Larinus planus
Canada thistle bud weevil
(Coleoptera : Curculionidae)

Photos: Larva    Adult    Gallery

Origin: Europe, was then brought to Pennsylvania. (4)

Life Cycle:
Overwintering State: adult in the soil. (3, 4)
Egg Stage: The female weevil will lay her eggs on an unopened bud. She will do this by drilling a hole into the side of the bud. If by some reason, more than one egg is laid in a hole, only one of the larva will survive. (3, 4)
Larva Stage: While growing they feed on the tissue part of the seeds and other flower parts. (2, 3, 4)
Pupil Stage: This takes place in the cocoon made in the bud. (3, 4)
Adult Stage: The average body length for these insects are from 5-8 mm. They develop in the bud and then emerge late May and June. The adult weevils can begin mating after about one week. They then must lay their eggs within 14-26 days after the mating. (3, 4) Type of Damage to Host:  Larva: This is the most destructive stage. It destroys the seeds, pappus, and receptacle within the flower bud.
Adult:  This stage stops the growing of buds and the upper leaves of Canada thistle.

Plant Species: Canada thistle (Cirsium arvense)

Location: New buds, leaves, pappus, and seeds (3, 4)

Host Impact:
The adult weevil, will lay its eggs by drilling a hole into an unopened bud.  Once they hatch, the larvae will start eating the tissue part of the seed. They will then develop into the pupa stage. The most damaging stage is the larval stage.  This is where the bud is ruined, and therefore the bud will fail to open all the way. In the end, the thistle has trouble reproducing. (2, 4)

Release Habitats:
The weevils do well in a wide range of climates. This means that they are very good at surviving many places. (2)

Collecting, Transporting, and Releasing:
After you decide to collect  your weevils, use a sweep net to gather them.  Once you have enough, store them in a cool place. They should be in a cardboard box or container.  Try your best to release the insects within several days of your gathering.  You should collect and release these insects in late May to early June. (1, 2, 3)

If you would like to purchase this insect, contact your county extension office or Weed District.  You can also visit these web sites:  Bio-control, Integrated Weed Control, and other places.

Larinus planus is a bud weevil that feeds mainly on Canada thistle. It seems that once these insects are set into a big patch of Canada thistle, they do extremely well. The most destructive stage is the larva stage.
Useful Links:

Literature cited:
1. Burnett, Tom, Sprig 2000, Biological Control Information [web site], Available:, Last updated: 2000

Harris, P., Lethbrigge Research Center [web site], Available: , Last updated: 12/28/2000

Unknown author, PRIDE, [web site]: updated last: unknown.

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.
By: Kara Voeks 1/9/02.
Updated By: Tyrell Frazer 2/15/08.

Back to Biological Control HOME