Effect Of Wolbachia On Development And Reproduction Of Echinothrips Americanus Morgan

The research of relationship between the insects and endosymbionts has important biological and ecological significance.The inherited bacterium,Wolbachia pipientis,is a secondary symbiotic bacterium widely existed in arthropod.In its hosts,Wolbachia induces a variety of reproductive alterations and change its biological characteristics,thereby changing the fitness of a specific host population.Echinothrips americanus Morgan is a invasive greenhouse pest originated in the east of the United States and spreads to China which damages the vegetables and ornamental in greenhouse.Wolbachia also has a significant impact on Echinothrips americanus.The situation of the endosymbionts in E.americanus and their interactions would help us to manage the pest,and which was valuable in research and application.By identifying the symbionts within E.americanus population and analyzing the sequence,we detected the distribution of Wolbachia in E.americanus,chose the right treatment method to eliminate the symbionts in thrips,and discussed the mechanisms of symbionts in thrips.The results were showed as follows:1.Molecular technique was used to test the symbionts in E.americanus.Results showed the thrips was only infected by Wolbachia,and we identified that the bacterium was belonged to subgroup Mel of A group by a pair of specific PCR primers which arranged from wsp（surface protein of Wolbachia）gene.2.Transmission electron microscopy results showed that Wolbachia in E.americanus were in coccoid form and rod form.Reproductive mode is binary fission.Wolbachia existed in head,thorax and abdomen of the thrips host.In abdomen of the female,ovary was the most density distributed area;a few Wolbachia were found in testicle of male.3.The copy numbers of Wolbachia in different tissues and at different developmental stages of E.americanus was tested by Quantitative PCR.The results showed that the number of Wolbachia gradually increased with the hosts development.The copies of bacteria in egg stage were about 7-8×10⁸copies which increased to 2.1×10¹⁰copies in pupa stage.In adults,the copies number of Wolbachia in female thrips was much higher than that in male thrips.Wolbachia existed in head,thorax and abdomen of E.americanus,and the density of Wolbachia in the head was the lowest,while in the abdomen was the highest,which taking up about 60%-70%of the total copy number in female.The number of Wolbachia in 8-10segments of abdomen was account to 20%-40%of the total abdomen quantity,and the rate in female was significant higher than in male.4.Using three antibiotics（tetracycline,rifampicin and ampicillin）and different treatment methods,we attempted to eliminate Wolbachia from E.americanus.The results showed that if considering the developmental time and fecundity of population,rifampicin was verified to be the most safe and sensitive antibiotic for this microorganism eliminating in E.americanus.Life table of different populations under different antibiotic concentrations was made to evaluate the safe and effective way of eliminating the symbiont Wolbachia.By comparing population parameters,developmental time and reproductivity,the group of feeding the wheat leavies which pouring with 50mg/mL rifampicin solution was verified to be the more effective and safe method for eliminating Wolbachia from E.americanus.5.After the Wolbachia-free E.americanus population was stably inherited,life tables of two populations were built.The results show that there was significant difference of longevity between these two populations.Net reproductive rate and finite rate of increase of the natural population were both lower than those of Wolbachia-free population.While the fecundity,APOP and oviposition period of Wolbachia-free population were significantly higher than those of natural population.Longevity of female in Wolbachia-free population was significant higher than the natural population,sex and Wolbachia’s existence were interactive affect on longevity.Sex ratio difference between these two groups was notability.It was expected that Wolbachia could restrain female ratio in natural population and reduce the fitness of E.americanus population.6.The existence of adults and their offspring were observed through crossing experiments between the natural and Wolbachia-free populations.The results show that longevity of female was influenced by self-infection condition and its mate’s infection condition.Fecundity of uninfected female and natural male hybridizated group was significantly higher than other groups,while this group’s hatching rate and adult eclosion rate were notably lower than those of other groups.Sex ratio of this group was 0.81:1 which was far lower than other two groups.These results demonstrated that Wolbachia in E.americanus could cause cytoplasmic incompatibility effects in low level.