After my last post, many people wanted to know “What the heck is guanine?” Very simply, guanine is one of the four nitrogen-containing bases found in DNA. You’ve probably seen strings of letters representing DNA structure that look something like this: ATGGATGTCGACGGT and so on. The four letters represent the four bases: adenine, cytosine, guanine, and thymine.
However, that is more than you need to know for beekeeping purposes. It just so happens that the excrement of Varroa mites contains about 95% guanine. Guanine so pure shows up as a bright white glob—a deposit the mites leave on the inside of brood cells. After all, there are no “facilities” for them to use while they are locked under a capping, squeezed between a bee pupa and a wall of wax, so they leave it where they are.
If you find that your empty brood cells are loaded with irregular white deposits, it is a sure sign of a heavy mite infestation. If you hold a frame up to the light with the sun at your back, the deposits are especially easy to see. They are usually found in the top of the cell, so rotate the top of the frame away from you for easiest viewing.
The best part about guanine is its name. Guanine was first discovered in bat and bird excrement, a substance known as guano. In 1850, when scientists were able to isolate this white chemical from the rest of the stuff in the droppings, they named it guanine. How dainty.
Luckily for beekeepers, mites and bats and birds have something in common—a lot of guanine in their poop, a fact that lets us know who has been hanging around and where. The photo shows an adult mite in a brood cell amid lots of excrement. A mite is one of those things I would rather not be.