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Mecinus janthinus Germar
(Coleoptera: Curculionidae)

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

Mecinus janthinus was approved for release in the US in 1995. Field releases have been made at sites in western Canada and the western US. Some Canadian populations are established , but establishment at US sites has not yet been confirmed. (Background information about Dalmation toadflax and yellow toadflax is available.)

Appearance

Mecinus janthinus adults are shiny black, slender weevils about 3-4 mm long, with a pronounced snout. Beetles are found on toadflax foliage. The legless larvae are creamy-white in color with a light-brown head capsule, and appear C-shaped when viewed from the side. M. janthinus larvae are found tunneling within toadflax stems.

Habitat

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

Pests attacked

M. janthinus attacks both Dalmatian and yellow toadflax. Host specificity tests indicate that only a few plants within the genus Linaria are utilized as hosts.

Life cycle

Mecinus janthinus adults emerge in late spring or early summer and feed on toadflax leaves and stems, and may live for several weeks to about a month. After a feeding period, adults mate and female weevils begin laying eggs in toadflax stems. Eggs are deposited singly in cavities chewed into the stems and sealed with a lid of chewed plant material.

Young larvae begin feeding within toadflax stems, creating tunnels that increase in size and length as larvae mature. Wilted shoots are an external symptom of this larval feeding. Larval development is completed in about a month, and mature larvae construct a cell within the mined stem in which pupation occurs.

Pupal development is completed in several weeks; newly-eclosed adults remain within pupal cells and overwinter. There is one generation per year.

Relative effectiveness

Mecinus janthinus larvae mine in toadflax stems. Though this damage does not typically kill plants, mined stems wilt and die with a corresponding reduction in flowering and seed production. This impact may be more pronounced in plants experiencing drought stress. However, long-term effects of M. janthinus on weed density are not yet known.

Pesticide susceptibility

Unknown.

Conservation

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

Commercial availability

Mecinus janthinus is not yet generally available in the US.

References

Jeanneret, P. and D. Schroeder. 1992. Biology and host specificity of Mecinus janthinus Germar (Col.: Curculionidae), a candidate for the biological control of yellow and Dalmatian toadflax, Linaria vulgaris (L.) Mill. and Linaria dalmatica (L.) Mill. (Scrophulariaceae), in North America. Biocontrol Sci. and Technol. 2: 25-34.

Saner, M.A., P. Jeanneret, and H. Müller-Schärer. 1994. Interaction among two biological control agents and the developmental stage of their target weed, Dalmatian toadflax, Linaria dalmatica (L.) Mill. (Scrophulariaceae). Biocontrol Sci. & Technol. 4: 215-222.

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