Today I did a scheduled hive inspection and discovered that I had a varroa mite problem. This is common in hives.
Most of my beekeeping books say the most common treatment is to generously sprinkle powdered sugar on all the bees. This keeps the mites from being able to climb on to the bees and prompts the bees to clean the sugar (and mites) off of eachother.
Then I inserted a white plastic board under the hive coated with vegetable oil. When the mites fall through the screened bottom board they will stick to the plastic oil coated board. This board should make it easier to keep track of whether or not the mite infestation has decreased to a number the bees can manage themselves.