Ontario scientists are using caterpillars to combat an invasive aquatic plant

Ian Jones wades through a forest of aquatic plants, his feet sinking into the muddy ground. He's surrounded by invasive phragmites, a reed that can grow five-metres tall, and whose roots release biochemicals impeding the growth of other plants.

In this particular patch of land, near the Binbrook conservation area in southeast Hamilton, the phragmites haven't fully taken over. But in many parts of Ontario, the reed has outcompeted and replaced native species in previously diverse environments.

Jones is here on a mission, and if he and his team are successful, sites like this may yet resist the invasion.

Weaving between stems, he crouches down by a canister staked about knee-high off the ground. Opening the lid, he reveals his team's secret weapon: multiple tiny caterpillars. 

Since 2021, Jones' team has released over 21,000 caterpillars and larvae at around 30 locations across Ontario such as this. The Canadian Food Inspection Agency approved two moth species, Lenisa geminipuncta and Archanara neurica, for use as biocontrol in 2019. The caterpillars only eat phragmites, Jones said, and as they grow, they'll "hopefully" munch through three or four stems and "do a fair amount of damage to the phragmites."

WATCH | Ian Jones explains how his team is using moths to fight phragmites

"This biological control is hopefully something that will be longer term and sustainable," Jones told CBC Hamilton. 

In most cases they've seen, he said, the insects damage nearby phragmites, and in all cases where they've damage within a year, the moths return the year following.

"We know they're reproducing successfully in Canada and they're overwintering successfully, which are both big steps to make in the early stages of a biological control program."

The scientist is working with Ducks Unlimited Canada, federal department of Agriculture and Agri-Food Canada, the University of Toronto and the Centre for Agriculture and Bioscience International in Switzerland. 

In addition to canisters, Jones and his colleagues release caterpillars from cut phragmites stems they secure in florist foam blocks and leave on the ground. 

Jones said the caterpillars have been used in other countries, but it took about a decade for their potential impacts to be studied and approved in Canada. That research shows that the moths should only impact phragmites, he said. 

"We were very comfortable to start releasing them in Canada."

The work in Ontario extends from Windsor in the southwest, to North Bay, to east of Ottawa. Ducks Unlimited Canada helped select the sites based on a number of criteria including geographic distribution, the organization's Ontario invasive species lead Matt Bolding said.