Gymnetron antirrhini  (Paykull)
(Coleoptera: Curculionidae)
toadflax capsule weevil

Insect Links     Photos: Adult     Larva     Eggs     Damage to plant

Gymnetron antirrhini:  Photo by Greg McDermott, from slide show Biological Control of Noxious Weeds by Reeves Petrof.

These weevils were introduced in the1900's in N. America by accident. (3, 4)  They appear where yellow toadflax occurs and tend to favor yellow toadflax over Dalmatian toadflax. (1, 2)  It is speculated that the weevil may have been originally introduced accidentally in California. (3, 4)

Life Cycle
1) during the winter it spends its time as an adult in leaf litter or in toadflax (yellow mainly, or Dalmatian) seed capsules.
2) Adults emerge in spring, typically May - June.
3) Eggs are laid within toadflax flowers, inside the ovary wall.
4) Larval stage lasts from 3 to 5 weeks in the seed capsules.  Larvae feed on "inactivated," abnormal seeds.
5) The mature larvae construct oval cells within seed capsules where pupation occurs.
6) After several weeks, adults eclose (emerge) and may feed on toadflax shoots for a short period of time before entering diapause (going dormant for the winter).  By this time the year-old adults have laid their eggs and are mostly dead.
7) Adults are about 2.5 mm long; the gray weevils feed on young shoots and flowers of toadflax in late summer and early fall. (1,     2) (3, 4)

Damage to Host stage- Larval seed feeding and somewhat adult feeding on young shoots and flowers.

Plant species- yellow toadflax and somewhat Dalmatian toadflax.

Location- larval: attack immature seeds inside the seed capsules.  Adult: shoots and flowers. (1, 2)
It reduces yellow toadflax seed reproduction, but its effect on Dalmatian toadflax is unclear. (3, 4)

Host Impact-Method- damage shoots and flowers.  Focus- they focus on mainly yellow toadflax and not so much Dalmatian toadflax. (1)

Favorable Places
The most favorable places for theses insects are places with heavily shaded areas with lots of rainfall. (1, 2)

Unfavorable Places
Unfavorable places would include areas lacking in heavily shaded areas and/or with very little rainfall.  (1, 2)     They do not do as well in the cold but can survive in the cold. (3, 4)

You can collect these insects wherever there is yellow toadflax.  You will most likely find adults using a sweep net.  You can also collect them in insectaries with permission from the person who owns the insectaries.  (1, 2)

Transporting Them
To transport these insects when they are adults, place them in a suitable container such as a paper can with some fresh toadflax foliage and then keep them in a cooler with a small ice pack.  You can also transport infected seed capsules but realize that you are transporting seeds as well. (1,2,3)   Release in places where there is lots of yellow toadflax; make sure there are heavily shaded areas and lots of rainfall.  Try to not put them anywhere that it is very cold or prone to large quantities of snow in the winter.  (2, 3)  Release the Dalmatian strain where Dalmatian toadflax is present. (4)

It is best to use a sweep net on the yellow toadflax plants, sweep low to the plant near the roots where they spent their time if it is cold out.  These weevils usually redistribute themselves quite well by flight and tend to be found where ever yellow toadflax occurs.  (2, 3)   The Dalmatian strain seems to be spreading on Dalmatian toadflax in our part of SW Montana and is collectable in the same way.  (4)


1) Biological Control Agent Matrix, 1997, Ministry of Forests, Province of British Columbia, Canada [Online] Available:

2) Hansen, Rich, USDA-APHIS-PPQ, Forestry Sciences Lab, Montana State University, Bozeman, MT 59717-0278. [Web Site] Biological Control: A guide to Natural Enemies in North America, Cornell University [Online] Available: Last modified April 10, 1998. 

3) Arnold, R. M. 1982. Pollination, predation and seed set in Linaria vulgaris (Scrophulariaceae). American Midland Naturalist, 107:360-369.

4) Breitenfeldt, Todd A., Personal Interview, Whitehall Schools, P.O. Box 1109, Whitehall, Mt, 59759, (406) 287-4862, 9-14-99. 

By: Zach Housman     last updated by: Sari Dersam 6/16/16
Published By: Matt Jensen