Using DNA markers and isotope marking to test the effectiveness of fluorescent dust marking during a sterile insect technique program targeting Bactrocera tryoni (Diptera: Tephritidae) in Australia

Fluorescent dust marking is widely used in tephritid sterile insect programs to differentiate mass reared sterile individuals from the wild individuals. While fluorescent dust marking is economical, it does not guarantee 100% marking success. In programs releasing millions of sterile flies, even a very low rate of misclassification of sterile individuals (due to a failure of dust marking) could greatly over-estimate the number of resident wild individuals. This could be an important outcome since, in some horticultural production areas, detection of as few as two wild individuals trigger suspension of exports. In this study, we sought to test the accuracy of fluorescent dust marking for the identification of sterile Bactrocera tryoni (Froggatt) during a sterile release technique (SIT) program in New South Wales, Australia. We used DNA microsatellite data to as an independent discriminator between wild from sterile flies. Our results confirm earlier suspicions that a small proportion of sterile flies remain unmarked during these releases. We also found that wild flies can be misclassified as sterile due to the presence of acquired dust grains on the body. These results indicate that any B. tryoni SIT program should not rely on fluorescent dust alone to unambiguously identify sterile released individuals. We show that additional methods, such as carbon isotope ratio measurements, are practical for use in B. tryoni SIT programs.