| Aphis gossypii Glover is an important pest in Xinjiang’s cotton area.The prevention and control of A.gossypii hazards through chemical spraying has become an irreplaceable process to protect cotton production.However,the overdose of chemical pesticides is common in the control process of A.gossypii,leading to unsatisfactory effect of prevention.Overdosing also increases the resistance of A.gossypii against pesticides,and kills a large number of insects which are natural enemies of A.gossypii.Plant protection UAV（unmanned aerial vehicle）,which is a cost-effective measure that saves water,chemicals and labour,are applied to the control of A.gossypii fields in Xinjiang.However,little research has done on the critical period of drone control of A.gossypii.The current prevention and control of A.gossypii by UAV in Xinjiang mainly focus on finding out the critical period of UAV prevention and control of A.gossypii,reducing the number of chemical control of A.gossypii,screening out agents with strong selectivity,and increasing the safety for natural enemies.In this paper,the dynamic changes of A.gossypii population were analyzed in combination with meteorological factors.The virulence of five insecticides on A.gossypii and the safety of polydisperm were evaluated using indoor virulence measurement.Chemical agents with high virulence to target pests and beneficial to natural enemies in cotton fields were selected.The key period of UAV pesticide application and control of A.gossypii was explored via field experiments.Our study provides the rational and scientific use of pesticides for the UAV in the cotton fields of southern Xinjiang.Our findings can fully utilize the ecological control role of natural enemy insects,and reduce the frequency of chemical spraying and the quantity of chemicals in each spray.Our study has scientific and practical significance in maintaining the stability of farmland ecosystems.Based on the content of this paper,the conclusions of the study are as follows:1.Correlation analysis between A.gossypii occurrence and meteorological factorsA.gossypii began to occur in the beginning of May when the average temperature was 24.73°C and the relative humidity（RH）was 21.34%.The number of A.gossypii increased as the temperature increased.In the case of rainy weather,the aphid plant rate and the amount of hundars aphids in the cotton fields decreased in a small range,The occurrence of A.gossypii peaked on July 12（25.28°C,49.33%RH）when 93%of the plants were infested with aphids.The number of A.gossypii began to decline in mid-to-late July when environmental conditions were changing.By mid-to-late August（24.6°C,45.75%RH）,the number of aphids per hundreds plants was 1208.The occurrence of A.gossypii was greatly affected by meteorological factors because there was a significant positive correlation between the average temperature and the aphid rate and the amount of hundreds aphids.The occurrence of A.gossypii was also positively correlated to RH and negatively correlated to rainfall,but was not correlated to average wind speed.Therefore,temperature and humidity can be used to predict the dynamics of A.gossypii populations in cotton fields.2.Indoor virulence and field prevention effects of 5 types of agents on A.gossypii and H.variegateThe results from indoor toxicity tests showed a large difference in the virulence of the five agents on A.gossypii,which was afidopyropen 50 g·L-1 dispersible concentrate>acetamiprid 20%soluble liquor>flonicamid·thiamethoxam 60%water dispersible granule>flonicamid·acetamiprid 35%water dispersible granule>spirotetramat·Buprofezin 39%suspension concentrate.The relative virulence index of five agents on adult H.variegate is acetamiprid 20%soluble liquor>flonicamid·thiamethoxam 60%water dispersible granule>afidopyropen 50 g·L-1 dispersible concentrate>flonicamid·acetamiprid 35%water dispersible granule>spirotetramat·Buprofezin 39%suspension concentrate.From the perspective of toxicity selection index,the selection of virulence of five agents for A.gossypii and H.variegate is:afidopyropen 50 g·L-1dispersible concentrate>spirotetramat·Buprofezin 39%suspension concentrate>flonicamid·acetamiprid35%water dispersible granule>acetamiprid 20%soluble liquor>flonicamid·thiamethoxam 60%water dispersible granule.The toxicity of five insecticides to H.variegate was comprehensively evaluated using two indicators:safety factor and toxicity selection index（STR）.The results show that afidopyropen 50 g·L-1 DC agent had the highest virulence to A.gossypii,and the virulence to H.variegate was much less than that of A.gossypii,and its safety factor and toxicity selection index were 2.37～3.8 and 5.43,respectively,showing strong positive selectivity.The results of field experiments showed that the five agents had a good control effect on A.gossypii,and there were significant differences in the control effects between the treatments.7 days after application,the treatment of A.gossypii control effect reached the highest.Flonicamid·thiamethoxam 60%WG had the best control effect on A.gossypii,reaching 93.41%,following with afidopyropen 50 g·L-1 DC and spirotetramat·Buprofezin 39%SC agent,（91.22%and 89.43%,respectively）.3.Effects of 3 kinds of additives on different pharmacochemical propertiesAmong the three kinds of additives,ethoxy-modified polytrisiloxane（one point of transparency）had the best effect on reducing the surface tension of the liquid,and the surface tension of the liquid after adding a little permeable auxiliary was 20.21～20.35 m N·m-1,which was significantly different from that of other treatments.It is 30.43～35.25 mm2,which was significantly different from the treatment of adding two other auxiliaries and not adding additives;the shortest drying time of the liquid after adding a little permeable auxiliary was 8.5 min.Therefore,ethoxy-modified polytrisiloxane additives（a little transparent）can change the interface tension between pesticide spray droplets and plant leaf surfaces when pesticides are used,so that the agent can obtain better wetting,spreading,retention and absorption properties,thereby improving pesticide utilization,reducing application amount,reducing the waste of liquid medicine,and protecting ecology.4.Research on the key period of cotton field UAV prevention and control of A.gossypiiWith ethoxy-modified polytrisiloxane as an additive,afidopyropen 50 g·L-1 DC,flonicamid·acetamiprid 35%WG and spirotetramat·Buprofezin 39%SC were used as experimental agents to study the control effects of drone spraying in mild occurrence areas（0<II≤25）,moderate occurrence areas（25<II≤50）,severe occurrence areas（50<II≤75）and extremely severe occurrence areas（75<II≤100）.The results show that the occurrence of A.gossypii and the effect of UAV prevention and control were different.The prevention effect was mild>moderate occurrence>severe occurrence>extremely serious,and with the increase of the incidence of A.gossypii,the amount of medication also increases accordingly,but the prevention and control effects were reduced,indicating that the key period of A.gossypii prevention and control was in the mild and moderate occurrence period.It is recommended that the time of UAV application to control A.gossypii in production should be determined when A.gossypii occur mildly and moderately.This can achieve the dual goals of efficient control and cost reduction. |
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