Not sure is this has been posted here yet but was presented at the 2010 American Bee Research Conference. 

Interactions between Nosema microspores and a
neonicotinoid weaken honeybees 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2847190/pdf/emi0012-0774.pdf

>Summary
Global pollinators, like honeybees, are declining in
abundance and diversity, which can adversely affect
natural ecosystems and agriculture. Therefore, we
tested the current hypotheses describing honeybee
losses as a multifactorial syndrome, by investigating
integrative effects of an infectious organism and an
insecticide on honeybee health.We demonstrated that
the interaction between the microsporidia Nosema
and a neonicotinoid (imidacloprid) significantly weakened
honeybees. In the short term, the combination of
both agents caused the highest individual mortality
rates and energetic stress. By quantifying the strength
of immunity at both the individual and social levels, we
showed that neither the haemocyte number nor the
phenoloxidase activity of individuals was affected
by the different treatments. However, the activity of
glucose oxidase, enabling bees to sterilize colony and
brood food, was significantly decreased only by the
combination of both factors compared with control,
Nosema or imidacloprid groups, suggesting a synergistic
interaction and in the long term a higher susceptibility
of the colony to pathogens. This provides the
first evidences that interaction between an infectious
organism and a chemical can also threaten pollinators,
interactions that are widely used to eliminate insect
pests in integrative pest management.<

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