Understanding the epidemiology of pathogens within bee communities in Pennsylvania

Understanding the epidemiology of pathogens within bee communities in Pennsylvania

Summary

Bee declines pose a serious risk to human food supply, crop production, wild plant diversity, and the commercial bee industry. Pathogens are a leading factor implicated in these declines.  Management of bee diseases requires understanding the macroscale seasonal trends of pathogen cycles, pathogenicity in different types of bees, and how the type of landscape (e.g. agricultural, urban, natural) can impact pathogen incidence and transmission. The purpose of this research is to better understand the epidemiology and transmission of pathogens for the whole bee community and to develop predictive epidemiological models for bee pathogens. To achieve the goals of this study we will examine (1) the seasonal prevalence of pathogens in bumble bees, honey bees, and solitary bees, (2) how the influence of pathogens differ between the previously mentioned bee groups, and (3) if landscape or plant type impacts pathogen prevalence.

Preliminary sampling of honey bees, bumble bees, solitary bees, and pollen were collected throughout the active season (early spring to late summer) of 2016 at six sites within Centre County, Pennsylvania. These sites included two farms, two urban areas, and two natural areas. During each of the four collecting periods, 30 honey bees, 30 bumble bees, and an assortment of solitary bees were collected.

We have begun to test the 2016 samples for pathogens. In particular, we have focused our screens on the following pathogens: Deformed Wing Virus (DWV), Black Queen Cell Virus (BQCV), Chronic Bee Paralysis Virus (CBPV), Crithidia, Nosema bombi, Nosema ceranae, and Ascosphaera. Preliminary data suggests that there is a general seasonal trend with pathogen prevalence being lowest at the beginning of the season for the viruses. Furthermore, it seems that each site harbors a distinct community of pathogens, however, the prevalence of these pathogens does not differ when present at all sites. This suggests that the scale at which pathogens are shared in the landscape can be quite small.

Objectives/Performance Targets

The overall goal of this project is to develop a predictive model of pathogen incidence within bee communities. We believe that this model will greatly benefit growers and bee keepers because it will allow us to understand disease epidemiology in pollinator communities. Utilizing this information, we will be able to create more informed management strategies and decisions.

To achieve this overall goal, we need to understand when pathogens occur and how pathogens are being transmitted within the pollinator community. The factors that drive disease patterns include the temporal and spatial patterns of disease transmission among pollinator communities and the natural history factors (e.g. sociality, network connectedness) that promote pathogen transfer among species and communities. Therefore, we will address the following questions:

1. Is there a seasonality to pathogen prevalence in bees and does this differ between bee types (honey bees, bumble bees, solitary bees)?
2. Does overall pathogen prevalence differ between honey bees, bumble bees, and solitary bees, suggesting that life history and limited transmissibility between taxa may impact pathogen spread?
3. What role do specific landscape (agricultural, urban, or natural) types or plant species play in pathogen prevalence?

To achieve these goals, the project will be separated into the following tasks:

• Collect bumble bees, honey bees, solitary bees, and pollen samples for two years (2016 and 2017) during the active period. Samples will be collected at 6 sites each year (2 agricultural, 2 urban, and 2 natural).
• Assess the pathogens present in the bee types and communities.
• Utilize the data collected to parameterize a predictive model of disease patterns in bee communities.

Accomplishments/Milestones

From mid-March to early September 2016, bees were successfully collected. We were able to collect 30 bumble bees, 30 honey bees, and an assortment of solitary bees from each of the six sites at all four time periods. Samples were brought back to the lab alive and placed directly into the -80^oC freezer for later processing.

We have been processing the 2016 samples focusing first on the incidence of viruses. To date we have found data that suggests there is a general seasonal trend with pathogen prevalence being lowest at the beginning of the season for the viruses. Furthermore, it seems that each site harbors a distinct community of pathogens, however, the prevalence of these pathogens does not differ when present at all sites. This suggests that the scale at which pathogens are shared in the landscape can be quite small.

The quality of the landscape was assessed at each of the sites following the assumption that greater bee diversity suggests better bee habitat. To do this we conducted timed abundance counts of bees visiting flowers and placed out bee bowls at each of our sites. The diversity at 1 agricultural, 1 urban, and 1 natural site was calculated using the Shannon-Wiener Diversity Index (Agricultural = 1.004642; Urban = 1.202368; Natural = 1.01288888). Additionally, we are planning on running the Lonsdorf model as another means to evaluate landscape quality.

We are in the process of screening the remaining 2016 samples to determine the incidence of pathogens. Beginning in March, we will collect bee samples for 2017.

Impacts and Contributions/Outcomes

Preliminary findings from this research have been presented at two international conferences and a local meeting by the project coordinator:

• Ezray B, Hines H. (2016) Seasonality of pathogens in bumble bees and honey bees. The Pennsylvania State University Center for Pollinator Research Spring 2016 Symposium. State College, PA.
• Ezray B, Hines H. (2016) Understanding pathogen dynamics in bee communities. 2016 XXV International Congress of Entomology Student Oral Ten Minute Paper Competition. Orlando, FL.
• Ezray B, Hines H. (2016) Understanding pathogen dynamics in bee communities Poster Presented at: 3^rd International Conference on Pollinator Biology, Health and Policy.State College, PA.

Two undergraduate students were trained how to collect bees and one undergraduate student was also trained to identify solitary bees. Furthermore, two undergraduate students have been trained how to conduct molecular screens for pathogens.

In January, I will post a blog post on the Hines’ Lab webpage which will discuss the project goals and preliminary results. With the help of Hines’ Lab members this post may include a video blog as well.

Ultimately this project will have a large impact on agricultural sustainability because we will be able to understand drivers of disease transmission and incidence among bees and therefore better manage these diseases.

Collaborators: