Critical Photoperiod and Geographical Variation of Diapause Induction in the Two-Spotted Spider Mite, Tetranychus urticae Koch (Acarina: Tetranychidae), in Japan

Abstract

Critical photoperiod and geographical variation of diapause induction in the two-spotted spider mite collected from various districts of Japan were analysed with reference to susceptibility to malathion. Under various light regimes, the diapause rate of the Sapporo population increased with decrease in temperature, although under the 13.5L-10.5D regime, no diapause was observed even at 15°C. Critical photoperiods at 15°C for the various populations were 12 hr 50 min for the Sapporo and Morioka, 12 hr for the Fukushima and 9 hr 40 min for the Ichikawa population. The Fukuoka and Kagoshima populations did not diapause under the experimental conditions. When the mites from Sapporo, Fukushima and Ichikawa were reared on the field in Matsudo District, the diapausing females appeared from eggs laid at the beginning of October when the observation was started. However, in the Kagoshima population, no diapausing females appeared even as late as at the beginning of November. LC50 values obtained from the experiment on the mite populations susceptible to malathion were 44, 250, 148, 218, 683 and 161 ppm for the Sapporo, Morioka, Fukushima, Ichikawa, Fukuoka and Kagoshima populations, respectively. No distinct relationship was noted between the diapause and the susceptibility to organophosphorus insecticide. © 1981, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.