Limited survival strategy in starving subterranean termite colonies

Abstract

Termites feed on a carbon-rich but nitrogen-poor diet and evolved efficient nitrogen conservation strategies. It was previously suggested that during time of low access to resources (i.e., starvation), subterranean termites (Rhinotermitidae) colonies would adopt an energy conservation strategy by cannibalizing soldiers, a dependent caste. However, such hypothesis was tested with relatively small groups of foragers, which may not have reflected how resources are reallocated in whole colonies when food (carbon) is scarce. The current study subjected 2-year-old colonies (≈\u20093000 termites with all castes and instars) to starvation, in order to reexamine if cannibalism is part of an active energy conservation strategy. Within 12\xa0days of starvation, eggs and larvae were all cannibalized, followed by young workers. Soldiers then died marginally faster than old workers. By 22\xa0days, cannibalism was no longer observed, and the king and queen were among the last individuals to die. Termites that engaged in the process of ecdysis with no energetic resources, failed to molt, died in the process, and the subsequent cannibalism was a passive mortality-driven process. Therefore, cannibalism was primarily the result of the inherent termite behavior for recycling nitrogen resources. The hemimetabolous developmental pathway, the difference of timing in the molting cycle of termite instars and the relatively rapid exhaustion of soldiers, indirectly determined the sequence of starvation-induced mortality and subsequent cannibalism. Although termites have evolved efficient nitrogen conservation strategies, they have not evolved an efficient carbon conservation strategy, which is essentially limited to keeping the primary reproductives alive as long as possible.