema and certain pesticides) are known to suppress the immune system thus decreasing a bee's ability to fight infection from other things like viruses and bacteria which can then take advantage and "overcome" the bee's cellular immune defenses.  In that case, a decreased immune response could be viewed as a bad thing.  

However, if you think about otherwise healthy bees (i.e. not parasitized by Varroa mites) a lower immune response would be indicative of overall better "health" than bees with an up-regulated immune system - just like in humans where our immune system, if working properly, only ramps up when we are challenged with a disease, and is otherwise quiet(er) when healthy. 

A high immune response is costly in terms of nutritional resources that could otherwise go into other functions like nutrient storage.  Whats more, a consistently high immune response can damage cellular machinery and/or result in autoimmunity where the immune system is attacking "self".

Up-regulation means that the bees are fighting something off like a bacterial or fungal infection which is good if they are sick, but at the same time, wouldn't it be better to not be sick in the first place? 

In my study I was looking at the background nutritional stores and immune responses of honey bee colonies positioned in agricultural landscapes surrounded by varying "quality" forage (area of land with flowers usable by bees basically).  Bees from colonies at the best site (most land with forage) had higher fall nutritional stores and a decreased immune response compared to the worst site which had lower nutritional stores and an increased immune response.  Significantly more colonies survived at the best compared to the worst site.  What I think could be happening is a trade off occurring between the nutritional and immune systems for the limited resources in the body of the bees, which is ultimately influencing survival or death of colonies.

I hypothesize that landscape nutrition (specifically pollen=protein which is made up of amino acids which make up the nutritional and immune molecules I am talking about here) is influencing the relationship between individual bee nutritional storage and the immune response, i.e. bees eating a better diet have greater nutritional stores to get them through the winter (vitellogenin, lipids) and a quieter immune system (a decreased susceptibility to disease = better "health") compared to bees on a poorer diet, or in a less abundant forage landscape.  Therefore the bees in the better landscape don't get as sick from all of the diseases they come in contact with (aren't as susceptible to disease because of their robust health from eating a quality diet) and have a better chance to survive the winter.

Lab studies that I conducted at the University of Minnesota corroborate this - bees on different diets respond differently (in terms of nutrition and immunity) to a bacterial challenge, with bees on the "better" diet having increased nutritional stores and decreased immune response compared to bees on the "worse" diet.  There is still a lot of work to do in this area and a lot of unknowns - I hope to clear up some of these questions and relationships with more lab work in the near future.

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