Invasive moth didn't exist in Ontario until 2018 and now it's everywhere

An invasive moth species that first appeared in Toronto eight years ago has since taken over much of Ontario, and its favourite food might be growing right in your backyard.

As its name suggests, the box tree moth (Cydalima perspectalis) is an invasive pest native to Asia that feeds on boxwood plants. Although it wasn't documented in Ontario until 2018, the species has since rapidly spread across the province and into other parts of Canada, including Quebec, New Brunswick, Nova Scotia, Prince Edward Island, and Newfoundland and Labrador.

The species is suspected to have entered Ontario via a shipment of boxwoods from Europe, after which several specimens were reported in late August 2018. This summer, dozens of sightings across Ontario have already been reported on the biodiversity social network, iNaturalist.

Box tree moth observed near Hamilton, Ont. Photo: nikolett6ttn/iNaturalist.

Now a regulated pest in Canada, the pest is particularly problematic due to its ferocious feeding on the foliage of boxwood plants, which are commonly used in gardens and landscapes throughout southern Ontario and beyond.

Adults have an average wingspan of four centimetres, and typically come in two colour variants. The first, more common variation features white wings with thick dark brown borders, while the second, less common variation has brown wings with a small white streak on the forewing.

According to the Invasive Species Centre, two generations of adult moths have been observed in Ontario, one in late June to early July and the other in late August to early September.

During a heavy infestation, box tree moths can completely defoliate host plants, and even after all the leaves are gone, they'll move on to feeding on the bark, which effectively kills the plant. Box tree moth caterpillars are particularly known to feed ravenously on host leaves, leaving behind skeletonized foliage.

Box tree moth observed in Newmarket, Ont. Photo: medeajade/iNaturalist.

According to the federal government, if you have boxwood plants on your property, you should inspect them from May to September for any signs of the pest. Adults, pupae, mature larvae, and leaves with eggs on them can be removed by hand and destroyed by placing them in alcohol, soapy water, or an airtight container.

Larvae can also be controlled with a biological pesticide that contains Bacillus thuringiensis subspecies kurstaki, although multiple treatments may be required to control their spread.