Europe
Primarily spotted knapweed (Centaurea stoebe subsp. micranthos), but also diffuse knapweed (C. diffusa) and the meadow knapweed complex (Centaurea ×moncktonii complex)
Eggs are elongate, oval, and reddish-brown when first deposited, but turn yellowish as they mature. Larvae are 4–5 mm long, white, and with dark brown head capsules. They have distinct body segments and several pairs of prolegs. Pupae, enclosed in a cocoon, are brown with appendages fused to the body. Adult moths are small (8 mm long). Their forewings are slightly fringed and mottled light gray and gold with peppery spotting. When at rest, the wings are folded over their backs, giving them a slender appearance.
Adults begin emerging and mating in late spring and early summer when knapweeds are in the rosette and bolting stages. They fly at dusk and are rarely seen. Female moths may lay 60–100 eggs, beginning in early summer. Eggs are placed singly on bracts at the base of young buds, or on stems just below the flower head. Larvae hatch in 10–12 days as flower heads are opening. Larvae enter opened flower heads and feed on florets, seeds, and receptacle tissue (which reduces the viability of uneaten seeds). There are five instars. Several young larvae can occupy a flower head early in the season, but only one larva survives beyond the third instar. Larvae overwinter in flower heads. Pupation occurs in the flower head in spring and lasts 3–4 weeks. There is one generation per year.
Feeding larvae can destroy eight seeds per larva (on average) and reduce the viability of other seeds. Older larvae bind seeds together, preventing seeds from dispersing over long distances.
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