AgResearch scientists tackling costly farm pests have shown their skills as amateur detectives, tracking down and using DNA from decades-old museum collections to prove their case.

Research associate Nicky Richards and her colleagues were recently confronted with a Porina (Wiseana) caterpillar found in Southland – and in line with broader efforts to better understand this major pasture-munching pest, needed to establish which species of Porina they were looking at.

Some species of Porina pose a much greater threat to pasture on New Zealand farms than others. Although seven Porina species are recognised, and the species can be identified by sight at the adult moth stage, it is impossible to do the same with the caterpillars as they look identical.

“We suspected the caterpillar found in Southland was from an elusive Porina species known as Wiseana (W.) fuliginea, but to confirm it we needed to analyse an adult moth of that same species,” Mrs Richards says.

“Unfortunately, no adult W. fuliginea had been found by us in our previous 20 years of field collections. So we had to find another way. Our connections led us to museum specimens held in the New Zealand Arthropod Collection hosted by Landcare Research. There we found dried adult W. fuliginea specimens that had been identified and preserved after their deaths 33 years ago.”

“We took legs from these long-dead moths to generate genetic sequences – which takes more work when the DNA has broken down over time. It’s basically like putting together pieces of overlapping Lego to build what you need.”

“What we generated from these 33-year-old specimens proved identical to the sequence from the caterpillar found in Southland. In other words, we had a DNA match.”

“This work has helped us develop a new DNA-based method to identify Porina caterpillars. By building our understanding of this pest, we can learn how best to help farmers prevent the hundreds of millions of dollars of damage it can do to pasture on New Zealand’s farms each year.

“We can now explore environmentally friendly treatments for Porina outbreaks and target the species that are the key pasture annihilators – and giving all Porina species a bad name.”

Learn more about Porina and other pests

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