Interaction Among Sogatella Furcifera,Bacterial Symbionts And Host Plants

The white-backed planthopper(WBPH)Sogatella furcifera(Horváth)(Homoptera: Delphacidae)is one of the most important rice pests with a wide distribution in South Asia,Southeast Asia and East Asia,and almost all rice areas in China.Adults and nymphs of WBPH damage rice plants by sucking phloem sap which ultimately leads to reduced tillering,stunted growth,leaf yellowing,and unfilled grains;heavy infestation may cause “hopper burn”,resulting in the complete death of rice plants.Apart from direct feeding damage,WBPH also transmit the Southern rice black-streaked dwarf virus(SRBSDV),which wrecked rice crop in China and other Asia countries in the recent years.There are many kinds of symbiotic bacteria in host insects,which have multiple important functions in their host.Symbionts provide nutrients and participate in the metabolism of host insects;affect the growth,development and reproduction of host insects;affect host insect behavior;protect host insects.Symbiotic bacteria also play an important role in WBPH.For example,Yeast-like symbionts participate in the nitrogen cycle of WBPH and provide sterols for WBPH.Both Wolbachia and Cardinium can regulate the reproduction of WBPH,and Cardinium promotes the growth and development of nymph of WBPH.However,the systematic study of symbiotic bacteria in WBPH is still seriously lacking.This study determined the diversity of the symbiotic bacteria,the population dynamics of the symbiotic bacteria and the function of symbiotic bacteria on WBPH.The results are summarized as follows: 1.Diversity and population dynamics of symbiotic bacteria in WBPHThe 16 S r DNA high-throughput sequencing of symbiotic bacteria in WBPH showed that the relative abundance of Wolbachia,Cardinium and Asaia reached 97.99%.The investigation on the symbiotic bacteria of WBPH in six regions showed that the infection rate of Wolbachia in female and male WBPH were significantly different,and the infection rates of Wolbachia were 98.9% and 55.0%,respectively.The infection rates of Cardinium in female and female WBPH were almost 100%.Infection rates of Asaia were dynamic changes in female and male WBPH.The density of Wolbachia,Cardinium and Asaia in female were higher than that in male,which changed with the development of WBPH.Wolbachia,Cardinium and Asaia also had different infection densities in different WBPH tissues.2.Biotin nutrient function of Cardinium for WBPHBiological assays were performed on Cardinium-infected and Cardinium-free WBPH populations.Cardinium enhanced the fitness of WBPH by promoting the growth,development and longevity of WBPH,increasing the weight and feeding of WBPH.We assessed the effects of Cardinium infection on the developmental duration and adult weight of WBPH feeding on artificial diets without biotin,low,standard and high biotin,respectively,by plastic bottles.The results showed that the growth and development of Cardinium-infected WBPH were significantly faster than Cardinium-free WBPH.However,only when feeding on artificial diet without biotin,the weight of Cardinium-infected WBPH was significantly heavier than that of Cardinium-free WBPH.In addition,the biotin content of WBPH increased significantly with the increase of biotin content in artificial diet.3.Host plants-mediated horizontal transmission of bacterial symbiontsDiagnostic PCR was used to determine the vertical transmission efficiencies of symbiotic bacteria in WBPH,and horizontal transmission of symbiotic bacteria was studied by quantitative PCR and fluorescence in situ hybridization.The results showed that the efficiency of vertical transmission of Wolbachia to offspring is significantly different between male and female(98.3% and 51.7%,respectively).The vertical transmission efficiencies of Cardinium to offspring were almost 100%.There were no significant differences in vertical transmission efficiencies of Asaia between offspring males and females.After feed by Cardinium-and Asaia-infected WBPH,rice leaf sheaths infected Cardinium and Asaia.Cardinium-and Asaia-free WBPH can infected Cardinium and Asaia by feeding on infected rice leaf sheaths.4.Effect of host plants on WBPH and its bacterial symbiontsWBPH feed on the host plant rice,barnyardgrass and wheat,of which the amino acid,riboflavin and biotin concentration were measured by HPLC,in which the infection rates and densities of Wolbachia,Cardinium and Asaia were determined by quantitative PCR.The results showed that the fitness of WBPH was the highest in rice,followed by barnyardgrass and the lowest in wheat.The total concentration of free amino acids in rice was the highest,followed by barngrass and the lowest in wheat.The riboflavin concentration in wheat was the highest,followed by barngrass and the lowest in rice.The biotin concentration of rice was the highest,but there was no significant difference between barnyardgrass and wheat.The infection rates of Wolbachia,Cardinium and Asaia in WBPH feeding on each host plant were not significantly different.The infection density of Wolbachia in WBPH was the higher,when feed on host plant with the lower riboflavin concentration.The infection density of Cardinium in WBPH was the higher,when feed on host plant with the lower biotin concentration.The host plant did not affect the infection rates of Wolbachia,Cardinium and Asaia in WBPH,but its low riboflavin concentration increased the density of Wolbachia,and its low biotin concentration increased the density of Cardinium in WBPH.