Spread of the distributional range ofNarathura bazalus (Hewitson) (Lepidoptera, Lycaenidae) in Ibaraki prefecture, central Japan

摘要

In Ibaraki prefecture, Narathura bazalus was first recorded in 2000, when the species was observed in 20 municipalities in the prefecture. It then spread rapidly over the prefecture, so that by 2004, N. bazalus had been recorded in 83 of the prefecture's 85 municipalities.In Ibaraki prefecture, Narathura bazalus was first recorded in 2000. In order to measure the change in the distribution of N. bazalus, the occurrence of larvae was checked at 269-412 locations in the prefecture every year from 2000through 2004. In 2000, the species occurred only in the southern part of the prefecture and the urbanized area of the northeast, but it subsequently spread rapidly over the prefecture. N. bazalus including feeding marks was observed in 20, 46, 74, 49 and 82 of the 85 municipalities of Ibaraki prefecture in 2000, 2001, 2002, 2003 and 2004, respectively. A cool summer in 2003 slowed the spread but it was again accelerated by the hot summer of 2004. The degree of occurrence damage by larvae positively correlated with the number of host trees planted. In 2004, very severe damage was observed at 38% of all locations examined. In recent years, there has been an increase in the number of host trees, Lithocarpus edulis, planted in the Kanto region. Moreover, because pruning operations are frequently conducted, particularly in urbanized areas, many lammas shoots are produced on the host trees. Although several factors may affect the recent spread of N. bazalus, the main factor appears to be a continual abundant supply of larval food beyond the spring.