Genetic Improvement Of Reproductive Traits Of Trichogramma Dendrolimi

The egg parasitoid,Trichogramma dendrolimi,has been widely used as an efficient biological control agent against lepidopteran pests.The females of some lines of T.dendrolimi can produce nearly 100%offspring females even without mating,which is called parthenogenesis and induced by Wolbachia.The Wolbachia-induced parthenogenetic line of T.dendrolimi has long been considered as an superior agent during mass-rearing procedure and field application for several advantages,such as high reproductive efficiency,easy colonization in fields,and low cost during mass-rearing.However,the fitness parameters of Wolbachia-induced parthenogenetic line of T.dendrolimi including fecundity may decline because of low genetic diversity.Besides,bisexual T.dendrolimi populations are collected in field conditons,and has never been selected.The selection of Trichogramma with superior traits is the key factor for the improvement of biological control agent.Compared with the breeding of crops,livestocks,and economic insects,the breeding of natural enemies,including Trichogramma spp.,is still at primitive stage.In this study,the genetic improvement methods were applied for the genetic improvement of fecundity traits of T.dendrolimi The fitness parameters of bisexual lines and parthenogenetic lines of T.dendrolimi were evaluated.The iso-female line of T.dendrolimi with high fecundity trait was established after the selection of ten generations.The stability of fecundity trait was tested.The introgression method was applied for the genetic improvement of parthenogenetic line of T.dendrolimi The results will provide a new insight for the genetic improvement of Trichogramma dendrolimi.The results as follows:1.I compared biological parameters of females and their offspring of bisexual lines or parthenogenetic lines of T.dendrolimi,and found that fecundity of“Liaozhong 1”population（LZ1-W^-,133.65±5.95）and“Hongan”population（HA-W^-,118.74±8.17）significantly higher than that of the rest of the populations.Adult lifespan of LZ1-W^-population（12.71±0.71 d）,HA-W^-population（11.48±0.83 d）,and“Zhangwu parthenogenetisis”population（ZW-W⁺,11.55±0.73 d）significantly higher than that of other populations.Offspring number per egg of“Huanren”population（HR-W^-,1.01±0.01）was the highest.Body size of bisexual female was significantly larger than that of parthenogenetic female.Development time of“Chaoyang”population（CY-W^-,11.48±0.12 d）was the longest.Development times of HR-W^-population（10.36±0.05 d）and HA-W^-population（10.30±0.05 d）were significantly shorter than the rest.The results showed that the bisexual lines of T.dendrolimi performed a superior fitness than parthenogenetic line.LZ1-W^-and HA-W^-population were superior in fitness index among bisexual lines.2.After continuous selection of the fecundity of females for 10 generations,which the females with top 20%fecundity index were selected every generation.The fecundity of all females,selected females,and eliminated females increased with generation respectively.The fitness parameters of females of the selected iso-female line were tested for five generations,and found that fecundity（χ²=8.75,P=0.068）,offspring number per egg（χ²=1.22,P=0.88）,proportion of females（χ²=3.13,P=0.54）,and body size（χ²=3.49,P=0.48）were not affected by generation,but lifespan of female was significantly affected by generation（χ²=58.29,P<0.001）.The lifespan of F₁generation and F₅generation were significantly higher than that of other generations.3.Fecundity of 12 geographical populations of T.dendrolimi were evaluated.The fecundity of the“Tongliao”population（TL-W^-,73.33±6.09）and the CY-W^-population（82.38±5.23）significantly lower than that of the rest populations except for“Jilin Baicheng”population（JB-W^-,86.81±5.00）and“Jilin Nongda”population（JD-W^-,91.11±5.41）.Offspring number per egg of TL-W^-population（0.76±0.02 heads）was the lowest.The distribution of fecundity of low fecundity population（LF,χ²=5.73,P=0.33）and high fecundity population（HF,χ²=12.06,P=0.06）fit the normal distribution（LF:Skewness=-0.12,Kurtosis=-0.77;HF:Skewness=0.83,Kurtosis=1.17）,but that of F₁did not comply normal distribution（F₁:Skewness=0.74,Kurtosis=-0.64;The dominance coefficient D=0.0064,h=0.51）.4.The introgression method were applied by introducing the geneome of bisexual females into parthenogenetic females.The fecundity,life span,emergence rate,and body size of the hybrid female were observed by generation.The fecundity of female was significantly affected by the interaction of T.dendrolimi strains and generations（χ²=60.77,P<0.001）.The difference between fecundity of hybrid line of F₀（70.66±3.61）and parthenogenetic line of F₀was insignificant（55.54±3.77;z=1.27,P=0.45）,but the fecundity of hybrid F₁（156.10±5.36）,hybrid F₂（189.89±6.42）,and hybrid F₃（176.10±5.89）significantly higher than those of parthenogenetic line of F₁（55.51±5.11;z=10.53,P<0.001）,F₂（54.31±6.78;z=9.68,P<0.001）,and F₃（88.00±5.96;z=9.19,P<0.001）.