Establishment of the biological control agent Aphalara itadori is limited by native predators and foliage age
Citation
Jones, I.M., Smith, S.M., Bourchier, R.S. (2020). Establishment of the biological control agent Aphalara itadori is limited by native predators and foliage age. Journal of Applied Entomology, [online] 144(8), 710-718. http://dx.doi.org/10.1111/jen.12792
Plain language summary
The sap-sucking psyllid, Aphalara itadori has been released for biological control of invasive knotweeds in Canada and the UK. To date we have not been able to get consistent establishment and growth of the psyllid populations at release sites. We suspect this is because of low survival of the first stage nymphs after hatch from eggs. The experiments in this paper test two possible explanations for low survival. The first experiment in this paper assesses the potential impact of predators on psyllid eggs to test a possible mechanism for poor population growth. The second experiment compares the survivorship of psyllids on young foliage which is soft versus old knotweed foliage, which is much tougher and may be difficult for the young psyllids to feed on. The results showed that predators were have a significant impact on survival of psyllid nymphs and that nymphs survived much better on young foliage than on old foliage. The results will assist with integration of psyllid releases with other management tools. A specific recommendation is that future releases of the psyllid be concentrated shortly after cutting knotweed patches or herbicide treatments, in order to maximize the availability of young tender foliage and increase the likelihood of establishment.
Abstract
The 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.