Characteristics Of Symbiont And Tomato Yellow Leaf Curl Virus Infection In Bemisia Tabaci, And Effects Of Extract From Agrimonia Pilosa On Natural Enemies

Bemisia tabaci (Hemiptera:Aleyrodidae) is a worldwide insect pest which is a threat on lots of crops. It is a major problem not only as a pest, but also as a vector of plant viruses. At present, B. tabaci has developed resistance to some chemical pesticides. And at the same time, requirements for pollution-free agricultural products are increasing. Therefore, biological control technologie against B. tabaci is urgently required. In order to expore practical biological technologies on B. tabaci, firstly we identified the biotype of B. tabaci, and surveyed the predominant species of natural enemies of B. tabaci in Jiangsu province, China. Then we studied the diversity of symbionts of female and male B. tabaci. Based on these, we investigated the influence of extracts from two species of plants on predominant natural enemies of B. tabaci. At last, we also investigated the variation of viruliferous B. tabaci on host plants, and the effect of host plant transfer on viruliferous B. tabaci. All these are benefical to develop new propriate biological control technologies to prevent the spread of B. tabaci effectively. The main research results are as follows:(1) The biotype and the predominant species of natural enemies of B. tabaci were surveyed in main areas of Jiangsu province. At the six collecting sites in Jiangsu, it was found that, in five of them, B. tabaci was Q biotype, and only at one site, Fengxian Xuzhou in north part of Jiangsu, B. tabaci were B biotype. Parasitism of B. tabaci varied with its location, while parasitic rates in all tested samples were under5%. The predominant parasites of B. tabaci were different among different time and host plants, and it was found that Encarsia formosa was the predominant species on cotton and E. sophia was predominant on vegetables. At the same time, a kind of predominant microorganism, Paecilomyces fumosoroseus was isolated from B. tabaci in Nanjin, Jiangsu.(2) The diversity of symbionts in B biotype and Q biotype B. tabaci within population was investigated. It was firstly found that not all B. tabaci in the field harbored obligate symbionts, and both in B and Q biotype, there was difference in infection frequencies between male and female, and more femles than males harbored obligate symbiont. There were four kinds of facultative symbionts including Hamiltonella defense、Cardinium、 Wolbachia and Rickettsia in both B and Q biotype B. tabaci in Jiangsu. Among the above four symbionts, Hamiltonella was the most common facultative symbiont in all the tested populations, and there was also infection difference between female and male, and this difference varied with host plants and biotypes. In B biotype on cotton and Q biotype on sweet potato, Hamiltonella infection frequencies in females were all significantly higher than that in males. Genetic difference in Hamiltonella from different symbiontic combination within population was also found in both B and Q biotype B. tabaci, and three and two nucleotides change of16S ribosomal RNA gene from Hamiltonella was detected in B and Q biotype, respectively.(3) Carrying rate of tomato yellow leaf curl virus (TYLCV) by female and male of B. tabaci on different host plants in the field was compared, and the effect of host transplantation of B. tabaci on carrying rate of TYLCV was also investigated. The results showed that there was significant difference in the proportion of viruliferous B. tabaci among different host plants. Both B and Q biotype from cotton were all not infected with TYLCV, and there was difference in ratio of viruliferous B. tabaci between female and male. On tomato, sweet potato and cucumber, the rate of viruliferous whitefly in females were all higher than that in males. There was positive relation between TYLCV infection and Hamiltonella infection in B. tabaci. Further host transplantation showed that, after B. tabaci tranfering from tomato or cucumber to cotton, rates of viruliferous female and male were all significantly decreased except male whitefly from cucumber. All the results indicated that intercropping might be a promising method to effectively control TYLCV.(4) In this study, we investigated the effect of ethanol extracts from Agrimonia pilosa and Melia azedarach on predominant natural enemies of B. tabaci in Nanjing. It was found that the ethanol extracts of A. pilosa significantly improved the fungus infectivity on B. tabaci harboring Hamiltonella, and the mortality of B. tabaci caused by105pores/mL Paecilomyces fumosoroseus combined with2mg/mL extract from A. pilosa was81.6%, which was significantly higher than that caused by fungus only, and M. azedarach didn’t improve fungus infectivity. The predation capacity of Pardosa pseudoannulata was not affected by the extracts, while its tolerance to insecticide was improved by20mg/mL ethanol extract from A. pilosa. And the longevity of the parasitoid Encarsia formosa was not affected by ethanol extract from Apilosa and M. azedarach. It was also found that ethanol extracts from M. azedarach decreased the infection frequency of Hamiltonella in B. tabaci. All the results indicate that extract from A. pilosa is hopeful to be used as synergist to improve biological control efficacy of natural enemies of B. tabaci.