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Aphidius gifuensis is the dominant parasitic wasp of Myzus persicae, however there are some problems in the process of artificial or large-scale production and propagation of A. gifuensis, such as the body size becoming smaller and the parasitism decreasing. The purpose of this study is to analyze the effects of different regulation methods on the parasitism rate, body size and the content and activity of enzymes related to the growth and development of offspring A. gifuensis, so as to improve the population rejuvenation technology of the degraded A. gifuensis and ensure the scale and stability of artificial reproduction.
Indoor selection of A. gifuensis, which showed significant population degradation after 10 generations, was conducted for wild population hybridization rejuvenation, indoor exercise rejuvenation, and outdoor exercise rejuvenation. The formation of stiff aphids was observed every 12 h. After the formation of stiff aphids (during the yellow brown period of stiff aphids), the number was counted and the parasitism rate of A. gifuensis was calculated. After the metamorphosis of the aphid, six representative female adults A. gifuensis that could reflect the overall characteristics of each treatment group were randomly selected and the metathoracic tibia length was measured under a stereomicroscope as an indicator of body size. The stiff aphids with different treatments were collected and placed separately. The standard curve was made by Coomassie brilliant blue G-250 method within 12 h after emergence, and the content and activity of growth and development related enzymes were determined by ultraviolet spectrophotometer colorimetry.
Wild population hybridization rejuvenation and outdoor exercise rejuvenation had good regulatory effects on the parasitic ability of A. gifuensis (P<0.05), but indoor exercise rejuvenation had no significant regulatory effect on the parasitic ability of A. gifuensis (P>0.05). The hybridization between wild female A. gifuensis with the indoor degraded male one (1∶1) had the best rejuvenation effect on the parasitic ability. Compared with the control group, the parasitism rate and offspring body size were increased by 17.83% and 18.98%, respectively. The contents of carboxylesterase, phenoloxidase and trehalase in the offspring and the activity of phenoloxidase were significantly increased (P<0.05). After six generations of outdoor exercise, compared with the 0 generations, the parasitism rate and body size of offspring A. gifuensis were increased by 24.67% and 49.33%, respectively, and the contents of carboxylesterase, phenoloxidase, superoxide dismutase (SOD) and trehalase in the offspring were increased significantly (P<0.05), the activities of phenoloxidase and SOD were also significantly increased (P<0.05).
In production, the field hybridization rejuvenation and outdoor exercise rejuvenation of the degraded A. gifuensis population can improve the parasitic ability of A. gifuensis to M. persicae.