The role of deformed wing virus in the initial collapse of varroa infested honey bee colonies in the UK

The mite Varroa destructor has been associated with the collapse of millions of Apis mellifera honey bee colonies world-wide. During the past decade, a large body of research has revealed various interactions between varroa, the honey bee and various viral pathogens. One pathogen in particular, deformed wing virus (DWV), has emerged as the key pathogen involved in colony collapse. As varroa has permanently changed the viral landscape in which honey bees exist, we present a large body of data on the effects of DWV during the initial phase of varroa infestation in the UK during 1998. This provides baseline data for further comparative studies. We carried out DWV transmission studies, and observed the effects of DWV on bee longevity. As the ELISA technique used in these studies had a detection limit of similar to 10(7) viral particles per bee, only high viral (overt) titres were detected. During the initial phase of varroa establishment, DWV was detected in 0.6% of non-infested sealed brood, but in 89% of sealed brood invaded by varroa. Once DWV was introduced into the bee's haemolymph via mite feeding on either pupae or adults, an overt virus infection was rapidly produced in 3-4 days. In sealed brood the presence of varroa was fatal for 21% of the brood, caused wing deformity in some emerging adults and significantly reduced longevity as an adult. However, adult bees that became infected after they had emerged, did not develop wing deformity nor show any reduced longevity, but acted as reservoirs of DWV infection.