A very interesting study of the effects of two pesticides and the synergy or lack thereof with nosema.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3960157/

From the conclusion:

Our result showed that N. ceranae-fipronil and N. ceranae-imidacloprid combinations do not systematically lead to a synergistic effect on honeybee mortality. Such variability in impact on mortality could be due to additional unexpected stressors related to life-history traits of the sampled honeybee colonies. In our study, gene expression profiles in honeybee midgut showed that insecticide treatments had no impact on detoxifying genes but led to a significant downregulation of immunity-related genes (Figure 3), suggesting a possible immunotoxicity of neonicotinoid and phenylpyrazole insecticides under chronic exposure. Honeybees treated with N. ceranae, alone or in combination with an insecticide, showed a strong alteration of midgut immunity visible after 7 days, together with significant modifications affecting barrier defence and trehalose metabolism. The increasing impact of the treatments with time suggests a growing imbalance of the honeybee transcriptome that would reflect an absence of stress recovery and could explain the observed higher mortality rates.