Risk Assessment Of Resistance To Cycloxaprid In Diaphorina Citri

Citrus Huanglongbing（HLB）is a devastating disease widely found in the world,which has caused immeasurable economic losses to the citrus industry.Diaphorina citri is not only a pest during the germination of citrus shoots,but also a vector of citrus greening disease.Its control is particularly important for the healthy development of citrus industry.The control of D.citri in the field still depends on chemical insecticides,and a single and large amount of drugs have resulted in different degrees of resistance to common insecticides.At present,it is urgent to seek new pesticides that can delay and have no obvious cross-resistance against D.citri.Cycloxaprid is a neonicotinoid pesticide independently developed in China.It is an acetylcholine receptor antagonist with unique cis-nitro structure,which makes its mechanism of action different from that of neonicotinoid pesticides represented by imidacloprid.Therefore,it can be used alternately as a rotating agent.At present,the research related to cycloxaprid focus on insect pests such as Sogatella furcifera,Nilaparvata lugens,Myzus persicae,Aphis gossypii,etc,it has not been widely used in D.citri.In order to evaluate the control potential and resistance risk of cycloxaprid against D.citri,the field resistance of D.citri to cycloxaprid and four other commonly used agents was tested in Guilin and Nanning,Guangxi.The effects of cycloxaprid sublethal concentration LC₂₀on life activities and population dynamics of D.citri at different developmental stages were investigated.The risk assessment and prediction of resistance development of D.citri to cycloxaprid were carried out,and the detoxification metabolic mechanism of D.citri to cycloxaprid was analyzed.The main results are as follows:1.The D.citri reared indoors for many years without exposure to chemicals was selected as the sensitive strain,and the sensitive baselines of the five agents were determined by leaf dipping method.Based on the sensitive baselines,the field resistance of D.citri in standardized management orchards in Guilin and Nanning of Guangxi was tested.The results showed that the field orchards under standardized management in Guilin and Nanning had different degrees of resistance to the five agents.the D.citri was sensitive to thiamethoxam and cycloxaprid,and had low,medium and high levels of resistance to imidacloprid,fenpropathrin and dinotefuran,respectively.The D.citri under standardized management in Nanning area showed low resistance to thiamethoxam and fenpropathrin,medium resistance to dinotefuran,and were sensitive to cycloxaprid and imidacloprid.2.The treatment of adult D.citri with the sublethal concentration LC₂₀significantly reduced the fecundity and hatchability of infected individuals（F₀generation）.There was no significant difference in longevity,but it was decreased compared with control.The sublethal effect continued to affect the growth of F₁population,which effectively controlled the number of pest populations.Specifically,the development rate of F₁generation was significantly delayed,and the development time of each age of the offspring generation was extended.l_xcurve showed that the survival rate and survival time of adult D.citri were significantly decreased under the treatment of sublethal concentration LC₂₀.m_xcurve showed that the propagation of D.citri was significantly inhibited after sublethal concentration treatment.In conclusion,the treatment of cycloxaprid LC₂₀inhibited the growth of the first generation population of D.citri.3.In the process of screening the resistance of cycloxaprid against D.citri,the development of resistance of D.citri to cycloxaprid showed an overall trend of increasing slowly at first and then accelerating.After 10 generations of insecticide cycloxaprid resistance screening,D.citri developed 7.40 times resistance to insecticide cycloxaprid,and the estimated realistic heritability of resistance in F₀-F₁₀generations was 0.0395.According to the actual heritability results,it was predicted that when the field control efficiency was 70%-90%,it would take 18～27 generations for the resistance to D.citri to increase by 10 times after continuous and uninterrupted use of cycloxaprid.Under the condition of intermittent or alternating use with other agents,that is,when the field control efficiency is about 20%,it takes 88 generations for the resistance to increase 10 times.The results showed that D.citri had a certain risk of resistance to cycloxaprid if they were used continuously,but the risk would be greatly reduced if they were used alternately with other agents.4.The role of detoxification metabolizing enzymes in the resistance formation of cycloxaprid in D.citri was investigated by using the enzyme inhibitors triphenyl phosphate TPP,diethyl malebutanate DEM and piperonyl butoxide PBO.The results showed that multifunctional oxidase played a major role in the resistance of D.citri to cycloxaprid,while esterase and glutathione S-transferase had no effect.Further observation on the changes of detoxification metabolic enzyme activities in D.citri during the screening process of cycloxaprid resistant strains showed that metabolic resistance of D.citri to cycloxaprid was mainly related to the increase of Car E,GSTs and P450 activities in D.citri.Moreover,the increased activity of P450 plays a major role in the formation of metabolic resistance of D.citri to cycloxaprid.