Mosquitoes, caterpillars normal amid concern for ash trees

Some of Saskatoon’s more noticeable insects are behaving normally for this time of year, but the city’s chief bug expert says he’s worried about a pair of invaders that target ash trees.

City of Saskatoon entomologist Jeff Boone told 650 CKOM that while the city doesn’t have a formal monitoring program for tent caterpillars, it appears they are subsiding for the year.

“We’re mostly seeing the feeding period has ended, typical for this time of year.”

Boone said outbreaks typically last between three and seven years. With other parts of the province reporting tent caterpillar populations starting to collapse, he said he was hopeful Saskatoon could soon be done with the ugly but harmless swarms of bugs.

“So we could be coming to the end of our outbreak cycle, which started about 2015 in Saskatoon,” he said.

Dry weather keeps mosquito numbers down

While those getting out to enjoy the warm weather will doubtless have taken a few bites, Boone said mosquito numbers are about where they should be for this time of year.

“A lot of the precipitation that we’re getting, it’s soaking in very quickly so it’s not leaving a lot of standing water for mosquito habitat,” he said.

He said city traps have so far been free of the Culex tarsalis species of mosquito — which can carry West Nile virus.

“It’s usually a later season mosquito that tends to peak around that August long weekend,” he said.

The city has a spraying program for larger bodies of water, but Boone said people can do their part to keep the bloodsuckers at bay by making sure to remove sources of standing water in their yards.

He said that means putting mosquito netting over rain barrels, draining things like kiddie pools and making sure to regularly change water in bird baths.

Invasive species targets Saskatoon ash trees

The city is currently dealing with an outbreak of cottony ash psyllid, an invasive species that devours black ash trees.

“It’s kind of similar to an aphid, in that it’s a piercing sucking insect. It feeds on the new buds as they’re developing,” Boone said.

An adult cottony ash psyllid. (Natural Resources Canada)

The city came into the year with about 7,000 potentially affected black ash trees. They’ve already had to remove 1,000 of those, with Boone estimating they’ll have to take out and replace at least 2,000 to 3,000 more.

“This insect, probably combined with dry conditions, caused the decline of a lot of trees in a very short period of time,” he said.

Boone said there doesn’t seem to be an effective spray to control the psyllids, which makes handling the outbreak a matter of trying to manage tree losses as best as possible.

He said the psyllids likely first came to Saskatoon in 2006 via infected tree nursery stocks, which is a common way for the bug to move from place to place.

Concern in Saskatoon as major bug outbreak hits Manitoba

While the cottony ash psyllid has already established a presence in Saskatoon, Boone said he’s far more worried about the emerald ash borer, a tiny green beetle native to Asia that’s been causing major damage to North American ash tree populations over the last several years.

“The cottony ash psyllid is a story that’s just telling us a little bit about the potential impact of an invasive species,” he said.

Emerald ash borers, a type of beetle native to Asia, feed on green ash trees. (Government of Ontario)

The psyllids stick to black ash or mancana ash trees, but the emerald borer targets green ash, which is much more common in Saskatoon.

Boone said there are about 27,000 green ash trees in the city. He explained the tree became popular during the 1980’s, when concerns about Dutch Elm disease prompted a shift to planting ash trees.

He said green ash is especially common to newer parts of Saskatoon located outside the boundary of Circle Drive.

Emerald ash borers were first spotted in Canada in Windsor, Ont. in 2002, according to Natural Resources Canada.

They’ve since moved west and have now been found in Manitoba.

Boone said the impact in Saskatoon could be major if the beetles make their way here.

“It’s very important not to move firewood. Infested firewood is the number one way this insect is being moved around,” he said.