| Insect populations feeding on different plant species are under selection pressure to adapt to natural selection and environmental changes,leading to the formation of different specialized host-adapted biotypes.Host specialization is a very common phenotype in sap-sucking insects,the most typical is aphids.Myzus persicae(Sulzer),also named the green peach aphid,belongs to Myzus of Aphididae in Hemiptera.M.persicae is one of the most widely distributed pests,and it has been reported in Neotropical Region,Africa Region,Oriental Region,Nearctic Region,Australia Region and Palaearctic Region.Besides,the host range of M.persicae is quite wide,up to over 400 plant species in more than 50 families.In this paper,the number and time of occurrence of tobacco aphids were studied by using yellow trapping plates in the whole field stage from the group stage to the maturity stage.The results showed that the aphids had two peaks in the tobacco field,the first peak was in the middle and late June,when which the tobacco was in the stage of the regimental period,and the second peak was in early July.It is presumed that the first peak is due to the large migration of the aphids from the surrounding vegetable area.The second peak may be the need for rapid expansion of the population after the successful breeding of the winged aphids.Through the observation of the environment near the trapping point of the tobacco field,it was found that there were two types of environments including vegetables and small woods,and the numbers of winged aphids trapped in the points near these two types of environment were compared.Especially in the late June,the difference was most obvious.And in late June it was the stage that the aphids moved from the outside to the tobacco fields,indicating that the initial occurrence of tobacco aphids was closely related with nearby habitats.Through the investigation of the types of vegetables near the trapping point of the tobacco field,it was found that there were cabbages,peppers,broad beans and radishes.And then the relationship between the terrain conditions of tobacco planted and the amount of M.persicae was analyzed.It was found that the number of winged aphids trapped in three kinds of terrain was in the order of valley> slope>top.In mid-July,the difference was particularly prominent,which was the successful breeding of M.persicae after the rapid expansion of the period,proved that the second peak was closely related with the terrain of the tobacco planted.At the same time,the occurrence of virus disease in tobacco fields was investigated.The results showed that the middle of July was the fastest growing period of virus disease,and the virus disease slowed down even stopped after the beginning of July.In the middle of July,the period of rapid expansion of the population was successful,and the activity of the tobacco aphid in the tobacco field usually stopped after the end of July,which proved that the development of tobacco virus disease was close to that of the winged aphids.In addition,the incidence of virus disease at the trapping point of tobacco field under different terrain conditions was also compared.It was found that the occurrence in the valley was significantly higher than that in the slope and the top.Therefore,the occurrence of virus disease in tobacco fields is not only closely related to the development of the population of winged aphids,but also the external environmental conditions.Based on the understanding of the occurrence and host range of the aphids,the five plants of tobacco,pepper,radish,rape and broad bean were selected,and then the aphids were studied under the laboratory condition The growth and reproduction of aphids on these hosts were recorded and the corresponding life table was set up.Finally,TWOSEX-MSchart software was used to analyze the life table parameters of the aphids on different host plants.The results showed that the intrinsic growth rate r was 0.383 d-1,which was significantly higher than that of the other four crops,and the growth rate of the aphids on the broad bean was the highest.Intrinsic growth rate refers to the maximum instantaneous growth rate of the population under ideal conditions,which represents the ability of the population to expand.Compared with the intrinsic growth of M.persicae in the Solanaceae and Cruciferae Vegetables reported a decade ago,M.persicae in this study was significantly improved,due to the abuse of chemical pesticides over the years.APOP and TPOP of aphids on the broad bean were significantly lower than those of the other four species,suggesting that there was a certain relationship with the intrinsic growth ability.However,during the course of the experiment,the aphids also escape the most,so the higher capacity of the population dose not prove the more advantages,but also may be in response to the ideal environment changes to ensure the continuation of the population.And the net reproductive rate R0 is more able to reflect a population whether is adaptable to the environment,and the aphids on radish showed a rate of 80.83,significantly larger than the other four hosts.The reproducibility of M.persicae was significantly higher than that of the other four species(P <0.01).The correlation analysis showed that the net reproductive rate of M.persicae was positively correlated with its reproductive ability.At the same time,it was found that the adult life and total life span of the aphids on radishes were longer than those on the other four species(P <0.01).Long life span has a longer breeding period,so the net rate of proliferation can be higher than the broad bean population with the highesr intrinsic growth ability.In this paper,we compared the survival rate sxj,female fecundity fx,female,life expectancy exj,and reproductive value vxj at different ages and stages,and found that the survival rate of aphids on radishes was the highest and the life expectancy was also the longest,which once again explained the maximum net growth rate of aphids on radish.In order to further explore the effects of host plants on population development,high-throughput transcripts were sequenced for more than 10 generations of tobacco aphids.A total of 4,610,008,620 bases(nt)were produced by the Illumina Hiseq 2000 platform sequencing yield of 51,222,318 reads.These reads were obtained by assembling 50,177 contigs with an average length of 470 nt.These contigs were further assembled and finally got 30,293 unigenes with an average length of 966 nt.The unigenes were predicted by using NR,NT,Swiss-Prot,GO,COG and KEGG databases,respectively,and 22,736,24,498,16,856,10,194,8,232,and 15,512 unigenes have been annotated,and finally there were 4,271 unigenes not annotated because the expression level in the transcriptome is too low to obtain sufficient sequencing samples.After using the NR database annotations,it was found that the vast majority of unigenes(20,896,91.91%)were highly homologous to Acyrthosiphon pisum,and the genome sequence of the pea aphid and the full-length c DNA library which was published in 2010 should be of the important reasons,which also proved the close relationship between the tobacco aphids and the pea aphids.But the results also show that there are only 67 unigenes homologous to M.(Nectarosiphon)persicae,accounting for only 0.29% of the total,which indicated the lack of information on the transcriptome of the aphids.10,194 unigene of the GO database was divided into 58 functional groups of the Biological Process,Cellular Component and Molecular Function groups,and unigenes in the "Cellular process"(6,525)was the most,followed by the "Single-organism process"(5,122)and "Metabolic process"(4,813).The COG database is mainly used to predict the possible functions of unigenes and classify them.Based on sequence homology,a total of 8,232 Unigene is divided into 25 subclasses,of which "General function"(2,931)was the largest.Followed by the use of the KEGG database to predict metabolic pathways of 15,512 unigenes,a total of 255 were found,including the most unigenes "Metabolic pathways"(ID: ko01100)(2132,13.74%).This paper also explored many of the pathways and unigenes that were closely related to the process of feeding and digestion of aphids,such as "Starch and sucrose metabolism"(213 unigenes,1.37%)associated with carbohydrate metabolism,and "Lysine degradation"(188 unigenes,1.21%)associated with amino acid metabolism,"Glycerophospholipid metabolism"(161 unigenes,1.04%)associated with lipid metabolism,and "Bile secretion"(310 unigenes,2.00%)involved in digestive system metabolism. |
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