The Analysis Of Aphid-parasitoid Food Web Structure In Wheat And Cotton Fields

At present,the aphid-parasitoid interaction models are usually used in the researches of arthropod food web structure and functions.The taxonomic problems and large amount labour of traditional methods impede the study process.Aphids are the important pests in wheat and cotton fields of North China.But,the absenence of systematic knowledge of aphid-parasitoid food web limits the exploration and application of parasitoids' biological control effects.Here,we investigated the parasitoid species in wheat and cotton field of North China and present a molecular detection method to compare the aphid-parasitoid food webs in monoculture and intercropping patterns.In 2014 and 2015,we colletected the mummy samples in wheat and cotton fields and identified the collected parasitoid specimens.For the primary parasitoids,there are three species in wheat fields,Aphidius uzbekistanicus Luzhetski,Aphidius gifuensis(Ashmead)and Aphidius ervi Haliday,and three species in cotton fields,including Aphidius gifuensis,and two new speicies,Binodoxys communis(Gahan)and Aphelinus albipodus Hayat and Fatima.The most abundant primary species are A.uzbekistanicus and B.communis in wheat and cotton,taking up 86.21% and 99.7% of the total primary parasitoids at most respectively.The wheat aphid hyperparasitoid guild is made up by 14 hyper species,Alloxysta fracticornis(Thomson),A.japonicus(Ashmead),A.pusilla(Kieffer),A.victrix(Westwood),Asaphes suspensus(Nees),Asaphes vulgaris Walker,Dendrocerus carpenteri(Curtis),Dendrocerus laticeps(Hedicke),Pachyneuron aphidis(Bouché),Phaenoglyphis villosa(Hartig),Syrphophagus aphidivorus Mayr,S.eliavae Japoshvili,S.taeniatus(F?rster)and Syrphophagus sp.The cotton fields have 10 hyperparasitoid species,including A.suspensus,D.laticeps,P.aphidis,S.aphidivorus?S.eliavae?S.taeniatus and Syrphophagus sp.and two new speicies,Alloxysta brevis(Thmoson),A.pusilla(Kieffer),.P.villosa and Syrphophagus species are the dominant hyper species.Based on the species information above,targeting on the mtDNA gene,the aphid-parasitoid multiplex PCR systems were designed.The wheat aphid-parasitoid multiplex PCR includes three multiplex PCRs(MP)and five singleplex PCRs(SP)which can detect four common wheat aphid species,four primary parasitoids and 9 hyperparasitoids.The DNA template detection limits are 1000 copies at least?The similar MP system was established for the cotton aphid parasitoids.The system is consisted of two MPs and three SPs.The detection species are one cotton aphid,three primary species and six hyper species.DNA detection limits are also 1000 copies at least.The application of the molecular detection method can increase the detection accuracy and decrease the detection period.This will facilitate the establishment of aphid-parasitoid food webs.During the investigation from 2016 to 2017,there was no significant difference of parasitism rates,species composition and food web indices between monoculture and intercropping patterns,except for the aphid population in different cotton fields with different cropping patterns.This could be explained by the different aphid species and primary parasitoid species.The intercropping of this two crops failed to enhance the biological control effects on aphids and to influence the aphid-primary parasitoid and primary parasitoid-hyperparasitoid food web relationships.The outcomes first give out a comprehensive parasitoid species information and offer an efficient method which could be applied to the further study of the influence of landscape complexity on the aphid-primary parasitoid-hyperparasitoid food webs.