To contribute to conservation of Ranatra unicolor Scott, 1874, rearing experiments using only laboratory-bred food insects were conducted to elucidate the nymphal period of each instar stage of the hemipteran insect. The developmental period for each immature stage was as follows: first instar, 3–5 d (4.0±0.5 d, N=28); second instar, 3–5 d (4.0±0.5 d, N=27); third instar, 3–5 d (4.1±0.5 d, N=27); fourth instar, 4–7 d (5.5±0.7 d, N=26); and fifth instar, 9–11 d (9.6±0.6 d, N=21). The survival rate of nymphs to adults was 70％. The body length of the adult insects fed laboratory-bred prey did not significantly differ from that of field-collected adults. In this study, efficient rearing methods for this species are proposed.
The Japanese bumblebee Bombus cryptarum florilegus is threatened with extinction, and for the first time, a detailed study of their nests has been successfully conducted in the Nemuro Peninsula, Hokkaido Island. This bumblebee nested in a dead grass nest of small animals built in a closed space covered by grass on the ground. The number of cells in the nest was 511. It was estimated that 76 new queens were born in this nest, which was the largest among bumblebee species in Hokkaido. Adult new queens (average 5.36 mm in head width) were larger than those of workers (average 4.55 mm in head width). The sex ratio of the mature nest examined in this study was highly female-biased, suggesting the possibility of a split sex ratio in the Nemuro population. The nesting biology of B. cryptarum florilegus revealed in this study is essential for future conservation.
Appasus japonicus (Heteroptera: Belostomatidae) inhabits paddy fields and ponds. Females lay eggs on the dorsal surface of the male’s body; males then care for the egg mass. The predation risk for Belostomatinae males may increase because their swimming ability is compromised while caring for the egg masses. However, there are currently no records of predators of these males and the eggs in their care. In this study, we observed the capture of the egg mass of A. japonicus by Cybister tripunctatus lateralis (Coleoptera: Dytiscidae) larva in the field. This may be the first record of Dytiscidae larvae feeding on A. japonicus egg masses, suggesting that these larvae may exert predation pressure on A. japonicus individuals that care for the egg mass.
We report the distribution, infestation, and feeding plants of the alien longhorn beetle Apriona swainsoni swainsoni (Hope, 1840), recently discovered from Fukushima Prefecture, Japan, which is a serious pest of Styphnolobium japonicum in China. We found a specimen collected at Sukagawa City in 2014, suggesting that this species was introduced in Japan by 2014 at the latest. In some areas of Sukagawa and the adjacent Koriyama Cities, where A. swainsoni swainsoni has been found, S. japonicum and Maackia amurensis, which are planted as a roadside tree, especially the latter, have been infested by this alien species. Additionally, in captivity, we found that A. swainsoni swainsoni can eat two native Fabaceae species, Lespedeza bicolor and L. homoloba, which are widely distributed from hilly to montane areas in Japan. It is necessary to consider whether A. swainsoni swainsoni will be expand its distribution in Japan.