How a 'biological weapon' can save forests in Siberia & North America

Wildfires are not the only serious threat to pine forests across our planet. Bark beetle outbreaks in North America and Siberia have ravaged natural forests so extensively that in some areas the tree death toll has neared 100%.

Scientists from the University of Tyumen have come up with a solution that may surprise you: to use microscopic mites as a sort of natural, “biological weapon.”

Fluctuating temperatures and severe droughts during the 1980-90s not only weakened pine trees across North America, making them more vulnerable, but they also made normally harmless mountain pine beetles as dangerous for pine forests as wildfires.

Warmer winters can lead to a dramatic rise in the bark beetle population, because more beetles than usual survive the cold season and, subsequently, their increased numbers also lead to a reduction of their reproduction cycle from 2 years to 1.

As a result, beetles that normally feed on dead or old trees start "attacking younger [and stronger] trees" and migrating to new areas in search of food.

According to National Geographic, "since the 1990s, more than 60 million acres of forest, from northern New Mexico through British Columbia, have suffered die-offs."

The Canadian Forest Service called the mountain pine beetle outbreak "the largest known insect infestation in North American history."

In some areas, the tree death-toll has almost reached 100 percent.

Currently, the only effective way of dealing with bark beetle outbreaks is by thinning and burning the infested areas.

Forest Biosecurity Research Center launched

In order to better understand how to protect forests, University of Tyumen, in partnership with Northern Arizona University, opened a joint Forest Biosecurity Research Center in March 2019.

Dr. Richard Hofstetter from the School of Forestry at the Northern Arizona University, says it’s important for his work to study the Siberian pine forest’s ecosystems.

“Siberia and North America have a very similar community of plants and beetles and other insects. The species are different. By comparing different communities in different places, different systems, we can look for patterns or differences that can help us solve the problems,” he says.

One of the center’s current focus is to share knowledge and find solutions to preventing insect outbreaks that damage forests.

Biological weapon against bark beetles

Scientists from the University of Tyumen now believe they’ve come up with a promising solution.

Their studies of the Typographus bark beetle - or the European spruce bark beetle, as it’s commonly called - show that the beetle population may be controlled with a specific “biological weapon” - microscopic mites that feed on beetle eggs.

“Mites are one of the main natural controllers of the bark beetle population,” says Alexander Khaustov, leading researcher in X-BIO Institute, University of Tyumen.

There are dozens of different mites associated with beetles. European spruce bark beetles, for example, coexist with more that 60 mite species.

Parasitic mites are just a small portion of this diverse group and they are the mites that actually control the beetle population by feeding on their eggs.

“If we find effective parasitoids that can reduce beetle population within a short time, it will be a very promising biological weapon against forest pests,” says Andrey Tolstikov, Director of X-BIO Institute, University of Tyumen.

The main idea is to find mites that not only feed on eggs, but use them to resettle. Thus they don't need to be grown.

“One mite will be enough for its mass reproduction,” says Alexander Khaustov.

How to deal with an Asian invader?

Siberia's biggest problem is another bark beetle species - the Polygraphus proximus.

It's an invasive species native to Japan and China that came from the Russian Far East and took Siberia by storm.

One of the reasons it succeeded in ravaging vast Siberian forests is that it seems to have left its parasitic mites back home.

Faced with the urgent task of stopping the Polygraphus proximus, Tyumen scientists nearly succeeded finding a parasitic mite for the Asian invader.

“We grew Polygraphus proximus [...] and tried to artificially plant mites on it. Mites ate well beetle larva, bred well, but failed to attach to it, which is very important, because only mites that can resettle with a beetle species can control its population”

What the specific reasons mites choose to be associated with beetles are yet unknown.

Scientists say it may be subject to very intimate chemistry that’s yet to be explored.

The ideal “biological weapon”

Mites seem to be an ideal weapon against beetles, because they are only associated specifically with the bark beetle species.

“These mites are associated with bark beetles. Many of them are highly specialised. It means that we do not interfere with nature,” says Alexander Khaustov.

According to Richard Hofstetter, “The use of mites can be effective when beetle populations are low, it can keep the population down.”

He says that “these are native mites, naturally found on beetles, so there are ways to increase their abundance. Then, it can be a tool to keep reproduction down and increase the beetle mortality rate within trees.”

And even if scientists fail to find parasitic mites for most dangerous bark beetle species, there are other organisms in the pipeline that could be used as a “biological weapon”.

Like the parasitoid wasp or even bacteria and fungi.

Gleb Fedorov, RBTH