Much is made of the possibility that environmental contaminants and pathogens might interact to worsen the effect of each of these. An alternate point of view is expressed in this new paper:

> Pesticide exposure and pathogen infection are recognised as potential stressors impacting upon bee populations and recently there has been a surge in research on pesticide–disease interactions to reflect environmentally realistic scenarios better. We critically analyse the findings on pesticide–disease interactions, including effects on the survival, pathogen loads and immunity of bees, and assess the suitability of various endpoints to inform our mechanistic understanding of these interactions. 

> We show that pesticide exposure and pathogen infection have not yet been found to interact to affect worker survival under field-realistic scenarios.  Colony-level implications of pesticide effects on Nosema infections, viral loads and honey bee immunity remain unclear as these effects have been observed in a laboratory setting only using a small range of pesticide exposures, generally exceeding those likely to occur in the natural environment, and assessing a highly selected series of immune-related endpoints.

> Pesticide exposure and pathogenic infection, when investigated separately, may alter expression of genes associated with the individual immune response, but there is no evidence that pesticide exposure reduces immunocompetence following natural pathogen infection in the context of honey bee individual immunity at a physiological level, or individual or social defence behaviours.

Collison, E., Hird, H., Cresswell, J., & Tyler, C. (2015). Interactive effects of pesticide exposure and pathogen infection on bee health–a critical analysis. Biological Reviews.

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