Progress towards the biological control of invasive knotweed species in Massachusetts

Knotweeds, Reynoutria spp. Houtt. (Caryophyllales: Polygonaceae), are among the 100 most damaging invasive species in the world and have become widely established in many countries due to their historical use as ornamental plants. In their invaded ranges, knotweeds have been shown to reduce the abundance and species diversity of vertebrates, invertebrates, plants, and fungi. Chemical, mechanical, and cultural controls can be partially effective in the management of small knotweed stands. Unfortunately, these methods are ineffective over larger areas, may not be appropriate in wetlands, and require frequent interventions, making them costly and ultimately impractical. As a result, extensive effort has been put into identifying suitable biological control agents for invasive knotweed species. During subsequent surveys of Japan (the native locality of the invasive knotweed plants in Europe and North America), various pathogens were observed feeding on or attacking knotweeds. However, to date, only one agent, the psyllid Aphalara itadori Shinji (Hemiptera: Aphalaridae), has so far been approved for release in Europe and North America. Initial introductions of A. itadori were disappointing, with limited survivorship observed in the field. Over several years we have undertaken a research project in Massachusetts to identify the ecological and biological factors that limited the initial establishments, and identified strains of A. itadori that are better environmental and genetic match for invasive knotweed plants in our region. After four years of field releases, we have observed considerable damage to plants in the field, and hope to continue this success globaly.