**Knotweed Psyllids** (*Aphalara itadori*) are a species of highly specialized, sap-feeding jumping plant louse native to Japan that has been released as a **biological control agent** against the aggressive invasive weed **Japanese Knotweed** (*Reynoutria japonica*). The adults and nymphs feed on the sap of the knotweed’s leaves and stems, stressing the plant, reducing its height, and decreasing the amount of stored energy in the root system. They are managed as a beneficial insect, and their conflict is directed entirely at the invasive knotweed plant.
Taxonomy and Classification
Knotweed Psyllids belong to the order Hemiptera, closely related to aphids and scale insects. They undergo incomplete metamorphosis. Psyllids are commonly known as jumping plant lice due to their ability to leap rapidly when disturbed. This species is highly host-specific, having co-evolved to feed only on Japanese Knotweed, a factor critical to its use as a biocontrol agent.
Physical Description
Adult Knotweed Psyllids are small, winged insects, 1/16 to 1/8 inch long.
- **Appearance:** The body is often light green or reddish-brown. They hold their wings roof-like over their body at rest.
- **Nymphs:** Flat, oval, and often secrete small, white, waxy strands. They are generally stationary on the undersides of leaves.
- **Feeding:** They possess piercing-sucking mouthparts used to drain sap from the plant’s vascular tissue.
- **Impact:** Visible symptoms on the knotweed are stunted growth, leaf deformation, browning, and reduced height compared to uninfested stands.
Distribution and Habitat
Knotweed Psyllids are native to Japan and have been released in the UK, Canada, and parts of the U.S. to combat Japanese Knotweed infestations. Their habitat is restricted to the leaves and stems of the knotweed plant. They rely on the persistent knotweed patches to complete their life cycle.
h2 class=”wp-block-heading”>Behavior and Conflict
The psyllids are a highly desired agent of conflict against a severe invasive plant.
- **Weed Suppression (Primary Role):** Their feeding reduces the plant’s ability to photosynthesize and store energy, gradually weakening the massive, aggressive root (rhizome) system that makes knotweed so difficult to control.
- **Host Specificity:** Extensive testing confirmed that the psyllid would only feed on the target knotweed, posing no threat to native plant life.
- **Control Rate:** They are intended to provide long-term, self-sustaining suppression of knotweed, not immediate eradication, allowing native plants to compete more successfully.
Management and Prevention
Management focuses entirely on **conservation and augmentation** of the psyllid population.
- **Conservation (Key):** Do **not** use insecticides or broad-spectrum herbicides on or near knotweed patches where the psyllids have been released, as this will kill the beneficial insects.
- **Monitoring:** Biologists track the psyllid population to ensure establishment and measure the resulting decline in knotweed vigor.
- **Relocation:** Successful colonies are often collected and released into new knotweed stands to accelerate the spread of the biocontrol agent.
Conservation and Research
Knotweed Psyllids are managed as a high-value biological control agent. Research focuses on maximizing the psyllid’s dispersal rate, integrating their presence with mechanical cutting strategies, and determining the long-term impact on large, established knotweed rhizome systems.