By Olivia Bergeron

I joined our friends at Park County Weed and Pest for a fascinating field tour to locate the Houndstongue Root Weevil. These weevils, Mogulones crucifer, have been used in Canada since 1997 to manage populations of houndstongue, Cynoglossum officinale, an invasive biennial plant with reddish-purple flowers and prickly seeds that cling to fur and clothing. All parts of the plant are toxic, containing pyrrolizidine alkaloids, which can be fatal to horses and cattle if ingested. Houndstongue was introduced to North America from Europe in the mid-1800s.

My curiosity about these insects started with a simple question. I asked Mary McKinney if there were any interesting bugs I should add to my insect identification game at Livingston Elementary's STEM Day. The next day, she walked into our office with two funny-looking insects. They resembled ticks in size and shape, but on closer inspection, I noticed a distinct white cross on their backs and long, snoutlike faces.

These weevils feed on the houndstongue plant and lay eggs in its root system. In Canada, they have been so effective in wiping out houndstongue populations that the weevils themselves often die off soon after due to a lack of food. While they have shown a high level of host specificity, they are not approved as biocontrol in the United States due to the risk they might impact other species in the borage family under extreme conditions.

Since these weevils are already here however, it is legal to move them as long as they do not cross state lines. Mary invited me on a field tour to collect some with Weed and Pest staff from across the state. To my surprise, we were each given an aspirator. They explained that these weevils were quite shy insects. When they sense nearby movement, they curl their legs up and fall to the ground where they blend right in with the soil. These aspirators allowed us to suck each weevil off the aerial parts of the plant without alerting the rest of the weevils.

We visited three sites at different stages of houndstongue invasion. The first area’s houndstongue had been almost completely wiped out. Every remaining plant had small, circular holes in the leaves left behind by weevils. Grasshoppers will occasionally eat houndstongue as well, but the weevils leave smaller, rounder bite marks. Weevils had only moved to our second field site recently, and there were still many healthy houndstongue plants. The weevils were thriving, so this second site was our most successful collection site. Our third site had only just been discovered by the weevils, so we did not collect many there. By the end of the day, I had collected 88 weevils!

Mogulones crucifer was first spotted in Park County in the fall of 2022 along the Game and Fish river access road off Road 2AB. Their presence here has already given Weed and Pest hope in the treatment of a particularly noxious invasive. The weevils we collected will be transported throughout the state to be released at other houndstongue-infested sites. Next time you see houndstongue’s distinct red and purple flowers, take a look and see if you can find these fascinating little insects!