Simulation of Diapause Induction in Spider Mites (Tetranychus urticae and T. kanzawai) by Reproducing Field Environments in the Laboratory

Abstract

‌Backgroud: Diapause as the basic mechanism, helps insects and mites to synchronize their life cycles with local seasonal changes. Field tests are desirable to determine the timing of diapause accurately, but the environments are variable, making it challenging to validate the reproducibility of results. Materials and Methods: We designed an environmental simulator that reproduces the field variation in the laboratory based on the installation of 20 years of climate data in the Hokkaido region. We computed a regression equation to predict the light intensity and temperature between the laboratory simulator and field data and its accuracy was clearly demonstrated. Findings: Photoperiodic reaction curves of T. urticae and T. kanzawai indicated a generic short-day reaction type with critical photoperiods at 18.0°C of approximately 13.5 h for T. urticae and 12.5 h for T. kanzawai. Diapause of T. urticae and T. kanzawai in the field was induced on 22 and 23 September, respectively, which is close to the dates of diapause induction estimated by using critical photoperiods (19 and 30 September, respectively). Little variation between observed and estimated critical photoperiods of the mentioned species may be due to minor deviations in temperature in the simulator. Conclusion: The present study demonstrates the importance of factoring in variable temperatures in the field for accurate prediction of the timing of diapause induction in spider mites. Our experimental system may also be useful in pest mite forecasting by predicting its diapause termination and spring emergence in any geographic area where environmental data are available.