Diversity Of Wolbachia In The Laboratory Populations Of Trichogramma

Trichogramma is the most important natural enemy insects in the modern agriculture and forestry pest biological control.The sexuality of Trichograma is determined by haplodiploid.The arrhenotoky produces male progenies（haploid,n = 5）,sexual reproduction and thelytoky produce daughters（diploid,2n = 10）.The intracellular symbiotic bacteria Wolbachia of Rickettisiaceae inregulates the reproductive mode of most of arthropods by the vertical transmission in the population and the horizontal transmission among different species.The Wolbachia infection results in the cytoplasmic incompatibility,parthenogenetic induction,feminization,male-killing and enhanced fecundity and fertility-modifying to the arthropod hosts.The infection of Wolbachia in the Trichogramma affects the bio-control agents through the involvement of Wolbachia in the reproductive mode of Trichogramma.In the present thesis,33 laboratory populations belong to the 10 species of the genus Trichogramma were identified based on the morphological characters and the sequence of Internally Transcribed Spacer 2（ITS2）of rRNA.The infection of Wolbachia in these populations were investigated.The sex ratio of isofemale lines in these populations were determined.Moreover,the identity of DNA sequence of the infected Wolbachia in the populations were analyzed by using the Multilocus Sequence Typing（MLST）.Phylogenetic methololgy was used to constructe the phylogenetic tree of Wolbachia we determined.The experimental results were showed as follows:1.In addition to a population of Trichogramma chilonis（T.c₂）,all investigated populations were infected by Wolbachia.The infection rate ranged from 4.29% to 100%,and the sexual ratio ranged from 54% to 100%.The correlation coefficient of the Wolbachia infection rate and the sexual ratio of Trichogramma is r = 0.4091.This result suggested the infection and the sexual ratio are not related.2.Female-biased offspring sex ratio（thelytoky）was found from seven populations of three species of investigated Trichogramma,Trichogramma pretiosum（T.pr）,Trichogramma cacoeciae（T.ca）,Trichogramma embryophagum（T.em）.Among these parthenogenetic female populations,only two populations of T.pretiosum were 100% infected by Wolbachia,whereas other four populations,one of Trichogramma cacoeciae（T.ca₁）,three of Trichogramma embryophagum（T.em₁,T.sp₁,T.sp₂）,were with the infection rate less than 50%.Moreover,the 16 S rRNA sequences of Wolbachia which detected from populations of T.ca and T.em are the 100% identical to the 16 S rRNA sequences of Wolbachia of their host,Corcyra cephalonica.These results indicated that thelytoky individuals uninfected Wolbachia would be regulated by other mechanisms.3.The Wolbachia 16 s rRNA gene,Wolbachia surface protein gene（wsp）and five genes（gatB,coxA,hcpA,ftsZ,fbpA）combined MLST were sequenced and analyzed.Phylogenetic trees were constructed based on these sequences.The phylogenetic trees indicated that all of the Wolbachia infected the Trichogrammma and their host Corcyra cephalonica are in the B supergroup.Sequences from Trichogramma were highly identical to that of Wolbachia from their host egg of Corcyra cephalonica.These results suggested that Wolbachia strain may have horizontal transmission from the eggs of Corcyra cephalonica to the individuals of Trichogramma.In conclusion,the details of reproductive modes of Trichogramma and its relationship with the infection of Wolbachia strains provided basic information for understanding the mechanism of Wolbachia involved Trichogramma reproduction.The possibility of horizontal transmission from the host egg to the Trichogramma is worth to be further studied.