| Background:Mosquitoes are one of the most important medical insects that not only disturb and bite people,but also can spread a variety of diseases,such as malaria,filariasis,dengue fever,Japanese encephalitis,etc.,which pose great harm to human health.Ae.albopictus is the main vector of dengue virus(DENV)in China,and also is the vector of Chikungunya virus(CHIKV)which is a new infectious disease epidemiced in China.As of 2019,according to the Global Invasive Species Database,Ae.albopictus is one of the 100 most invasive species in the world.Therefore,Ae.albopictus is a critical medical mosquito that needs to be controlled.Female mosquitoes depend primarily on olfactory cues to survival and reproduction.For example,sex pheromones can be released after mosquito emergence,then male and female mosquitoes can mate through olfactory recognition After mating,female mosquitoes need to find a suitable host to get blood,and then they need to find a suitable oviposition site to lay their eggs.Given that olfactory plays a pivotal role in different life stages,it is important to develop odor-baited traps or repellent for specific stages of specific mosquitoes using chemical ecology methods based on mosquito olfactory system to lure-and-kill or repel mosquitoes,thus reducing mosquito harassment and the occurrence of mosquito-borne infectious diseases.Different mosquito species respond differently to different mixtures of volatile compounds when they are looking for a mating partner,oviposition sites or a meal,and studies have shown that mixtures can play a synergistic role compared to a single compound.Analytically the challenge lies not only in correctly identifying these semiochemical but also in developing formulations that effectively mimic blend ratios that Ae.albopictus different life stages respond to.Objectives:This study aims at Ae.albopictus host-seeking and oviposition site selection to develop attractants.Based on the mosquito's olfactory characteristics,orthogonal experiment design is used.Furthermore,we evaluated the trap efficiency of these two attractants in the laboratory and field.We aim to provide new technologies and methods for the surveillance and control of Aedes vector and its infectious diseases.Methods:1.A 60cm ×60cm × 60mm four-arm olfactometer was used to test the attractiveness of Ae.albopictus to candidate odors;2.Orthogonal design screens the best ratio and combination of candidate odors to get Mix-5;3.Evaluate the effect of Mix-5 in Mosq-ovitraps and Electric Mosquito Killers under laboratory conditions;4.Compare the mosquito trapping efficiency of Mix-5,BG-lure and blank control according to 3x3 Latin square design under field conditions;5.Under the laboratory conditions,test the effect of oviposition-attractant and oviposition-stimulation compounds,which produced by the plant fermentation and the bacteria in the oviposition site reported by other study;6.Orthogonal design to screen the best ratio and combination of them;7.Screen some cheap alternative oviposition attractants;8.Combining attractant with Bti sustained-release block(Bti-block)to explore the strategy of "lure-and-kill";9.GC-MS explores the odor that plays the role of attracting oviposition in alternative attractant;10.Test the effect of the odor detected by GC-MS;11.Development and evaluation of artificial ovitrap suitable for container Aedes to lay eggs;Results:1.Among the 7 candidate odors tested,there were no significant differences among the five different concentrations of ammonia and four different concentrations of L-lactic acid.Hexanoic acid at 10%(F(4,45)=5.03,p=0.002),3-methyl-1-butanol at 0.1%(F(4,45)=6.52,p=0.0003),1-octen-3-ol at 10%(F(445)=9.46,p<0.0001)and 6-methyl-5-hepten-2-one at 0.1%and 0.001%(F(445)=8.06,p<0.0001)attracted significantly higher numbers of mosquitoes than the control treatment and other concentrations of the same compound.For cyclopentanone in the range of 0.01%to 10%(F(4,45)=9.15,p<0.0001),the attractiveness increased with an increase in concentration.2.A mixture of hexanoic acid at 0.1%,3-methyl-1-butanol at 1%and