Central Asia
Russian knapweed (Rhaponticum repens)
Larvae are up to 2 mm long, curved, and legless. They are typically white with rosy or orange hues and lack a true head capsule. Pupae are pale in color and approximately 2 mm long. Adults are light brown with long, slender legs and large eyes. Females have orange abdomens and large transparent wings. Males are just under 2 mm long while females are slightly larger.
Adults are short-lived (males 1 day and females 2–3 days) and mate soon after emerging in spring. Multiple eggs are laid around and in the tips of growing Russian knapweed shoots. Larval feeding causes leaves to grow together in layered galls. Galled leaves have long whitish hairs, giving the gall a frosted or cotton ball appearance. Larvae develop through three instars among silky hairs between the growing leaves of the infested shoot. Preliminary evidence indicates four or more generations (each usually one month long) per year occur in North America. Provided there are sufficient green, growing stems available, galls can be observed throughout the growing season from late spring to mid-autumn. At the end of the season, larvae are thought to drop from galls to overwinter in the soil.
Galls stunt the growth of infested shoots. Gall development prevents flower formation, reducing seed production and plant height. Under some conditions, galls may sufficiently stress plants to reduce their competitive ability.
Bean, D.W., J. Littlefield, P. Weyl, S. Daly, and T. Collier. 2023. Russian 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-2023-1-RUSSIAN KNAPWEED-A. https://bugwoodcloud.org/resource/files/28120.pdf