Earth Notes: Stem-Boring Weevils
This summer nearly five thousand weevils were released in the Pipeline Fire burn scar north of Flagstaff. No larger than a fingernail, they have elephant-like snouts and a black, metallic-blue complexion. The weevils were released with one purpose in mind: to control populations of invasive Dalmatian toadflax.
Dalmatian toadflax is an ornamental and medicinal plant that has permeated much of the American west and displaced native plants. It tends to flourish in areas burned by wildfires.
The plant can produce half a million seeds annually and remain viable in the soil for ten years.
The weevils evolved alongside toadflax in its original range in Europe and Asia, and are its natural predator. Weevils are host-specific, meaning they eat nothing else. Adult weevils overwinter in toadflax stems and emerge in spring, with female weevils laying eggs in the stems quickly afterward. Larvae hatch, feed on the stem, grow into adults, and hibernate until temperatures are warm enough to emerge again.
The U.S. Forest Service introduced these stem-boring weevils in Montana in 1996 and have used them in Northern Arizona for nearly a decade.
When combined with traditional methods like hand pulling, the weevil is a formidable way to avoid large toadflax monocultures and conserve native plants.