Abstract: 【Aim】 This study aims to clarify the feasibility of using the cocoon breaking rate and time required for cocoon breaking as the indicators for diapause termination of the wheat midge, Sitodiplosis mosellana, a typical insect pest with obligatory larval diapause, and to explore the potential roles of ecdysone receptor gene EcR and heat shock protein 70 and 90 genes (Hsp70 and Hsp90) during diapause termination under low temperature conditions. 【Methods】 The field-collected diapausing larvae of S. mosellanain early September were exposed to low temperature (4℃) and natural temperature, respectively, for different time (0-90 d) prior to pupation at 24℃ in the laboratory, their cocoon breaking and pupation rates and the time required for their cocoon breaking and pupation were investigated. The mRNA levels of EcR, Hsp70 and Hsp90 in cocooned larvae of S. mosellana after diapause termination stimulated by low temperature (4℃) and followed developmental resumption at 24℃ were assayed by qPCR. 【Results】 The cocoon breaking and pupation rates and the time required for cocoon breaking and pupation of S. mosellana larvae exposed to low temperature (4℃) and natural temperature for different time differed significantly. Larvae not subjected to low temperature  (4℃) treatment were unable to pupate, but 71.3% of individuals were able to break cocoons when enough water was supplied. Both the cocoon breaking rate and pupation rate increased, the time required for cocoon breaking and pupation gradually shortened with the increasing of the low temperature (4℃) treatment time within 60 d. The pupation rate of S. mosellana larvae exposed to natural temperature for 30-60 d was significantly lower than that of larvae exposed to 4℃ for 30-60 d. After the larvae were exposed to low temperature (4℃) for 60 d and natural temperature for 90 d, more than 91% of individuals pupated. Low temperature treatment at 4℃ significantly increased the expression levels of EcR, Hsp70 and Hsp90 in S. mosellana larvae, and their expression levels in larvae exposed to low temperature for 30 d were the highest. The expression levels of EcR, Hsp70 and Hsp90 in S. mosellana larvae exposed to low temperature decreased gradually with the increasing of the treatment time, and became stable in most larvae after diapause termination. 【Conclusion】 Low temperature can significantly promote the diapause termination of S. mosellana. Low temperature affects diapause termination more strongly than the natural temperature of September and October. Cocoon breaking rate and the time required for cocoon breaking can reflect the diapause intensity of S. mosellana larvae to a certain extent, but are not suitable separately as indicators for diapause termination. The expression levels of EcR, Hsp70 and Hsp90 are closely related to diapause intensity, and they might play potential roles in the diapause termination of S. mosellana.

Key words: Sitodiplosis mosellana, diapause, low temperature, diapause termination, ecdysone receptor, heat shock protein