Overwintering biology and morphological characteristics of the migratory locust, Locusta migratoria after outbreaks on Iheya Island, Japan

抄録

Outbreaks of the migratory locust, Locusta migratoria L., occurred in 2005–2006 on Iheya Island, Okinawa, Japan. The present study was initiated in autumn 2006 to investigate the morphological characteristics of adult locusts after the outbreaks. Although most adults collected in the field showed morphometric traits typical of solitarious forms, a few adults were characterized by dark body coloration, a concave pronotum, relatively small F/C ratios and large E/F ratios, often recorded in outbreaks. Locusts were sampled every month from October 2006 to March 2007 to determine the status of ovarian development. A few females with developing oocytes or eggs were always present in the samples, but most females had small oocytes until January. The mean time required to start oviposition after transfer to the laboratory (12L12D and 30°C) was 16–18 days in females collected in the autumn, but decreased significantly in those collected in late December onward. Eggs had a capacity for diapause at 20°C, but not at 25 or 30°C. The induction of diapause was influenced by the parental photoperiod. These results suggest that this locust overwinters mainly in the adult or egg stage on this island.