The Effects Of Fruit Trees-cotton Intercropping On The Aphid-parasitoid Food Web Structure

Charactersitic forestry-fruit industry and cotton planting are two major agricultural industries in Xinjiang.In South Xinjiang,the intercropping of fruit trees and cotton are widely adopted to increase the land utilization rate and keep the superior staus of both two industries.The intercropping of fruit trees and cotton may affect the food relationship between natural enemies-pest by changing the biodiversity and microenvironment,and then may alter the efficiency of natural enmies in pest suppression.In this study,multiplex PCR assays of cotton aphid-parasitoid and walnut aphid-parasitoids were established based on the composition of parasitoids identified in our study.And the influence of intercropping on aphid-parasitoid food web was investigated with multiplex PCR assay in South Xinjiang.This will explicit the effect of different cropping patterns on the aphid biological control regulation mechanism and offer the scientific basis for the aphid integrated management.The main results are below:1.The improvement of parasitic wasp imformation of cotton aphids and fruit tree aphids1.1 The composition and abundance of cotton aphid parasitoids were achieved with mummy rearing.The parasitoid community,identified with morphological characteristics and molecular method,consisted of four primary parasitoid and twelve hyperparasitoid species.Of the primary parasitoids,Binodoxys communis(Gahan)accounted for 95.19% of the total,followed by Praon barbatum Mackaue(3.15%),Trioxys asiaticus Telenga(1.01%),and Lysiphlebus fabarum Marshall,and they are all Aphidiinae.Twelve hyperparasitoid species belonging to six genera were found in our study,of which Syrphophagus taeniatus(F?rster)(35.77%)?Pachyneuron aphidis(Bouché)(27.32%)and Syrphophagus sp.(22.11%)were the dominant species.The proportion of each of the rest nine hyperparasitoid species,including Syrphophagus aphidivorus(Mayr)(3.10%),Asaphes suspensus(Nees)(0.30%)and Dendrocerus laticeps(Hedicke)(5.51%),were below 10%.1.2 The composition and abundance of walnut aphid parasitoids were achieved with mummy rearing: the emerged parasitoids from Chromaphis juglandicola aphid mummies were identified and the primary parasitoids were comprised of three species,Trioxys pallidus(63.07%),B.communis(21.55%)and T.asiaticus(15.38%).The hyperparasitoids were made up of six species,including S.taeniatus(53.75%)and P.aphidis(39.38%).2.The establishment of multiplex PCR detection system of cotton aphid-parasitoids and walnut aphid-parasitoidsBased on COI sequences,the species-specific primers of each targeted species were designed to establish the multiplex PCR detection systems.The cotton aphid-parasitoid detection system included three multiplex PCRs and one singleplex PCR targeting on four aphid species(Aphis gossypii,Acyrthosiphon gossypii,Aphis atrata and Myzus persicae),four primary parasitoid species and five hyperparasitoid species/groups.The detection system could cover the 97.74% morphologically-identified species and detect the cotton aphid parasitoid species efficiently.The C.juglandicola aphid-parasitoid detection system was constituted of two multiplex PCRs and three singleplex PCRs,which could be used to detect C.juglandicola,three primary parasitoid species and five hyperparasitoid species/groups.The detection system covered all the species identified from the emerged species and its effectiveness for the walnut aphid parasitoid species detection had been proved.The sensitivity and specificity of each detection systems had been evaluated to guarantee a stable,sensitive and accurate detection result.3.The influence of fruit trees-cotton intercropping on cotton aphid-parasitoid food webThe effects of different fruit trees-cotton intercropping(jujube-cotton,apple-cotton and walnut-cotton intercropping)on the food web of cotton aphid-parasitoids were evaluated,using multiplex PCR system designed.3.1 The influence of jujube trees-cotton intercropping on cotton aphid-parasitoid food web structure.Intercropping of jujube trees and cotton significantly increased the interaction eveness of the cotton aphid-primary parasitoid food web,and significantly decreased the linkage density of primary parasitoid-hyperparasitoid food web.The result demonstrated the intercropped jujube trees could strengthen the food relationship between cotton aphids and parasitoids and weaken the control of hyperparasitoids on primary parasitoids.The jujube trees-cotton intercropping increased the parasitism on cotton aphids.3.2 The influence of apple trees-cotton intercropping on cotton aphid-parasitoid food web structure.The weighted connectance and interaction eveness of primary parasitoid-hyperparasitoid food web had a significant decrease in the intercropping cotton fields,indicated that intercropping with apple trees weaken the primary parasitoid-hyperparasitoid food relationships.3.3 The influence of walnut trees-cotton intercropping on cotton aphid-parasitoid food web sturcture.The intercropping of walnut trees and cotton significantly enhanced the vulnerability and lingkage density of primary parasitoid-hyperparasitoid food web,and the average parasitism rates significantly increased and the aphid population significantly decreased.4.The influence of fruit trees-cotton intercropping on fruit tree aphid-parasitoid food web sturcture.Since there is no aphids found in jujube tree and low parasitism level presented of apple tree aphids,only walnut aphid parasitoids were studied.The effects of walnut-cotton intercropping on the food web of walnut aphid C.juglandicola-parasitoids were evaluated,using multiplex PCR system designed.And the results showed that a simple aphid-parasitoid food web structure presented in walnut aphid-parasitoids and intercropping of walnut-cotton had no significant influence on the food web structure.In summary,the effects of fruit trees-cotton intercropping on aphid-parasitoid food web were studies,using the multiplex PCR system which established with the parasitoid species of cotton and fruit tree in Xinjiang.And the results showed,intercropping of fruit-cotton altered the structure of aphid-parasitoids food web and had an effect on the parasitism level of aphids.Furthermore,influence on aphid-parasitoid interaciton was different with different intercropping system of fruit trees-cotton.This study provided some ideas and reference to the multiple crop planting,habitat management and utilization of the natural enemy's ecological service function in the future.