As part of the People’s Garden Initiative for Gastonia, North Carolina, the National Science Laboratory (NSL) built two beehives to produce honey without the use of pesticides. If insect control was needed, we planned to use only what was allowed for use in organic products. When Varroa mites were discovered in the hives, we used thymol, a natural oil, to control them.
Several weeks ago, we collected honeycomb samples from each of our hives to test for about two hundred different pesticides. The NSL has built a reputation for quality pesticide residue analysis. Many members of its staff have performed this work for over 20 years. The equipment we use for analysis is the latest and greatest, producing detection limits of 1 part per billion—the equivalent to one drop of water diluted into 11,008 gallons, or about three seconds out of a century.
Although we realized that our bees would forage in an almost urban environment—Gastonia is a city of about 72,000 people twenty miles west of Charlotte—it was surprising to find more pesticides than expected. In addition to thymol, which we applied to the hive, we found Coumaphos, Fluvalinate and Chlorothalonil.
Thymol was present at 0.5 and 1.6 parts per million. The three other residues were present at very low levels, and well below the safety levels established by the EPA.
As an explanation, it is possible that both Coumaphos and Fluvalinate were already present in the wax foundation purchased to help the bees build their honeycombs. We have learned that this low level presence is not uncommon in wax honeycomb foundations, since these are two of the three synthetic miticides used to control the Varroa mite.
Chlorothalonil is a fungicide that is commonly used in gardening. It is frequently found in pollen, which is a favorite food for bees. Chlorothalonil was present at less than 1 part per million.