Preliminary Identification Of Pathogen Causing Gray Eggs Of Antheraea Pernyi And Its Effects On Host Selection And Suitability Of Trichogramma Dendrolimi

Currently Chinese oak silkworm Antheraea pernyi egg has been used as an important factitious host for mass production of Trichogramma parasitoids which plays a vital role in the biological control of lepidopterous pests.With the increasingly demand for Trichogramma and the popularization of technology,the demand for A.pernyi eggs has been also increased.Recently,the emergence of gray eggs has seriously affected the production and quality of Trichogramma production.In this study,Trichogramma dendrolimi was used as a test parasitoid,and A.pernyi eggs were used as intermediate hosts.By comparing the differences in the lifespan,fecundity,host selection and adaptability of the T.dendrolimi,the size and number of eggs and the eggs loads of the offspring,as well as the parasitic ability of the offspring,the effect of gray eggs on Trichogramma during production are clear.Finally,it provides a theoretical basis for improving the quality of commercial production of Trichogramma and the next step in controlling gray eggs.The main results are follows:1.Preliminary identification of pathogenic bacteria in the gray eggs: The strain was isolated and purified from the pathogen of the gray eggs,and the 16 S rDNA sequence of the obtained strain was aligned with the existing nucleic acid sequence in GenBank,of which similarity with the Serratia marcescens reached 99%.Determining the pathogenicity of healthy A.pernyi eggs,and the pathogen of gray eggs was confirmed to be S.marcescens.2.Through the parasitic behavior of Trichogramma,the horizontal transmission of gray oocysts was determined.It was found that Trichogramma can cause healthy egg disease after cross-parasitic gray eggs and healthy eggs.The horizontal transmission test by egg immersion found that gray eggs were found.Contact with gray egg liquid can cause disease in healthy A.pernyi eggs.It is indicated that the gray eggs’ bacillus can be horizontally transmitted through the cross parasitization of Trichogramma and the contact of egg liquid.3.Effects of gray eggs on the longevity and fecundity of T.dendrolimi: After 24 hours of exposure to gray eggs,the average lifespan of T.dendrolimi was 4.87 d,which was significantly shorter than the average lifespan of T.dendrolimi,which was exposed to healthy eggs,9.64 d relatively.However,there was no difference in the number of parasitic species on the eggs of the Corcyra cephalonica,which indicated that the lifespan of the Trichogramma was shortened after the parasitic contact with the gray eggs,but had no effect on the fecundity of the Trichogramma.4.Effects of gray eggs on host selection,adaptability and individual size of T.dendrolimi: Regardless of whether only one host egg is provided or two host eggs are provided at the same time,the parasitism rate,the emergence rate,the number of adults emerging and the total number of adults emerging on the gray eggs of the T.dendrolimi are significantly lower than those on the healthy eggs.However,there was no significant difference in the developmental duration and the female ratio of the offspring between the gray eggs and healthy eggs.The T.dendrolimi,which emerged from the gray eggs and healthy eggs,were measured and dissected.It was found that the body length,the length of the hind paws,and the eggs loads of the T.dendrolimi that emerged from the gray eggs were significantly lower than those in the healthy eggs.5.Comparison of parasitic ability of T.dendrolimi from gray eggs and healthy eggs: The T.dendrolimi,which are bred in both eggs,when comparing the parasitic numbers,the ones which are emerged from the gray eggs are lower than those from the healthy eggs when parasitize either the C.cephalonica eggs or the eggs of Ostrinia nubilalis.On the C.cephalonica eggs,there is a significant difference in the number of parasitic eggs between the 1-and 2-day old.And the parasitic tendency of the T.dendrolimi from the gray eggs on the eggs of C.cephalonica is also different,which is the parasitic number of eggs on the 0-and 3-day old C.cephalonica eggs is higher than that of the 1-and 2-day old;On the eggs of O.nubilalis,there is a significant difference in the number of parasitic eggs on the 1st day of age between the two,but the T.dendrolimi from two different eggs are better only for the 0-day-old eggs of O.nubilalis.However,there are few or almost not parasitic on the 1-and 2-day old eggs.Based on the above results,the pathogenic bacteria of the gray eggs were initially identified as S.marcescens,which can be transmitted horizontally through the contact of the egg of broken eggs and the cross parasitic of Trichogramma;By comparing and analyzing the parasitic selection and developmental fitness parameters of T.dendrolimi on silkworm eggs and healthy eggs,it is found that the gray eggs have a certain adverse effect on the lifespan,host selection and adaptability of the T.dendrolimi,the size of the individual and the amount of eggs,and the parasitic ability of the offsprings,which provides a theoretical basis on studying the relationship between the gray eggs and Trichogramma.