To date, the precise reasons for colony losses are not yet known.
Honey bees are the most economically valuable pollinators of agricultural crops worldwide. Scientists at universities and the U.S. Department of Agriculture (USDA) frequently assert that bee pollination is involved in about one-third of the U.S. diet, and contributes to the production of a wide range of fruits, vegetables, tree nuts, forage crops, some field crops, and other specialty crops. The monetary value of honey bees as commercial pollinators in the United States is estimated at about $15-$20 billion annually.
.... "it now seems clear that no single factor alone is responsible for the malady." This has led researchers to further examine the hypothesis that CCD may be "a syndrome caused by many different factors, working in combination or synergistically." Currently, USDA states, researchers are focusing on three major possibilities:
- pesticides that may be having unexpected negative effects on honey bees;
- a new parasite or pathogen that may be attacking honey bees, such as the parasite Nosema ceranae or viruses; and
- combination of existing stresses that may compromise the immune system of bees and disrupt their social system, making colonies more susceptible to disease and collapse. Stresses could include high levels of infection by the Varroa mite; poor nutrition due to apiary overcrowding, pollination of crops with low nutritional value, or pollen or nectar scarcity; exposure to limited or contaminated water supplies; and migratory stress.