Seed Dressing With Imidacloprid And Other Neonicotinoids Against Wheat Aphids And Control Mechanism

Wheat aphid is an important pest of winter wheat. In normal case, the main method tocontrol wheat aphids was use chemical pesticide. Neonicotinoid pesticides are widely used tocontrol wheat aphids in recent years. Imidacloprid, as the representative of neonicotinoids,coating wheat seeds against aphids showed good control effect and has less impact on thenatural enemies insects and convenient to use. The application of other neonicotinoids seedcoating to control wheat aphids were rarely reported. While there were few studies on themechanism for imidacloprid seed coating control wheat aphids for the whole growing period.Wheat seeds were treated with either imidacloprid, thiamethoxam, acetamiprid, nitenpyram orthiacloprid before sowing and the control effect and safety of seed dressing with differentpesticides against wheat aphid and the pesticide residue in wheat kernels and yield and theinfluence on natural enemies of wheat aphids were investigated in order to study thefeasibility of seed dressing with neonicotinoid insecticides against wheat aphid. In order toexplore the reason of wheat seeds treated with imidacloprid control wheat aphids for theentire developmental period. The species and the population density of wheat aphids and theamount of pesticide residue in different parts of the wheat were determined at different growthperiods after winter seed were treated with imidacloprid. The main contents are as thefollowing aspects:1.The safety of seed dressing with2.40，3.60and4.80g (a.i）/kg of either imidacloprid,thiamethoxam, acetamiprid, nitenpyram or thiacloprid before sowing was studied and with thetreatment of spraying clear water as CK. The results showed that under different treatments,all of the pesticides had no influence on the emergence rate except acetamiprid.2.Wheat seeds were treated with2.40，3.60and4.80g (a.i）/kg of either imidacloprid,thiamethoxam, acetamiprid, nitenpyram or thiacloprid before sowing and the control effectagainst wheat aphid was investigated. The results shows that seed dressing with imidacloprid,thiamethoxam and nitenpyram had good control efficacy to wheat aphids and the controlefficacy was ranked as that imidacloprid＞thiamethoxam＞nitenpyram. Seeds dressed with3.60and4.80g (a.i）/kg of either imidacloprid or thiamethoxam were effective in reducingpopulations of wheat aphids at earlier and middle stage, but in booting stage the control efficacies on wheat ears and leaves were28.03%~42.52%and64.52%~94.96%, respectively.The population density and percentage in all treated plots lower than untreated plots forRhopalosiphum padi after winter result from the number of aphids were controlled in alltreated plots.Acetamiprid and Thiacloprid have no effect on wheat aphids.3.The pesticide residue in wheat kernels and yield and the influence on natural enemies ofwheat aphids were investigated after seeds were treated with2.40，3.60and4.80g (a.i)/kg ofeither imidacloprid or thiamethoxam. There is no distinguishable difference in thousand grainweight and yield between imidacloprid either thiamethoxam treated with3.60and4.80g (a.i)/kg seeds and spray imidacloprid WP. Aphid natural enemies insects can be well protected inall plots treated with imidacloprid or thiamethoxam. The residue of imidacloprid andthiamethoxam in wheat kernels were0.023~0.039and0.029~0.046mg/kg, respectively.4. Wheat seeds were treated with2.40,3.60and4.80g (a.i)/kg of imidacloprid beforesowing and the amount of pesticide residue in different parts of the wheat were determined atdifferent growth periods. The results revealed that the content of imidacloprid in coats rapidlyreduce after the plant emergence, and then remain unchanged for some time, and thendecreased speedy until cannot detected in booting stage. The content of imidaclopriddecreased slowly through a period of accumulation in roots and leaves. The residue ofimidacloprid in wheat leaves were0.015,0.042,0.078mg/kg at booting stage. In the earingstage, the residues of imidacloprid in ears were0.01,0.017and0.016mg/kg.5.Toxicity determination of imidacloprid against Sitobion avenae and R. padi after roottreatment were studied. The LC50were10.93and4.13mg/L for S. avenae and R. padi. Whenthe content of imidacloprid was0.4mg/kg in wheat leaves, the toxicity to R. aphid S.avenaeand were55%and27.5%, respectively.