Exploring the synergistic potential of fungicides and parasites as stressors of bumble bee health and pollination services in greenhouse tomatoes
Bumble bees (Bombus spp.) are important native pollinators critical for the commercial production of tomatoes. However, bumble bees are experiencing global population declines due to an array of known and unknown factors. Recent studies have highlighted the link between fungicide exposure and bee health, and suggested that fungicide exposure may increase susceptibility to other stressors. Thus, it seems likely that multiple stressors may have synergistic negative effects on bumble bee health and threaten the sustainability of this important natural resource base on which agriculture depends (NCR-SARE broad-based outcome).
Ensuring bumble bee health is essential for Ohio tomato greenhouses, a $32 million dollar industry with over 300 operating locations. Commercial greenhouses are also an ideal system to evaluate the effects of multiple stressors. Tomatoes grown in greenhouses regularly have a range of fungicides applied, many of which are systemic, detectable in pollen, nectar, and in the bees themselves. At the same time, growers purchase commercial bumble bees to pollinate their tomatoes, and these colonies can arrive infected with various pathogens. Sub-lethal effects of chemicals can reduce bumble bee foraging efficiency, and it is possible that greenhouse tomato growers are not reaching maximum yield potential when their bumble bees are impacted by this suite of stressors. The goal of my study is to analyze the combined effects of pathogen infection and fungicide exposure in tomato greenhouses on bumble bee health and pollination efficiency, to provide growers with insights that will improve their use of commercial bumble bee pollination services.
I will place bumble bee colonies established from field-collected queens, confirmed to be parasite free, into commercial greenhouses during tomato pollination. I will collaborate with growers to place colonies in greenhouses exposed to a gradient of fungicide applications. These colonies will be equipped with pollen traps to measure fungicide levels in bumble bee-collected pollen. These greenhouses will also contain commercial bumble bee colonies, which I will sample for the presence of the gut parasite, Crithidia bombi. At the end of the study, I will evaluate the relationships between fungicide levels and a series of bee health metrics and pollination efficiency. The key outcomes of this study will be a functional risk assessment for growers of the impacts that fungicides, and potentially pathogens, have on yield due to altered pollinator foraging behavior and health.
Project objectives from proposal:
(1) Greenhouse tomato growers will learn how fungicide use impacts the bumble bees they purchase for pollination services. I will provide them with an analysis of pollination efficiency related to fungicide exposure, to increase grower understanding of how fungicides affect bumble bee foraging behavior and ultimately crop yield and quality.
(2) Growers will gain knowledge of the prevalence of pathogens in their commercial bumble bee colonies and if the presence of pathogens affects pollination efficiency. I will provide growers an analysis of the infection rate of pathogens in their commercial bumble bees. This is important for growers to understand the quality of the bumble bees they are paying for. I will create extension fact sheets that describe how fungicides affect important bumble bee colony health metrics.
(1) After learning how fungicides affect their bumble bees, tomato greenhouse growers may modify their use of fungicides to maximize the effectiveness of their bumble bee pollinators. If fungicides are shown to have adverse effects on the pollination efficiency of greenhouse bumble bees, then growers will consider this tradeoff before applying fungicides.
(2) After learning about parasite prevalence in commercial bumble bees, tomato greenhouse growers may encourage the commercial bee-keeping industry to implement additional safeguards to prevent against parasite infection. This will be beneficial not only for the tomato growers, who will receive healthier, potentially more efficient bumble bees, but also the natural environment, because there will be less pathogen spillover into wild bee populations.