Impact of Stem Mining Weevil (Hadropontus litura) population density on Canada Thistle Suppression
Canada thistle (Cirsium arvense) is an aggressive, colony-forming perennial weed which reproduces by both seeds and horizontal creeping root systems. It is listed under the Alberta Weed Control Act as noxious. Canada thistle has a high tolerance to many different environmental conditions and is highly competitive with other vegetation. It is prevalent in many locations such as riparian areas that do not allow for chemical or mechanical control methods.
The adult lifespan of the Stem Mining Weevil, Hadropontus litura, is approximately 10 months as they overwinter in the soil and leaf litter, and emerge in the spring to feed on rosette leaf foliage and stem tissue. Eggs are laid in May and June in the mid vein of the leaf and eggs hatch 9 days later. The larva mine down the stem into the root collar consuming plant tissues.
The majority of previous research on Hadropontus litura has been dependant on geographic location. On the west coast of British Columbia and California the weevils have not been very successful compared to the Midwest including Montana. Montana has similar climate to Alberta, therefore weevils may be effective across the region.
Hadropontus litura offers a viable option for Canada thistle suppression in sensitive areas or in conjunction with other control options. The success of Hadropontus litura on suppression of Canada thistle will demonstrate:
- Use of 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 able to be utilized
In 2012, as part of the provincial ARECA Environmental Team protocol, LARA released 1260 adult weevils across 4 sites at various population levels. Each site had a Canada thistle population density of 5 – 10 plants per square meter. Sites were revisited in 2013 to monitor for plant damage and presence of weevils. Adults were found this past year and notable damage to the plants was observed. Sites will continue to be monitored in 2015.