Abstract: 【Aim】 This study aims to clarify the effects of parasitization by Aphidius gifuensis on the growth, development and reproduction of the green peach aphid, Myzus persicae, and its role in the control of this aphid. 【Methods】 After M. persicae at different developmental stages (the 1st, 2nd, 3rd and 4th instar nymph and adult) were parasitized by A. gifuensis, the developmental duration, life span and litter size of the F₀ and F₁ generations of M. persicae were evaluated by breeding in Petri dish using tobacco leaves in the laboratory. 【Results】 After the 1st instar nymphs of M. persicae were parasitized by A. gifuensis, the developmental duration of the 1st instar nymph of M. persicae was significantly shortened by 0.65 d (33.00%) as compared with that of the unparasitized control, while the developmental duration of the 2nd instar nymph to adult of M. persicae was not significantly affected. After the 2nd instar nymphs of M. persicae were parasitized by A. gifuensis, the developmental duration of the 4th instar nymph and adult of M. persicae was significantly shortened by 1.50 d (100.00%) and 0.83 d (100.00%), respectively, as compared with that of the unparasitized control, while the developmental duration of the 2nd and 3rd instar nymphs of M. persicae was not significantly affected. After the 3rd instar nymphs of M. persicae were parasitized by A. gifuensis, the developmental duration of the 4th instar nymph and adult of M. persicae was significantly shortened by 1.50 d (100.00%) and 0.83 d (100.00%), respectively, as compared with that of the unparasitized control, while the developmental duration of the 3rd instar nymph of M. persicae was not significantly affected. After the 2nd instar nymphs of M. persicae were parasitized by A. gifuensis, their life span was significantly shortened by 8.39 d (54.00%) and the litter size per female was decreased by 48.67 individuals (100.00%), as compared with those of the unparasitized control. Additionally, after the 2nd and 3rd instar nymphs of M. persicae were parasitized by A. gifuensis, the developmental duration of the 1st instar nymph of M. persicae offspring (F₁) was shortened by 0.80 d (40.00%), and this decrease was more significant for the 1st instar nymph of M. persicae offspring (F₁) than for the other instar nymphs. The average life span of the parasitized M. persicae offspring (F₁) significantly increased by 5.72 d (41.20%) as compared with that of the unparasitized aphid offspring, while their litter size was not significantly different from that of the control. 【Conclusion】 After M. persicae at different developmental stages were parasitized by A. gifuensis, the developmental duration and life span of M. persicae were significantly shortened, and its litter size was significantly decreased as compared with that of the unparasitized aphids. The average life span of the offspring (F₁) of parasitized aphids was longer than that of the offspring of the unparasitized ones, while the litter size of the offspring of the parasitized and unparasitized aphids was not significantly different. The 2nd instar nymph of M. persicae is the key stage for controlling this aphid by A. gifuensis. These results provide important data for determining the optimal control time and understanding the underlying mechanism for the control of M. persicae by A. gifuensis.

Key words: Myzus persicae, Aphidius gifuensis, parasitism, developmental duration, life span, litter size