Effects Of Plant Growth Regulators On Winter Wheat, Sitobion Avenae(Hemiptera: Aphididae) And Aphidius Gifuensis(Hymenoptera: Braconidae)

Biological control is often influenced by many biotic and abiotic factors. In order tomake the biological control more cost-effective, we attempted to develop a banker plantsystem to control pests more continuously. Plant growth regulators (PGRs) or phytohormonesplay important roles in regulating plant growth and defense by mediating developmentalprocesses and signaling networks involved in plant responses to a wide range of bioticinteractions. In this study, we examined the effects of three plant growth accelerators:indole-3-acetic acid (IAA), naphthalene acetic acid (NAA), and gibberellic acid (GA3), andone plant growth retardants paclobutrazol (PBZ), on wheat (Triticum aestivum L.) seedlingsand their indirect effects on the English grain aphid, Sitobion avenae Fabricius (Hemiptera:Aphididae), which is used to rear a generalist parasitoid, Aphidius gifuensis Ashmead(Hymenoptera: Braconidae), which is used in our banker-plant system to control aphids onvegetables. We found that the PGRs-mediated effects strongly influence not only plant growthbut also performance of the aphid and its parasitoid. The main results were as follows：(1) Application of PGRs significantly affected the growth of wheat plants. Foliarapplication of IAA, NAA and GA3on wheat caused a significant increase in plant height incomparison with the control. However, drench application with PBZ reduced plant heightcompared with control. Foliar application of IAA, NAA and GA3caused a significantincrease in the length of leaves, while PBZ application reduced the length of the leaves. Foliarapplication of IAA, NAA and GA3increased the mean fresh and dry weight of wheatseedings. Drench application of PBZ increased the mean fresh and dry weights of seedingcompared with control.(2) PGRs did not have significant effects on development time of S. avenae. However,the mean fecundity of S. avenae was lower on plants treated with IAA150mg L-1, PBZ100and150mg L-1than control. The intrinsic rate of S. avenae in the treatments of NAA150mgL-1and PBZ100and150mg L-1was decreased significantly. PBZ induced a significantreduction of S. avenae adult weight at the dose of150mg L-1.(3) The parasitism rate of A. gifuensis reared on S. avenae larvae exposed to wheat treated with different PGRs significantly lower than those developed on untreated hosts. GA3treatment reduced the emergence rate of A. gifuensis. In contrast, the GA3had no effect onthe female ratio of A. gifuensis. However, IAA, NAA, and PBZ all decreased the female ratio.The female and male body weight of parasitoids was significantly decreased after IAAtreatment. The development time of female A. gifuensis was significantly longer in the NAAtreatment than that in control. The results indicate that the PGRs-mediated effects stronglyimpact not only plant growth but also the herbivore and parasitoids. The PGRs could be usedin a plant-herbivore-natural enemy system when manipulation is needed.