Item

Isotopes and trace elements as geographic origin markers for biosecurity pests

Holder, Peter W.
Date
2012
Type
Thesis
Fields of Research
ANZSRC::0502 Environmental Science and Management , ANZSRC::0603 Evolutionary Biology , ANZSRC::060302 Biogeography and Phylogeography
Abstract
Protecting a nation’s primary production sector and natural estate is heavily dependent on the ability to rapidly determine the risk presented by incursions of exotic species. Accurate point of origin discrimination in such biosecurity incursions can direct appropriate operational responses in exotic pest eradication and post-border incursion campaigns, as well as identify risk pathways. Reading natural abundance biogeochemical markers via mass spectrometry methods is a powerful tool for tracing ecological pathways as well as provenance determination of agricultural products and items of forensic interest. However, the application of these methods to trace insects – man’s most damaging competitors – has been under utilised to date because our understanding in this field is still in a phase of basic development. The internationally distributed moth, Helicoverpa armigera (Noctuidae), has been used to examine processes that are fundamental to the location-to-plant-to-insect imprinting of light and heavy element isotope ratios and trace element profiles. The validity of using multivariate biogeochemical profiles to differentiate insects of New Zealand natal origin from insects of exotic origin was also assessed. This study initially required the development of an integrated method for the collection of natural abundance δ²H, 87Sr/86Sr, 207Pb/206Pb and 208Pb/206Pb isotope ratios and trace element concentration profiles from single insect specimens. In a comparison of moths from Australia and New Zealand, none of these biogeochemical markers were individually able to separate moths from the different experimental regions (150 to 3000km apart). Conversely, the region of origin was able to be distinguished for approximately 75% of individual H. armigera samples using multivariate analysis. Therefore, the determination of whether a biosecurity sample has originated from its collection point, or not, is likely to be successful.In addition, the primary constraints and limitations of natural abundance biogeochemical science in an entomological context have been quantified sufficiently to enable further application of biogeochemical markers. These limiting factors are: 1) the expression of short term, input signal δ²H variation in insects, not the average annual rainfall δ²H; 2) hydrogen turn-over in adult moth wing tissue over the first four days post emergence affects the δ²H signal; 3) adult diet affects trace elements expression in whole insect preparations; 4) polyphagy introduces biogeochemical signals from more than one host species into the insect population, and affects both light element isotope and trace element biogeochemical signals; and 5) there is a significant degree of intra-population variation in marker expression. These limiting factors need to be either resolved by subsequent research, or taken into account when using biogeochemical markers in entomology. Given the geographic resolution demonstrated, with further adaptation of the biogeochemical methodology to accommodate additional global regions and insect-host relationships, this approach to geo-location has considerable potential for biosecurity as well as other disciplines including forensics, ecological studies and pest management.
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