Invasive pathogens and arthropods: biogeography, drivers of invasion success, impacts on indigenous forest trees and emerging management strategies

Frank Chidawanyika^{1, 2*} Komivi S. Akutse^1* Tendai Musvuugwa³ Abdullahi A. Yusuf⁴ Casper Nyamukondiwa⁵

• ¹International Centre of Insect Physiology and Ecology (ICIPE), Kenya
• ²University of the Free State, South Africa
• ³Sol Plaatje University, South Africa
• ⁴University of Pretoria, South Africa
• ⁵Botswana International University of Science and Technology, Botswana

With the ongoing global anthropogenic climate change, a silent war rages in forests, the lungs of the earth. Invasive pathogens and insect pests are decimating native trees, compromising ecological function, biodiversity, and ecosystem services. Many of the processes surrounding successful biotic invasions are broad and have been previously analyzed (Hobs et al., 2006;Blackburn et a., 2011). For invasive insect pests and pathogens, globalization, the rise in human population and associated environmental disturbances are recognized as fundamental drivers of introduction of propagules of nonnative species to novel environments. Superior tolerance of extreme climate environments, in particular temperature, is also associated with invasion propensity among ectotherms such as insect pests (Nyamukondiwa et al., 2022). A broad host range also contributes to the success of invasive species as it ensures population persistence even when otherwise favorable hosts may not be present in the invaded ranges (Kelley 2014). The ecological and economic impacts of such invasions are diverse, and the latter hugely underestimated (Diagne et al., 2021). However, it is increasingly apparent that there is modification of trophic interactions, eliciting both top-down and bottom-up feedback, that can compromise native biodiversity. These diverse attributes and consequences of species invasions call for an in-depth understanding of the factors contributing to invasion success. In particular, the role of climate stress resistance in geographic range expansion and chemically mediated below and above ground pest-pathogen interactions with trees are paramount. Such an understanding will significantly enhance management strategies through both improved prediction of potential outbreaks and development of biologically intensive novel approaches for invasive species pest control through disruption of trophic interactions that aid invasions. This research topic highlights how the knowledge on the biology, physiology, and ecology of the invasive organisms, as well as the mechanisms behind their successful expansion and establishment could aid protection of native forests. 2022) tested a novel early warning system detecting asymptomatic 61 beech leaf disease (BLD) in infected trees using near-infrared spectroscopy and machine learning. 62Although validation using qPCR-based protocols could not fully attribute spectral differences due to 63 sole pathogen presence, such techniques could be key in tree disease surveillance and in-field 64 diagnostics for BLD enabling timely mitigative measures if precision is improved. 65In another study, molecular-based surveys together with cultivation-based growth experiments and 66 microscopy were used to investigate the host and abiotic constraints mediating the distribution of 67 Sphaeropsis sapinea (syn. Diplodia sapinea), a causal fungal agent of Diplodia tip blight, which is a 68 major pathogen of economic importance in pine forestry worldwide (Roy et al., 2022). The pathogen 69 was detected on all the seven Pinus species that were studied. Interestingly, only P. sylvestris and P. 70 nigra could host the pathogen with asymptomatic needles, suggesting that they may potentially be the 71 original hosts. The distribution of the pathogen was also delimited by altitude, where trees in elevation 72 above 800 m did not have any infections. This could also be explained by the fact that under controlled 73 conditions, lower temperatures reduced the growth of S. sapinea isolates. Prior exposure at 35 °C 74 improved the growth of the pathogen isolates at high temperatures with optimal range being 20-30 °C, 75 suggesting presence of phenotypic plasticity for survival at higher temperatures. Thus, as climate 76 change ensues, warming temperatures are projected to increase the geographic range of S. sapinea 77 infection. 78Articles published in this Research Topic "Invasive pathogens and arthropods: biogeography, drivers 79 of invasion success, impacts on indigenous forest trees and emerging management strategies" highlight 80 the processes mediating invasion patterns in indigenous forests and potential strategies for surveillance 81 and management. Through this Research Topic, our goal was to showcase recent global advances in the 82 biology and ecology of invasive insect pests and pathogens, and their management. The collected 83 articles show potential for monitoring tools, even for cryptic species, and management through in-depth 84 understanding of the biology and ecology of pest-pathogen and tree interactions. The role of 85 temperature in defining geographic ranges of organisms was also highlighted. Under the ongoing 86