Diversity and diagnostics of sugarcane stemborer moths: recent advances and remaining gaps

Moth borers present a major biosecurity threat to the Australian sugarcane industry, particularly the diverse and under studied fauna of Southeast Asia. Accurate identification of moth borer species is very challenging as adults generally lose key external diagnostic characters through incorrect handling. However, genitalia dissections yield robust identifications even though those features are subtle and the lack of a modern systematic review of stemborers, hampers identification. In addition, the larval life stage that attacks cane cannot be reliably identified unless reared through to adults, or DNA-based methods are used. One modern innovation that was expected to advance identification is DNA barcoding, but the uncritical use of DNA barcode sequences has been equally problematic, due to incorrectly identified specimens used to generate publicly available DNA barcodes. These issues were addressed by integrating morphological studies of adult specimens with the generation of new DNA barcodes and nuclear genes using high-throughput (‘next-generation’) sequencing from the largest sample of borer species examined to date. Previous work identified at least 36 exotic borer species posing risks to Australia. We studied all seven high-risk species, 12 of the 14 medium-risk species, and further low-risk and related species. Nuclear gene data from a subset of samples suggests that in most cases the very high levels of barcode diversity represent within-species geographic diversity. There is at least one case of a previously undetected species that requires further investigation. Results clarify the identity and distributions of the major pest species and demonstrate that DNA barcoding is effective as an identification tool when used correctly. This provides another tool for rapid diagnosis and a clear path to refining and extending borer diagnostics in the future. Key words Chilo, Scirpophaga, Sesamia, biosecurity, quarantine