Firefighters battling a wildfire that has blackened nearly 290 square miles and burned 26 homes faced a new challenge, authorities said Wednesday: bees.

The blaze that started with lightning on Aug. 22 has forced hundreds to evacuate. After being grounded by smoke for a day, firefighting helicopters returned to work Wednesday, pouring water on the fire that was 45 percent contained.

Bee stings among firefighters have surged to as many as 50 a day, information officer Joan Dickerson said. Some of those stung required medical attention.

"We've had a couple of our leaders taken to the hospital," she said, but added that she had no explanation for the surge in stings.

An evacuation order for 265 homes remained in effect, three days after it was issued. An alert for evacuation readiness covered another 20 homes.

Smoke from the fire and others triggered air-quality warnings in southwestern Montana. The Department of Environmental Quality said the air in Bozeman and in the area of the fires was "very unhealthy."

Smoke may linger until Friday, forecasters said.

"We're not sure what the weekend is going to bring," Dickerson said. "We're prepping for a cold front" that could shift the wind.

Air quality advisories were also issued across eastern Washington state, warning residents to take precautions against heavy smoke from more than a dozen wildfires.

U.S. and Canadian fire crews were working together on two blazes, the larger of which had burned almost 255 square miles northeast of Winthrop. Nearly 1,400 firefighters were battling the blaze, which was 56 percent contained.

The smaller fire, which had burned more than 53 square miles, had already crossed into British Columbia and could pose a threat to dozens of cabins in the Pasayten River Valley, about 125 miles east of Vancouver. Residents in Eastgate, which has about 50 year-round residents and an estimated 180 cabins, were put on notice they might have to evacuate.

Helicopters and tankers were grounded for a second day Wednesday due to the heavy smoke, said Kelly Baraibar, a U.S. Forest Service spokeswoman.

Several other wildfires burned across Washington, including three reported Wednesday on the Yakama Indian Reservation. A 145-square-mile fire complex near Dayton in southeast Washington was 40 percent contained. Owners of 50 to 75 cabins in the area remained evacuated, said Mike Ferris, Forest Service fire information officer.

In California, a Department of Forestry and Fire Protection plane with a pilot and firefighter aboard crashed Wednesday in remote foothills of Tulare County, about 70 miles southeast of Fresno.

Department spokeswoman Becki Redwine could not confirm whether they were alive. The names of the pilot and firefighter were not released.

The pilot was contracted to help battle a fire about 170 miles north of Los Angeles, Redwine said. The crash sparked a three-acre wildfire near where firefighters battled the other blaze.

Officials were investigating the cause of the crash.

In Nevada, crew leaders were hoping the arrival of more firefighters would help them gain ground on wildfires that have blackened nearly 375 square miles across the state's northeastern area during a four-day span.

Officials reported 32 fires touched off by lightning since Sunday, including one in Lander County that had exploded to more than 200 square miles and was only 10 percent contained.

No damage to homes or injuries were reported, but the fires continued to pose a threat to scattered ranches and mines as well as wildlife habitat, said fire information officer June McMillen.

McMillen was unsure how many new firefighters would join the lines Wednesday.