The book, Honey Bee Colony Health - Challenges and Sustainable Solutions, published in December 2012 provides a great deal of information about the possible causes of increased bee decline. The first chapter ‘Potential Role of Microbes’ is the most important part, because basic attention is paid to the nutritional aspects. Here we quote the first few sentences of the paragraph ‘Areas for Future Research’.

We are just beginning to learn about the role of microbes in the health of all organisms, including honey bees. We know that many metabolic processes are not directed by host genes but rather those of symbiotic microbes. This implies that optimum health depends on maintaining conditions that encourage the growth of those microbes needed to process food, and either convert it to energy or use it to synthesize more complex molecules via anabolic pathways. Though most of what we know about microbes in honey bees is their role in food processing and conservation, there are many areas yet to be explored.

That microorganisms play a decisive role in the occurrence of winter mortality is closely related to the hypothesis in the early phases of our research (May 2011) to the effect of iron on winter mortality. It was indicated at that time that microorganisms, associated with the Varroa mite, play a very important role in the origin of problems with the Varroa mite.