Annual Life Cycle of the Spider Mite, Eotetranychus dissectus Ehara (Acarina: Tetranychidae) on Mono Maple

Abstract

The annual life cycle and diapause induction of Eotetranychus dissectus Ehara on mono maple, Acer mono MAXIM., were studied in Sapporo, Hokkaido. The mites utilized only the concave underside of malformed leaves, which presumably resulted from the attack of insects or the mite itself, for the formation of stratiform webs. In autumn, the adults migrated from the malformed to the flat leaves and formed a group resembling a brood cluster of spiders, and then moved into crevices in the bark. Overwintering females appeared on leaves in early May and disappeared between mid-October and early November. This active period corresponded to the phenology of mono maple. It was estimated that there were 3 to 4 generations a year. The density of mites per leaf reached a maximum in late May, followed by an abrupt decline in July, and then another increase began in September. Maximum density may have been associated with the oviposition of the overwintering females, and the abrupt decrease may have resulted from the dispersal of adults emerging in July. The high density in September was ascribed to the aggregation of adults onto flat leaves. The photoperiodic response curve of diapause induction was of the long day type, and the critical photoperiod was 14.5 hr at 18°C. Diapause was induced in early September in the field, which corresponded to the timing predicted by the critical photoperiod mentioned above. Mated females showed a higher oviposition rate than virgin females. The latter produced only male progeny, whereas the former produced individuals of both sexes and the sex ratio in the progeny was heavily skewed to females (ca. 90%). © 1988, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.