Stable Isotope Markers Differentiate between Mass-Reared and Wild Lepidoptera in Sterile Insect Technique Programs

In this study we identified a number of moth (Lepidoptera) species that are potential targets for the sterile insect technique (SIT), and we assessed the feasibility of using stable isotope signatures as markers to distinguish mass-reared from wild moth species. Large natural differences in the isotopic signatures of commercially available sugars render them novel markers for mass-reared insects. Sugar beet (Beta vulgaris L.; Caryophyllales: Amaranthaceae), a C3 plant, has a stable isotopic signature (a measure of the ratio of the stable isotopes ¹³C:¹²C) of around -27‰ relative to Vienna Pee Dee Belemnite (VPDB; the international C isotope standard for the stable isotopes, ¹³C and ¹²C), and sugarcane (Saccharum spp.; Poales: Poaceae), a C4 plant, has an isotopic signature of around -11‰. Thus by means of such a distinct isotope ratio in the sugar in the diet, mass-reared insects can be easily distinguished from wild insects with a high degree of certainty. It was shown that the method could be extended using a multiple isotope approach, with ¹⁵N or a full suite of C, N, S and O isotopes. Intrinsic isotope marking of mass-reared moths proved to be an accurate means of distinguishing wild from mass-reared populations, based on isotopic differences between the wild host plant species and the diets used in mass-rearing, which where possible, had been manipulated to contain the isotopically divergent sugar type. This intrinsic labeling using stable isotopes could be useful in the assessment of the quality of mass-reared moths, because a stable isotope is a marker that does not affect the insect in any detrimental manner.