The Canada thistle stem-mining weevil (Hadroplontus litura) is native to Austria, Britain, France, Germany, Switzerland, and southern Scandinavia; it is not native to Canada. The stem-mining weevil is an introduced species brought to Canada in 1965 as a biological pest control.

The adult lifespan of the stem-mining weevil is ~10 months. They overwinter in soil and leaf litter, and emerge in the spring to feed on rosette leaf foliage and stem tissue. Eggs are laid from May and June in the mid vein of the leaf and hatch 9 days later. The larva mine down through the stem into the root collar eating plant tissue as they go.

Previous research on Hadropontus litura has looked at geography. On the west coast of British Columbia and California, introduced weevils have not been as successful compared to those introduced in the Midwest (including Montana). Montana has a similar climate to Alberta suggesting weevils may prefer this environment.

The stem-mining weevil is an option for Canada thistle control in sensitive areas or together with other control methods.

If we can show a high success rate of Hadropontus litura on the control of Canada thistle this could mean:

• The option of using a biological control as an alternate means of pest control
• A possible reduction in chemical use
• Weed control in sensitive areas where other traditional methods are not an option

In 2012, as part of the provincial ARECA Environmental Team protocol, LARA released 1260 adult weevils across 4 sites. Each site was given a different weevil population size, but all had a thistle population density of 5 – 10 plants per square meter.

Sites were revisited in 2013 to 2016 to monitor plant damage and presence of weevils. Adults weevils were found and notable damage to the plants was observed.

If you are considering trying out the Canada thistle stem mining weevil on your operation you will need an import permit from the CFIA

Weevils can be purchased from

• Weedbusters Biocontrol, Montana
• Integrated Weed Control, Montana