Abstract/Summary

Japanese knotweed (Fallopia japonica) is a highly damaging invasive species affecting UK infrastructure and biodiversity. Under laboratory conditions, the psyllid Aphalara itadori has demonstrated its potential to be a successful biocontrol agent for F. japonica. However, this potential has not materialised in the field where long-term establishment of A. itadori has been unsuccessful and faces the added challenge of climate change. Intraspecific variation (variation among individuals of a species) has been shown to support establishment in alien species and improve resilience to changing environmental conditions, here we propose it could improve the performance of biocontrols. To test this possibility we compared the performance and impact on F. japonica of three strains of A. itadori with different genetic backgrounds, including a newly created hybrid. We hypothesize that genetic variability would be increased in hybrids resulting in greater biocontrol effectiveness (greater impact on plant growth). We also explored the potential influence of changing climate in performance, testing all strains under two humidity conditions (with the same temperature). Contrary to our expectation, the hybrid strain had the worst performance (slowest development rate and lower survival from egg to adult emergence) under both environmental conditions. Exposure to different strains of A. itadori did not result in consistent differences in plant growth, suggesting similar biocontrol effectiveness among strains. Under the drier, more stressful, conditions plants exposed to A. itadori had fewer leaves and accumulated less above-ground biomass. Overall, our results suggest that genetic variability may not be the key to improve A. itadori biocontrol effectiveness, but that predicted climate change, which anticipates drier and hotter summers in the UK, could reduce the growth potential of F. japonica when exposed to A. itadori.