Project Leader, Organisation
David Murphy, Queensland University of Technology
PBCRC2111 (https://www.pbcrc.com.au/publications/pbcrc2272/) demonstrated Sr isotopes and trace metals as a powerful tool for geographic discrimination, but the method was limited to fruit flies and required pooling of samples (5-20 flies per analysis).
Continued method development at QUT has led to a novel MS-MS mode Sr isotope analysis and improved digestion methods that, importantly, allow analysis using single flies (PBCRC SI20074).
This project intends to extend this ew technique to beetles, bugs and moths relevant o the National priority plant pests lists (NPPP, 2016), testing digestion methods and detection limits towards a generic tool for determining natal origins of any biosecurity risk pest.
Objectives and impact
The ability to discriminate geographic origin of a biosecurity threat is immensely valuable for biosecurity decision-making. Unfortunately, when a biosecurity threat is first encountered there is generally limited material available. Knowing how much material is required for successful analysis of different species will pre-empt sub-sampling needs for timely outcomes.
Insect species relevant to the National Priority Plant Pest List will be chosen based on a variety of functional groups such as leaf-chewing moths (eg Lymantria), sap-sucking busg (eg BMSB) and wood boring beetles (eg longhorn beetles). This is vital as it is hypothesised from preliminary data that different feeding methods produce different trace metal content, eg BMSB has Sr concentrations 6x lower that of fruit flies. The consequence impacts on Sr isotope analysis which is critical to origins assessment. Viability of additional Pb isotope analysis will also be investigated. The key output will be a manuscript with the impact is peer-reviewed evidence of the potential for this technology beyond fruit flies and methods tailored accordingly for timely assessment of origins.
There is an urgent need for a method of provenance determination of biosecurity samples, insect incursions in particular. Biogeochemical markers, which are non-inherited but linked to geographic variation, are presently the only viable option for this. However, the existing techniques are not fit-for-purpose, as they are too slow, expensive, and lack the required analytical sensitivity.
A new method of Sr isotope analysis has been developed that allows for 88Sr/86Sr ratios to be obtained with 99.8% precision on 2-4 ng of Sr using a Thermo iCap TQ ICP-MS in MS-MS mode This equates to approximately 0.4 mg of insect tissue. In addition, we investigate the Pb concentration in insects and link this to preliminary method development for Pb isotopes that indicate Pb isotope ratios can be obtained on the Thermo iCap TQ ICP-MS on 4 mg of Pb. This equates to minimum of 5 mg of insect tissue. These methods now enable the use of Sr and Pb isotope analysis to help answer biosecurity questions about provenance as it allows for very small amounts of tissue to be analysed. The technique is relatively inexpensive and has a fast turnaround, and is thus suitable for biosecurity operations as well as population-scale studies.
Here we assessed how variation in feeding styles affects the concentration of the provenance sensitive elements Sr and Pb in insects, and therefore if there were limits to the use of single specimens for measurement of their isotopes. Ten insect species were studied to include the functional groups of leaf-chewing moths, sap-sucking bugs, wood boring beetles, root feeders, nectar feeders and carnivores. There was no distinction in Sr or Pb concentrations for the ten different insect species. From this we conclude that functional group does not influence the Sr and Pb concentration of insects and the weight of single specimens suffice for analysis except very small species such as scale insects.
The full report can be downloaded here …