Henosepilachna vigintioctomaculata depends basically on Solanum tuberosum as the host plant. In the present study, we investigated the developmental ability of larvae on and adult feeding acceptance/preference for the alien plant S. carolinense under laboratory conditions. The host suitability of S. carolinense for H. vigintioctomaculata was slightly lower if compared with that of the ordinary host S. tuberosum. We also investigated the distribution of S. carolinense and the use of this plant by H. vigintioctomaculata in the wild at Yamagata prefecture, based on the field surveys and the inspection of literatures and herbarium specimens deposited at the museums. The use of S. carolinense by H. vigintioctomaculata was detected at four sites among 25 sites where S. carolinense occurred. Although it was evident that H. vigintioctomaculata completed its life cycle on S. carolinense at one site, the use of S. carolinense by the beetles at Yamagata prefecture seemed to occur subsidiarily and accidentally in general. Based on the line of evidence, we suggest that S. carolinense is acting as a weak “ecological trap” for H. vigintioctomaculata at the present.

A new locality of Helophorus auriculatus Sharp, 1884 was recorded in Tochigi Prefecture, which is the northern limit of this species in Japan. In this study area, this species was observed in small ponds, puddles, and slow-flowing pools scattered along riverbeds, where the water temperature was consistently below 20°C even in summer owing to spring water. Some diving and water scavenger beetles that inhabit the middle of the stream, were consistently observed along with this species. Helophorus auriculatus adults emerged in February, April, May, October, and December and disappeared during the summer; individuals collected in October were confirmed to be mating, and those collected in December laid eggs. The annual life history of H. auriculatus was similar to that of this species in Ibaraki Prefecture, but the peak of adult emergence occurred slightly later in this study area.

The Japanese species Sphaerites glabratus (Fabricius, 1792) is redescribed. Scanning Electron Microscope photos, as well as illustrations of mouthparts and female genitalia of the species are provided. Important external morphological characters for the family Sphaeritidae are discussed.