Moth larvae enlisted in the battle against phragmites

Researchers from the University of Toronto and Agriculture and Agri-Food Canada with help from Ducks Unlimited are marking National Invasive Species Action Week by taking action against the phragmites in Windsor and Essex County.

They are introducing the larvae of two types of moths into two conservation areas which are supposed to eat into the stems of the phragmites and kill the plants.

"As caterpillars they bore into the phragmites stems and eat them from the inside out," said University of Toronto researcher Ian Jones.

"Then eventually they emerge as adults and then lay eggs underneath the leaf sheaths of these phragmites stems. So the next year, hopefully we have an even bigger population of these moths to start having a bigger effect ... year on year."

Jones recently placed six bunches of stems in various locations in the Petite Côte Conservation Area marsh in LaSalle. They've been injected with the larvae. As the larvae eat their way through the stems they will eventually move over to the phragmites plants in the marsh.

"We'll monitor these areas to see how these populations grow," he said.

Phragmites is an invasive species that is almost impossible to get rid of by any other means.

Kate Arthur, restoration biologist with the Essex Region Conservation Authority (ERCA) said it competes for space with the natural species of plants and makes it very difficult for wildlife to survive in the marsh.

Arthur said the biological control program is not a silver bullet.

"It won't actually get rid of [it] but the idea is that it will knock it back a little bit, which can then allow some of our native wetland species to start to regenerate." 

Phragmites is native to Switzerland, so Jones said when the program began in 1998, scientists searched the Central European country to find an insect that controls it.

The larvae of the moths chosen, the Lenisa geminipuncta and Archanara neurica, only eat phragmites stems and do not affect other plant species. 

"Even when we found those insects we do years of house range testing and risk assessments to make sure that if we release these insects in Canada they're not going to do any damage to any other Canadian species," said Jones.

According to a news release, over a decade of intensive research and testing was conducted by an international research team from Switzerland, Canada and the USA before the moths were approved for release in 2019 by the Canadian Food Inspection Agency.

"Since that time we've released nearly 40 sites. At almost all those sites where we've released we've seen damage from the moths in the year of release. And beyond that in subsequent years we've seen damage in 100 per cent of those sites where the initial releases worked," according to Jones.

Last year, larvae were released in the Collavino Conservation Area in Amherstburg. Jones said they will be back later this summer to check the progress of that site where he said they have already seen some success. He will also check the progress at Petite Cote.

Jones said they are also putting moth eggs in special containers which will allow the larvae to drop out and attack the phragmites, but those are being done in other areas of the province.