Stem boring weevil, toadflaxes
*The species name has been changed as this insect will only eat Dalmation toadflax, while the Mecinus janthinus will only eat yellow toadflax. This is a new discovery.*
Photo by: Bob Richard, USDA-APHIS-PPQ.
Origin: South central Europe to south-western Russia between latitudes or 40-50° N. It occurs in summer-moist and summer-dry climates. (1)
Egg: A single white egg oval in shape at about a 0.60 x 0.65 mm. The egg is laid in a spot where the female has chewed into flowering stems. A stem may have many eggs laid in it, not just one. Stems of non-flowering Dalmatian toadflax are favored. (1)
Larva: Entire development takes about 24 days and temperatures between 18°C and 24°C to complete. The larva will mine about 3 cm of the stem. Over 100 larvae can be in one stem at a time. Larvae fight to survive in stems of non-flowering plants when the nutrition so poor. (1)
Pupil: Formed in the stem after 30-40 days. It is 3.0 to 4.5 mm long, starts out white but eventually turns black. (1)
Adult: Feeds mostly on the stem and leaves. Weevils from yellow toadflax are smaller than the ones from Dalmatian toadflax but egg production is not affected. (1)
Overwintering: As an adult in pupil cell in a toadflax stem. Development from egg to adult takes 50-63 days. There is heavy winter mortality in colder regions but enough beetles survive to infest most stems in the following year. (1)
Host Impact: All damage to the host is done in the larval stage. Targeted plants are yellow and Dalmatian toadflax. Mostly damages the stems and lowers seed production. (1)
Favorable and Unfavorable Release Habitats: Release adults in groups (200 is effective) as soon as foliage is available in the spring. This is mid to late May on yellow toadflax on the prairies. (1)
How and Where to Collect: 1. Collect the adults with a sweep net in late summer at sites where they are established (with permission of course!). 2. They can also be collected in the spring with sweep nets or by shaking them off the stems into a bucket. 3. Another method is to collect infected toadflax stems in the fall and store them in a refrigerator until next spring when you can release the adult weevils. In cold areas this greatly increases the number of weevils that survive the winter because the environment is less harsh in the refrigerator.
Where and How to Purchase: They are not well established yet in the United States. Contact your local weed fighters to see if this insect is available. (2)
Comment from Mr. Breitenfeldt: [3/2006] They are rapidly increasing in Western/SW Montana and should soon be available in greater numbers. They seem to be a quite good bio-agent and we are really excited about them.
(1) 2/2/02, Mecinus janthinus Germar (Coleoptera: Curculionidae) Rich Hansen, Cornell University, http://www.nysaes.cornell.edu/ent/biocontrol/weedfeeders/mecinus_janthinus.html
(2) 2/2/02, Dalmatian toadflax Linaria dalmatica (L.) Miller, 1997 Ministry of Forests, Province of British Columbia, Canada, http://www.for.gov.bc.ca/HFP/PUBS/INTEREST/Bioagent/dalmat.htm
By: Trent Pietsch 2/02/02. Updated by: Jessica Kostman 2/14/2006. Ryan Murphy 6/15/16
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