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Confidence in stable isotopes to verify a high risk pest incursion as foreign or NZ established

This three-year project finished in mid-2022.

Project abstract

Understanding if an exotic insect belongs to a locally breeding population or not is valuable information for incursion responses. As markers of provenance, natural abundance, geologically linked, bioavailable strontium isotope ratio (87Sr/86Sr) signatures of an organism are useful for this. The aim was to develop a fit for purpose geographic reference dataset and spatially explicit scalable model to predict continuous 87Sr/86Sr values across the landscape. The resulting isoscape could then be interrogated to determine the probability that a specimen is from the place it was found.

Georeferenced leaves were sampled at high-risk surveillance sites in Northland, Auckland, Bay of Plenty and Christchurch and their 87Sr/86Sr determined by inductively coupled plasma tandem mass spectrometry. Together with data from a New Zealand collaborator, the first New Zealand isoscape was produced using a random forest model framework and validated for provenancing using geo-referenced cows milk. A subsequent B3-updated isoscape was used to confirm that Queensland fruit fly detected in New Zealand, of unknown origin from trap detections in Auckland (2019) or known origin from rearing on New Zealand fruit, were reared at the place they were found. However, assessment of the isoscape for use with other insects, especially those feeding on different plant parts, was difficult to evaluate with the variation observed within and amongst leaf, sap, or fruit feeders; further study is needed.

This project concludes three phases of research to prove the principle that stable isotopes are useful for provenancing insects in a biosecurity context. Details of all the analytical and statistical protocols for operational use have been documented. Australian 87Sr/86Sr and lead isotope data from B3-aligned projects is also available towards a trans-Tasman regional isoscape to improve confidence in assignment of New Zealand or Australian breeding populations.

Biosecurity outcome

  • Stable isotope (SI) signatures of origin will aid MPI decisions on the level of response needed for a new high risk, post-border pest detection, by providing supporting evidence of a locally breeding population or fresh overseas arrival.
  • The first evidence of whether the plant part (fruit, leaf, sap, wood) used for insect growth, and acquisition of its SI signature, influences use of that data.

Science outcome

  • A novel statistically-based method of landscape isotope (isoscape) data to distinguish the origins of insects will be generated.

For more information and publications from this and other B3 projects, visit Zotero.

The Zotero database is on the B3 homepage under ‘Outputs’.