To elucidate population‐increasing factors in the diving beetle Cybister tripunctatus lateralis (Fabricius) (Coleoptera: Dytiscidae) in Japan in recent years, life histories and oviposition patterns were compared among three endangered diving beetle species, Cybister brevis Aubé (qualified by the Japanese Red Data List as ‘near threatened’), Cybister chinensis Motschulsky (vulnerable), and C. tripunctatus lateralis (vulnerable). Oviposition in C. brevis, C. chinensis, and C. tripunctatus lateralis was observed from late April to mid‐June, from late April to early July, and from late May to mid‐August, respectively, under semi‐outdoor conditions. There were no interspecies differences in total hatchling production during the reproductive season. In rearing experiments at various temperatures (20, 23, 25, 28, and 30 °C), the mortality of C. tripunctatus lateralis larvae was higher at 20 °C, and gradually lower with increasing temperature up to 30 °C. Adult body size of females in C. tripunctatus lateralis is larger than that of males but there were no significant differences among temperatures (25–30 °C). Cybister brevis had a higher emergence rate at 23–28 °C than at 20 and 30 °C. In C. brevis, the body size of adults reared at 25 or 28 °C was significantly larger than at other temperatures. Cybister chinensis did not differ in emergence rate and adult body size among the five temperature conditions. The developmental zero (i.e., the lower developmental threshold) from the first instar to adult emergence was 11.1 °C for C. brevis, 8.7 °C for C. chinensis, and 16.8 °C for C. tripunctatus lateralis. We speculate how the influence of global warming may have a positive impact on the growth and survival of C. tripunctatus lateralis.

The poleward range expansion of species native to lower latitudes brings them into competition with closely related species with overlapping habitat niches that are native to higher latitudes. If species of southern origin dominate in such interspecific competitions, this may cause a decline in closely related native species. Since 2010, there has been an increase in the distribution and rediscovery records of a diving beetle species, Cybister tripunctatus lateralis (Coleoptera: Dytiscidae), primarily in western Japan. This trend suggests that global warming may have a positive influence on the growth and survival of C. tripunctatus lateralis. Here, we compare the behavioural patterns and foraging abilities of three species of diving beetles in genus Cybister: C. tripunctatus lateralis (the species with an expanding distribution), C. brevis (a native species), and C. chinensis (a native species). We found that C. tripunctatus lateralis individuals swim more frequently, find food more easily, and consume more food than individuals of either C. chinensis or C. brevis. Our results suggest that the continued population increase and range expansion of C. tripunctatus lateralis may lead to resource competition with other closely related species.