Japanese knotweed is a serious invasive weed in the UK, North America and large parts of Europe. Current control measures are difficult to implement, unreliable and expensive. In 2003, a classical biological control programme was initiated, one that could lead to the first ever authorised release of a biocontrol agent against a weed in the European Union. Literature studies and surveys in the Japanese native range revealed over 180 species of arthropod natural enemies but only a psyllid, Aphalara itadori, has reached the point of official assessment for release. Aphalara itadori passes from egg to adult through five nymph stages in just under 33 days at 23oC and the timing and physical appearance of these stages is presented. Multiple-choice oviposition studies using 87 species/varieties of test plants showed that only 1.52% of 146,885 eggs were laid outside what we call the invasive knotweed group. None of these eggs laid on non-targets plants were able to develop to adult, however, subsequent nymph transfer experiments revealed limited development on some closely related members of the Polygonaceae and the development to adult on Meuhlenbeckia complexa (7% of cases). Adult survival, used as a surrogate for feeding tests, further revealed that survival on non-targets was severely compromised. These results coupled with an assessment of likely overwintering habits show A. itadori to have a narrow physiological and behavioural host range making it an ideal candidate for the first official release of a classical biological control agent against an alien invasive weed in the European Union. © 2009 Elsevier Inc. All rights reserved.
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