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United States Department of Agriculture

Agricultural Research Service

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Research Project: Probiotics and Chalkbrood Disease in the Alfalfa Leafcutting Bee

Location: Pollinating Insect-biology, Management, Systematics Research

2013 Annual Report

1a. Objectives (from AD-416):
Our goal is to understand how microorganisms in the bee gut affect bee health, and to identify possible probiotics that might help control chalkbrood (a disease of bee larvae) and other leafcutting bee diseases. To do this, we will address the following questions: 1) What microorganisms occur in the intestines of alfalfa leafcutting bee larvae? 2) If we remove certain bacteria or fungi from the gut, does this affect bee resistance to chalkbrood and other diseases? 3) How does the presence of the chalkbrood fungus (Ascosphaera aggregata) affect gut microorganisms?

1b. Approach (from AD-416):
Probiotics are beneficial microorganisms that occur in the gut and help stave off disease. These are well studied in humans and livestock. Chalkbrood first develops in bees by way of an infection that starts in the gut. It is possible that probiotics occur in bees and affect their susceptibility to chalkbrood. However, little to nothing is known about the bacteria and fungi that occur in healthy alfalfa leafcutting bees, and nothing is known about the interaction between these microorganisms and the chalkbrood pathogen. We will take advantage of modern DNA-sequencing technology to identify gut-associated microbes, as a first step towards identifying beneficial symbionts and whether they can prevent infectious disease. Old DNA sequencing techniques were both costly and time-consuming, but new high-throughput DNA-sequencing techniques allow scientists to conduct broad surveys of microbial communities rapidly, at a much lower cost per sequence. Thus, it is now possible to collect a very large number of microbial DNA sequences from bee guts and use these to identify what microbes are present.

3. Progress Report:
Chalkbrood infection develops in the guts of alfalfa leafcutting bees, but whether these bees have beneficial gut microbes is unknown. We used modern, cost-effective “next-generation” DNA sequencing to answer the following questions: 1) What microorganisms occur in the intestines of alfalfa leafcutting bees; 2) if we remove bacteria or fungi from the gut, does this affect bee resistance to chalkbrood; and 3) how does the presence of the chalkbrood fungus affect gut microorganisms? We found the gut microbial communities to be quite simple. Most gut communities contained large numbers of one to five types of fungi and two types of bacteria, including a lactic acid bacterium that is common and thought to be beneficial in honey bees. The alfalfa leafcutting bee guts almost always contained the chalkbrood pathogen. When we fed bee larvae antibiotics, antifungal compounds or infectious chalkbrood spores, it altered the microbial communities in the gut. Bacteria in the gut did not appear to have any effect on the chalkbrood fungus, and thus, bacteria probably do not protect bees from this pathogen. However, eliminating the chalkbrood pathogen led to an increase in other kinds of fungi.

4. Accomplishments

Last Modified: 10/16/2017
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