Honeybees at work on their hive.

Home Depot and Lowe's are under fire for selling pesticides that some believe are partly to blame for killing billions of the nation's honeybees.

Petitions with thousands of signatures are being delivered to the home-improvement retailers this week, demanding they stop selling the pesticides—called neonicotinoids—along with any plants in the stores that have been treated with them. Neonicotinoids are the most widely used class of pesticides in the world.