Cyphocleonus achates
(Coleoptera: Curculionidae)
Insect: beetle, weevil.

 Photos: [damaged knapweed plants] [Adults] [larvae and pupa] [insectary rearing] [How To Monitor Release Sites] [The Whitehall Project]

 Origin:  The original source of this species is in Austria, Greece, Hungary, and Romania.  The native distribution of the species is Eastern Europe and Asia. (1)

Common name:  Knapweed root boring weevil. (3)

Life cycle:

The Wintering stage: Cyphocleonus achates over winters as a larvae in the root.  (1)

The Egg stage:  The eggs are laid in a notch on the root crown, right below the soil surface.  The females may lay up to 100 or more eggs usually one per plant.  The eggs are oval and a whitish pale yellow.  As they get older the eggs turn a more yellow color.  It takes 10 to 12 days for them to hatch. (1)

The Larval stage:  After hatching the larvae migrate (tunnel within the root) toward the cortex (center) of the root.  Then the second of four instars (each time a larva sheds its skin, that is called an instar) are the over wintering stage.  In the third and fourth instars the larvae causes a gall-like enlargement in the root and much internal damage from feeding. (1)

The Pupal stage:  The pupal stage lasts for about two weeks and occurs in the galled root in mid summer. (1)

The Adult stage:  Adults emerge from late July to the middle of September.  Adults vary from 9-15 mm in length and normally live eight to 15 weeks.  The adults though very hardy, do not survive over winter but their larvae do [in the Whitehall area the adults often survive well into October and some times into November] (4). Adult weevils eat knapweed leaves, mostly on young plants.  This feeding does not usually severely damage the plant. (1)


Destructive stages:  Cyphocleonus achates destructive stage is larval.  The larval root feeding often kills the plant when 2 or more weevil larvae are in the tap root(s).  The adults do not cause much noticeable damage. (1)

Plant species attacked: Cyphocleonus achates prefer spotted knapweed but they also attack diffuse knapweed. (1)

Damage to host:  The weevils prefer to lay their eggs on larger knapweed plants.  Small plants are damaged the most.  This larval feeding often kills small plants outright and damages large plants.  The large plants then often die with subsequent reinfestation by the weevil larvae.  (1)  The adults feed off the plants above ground. (2)


First introduced into the United States:  In 1987 Cyphocleonus achates was first introduced into the U.S. (3)

Now established in: Weevils are found in Colorado, Montana, Minnesota (7), Oregon, and Washington. (1)

Habitat:  Cyphocleonus achates live in spotted knapweed and diffused knapweed.  (3)  They do best in hot, dry fairly open sites with many large knapweed plants.  Flooding will often kill the larvae. (4)

Despersal: C. achates is sedentary, meaning the beetles are individuals that move at a neutral distance of about .3 m/day. (5)

There are large numbers of weevils in Montana and Colorado, check with your local County Weed District or biocontrol retailer. (1) A Cyphocleonus achates releases can be purchased form private companies:  See: (6)

Stage to transfer: The Cyphocleonus achates stage to transfer is the adult.  They are usually available in August and September.  (1)

Redistribution: Adults can be found and collected in fields that are infested with spotted knapweed and diffuse knapweed.  They can be caught and placed in a sleeve box, fit for their size. (1)  We also rear them here in Whitehall in a knapweed insectary.  See:  The weevil does not fly so humans need to redistribute this bio-agent. (4) To catch and collect these weevils, spread an entire spotted and/or diffuse knapweed to find these camouflaged beetles; they should be normally found at the bottom of the plants. On warm days many of the weevils will climb to the tops of knapweed and adjacent plants.  They don't bite, however they have the grip of "Tarzan on a swinging vine." You should try and make them drop into a collection pan, net, or container. We try for a release of 100 adult weevils every 1/4 section (4 releases per square mile) in the Whitehall, MT area. You can also sweep net for these weevils on warm afternoons.  (2)    

Comments:  Cyphocleonus achates is widely spread throughout Europe.  The weevil is a harmless insect to plants other than spotted and diffuse knapweed and does a good job in killing knapweed.  A good way to mass produce these is in a knapweed insectary.  We think that the weevil is a very good insect to help us control knapweed plants.  Many other Montana schools have started Cyphocleonus rearing/redistribution programs and either field collect or have knapweed insectaries or, both. (4)


1.  Rees, Norman, et. al., Ed., Biological Control of Weeds in the West, Western Society of Weed Science, in Cooperation with USDA ARS, MT Dept. of Ag, and MT State Univ., Color Printers, Bozeman, MT, Feb., 1996.

.  Stevens County Noxious Weed Control Board, 230 Williams Lake Rd., Colville, WA 99114, (509) 684-7590 (online) available: , Page last edited: Aug. 8, 2002.

3.  Lang, R.F Biological Control: A Guide to Natural Enemies in North America, (online) available: , Page last modified: Feb. 9, 2000 Text last modified: April 18, 1997.

4. Breitenfeldt, Todd, Personal Interview, Whitehall High School Biology Teacher and Whitehall Project Coordinator, Whitehall High School, P.O. Box 1109, Whitehall, MT 59759.  2003.

5.  Kimberly J. Rondeau, " Dispersal of the biocontrol agent, Cyphocleonus achates (Coleoptera: Curculionidae), on diffuse knapweed (Centaurea diffusa) (Asteraceae)", University of Alberta: Department of Biological Sciences: Department Calendar
February 4, 2008.

6. Integrated Weed Control 4027 Bridger Canyon Road Bozeman, MT 59715-8433, February 6, 2008.

7.  Northrop, Natasha, Research Scientist; Minnesota Department of Agriculture, 601 N Robert St., St. Paul, MN 55155; 651-201-6540; from email correspondence. 

By: Brianne Ward and Janelle Anderson, 02/2003.  Updated by: Cullen Severance, 2/7/08.
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