Toxic and developmental effects of piperine on Aedes albopictus larvae
Objective To explore the toxic effects of piperine on Aedes albopictus larvae and to provide a scientific basis for the research and development of environmentally friendly insecticides.Methods The larvae dipping method was used to observe the effects of different concentrations of piperine(5,10,20,30 mg/L)on the growth and development of Aedes albopictus larvae.The morphology of larvae with developmental abnormalities,as well as the number of larvae that pupated,emerged and died were recorded.The pupation rate,eclosion rate and mortality rate were also calculated.The mortality rate of Aedes albopictus larvae was observed after 48 h of treatment with various concentrations of piperine(5,10,20,25,30 mg/L).Regression analysis was performed to calculate the lethal concentration of 50％(LC50)and 95％CI of piperine for fourth instar larvae.Results In the early stage of piperine treatment,the activity of Aedes albopictus larvae was normal,but the frequency of larval activity decreased after 1 h.The frequency of larval activity in the high concentration(20,30 mg/L)group was significantly lower than that in the low concentration group(5,10 mg/L).After 12 h,different numbers of larvae died in each concentration group.Some larvae moved slowly,but they could escape and surface after being stimulated by light touch with a slender glass stick.Most of the dead larvae sank to the bottom of the water,and its trunk was atrophic,stiff and partially black.Some dead larvae floated on the surface and sank after being touched.The surviving larvae treated with piperine entered pupal stage,but some of them died in pupal stage.There were two main forms of dead pupae,including naked pupae without new epidermis and pupae with pigmentation epidermis.Compared with the blank control group,the pupation rate(x2=25.185,63.602,241.359,322.105)and eclosion rate(x2=5.046,14.203,68.629)of Aedes albopictus larvae treated with piperine at different concentrations(5,10,20,30 mg/L)decreased significantly;The mortality rate increased significantly(x2=37.600,84.050,272.046,291.256);The differences were statistically significant(all P＜0.001).The LC50 of piperine for fourth instar larvae of Aedes albopictus was 10.068 mg/L,95％CI was 6.108-13.930 mg/L,and toxic regression equation as follows:y=3.301x-3.310.Conclusions Piperine was toxic to Aedes albopictus larvae by affecting pupation and eclosion.Therefore,it could be used as a potential environmentally friendly insecticide for Aedes albopictus.
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