Insect: Weevil (Coleoptera: Curculionidae)
Seedhead weevil, Lesser knapweed flower weevil
Photos: Adult & damaged seed head Release More adults
Larinus minutus: adult weevil. Photo by R. Richard (1)
Origin: Larinus minutus, was originally collected from Europe, was introduced into the United States in 1991. They have established in Montana, Oregon, Washington, and Wyoming. They were also released in Arizona, California, Colorado, Idaho, Minnesota, Nebraska, South Dakota, and Utah (1).
Overwintering State: These insects overwinter as adults in the ground litter (3).
Egg Stage: Eggs hatch after three days. The female usually lays about 130 eggs in clusters of five (2).
Larva Stage: It takes four weeks for larvae to develop into pupa (2). During this time, they feed on the pappus hairs of the flower (1), later moving to the achenes, where they feed on the seeds (2).
Pupil Stage: Larinus minutus makes a white cocoon (2) inside the seedhead (1).
Adult Stage: Adults come out of the cocoon May through August. They mate and lay eggs for 11 weeks during the months of June, July, and August (2). The weevils are a brown-grey color and have a very large snout. They are about 4-5 mm in length (1).
Damage to Host: During the larvae stage, the larvae obliterate almost one hundred percent of the seed in the seed head (1). The adults eat the leaves of the spotted and diffuse knapweed (2). Later on in the summer, the adults eat the flowers (3).
Impact on Host: The insects eat the seeds of the weeds, and as a result, both the spotted and diffuse knapweed suffer from less seed production (2).
Favorable Release Habitats: Larinus minutus prefer warm and dry climates. The knapweed infestations should have plants 1-2 feet apart and should be available for long term (5-10 years) use (2).
How to Collect: A sweep net or aspirator can be used to capture adults (2). You can use a sweep net by gently bending the plant into the net and shaking the insects off (3). Also, infested seed heads can be collected for moving while larvae are present (2).
How to Redistribute: About 500 Larinus minutus adults should be released on areas of knapweed plants. The weeds should be about 1-2 feet apart and the area should be open, not shaded (3).
How and Where to Purchase: Adults sometimes can be acquired from County and State weed management agencies for no cost (1). Commercial: 105 insects for $100 are available from the Biological Control of Weeds website (4).
Remarks: This weevil has been very successful at reducing the seed production of spotted and diffuse knapweed (2). Some patches of diffuse knapweed have been almost totally wiped out because of this biocontrol agent (3). This insect has recently established in the Whitehall and Cardwell area of S. Jefferson Co., MT.
Notice: Larinus minutus and Larinus obstusus are so much alike that some experts are thinking of classifying them together.Also, in the Whitehall area, minutus has grown so much that there is no need to introduce them. They have dispersed throughout the area.
1. Biological Control: Cornell University - Larinus minutus
3. Stevens County Noxious Weed Control Board - Larinus minutus
5. Noxious Weed IVM Guides - Spotted, Diffuse, and Russian Knapweed
7. Biological Control of Weeds Pricing
8. Montana State University Biocontrol Agents of Spotted Knapweed
1.) Lang, Ronald. USDA-APHIS-PPQ, Bozeman Biocontrol Facility, Forestry Sciences Laboratory, Montana State University, Bozeman, MT 59717. Available:
http://www.nysaes.cornell.edu/ent/biocontrol/weedfeeders/larinus_minutus.html Last modified April 18,1997.
2.) Burnett, Tom. Marathon Biological. 520 W. Griffin Dr., Bozeman, MT 59715. Phone: 800-735-2769, 406-587-4001 Fax: 406-587-4860 [Online] Available: http://www.marathonbiological.com/lminut.htm 2000.
3.) Stevens County Noxious Weed Control Board. 230 Williams Lake Road, Colville, WA 99114. Phone: (509) 684- 7590 [Online] Available: http://www.co.stevens.wa.us/weedboard/htm_bio/larinus_minutus.htm Last modified May 3, 2000.
4.) Biological Control of Weeds, Inc., 1418 Maple Drive, Bozeman, MT 59715. Phone: 406-586-5111. Fax: 406-586-1679. Email: firstname.lastname@example.org [Online] Available:
By: Anna Marx and Jenelle Hanson 01/09/02. Updated by: Christopher Bryson 3/1/07.
Back to Biocontrol mtwow.org HOME