Farm Forestry New Zealand

Forest Protection SSIF research on species other than radiata pine 2020/21

By Toni Withers, Roanne Sutherland, Nicolas Meurisse, Andrew Pugh, Darryl Herron, Te Whaeoranga Smallman, Stuart Fraser, July 2021.

Download SWP-T130 (pdf)

Executive summary

Plantation species other than Pinus radiata (radiata pine), such as Douglas-fir, cypresses and eucalypts, continue to be of pivotal importance to ensuring New Zealand has a diversified forest estate, resilient against biosecurity threats. As part of the SWP partnership, Forest Protection (now the Ecology and Environment research group) contribute research findings from core funding (SSIF) research that is highly responsive to biosecurity threats in the diverse species areas, to ensure sustainable growth of alternative tree species. This report summarises research findings in the last financial year in the aligned projects.

Firstly, a new polyphagous ambrosia beetle known as GAB, Xylosandrus crassiusculus, has been introduced into New Zealand in 2019. It is native to East Asia and has been a highly successful invader worldwide. Like most invasive ambrosia beetles, X. crassiusculus can attack a wide range of woody plants. Adult females colonize physiologically stressed trees by excavating galleries in which they lay eggs and inoculate a symbiotic fungus, Ambrosiella roeperi. Both the founding female and its larval progeny feed on the fungus, not on the wood. Often the first sign of an attack is the sawdust released by the excavating adult, which takes the form of compacted “noodles” extruding from the tree trunk. Scion initiated population monitoring in November 2019 in Kumeu, Blockhouse Bay and Titirangi using panel traps baited with ethanol. Additional traps consisting of Eucalyptus fastigata, avocado and cherry wood bolts pre-soaked in ethanol were established at Kumeu from October 2020 to April 2021. Based on the results presented in File Note 36316895, Taiwan cherry ethanol-infused bolts were more attractive to GAB than E. fastigata and avocado. Wood bolts not soaked in ethanol received zero attacks. We hypothesize that Eucalyptus trees (among other hardwoods), but only those under stress (emitting ethanol as a stress response), will be under threat of attack from this pest, but may not be as susceptible as other species of woody trees in New Zealand. Maintaining stress-free young trees within forest nurseries will be important to avoid attacks from this new pest. We recommend FGR support Scion undertaking more research to understand this pest, how to manage it, and the relative susceptibility of alternative tree species to GAB in New Zealand.

Significant progress has also been made through the Better Border Biosecurity collaboration (b3nz.org.nz) on the safety of insect releases for biological control (through the development of a risk assessment model). Recognition of biosafety risks associated with introduced biocontrol agents (BCAs) is globally increasing, and pre-release assessments of these agents have become more rigorous in many countries, especially New Zealand. We advocate for adoption of a more comprehensive, ecologically- based, probabilistic risk assessment approach to BCA releases. An example is provided using a Bayesian network that can integrate information on probabilities and uncertainties of a BCA to spread and establish in new habitats, interact with non-target species in these habitats, and eventually negatively impact the populations of these non-target species. The new model, BAIPA (for “Biocontrol Adverse Impact Probability Assessment”), could eventually be incorporated into a structured decision-making framework that has potential to support national regulatory authorities such as the EPA (Environmental Protection Authority) in New Zealand. The authors of the File Note 36316811, along with international collaborators, have had a scientific manuscript accepted describing ecological models on biocontrol risk and proposing development of the new BAIPA model. We summarise the content, but cannot permit the entire manuscript be released publicly on the FGR website at this time, as the publication rights have been signed over to the journal.

Cypress canker disease expression is observed irregularly within New Zealand; however, it tends to be more severe in warmer areas. Because species of Seiridium on Cupressaceae in New Zealand have not been well characterised, there is a lack of knowledge regarding pathogenicity and distribution. Molecular research was undertaken on 63 Seiridium isolates in the Scion culture collection (NZFS). One gene region was sequenced, and it groups the isolates into 6 different clades, representing four described species (Seiridium unicorne, S. neocupressi, S. kartense and S. carnicum) and two possible novel species (Seiridium sp.) (File Note 36317015). Based on earlier pathogenicity data, it seems that S. neocupressi, S. carnicum and Seiridium nov. sp. 1 are the species pathogenic to C. macrocarpa and Ch. lawsoniana. This is new knowledge for New Zealand. Scion believes additional research will be required to explore the pathogenicity and identity of the possibly novel Seiridium species in New Zealand.