What is a Weevil?

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By Ty Reinnemann

Find out what the ERC Pesticide Action interns were up to this summer!

Cyphocleonus achates (Cypho), commonly known as knapweed root weevil, overwinters in the large taproots of the spotted knapweed. This aggressive invasive weed has wreaked havoc on the American rangelands and forests since its introduction. Thus a solution had to be found that didn’t revolve around yearly spraying of glyphosate and other herbicides. A growing field has emerged in controlling weed populations by introducing their natural predators. This biological control method is usually focused on the insects that live on the seeds, roots, or foliage of a specific plant. This reduces seed viability and plant survivability to help reduce biodiversity loss. Although biological control is not restricted to insects, my past experiences have been with Cypho and Larinus ssp. (knapweed flower weevils). When paired together, these two species will reduce adult survivability and seed production of both spotted and diffuse knapweeds.

Figure 1. Two seedhead weevils like feeding on or laying eggs on spotted knapweed flower.

Introducing non-native insects to control non-native plants is a logical solution based solely on how these plants quickly over compete in native ecosystems. The chemical defense of knapweed and other weeds are currently unchecked and unbalanced. While livestock can graze some weeds, many native animals have not taken any interest to the weeds. This is where many government agencies and universities got involved studying insects. After decades of research in labs, the USDA began permitting the release of biocontrol insects. Some programs, especially for agriculture, started as early as the 1880’s. In central Idaho, spotted knapweed and diffuse knapweed have begun to devastate our treasured sagebrush habitat. These plants use allelopathic chemicals in the soil to outcompete native plants, especially in recently disturbed areas: trails, parking lots, pullouts, and burned areas.

While in college, I worked the summers of 2015 and 2016 in the Sawtooth National Forest. During that time, I began monitoring biocontrol treatment sites as well as other weed control methods. I also helped maintain our forest’s Cypho insectary. Lastly, I released my own group of Cypho on a field of spotted knapweed in the forest. This hillside had been turned into a monoculture of knapweed because it was inaccessible to herbicide treatments. Insects are currently the only treatment feasible for some remote and environmentally sensitive areas.

Figure 2. Adult Cypho found on basal leaves of spotted knapweed.

This year I got accepted to graduate school at University of Idaho and headed back to Idaho. The Environmental Resource Center luckily hired me again for one last hurrah. This year I was excited to work with Jake Gorham, a senior in high school. As I was once mentored in this field, I hoped to pass on my knowledge and passion to Jake. This summer we worked closely with the Ketchum Ranger District of the Sawtooth National Forest on a number of projects. In addition to continuing the invasive weed monitoring, we established native seed collection areas and begun a new aspen monitoring program. Native seed banks from the local area are extremely important, not only restoration projects, but to saving the local genetic biodiversity that promotes unique phenology. The Sawtooth National Forest has an extensive history of wildfires that is both opportunistic for native and non-native plants. With the ability to have seed ready to disperse after a fire, our community will help preserve our native landscapes.

Figure 3. One year after the Sharps Fire. Aspen shoots already three to four feet tall.

Fires that partly or fully burn aspen stands cause the trees to send up new stems to recolonize. Our monitoring this summer was focused in the postburn area of the Sharps Fire from July of 2018. With the guidance of the Western Aspen Alliance and the Salmon Valley Stewardship, the Sawtooth National Forest started a monitoring program to follow the recovery of the aspen stands. As the so called “asbestos forest” does indeed burn, aspen stands recovery remarkably faster than their pine tree neighbors. Aspens provide habitat for an immense amount of biodiversity that is found nowhere else.

I feel a great honor having the support of the National Forest Foundation this summer; without them I would not have the ability to help my community. In addition, this internship could not be more tailored to my interests of community education and forest health. I hope to continue these goals long into my future.

*Blog written for National Forest Foundation

What is a Weevil?