Risk Assessment And Screening Of Control Chemicals For Spodoptera Frugiperda In Ningxia

In July 2019,the major dangerous pest Spodoptera frugiperda invaded Ningxia,posing a serious threat to agricultural production in Ningxia and its surrounding areas.Research on Spodoptera.frugiperda is urgently needed to deal with the occurrence of this pest.This paper clarified morphological characteristics,developmental duration,living habits,subcooling point and freezing point,and survival time under low temperature stress of S.frugiperda.Simultaneously,We also studied the selectivity and growth response of S.frugiperda to 7 host plants and measured the indoor activity and virulence of 12 pesticides on the eggs and larvae of S.frugiperda;Finally,the risk assessment was carried out on the occurrence of S.frugiperda in Ningxia.The main results were as follows:1.Through the research on the basic biology characteristics of S.frugiperda,the results showed that S.frugiperda larvae could be identified by the "square"-shaped black dots on the back of the eighth abdominal segment of the larvae,and the "Y"-shaped stripes on the head of the 3 instar to mature larvae’s head and the dorsal line.Under the conditions of temperature 26℃,humidity 40%RH,and photoperiod 16 L:8 D,S.frugiperda completed one generation in an average of 45 days.The study found that the young larvae have the habit of spinning and gathering hazards,the older larvae have the habit of cannibalism and overeating,and the mature larva burrow into the soil at a position of 5-8 cm to pupate.The subcooling point and freezing point of different states of S.frugiperda were determined,and the value of pupa was the lowest(subcooling point:-18.46±0.55℃ and freezing point:-13.11±0.64℃).The supercooling point and freezing point of the larvae increased as the instar age of the 3-6 instar larvae increased.Under the low temperature stress of 2℃,S.frugiperda of all the stages stopped developing,and after 32 days of low temperature stress,S.frugiperda of all the stages died.2.In order to find out the selectivity of S.frugiperda to common host plants in Northwest China and the influence of the host on its growth and development,we selected maize(Zea mays),wheat(Triticum aestivum),potato(Solanum tuberosum),alfalfa(Medicago sativa),celery(Apium grave liens),cabbage(Brassica oleracea)and quinoa(Chenopodium album)seven host species were studied.The results showed that the host preference for adult eggs was maize>wheat>cabbage,and no eggs were laid on alfalfa,potato,celery and quinoa.The 1st-3rd instar larvae preferred to feed on alfalfa,the 4th-6th instar larvae preferred to feed on maize,and none of the larvae preferred to feed on celery and potatoes.The larvae could grow and develop normally when they feed on 7 host plants.Among them,the development periods were the shortest when fed on maize,followed by alfalfa,and the growth and development were the slowest cabbage.The larvae were fed on 7 host plants,and all showed high survival rate and adult emergence rate.The values of pupa weight,pupa length,pupa width,adult wingspan and body length were the highest when the host was maize,higher values were fed by wheat,quinoa and alfalfa,but values were relatively low when the hosts were potato,cabbage and celery.3.The risk assessment of the occurrence of S.frugiperda in Ningxia mainly drew the following conclusions:S.frugiperda could not overwinter in Ningxia,and no outbreak of S.fiugiperda larvae has occurred at present,but adults of S.frugiperda would emerge from Hainan and Taiwan,Yunnan,Guangxi,Guangdong and Fujian,some areas of S.frugiperda annual breeding area migrated,and the adult F.frugiperda in Panxi,Sichuan and parts of Qianxinan Prefecture,Guizhou,migrated to Shaanxi and Shanxi via Guizhou and Sichuan.The southern part of Gansu then gradually migrated to the northern part of Gansu and Shaanxi and the southern mountainous area of Ningxia.In the southern mountainous area of Ningxia,adults generally began to be seen in the middle and early July,and were immediately detected in the central arid zone,and the latest detection in the Yellow River Irrigation Area.One generation per year may occur in Ningxia,but due to the continuous migration and invasion of Spodoptera frugiperda,Spodoptera frugiperda has a wide range of food sources in Ningxia,and the larvae might continue to damage from mid-July to late September.In september,older larvae were most likely to be damaged,while in october and november,S.frugiperda would develop slowly or even fail to grow and develop.4.12 pesticides were selected in the experiment.The oviticidal activity of the pesticides on S.frugiperda eggs was determined by dipping method,and the insecticidal activity and virulence of the pesticides on S.frugiperda larvae were determined by leaf dipping method and insect dipping method.The results of the study showed that 10 pesticides,including 2%methylaminoabamectin benzoate ME and 10%spinosad SC,could be used as ovicides for S.frugiperda.Toxicity determination of 9 pesticides with good insecticidal activity,after 48 hours,the LC50 values of the pesticides from low to high are:2%methylamino abamectin benzoate ME<10%spinosad SC<60%spinosad SC<10%tetrachlorantraniliprole SC<10%chlorfenapyr SC<1.3%matrine AS<10%cytraniliprole OD<20%chlorantraniliprole SC<4.5%efficient cypermethrin EC.Except for the higher LC50 value of 4.5%beta-cypermethrin EC,the LC50 values of the other 8 agents ranged from 0.0132-6.8986 mg/L,which were recommended as S.frugiperda insecticides.