Invasive alien species have caused significant damage to global forest ecosystems and tree industries. The increasing frequency of invasions is attributed to economic globalization, changing land-use, and environmental change (Hulme et al. 2008, Hulme 2009, Chown et al. 2015). In particular, live plant imports and the use of wood as packaging material confer opportunities for colonization and long-distance human-mediated dispersal through international trade networks (Brasier 2008, Liebhold et al. 2012, Meurisse et al. 2019). Additionally, anthropogenic climate change exacerbates host range shifts and expansions, introducing invasive species to novel and naïve hosts (Richardson et al. 2000, Hanewinkel et al. 2013).
Some adventive species have dramatic effects on the newly encountered vegetation, resulting in impacts on ecosystem functioning, alterations of forest community dynamics, and damage to human health and economies (Parker et al. 1999, Binimelis et al. 2007, Kenis and Branco 2010, Sanders et al. 2010, Vilà et al. 2011). However, the damaging species represent only a small percentage of all the newly established species, while the greater majority have only negligible negative effect on native vegetation (Williamson and Fitter 1996). This low probability of high impact is a problem in effective pest risk assessment, focused monitoring, and rapid response to consequential invasions (McGeoch et al. 2012).
Protection against pest invasion typically include pest risk analysis and early detection and rapid response (Baker et al. 2009, Koch et al. 2011, Early et al. 2016, Roy et al. 2018, Rabaglia et al. 2019). Pest risk analysis processes evaluate the known scientific evidence and consider potential ecological, economic, and social consequences of invasion. A decision is then made whether regulation is warranted.
Given the uncertainty of eventual impact, however, regulation of newly detected forest pests is often reactive, not proactive (Keskitalo and Pettersson 2012). Undesirable species are often determined as such only on the basis of being invasive elsewhere (Kulhanek et al. 2011, McGeoch et al. 2012). However, many new forest pests were not known to be invasive before their invasion. Therefore, the risk assessment of potential invasive species should include their intrinsic biological features (Roy et al. 2014, Groom et al. 2017). Without baseline biological data, risk assessment and invasion responses are over-reliant on assumptions, which reduces their effectiveness (Roy et al. 2018).
The research presented here aims to proactively identify potentially invasive and damaging wood borers in Asia that may threaten trees in North America. Among the most destructive forestry invasive species belong to the longhorn beetles (Cerambycidae), jewel beetles (Buprestidae), and wood boring weevils (Curculionidae), particularly the bark and ambrosia beetles in the subfamilies Scolytinae and Platypodinae (Evans et al. 2007, Vega and Hofstetter 2014). Woodborers have caused mass mortality events in natural and planted forest ecosystems (Hoffmeister et al. 2005, Mayfield et al. 2008, Haack et al. 2010). Some species can act as primary pests, which can attack and kill trees that are healthy or under minor stress. Woodborers can also vector tree pathogens(Harrington et al. 2005).
Woodborers have traits and characteristics advantageous in dispersal. Many are small, have cryptic lifestyles, and can take a long time to emerge (Cherepanov et al. 1988, Liebhold et al. 2012). Wood-packaging material, live plants, and firewood can all harbor invasive wood borers (Meurisse et al. 2019). While inside the wood, the insect is protected from pesticide application methods (Frank and Sadof 2011). This habit also confers protection from inspection by predators and biosecurity agents alike.
This project employed the principle of sentinel gardens to identify Asian wood borers that present the potential to be damage important tree species in North America. Sentinel gardens are a versatile method that uses host plants planted in a non-native range (ex-patria planting) to document the local, potentially invasive damaging agents (Britton K.O. 2010, Roques et al. 2015, Vettraino et al. 2015, Eschen et al. 2019). Native plants rarely suffer mass-mortality events by native pests and pathogens, and their potential impacts of these as invasive species are hard to predict(Liebhold et al. 2012, Roques et al. 2015). Using non-native trees reduces the uncertainty in pest risk assessments. Pest-host associations documented in this way are more demonstrative of invasive behavior in the invaded region and align with recommendations outlined by Roy et al. (2018) for determining invasive species.
In this project we amend the sentinel garden approach by adding a second key component: tree stress. Some woodborers target trees in their native area that are weakened or stressed, and this trait is often manifested as the attraction to, and killing of, healthy but susceptible species in the invaded areas (Hulcr et al. 2017). This scenario has been shown in some of the most damaging wood borers, including the Asian longhorn beetle (Haack et al. 2010), the redbay ambrosia beetle (Xyleborus glabratus Eichoff) (Mayfield et al. 2008) and the Emerald ash borer (Agrilus planipennis) when introduced into North America. All three demonstrated the aggressive trait of colonization of living trees in their native range, indicating that damage to susceptible tree species in invaded regions may have been predictable (Hulcr et al. 2017). Therefore, we added the stress component in order to identify wood boring species with preference for stressed but living trees in their native range.
China and the United States are the world’s largest business partners, which increases the risk of invasive species exchange. Many of the invasive woodborers established in the USA are native to East Asia (Poland and McCullough 2006, Aukema et al. 2010, Kenis et al. 2017). In addition, China encompasses many regions of high biological diversity (Mattson et al. 2007). Lastly, the flora of China is phylogenetically similar to that of North America. Herbivorous insects, often specialized at a plant genus or family, benefit from the presence of congeners in invaded regions (Mech et al. 2019).