cyclopentanone at 1%attracted the highest number of mosquitoes.The blend termed Mix-5,which contained ammonia(1%),lactic acid(0.1%),hexanoic acid(0.1%),3-methyl-1-butanol(1%)and cyclopentanone(1%),was the most potent synthetic attractant for Ae.albopictus.3.In the laboratory,Mix-5 has a statistically significant mosquito trapping effect compared with the control in different types of traps;The average number of mosquitoes attracted by Mix-5 with Mosq-ovitraps was 2.25 times compared to the control(t(10)=3.45,p=0.006),while in Electric Mosquito Killers was 1.86 times(t(10)=6.67,p<0.0001).4.Under field conditions,the effects of Mix-5 on trapping female Ae.albopictus was statistically difference compared with control and BG-lure.5.At several concentrations we tested,there were no statistical differences between the candidate oviposition attractants and oviposition stimulating compounds with control on the effects of Ae.albopictus oviposition.Furthermore,the orthogonal design did not screen combination for significant attract Ae.albopictus oviposition.6.Among three types of fermented teas,Guangxi Liubao tea was a successfully ovipositon attractant for Ae.albopictus.In one month of soaking at 3 concentrations(0.5g/L,1.5g/L,5g/L)we tested,5g/L Liubao tea soaking for 7d(t=14.37,p<0.0001)and 14d(t=13.65,p<0.0001),attracting more eggs layed compared with the control;and 1.5 g/L Liubao tea soaking for 7d(t=7.48,p<0.0001),14d(t=6.05,p=0.004)and 28d(t=5.15,p=0.0004),attracting more eggs layed compared with the control.Except 0.5 g/L and 1.5 g/L soaking for 1d,0.5 g/L and 1.5 g/L soaking for 21d,its average oviposition activity index(OAI)was less than 0.3,while the average OAI were all greater than 0.3 at other doses in different times within 28 days.In summary,it can be speculated that the higher the concentration of Liubao tea within 5 g/L,the better the effect of attracting Ae.albopictus to lay eggs,and the attracting effect of soaking between 7d-14d was better than other days.Furthermore,we tested the effects of the lowest dose of Liubao tea 0.5g/L soaking for 28 days on the effect of Aedes aegypti to lay eggs,and we found that there was statistics significant difference on attracting Aedes aegypti to lay eggs compared to the control at 21 days(t=9.10,p=0.0008)and 28 days(t=6.33,p=0.003).The average OAI were 0.89 and 0.63,respectively.Compared with Ae.albopictus,the time of its attracting effect was significantly shifted back.7.The larval mortality of the 5%Bti and 0.5g/L tea combination sustained-release block was greater than 90%within 35 days in the laboratory,and the average OAI was greater than 0.3 at the other time points except 1d.8.One of the odor compounds that attract gravid mosquito to lay eggs in Liubao tea was cedrol;9.The concentration of cedrol attracting gravid mosquito was 1mg/L,with the average OAI was 0.382,but the effect was not as good as that of Liubao tea itself.The next step should continue to explore the effects of other ingredients in Liubao tea on the oviposition of Ae.albopictus.10.An artificial ovitrap suitable for Aedes albopictus to lay eggs and without frequent maintenance was successfully developed.The effect of 5g/L Liubao tea under field conditions showed that within about 1 month,except for the 7d day,the average OAI of other times were greater than 0.3.However,the 0.5g/L of Liubao tea powder and Bti-block,only the 7d and 35d had an average OAI greater than 0.3,with 0.45 and 0.38 respectively.Conclusion:1.Screened and developed the odor blend Mix-5,which enhancing the trapping efficiency of host-seeking Ae.albopictus;2.Screen and develop some cheap alternative oviposition attractants,and we revealed their candidate substances that attract gravid mosquito to lay eggs;3.Developed an artificial ovitrap suitable for Ae.albopictus to lay eggs and do not require frequent maintenance.In the field,we have also explored the"lure-and-kill strategy" of Ae.albopictus.The above results will provide new technologies and products for the control of dengue fever vector Ae.albopictus. |
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