According to the University of Florida Extension, colonies nearing collapse have symptoms that include an inability of the adult bees to sufficiently maintain brood (young) because of low numbers; a colony workforce with disproportionately high numbers of young adults; lack of a queen; and bees' reluctance to consume food provided by beekeepers. Collapsed colonies exhibit no or few adults bees; a capped brood; and bee food stores (storage of honey, for example) that colony pests won't rob.
One cause of CCD, according to the University of Florida Extension, is a lack of genetic diversity and poor lineage created by the queen. Another natural cause is common pests, like the greater wax month. The moth eats the bee brood cappings, which results in deformed or dead bees, according to the website All About Bees.
Chemicals used by bee specialists to control disease could negatively impact colonies, which includes queens, workers and drones. Chemicals may also affect bees during foraging as they come into contact with toxins in their drinking water. Bees also directly inhale commercial chemicals outside the hive, according to the University of Florida Extension.
Genetically modified crops, first dipped in insecticide and then later reappearing in plants' nectar and pollen may be a significant contributor in die-offs, according to the University of Florida Extension.
Varroa mites are the world's most potent honey bee killer. They transmit viruses and create a chemical response in the bees that results in death. Malnutrition is another potential cause of mass die-offs, causing stress and depleting bees' immune system. Causes of malnutrition include parasitic mites and microbes, according to the website Environmental News Network.