Nearly 25 years of research precedes release of seed-feeding weevil to fight garlic mustard in North America

After nearly 25 years of research, permission has been granted by the Canadian Food Inspection Agency (CFIA) to release the seed-feeding weevil Ceutorhynchus constrictus to sustainably control invasive garlic mustard plant in Canada.

Garlic mustard (Alliaria petiolata) was accidentally introduced to North America in the 19th century. It is one of the few non-indigenous herbaceous species that can invade and dominate the understory of North American forests.

The plant blocks sunlight to native species, stunting their growth and out-competing them for moisture and vital nutrients. Its spread has also been negatively impacting the rare West Virginia white butterfly (Pieris virginiensis).

Garlic mustard is considered one of the most serious invaders

After nearly a quarter of a century of research, the seed-feeding weevil Ceutorhynchus constrictus has been approved for release to sustainably control invasive garlic mustard in Canada (Credit: CABI).

In the northeastern and midwestern USA and eastern Canada, garlic mustard is a serious invader and control methods include hand removal, burning, cutting and herbicide treatments to reduce large densities.

However, these treatments are costly with the size of the invasion and require repeated effort over several years and in the case of herbicides may not be possible at all sites.

With partners at the University of Minnesota, Agriculture and Agri-Food Canada and the University of Toronto, CABI has investigated the possibility of using specially selected and tested insects from the native range to safely control the plant’s spread and impact in the introduced range.

CABI’s work with colleagues from the University of Minnesota has demonstrated that C. constrictus has the potential to achieve considerable impact on garlic mustard populations.

Provide an effective way to control garlic mustard

A CABI scientist conducts research into the seed-feeding weevil Ceutorhynchus constrictus to sustainably manage invasive garlic mustard in Canada (Credit: CABI).

In February 2025, the release of the seed-feeder was recommended by the USDA-APHIS Technical Advisory Group (TAG) for the USA, and it was approved by CFIA for release in Canada.

Dr Rob Bourchier, of Agriculture and Agri-Food Canada, said, ″Weevils from a rearing colony at CABI in Switzerland will be shipped to Agriculture and Agri-Food Canada and field releases are expected in spring/summer 2025.″

Dr Jeanie Katovich, researcher at the University of Minnesota, said, ″The ability to release C. constrictus into areas with garlic mustard in Canada is great news. Garlic mustard spreads exclusively by seed, so release of this seed-feeding weevil can reduce the number of garlic mustard seeds produced. The release of C. constrictus, in combination with the crown-mining weevil, C. scrobicollis, provides a method for long-term management of garlic mustard in woodlands.″ 

Project page

Find out more about CABI’s work on the biological control of garlic mustard from the project page here.