The Neonicotinoids Thiacloprid, Imidacloprid and Clothianidin affect the Immunocompetence of Honey Bees (Apis mellifera L.)
1Landesbetrieb Landwirtschaft Hessen, Bee Institute, Erlenstrasse 9, 35274 Kirchhain, Germany
For successful beekeeping we need healthy and resilient honey bee colonies. The main thread of honey bee colonies is assumed to be the parasitic varroa mite that not only feeds on the bees but also transmits a number of harmful diseases. For the health of the honey bees, it is crucial to have strong defence mechanisms against those parasitic infections and diseases. This defence can be weakened by environmental factors like pesticides, which may leave the bees more vulnerable for parasites and pathogens.
We investigated the sublethal effects of the neonicotinoids thiacloprid, imidacloprid, and clothianidin on individual immunity, by studying three major aspects of immunocompetence in worker bees: total hemocyte number, encapsulation response, and antimicrobial activity of the hemolymph. In laboratory experiments, we found a strong impact of all three neonicotinoids. Thiacloprid (24h oral exposure, 200 µg/l or 2000 µg/l) and imidacloprid (1 µg/l and 10 µg/l) reduced hemocyte density, encapsulation response and antimicrobial activity even at field realistic concentrations. Clothianidin had an effect on these immune parameters only at higher than field realistic concentrations (50 - 200 µg/l).
These results suggest that neonicotinoids affect the individual immunocompetence of honey bees, possibly leading to an impaired disease resistance capacity. Our data will contribute to a better understanding of the complex and multi-causal colony losses and may help to establish indicators for the health status in order to avoid bee damage in practice.