A few weeks ago Dennis received a call regarding a Maryland beekeeper concerning what was believed to be a pesticide kill. Throughout the conversation it was learned that there was an abundance of the common pasture weed, buttercups (Ranunculus species), growing in close proximity to the hives. The beekeeper noted that the bees appeared to be struck with a form of paralysis, twitching and exhibiting convulsive movements. While we are not ruling out a pesticide kill (the samples are still being tested), there have been cases where bees have been poisoned from ingesting buttercup pollen. Since it was mentioned that there were buttercups blooming nearby in this case, we decided to take a closer look.
Buttercups flourish abundantly in the warmer months. I am sure you are familiar with their bright, yellow flowers littering yards and pastures. The weed contains a chemical called anemonol which breaks down into the toxin protoanemonin, which is highly lethal to bees. When the plant dies, the protoanemonin no longer retains its toxicity as it is only present in the growing buttercup. However, pollen collected from a buttercup can retain deadly protoanemonin for a period of up to three years. Right now, buttercups are in full bloom creating a haven of toxicity for unsuspecting honey bees.
When bees eat this stored pollen they experience certain symptoms from the poison within minutes. Paralysis, body convulsions, and leg twitching can affect not only workers, but drones and queens alike. A number of titles have been given to identify these strange symptoms from Ranunculus poisoning such as May disease and Bettlach disease.
We were rushed a sample of bees in alcohol, buttercups picked from the area and a frame chock full of pollen taken from the hives. I identified the buttercup pollen and crushed up the bees to see if there was any buttercup pollen in their mid gut; however, there were very few traces of pollen found and it did not appear to be from the buttercups. I had higher hopes to find some in the frame, however when I took a look at the pollen on the frame I found no buttercup pollen. It will be difficult to find out if buttercup pollen is really the cause of these unusual symptoms through pesticide analysis because protoanemonin is naturally occurring ‘pesticide,’ so there is no specific pesticide test for it. Because the samples are being analyzed for pesticides; however, we will be able to see those levels of man-made pesticides, possibly leading us to another conclusion, but until then, the mystery continues…