(CRAIG GLOVER/QMI AGENCY FILE PHOTO)

LONDON, Ont. — The ongoing investigation into honeybee deaths that struck hives across southwestern Ontario this spring has turned up a pesticide used to protect corn and soybean seeds.

Thousands of dead bees were found in piles outside hives in early May, triggering an investigation by Health Canada and the province's agriculture and environment ministries.

An agriculture ministry spokeswoman said Health Canada found residues of the insecticide clothianidin in 28 of 37 samples of bees from various sites.

Clothianidin was banned in Germany after widespread honeybee deaths and U.S. beekeepers and environmental groups are campaigning to have it banned there.

The spokeswoman wrote in an e-mail that given the large number of potential factors involved, Health Canada hasn't drawn any conclusions yet.

Health Canada must still screen for other pesticides and other factors related to overall bee health, she wrote.