Steve Dewey, Utah State University, Bugwood.org

Steve Dewey, Utah State University, Bugwood.org

Yellow Toadflax

APPROVED BIOLOGICAL CONTROL AGENTS


Mecinus janthinus

Adult Mecinus janthinus, or the toadflax stem weevil, are small, somewhat elongated bluish black weevils which emerge from last year’s Dalmatian toadflax stems in April-May. Adults feed on leaves and stems before mating and laying eggs inside new shoots from June to mid-July.

The incubation period is typically six to seven days. Adults target stems that are at least 0.9 mm in diameter and are active into July.The eggs hatch and larvae tunnel within the stem as they feed, moving no more than 30 mm from where the egg was laid before pupating. Larval development takes between 23 and 34 days.

Pupation occurs within the stem. Adult feeding on stems and leaves has a limited effect on the plant, but larval mining impacts the plants causing premature wilting of shoots and suppressing flower formation. Mecinus overwinter as adults inside their pupation chamber. The effects of the weevil on the plant are reportedly enhanced under drought stress. Adults can be collected using an aspirator or sweep net while they are feeding and ovipositing.