Effect of humidity and temperature on the performance of three strains of Aphalara itadori, a biocontrol agent for Japanese Knotweed
Citation
Fung, C., González-Moreno, P., Pratt, C., Oliver, T.H., Bourchier, R.S., González-Suárez, M. (2020). Effect of humidity and temperature on the performance of three strains of Aphalara itadori, a biocontrol agent for Japanese Knotweed, 146 http://dx.doi.org/10.1016/j.biocontrol.2020.104269
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. The experiments in this paper tested the role of high and low humidity levels on psyllid survival and compared the impact of three psyllid lines: lab line started in 2004, lab line started in 2015 and a hybrid cross, between lines from different host plants. Humidity was of interest because field data had suggested higher humidity may increase survival of the young psyllid nymphs. Contrary to our expectation, the hybrid strain had the worst performance (slowest development rate and lower survival from egg to adult emergence) under both levels of humidity. Exposure to different strains of the psyllid resulted in non-significant differences in plant growth, suggesting biocontrol effectiveness was similar among strains. Although under lower humidity conditions plants exposed to the 2015 line of A. itadori had fewer leaves and accumulated less above-ground biomass. The results suggest that any climate change that leads to drier and hotter summers, could reduce the growth potential of knotweed, when exposed to A. itadori. Genetic bottlenecking of long term lab colonies is an issue for this insect and additional comparisons of recently collected field lines with long term lab colonies are recommended.
Abstract
© 2020Japanese 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 on 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.