Termite Pest’s Faecal Fortress Is Part Of Its Immune System

Formosa is the Portuguese word for “beautiful”. It was the name given to Taiwan by sailors passing by in the 16th century. The name was changed in 1949, but it still lingers on in people’s minds, in the names of local businesses, and in one annoying global pest.

The Formosan subterranean termite (Coptotermes formosanus) was first described in Taiwan in the early 1900s and although it originated in China, the name stuck. From there, wandering humans took it all over the world. It’s what most people think of when they hear the word “termite”—a small, white insect that eats wood and sometimes, specifically, the wood in your house. Each individual is no more gluttonous than your average termite, but the million-strong colonies are so big that they inflict serious damage upon buildings.

There are around 3,000 species of termites, and while many build huge towers and castles, the Formosan termite’s kingdom is entirely underground. There’s a core nest and several satellite chambers, connected by long foraging galleries, which occasionally rise up to find houses, trees, and other wood sources.

Even as the Formosan termites are destroying your house, they are building their own. Their construction material is… well… your house, but chewed up, digested, and excreted out the other end. They use their faeces to coat the walls of their foraging galleries. And they pack it together with chewed wood and soil to create a spongy “carton material”, which fills the empty spaces of their nests and foraging sites. A termite is effectively a machine that converts a house or tree into an underground faecal fortress.

But the faeces are more than just a building material. They’re also part of the termite’s immune system.

The termites encounter many dangerous diseases in their underground incursions, including many insect-killing fungi.  Scientists have actually tried to use these fungi to kill termite colonies for 50 years, but none of the field trials succeeded. The insects are just too good at controlling the infections. They secrete antifungal chemicals, groom each other to remove spores, and bury dead infected nestmates.

Thomas Chouvenc from the University of Florida has been studying these strategies for many years. But recently, he started to realise that the nest itself might help to keep the insects healthy.

His team collected carton material from five Formosan termite nests and showed that they’re rich in Actinobacteria. These microbes are a regular part of insect healthcare, protecting them against fungal diseases. Indeed, Chouvenc showed that a single species of these bacteria—Streptomyces—slashed the growth of the deadly fungus Metarhizium anisopliaei by two-thirds.

The fungus grows inside the bodies of insects, consuming them from within before erupting out as a white mould. But Streptomyces secretes chemicals that stop the fungus from germinating or growing.

To see if this actually helps the termites, Chouvenc added 50 termites to small mini-nests, which he built using sterilised carton material. If he added M.anisopliae, around half the termites were dead within two months. If he added Streptomyces first, the survival rate shot up to 90 percent, rivalling that of colonies that never encountered the fungus at all.

The Formosan termite is an aggressive forager, always digging new tunnels to find food. Workers regularly come across fungal spores, which they can inadvertently bring back to the nest. But since the entire nest is laced with bacteria, and saturated by their antifungal chemicals, the spores rarely germinate.

And the nest itself is important. If Chouvenc used an artificial nest made of sand, the bacteria don’t protect the termites against the fungi. It seems that the bacteria need to feed upon the carton material in order to make their fungus-beating substances.

“Our new publication is a new nail in the coffin of biological control, as another layer of protection has now been identified,” say Chouvenc. Traps, baits, and pesticides can still work, but controlling termites with diseases looks like an unworkable option.

Leafcutter ants also use Actinobacteria  to protect themselves from fungi, but they house the microbes in special structures on their bodies. The termites lack such body parts; instead, they grow their beneficial bacteria in the walls of their nests. It’s the equivalent of spraying your entire house, and every bit of public transport you take, with living antibiotics.

Reference: Chouvenc, Efstathion, Elliott & Su. 2031. Extended disease resistance emerging from the faecal nest of a subterranean termite. http://dx.doi.org/10.1098/rspb.2013.1885

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