Europe, Western Asia, the Mediterranean
Yellow starthistle (Centaurea solstitialis)
Eggs are translucent, oval, and tiny. Larvae are up to 6 mm long with white, C-shaped bodies and brown head capsules. Pupae are typically creamy white with obvious appendages and a long snout. Adults are 4–6 mm long with oblong, cylindrical bodies and long, slender snouts. Adult bodies are brown with lighter-colored longitudinal stripes and are covered with long hairs.
Overwintering adults emerge in spring when yellow starthistle is boltin. They feed heavily on early immature starthistle buds. Females chew holes in the sides of mature, closed buds (pre-flower) in early to midsummer, lay eggs inside, and cap holes with a dark substance. Larvae hatch throughout summer and feed on developing seeds through three instars. Pupation occurs in seed heads in chambers made of damaged seed and receptacle tissue. Adults emerge in late summer and overwinter in soil litter. There is one generation per year.
Larvae feed on receptacle tissue and developing seeds. Adult feeding can lead to a high percentage of mortality of young flower buds. Both forms of feeding do not kill existing plants, but reduce seed production which may help decrease the rate of spread of yellow starthistle populations and may reduce infestations in some habitats.
Randall, C.B., L. Smith, and J. Milan. 2023. Yellow Starthistle 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-2023-14-YELLOW STARTHISTLE-A. https://bugwoodcloud.org/resource/files/27955.pdf