Effects Of Host Plants On Development And Host Selection Behaviour Of Aphidius Gifuensis(Hymenoptera: Aphidiidae)

Banker plant system is a new method for biological control of certain arthropod pests. Banker plant can supply a non-pest prey or parasituic species to support a continual source of natural enemies that provide long-term pest suppression, and make the biological control more effective under greenhouses. In the tritrophic interactions of host plants, phytophagous insects and natural enemies, host plants can directly or indirectly affect the behaviour and performance of natural enemies though supplying the habitat and nutrition for beneficial and affecting the quality of herbivores.The green peach aphid, Myzus persicae(Sulzer), is one of the most important pests worldwide on many species of greenhouse vegetables. The parasitoid, Aphidius gifuensis(Ashmead), is widely applied for biological control of M. persicae. The suitability and host selection of A. gifuensis originated from Sitobion avenae(F.) on M. persicae that reared on three plant species,,sweet pepper(Capsicum annuum L.var. grossum), cabbage(Brassica oleracea L.) and crown daisy(Chrysanthemum coronarium L.), were studied in the laboratory. I tested(1) parasitism, emergence rate and progeny sex ratio(female ratio), development time, body weight of four continuous generations of A. gifuensis on M. persicae reared on three vegetables;(2) oviposition behavior of A. gifuensis on M. persicae reared on three host plants;(3) host selection of A. gifuensis towards M. persicae on different host plants; and(4) olfactory responses of females A.gifuensis to different odors of host plants. The main results were as follows:1. Aphidius gifuensis could complete their life cycle on M. persicae reared on all three different plants. However, host plant affected performance and host acceptance of A.gifuensis. They performed better on sweet pepper-fed M. persicae than on those originated from other host plants. There were significant differences in parasitism, emergence rate, progeny sex ratio and female weight of A. gifuensis among the three host plants: sweet pepper > crown daisy > cabbage, and the differences were consistent in each generation. The body weight of male parasitoids on sweet pepper aphids was significantly higher than that on cabbage-fed aphids, so did the number of attacks, larvae in aphids and parasitized aphids according to the observations of female parasitoids’ oviposition behavior. The development time of A. gifuensis was significantly influenced by host plants. Both male and female parasitoids developed the slowliest on crown daisy.2. With A. gifuensis continued breeding, the parasitism level and the performance were different between three plant species. No significant change was found about parasitism, emergence rate of A. gifuensis on sweet pepper and crown daisy-fed aphids between different generations, but their female offspring proportion decreased. There was no significant change in progeny sex ratio of A. gifuensis on cabbage between different generations, and the parasitism and emergence rate in F3 generation(parasitic rate: 26.81%, emergence rate: 67.25%) achieved the highest. Both male and female parasitoids in F1 generation developed slowest on all three host species. Body weight of both male and female A. gifuensis increased with the generation added on all three host species, except for female A. gifuensis that originated from sweet pepper-fed aphid.3. Female A. gifuensis significantly preferred to sweet pepper-fed aphid. The parasitism rate and progeny sex ratio were highest on the aphids fed on sweet pepper(18.46% and 43.46%), and lowest on the aphids fed on cabbage(2.63% and 11.25%), crown daisy aphids fed on was intermediate(9.25% and 27.76%) as the results in the no-choice tests.4. Compared with clean air, A. gifuensis significantly attracted to sweet pepper and crown daisy that were undamaged or infested with aphid, but not to cabbage. And they preferred infested plants more than undamaged plants. A. gifuensis adult females showed preferences to sweet pepper than crown daisy in all combinations. Compared with clean air, A. gifuensis did not show any preference to the odors of undamaged or infested cabbage. When tested between with crown daisy and cabbage, they significantly preferred to cabbage.