Study On The Mechanism And Control Of Cypermethrin In Culex Pipiens Pallens

Culex pipiens pallens is a harassment of major mosquito species, mainly distributed in eastern and northern in China.It is the vector of Japanese encephalitis, bancroftian filariasis and West Nile virus. The control of mosquitoes mainly depends on the chemical synthetic pesticides, which pyrethroid insecticides are widely used. many pests continue to have the resistance owing to their prevalence, and the gradual emergence of cross resistance and multiple resistance, even the emergence of united resistance.So the study with in-depth of resistance of the molecular and physiological biochemical mechanism for establishing high sensitive methods for the resistance of detecting and comprehensive prevention and control measures has important implications.This study concentrate on the following five aspects: Bioassay the level of resistance of C.p.pallens; The cloning of gene of S6 segment of domain Ⅰ, S4 to S6 segments of domain Ⅱ, the total of domain Ⅱand S6 segment of domainⅢ of para-sodium channels of C.p.pallens; Compare the enzyme activity of carboxylesterase(Car E), glutathione transferase(GSTs),O-demethylase and acetylcholinesterase(ACh E)in different ages and gender comparison of mosquitoes; And evaluate the efficacy of chlorfenapyr only and with the mixture of PBO and cypermethrin for C.p.pallens.In the bioassay of the lavae and adults, the resistance coefficients were 376.79, 22.98 and 62.73 after exposure 24 h.And they showed high levels of resistance and significant difference.Bioassay the larvae and adults of C.p.pallens.The resistance coefficient were 376.79-fold for larvae, 22.98-fold and 67.32-fold against adults by using topical application and WHO contact tube method after exposure 24 h with susceptible strains, respectively.There was significant difference and showed high resistance. The synergistic coefficient were 6.97-fold and 115.32- fold for larvae, 3.62-fold, 18.26-fold and 3.94-fold and 443.64-fold against adults by using topical application and WHO contact tube method after exposure 24 h with SS and CR strains, respectively. Synergistic effect was significant difference.And it showed that PBO has a synergistic effect obviously.The cloning of Na+ channels gene with fragments of different domains was done successful by looking up the related sequences of knockdown resistance(kdr), respectively. They contain the 333 bp in I S6 fragment, 371 bp in II S4-S6 fragment and 701 bp in IIS fragment and 666 bp in III S6 fragment. There were the differences of amino acids in II S4-S6 and in III S6 only, and no difference in I S6. Inside, the difference of amino acid in II S4-S6 has been found in early. Yet the difference of amino acid in III S6 in this experiment has not been reported. Whether it associates with resistance and how the correlation is need for further research.The dosges of protein increased along with the age, especially the highest were 13.22μg/μl and 14.17μg/μl in pupae for both SS and CR strains, respectively. The dosges of protein in two strains were no difference in larvae and pupae. Adults were different, and the CR strain was higher than that of SS strain. Furthermore, the female adults were higher than male.Testing the enzyme activity of mosquitoes. The specific activities of Car E and O-demethylase of CR in larvae were higher than that of SS strain. The specific activities of Car E, O-demethylase and GSTs of CR in pupae were also higher than that of SS strain. The specific activities of above three anzyme in female adlts were also higher than that of SS strain, and there was significance for ACh E. The specific activities of O-demethylase and GSTs also showed difference in male aduts.So the enzyme activity was difference with different ages and sexes in each strain.The sublethal doses of PBO against C.p.pallens larvae and adults were selected. They were 100 ppm against larvae dipping method, 0.2% against adults with topical application and 10% against adults WHO contact tube method, respectively.The synergistic coefficients of compound of cypermethrin and PBO 6.97 and 115.32, 3.62 and 18.26, 3.94 and 443.64 against lavae and adults of SS stain and CR strain after exposure 24 h.Chlorfenapyr was an insectide with slow acting and low toxicity, and the observation time is about 72 h in this study. No difference was showed both two strains as only. The resistance coefficient were 1.2-fold against larvae, 1.23-fold and 1.33-fold against adults by using topical application and WHO contact tube method after exposure 72 h with susceptible strains, respectively. There was no significant difference.It exhibited antagonistic effect mixing PBO for larvae and adults. And it showed chlorfenapyr was no cross resistance to cypermethrin and had good efficacy for CR strain.What′s more.Bioassay the con-toxic of cypermethrin and chlorfenapyr with mixture of cypermethrin and chlorfenapyr.The results showed that the mixture of 0.5ppm cypermethrin and 0.01 ppm and 0.02 ppm chlorfenapyr had antagonistic effects. The mixture of different insecticides or combinations of synergists were powerful alternative strategies for controlling diseases vector-borne.