No discussion of beekeeping is complete without talking about the varroa mite. This parasitic pest, no larger than the tip of a needle, first arrived in the U.S. in the late 1980s and has quickly become the most common cause of bee death and colony failure. According to the USDA, 42 percent of commercial beehives were infected with varroa in the spring of 2017 [source:USDA].
Varroa mites harm bees in several different ways. A mated female mite will crawl into the brood chamber of a developing bee and lay eggs on the larvae. The baby mites will feed on the bee pupae, either killing it or deforming it. Other mites will attach themselves to adult bees and feed on their blood. While the blood-sucking alone can kill bees, it's also a portal for infecting the bees with a number of deadly viruses that can spread quickly to take out a whole colony [source: NC State Extension].
It's important to test for varroa infestations throughout the year and treat your hives accordingly. One of the most popular ways to test for varroa is to buy a special sticky board from a bee supply company. The board sits below a mesh on the bottom of the hive box, which keeps bees from getting caught on its gluey surface, while allowing dead mites to fall through. After 24 hours, you check the board and count the number of mites.
Another method is the sugar shaker technique. First, you equip a small mason jar with a lid made from 1/8-inch (3-millimeter) mesh cloth. Remove the lid and dump in approximately 200 bees from the hive. Add 2 to 3 tablespoons of powdered sugar, screw on the lid and shake. The open the jar and shake the sugar-covered bees over a white napkin or cloth. The mites should fall out onto the cloth, allowing you to count them. More than 10 mites for every 200 bees means that you have a mite problem [source: NC State Extension].
Treatment methods for varroa mite range from powerful insecticides to dusting the brood frames with powdered sugar or talcum powder, which causes the mites to lose their grip on adult bees [source: NC State Extension]. Organic beekeepers looking for a stronger but natural solution often use formic acid. Pads soaked in the acid, first isolated from ants, are laid on the top of the hive, but only when the temperature is within a certain range and not during the nectar flow season. The fumes from the acid can even penetrate brood cells and kill mites feeding on bee larvae [source: Bayer].
Another common honeybee disease in the U.S. is American foulbrood, a bacterial disease that kills brood larvae in their cells, eventually leading to colony failure. American foulbrood gets its name from the distinctive sulphurous odor emitted by a brood frame infected with the disease. Telltale signs of foulbrood are sunken and darkened caps on the brood cells or irregular brood patterns on the frame.
Unfortunately, there's no cure for American foulbrood, which means the colony and all hive equipment must be destroyed.