One phenomenon that has increasingly stung honeybee hives is colony collapse disorder (CCD), which is characterized by worker bees abandoning the hive. Environmental activists have linked neonicotinoid pesticides to CCD, but scientists have said it is likely caused by multiple factors, because afflicted colonies often suffer infections from deformed wing virus (DWV) and other pathogens. Now comes evidence that the pesticides and disease are linked. Francesco Pennacchio of Italy-based University of Naples Federico II and colleagues say some neonicotinoids could impair honeybees’ immunity (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1314923110). For example, they found that in honeybees exposed to the neonicotinoid clothianidin, genes for an immune-signaling inhibitor protein turn on six times as often as in a nonexposed control group. Separately, in honeybees infected with DWV, viral levels rise with dosage of neonicotinoids clothianidin and imidacloprid. Although the findings suggest that neonicotinoids may worsen DWV infections, the researchers say whole-colony studies are needed to determine whether the harmful effects extend beyond individual bees. Eventually, the findings could improve pesticide risk assessment by adding laboratory tests for nonlethal effects, says Ohio State University entomologist Reed M. Johnson.