Microbial ecology

Microbial ecology of the bee brood cell

Solitary, ground-nesting bees, which comprise the vast majority of bees in the world, store a mixture of nutrient-rich pollen, nectar and, sometimes, floral oils in brood cells excavated from the soil. The semi-liquid provision mass represents a rich store of resources in the form of carbohydrates (primarily from nectar), proteins (primarily from pollen), and diverse plant secondary compounds. This pollen provision mass not only sustains the larval bee, but it can also be host to a diverse microbial fauna, although the role of these microbes in this mini-ecosystem is largely unknown. 

Brood cell of Anthophora plumipes (from Loonstra 2012)

Microbes play an especially important role in ground-nesting bee health, as their pollen provision masses are particularly susceptible to spoilage. Bacteria and fungi that cause fermentation can lead to secondary fungal infections, rendering the pollen provisions unusable for the bee larva, ultimately leading to larval mortality. Other microbes may be able to mitigate these effects through the production of anti-microbial compounds. 

There is increasing evidence that some bees benefit from mutualistic microbes (e.g., fungi and bacteria) that inhabit their pollen/nectar provisions. While previous work has focused on honey bees, we know very little about the microbial communities inhabiting solitary, ground-nesting bee nests. Aside from direct toxic effects, pesticides can impact bee health indirectly through interactions with the microbial community of bee brood cell. Few studies have investigated the effects of these varying factors on native bee health. 

Current work in the lab focuses on studying the interacting effects of pesticides and microbes on the health of unmanaged wild bees. Ongoing projects include:  

1. assessing the pesticides and microbial community in solitary bee nests 

2. identifying the main source of microbial transmission

3. determining how pesticides affect the prevalence of microbes in solitary bee nests 

4. evaluating how these factors affect larval development

Current research in this area is being conducted by graduate student Kristen Brochu, and focuses on the hoary squash bee Peponapis pruinosa in New York State. This bee is an ideal study species because its nests can be easily excavated allowing pollen provisions to be collected for analysis of pesticides, and screened for the presence of pathogenic and mutualistic bacteria and fungi. Although managed bees, such as honey bees, can be effective pollinators in many crops, colonies are costly to rent, and some high value crops, such as cucurbits (squashes and pumpkins), are actually pollinated more effectively by solitary, ground nesting bees such as P. pruinosa. Managing wild bees is therefore a more economic and efficient strategy to improve crop yield. This research will ultimately provide specific management guidelines for maintaining healthy populations of wild ground nesting bees in agroecosystems in New York State.