Abstract:

【Aim】 The purpose of this study is to screen the best rejuvenation methods by determining and analyzing the effects of rejuvenation by supplementing different concentrations of hormones and Myzus persicae supplied with peach leaf juice on the parasitization ability, body size of offspring adults, and the contents and activities of the growth and development-related enzymes in the offspring adults of Aphidius gifuensis, so as to rejuvenate the degenerated A. gifuensis population and maintain the parasitization ability of A. gifuensis in a healthy state during artificial propagation. 【Methods】 A. gifuensis adults of the obviously degenerated population after being reared in laboratory for 10 generations were fed with different hormones (estradiol, methyltestosterone and cortisol) at different concentrations (0.32, 1.6, 8, 40 and 200 mg/L) for 24 h, the parasitism rate, body size of offspring adults, and the contents and activities of the growth and development-related enzymes including carboxylesterase (CarE), phenoloxidase (PO), superoxide dismutase (SOD) and trehalase in the offspring adults were determined. After 10 generations of indoor rearing, the degenerated and mated female adults of A.gifuensis were introduced into small insect cages containing tobacco plants infested with 100 nymphs of M. persicae at the 2nd-3rd instar (1∶100 ratio of female wasp to aphids). The tobacco leaves were sprayed evenly with peach leaf juice at different concentrations (dilution fold: 1, 10, 100, 1 000 and 10 000) and M. persicae nymphs were allowed to feed for 24 h. The parasitism rate, body size of offspring adults, and the contents and activities of CarE, PO, SOD and trehalase in the offspring adults of A. gifuensis were determined. 【Results】 In hormone rejuvenation, 1.6 mg/L methyltestosterone had the best rejuvenation effect. When A. gifuensis adults were fed with 1.6 mg/L methyltestosterone, the parasitism rate was 33.67%, which was increased by 14.34% as compared with that in the control group (fed with purified water and ethanol in a volume ratio of 1∶5), however, 1.6 mg/L methyltestosterone had no significant effect on the body size of A. gifuensis offspring adults. When A. gifuensis adults were fed with 1.6 mg/L estradiol, the hind tibial length of the offspring adults was increased by 22.25% as compared with that in the control group. When A. gifuensis adults were fed with 1.6 mg/L methyltestosterone, the CarE activity and the PO content in the offspring adults were the highest, which were increased by 41.00% and 40.81%, respectively, as compared with those in the control group. When A. gifuensis adults were fed with 1.6 mg/L cortisol, the SOD content in the offspring adults was the highest, which was increased by 48.92% as compared with that in the control group. Feeding different hormones had no significant effect on the trehalase content in the offspring adults of A. gifuensis. In M. persicae supplied with peach leaf juice rejuvenation, feeding M. persicae nymphs with different concentrations of peach leaf juice had no significant rejuvenation effect on the parasitism rate of A. gifuensis adults. However, the parasitism rates of A. gifuensis adults in various treatment groups in which M. persicae nymphs were fed with different concentrations of peach leaf juice were higher than that in the control group. Among them, the parasitism rate of A. gifuensis after M. persicae nymphs were fed with peach leaf juice in 1-fold dilution was the highest. Feeding M. persicae nymphs with different concentrations of peach leaf juice had significant effects on the body size of A. gifuensis offspring adults. Among them, the hind tibial length of offspring adults of A. gifuensis in the treatment group with peach leaf juice in 100-fold dilution was the longest and 0.018 mm longer than that in the control group. Feeding M. persicae nymphs with the peach leaf juice in 1-fold dilution resulted in the significant increase (11.34%) in the SOD activity in the offspring adults of A. gifuensis, but had no significant effect on the contents and activities of the other enzymes in the offspring adults of A. gifuensis. 【Conclusion】 In production, 1.6 mg/L methyltestosterone, 1.6 mg/L estradiol or M. persicae supplied with peach leaf juice in 1-fold dilution can be added as a rejuvenation measure to improve the artificial reproduction of A. gifuensis.

Key words: Aphidius gifuensis, Myzus persicae, hormone, peach leaf juice, parasitization ability, rejuvenation, enzyme activity