Eurasia
Russian knapweed (Rhaponticum repens)
All stages of this nematode are small and most easily viewed with a microscope. Both juveniles and adults are translucent, elongated, 1.5 mm, and slim in shape, often s-shaped or coiled in posture.
Infective juveniles penetrate plant shoots in early spring as stems are emerging from the soil. Juvenile feeding induces gall formation. There are two or more generations per year; all development, feeding, and reproduction occurs within galls. Juveniles overwintering in gall remnants on or just below the soil surface may remain dormant for extended periods and become activated with adequate moisture. Juveniles must be active for approximately one month to become infective.
Gall development may divert nutrients from flower formation, 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