关键词: 桃小食心虫, 蜕皮激素, 20-羟基蜕皮酮, 滞育, 甲氧虫酰肼

Abstract: 【Aim】 Under short and long light photoperiod, the mature larvae of Carposina sasakii undergo diapause and non-diapause development, respectively. This study aims to interfere with the diapause of C. sasakii by using the ecdysone analog methoxyfenozide so as to lay a foundation for the new control technologies for C. sasakii. 【Methods】 The 20E titer dynamics in C. sasakii during larvae diapause and non-diapause developments were measured by ELISA. The interference effect of methoxyfenozide (0.05, 0.1, 1, 2, 5, 7.5 and 10 mg/mL) and 20E (0.5 and 1 mg/mL) on the cocoon formation of C. sasakii was determined using the sandblast method with pure water as the control. The effects of 5 mg/mL methoxenozide and 1 mg/mL 20E sandblasting treatments on the 20E titer of C. sasakii were measured, and the effect of sandblasting with 0.1 and 5 mg/mL methoxenozide on the diapause of C. sasakii were investigated subsequently. 【Results】 There was no difference in 20E titer in the developmental process between diapause and non-diapause larvae of C. sasakii under two photoperiods (15L∶9D and 12L∶12D), and both gradually decreased with the increase of instar and reched the lowest when they escaped off fruits. However, the 20E titer in non-diapause larvae escaping off fruits under long photoperiod (0.473 ng/g) was significantly higher than that in diapause larvae escaping off fruits under short photoperiod (0.254 ng/g). The non-diapause developmental larvae entered the long cocoon pupation after defruiting, and the 20E titer increased significantly and maintained a high level (0.652-1.217 ng/g) in the pupal stage. The diapause developmental larvae entered the 
round cocoon diapause after defruiting, and the 20E titer slowly increased in the first four days, reaching the first peak (0.656 ng/g) on the 4th day, then decreased and then increased again, reaching the 2nd peak (0.790 ng/g) on the 8th day. With the entry of diapause stabilization period, the 20E titer gradually decreased. After 70 d, the diapause was relieved, and the 20E titer remained at a low level. The lowest titer (0.424 ng/g) of diapause period was reached on the 90th day, and then the 20E titer began to rise. Methoxyfenozide at the concentration of 0.05 mg/mL could interfere with the formation of diapause round cocoons of C. sasakii larvae escaping off fruits under short photoperiod, and the LD₅₀ value of methoxyfenozide to mature defruiting larvae of C. sasakii was 7.039 μg/individual. Both methoxyhydrazine and 20E at the concentration of more than 0.05 mg/mL sprayed on the sand surface could effectively interfere with the formation of diapause round cocoons of C. sasakii, and 20E showed higher interference activity than methoxyfenozide at the same concentration of 1 mg/mL. Both of them could make the diapause larvae produce long cocoon, abnormal cocoon and non-cocooning reaction, and the 20E titer in abnormal cocoon and non-cocooning larvae increased significantly. The percentages of cocooning failure in 5 mg/mL methoxyfenozide and 1 mg/mL 20E sand spraying treatments were 70.0% and 66.7%, respectively. The 20E titers in abnormal cocooning larvae significantly increased by 16.3% and 143.0%, respectively. The 20E titers in non-cocooning larvae significantly increased by 149.3% and 278.6%, respectively. Although some larvae could form round cocoons after being exposed to 0.1 mg/mL methoxyfenozide, the proportion of larvae successfully completing diapause and eclosion reduced, and the eclosion rate was only 20.8%. 【Conclusion】 The 20E titer in C. sasakii keeps a low titer during the diapause process, and a higher titer is needed in the reproductive developmental stage. Moreover, methoxyfenozide and 20E can interfere with its diapause state forming round cocoons. The increase range of 20E titer is consistent with the change of cocooning phenotype, and 20E shows higher interference activity than methoxyfenozide at the same concentration. Methoxyfenozide reduces the proportion of larvae successfully completing diapause.

Key words: Carposina sasakii, ecdysone, 20-hydroxyecdysone, diapause, methoxyfenozide