Worker Emergence Following Fungal Fruiting May Facilitate Symbiont Acquisition in a Fungus-Growing Termite

Fungus-growing termites depend on symbiotic Termitomyces fungi; establishing this association is a critical step during colony foundation. However, a seasonal relationship between early colony development and fungal reproductive phenology in natural populations remains poorly resolved. In this study, the timing of colony foundation behavior in the fungus-growing termite Odontotermes formosanus on Okinawa Island was examined by integrating long-term observations of field alate dispersal, controlled rearing experiments, and fungal fruiting records. Alates occurred within mature nests from the middle of March, but opportunistic field records spanning eight years showed that nuptial flights started only from April and were consistently associated with heavy rainfall before sunset. In incipient colonies established from alate pairs (n = 793), the first foraging workers predominantly began appearing 11–13 weeks after colony initiation. Such a developmental schedule predicts peak worker emergence from July to August for colonies founded during the main swarming period. In contrast, fruiting of two Japanese Termitomyces fungi began earlier during the season and mostly preceded worker emergence. These results suggest a consistent temporal ordering, which likely increases the probability of founding workers encountering abundant fungal spores when collecting plant substrate for constructing a fungus comb. Such ordering may also buffer symbiont acquisition against interannual climatic variations. These findings highlight the processes by which seasonal behavioral timing structures the establishment phase of an obligate insect–fungus mutualism.