Effects of temperature, soil moisture and photoperiod on diapause termination and post-diapause development of the wheat blossom midge, Sitodiplosis mosellana (Gehin) (Diptera: Cecidomyiidae)

Sitodiplosis mosellana, one of the most important wheat pests, goes through larval diapause in a cocooned form. It is univoltine, but some individuals exhibit prolonged diapause. In this study, we documented diapause termination rate of cocooned larvae at different diapausing periods and time required for adult emergence when they were brought to 25 degrees C from the field in northern China. We found that field larvae all entered diapause by June, but none terminated diapause until late September when the daily average temperature dropped to below 20 degrees C. Furthermore, termination rate increased significantly as diapausing larvae underwent increasing chilling duration, reaching > 95% from early December to early March. Our results suggest that chilling was necessary for diapause to terminate and that field diapause termination ended in early December. To explore low temperature and duration required, we cold-treated field diapausing larvae of different periods at different low temperatures for various lengths of time prior to the 25 degrees C incubation. Chilling at 4-8 degrees C for 60-90 days resulted in a higher termination rate ( > 90%) and shorter adult emergence time in general. Additionally, we investigated the combined effect of temperature (18-30 degrees C) and soil moisture (20-60%, on dry weight basis) as well as the effect of photoperiod (24:0-0:24 L:D) on post-diapause development. While photoperiod did not affect adult emergence, soil moisture ranging from 30 to 50% and temperature from 22 to 26 degrees C resulted in the highest adult emergence rates ( > 46%) within relatively short time ( < 18 days). Mortality and/or prolonged diapause rate drastically increased when incubation conditions were outside the optimal range, especially at 30 degrees C. These findings provide new insight into the diapause process of S. mosellana, and information will be useful for development of field forecasting and laboratory rearing techniques of this pest insect.