Arthropod Community Dynamics And Major Pest Control In Alfalfa Seed Fields In Northern Ningxia Irrigation Area

Grass and livestock industry is one of the advantageous characteristic industries of Ningxia agriculture,with the vigorous development of grass and livestock industry,the planting area of forage gradually expanded,alfalfa as the "king of forage" is one of the most important forage in the development process of Ningxia grass and livestock industry.With the expansion of alfalfa planting area and the extension of planting years,pest outbreaks are becoming increasingly serious and alfalfa yield and quality are greatly reduced,resulting in serious restrictions on the development of the alfalfa industry.At the same time,alfalfa is a cross-pollinated crop and needs to be pollinated by insects.Therefore,it is especially important to choose suitable agents for pest control in alfalfa seed fields,which should not only ensure the effectiveness of pest control,but also consider the safety of pollinating insects and natural enemies.In order to clarify the occurrence and damage rules of alfalfa pests,develop sustainable control technologies for alfalfa pests,reduce yield losses caused by alfalfa pests,this study systematically investigated the arthropod species in alfalfa seed fields in Pingluo County,Ningxia,clarified the arthropod community composition and timing dynamics and analyzed the arthropod diversity characteristics,and conducted a study on the pests in alfalfa seed fields with high efficiency and low toxicity.The indoor screening and field efficacy tests of high efficiency and low toxicity insecticides and biocontrol preparations were conducted for the main pests in alfalfa seed fields,and the effects of the application on pollinators were investigated.The main results obtained were:1.The study determined the arthropod situation in the alfalfa seed fields of Pingluo County,Ningxia:There are eight orders of insects and one order of arachnids,with a total of 29 species.Among them,five species of Lepidoptera,six species of Coleoptera,five species of Diptera,six species of Hemiptera,three species of Hymenoptera,one species of Plecoptera,one species of Tasseloptera and one species of Dragonflies,and one species of Arachnida.Lepidoptera,Hymenoptera,Diptera,Hemiptera and Hymenoptera accounted for 13.04%,13.03%,21.74%,21.74%and 13.04%of the total number of families,respectively.There are more species of Coleoptera and Hemiptera,accounting for 41.39%of the total number of insects.2.The community diversity index was used to analyze the arthropod community structure of alfalfa seed fields,The arthropod community in alfalfa seed fields fluctuated significantly in all indicators over time,with a high abundance and a certain stability.From late May to early July,the abundance of arthropod communities in alfalfa seed fields gradually increased,peaked on July 4,and gradually decreased in mid-July.Diversity varied with abundance,with the highest diversity index greater than 2.5 in mid-June and early July;the community concentration index was higher in late June and late July due to the huge occurrence of Odontothrips loti,Acyrthosiphon pisum and Flies community size,and the diversity index evenness index decreased in mid-and late July as the community abundance decreased.The pollinator abundance index began to increase at the beginning of flowering in alfalfa and peaked at the peak of flowering.3.The survey clarified the occurrence pattern of four pests in alfalfa seed fields.Odontothrips loti began to occur in late May and reached its peak on July 12.Flies began to increase rapidly in mid-June,basically damaging the entire alfalfa reproductive period and causing alfalfa leaves to dry out.Acyrthosiphon pisum reproduced extremely fast and reached its peak in mid-July with an average of about 250 heads per hundred branches.Helicoverpa armigera reached its peak in July.Although the number of individuals is small,the generations overlap when they become adults and cause double damage to alfalfa.4.The indoor toxicity of Odontothrips loti and Acyrthosiphon pisum was determined by leaf dip method and the results showed that the LC50 of 0.3%Azadirachtin was relatively high at 1.093 mg·L-1 and 2.864 mg·L-1 for Odontothrips loti and Acyrthosiphon pisum,respectively.the results of field trials showed that 70%Imidacloprid and 4%Abamectin-Acetamiprid had high control effect on both Odontothrips loti and Acyrthosiphon pisum.The highest efficacy against both pests reached more than 85%.They showed good quick-acting and sustained effect,and can be used reasonably in the field according to the occurrence of pests.The two agents,70%Imidacloprid and 4%Abamectin·Acetamiprid,were more threatening to pollinators and reduced the number of individual pollinators more after application,while 0.3%Azadirachtin was less threatening to pollinators and the number of individual pollinators differed less from the clear water control plots after application and could recover a certain number of pollinators in a short period of time.The results of the above experimental study,the biological agent 0.3%Azadirachtin diluted 1000 times is recommended for the protection of pollinators in alfalfa seed fields during the flowering period,while 70%Imidacloprid diluted 1000 times and 4%Abamectin·Acetamiprid diluted 1000 times can be used alternately during the non-flowering period.