For 10 weeks, we continually exposed full sized colonies of
bees (30–40,000 adults) to 5 and 20 ppb imidacloprid by
provisioning colonies with protein supplement patties
spiked with the pesticide. After 5 and 8 weeks of exposure
(ca. 1.5 and 2.5 generations of exposure), wax combs with
emerging brood were taken into the laboratory and groups
of newly emerged adult bees from selected colonies were
removed and either used to determine fresh weight or caged
and fed a suspension containing spores of the known bee
pathogens N. apis and N. ceranae over the first 2 days of adult
life. Ten days later, bees were sacrificed and the development
of Nosema infection in individual bees determined.

A pronounced increase in Nosema growth was evident
within individual bees reared in colonies exposed to a low,
sub-lethal level of the pesticide imidacloprid. Two trials
were conducted in this experiment.

We suggest new pesticide testing standards be
devised that incorporate increased pathogen susceptibility into
the test protocols. Lastly, we believe that subtle interactions
between pesticides and pathogens, such as demonstrated here,
could be a major contributor to increased mortality of honey
bee colonies worldwide.

Pesticide exposure in honey bees results in increased
levels of the gut pathogen Nosema
Jeffery S. Pettis & Dennis vanEngelsdorp &
Josephine Johnson & Galen Dively
Naturwissenschaften

Open Access This article is distributed under the terms of the
Creative Commons Attribution Noncommercial License which permits
any noncommercial use, distribution, and reproduction in any medium,
provided the original author(s) and source are credited.

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