Effects Of Sublethal Doses Of Tetracycline Hydrochloride On The Biological Characteristics And Wolbachia Titer In Parthenogenesis Trichogramma Pretiosum

Wolbachia is a symbiotic bacterium widely existed in the reproductive tissues of their hosts,it can be inherited through the cytoplasm of the hosts.Wolbachia can participate manipulations of reproductive activity of its hosts,including the host parthenogenesis,cytoplasmic incompatibility,feminization of genetic,male-killing and improving female fecundity and male fertility,and that causes changes in the reproductive behaviors of the host.As important egg parasitoids of many species of Lepidopterous pests,the most widely used natural animies,Trichogramma spp can also be infested by Wolbachia.After being infested,Trichogramma produces female offspring via parthenogenesis.For this study,Trichogramma pretiosum infested by Wolbachia was selected as experimental material.The toxicity of tetracyline hydrochloride on T.pretiosum was determined by feeding method under laboratory conditions.The sublethal effects of tetracyline hydrochloride on development and reproduction of T.pretiosum was also studied,as well as the determination of Wolbachia content after tetracyline hydrochloride treatment through RT-q PCR.And the differences between parthenogenetic and bisexual recovered strain of T.pretiosum on biological characters were also be assayed.The main results are as follows:（1）Sublethal doses of tetracyline hydrochloride on Trichogramma pretiosumSublethal doses of tetracyline hydrochloride on T.pretiosum was determined under laboratory conditions.Results indicated that tetracyline hydrochloride was toxic to adult T.pretiosum,the LC₅₀ and sublethal dose(LC₃₅,LC₁₅ and LC₅)values were 3.48mg/ml、2.46mg/ml,1.37mg/ml and 0.79mg/ml.（2）Effects of sublethal doses(LC₅,LC₁₅ and LC₃₅)of tetracyline hydrochloride on Trichogramma pretiosumTo determine the effects of sublethal does of Tetracyline hydrochloride on T.pretiosum,the life-table method of the surviving parasitoids was conducted.Results indicated that sublethal doses(LC₅,LC₁₅ and LC₃₅)of tetracycline hydrochloride had significantly effects on T.pretiosum,such as decreasing the longevity of females（2d～6.47d）,reducing the fecundity（23.13～63.14）,parasitising numbers of offspring（21.75～59.68）,and the percentage of female offspring（41.45%～76.29%）,as well as reducing the life-table parameters（R₀,r_m,λand T）of T.pretiosum.In addition,results indicated that the adaptability of T.pretiosum to tetracyline hydrochloride was gradually increased as the generation treated increased.The longevity of females,fecundity,number of offspring,as well as the life-table parameters（R₀,r_m,λand T）of T.pretiosum will be increased as the number of treatment generation increased.Tetracyline hydrochloride treatment didn’t induced the increase in the rate of deformity of offspring,but could cause a significant increase in the percentage of hermaphroditism offspring.（3）Effects of sublethal does(LC₅,LC₁₅ and LC₃₅)of tetracyline hydrochloride on the titer of Wolbachia in Trichogramma pretiosumWolbachia content in T.pretiosum was determined by assessing the copy numbers of the wsp genes of Wolbachia using real-time quantitative（RT-q PCR）,after exposure to the sublethal does(LC₅,LC₁₅ and LC₃₅)of tetracyline hydrochloride.The results showed that the copy number of Wolbachia wsp was significantly reduced in female T.pretiosum after treatment with tetracyline hydrochloride.The Wolbachia content was still at a lower level（32.75～259.51 copies/μL）,even after treatment with tetracyline hydrochloride LC₅ for many times.However,after exposure to tetracyline hydrochloride LC₁₅ and LC₃₅,the titer of Wolbachiawould show varying degrees of ups and downs as the treatment times increased.（4）The difference between the parthenogenetic and the bisexual recovered strains of Trichogramma pretiosumThere was significant difference between the parthenogenetic and bisexual T.pretiosum on the biological parameters.Compared with the parthenogenetic T.pretiosum,bisexual T.pretiosum have the significantly shorter longevity（8.2 d）,lower fecundity（70.67,the number of eggs parasitized per female adult）and life-table parameters（R₀,r_m,λand T）.In addition,the bisexual T.pretiosum females did not produce hermaphroditism offsprings.Based on the results,tetracyline hydrochloride treatment could cause a change of the reproduction mode in parthenogenetic T.pretiosum.After treatment with the sublethal does of tetracyline hydrochloride,parthenogenetic T.pretiosum began to change their reproduction mode to bisexual,this phenomenon was caused by the decrease of Wolbachia titer in T.pretiosum.However,T.pretiosum will gradually increase its adaptability to tetracyline hydrochloride as the number of treatment generation increased.