Some termites are also farmers. They grow a certain fungus called Termitomyces inside their nests as a food source. They build and maintain special structures called fungal combs, where this crop fungus grows. But like any farm, these fungal gardens are at constant risk of being overrun by invaders. One of the most dangerous invaders is a fast-growing weedy fungus called Pseudoxylaria, which can quickly spread through the comb and take over the termites’ food crop if left unchecked. Scientists already knew that termites somehow keep this weed under control, but exactly how they do it has remained unclear.

A study published in Science, from the Indian Institute of Science Education and Research (IISER) Mohali, shows that the termite Odontotermes obesus uses a clever trick to manage this threat. Instead of directly killing the weed, the termites detect infected areas, physically isolate them, and cover them with small pellets of soil called soil boluses. These boluses contain microbes with fungistatic properties. Together, the termites’ behaviour and the microbes in the boluses help contain the invading fungus while protecting the crop fungus they depend on.

To understand how this works, the researchers first introduced small tufts of Pseudoxylaria onto healthy fungal combs and watched how the termites responded. In many cases, they removed the fungal tuft, then covered it with soil boluses, and sometimes also scraped and cleaned the part of the comb where the infection had touched. In other cases, they simply removed the tuft or removed it and cleaned the area. In most of the test plates, the termites successfully stopped the weed from spreading, while in control plates without termites, the fungus grew freely. This showed that termites can detect very early infections and respond quickly before the weed takes hold.

The team then tested what happens when the infection is already severe. They gave termites pieces of comb that were heavily infected with Pseudoxylaria. This time, instead of removing the fungus piece by piece, the termites mainly responded by covering the infected comb with soil boluses, either partially or completely. Complete encasement was much more effective than partial coverage. The termites did not cover healthy combs in the same way. This suggests that they can distinguish between infected and healthy areas and adjust their response depending on how serious the infection is.

In another experiment, the researchers attached a healthy piece of comb to an infected one and asked whether termites would sacrifice the whole structure or save the healthy part. The termites usually separated the healthy comb from the infected section and then covered only the infected part with soil boluses. When they successfully cut off the infected section and sealed it, they prevented the weed from spreading. This showed that termites behave differently based on the situation, taking more selective decisions and isolating only the damaged part of their fungal farm while preserving the usable crop.

But how exactly do soil boluses work? The researchers tried artificially covering infected combs with sterile soil. That did not stop the fungus from growing. So the physical barrier alone was not enough. The team then collected real soil boluses made by termites and tested extracts from them against both the weed fungus and the crop fungus in the lab. These extracts slowed the growth of both fungi, showing that the boluses have genuine fungistatic properties. The termites are not just burying the weed; they are using biologically active material to suppress fungal growth.

The next step was to locate the source of this antifungal effect. The researchers found that it is most likely caused by microbes in the boluses rather than by chemicals from the termites themselves. When they looked at the microbial community in the boluses, they found a large number of bacterial and fungal species, some of which strongly inhibited Pseudoxylaria. When these bacteria were combined into a partially reconstructed microbial mix, they were still able to suppress fungal growth. This suggests that the termites are using a microbe-rich tool as a kind of living pesticide and applying it very specifically where it is needed.

The researchers found that these fungistatic boluses could also slow the growth of the termites’ own crop fungus, Termitomyces. So if the termites spread the boluses everywhere, they would damage their own food source. Instead, they avoid placing them on healthy combs and mostly use them only on infected fungal tufts or infected comb sections.

This study demonstrates how fungus-farming termites manage their crops - their success depends on more than just having helpful microbes in the nest. It also depends on their precise behaviour: detecting infection early, removing or isolating diseased material, and applying microbial soil boluses only where they will do more good than harm. In a way, the termites are using their own version of integrated pest management.