Insecticide Resistance Monitoring And Symbionts Detection In Rhopalosiphum Padi Field Populations From Guanzhong Area Of Shaanxi Province

The bird cherry-oat aphid,Rhopalosiphum padi,is an important pest of wheat.This species distribute in all wheat-growing regions.Aside from direct feeding damage,R.padi also transmits the barley yellow dwarf virus(BYDV),which causes economically important disease of small grains and leads significantly reduced quality and yield.Multiple types of insecticides were excessively used in aphid control.However,the long-term irrational use of pesticides has resulted in different levels of resistance to pesticides of aphids.This study evaluated the resistance levels of R.padi to various insecticides in Guanzhong area of Shaanxi Province in the year 2016 and 2017.We detected the symbiotic bacteria of R.padi in the field populations,and analyzed the relationship between the symbiotic bacteria and the insecticide resistance of R.padi.1.The leaf dipping method was adopted for the toxicity bioassay of R.padi field populations.The results showed that the field population of Liquan developed high resistance to beta-cypermethrin with a resistance ratio about 40.272 fold in 2016.The R.padi field populations from Liquan,Qishan and Fuping showed low levels of resistance or sensitivity to beta-cypermethrin,imidacloprid,chlorpyrifos and isoprocarb.In 2017,Fengxiang population showed a high resistance level to beta-cypermethrin(72.495 fold);the field populations showed low-level resistance(5<RR≤10)or decreased sensitivity(3<RR≤5)to imidacloprid,chlorpyrifos,isoprocarb,deltamethrin,and avermectin.All aphid samples were sensitive to sulfoxaflor in the two years(RR<3).2.PCR technique was used to detect the symbiotic bacteria in R.padi field populations from Jingyang,Xingping,Chunhua,Fengxiang,Fufeng,Qishan,Liquan,and Yangling regions.The results showed that all R.padi individuals were infected with the primary symbiotic bacteria,Buchnera aphidicola.The infection rates of the facultative endosymbitont of S.symbiotica,Wolbachia,H.defensa and R.insecticola varied in different regions.3.The 16 s rDNA amplification sequencing showed that the relative expression of the primary symbiotic bacteria B.aphidicola in the resistant population(Fengxiang)was higher than that in the lab-sensitive strain.By using absolute quantification PCR,the results also showed that the number of plasmid copies in individuals of Fengxiang was significantlyhigher than that in individuals of susceptible strain.The results suggest that the B.aphidicola may play roles in the insecticide resistance of R.padi.