Population dynamics and geographical distribution of the gypsy moth, Lymantria dispar, in Japan

The gypsy moth, Lymantria dispar L. (Lepidoptera: Lymantriidae), is distributed throughout most of the northern hemisphere and known as one of the most significant insect pest both in its native and introduced regions. The aim of this study was to examine whether there are differences in the outbreak pattern of L dispar, and these differences can be explained by different subspecies or divided populations across Japan for appropriate management of L. dispar. We reviewed the records of outbreaks of L. dispar in Japan using available literature and internet sources. We also examined phylogenetic relationships between L. dispar populations in Japan and other global populations to clarify current debated classification of the Japanese L. dispar. We then estimated the distribution of Japanese L. dispar with a species distribution model (Maxent). Phylogenetic mtDNA analysis revealed that Lymantria species consisted of four clusters: the first cluster contained three L. dispar subspecies from Europe and continental Asia (classified into L. dispar dispar), the populations of Honshu and western Hokkaido (L. dispar asiatica), and the central and eastern Hokkaido populations of L. dispar hokkaidoensis, while the second and third clusters comprised L. albescens and L. postalba, respectively. According to historical records, L. dispar outbreaks occur in approximately 11 year-cycles in Hokkaido, regardless of its classification at the subspecies level. Within northeastern Japan, L. dispar outbreaks occurred simultaneously from 2014 to 2015, whereas there were few reports of outbreaks in southwestern Japan. The distribution ranges of L. dispar were determined mainly by the maximum depth of snow cover (100-250 cm), forest patch area (0-0.6 km(2)), and elevation (600-1400 m); clearly divided at the species level but not at the subspecies or divided population level. On the other hand, the forest types are likely to contribute to the population dynamics and geographical distribution of L. dispar.