Selective Toxicity And Its Mechanism Of Pyraclofos Enantiomers To Locusta Migratoria Manilensis

Locusta migratoria is recognized as agricultural pestsand,there are threatened by locusts erery year.At present,persistent prevention and emergency control are the two main strategies in locust control.As the means of emergency prevention,there are many advantages and playing an irreplaceable role.Organophosphorus pesticides(OPs)is still a class of widely used pesticides,but more than 30% of them have chiral and enantiomers from one OPs often have different toxicity to the target organisms.This article will explore the enantioselective toxicity of pyraclofos on locust and analyse its mechanism.It will be a theoretical basis for developing high efficiency and low toxicity OPs.The enantiomers of pyraclofos were separated by HPLC and the median lethal dose(LD50)of each enantiomer toward third instar nymphs was calculated.The result showed that LD50 of(+)-enantiomer and(-)-enantiomer of pyraclofos were 0.323 and 22.662 μg/g respectively,after24 h exposure,display 70.16 folds difference between the enantiomers.To emploring the mechanism of the enantioselective toxicity of pyraclofos,activity in vivo and inhibition in vitro of CarEs,GSTs and AChE were detected and their relevant gene expression levels were analyzed by RT-PCR.When using α-NB and β-NA as substrate,CarEs activity of(+)-pyraclofos groups is higher than(-)-pyraclofos groups and α-NA as substrate,CarEs activities of the two groups are close to each other.In vitro,enantiomers both have significantly inhibition activity to CarEs.The CarEs inhibitary activity of(-)-pyraclofos is 6.86 and 10.27 times than(+)-pyraclofos using α-NA and β-NA as substrate.On the contrary,the CarEs inhibition activity of(+)-pyraclofos is 3.49 times than(-)-pyraclofos using α-NB as substrate.The expression levels of LmCesA5 was down-regulated in all groups and in(+)-pyraclofos group it was significantly lower than in(-)-pyraclofos group.The LmCesA4 gene has be up-regulated at low concentration of(+)-pyraclofos and(-)-pyraclof,up-regulattion occurredat high concentration of(+)-pyraclofos but down-regulation for(-)-pyraclofos.In vivo,GST activity was increased significantly by(-)-pyraclofos and decreased by(+)-pyraclofos.In vitro,IC50 of(-)-pyraclofos far more than that of(+)-pyraclofos.Analysing the expression levels of related genes from 10 GSTs,LmGSTs2,LmGSTs5,LmGSTt1,LmGSTd1 and LmGSTu1 of(-)-pyraclofos treatment group had higher expression levels than(+)-pyraclofos treatment group.In vivo AChE activity increased at the low concentrations of pyraclofos and the increasing ratio of(-)-pyraclofos was greater than(+)-pyraclofos.In vitro,the ACh E inhibitary activity of(-)-pyraclofos was 4.14 times than(+)-pyraclofos.But the(-)-pyraclofos treatment group had a higher expression level at low concentrations of Lm-ace1.In summary,both pyraclofos enantiomers were toxic to the locust,but the toxicity of(+)-pyraclofos was 70.16 times than(-)-pyraclofos.The reason for this difference may be following: LmCesA5,LmGSTs2,LmGSTs5,LmGSTt1,LmGSTd1,LmGSTu1 and Lm-ace1 have the higher expression levels in(-)-pyraclofos treatment group,and higher activity of the corresponding CarEs,GSTs and AChE.Those may be increase the capacity of hydrolyzing(-)-pyraclofos,leading to(+)-pyraclofos has higher toxicity than(-)-pyraclofos.The deeper reasons of enatioselective toxicity of pyraclofos enantiomers still need to be further explored.