Larval prey options for the endangered species Dytiscus sharpi (Coleoptera: Dytiscidae: Dytiscinae) for sustainable ex-situ conservation

Abstract

Dytiscus sharpi is defined as “Critically Endangered” in the Red List of Japan and designated as a “nationally endangered species of wild fauna and flora” of the Japanese “Conservation of Endangered Species of Wild Fauna and Flora” Act. In previous studies, tadpoles of Red List species (Rana ornativentris) were collected, and approximately 300 tadpoles were needed to raise one D. sharpi adult. A rearing experiment was performed to identify alternative prey for D. sharpi larvae. Larvae were reared on cultivable prey (Asellus hilgendorfii, goldfish, and crickets), and the quality of alternative prey was compared to that of tadpoles based on three criteria: adult size, survival rate, and development speed. Adult size, survival rate, and development speed values showed that alternative prey, i.e., A. hilgendorfii, goldfish, and crickets, were of adequate quality as larval prey according to all monitored parameters when compared to tadpoles. Dytiscus sharpi larvae can be raised using only cultivable prey, and multiple choices are available. The elimination of the need to overcollect endangered tadpoles from the field by using alternative prey for rearing will contribute to the conservation of both D. sharpi and R. ornativentris. This result would make ex-situ conservation of D. sharpi sustainable.