| Background:Dengue fever is an important human arbovirus disease infected by dengue virus(DNEV)and transmitted by Aedes mosquitoes,which causes a serious disease burden around the world.The prevention of dengue fever still largely depends on the control of the vector,Aedes mosquitoes.Aedes albopictus is the main vector of dengue fever in China,and Bacillus thuringiensis subspecies israelensis(Bti)is considered to be the most successful biological insecticide in the mosquito vector control for several decades.Therefore,Bti shows promise as a long-lasting larvicide for dengue fever vectors by optimizing it into a sustained-release formationObjective:Bti is suitable for the application on breeding sites and ovitraps of Ae.albopictus by optimizing it as a sustained-release tablet,which could become an effective long-lasting larvicide targeting the main dengue fever vector,Ae albopictus,in China.Methods:It was divided into two parts for Aedes control:(1)in the laboratory and(2)in the field.On one side in the laboratory,the sustained-release test,fast killing test,the long-lasting killing test of Bti-BLOCK was performed and further the influence of ultraviolet(UV),and also an important factor of Bti,on Bti-BLOCK was evaluated in the semi-field area.Furthermore,the influence on the spawning behavior of Ae.albopictus was evaluated in large cages.While on the other side in the field trials,from July 8th to December 14th,2017,which lasted 159 days.Three different urban areas were selected in the Baiyun District in Guangzhou City including one park,one neighborhood and one yard of an institution.Combined with the investigation and cleaning of Aedes breeding sites,30,20,and 20 pairs of lethal ovitraps(LOs)were arranged in the three study sites respectively.Bti-BLOCK(1 g/500 mL),Pyriproxyfen(PPF)net(10-2 mg/L),and 500mL tap water were supplemented into the test groups and 500mL tap water into the control groups,while the two groups were set 25 cm apart.The number of eggs,immature stages(larvae and pupae),adults in the LOs and the survival situations of immature stages and adults were recorded once a week.The positive ones were replaced weekly and Bti-BLOCK were renewed monthly.Positive control groups were arranged,and FourStar(?)Briquets was added into them(containing 6%Bacillus sphaericus Neide(Bs)and 1%Bti)in order compare with the test groupsResults:In the laboratory,Bti-BLOCK achieved the sustained release of Bti toxins,which could maintain in the water and reach a lethal concentration.The on-setting time of Bti-BLOCK maintained within 12 h.And the long-lasting killing effect could guarantee 95%mortality rate over two months.There was no evasion effect on spawning,but it showed an attractive effect on it to an extend.Moreover,UV could still impair the effect of Bti-BLOCK,on-setting time of whom increased to 120 h.In the field test,Bti-BLOCK applied to LOs did not impair the ability to capture eggs.In terms of killing effect,the survival rate of immature Aedes in the test group decreased significantly compared with the control groups.In terms of specificity,the percentage of LOs capturing Ae.albopictus was 99.62%.Conclusion:Bti-BLOCK had a sustained-release effect,together with a fast killing effect within 12 h and a long-lasting killing effect for two months.It could attract gravid Ae.albopictus to lay eggs.However,UV was the important factor still and Bti-BLOCK played a good effect on the immature Ae.albopictus in the LOs in the field.In short,Bti-BLOCK is suitable as a sustainable and long-lasting control measure for Ae.albopictus in China. |
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