London plans to spray for gypsy moths: Here's what you need to know

Facing a difficult infestation of tree-killing gypsy moths, the city is considering a limited aerial spraying program aimed at killing the caterpillars before they can consume the trees.

Staff report lays out plan to use the BTK bacterium to help save city trees

The city of London is considering a program to carry out aerial spraying to help control the spread of gypsy months, whose voracious appetite can decimate trees. (Submitted)

The city's planning committee on Monday endorsed a staff report that lays out a plan to combat an ongoing infestation of European gypsy moths. The plan still needs to be ratified at full council, but here's what you need to know about the spraying program under consideration. 

What are gypsy moths? 

European gypsy moths are an invasive and voracious species brought to Canada from Europe in the 1860s. A plan to import and breed the moths with local species to create a domestic silk industry didn't pan out and worse, the moths escaped and spread.

The moths and the damage done

Each gypsy caterpillar can consume up to a square meter of tree foliage. Continued over time, this defoliation this can weaken trees or kill them outright. Oak trees are particularly vulnerable, which is a problem because each oak supports multiple species. Gypsy moth infestations come in cycles that tend to peak about every 10 years or so and each outbreak can last a few years.

The staff report says the current EGM infestation in London is "healthy, growing and stable, and has resulted in unprecedented levels of tree defoliation."

What would be sprayed? 

The staff report calls for a controlled aerial spraying of the Bacillus thuringiensis kurstaki (BTK) in select city parks.

Gypsy moth caterpillars crawl on a tree outside London, Ont, in 2020. (Travis Dolynny/CBC)

BTK is a bacterium found naturally in soils and only becomes toxic when it gets inside the gut of a specific group of caterpillar-type insects, including the kind that turns into gypsy months. "Because of this, it does not affect adult moths and butterflies, other insects, honeybees, fish, birds or mammals," the report says.

Jeremy McNeil is a biologist at Western University whose work has contributed to the development of ecologically acceptable alternatives to insecticides for pest management. He said BTK has the potential to affect other insects but said this should be minimal if the spraying is done carefully. As for concerns about affecting caterpillars that turn into Monarch butterflies? He said this isn't a big worry because Monarch caterpillars feed on milkweed which grows in fields, not forests. 

Included in the report to council is a statement from the Middlesex-London Health Unit that BTK poses "little threat to human health."

Jill-Anne Spence is the city's manager of urban forestry and says they've studied two years worth of data in areas with significant stands of oak trees. They plan to pinpoint areas with significant stands of oak that were badly defoliated last year. 

"In some cases over 90 per cent of their leaf mass has been lost over the past two seasons and the goal is to help them get through this year," said Spence. 

Where will it be sprayed and when? 

The aerial spraying will happen using a helicopter at the following five locations on public land in London:

  • Fairmont Park.
  • Grandview Park. 
  • Griffith Street Park.
  • Crestwood Woods.
  • Somerset Woods.

The spray is most effective once the leaves are out in spring and shortly after the caterpillar hatches. Weather, including wind and rain, are other factors that affect the timing but generally spraying happens in late May or early June. 

What else is being done?

There's also a plan to carry out backpack spraying at the following locations: 

  • Springbank park. 
  • Thames Valley Golf Course.
  • Clara Brenton Woods.

Also, homeowners can help by scraping egg sacks off trees on their own property. 

In this video Spence demonstrates how that's done. 

How to remove gypsy moth egg sacs

2 years ago
Duration 2:40
Jill-Anne Spence, the manager of urban forestry for the City of London, explains how to remove gypsy moth egg masses.

City crews will also scrape egg masses off trees on 37 streets in the following areas: 

  • Somerset/Byron.
  • Oakridge/Sanatorium Road.
  • Hamilton Road/Fairmont Park.

What's next?

If council clears the plan, the city has to get permits for the spraying from the provincial environment ministry and the federal transport ministry. After that, notification will go out on social media.

The city has more information about gypsy moths and how to reduce their numbers at this website