Europe
Preferred host is yellow toadflax (Linaria vulgaris), also attacks Dalmatian toadflax (L. dalmatica)
Eggs appear milky white at first, becoming yellow just before hatching. Larvae are yellow and up to 7 mm long. The larval head capsule starts out dark brown to black and wider than the abdomen, but by the third instar, lightens to a golden brown and becomes more slender than the body. Pupae are up to 3 mm long and 2 mm wide. Adults are 2–3 mm long and somewhat oval-shaped with short elytra (hardened outer wings) that do not completely cover their abdomens. Adults are shiny dark brown to black or sometimes black with brown mottling, and they have maroon feet and antennae.
Adults emerge in late spring and feed on young toadflax shoot tips. Females lay eggs singly into unopened toadflax buds, just beneath the folded petals. Larvae feed on pollen, anthers, ovaries, and immature seeds. They develop through three instars and drop to the soil in fall to overwinter as pupae in soil or plant litter. There is one generation per year.
Adult feeding can delay flowering and reduce the number of healthy flowers (and thereby seeds) produced by yellow toadflax. At high densities, adult feeding increases branching and reduces the height of Dalmatian toadflax plants. Injury from larval feeding is generally more significant, reducing seed output by more than 75% in attacked flowers. Seeds surviving to maturity in attacked flowers are smaller, lighter weight, and less viable. Decreasing seed output does not kill existing plants but can help reduce the rate of spread and genetic diversity of toadflax populations.
Sing, S.E., R.A. De Clerck-Floate, C.B. Randall, and I. Toševski. 2022. Toadflax 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-2022-29-TOADFLAXES-A. https://bugwoodcloud.org/resource/files/27419.pdf