| The diamondback moth,Plutella xylostella(L.),an important cruciferous crop pest,has developed resistance to almost all types of insecticides due to its long-term reliance on chemical pesticides for control.The development of resistance increases the difficulty and cost of control,as well as the ecological risk.Therefore,it is urgent to develop and introduce new insecticides to solve this problem.Pyridalyl is a new type of dichloropropyl ether insecticide developed by Sumitomo Chemical Co.,Ltd.,Japan.It has high efficiency,low toxicity,novel mode of action,and no cross-resistance with existing insecticides.It can effectively control lepidopteran pests,especially diamondback moth and other resistant pests.As a new insecticide,pyridalyl has been temporarily registered in China in 2007,mainly used for the control of P.xylostella.In order to fully understand the insecticidal activity of pyridalyl to P.xylostella,the lethal and sublethal effects of pyridalyl against P.xylostella were measured,and the effects of pyridalyl against different developmental stages were evaluated.This study will provide theoretical basis for field control of Plutella xylostella.The LC50 value of pyridalyl to the 2nd instar larvae of P.xylostella was 5.85 mg/L,and the LC50 value of the 3rd instar larvae was 19.49 mg/L,indicating that the younger the instar larvae were,the more susceptible they were to pyridalyl.The third instar larvae of P.xylostella were treated with LC10 and LC25 at sublethal concentrations of pyridalyl,which had certain effects on the growth and reproduction of the larvae.LC10 and LC25 treatments significantly reduced the survival rate,pupation rate and emergence rate of larvae,and decreased the pupal weight,and the higher the concentration,the greater the effect.The treatment with two sublethal concentrations significantly prolonged the larval and pupal stages.LC25 treatment significantly reduced the proportion of eclosion females and shortened the life span of female and male adults.Both LC10 and LC25 treatments reduced fecundity,but there was no significant difference compared with that of the control.There was no significant difference in the egg hatching rate between the two sublethal concentrations and the control,indicating that pyridalyl had little effect on the egg hatching rate.In addition,the net reproductive rate(R0),intrinsic growth rate(rm)and finite rate of increase(λ)of population parameters at sublethal concentrations were significantly lower than those of the control group,indicating that the sublethal concentration of pyridalyl had a certain inhibitory effect on the growth of diamondback moth population.Pyridalyl had a certain ovicidal action,and the egg hatching rates treated with the field recommended concentration and 1/10 field recommended concentration were significantly lower than that of the control.In addition,the field recommended concentration also had a certain killing effect on hatching larvae,which could significantly reduce the survival rate of larvae(7.66% vs.81.85% of the control).The emergence rate of treated pupae was significantly reduced,especially the emergence rate of pupae treated with the field recommended concentration was only 10.00%,which was significantly lower than that of control pupae(78.00%).In spite of adults contact and feeding pyridalyl,the mortalities were improved,especially the 72 h mortality of the recommended concentration treated with residual film method was 70.00%,which significantly higher than that of control(7.50%),while that of treatment with feeding method was 90.00%,which significantly higher than that of control(9.91%),These results also proved that the stomach toxicity of pyridalyl was higher than contact toxicity.In conclusion,pyridalyl had lethal and sublethal effects on diamondback moth larvae.Most of the second and third instar larvae could be killed at the field recommended concentration,and the sublethal concentration of pyridalyl could inhibit the population growth by reducing the survival rate,pupation rate and emergence rate of diamondback moth larvae.In addition,at the filed recommended concentration,pyridalyl could significantly reduce egg hatching rate,emergence rate of treated pupa and adult survival rate of P.xylostella. |
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