| Summary: | Fallopia japonica is a damaging invasive weed that is difficult to control in the UK. In 2010, Aphalara itadori (Hemiptera), an insect herbivore native to Japan, was released in the UK as a biocontrol agent. Classical biocontrol of weeds has a long history across the world but this is an unprecedented type of release for the European Union. This provided the opportunity to investigate the conditions for establishment and the potential impacts of A. itadori under semi-natural conditions awaiting the potential establishment of large field populations in the UK. A meta-analysis, using global data, was carried out to see if classical biocontrol is an effective method of weed management. Field cage trials were then used to assess some life-history traits of A. itadori, including fecundity and longevity. Factors influencing establishment, including rainfall, competition and the role of generalist predators were investigated. The ability to cause damage to F. japonica is essential for a successful programme and this was tested, both directly and indirectly considering the performance of native plant species grown with F. japonica with and without biocontrol. Finally, the integration of biocontrol with existing control methods and preliminarily with another biocontrol agent, Mycosphaerella polygoni-cuspidati, a leaf-spot pathogen was investigated. Aphalara itadori showed the potential to be an effective biocontrol agent with the capacity to successfully reproduce outside, with potentially two generations per year in some areas of the UK. There were demonstrable impacts of A. itadori herbivory on F. japonica within a single growing season. Nonetheless, there was a discrepancy between the predicted performance from this study and what has been observed at the open field release sites. This is possibly a result of the effect of predation on A. itadori survival so recommendations, such as the use of protective cages, are suggested to inform the release strategy.
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