Key points
- Pine Wilt Disease has caused devastating loss of pine forests in Asia and Europe, but is absent from Australia—and we want to keep it that way.
- Pine Wood Nematode is a tiny roundworm and the lead character in this biosecurity story.
- A new National Diagnostic Protocol will help keep Australian pine plantations safe from this pest.
We’re all familiar with animal disease vectors, such as mosquitoes that spread malaria parasites. The carrier and the disease agent work in a team of two.
Pine Wilt Disease is a disease of pine trees. Its spread involves a complex interplay between a trio of characters.
A three body problem
In the popular science fiction novel, and now Netflix series, The Three-Body Problem involves celestial bodies the size of planets and suns.
Our three body problem is science, not fiction. It involves three much smaller bodies: a nematode, a fungus and a beetle. (There’s also bacteria involved, but let’s keep things simple for now!).
The nematode in our story is a tiny roundworm only one millimetre long. It’s called Pine Wood Nematode (Bursaphelenchus xylophilus).
You might be able to guess from its names that Pine Wood Nematode is a problem for pine trees. It causes Pine Wilt Disease.
When Pine Wilt Nematode is carried to a pine tree by a beetle, it feeds on cells inside the tree and multiplies very rapidly. Billions of nematodes — and the tree’s response to them — prevent water flow, causing the tree to wilt and die.
The nematodes themselves vector strains of blue stain fungi, which can grow inside the tree and provide extra food for the nematodes once the tree dies.
Trees killed by the nematodes are attractive to several species of beetles, which breed inside the damaged tree. The nematodes gather in the breeding chambers of the beetles, attach to the bodies of the beetles, and travel with them to new host trees.
A tree body problem
Dr Dan Huston is a postdoctoral researcher at the Australian National Insect Collection. Dan is so passionate about his work on parasites he named a marine trematode after his baby daughter, Petra. Enenterum petrae is a parasite that lives inside a species of marine fish, the Brassy Drummer. It’s an honour to have a species named after you!
Dan said Pine Wood Nematode is native to North America. It can take out a pine tree in as little as six weeks and is a huge threat to timber plantations. But it's not currently found in Australia.
"This nematode is a devastating pest of pine trees around the world and a biosecurity priority for Australia," Dan said.
"It could enter Australia in shipping containers, wood chips or timber palettes. And although we don’t have the same species of beetles here, they may be picked up by a local species, as has happened when it invaded Asia and Europe.
"The big problem with protecting Australia from Pine Wood Nematode is that it looks like a lot of other tiny nematodes."
Diagnosis: nematode!
Nematodes live just about everywhere on Earth. They are so abundant that all of them lined up head to tail would stretch across space beyond the home planet of the San-Ti (the aliens in The Three-Body Problem). But most nematodes are so small we don’t even think about them.
Dan and his colleague, Dr Mike Hodda, researched and wrote National Diagnostic Protocol for Pine Wood Nematode. It’s a huge achievement that provides the tools and information for Australia to diagnose Pine Wood Nematode.
"The diagnostic protocol means that whenever there’s a suspected incursion of Pine Wood Nematode, it can be quickly identified and dealt with," Dan said.
The work relied on specimens of nematodes held in our Australian National Insect Collection. Despite its name, this collection includes many kinds of invertebrates that aren’t insects, like nematodes.
"There are lots of harmless native nematodes, many of them without scientific names. They are very difficult to tell apart from Pine Wood Nematode," Dan said.
"We have a reference collection of hundreds of specimens related to this project. They are stored on microscope slides, which lets us zoom in on the details of different species."
Dan is now working on another National Diagnostic Protocol for Cereal, Barley, Oat, Carrot and other Cyst Nematodes, which are destructive quarantine pests of grains and vegetables.
Unlike Pine Wood Nematode, Cyst Nematodes live in the soil and severely damage plant roots. Their main vector is humans!