Development of physogastry in the queen of the fungus-growing termite Macrotermes michaelseni (Isoptera: Macrotermitinae)

Abstract

Female reproductives of the fungus-growing termite Macrotermes michaelseni never showed signs of physogastry if they were kept in petri dishes to establish an incipient colony. During the 200 days of observation, their corpora allata volume, juvenile hormone titre and number of active ovarioles remained on a more or less constant level, and their gut was filled with soil. In contrast, these parameters are enhanced in partially and especially in fully physogastric queens, and these females had only a transparent liquid in the gut. Application of the juvenile hormone mimic ZR 515 to young females accelerated yolk incorporation, increased the number of active ovarioles and brought about the release of the soil from the gut. The same changes were induced by adding workers to increase the population of incipient colonies from about 45 to 400. This also resulted in an increase of the corpus allatum volume and of the juvenile hormone titre in young females. Their intestine was in this case filled with transparent liquid associated with the increased population of workers. It was, therefore, concluded that the development of physogastry depends on a positive feedback: the more workers are with the young female, the more nutrients are available and the more juvenile hormone the female produces, the more eggs are laid and the more workers can again develop to nurture the queen.