BIOLOGY: Adult M. janthinus emerge from stems in May, and reproduce until late June. Adults are appx. 4 mm long. Eggs are laid in cavities inside the stem. Eggs hatch in 7 days. Larvae development takes 20-30 days. Larvae are 1-2 mm long, cream colored and C-shaped with brown head capsules. Pupation occurs in stems. Adults overwinter in stems.
DESTRUCTIVE STAGE: Larvae (stem mining) and adult (feeding on foliage)
IMPACT TO HOST: Impact of weevils is most effective during drought years. Control is usually 60-75%, although several sites in Utah have collapsed after 6-7 years
REDISTRIBUTION: Adults can be collected in May and June using a sweep net and aspirator or by picking insects directly 0 of plants. A typical release is 250-500 weevils. Releases should be made in dense infestations of dalmatian toadflax.
BACKGROUND: Dalmatian toadflax was brought to the United States from Europe, Probably for ornamental purposes. It prefers rangeland and roadside habitat with sandy soils. It is very aggressive and hard to control due to deep roots and a thick, waxy leaf cuticle. It produces by seed and rootstock.
DESCRIPTION: This Creeping herbaceous perennial weed grows from 2 to nearly 4 feet tall. Multiple stems may come from the base. Blue-green leaves alternately line the stem. Leaves are wedge shaped, have thick, waxy cuticle, and partially clasp the stem. Flowers are yellow and may have white highlights and long tails, similar to snap dragon flowers. Bloom is in late spring into summer. Fruits are two-celled, berry-like capsules containing many seeds.
CONTROL: Biocontrol is available and offers fair control. Select herbicides can offer good control when applied from spring through fall. Contact your state or county weed specialist for specific, updated information.