Vol. 38 No. 1, 1999

Metaphase Karyotypes of Fruit Flies of Thailand (III): Six Members of the Bactrocera dorsalis Complex

Visut Baimai*, Jaros Phinchongsakuldit and Wachareeporn Trinachartvanit

Department of Biology, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand

Visut Baimai, Jaros Phinchongsakuldit and Wachareeporn Trinachartvanit (1999) Six species of fruit flies belonging to the Bactrocera dorsalis complex used in this study include B. propinqua, B. irvingiae, B. carambolae, B. pyrifoliae, B. arecae, and B. melastomatos. Wild samples collected from infested fruits of various host plants were examined cytologically. Analysis of mitotic karyotypes of these species has revealed distinct patterns of metaphase chromosomes due to different amounts and distribution of constitutive heterochromatin in sex chromosomes and autosomes. The general pattern of mitotic karyotypes of B. irvingiae and B. propinqua resembles that of B. dorsalis, and they are classified in Group 1. Likewise, B. carambolae and B. pyrifoliae exhibit mitotic karyotypes of Group 4 showing specific patterns of heterochromatin in the centromeric regions of the X chromosome and autosomes. Bactrocera arecae exhibits distinctive patterns of pericentric heterochromatin in autosomes and sex chromosomes. Interestingly, metaphase chromosomes of B. melastomatos do not match with any groups of mitotic karyotype categorized earlier because of the very small size of the X and Y chromosomes. These findings suggest the significance of heterochromatin differentiation in karyotypic evolution of these species of fruit flies in Thailand. Such distinctive patterns of heterochromatin in mitotic karyotype are useful as diagnostic characters for separation of these closely related species of the B. dorsalis complex.

Key words: Bactrocera dorsalis complex, Mitotic chromosomes, Heterochromatin, Karyotypic evolution.

*Correspondence: Tel and Fax: (662) 644-5422. E-mail: scvbm@mahidol.ac.th