The City Council in late June voted to ban city purchase and use of neonicotinoids. The ban does not apply to private use.
"There is enough evidence that it is harmful to bees," said City Council president Ben Stuckart, who pushed for the ban. "We should be a good global citizen and set an example."
The ban covers about 30 percent of the land in Spokane, including streets, parks, and rights of way, Stuckart said.
"Bees are so important we should be leading the way to protect them," he said.
Eugene, Oregon, last year became the first city in the nation to ban use of neonicotinoids. It is not clear how many other cities besides Spokane have followed.
The push to ban the pesticides in Spokane began more than a year ago, when more than 50,000 bumblebees died while feeding on linden trees in Wilsonville, Oregon. The cause turned out to be a company that applied a neonicotinoid-based spray to blooming trees in violation of label directions.
Officials for Monsanto, which uses neonicotinoids in some of its products, did not immediately return telephone and email messages seeking comment on the bans.
The nicotine-like insecticide has been around for years and is popular because of its low toxicity in mammals, birds and other higher-order animals. Neonicotinoids act on specific types of receptors in the nervous system of insects.
There are currently seven different kinds of neonicotinoids commonly available in insecticides for home and garden use on shrubs, trees and lawns. They also kill certain beetles, fleas, wood-boring pests, flies and cockroaches.
But several recent studies have indicated that prolonged exposure to neonicotinoids may build up in bees and other beneficial insects. As a result, the bees' ability to forage for nectar, their ability to learn and remember where flowers are located, and their ability to find their way back to the hive may be affected.
There is still no conclusive evidence that neonicotinoids are the cause of the huge declines of honeybees and other pollinators.
The neonicotinoid family includes acetamiprid, clothianidin, imidacloprid, nitenpyram, nithiazine, thiacloprid and thiamethoxam.
A 2012 study showed the presence of two neonicotinoid insecticides, clothianidin and thiamethoxam, in bees found dead in and around hives situated near agricultural fields. Other bees at the hives exhibited tremors, uncoordinated movement and convulsions, all signs of insecticide poisoning.
An October 2013 study by Italian researchers showed that neonicotinoids disrupt the immune systems of bees, making them susceptible to viral infections.