Europe and Western Asia
Spotted knapweed (Centaurea stoebe subsp. micranthos), occasionally diffuse knapweed (C. diffusa)
Eggs are white and flattened initially but turn yellow-red in a few days. Larvae are white with brown mouthparts and can be up to 7 mm long. Adults are usually 11 mm long with a wingspan measuring 15–23 mm. Forewings are bright yellow with brownish band markings; hind wings are light brown to dark gray.
Larvae overwinter in knapweed roots and feed within the roots the following spring. Pupation also occurs in the roots. Adults emerge from summer to early fall when knapweeds are in bud and flowering. They are most active in early mornings or evenings, and rest low on plants or on the soil surface during the day. Adults mate within 24 hours of emergence and are short-lived. Females deposit eggs on knapweed stem crevices and leaves as early as the following day. A single adult female lays 21–78 eggs in her lifetime. Larvae hatch in 7–10 days and migrate to the crown area and mine roots, developing through six instars. As they mine, larvae produce a whitish web tunnel that encloses them. They create a spiral trail downward before they turn back towards the top of the root. Larvae overwinter in roots, and there is usually only one generation per year.
When larvae feed within roots, root tissue can be completely consumed. This reduces knapweed biomass and density and may kill small plants.
Randall, C.B., J.E., Andreas, and J. Milan. 2023. Knapweed Biocontrol Agents: History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW-2023-34-KNAPWEEDS-A. https://bugwoodcloud.org/resource/files/27451.pdf