Discrimination of different generations of Zeugodacus scutellata using age grading technique and their local genetic variation

Abstract The striped fruit fly, Zeugodacus scutellata , exhibits generation overlap due to its relatively long lifespan. This study clarified the fly generations by age-grading technique and traced migration of local populations using genetic markers. Male adults were monitored using Cue-lure in two different places (Andong and Guri) of mainland Korea during the entire host cultivating period. They showed two occurrence peaks (from late July to early August and from mid-August to mid-October). A developmental model of Z. scutellata using rate summation method predicted four generations during this period. Pterin amounts in fly heads increased with adult age and indicated at least 3 cycles of age variation during the occurrence period with an additional adult generation after the third cycle. The additional peak was supported by field monitoring using protein diet supplemented with terpinyl acetate, which showed an additional occurrence peak during October. These seasonal populations were monitored through their migration by gene flow analysis using randomly amplified polymorphic DNA (RAPD) markers. In each locality, three seasonal populations at July, August, and September were discrete. Although local populations were genetically discrete at July, they were not separate at late seasons except for Jeju populations. These results indicate the usefulness of the head pterin quantification in age-grading of adult populations and suggest that Z. scutellata occurs at least four generations a year. In addition, gene flow analysis using RAPD suggests frequent movements among local populations along with season progression.