Gymnetron antirrhini adult. R.Richard, USDA-APHIS

Gymnetron antirrhini Paykull (Coleoptera: Curculionidae)

by Rich Hansen, USDA-APHIS-PPQ, Forestry Sciences Lab, Montana State University, Bozeman, MT 59717-0278.

Dalmatian toadflax infestation/plant in Wyoming. W.Hartung, NRCS

Gymnetron antirrhini was accidentally introduced into North America after 1900, presumably as a contaminant of imported ornamental toadflax plants. G. antirrhini now appears to occur wherever yellow toadflax is found in the US and Canada, but is apparently much less abundant on Dalmatian toadflax. A "strain" of G. antirrhini presumably more host-specific to Dalmatian toadflax was approved for release in the US in 1995. (Background information about Dalmation toadflax and yellow toadflax is available.)

Appearance

Gymnetron antirrhini adults are black, oval beetles about 2 mm long, with a pronounced snout. They may be found feeding on toadflax stems, buds, flowers, or fruits.

Larvae are 2-4 mm long, legless, and C-shaped when viewed from the side. They are creamy-white in color with a tan head capsule. Larvae are found within toadflax seed capsules.

Habitat

Grasslands, pastures, agricultural fields, and roadsides infested with yellow or Dalmatian toadflax.

Pests attacked

G. antirrhinifeeds on yellow and Dalmatian toadflax; different "strains" of this insect may preferentially utilize individual toadflax species. In general, G. antirrhini appears to only utilize several Eurasian Linaria spp. as hosts.

Life cycle

Adult weevils emerge in late spring or early summer, and feed primarily on young toadflax shoots and buds. After mating, female beetles lay eggs inside toadflax flowers, inserting them singly through the ovary wall. Oviposition causes abnormal growths within the ovary, and ovules and young seeds adjacent to these growths become distended and yellowish.

Larvae hatch from eggs and feed on these "inactivated," abnormal seeds. Larval development consists of three stages and last about three to five weeks. Mature larvae construct cells within developing seed capsules and then pupate.

In several weeks, adults eclose and may feed on toadflax shoots for a short period of time before entering diapause. Winter is spent as an adult in plant litter or within old toadflax seed capsules. There is one generation per year.

Relative effectiveness

G. antirrhini does not kill toadflax plants, but larval seed feeding can reduce a plant's seed production by more than 80%.

Pesticide susceptibility

Unknown.

Conservation

Specifics are unknown. For general information about conservation of natural enemies, see Conservation in the Tutorial section on this site, or the Volume II, No. 1 Feature Article on conservation in the Midwest Biological Control News Online.

Commercial availability

G. antirrhini may generally be collected from yellow toadflax stands throughout the US and Canada.

References

Groppe, K. 1992. Gymnetron antirrhini Paykull (Coleoptera: Curculionidae), a candidate for biological control of Dalmatian toadflax in North America. Intl. Inst. of Biol. Control European Station Final Report. 22 pp.

Harris, P. 1961. Control of toadflax by Brachypterolus pulicarius (L.) (Coleoptera: Nitidulidae) and Gymnetron antirrhini (Payk.) (Coleoptera: Curculionidae) in Canada. Can. Entomol. 93: 977-981.

Smith, J.M. 1959. Notes on insects, especially Gymnaetron spp. (Coleoptera: Curculionidae), associated with toadflax, Linaria vulgaris Mill. (Scrophulariaceae), in North America. Can. Entomol. 91: 116-121.

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