Vancouver's wild winter weather could aid battle against invasive beetle

Fluctuating winter weather in Vancouver,which sawwarmer January temperatures turn coldinFebruary, may have helped kill an invasive beetle with a ferocious appetite for plants, according to a University of British Columbia scientist.

Juli Carrillo, who studies plant-insect ecology and evolution at UBC, says the grubs of the Japanese beetle, which spend the winter in the soil, mayhave been lured to the surface during January's warm spell, but then frozeas below normal cold temperatures set in.

"Similar to the early flowers we saw in January, that bloomed and then died from the cold," Carrillo wrote in an email to CBC News.

In 2019, Vancouver experienced the coldest Februarysince Environment Canada began recording weather data in 1937.

"Sudden and prolonged freezing temperatures that cause those upper soil layers to freeze could potentially limit the beetle's population growth this year," wrote Carrillo.

The Japanese beetle was first discoveredin B.C. in Vancouver's False Creek in 2017. The beetle, Popilliajaponica, is a invasivepest that feeds on the roots of grass and the foliage of more than 300 plant species.

• Invasive Japanese beetle spotted in False Creek

Plants into skeletons

It's unclear how the pest came to B.C., but mostlikely it arrived on plants transported from other regions.

The province says the beetleposes a serious risk to plants, trees and agricultural crops.The pests turn healthy plants into skeletons by eating their soft green parts, ultimately causing the plants to die.

Adults have an oval outline and are approximately 10 millimetres long and 6 millimetres wide, with metallic green abdomens and heads, copper-brown wing coverings and white tufts of hair along their sides and rear.

• 'We are very worried about it escaping the area': Vancouver launches a battle against the Japanese beetle

Since the beetlewas discovered, the City of Vancouver along with the province and the federal government have worked together on measures to prevent its spread.

They'vesprayeda larvacideto kill the grubs, which livein soil, and also trappedadults. They have also restrictedthe movement of plants and soil and have askedpeople to report sightings.

There are no adults present in the wintertime, but grubs, which emerge from the soil in late June or early July, spend the winter underground eating on the roots of grass.

However, the province is not so certain the cold weather madea dent in Japanese beetle numbers.

The Ministry of Agriculture says grubs bury deep into the soil during winter and are also insulated by snow on the ground. While the cold may have killed some grubs, the most the cold weather will do, it says, is delay the time when grubs emerge from the soil and develop into adult beetles.

"We do not expect the temperatures were severe enough to significantly impact the overall larvae population," said the ministry in a statement.