The City of Toronto is sending a helicopter into the skies over parts of Etobicoke today, to spray an insecticide designed to target European Gypsy Moths.

The spraying had been due to begin Sunday, but had to be rescheduled because of windy conditions over the weekend.

Gypsy moths have become a threat to the city’s trees and city officials say infestation levels have reached a point where the usual manual control methods of egg scraping, sticky traps and ground spraying are no longer effective.

In its caterpillar stage, the gypsy moth eats tree leaves and causes the trees to become susceptible to disease and damage from weather or other insects.

To slow the spread of the bug, the city is spraying an insecticide called Btk, or bacillus thuringiensis subspecies kurstaki. The insecticide contains a naturally occurring bacterium that kills the moth’s young caterpillars when they eat the sprayed leaves.

The insecticide does not affect adult moths, butterflies, other insects, honeybees, fish, birds or mammals, the city says.

“Btk, when used as directed and sprayed by air, is not considered a health risk to humans,” the city said in a news release Sunday.

“No special precautions are required for residents in the spray zone. However, if you wish to avoid exposure to Btk, remain indoors during and immediately after the spraying. Residents can also cover patio furniture or outdoor playing areas prior to the spraying or hose them off afterward,” the city said.

The first spray day took place Monday, between 5 and 7:30 a.m. in seven areas of Etobicoke, while the second spray will take place in four more areas Tuesday morning:

  • Moore Park
  • Cherry Beach Park
  • Toronto Island Park
  • Tam O'Shanter Golf Course

A two-engine helicopter flies at a height of approximately 15 to 30 metres above the tree tops during the application.

The spraying will lead to local road closures, to minimize any potential risks associated with the low-flying helicopter. Notification signs will be posted along local roads to announce the closures, the city says.