West-Central Forage Association

Canada Thistle Stem Mining Weevils

*Orders now being accepted for 2017 delivery* (Orders must be in by June 15, 2017)

The Canada thistle stem mining weevil (Hadroplontus litura, formerly Ceutorhynchus litura), is a tiny insect introduced from Europe as a biological pest control agent against Canada thistle.

The bugs; which have been allowed in Canada since 1965, and in the US since the early 1970’s, restricts its feeding to this weed and a few close relatives, making it a natural choice for biological pest control.

The weevils are released into thistle infestations in the fall, when they are in their adult stage. These adults will live on the plants, eating the leaves, until heavy frost occurs in the fall, when they will then hibernate.

After wintering, last year’s adult weevils emerge in early spring as the first thistle rosettes begin to appear. The adults are present for several weeks, mating and feeding on the foliage of the Canada thistle.

Females lay their eggs into holes they make in the leaves of a young rosette.

When the larvae hatch a week or so later, they tunnel through the leaf into the lower stem and down to the root collar.

In early summer, once fully fed, the larvae emerge from the thistle shoot through small exit holes that they chew near or just below ground level. They work their way into the soil, and undergo metamorphosis. In late June to early July, after two to three weeks, the new adults emerge from the soil and continue to feed until winter.

Upon release at new locations the bugs spread slowly. Canadian field studies have shown an average spread of 90m in 6 years, but studies out of Montana have seen migration of 9km, 10 years after release.

Weevil feeding may allow a variety of other micro-organisms to enter the thistle stem, with adverse consequences for the thistle: field studies in Montana indicated that underground parts of stems are much more subject to winter kill if the aboveground stem is attacked by weevils during the growing season. Sites where weevils have been released have generally shown decreased stand vigor and patches thin out over time.

WCFA has been working to bring this chemical free weed control option to local producers since 2011. In the first year, 70 dishes (each containing 105 weevils individuals) were imported from Montana and introduced into local thistle patches. In 2012, 100 dishes were released; including 58 dishes for a regional trial set up by the Agricultural Research and Extension Council of Alberta. 90 trays were imported in 2013, and 240 trays in 2014. Numbers have continued to grow since 2014, with 790 trays having been ordered in 2016 for producers throughout the province. We are expecting numbers to continue to grow moving forward. 

New for 2017: We will begin using multiple suppliers for weevils to help ensure that we are able to supply weevils to all those that are interested in using them, as demand has grown substantially over the last few years. 

This project is currently being funded by: Stewardship Alliance for Conservation Agriculture (SACA)/Agriculture Opportunity Fund (AOF)

For more information view: Weevil Fact Sheet