Life history of Copelatus zimmermanni Gschwendtner, 1934 (Coleoptera: Dytiscidae) and the ecological significance of the larval period of three Copelatus species

Diving beetles (Dytiscidae) play an important ecological role in most aquatic water habitats. However, approximately 40% of dytiscids in Japan have been classified as threatened, and further knowledge on their life history is necessary to support conservation efforts. In this study, we collected adult Copelatus zimmermanni (Coleoptera: Dytiscidae) from an ephemeral rain pool and raised a generation under laboratory conditions. We then compared the larval period with two Copelatus species, C. parallelus and C. masculinus. Complete development (egg to adult) occurred in 39-61 days (n = 10) and comprised the following stages: egg (3-6 days, n = 20), first instar (3-8 days, n = 20), second instar (3-12 days, n = 15), third instar larvae (4-13 days, n = 14), and landing to escape (11-36 days, n = 10). The third instar and total larval periods of C. zimmermanni were significantly shorter than those of C. parallelus and C. masculinus. The differences in the duration of larval periods may be related to the permanence of water sources used as reproductive sites for each species. We suggest that the shorter developmental period of C. zimmermanni allows it to complete entire lifecycles even in highly ephemeral aquatic habitats. This is the first report on the immature stages of a species within the C. nigrolineatus species group.

Automated summary

Diving beetles are ecologically important in aquatic habitats, but many species in Japan are threatened. This study focused on Copelatus zimmermanni and found that its larval period is shorter than two other species, possibly due to differences in their reproductive sites.