Individual and colony effects of dietary imidacloprid on managed Bombus impatiens in Maine’s lowbush blueberry fields

Documented declines of native bumblebee populations have been recorded in Europe for the past six decades and have begun to be reported in North America. In contemporary times when the prices of rented honeybee hives are rising in the face of Colony Collapse Disorder (CCD), it is more important than ever to protect the native pollinators of our nation’s important crop systems. Although there is currently little consensus as to what is causing the bumblebee declines, there has been speculation about the possible role of systemic neonicotinoid insecticides in population losses. In the summer of 2013, I investigated the effects of imidacloprid (Admire® Pro, Bayer) on commercial Bombus impatiens by feeding colonies a range of field-realistic doses (0.08 µg L^-1, 0.51 µg L^-1, 3.2 µg L^-1, 20 µg L^-1, and 125 µg L^-1) of imidacloprid and then followed how those colonies performed throughout the season. A significant correlation between treatment group and colony weight at the end of the season was observed (P < 0.0001), along with the average number of individuals in each colony at the end of the season (P  < 0.0023). A significant linear relationship was found between treatment and average worker and drone size in each colony (P < 0.0456). A similar experiment was performed in the summer of 2014 and these data are currently being analyzed for similar effects on proxies for colony strength. Future directions include the effect of pulsed dietary imidacloprid exposure on immune strength (phenoloxidase) and susceptibility to parasitoid (Conopidae) infection.