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Thursday, October 6, 2022
Keeping it Green: Niagara faces gypsy moth population boom

This year’s surging gypsy moth population is threatening Niagara's meagre tree cover.

This invasive species prefers to eat oak, but will strip leaves from a variety of species, including birch, maple, beech, and even some coniferous trees.

A Very Hungry Caterpillar: Native to Europe, the gypsy moth was introduced to North America in the mid-1800s. Researchers had hoped to turn fine strands produced by these caterpillars into silk.

The caterpillars, which can each eat one square metre of leaves, spread after they were released in Massachusetts. They were first detected in Ontario in 1969 and infestations now exist as far north as Sault Ste. Marie.

Gypsy moth eggs hatch in spring and the caterpillars climb trees to eat new leaf growth. They may use their silk strands to drift to new food sources, including understory plants – shrubs and smaller plants below the tree canopy.

This week, I was dismayed to see hundreds of tiny caterpillars munching buds on my transplanted beech tree.

A Quick Shapeshift: Once they mature, gypsy moth caterpillars are four to six centimetres long, with tufts of hair and pairs of blue and red spots on their back. They might be mistaken for native tent caterpillars, which are also hairy, but have blue stripes and elongated white spots.

Mature caterpillars feed mostly at night, which can make them difficult to detect, but helps protect them from heat and hungry birds.

Gypsy moth caterpillars change into pupae in mid-July. They undergo metamorphosis in hairy, reddish-brown cocoons and emerge as adult moths in one or two weeks.

Female moths, which can't fly, are white and larger than males. They lay tawny brown egg masses on tree bark in late summer.

A Formidable Army: A group of caterpillars is called an “army” and gypsy moth caterpillars certainly fit the bill.

Large outbreaks occur every seven to 10 years, but Ontario's Ministry of Natural Resources and Forestry predicts that this year, the caterpillars could remove 75 per cent of leaves from infested trees.

Diseases and predators keep gypsy moth numbers in check. However, the fungus Entomophaga maimaiga that naturally reduces moth populations thrives in cool conditions.

Similarly, gypsy moth eggs are killed off by extended winter cold periods. Climate warming is likely making these natural mitigation measures less effective against the invasive species.

While leaf damage by caterpillars does not always kill trees outright, it makes them more likely to succumb to other pests or heat stress.

In such a bumper year for gypsy moths, taking individual action reduces damage and limits future infestations.

Wrapping burlap around tree trunks traps caterpillars that shelter during the day. At night, they can be dealt with by soaking the burlap with soapy water.

Bacillus thuringiensis kurstaki (Btk) bacterium can also be used before caterpillars pupate. This spray treatment is available locally from Home Hardware, Minor Brothers and other hardware stores, and should be applied in the evening since it breaks down in sunlight.

Because Btk is toxic to butterflies and moths, it should only be applied to leaves affected by gypsy moth caterpillars. Avoid spraying nearby flowering plants, but the Niagara Peninsula Conservation Authority notes that many species, including monarchs, are unaffected because these caterpillars hatch later in the year.

In June and July, keep an eye out for cocoons and destroy them. This fall and winter, we can also turn hikes into scavenger hunts by scraping gypsy moth eggs off trees.

Minor Brothers also carries pheromone traps for adult moths that can be deployed later this summer.

Kyra Simone is a NOTL-born nature lover with a master's degree in biology. In her spare time, she advocates for sustainable change, picks up garbage, makes recycled jewelry, and transforms furniture bound for the landfill.