Local hypoxia generated by live burial is effective in weed control within termite fungus farms

Abstract

Fungus-farming termites cultivate a mutualistic fungus Termitomyces inside their nest mounds in CO2-rich environments. For sustainable harvests, termites must control weedy parasitic fungi such as Pseudoxylaria that may exploit resources meant for cultivar growth. Earlier, we discovered that termites exploit fungal scents to distinguish between crop and weedy fungi leading to weed burial that could contribute to its control. While chemical antifungals have been reported in termite farms, live burial per se as an antifungal activity has never been investigated. In this study, major and minor worker castes of termites buried the weedy fungus with soil to a significantly greater extent than the crop fungus. This live burial by worker termites led to greater decrease in the survival of the weedy fungus compared to the crop fungus, even after controlling for the differential amount of soil deposition. Such a decrease in parasite survival could result from local hypoxia generated by the burial process. Our experiments with artificial burial revealed that, in the absence of chemical factors such as fungicides, weed survival is indeed negatively affected by the resulting hypoxia alone. However, hypoxia associated with artificial burial also decreased crop survival, explaining why natural burial of crop fungi is minimal. Farmer termites may, therefore, contain weeds in their fungus farms by selectively burying weed-infested areas, resulting in antifungal activity which in part could be due to local hypoxic conditions. These results show how organisms may exploit the abiotic effects of behavioural actions as an effective defence against parasites.