Effect Of Interplant Legumes On The Arthropod Community Structure And Dynamics In Cotton Fields

The cotton aphid,Aphis gossypii Glover(Homoptera:Aphididae),is a major pest of cotton (Gossypium hirsutum L.)in China and many other countries,especially in the seedling stage of cotton.High cotton aphid densities cause a negative impact on cotton yield and result in serious economic losses.In this study,the community structure,temporal dynamics,dominant natural enemies composition and dynamics of arthropod,increasing and decreasing tendency of cotton aphid and their predacious natural enemies were examined on cotton inter-planted legumes (Medicago sativa L.,Astragalus adsurgens Pall.,Vicia villosa Roth,and V.sativa L.)and different cotton-alfalfa intercropping systems from 2004 to 2005 at Dunhuang,western Gansu Province.The main results are summarized as the follows:1.The species numbers of arthropod community were increased in the fields of cotton inter-planted legumes.The species reached 81,76,75,72 and 68 in cotton-alfalfa,cotton-erect milk vetch,cotton-hairy vetch,cotton-fodder vetch intercropping fields and cotton field,respectively.The ratio of natural enemy and pest was enhanced in cotton inter-planted legumes,it reached 0.0734, 0.0625,0.0608,0.0531 and 0.0259 in cotton-alfalfa,cotton-hairy vetch,cotton-erect milk vetch, cotton-fodder vetch intercrop fields and cotton field,respectively.2.Evenness,abundance and diversity index of arthropod community in cotton inter-planted legumes were higher than that of in cotton field,and superiority concentricity and dominance index of arthropod community in cotton inter-planted legumes were lower than that of in cotton field.The evenness had a great influence over the diversity,and the species abundance had a slight influence over the diversity.The dominant species and groups were A.gossypii,Empoasca biguttula, Tetranychus dunhuangensis,leaf bugs,Thrips sp.,Adonia variegate,Spiders,Synharmonia conglobata,Orius minutus and lacewings.Niche width of spiders,Nobis palifer,syrphus flies,A. variegate,lacewings and A.gossypii were 0.7814-0.8563,0.6398-0.8689,0.5973-0.7642, 0.5969-0.7132,0.5531-0.6163 and 0.2428-0.3405,respectively.Individual number(N),species number(S),species abundance(R),dominance index(d),superiority concentricity(C),evenness(J) and diversity index(H)of arthropod community in cotton-alfalfa interplant field were higher than that of in cotton inter-planted other legumes. 3.Species abundance,dominance and diversity index of predacious natural enemy community in cotton-alfalfa interplant fields were higher than that of in cotton field,especially in the treatment of 120cm-wide cotton inter-planted 75cm-wide alfalfa Population niche width of O.minutus, Pardosa astrigera,A.variegate,Coccinella undecimpunctata,Misumenops tricuspidatus, Sphaerophoria scripta,Coccinella septempunctata and Erigonidium graminicola was higher within predacious natural enemy communities.Relative abundance of ladybirds,spiders,lacewings and flower bugs was 0.2059-0.3035,0.2229-0.2495,0.1524-0.1958 and 0.1199-0.1825,respectively in cotton-alfalfa interplant fields.4.Individual number of predators in cotton-alfalfa interplant fields(75cm-wide alfalfa belt every 120cm-wide cotton belt,50cm-wide alfalfa belt every 120cm-wide cotton belt,50cm-wide alfalfa belt every 2×120cm-wide cotton belt and 50cm-wide alfalfa belt every 3×120cm-wide cotton belt)were 249%,205%,164%and 135%of that in the cotton field,respectively.Population density of ladybirds,spiders and lacewings in cotton-alfalfa interplant fields showed a considerable increase over the cotton field.Population density of ladybirds,spiders and lacewings in cotton-alfalfa interplant field(75cm-wide alfalfa belt every 120cm-wide cotton belt)showed an increase of 318.0%,120.9%and 79.6%,and in cotton-alfalfa interplant field(50cm-wide alfalfa belt every 120cm-wide cotton belt)showed an increase of 204.7%,103.3%and 70.6%over the cotton field,respectively.In particular,population density of predators increased rapidly after cutting alfalfa twice on June 25 and July 25.5.Cotton aphis density in the cotton field was 554%,421%,329%and 781%of that in cotton-alfalfa interplant fields(50cm-wide alfalfa belt every 120cm-wide cotton belt,50cm-wide alfalfa belt every 2×120cm-wide cotton belt,50cm-wide alfalfa belt every 3×120cm-wide cotton belt and 75cm-wide alfalfa belt every 120cm-wide cotton belt)during the whole examined period, 542%,407%,332%and 896%after 10 days in the first cutting alfalfa(June 25),and 3 591%,1 849%,814%and 5 070%after 5 days in the second cutting alfalfa(July 25).The population density of cotton aphis was significantly controlled by predators in cotton-alfalfa interplant fields.It was very effective to force the predators from the alfalfa strips into the nearby cotton field to control cotton aphid.6.By measuring the output of ginned cotton,the output was 5461.80 kg/hm~2 in cotton-alfalfa interplant field(50cm-wide alfalfa belt every 120cm-wide cotton belt),5298.75 kg/hm~2 in cotton-alfalfa interplant field(75cm-wide alfalfa belt every 120cm-wide cotton belt),5017.95 kg/hm~2 in cotton-alfalfa interplant field(50cm-wide alfalfa belt every 2×120cm-wide cotton belt), 4853.10 kg/hm~2 in cotton field(controlled),4719.15 kg/hm~2 in cotton-alfalfa interplant field (50cm-wide alfalfa belt every 3×120cm-wide cotton belt),and 4173.15 kg/hm~2 in cotton field (no-controlled),respectively.