Assessing the applicability of nuclear 18S and ITS2-28S rRNA genes for diagnostics of Bactrocera dorsalis (Diptera: Tephritidae) in the Philippines

Abstract

Fruit flies belonging to the Bactrocera dorsalis species complex pose a significant threat to mangoes and other crops in the Philippines and worldwide. Identifying cryptic species within this complex is challenging, particularly when relying solely on morphological analysis. In this study, we sequenced two fragments of the nuclear 18S and ITS2-28S rRNA genes from specimens of Bactrocera dorsalis Hendel collected in the Philippines to assess their applicability for species diagnostics. Subsequent sequencing and analysis revealed that the 18S and 28S rRNA gene fragments matched B. dorsalis sequences in NCBI but also displayed high similarity with other Bactrocera and insect species. On the other hand, sequences of the ITS2 segment showed hits specific to B. dorsalis. Further analysis of the 18S rRNA gene in fruit flies collected from various sources and host plants in the country suggests conserved sequences among Bactrocera samples, irrespective of collection site and host plant species. In conclusion, our findings suggest that, among the tested nuclear DNA fragments, only the ITS2 demonstrates sufficient species-level nucleotide variation for effective use as a molecular diagnostic marker for B. dorsalis identification.