Description of the larval stages of the berosine genera Berosus and Regimbartia based on the Japanese species B. japonicus and R. attenuata (Coleoptera: Hydrophilidae)

Abstract: Larval morphology and head chaetotaxy are described for two genera of the tribe Berosini, Berosus Leach, 1817 and Regimbartia Zaitzev, 1908, based on reared and field-collected larvae of Berosus (Berosus) japonicus Sharp, 1873 and Regimbartia attenuata (Fabricius, 1801). We describe and illustrate the general morphology and head chaetotaxy of all three instars of both species. We review and discuss an ecological character, which is an adaptation to benthic lifestyle in Berosus. Berosus larvae do not have air-bubbles in alimentary canal, whereas majority of hydrophilid larvae have air-bubbles. Absence of the bubbles results in loss of buoyancy and would be an adaptation in two different ecological trends: benthic and swimming lifestyles. A detailed comparison of head chaetotaxy of both genera is provided. Chaetotaxy of Berosus and Regimbartia are not largely different, therefore benthic lifestyle will not strongly affect chaetotaxy. We also provide information of knowledge about immature stages of the tribe Berosini and provide the identification key to larvae of all five genera of the tribe. Biology of both studied species is briefly commented as well.

Key words: Coleoptera, Hydrophilidae, larva, Berosus, Regimbartia, Berosini, Hydrophilinae, chaetotaxy, Japan, Palaearctic