Opening a can of worms

Stemborer moths damage cereal and sugarcane crops globally. Identifying the major pest species is surprisingly difficult.

We constructed a DNA barcode library for the most serious stemborer moth pests from Africa and Asia to aid quarantine identifications. Our study fills some gaps in our knowledge of stemborer diversity but also highlights others.

Caterpillars of stemborer moths eat grasses and related plants–cereals and sugarcane–which provide half of the world’s daily calories. Some species can reduce crop yields by 40% and are on quarantine watch lists. But distinguishing the species is a challenge. Adult moths are small, brown, nondescript and one needs to dissect males to find characteristic differences. Their caterpillars have even fewer distinguishing features, but this is the life stage that feeds on crops, and they are more commonly intercepted by quarantine agencies. We resorted to DNA-based methods to identify them, particularly Chilo and Sesamia species.

Our study produced the most detailed DNA barcode dataset yet for stemborer moths, including all seven of the pest species considered to pose a “high risk” to Australian sugarcane, 11 of the 15 “medium risk” species, and 40 other species. Almost all of these species can now be identified using barcodes.

One of the difficulties we encountered was the extraordinarily high levels of mitochondrial DNA (mtDNA) diversity, suggesting that there are new species awaiting discovery. However, in some cases our only samples from a particular country were caterpillars, which cannot be independently identified using morphology. Interpreting such data was made all the more difficult by the two dozen cases of species misidentifications we found recorded in international DNA databases.

While our study has set the record straight, much remains to be done. Future studies will need larger samples of adult moths and comparative genome data to clarify the species status of certain pests.

This project is funded by Sugar Research Australia. Other collaborators include the Department of Agriculture and Water Resources, NT Department of Primary Industries and Resources, IRD (Institut de recherche pour le développement), and the South African Sugarcane Research Institute.

Andrew Mitchell, Senior Research Scientist

More information:

• Timothy R. C. Lee, Stacey J. Anderson, Lucy T. T. Tran-Nguyen, Nader Sallam, Bruno P. Le Ru, Desmond Conlong, Kevin Powell, Andrew Ward & Andrew Mitchell. 2019. Towards a global DNA barcode reference library for quarantine identifications of lepidopteran stemborers, with an emphasis on sugarcane pests. Scientific Reports 9: 7039.