In a "first" ever epidemiological research study conducted with 80 colonies over an entire season in cooperation with NC State, U of Maryland, Penn State and USDA, found that a little understood disease IBDS (idiopathic brood disease syndrome) is the largest cause of colony mortality and a great factor for predicting the eventual death of a bee colony.
Colonies with IBDS had a risk factor of 3.2, meaning those colonies were 3.2 times more likely to die than others, including those with and without varroa mites. Low levels of mites made little difference if the colony also had IBDS.
Coming in second? QUEEN EVENTS with a risk factor of 3.1. I think all beeks know this, some just don't want to admit it
IBDS is not understood very well but the study proves it is a significant problem and another part of the CCD Mystery.
The published paper can be found in the February issue of PREVENTIVE VETERINARY MEDICINE. Something else to worry about, heh?