Reproductive biology and postembryonic development in the basal earwig Diplatys flavicollis (Shiraki) (Insecta: Dermaptera: Diplatyidae)

Based on captive breeding, reproductive biology including mating, egg deposition and maternal brood care, and postembryonic development were examined and described in detail in the basal dermapteran Diplatys flavicollis (Shiraki, 1907) (Forficulina: Diplatyidae). The eggs possess an adhesive stalk at the posterior pole, by which they attach to the substratum. The mother cares for the eggs and offspring, occasionally touching them with her antennae and mouthparts, but the maternal care is less intensive than in the higher Forficulina. The prelarva cuts open the egg membranes with its egg tooth, a structure on the embryonic cuticle, to hatch out, and, simultaneously, sheds the cuticle to become the first instar. The number of larval instars is eight or nine. Prior to eclosion, the final instar larva eats its own filamentous cerci, with only the basalmost cercomeres left, and a pair of forceps appears in the adult. The present observations were compared with previous information on Dermaptera. The adhesive substance is an ancestral feature of Dermaptera, and the adhesive stalk may be a characteristic of Diplatyidae. The attachment of the eggs and less elaborate maternal brood care are regarded as plesiomorphic in Dermaptera. The number of larval instars in D. flavicollis (eight or nine) is remarkably larger than that in the higher Forficulina (generally four or five) and also exceeds that in another representative of basal Dermaptera or Pygidicranidae (six or seven). The largest number of larval instars among Dermaptera having been found in D. flavicollis confirms the perception of Diplatyidae being very primitive earwigs.