Preference of oviposition plant and hatchability of the diving beetle,Dytiscus sharpi (Coleoptera: Dytiscidae) in the laboratory

For the conservation of the diving beetle, Dytiscus sharpi (Wehncke) (Coleoptera: Dytiscidae), which is included in the Red List of Japan, it is critical to understand its ecological background. In the present study, oviposition preference and hatchability were investigated under laboratory conditions. Possible candidates of oviposition plants were observed in the natural breeding habitats of D. sharpi. Eight aquatic plants were identified, and Oenanthe javanica (Blume) was the major species present in March, when first instar larvae appeared. The number of eggs laid was investigated under the following conditions: (i) eight field plants were authentically recreated at a similar covering rate to that in the natural habitat; (ii) each of the eight plants was set at the same covering rate; (iii) a single plant taken from the field was placed separately. Significant oviposition preference for O. javanica was found when these eight aquatic plants were present in the same aquaria. In addition, hatchability in O. javanica was significantly higher than that in any of the other plants. These results suggest that O. javanica is an important aquatic plant for oviposition by D. sharpi.