Study system
Knotweeds were introduced in the 1800s as ornamentals and for erosion control but escaped cultivation and have now invaded 42 states in the USA, becoming particularly problematic in the northeast and Pacific Northwest (Grevstad et al., 2018). Knotweeds are herbaceous perennial plants with leathery leaves and hollow, bamboo-like stems that can grow 1-3 meters tall. They primarily reproduce vegetatively by cuttings and rhizomes (Grevstad et al., 2018). Knotweeds often create dense monocultures in forests, riverbanks, floodplains, and roadsides. They are difficult to control by chemical, physical and cultural methods because of constant regrowth from their extensive root systems (Grevstad et al., 2018).
The knotweed psyllid, A. itadori, feeds on the sap of knotweeds using their piercing mouthparts. This feeding can weaken plants and at high enough psyllid densities may kill them (Grevstad et al. 2013). Psyllids undergo incomplete metamorphosis with eggs hatching into nymphs that undergo five stages that resemble adults more with each successive stage (Hodkinson, 1974). Nymphs are largely sessile, and the development time from egg to adult is about 33 days at 23°C (Shaw et al., 2009). Adult knotweed psyllids are about 2 mm long and reach sexual maturity approximately 5 days after adult eclosion but are capable of mating as early as 48 hours after adult emergence. Females reach peak fecundity at 20 days old, and a single individual can lay up to 700 eggs over the course of its lifetime. Adult lifespan averages about 55 days for females and 38 days for males under ambient laboratory conditions (20°C, 50-70% RH) (Myint et al., 2012).