Study On The Sublethal Effects Of Imidacloprid And Flupyradifurone On Harmonia Axyridis

Chemical control is still the major mean of pests control in the integrated pest’s management strategy nowadays.However,a large number of active medicaments are still left in the environment except for killing the target pests directly in the process of application of chemical pesticides.With the passage of time and the change of environment,the chemical pesticide residues gradually decrease to sublethal concentration to affect the occurrence of insect natural population dynamics.New neonicotinoids insecticides are widely used in agricultural production due to their advantages of low toxicity and broad spectrum.The field residues of this medicament have an effect on insects in habitat and the sublethal effect is becoming more and more serious.The paper took imidacloprid（a classical form of new neonicotinoids insecticide）and flupyradifurone（one of the most recent forms）as the tested medicaments,to test the virulence of the two insecticides to the target pests Aphis craccivora and Harmonia axyridis under laboratory conditions.It also clarified the effects Harmonia axyridis’s growth,reproduction,feeding behavior and enzyme activity under duress of sublethal dose(LC₃₀)of the two insecticides.The test results will provide theoretical basis for the coordination of chemical control and biological control,meanwhile,the theoretical references will be provided to use the new medicament safely and rationally.The results are as follows:1.Relative virulence of two insecticides to Harmonia axyridis and Aphis craccivoraThe results under laboratory conditions showed that the LC₅₀ of imidacloprid and flupyradifurone on Aphis craccivora were 1.46 mg/L and 4.06 mg/L respectively,the LC50 on the2nd larvae of H.axyridis was 4.04 mg/L and 12.48 mg/L respectively.Combined with safety factor and benefit ratio,both the two insecticides have higher risks to the 2nd larvae of H.axyridis,and the virulence of imidacloprid to H.axyridis is higher than that of flupyradifurone.The LC₃₀of the two insecticides to the 2nd larvae of H.axyridis were 2.61 mg/L and 7.6 mg/L respectively.2.Effects of two sublethal doses of insecticides on growth and reproduction of Harmonia axyridisThe 2nd larvae of H.axyridis which were treated by imidacloprid and flupyradifurone LC₃₀could significantly decrease the survival rate of the 3rd larvae and the total immature stage（from the 3rd larvae stage to the pupa stage）.The development period of the above two instar stage would be extended,which could obviously inhibit the growth and development of H.axyridis.The investigation to the reproduction of female H.axyridis with 14 d have found that the amount of diurnal oviposition of H.axyridis of the two insecticide groups were all significantly lower than that in the control groups.There was no significant variation between the two treatment groups and the control groups at the later investigating stage（8-14 d）,the total amount of single and female accumulated spawning and the daily average oviposition of the two treatment groups all decreased obviously within 14 d.3.Effects of sublethal doses of insecticides on feeding capacity of Harmonia axyridisThe 2nd larvae of H.axyridis which were treated by imidacloprid and flupyradifurone LC₃₀could significantly reduce the intake of the 3rd and 4th instar larvae of H.axyridis,but HollingⅡwas still the reaction model of feeding function for the above ages.The maximum theoretical predation of the 3rd larvae were 33.22 heads/d and 35.46 heads/d in imidacloprid and flupyradifurone treatment groups respectively,which were significantly lower than that in control group（67.56 heads/d,）;the maximum theoretical predation of the 4th larvae were 196.08 heads/d and 192.31 heads/d respectively,lower than that of control group 217.39 heads/d.The 2nd larvae of H.axyridis which were treated by LC₃₀ of the two insecticides,the predation of the current generation the H.axyridis decreased slightly,but there was no significant variation compared with the control group,HollingⅡis their reaction model.4.Effects of sublethal doses of insecticides on enzyme activity in the larvae of Harmonia axyridisThe 24 h and 48 h of the 2nd larvae of H.axyridis which were treated by imidacloprid and flupyradifurone LC₃₀to test the activity of acetylcholinesterase Ach E glutathione-S-transferase GSTs,carboxylesterase and multifunctional oxidase MFO in the 2nd larvae of H.axyridis.These enzymes were all induced or inhibited at different levels.The detailed manifestations are as follows:All four enzymes were induced to varying degrees in the imidacloprid treatment group,among them,acetylcholinesterase only showed early induction,carboxylesterase showed induction first and then inhibition,multifunctional oxidase showed continuous induction,while glutathione-S-transferase showed inhibition first and then induction.Acetylcholinesterase and multifunctional oxidase in H.axyridis of flupyradifurone treatment group showed continuous inhibition,carboxylesterase showed continuous induction,while glutathione-S-transferase activity changed significantly during treatment time.It’s obviously to see from the above results that the use of imidacloprid and flupyradifurone LC₃₀ to treat the 2nd larvae of H.axyridis will have adverse effects on the growth,development,reproduction and feeding behavior of H.axyridis,which will affect the natural population of H.axyridis to exploit its potentials for biological control,and is not conducive to the coordinated application of chemical control and biological control.Therefore,the role of virulence of the two insecticides should be taken into consideration in the integrated control to the pests.