Some termites form symbiotic relationships with fungus. When harmful fungi invade their carefully cultivated crops, these fungus-farming termites fight back with the precision of skilled gardeners, a new study reveals, smothering them in soil clumps enriched with microbial allies that inhibit fungal growth. Fungus-farming termites, like Odontotermes obesus, maintain a vital symbiotic relationship with the fungus Termitomyces, cultivating it in specialized nutritional substrates called combs that provide both a reliable food source for the termites and an ideal habitat for the fungus. However, these nutrient-rich combs also attract invasive fungal weeds, particularly the fast-growing Pseudoxylaria, which can quickly overtake the crop if left unchecked. While Pseudoxylaria is typically suppressed in healthy combs under termite care, it rapidly spreads when termites are removed, suggesting a critical role of termite activity in maintaining their fungal gardens. While It's thought that termites use microbial agents to manage these fungal weeds, while sparing their cultivated crop, the precise behavioral mechanism by which they achieve such selective control remains unknown. Through experiments exposing O. obesus to varying severities of Pseudoxylaria outbreaks, Aanchal Panchal and colleagues found that the termites employ a flexible set of behaviors to suppress weeds, adjusting their tactics depending on the severity of the invasion.
When faced with small infections, termites actively remove Pseudoxylaria from contaminated comb and bury it under soil clumps (boluses), which effectively isolates the harmful fungus in an oxygen-deficient soil environment, suppressing further growth. In the case of severe outbreaks, termites fully isolate infected portions from healthy combs and, if necessary, smother entire sections in soil boluses to contain the threat. Notably, the authors found that the soil boluses the insects use are not just barriers – they contain a diverse community of microbes, including termite-derived bacteria with fungistatic properties. Termites deploy these fungistatic boluses only when weeds threaten their gardens, not on healthy fungal combs. According to Panchal et al., this indicates that O. obesus has evolved a highly targeted defense strategy, enlisting microbial allies to selectively combat harmful fungi while sparing their beneficial crop. "The findings of Panchal et al. elucidate how microbial symbionts can be used as part of a multifaceted pest management strategy," write Aryel Goes and Rachelle Adams in a related Perspective. "Efforts to understand the molecules involved, and their relationship to host fitness, may reveal beneficial microbes that lead to natural product discovery for medicine, agriculture, and bioremediation."
