Could fruit fly polyphagy compromise trace elements as markers of natal origin?

Abstract

The potential for trace element and/or stable and radiogenic isotope signals to differentiate high risk pest insects from different geographic places has been demonstrated elsewhere. However, one of the key questions is, how reliable is this as a tool for endusers if biological and environmental factors cause significant, spatially-unrelated, heterogeneity in the biogeochemical signal? One such factor might be the polyphagous nature of fruit flies. If different species of plant at the same geographic location differentially influence the signal from the soil, then that expressed by the developing larvae may also vary. This would be further compounded by not knowing which plant species the larva of a trapped adult fly had originated from. A preliminary experiment in South Australia to test this is described, using different fruit hosts from the same orchard area. Mass spectroscopy analysis of the resulting flies suggests that host has no effect for the majority of trace elements; those for which there did appear to be an effect were amongst the common, biologically active elements, which in any case were to be omitted as markers. Thus, for trace elements at least, polyphagy is unlikely to be of concern. The fly samples here were also used to show that, compared to use of an established method needing pooled flies for the highly laborious acid dissolution and solution ICPMS analysis, laser-ablation ICPMS is a much more efficient and sensitive method that enables use of individual fly body parts.