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Adult Knapweed Weevil Courtesy
Adult Knapweed Weevil Courtesy

Knapweed Root Weevil (Cyphocleonus achates)

Generations per year:  One

Growth:  4 stages of growth

Egg—laid singly in a notch excavated on the root crown just below the soil surface.  Females may deposit up to 100 eggs and they hatch in 10-12 days.

Larval—newly hatched larvae mine the cortex of the root.

Pupal—pupation occurs in the galled root and lasts for about two weeks. 

Adult—emerge from early August to mid-September to feed on knapweed leaves.   Adults are 0.56 to 0.6 inches long and live for eight to 15 weeks, but do not overwinter.  Females mate several times during her lifetime.

 Overwintering stage—larval—in the galled roots

Destructive stage—larval

Impact on Knapweed—the insect does not kill the plant, however, it causes considerable damage to the root and root cortex.

Habitat:  Well-drained soils that lack dense vegetation other than knapweed

Release Date:  Knapweed Root Weevil are typically released in July. 

Cost:  A carton of adult root weevils = approximately 105 insects

$100.00 plus overnight shipping costs to apply

If you are interesting in ordering Knapweed Root Weevil, please submit the following form or call (406) 485-2744 x100.

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