- Leafy Spurge
- Knapweeds
- St. Johnswort
- Yellow Starthistle
- Musk Thistle
- Canada Thistle
- Tansy Ragwort
- Toadflax
- Poison Hemlock
- Purple Loosestrife
- Educational Materials
(insect photographs)

Musk Thistle Insects

Thistle Rosette Weevil
Trichosirocalus horridus
The Thistle Rosette Weevil, Trichosirocalus horridus, attacks the rosettes and interrupts the apical dominance of the plant. Females often lay over 2000 eggs with the subsequent larval feeding stimulating the plant to form a multi-branched growth habit. This habit favors attack by R. conicus.

Considering how widespread "rhinos" are, this weevil is clearly the best choice for musk thistle control. T. horridus has been responsible for the crash of musk and plumeless thistles from Virginia to Kansas to Idaho, Wyoming, Montana... Releases of 105 adults are available from BCW for Montana shipments only during June and July for $80.00.

Sud Morishita, former Bonneville County, Idaho weed supervisor, estimates that bio-control has reduced the county's use of chemicals to fight musk thistle by as much as 60 percent.

The Thistle Seed Head Weevil, Rhinocyllus conicus, is very effective in reducing seed production in this biennial weed. Adult weevils lay an average of 190
Thistle Seed Head Weevil Larvae
Rhinocyllus conicus
eggs on the flower heads and stems of the thistle plant. The resulting larvae feed on the receptacle tissues inside the seed head and the upper portions of the plant's stem. Seed production is dramatically reduced by the feeding activity of this insect. "Rhinos" will also attack plumeless, Italian, and certain other large headed thistle species.

Because of the widespread success of this weevil, nationwide, we no longer offer this beetle. For additional information, please give us a call toll-free!

Biological Control of Weeds, Inc.
1418 Maple Drive • Bozeman, MT 59715
Phone 406-586-5111

Email: bugs@bio-control.com