Although the manner in which the bees died suggested that they had been poisoned by pesticides, the results did not agree. The department tested samples of dead bees and ran the results against a database of 300 pesticides. However, no pesticides were detected in the samples, according to Brett Gates, an agency spokesman.

The results have left officials scratching their heads because no known cause was found.

John George, vice president of the Ohio State Beekeepers Association, was surprised by the findings. “Something affected these bees,” he told Dispatch.com.

One of the reasons  officials suspected pesticides was because in January, Purdue University published the results of its study that found “extremely high levels” of a neonicotinoid in talc.