The effects of dietary imidacloprid on bumblebee health in lowbush blueberry fields in Maine

The effects of dietary imidacloprid on bumblebee health in lowbush blueberry fields in Maine

Summary

Declines of native bumblebee species have been recorded for over six decades in Europe and, more recently, are also being reported in North America. Bumblebees are a temperate species and are well-adapted to Maine’s cool spring climate, making them an important pollinator for the May to June bloom of lowbush blueberry. Bumblebee pollination is especially imperative in contemporary times as we see honeybee colony losses and the rising costs of honeybee hive rentals causing a burden on Maine’s growers. Although there is currently little consensus about the exact cause of bumblebee losses, there has been recent interest in the use of systemic neonicotinoid pesticides in North America’s crop systems and possible sublethal effects on bumblebee colonies.

This project seeks to investigate such effects using managed colonies of Bombus impatiens by feeding them a range of field-realistic doses of the neonicotinoid imidacloprid and then following the colonies’ progress during the lab dosing period and then through the season as the colonies are placed out into blueberry fields. Although B. impatiens is technically a native Maine species, another key component of this project will be to establish an effective rearing protocol for Bombus ternarius, one of the most common species in Maine’s blueberry fields. Using a native species raised from individuals from Maine will not only be useful in the investigation of the effect of imidacloprid on Maine’s bumblebees, but will also make for an interesting comparison with the managed B. impatiens colonies.

Finally, another component will be to measure the immunocompetence of individuals in the differentially dosed colonies to investigate if imidacloprid exposure affects the immune system. Levels of conopid fly parasitism will also be investigated to identify possible enhanced susceptibility of dosed colonies to parasites.

Objectives/Performance Targets

Objective 1. To dose colonies of commercial B. impatiens with a range of field-realistic doses of imidacloprid and track their progress through the season:

The technical start date of this project is 5/1/14, which would allow two weeks of dosing the colonies in the lab before placing them out in blueberry fields for the remainder of the season. Therefore, although this part of my project has not yet begun, connections with growers have been made to pin down field sites for the upcoming season in which the bees will be placed once the two week period of dosing is over.

Objective 2. To monitor levels of conopid fly parasitism in the commercially-raised dosed colonies as well as in wild caught native bumblebees collected from blueberry fields around the state:

This work will be carried out next summer once the project begins. However, I am currently carrying out dissections of bees collected in past field seasons and continue to read the literature to refine my dissection techniques in a manner that may allow me to identify the conopid larvae to species.

Objective 3. To establish an effective rearing method for the native bumblebee species B. ternarius in order to use true native colonies in similar experiments as in Objective 1.

I am preparing for the upcoming field season by reading the literature and structuring my protocol around what was successful for other researchers.

Objective 4. To measure the immunocompetence of the imidacloprid-challenged bees using measures of the enzyme phenoloxidase (PO) in bees collected from each colony before dosing, during dosing, directly after dosing, and at regular intervals throughout the season.

This work will be done this coming May and then throughout the season, but I have prepared for this by learning the technique of how to measure PO levels using the frozen thorax of bumblebees. 

Accomplishments/Milestones

Because the start date of this project is 5/1/14, no expenditures have been made on the grant yet, but I am preparing for the upcoming field season through researching the literature and reaching out to growers as well as to other researchers. The nature of my work is seasonal, but preparations are being made to ensure a successful field season.

Impacts and Contributions/Outcomes

I expect that this project will be a unique contribution to the study of the sublethal effects of neonicotonoids on bumblebees. Currently, similar work has been done but in a lab setting only and using the European managed bumblebee, B. terrestris. Therefore, this work will be the first using North American bee species that not only follows the colonies through the lab-dosing period, but also their progress throughout the season when the dosing period ends and the colonies are placed out in field sites. This will be key in determining susceptibility of exposed bees to parasites in pathogens in a natural setting, as well as their ability to raise a successful colony with an appropriate number of reproductives produced at the end of the season. It is expected that these findings will generate a publication or publications in a peer-reviewed journal for the focus on North American bumblebees. Although predicting possible effects on agricultural management practices is difficult, the results of this research will be informative in determining sublethal effects of imidacloprid on bumblebees, which will be useful in the future for making suggestions for best growing strategies in the lowbush blueberry system. Beyond this, the results will help shape future investigations into the effects of neonicotinoids on native bees and potentially lend clues as to why some bumblebee species are becoming more prevalent while others are in decline.

In addition, my cooperation with blueberry growers in Maine will enable me to not only relate my research findings to them directly, but also through an annual presentation at the Maine Wild Blueberry Field Day at the University of Maine’s research farm in Jonesboro, ME and an annual report submitted to the University on research in blueberry fields. As I am also on Specialty Crop Research Initiative (SCRI) grant, I will continue to work toward the goals outlined there in which I contribute to a “Pollinator Toolbox” to aid stakeholder growers in assessing pollinator efficacy and monitor the native bee populations in their fields. Electronic access to information about the SCRI pollinator security project will be available to stakeholders, as well as information specific to my project in the form of a video interview.

Collaborators: