Scientists in the school's Department of Environmental Health said their research provides "convincing evidence" of the link between imidacloprid and the phenomenon known as Colony Collapse Disorder, in which adult bees abandon their hives.
The problem is significant because bees are prime pollinators of roughly one-third of the crop species in the U.S., including fruits, vegetables, nuts, and livestock feed such as alfalfa and clover.
Massive loss of honeybees could result in billions of dollars in agricultural losses, experts estimate.
"The significance of bees to agriculture cannot be underestimated," Harvard researcher Alex Lu said in an HSPH release Friday.
"And it apparently doesn't take much of the pesticide to affect the bees. Our experiment included pesticide amounts below what is normally present in the environment."
Imidacloprid is one of a number of so-called neonicotinoid pesticides introduced in the early 1990s.
Bees can be exposed in two ways, the researchers said: through nectar from plants, or through high-fructose corn syrup beekeepers use to feed their bees, since most U.S.-grown corn has been treated with imidacloprid that is then present in the corn syrup.