WASHINGTON (Reuters) - Disease spread to wild bees from commercially bred bees used for pollination in agriculture greenhouses may be playing a role in the mysterious decline in North American bee populations, researchers said on Tuesday.

Bees pollinate numerous crops, and scientists have been expressing alarm over their falling numbers in recent years in North America. Experts warn the bee disappearance eventually could harm agriculture and the food supply.

Canadian researchers studied another type of bee, the bumblebee, near two large greenhouse operations in southern Ontario where commercially reared pollination bees are used in the growing of crops such as tomatoes, bell peppers and cucumbers.

The researchers first observed that the commercial bumblebees regularly flew in and out of vents in the sides of the greenhouses, escaping from the facilities.

The researchers then devised a mathematical model to predict how disease might spread from this "spillover" of runaway commercial bees to their wild cousins.