Clinical signs of deformed wing virus infection are predictive markers for honey bee colony losses

Emerging Apis mellifera worker displaying DWV clinical symptoms. Wing deformities in fall can be used as predictive marker of colony losses. [Display omitted] ► 29 Honey bee colonies monitored in Winter 2007/2008 in Switzerland. ► Workers with symptoms of deformed wing virus infections were counted. ► Numbers of workers with deformed wings are predictive markers for colony losses. ► Approach is cheap, easy and can be used as a field tool to estimate impact of viruses. The ectoparasitic mite Varroa destructor acting as a virus vector constitutes a central mechanism for losses of managed honey bee, Apis mellifera, colonies. This creates demand for an easy, accurate and cheap diagnostic tool to estimate the impact of viruliferous mites in the field. Here we evaluated whether the clinical signs of the ubiquitous and mite-transmitted deformed wing virus (DWV) can be predictive markers of winter losses. In fall and winter 2007/2008, A.m. carnica workers with apparent wing deformities were counted daily in traps installed on 29 queenright colonies. The data show that colonies which later died had a significantly higher proportion of workers with wing deformities than did those which survived. There was a significant positive correlation between V. destructor infestation levels and the number of workers displaying DWV clinical signs, further supporting the mite’s impact on virus infections at the colony level. A logistic regression model suggests that colony size, the number of workers with wing deformities and V. destructor infestation levels constitute predictive markers for winter colony losses in this order of importance and ease of evaluation.