A Research Of Conditions Of Diapause Termination And Emergence Of Carposina Sasakii Overwintering Larvae

The peach fruit moth, Carposina sasakii Matsumura, is one of the most damaging pests in apple orchards in North China. To explore diapause termination mechanism of C. sasakii overwintering larvae and further explore factors influencing the spring emergence of the pest, we researched the effects of photoperiod, temperature, soil moisture and soil porosity on the diapause development of this pest and the results obtained are as followed.(1) The results showed that C. sasakii overwintering larvae could complete winter diapause by mid-winter. And then it remained in a state of post-diapause quiescence for a period. The developmental threshold temperature and effective accumulated temperature of post-diapause quiescence were estimated to be 9.26 ℃ and 534.49 degree-days respectively.(2) There was no significant difference between the survival rate of C. sasakii overwintering cocoon in the different treatments under the conditions of 12~15 ℃ in different photoperiod and it was all above 87%. The rate of diapause termination of C. sasakii was between 78.91% and 82.39% and there was no significant difference under different treatments. Therefore, photoperiod had no significant effect to diapause development of C. sasakii overwintering larvae.(3) The C. sasakii overwintering larvae could not terminate diapause when sustained in temperature of-6、-3、0、18 and 23 ℃ for 82 d. When sustained in low temperature of 3 ℃ for 40 to 54 d, C. sasakii overwintering larvae could not terminate diapause, but to 61 d or longer, the rate of diapause termination was about up to 50% and could terminate diapause. The C. sasakii overwintering larvae could terminate diapause when sustained in 6~12 ℃ for about 40 d. Thus, low temperature is the necessary condition for C. sasakii overwintering larvae to terminate diapause, but it is not conducive to finish diapause for C. sasakii overwintering larvae if the temperature is too high(over 18 ℃)or too low(below 0℃). The appropriate temperature conditions for C. sasakii overwintering larvae to terminate diapause is sustained in low temperature of 3℃ for about 60 d and in 6~12 ℃ for about 40 d.(4) Based on the temperature and soil moisture, we established a multiple regression equation of the beginning period and peak period of emergence of C. sasakii overwintering larvae. According to the regression model, the higher the temperature is, the earlier the beginning period and the peak period occurs in certain soil moisture content. Effect of soil moisture on the emergence time of C. sasakii overwintering larvae was not significant, but the soil moisture influenced the rate of emergence significantly.(5) The emergence of C. sasakii overwintering larvae was discrepant under different soil moisture content and soil porosity. The most optimal condition for the emergence of C. sasakii overwintering larvae was soil porosity of 45.21% and soil moisture content of 11%. Some soils were too dry or the porosity was too high to the emergence of C. sasakii overwintering larvae.