Establishment of the biological control agent Aphalara itadori is limited by native predators and foliage age

Abstract

AbstractThe knotweed psyllid, Aphalara itadori, is a biological control agent for invasive knotweed species in North America and Europe. Initial releases were conducted in Canada in 2014 but establishment has been slow, seemingly as a result of low nymphal survival. We conducted two field experiments in Ontario, Canada, to explore the effects of native predators and the age of knotweed (Fallopia japonica) foliage on nymphal survival in A. itadori. Survival of A. itadori nymphs was significantly reduced on potted plants that were exposed to native predators in the field, compared to plants from which predators were excluded. The number of surviving nymphs was also significantly reduced on older F. japonica foliage, compared to recent regrowth after a summer cutting treatment. We discuss our findings in the context of biological invasion theory and emphasize the potential for increased overlap between the fields of invasion ecology and biological control. Finally, we advocate the use of A. itadori in combination with other control measures as part of an integrated pest management programme, rather than as a solitary measure. Specifically, we recommend that future releases of A. itadori be concentrated shortly after cutting or herbicide treatments in order to maximize the availability of young tender foliage.