Europe, the Mediterranean
Yellow starthistle (Centaurea solstitialis)
Eggs are elongated and white or pale yellow. Larvae are somewhat barrel-shaped (though slightly thicker at one end) and up to 4 mm long. They are white, turning yellowish with maturity, and they lack a head capsule but have a dark anal plate. Pupae are concealed in a barrel-shaped puparium up to 3½ mm long that is pale yellow with dark ends. Puparia are contained in woody galls. Adults have black bodies with a yellow spot on the rear part of the thorax. Their eyes are multi-colored and metallic, and their wings are clear with dark crossbands. Males are 3–4 mm long; females are 4–6 mm, including ovipositors.
Adults emerge in spring as yellow starthistle is bolting and starting to form buds. Females lay eggs in immature closed buds amongst the developing florets. After hatching, the larva follows a floret tube down to the ovule at the base of the floret. The larva enters the ovule (young achene), and the plant responds by beginning the formation of a gall. Multiple galls often occur in one flower head. There are three larval instars, prior to pupation within galls. Adults emerge in early to midsummer, mate, and lay eggs in more yellow starthistle buds. Larvae of the summer generation overwinter within hard galls inside the seed heads. There are two generations per year.
Floret feeding and gall formation reduce seed production. Galls are believed to act as nutrient sinks, diverting plant
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