Insect Community Dynamics And Pest Control Techniques In Alfalfa Fields In Cangzhou Hebei

Cangzhou is the main production area of alfalfa in Hebei Province,the planting area has reached 168.65 square kilometers.With the expansion of planting area and the extension of planting years,the yield and quality of alfalfa had been greatly reduced due to the outbreak of pests,and the development of local alfalfa industry had seriously been restricted.Therefore,this article had investigated the insect community of alfalfa field in Cangzhou Area of Hebei Province for two years.We clarified the composition and temporal dynamics of insect community,and analyzed the diversity characteristics of insect community.At the same time,the indoor screening and field efficacy test of high-efficiency,low toxicity and biological control agents were carried out for the main pests in alfalfa field.The main contents of this article are as follows:1.Basic composition of main insects in alfalfa fieldAfter the sampling survey from 2019 to 2020,12585 arthropod samples(including 111 arachnids)were collected from alfalfa field in Xian County,Cangzhou City,belonging to 57 species,38 families and 12 orders.There were 55 species of insecta,36 families,10 orders,1 family and 1 species of Arachnida,1 family and 1 species of acari.According to the number of individuals,the largest number of Thysanoptera was 3545,accounting for 28.17%;Lepidoptera had 14 species,accounting for 24.56%;Coleoptera;from number of species,Lepidoptera,Hemiptera,Diptera,6 families,accounting for 15.79%.The dominant pest species were Helicoverpa armigera Hubner,Therioaphis trifolii Monell,Odontothrips Loti Haliday.The dominant species of natural enemies were Coccinella septempunctata,Harmonis axyridis and Propylaea japonica(Thunberg).2.Analysis of insect community index in alfalfa fieldThe insect community structure in alfalfa field was analyzed by community diversity index.From May to the end of July,the abundance of insect community in alfalfa field increased gradually,and kept at a high level from July to August,but gradually decreased until the end of August.In June and August,The diversity index was changed with abundance.In June and August,the diversity index was the highest,and the diversity index was greater than 2;in the middle of July,due to the increase of cotton boll worm number and the decrease of other species,the concentration index first increased and then decreased;from late July to early August,due to the large population size of Therioaphis trifolii Monell and Odontothrips loti Haliday,the community concentration index was higher,up to 0.2554,while the community diversity index and evenness index were relatively low;with the decrease of aphid population and the increase of insect abundance,the concentration index gradually decreased and kept at about 0.1;in mid September,with the decrease of community richness,the diversity index and evenness index were decreased.3.Population dynamics of main pests in alfalfa fieldThe occurrence regularity of three pests in alfalfa field was investigated.The Therioaphis trifolii Monell began to appear in late May,and reached the first peak in the middle and late June,which seriously damaged the yield and quality of the second crop of alfalfa.It reached the second peak in early August,but then began to reduce due to the influence of weather.There were two peaks of Odontothrips loti Haliday from June to August,the number of cotton bollworm reached the maximum,with an average of 35 cotton bollworms per 100 plants.4.Screening of different insecticides for controlling Odontothrips loti Haliday and Therioaphis trifolii MonellThe results showed that the control effect of 10%imidacloprid Wettable powder was higher than that of 8%beta cypermethrin Microemulsion.The results of field trials showed that 70%acetamiprid Water dispersible granule and 10%imidacloprid Wettable powder had higher control effect on thrips,while 0.6%ethyl spinosad Suspending agent and 10%imidacloprid Wettable powder had higher control effect on Aphis,and the difference was not significant.5.Indoor screening of different strains to Therioaphis Trifolii MonellIn this study,the toxicity of different strains to Therioaphis Trifolii Monell.In this experiment,a spore concentration of 108 spores/mL bacterial suspension was used to calculate the half-lethal time.The results showed that different strains had certain pathogenicity after 1-7 days of treatment.The results showed that the fastest pathogenicity was B094,and the half lethal time was 2.721 d.The treatment of different spore suspension concentration gradients was used when the bioassay was carried out on the 3rd day(72 h)The LD50 of strain 202 was the lowest(0.5×104 spores/mL).6.Effects of different chemical treatments on the related enzyme activities of Therioaphis Trifolii MonellThe results showed that the enzyme activities of peroxidase,superoxide dismutase,Glutathione S-transferases and Acetyl cholinesterase in 8%beta cypermethrin Microemulsion treatment were decreased and inhibited compared with the control at 12 hours,and were activated and increased at 24 hours;the enzyme activities of peroxidase,superoxide dismutase,Glutathione S-transferases and Acetyl cholinesterase in the treatment of 70%acetamiprid Water dispersible granule were increased compared with the control,and peroxidase and Acetyl cholinesterase in the treatment of 36 hours were increased compared with the control(P<0.05),the activities of peroxidase,superoxide dismutase,Glutathione S-transferases and Acetyl cholinesterase in the treatment of 0.5%matrine Water agent,0.6%ethyl spinosad Suspending agent and 70%acetamiprid Water dispersible granule increased firstly and then decreased.In this study,the Glutathione S-transferases of 10%imidacloprid Wettable powder,0.6%ethyl spinosad Suspending agent,70%acetamiprid Water dispersible granule treatment for 12 hours was significantly higher than that of the control.With the extension of time,the enzyme activity in vivo continued to increase until the enzyme activity was inhibited and decreased at 36 hours.