Farmer termites keep the weeds away, but how?Sun, 2013-09-01 16:05
By Lakshy Katariya
As the cool morning breeze passed through the Ragi fields and hit my face, I looked around smilingly to see numerous conical structures, rising from the ground, some as small as the size of my palm and some as tall as an American athlete. These structures made up of soil, popularly but incorrectly known as ‘anthills’ were actually termite mounds and were present throughout the landscape as far as I could see. One termite mound was jutting out of the boundary between two fields, one in which a farmer was sowing seeds and another in which the crop was ready to be harvested. In other nearby fields, farmers were tending their crops- a set of young boys were adding manure, a man wearing a mask was spraying pesticide from a bag hanging down his shoulder, and women were laboriously plucking out the weeds growing along with the crop. As my mind drifted back to the termite mound in front of me, I was mesmerized thinking how successfully these “little termite farmers” have engaged in farming with fungi.
All the termites belonging to the sub-family Macrotermitinae grow Termitomyces, a basidiomycte fungus, as their food in an obligate mutualism. This means both the partners —termite and the fugus — are dependent on each other for survival. The fungus grows on the faecal matter, which is basically partially digested plant material that is passed through the termite gut and deposited in the form of a soft structure called a fungus comb inside the termite nest. The fungus growing on this comb produces tiny spherical structures called ‘mycotetes’ which are harvested by the termites as food and the spores present inside these ‘mycotetes’ act as seed for new fungal growth in the fresh field of termite faecal matter.
Through controlled “farming”, only Termitomyces grows predominantly inside the nest. However, whenever the termites abandon their nest or if a part of the fungus comb is brought outside the nest, another type of fungus starts to appear and overgrows the Termitomyces on the comb. This fungus belongs to the subgenus Pseudoxylaria and is considered a weed in this farming practice. Like humans, termites also use pesticides to kill the pests in their farms. Termites could also manually remove the weeds from their gardens or restrict the growth of weedy fungus by maintaing the nest environment in such a way that only the cultivar fungi Termitomyces is able to grow.
It will be interesting to know how similar or dissimilar the termite farmers are from the human farmers in employing all these different strategies to control the growth of their cultivar. Termites could be using antibiotics produced by bacteria belonging to the class actinobacteria to inhibit the growth of weedy fungi. But are such bacteria really present in the system? If yes, where are they present? Could it be possible that termite themselves produce their own antifungal compounds? If yes, what type of antifungal compounds are these? Manual weeding could also be a good strategy to remove the weedy fungi, but do termites actually have such behavioural adaptation? And do they kill the removed weeds by using antibiotic compound? The nest environment could also play an important part in the control of fungal growth. But can termites control their nest environment? If yes, what are the nest environment parameters like temperature, humidity, and pH? There are so many unanswered questions! And so as I walk in the direction of my lab ready to start my experiments, I can’t help but think whether the farmers, both human and termite alike, noticed the same cool breeze of excitement as I did just then.