Mecinus janthinus 
<<back to yellow toadflax
Common Name
Yellow toadflax stem weevil
Weed Impacted
This beetle attacks yellow toadflax but looks identical to M. janthiniformis which attacks Dalmatian toadflax. Larval feeding (or mining) within stems inhibits the ability of the plants to transport nutrients, resulting in premature wilting of shoots and reduced flower formation. Adults feed heavily on leaves and stems and can suppress flower formation and growth.
Insect Description
Adults are small (3.5-4 mm or approximately 1/8 inch), narrow, bluish-black weevils. Larvae are white, C-shaped grubs found within the stems.
Life Cycle
Adults emerge from stems in May to feed and mate. Females lay eggs from May to mid-July in cavities chewed into toadflax shoots. Eggs hatch after six to seven days and larvae begin mining stems. Pupation occurs, after 23 to 34 days of larval development, within the larval mine. Adults overwinter in the stem until the following spring.
Field Identification
Adults typically group together and feed in the top portions of stems, especially early in the growing season. Their bluish-black color and elongated shape distinguish them from other beetles (Brachypterolus pulicarius) that may be present. Individual toadflax stems can have from one to 100 beetles. Splitting open stems during summer will reveal larvae, pupae, adults and larval tunnels, however, the weevils will likely die once exposed. Previous year stems can also be examined for emergence holes (see picture) to determine insect presence.
Availability
The availability of this weevil is limited and is not currently known to have established in Washington. To inquire about availability and to request this biocontrol agent, please download, complete and submit this form.
Comments
The species-specific distinction between the weevils found on yellow and Dalmatian toadflax is relatively recent. The Dalmatian toadflax weevil name changed from M. janthinus to M. janthiniformis. The images on this webpage are of M. janthiniformis on Dalmatian toadflax but will closely resemble M. janthinus damage on yellow toadflax.
Initial observations indicate that M. janthinus is an effective biocontrol agent for yellow toadflax.
Using the Agent: Integrated Weed Management (IWM)
Mecinus janthinus should be released at yellow toadflax sites only where infestations are large and immediate eradication of the weed is not the primary objective. Impacts have been observable at some sites in 3-5 years. Most treatments are not directly compatible with the use of this biocontrol agent. Any control methods that prevent stem growth during the growing season will reduce or eliminate biocontrol populations. Biocontrol agents can be used within large patches and satellite patches (which lead to increased spread) can be controlled using other management tools.
Small or satellite populations of toadflax can be either hand-pulled or sprayed, but treatments must be repeated annually for up to 5 or 6 years. Root fragments can remain viable after pulling and herbicides will not immediately kill or penetrate all plants. Herbicide applications can be used on satellite patches and infestation edges to control weed spread. Consult with your county weed office, Extension office or an IWM practitioner to determine which herbicide treatments are safe and appropriate.
Burning toadflax is not recommended, as it increases the susceptibility of a site to further infestation. Plowing or disking can eliminate toadflax in cropland if repeated regularly. Mowing will not control the weed and can work against any potential agent impacts in areas of release.
Any management of toadflax should involve revegetation with native or other desirable plants. Revegetation promotes competition between plants, which stresses weeds and allows for more effective treatment. To learn more about revegetation and IWM, click here.
References
Coombs, E. M., J. K. Clark, G. L. Piper, and A. F. Cofrancesco, Jr. 2004. Biological Control of Noxious Weeds in the United States. Western Society of Weed Science, Oregon State Univ. Press, Corvallis.
Enloe, S., A. Norton, P. Meiman, and T. Collier. 2009. Integrating Biological Control with Herbicides for Dalmatian Toadflax Control: Do “Many Little Hammers” Really Work? Weed Science Society of America Abstracts 357. URL
Wilson, L. M., S. E. Sing, G. L. Piper, R. W. Hansen, R. De Clerk-Floate, D. K. MacKinnon, and C. Randall. 2005. Biology and Biological Control of Dalmatian and Yellow Toadflax. USDA Forest Service. FTET-05-13.
Photo Credits
Mecinus janthiniformis adult - Bob Richard, USDA-APHIS-PPQ, bugwood.org (insectimages.org), http://www.insectimages.org/images/768x512/1416019.jpg
Mecinus janthiniformis mining - Bob Richard, USDA-APHIS-PPQ, bugwood.org (insectimages.org), http://www.insectimages.org/images/768x512/1416039.jpg
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