Eastern Europe
Primarily diffuse knapweed (Centaurea diffusa), occasionally spotted knapweed (C. stoebe subsp. micranthos)
Eggs are oval, somewhat flattened, and have a strong outer shell with distinct ribs. Initially they are white, but they gradually turn dark yellow during incubation. The segmented larvae are whitish-yellow with brown head capsules. They are usually less than 10 mm long. Adult moths have wings mottled gray to gold (sometimes silvery) and fringed at their tips. They can be up to 10 mm long.
Adults emerge throughout summer when knapweed is bolting and flowering. They mate within 24 hours of emergence and lay eggs primarily on the lower surface of rosette leaves. Females can lay up to 120 eggs in warm dry weather, but this can be greatly reduced by cold, rainy conditions. Larvae hatch 7–9 days after oviposition, move to the center of the rosette, and mine into and down the root crown. Webbed tubes are produced along feeding tracks, which can be irregular, downward, or spiraling; tunnels are lined with a silken web. There are six larval instars. This species seems to prefer rosette plants as larvae that feed on roots of flowering plants develop poorly. Larvae overwinter in roots and complete development in spring or early summer. Pupation occurs within webbing inside the root. There is one generation per year.
Larval damage to the roots is similar to that caused by A. zoegana. Larvae reduce root storage capacity and expose the plant to pathogens, but only the third to sixth instars cause measurable damage. Small plants with a <10 mm root diameter can be completely destroyed. Plants that survive insect attack usually grow smaller and produce fewer flower heads than uninfested 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