Can stable isotope markers be used to distinguish wild and mass-reared Anastrepha fraterculus flies?

Victor Botteon,Maria De Lourdes Zamboni Costa,Thiago Mastrangelo,Adalecio Kovaleski,Luiz Antonio Martinelli,Samantha E M Munroe

doi:10.1371/journal.pone.0209921

Victor Botteon, Maria De Lourdes Zamboni Costa + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0209921

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Abstract

The availability of accurate techniques to discriminate between marked laboratory-reared flies and unmarked wild flies captured in monitoring traps is essential for programs that integrate the Sterile Insect Technique (SIT) to manage fruit flies. In this study, the feasibility of using a stable isotope marking technique for the South American fruit fly, Anastrepha fraterculus (Wiedemann), was assessed. Wild flies were collected from apple orchards, which are a target of a SIT project in southern Brazil. To verify if adult flies could be labelled by the stable isotopes from larval diets, larvae were reared on two different C4-based diets and fruits in laboratory. To evaluate the influence of the two most common attractants applied to capture A. fraterculus (grape juice and CeraTrapTM) and the most common preservation method in fruit fly collections (ethanol), laboratory-reared flies were immersed in McPhail traps containing the respective treatments for two periods of time. Samples were analyzed in an elemental analyzer coupled to a Continuous Flow Isotope Ratio Mass Spectrometer (CF-IRMS) at CENA/USP. The δ13C signatures of flies reared on artificial diets differed significantly from the δ13C of flies whose larvae were reared on fruits and from wild flies. In contrast, the δ15N values were less conclusive and the technique could not rely solely on them. In all cases considered, the δ13C and δ15N signatures from males did not differ from females. Despite the alterations caused by the attractants tested and ethanol, laboratory-flies could be distinguished from the wild ones based on δ13C signatures. This is the first comprehensive study to demonstrate that it is possible to distinguish wild A. fraterculus from flies reared on larval diets containing C4 sugar. The first experimentally derived trophic discrimination factors were also obtained for this species. Thus, intrinsic isotope labelling can serve as a backup to conventional dye marking.

Highlights

The Sterile Insect Technique (SIT), an autocidal method of control that relies on area-wide inundative releases of sterile insects, has been successfully applied by many operational programs to eradicate, suppress, and contain fruit fly pests [1]
A total of 59 wild flies collected in three different apple orchards from Vacaria were analyzed for δ13C and δ15N
The isotopic compositions of wild males did not differ from the compositions of females within each of the apple orchards (P > 0.05) (Table 1)

Summary

Introduction

The Sterile Insect Technique (SIT), an autocidal method of control that relies on area-wide inundative releases of sterile insects, has been successfully applied by many operational programs to eradicate, suppress, and contain fruit fly pests [1]. The fluorescent dye marking method is still the most used in SIT programs against fruit flies [4]. As fluorescent markings from wings, legs and other body parts of the sterile flies can be lost by weathering, grooming or other reasons, dye marks preferably in the ptilinial suture are sought under a UV lamp or epifluorescence microscope. In the Mexico/United States Mediterranean fruit fly eradication program, for example, the percentage of unmarked captured flies varied between 0.05 and 1% [5]. For flies whose heads do not present internal markings, their reproductive organs must undergo a detailed cytohistological study [6]

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