Weevils Biocontrol

Tiny Weevils, Big Impact: Biocontrol at Spiva Butte and Lower Sleepy Hollow

This summer, Chelan-Douglas Land Trust (CDLT) teamed up with some remarkable little helpers to protect native habitat at Lower Sleepy Hollow and Spiva Butte: Larinus minutus and Bangasternus fausti—two species of seed head weevils that specialize in battling diffuse knapweed.

CDLT released about 500 of these tiny insects across both sites as part of our ongoing efforts to control the spread of this aggressive invasive plant. This exciting project highlights the power of using nature to restore balance to our natural areas.

These weevils might be small, but they’re highly effective. Larinus minutus targets knapweed by laying eggs inside its flower heads. When the larvae hatch, they feed on the developing seeds, reducing the plant’s ability to reproduce and spread. Bangasternus fausti takes a similar approach but also forms small galls inside the seed heads, making life even harder for knapweed.

Together, these insects are a powerful biological control team, giving native grasses and wildflowers more room to thrive.

We received these biocontrol agents through the Washington State University biocontrol program, led by Jennifer Andreas, Director of the Integrated Weed Control Project. Her team works with partners across the state to apply carefully studied natural enemies to restore ecological balance and reduce the impacts of invasive species.

It’s always exciting to see biological control in action and even more exciting to think about the long-term impacts these little beetles could have. We’ll be monitoring both release sites over the coming seasons and look forward to sharing updates as our weevil partners get to work!