Infestation of the white grub Dasylepida ishigakiensis (Coleoptera: Scarabaeidae) in hayfields on Miyako and Ishigaki Islands, Japan

Abstract

To examine the local distribution of Dasylepida ishigakiensis Niijima et Kinoshita larvae (Coleoptera: Scarabaeidae) on Miyako Island and Ishigaki Island, a survey was conducted in hayfields on the two Islands in February and March 2011. Symptoms of white grub infestation, such as patches of wilted grass and thin, yellow grass stands, were observed in some of the 20 hayfields surveyed on Miyako Island. Three species of white grub were observed there: D. ishigakiensis, Anomala cpustulata cpustulata Matsumura in Hirayama, and Anomala albopilosa (Hope), in the ratio 92:7:1, respectively. The mean population density of D. ishigakiensis in the hayfields was 54.3 m−2 and the maximum was 225 m−2. No significant relationship was found between the damage levels of hay grass and the D. ishigakiensis larval densities. In contrast, no damage was observed in the 14 hayfields surveyed on Ishigaki Island, although some D. ishigakiensis larvae were found at a low density in 4 hayfields. In 2006, no D. ishigakiensis larvae were found in sugarcane fields on this island in a separately conducted intensive survey. These observations may suggest that D. ishigakiensis larvae are present in hayfields at a low density but that few individuals occur in sugarcane fields on Ishigaki Island.