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).