Effects Of Host Plant And Its Switch On Immunity Of Spodoptera Litura Larvae And Its Resistance Against SLNPV

The common armyworm Spodoptera litura is an important worldwide agricultural pest. With the adjustment of planting structure in China, expanding ofplanting area of vegetables and some economic crops has increased the frequency of the outbreak of the pest. Effects of host plants on herbivore population is one of the focuses of plant-insect interactions. Insect immunity is a key factor for insect individual to resist insect pathogenic microorganism and parasite infection. Due to their quality and qualitative differences in nutrition and secondary metabolites, host plants may affect the strength of the immunity and disease resistance, and then population dunamics. S. litura, as a kind of typical lepidoptera noctuidae insects, its active older larvae and adult easily moved in the field in which they will experience switch of host plants. This thesis focus on the effects of host plants and switch of host plant during the larval period and inter-generation on immunity and its resistance against S. litura nuclear polyhedrosis virus (SLNPV), including:(1) the effect of different host plants on the immune and disease resistance of the moth; (2) the effect of switch of host plant within moth larvae stage on the host immunity and disease resistance; (3) Effect of different parental feeding experience on the immunity of offspring and disease resistance. Immune index including cellular immune index (the amount of blood cells) and humoral immunity indexes (phenol oxidase activity, the content of lysozyme activity, antibacterial peptides) were used in the study. And disease resistances of the moth larvae under different treatment against S. litura nuclear polyhedrosis virus get (SLNPV) were tested in the study.The main results were as follows:1. Immunity and disease resistance of the 3rd and 5th larvae of the pest was significantly affected by the feeding host plants, but the effects on the four immune indexes of the larvae feeding on different host plants was not accordance with the the effect on disease resistance. SLNPV resistance of 3rd and 5th instar larvae feeding different host plants could be ranged in order from strong to weak:kale> white clover> cotton alternanthera herb (3rd instars), and kale = white clover> cotton alternanthera herb(5th instars). Plasma cells, total blood cell quantity and antibacterial peptide activity was of a positive correlation relationship with individual resistance, while phenol oxidase activity and lysozyme content had no significant correlation with individual resistance.2. Compared with alternanthera herb, kale and cotton plant with high quality. Switching of host plant between high and low quality host for feeding S. litura larvae had significant effects on immunity and disease resistance of the 5th instars larvae. Compared with larval only feeding high quality or low quality host plants, switching of feeding host plant between different quality of host plants, the activity of the immune factors in the haemolymph and disease resistance is generally between that feeding on high or low quality host. The host plant quality of the larvae feeding at later instar stage had stronger effect on immune and individual resistance against the virus.3. Based on quality difference of cabbage, cotton and alternanthera herb, effects of inter-generation switching of host plant were studied. The results indicated the that the parental feeding experience with different host quality was of significant effect on immunity and disease resistance of the early instar larvae of the offspring, but not for later instars. For early instar larvae, the number of blood cells was consistence with the disease resistance, but not with phenol oxidase activity in serum, serum lysozyme content and bacteriostatic activity of the larvae.