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Wetland biodiversity is currently declining on a global scale. Wetland biodiversity understanding is critical for determining the wetlands' conservation value. In this study, Macroplea Samouelle, 1819 (Coleoptera: Chrysomelidae) was discovered in Aomori Prefecture, Honshu Island, Japan. Only two Macroplea species have been recorded in Japan, M. japana (Jacoby, 1885) and M. mutica (Fabricius, 1792). Macroplea japana had been unrecorded for 60 years before being rediscovered in Honshu Island in 2022, and a single adult M. mutica female was discovered in Hokkaido Prefecture in 2003. The discovered individuals were concluded to be M. mutica based on morphological and molecular analyses. Although morphological differences were observed with the Eurasian M. mutica individuals, the male genitalia was nearly identical to M. mutica. For the molecular phylogenetic analysis based on COI and 28S sequences, Macroplea individuals in Japan were clustered with M. mutica on the Eurasian Continent. This is the first record of this species on Honshu Island (and the second in Japan), as well as the first record of adult males. This species would require conservation policies and additional distributional surveys. [ABSTRACT FROM AUTHOR]

Cymbella janischii, an invasive species of diatom, has been broadening its geographical range in Japan since 2004, flourishing in substantial colonies in river beds. As thick and mucilaginous colonies of this diatom often cover large areas of river beds, this elicits concerns regarding the potential alteration of sedimentary bottom structures and resultant effects on the native ecosystems. The presence of the diatoms growing on the body surface of two aquatic beetles, Grouvellinus nitidus (Elmidae) and Ectopria opaca (Psephenidae) in a Japanese river was confirmed. This constitutes the inaugural documentation of invasive diatoms having a specific relationship with native aquatic insects at an individual level. [ABSTRACT FROM AUTHOR]

The population of the diving beetle Cybister rugosus (Macleay, 1825) has been declining in recent years, and it is designated as "Vulnerable" (VU) in the Red List of Japan. However, there have been no quantitative studies on the feeding habits of the larval stage of this beetle. Revealing the feeding habits is indispensable for understanding the life history of C. rugosus. In the current study, we reared C. rugosus larvae on different prey taxa (Odonata nymph, fish, tadpole, and shrimp) and evaluated their growth and survival rates. Previous studies have shown that three congeneric Cybister species larvae feed mainly on invertebrates. However, all larval instars of C. rugosus were able to feed on invertebrates and vertebrates and grow. Thus, we considered C. rugosus to be a generalist compared to the other Cybister species. The larval periods were shorter for C. rugosus that fed on Odonata nymphs than on any other prey. Feeding different prey taxa had no significant effect on the body length of newly emerged adult males. However, the body length of newly emerged adult females was larger when the larvae fed on Odonata nymphs than when the larvae fed on fish. As in other Cybister species, we concluded that the Odonata nymph is an appropriate food from the viewpoint of increased growth rate in C. rugosus. [ABSTRACT FROM AUTHOR]