Tracking a tiny
but deadly menace
By David Baeta

OTTAWA — A ruthless killer is lurking in Canada's forests, but, unlike most criminals, this one's hard to trace and contain — that's because it's about one inch long.

The perpetrator is an insect called the Asian Longhorn beetle and it kills Canadian trees without mercy.

Trunks and branches of healthy trees are first to feel the wrath of this beetle as it tunnels through the bark, nestles in the hardwood, and eventually kill its host.

Scientists found a way to identify the Asian Longhorn beetle using its DNA—even if the beetle is in its larval or adult stage.

There are currently no detection procedures to track this beetle down, however the Canadian Forest Service (CFS) have scientists working on the case.

Dr. Arthur Retnakaran is one of the scientists. His study was recently published in the journal Archives of Insect Biochemistry and Physiology.

In essence, he has developed molecular markers for detecting not only the Asian Longhorn beetle but the Brown Spruce budworm and other allied invasive species. In other words, he found a way to detect the Asian Longhorn beetle using its DNA sequence—much like it is done in criminal investigations involving humans.

Ladies and gentleman: the beetle!

The black beetle sports white spots, a shiny shell, and a distinguishable antenna banded with black and white lines.

With the capacity to fly distances covering three city blocks, the beetle poses an even more serious threat to Canada's 420 million hectares of forest.

" Anything that can fly will be beneficial to the insect's propagation, as it makes it easier for it to move," says Dr. David MacLean, Dean of Forestry at the University of New Brunswick.

The beetle was accidentally introduced to Canada because it was lodged in wood used to make packing crates; it is originally from China and the Korean peninsula.

Once in Canada, the beetle found the perfect milieu where it could quickly wreak havoc. "It came from Northern China, where there are very similar conditions," says Dr. Retnakaran. "It has no predators to control them here. It's a perfect ecological match."

More specifically, it's the beetle's one-year life cycle that is damaging to trees. The cycle begins with the female beetle chewing holes in the bark of trees—called oviposition sites—to lay eggs. Within 10 to 15 days, the worm-like larvae tunnel under the tree bark and bore into healthy hardwood trees.

"Once they've hatched, the larvae will eat all the wood behind the bark to stay alive until they come out," says Dr. Retnakaran.

The larvae feed on wood during the fall and winter and emerge through exit holes in the spring. Now adult, the beetle feeds on tree exteriors for two to three days, then mate –restarting the cycle. The adult beetle remains active only during summer and early fall months before dying.

Tracking the unknown

A publication on invasive species by the CFS says the beetle could be quite damaging for Canada's forests if an epidemic occurred. Since the beetle loves maple trees, CFS claims it would be particularly damaging to the maple industry, which is worth $100 million annually.

Once the beetle has struck, the only way to save neighbouring trees is to completely destroy them.

The only existing solution to remedy the problem is to destroy infected trees. That's why Dr. Retnakaran says it is important to track this deadly killer before it does extensive damage.

Usually, invasive species are identified by the appearance of the adult insect, says Dr. Retnakaran. But that's not possible with insects.

"If I was a larva it would be harder to detect and define who I was in comparison to other larvae around me," says Dr. Retnakaran. Physically, they are all very similar; this is where DNA comes in. "They [CFS] wanted us to design a DNA system to detect the beetle, much like the ones used in forensics."

During crime scene investigations, criminals are often identified using their DNA sequence. DNA consists of two long chains of nucleotides twisted into a double helix and joined by hydrogen bonds. In other words, DNA is an imprint of the characteristics of an individual.

From humans to insects

The DNA extraction is very efficient in a crime scene involving humans, but when you're talking about insects things are a little different. In essence, Dr. Retnakaran wants to transpose DNA fingerprinting to the world of insects. However, this is problematic because the beetle's genome is unknown.

Dr. Retnakaran says that his study has solved this problem. He has identified genetic markers that can be used to distinguish the beetle from other closely related insects — without knowing the full genome.

Dr. Retnakaran says that, typically, when you don't know the genome of what you are studying you will use primers to analyse it. "Primers are small, random pieces of DNA, which are manufactured to stand out when the sequence is extracted," says Retnakaran.

Primers are combined to a single strand of DNA and they will force added-enzymes to synthesise a combination of matching bases on the DNA strand when it replicates itself.

Once that's done, the strand is an identical duplicate of the first DNA strand.

Using a procedure called electrophoresis, the size of DNA molecules and their respective primers can be established. During this procedure, which is comparable to sieving methods used to find gold, DNA will be placed in a gel-like substance similar to Jell-O.

Containing the pest

Dr. Retnakaran is not using electrophoresis to find gold. He uses it to establish a positive match between the DNA sample and the culprit. The size of the molecule and the primers he inserted in the sequence, help him to unambiguously make a link between the sample and culprit — just like in a crime scene investigation.

Dr. Retnakaran says this will help save millions of trees in Canada.

Right now, when a tree is infested, blanket measures are used to eliminate the beetle. In essence, all the trees in a given radius will be cut, chipped, and burned.

"From an ecological standpoint, they can be as damaging as a wild forest fire," MacLean says of the potential damage of insect outbreaks.

Thanks to Dr. Retnakaran's molecular markers, field workers will be able quickly and reliably identify where the beetle has struck — at the same time saving countless trees.