Effects Of Two Host Plants On Fecundity And Vitellogenin Gene Expression Of Spodoptera Litura Fabricius

Spodoptera litura Fabricius is a world-wide distributed polyphagous insect pest which may outbreaks in a very short time. In recent years, it’s strong reproductive ability induce serious outbreak and damage all around the world. A female S. litura can lay up to one thousand eggs. The diversity of host plants provides abundant food for S. litura, thus laying the foundation for the pest outbreak. Currently, there are many researches explore the influence of different host plants on S.a litura reproduction, most of these studies focus on physiological and biochemical indexes, such as fecundity, but only a few pay close attention to reproductive-related genes. Vitellogenin gene, closely related to oogenesis, is rarely studied in S. litura, and there are no clear findings suggest the effect of different host plants on Vg gene expression and it’s mechanism.This study focus on the fecundity and Vg gene expression of S. litura feeded on different host plants. Based on the significant different preference degree of S. litura to host we selected two plants, cabbage and alligator weed. Feeding on this two hosts, we mainly studied the effect on reproductive indicators, Vg gene expression and Vitellogenin expression in hemolymph of S. Litura through qPCR, RT-PCR and SDS-PAGE. Furthermore, transcription analysis was used to identify the key genes related to Vg gene and fecundity regulation of S. Litura feeding on different hosts, the main conclusions are as follows:1. Feeding on different host plants, the reproductive index of S. Litura were affected in different degrees. Preoviposition presented that cabbage was shorter than alligator weed. Oviposition period, fecundity, potential fecundity, female life expectancy were in the same trend, as cabbage> alligator weed. The fecundity of the pest feeding on cabbage was 2.7 times than feeding on alligator weed, while the intra-abdominal residual amount of eggs, hatching and yielding rate did not have significant difference. The ovary fresh weight, gonad index, ovariole length of each instar were in the trend that cabbage> philoxeroides, so as the soluble protein and sugar in fat body and ovarian of each develpment stage. The main nutritional components of the two host plants, soluble protein and sugar, were measured. Results showed significant differences between sugar content, cabbage was significantly higher than alligator weed but no difference between protein content.2. After feeding on different host plants, Vg gene expression of S. litura was affected in different degrees. Vg mRNA was found specifically in the female fat body. Temporal pattern of Vg expression indicated that in S. Litura feeding cabbage, Vg mRNA was first transcribed in 6th day female pupae and the protein band in hemolymph was detected in 7th day female pupae.While in S. Litura feeding alligator weed, Vg mRNA was first transcribed in 7th day female pupae and the protein band in hemolymph was detected in 8th day female pupae. Expression level of Vg of each instar feeding both hosts had significant differences. The maximum expression level gap was at the period of 24h adult stage. Vg mRNA relative expression level of S. Litura feeding on cabbage was 4.33, meanwhile, S. Litura feeding on alligator weed was 3.16, the former was about 1.37 times of the latter.3. We detected and spliced 30671 Unigene sequences from transcriptome analysis of S. litura feeding on different host plants, and there were 15,809 Unigenes have annotation in the database. Then we had functional classification for spliced Unigene, finding signal transduction mechanism was the main class in cluster of orthologous groups of proteins (COG); molecular function was the main class in gene ontology(GO). By KEGG analysis, we found Unigene mainly exists in metabolic pathway, and we came to a result that host plants affect the growth and reproduction of S. litura by influencing its metabolic processes.120 Unigenes were founded significantly different expressed in 24h female adult through transcription analysision, we selected 11 Unigenes significantly different expressed by Pathway analysis, then we chose some Unigenes standing in main pathway and may be related to reproductive, they were:calmodulin, Niemann-Pick C2 protein, cytochrome P450 and gave a discussion on these Unigenes.