| Aedes albopictus is a worldwide important vector insect,which belongs to Aedes genus,Culicidae family,Diptera order.Aedes albopictus has strong adaptability and proliferation ability,distribute widely in the world,including most areas of our country.Adult femalesof Aedes albopictus bite human,suck blood for reproduction,and transmit the pathogens of some important diseases,like Dengue fever,Zika virus disease,Chikungunya,Yellow fever and Rift valley fever,during their feeding process.In recent years,the incidence of Dengue fever increase in China,particularly serious in Guangdong province,and the affected areas has gradually expanded to the north where Dengue was used to be an uncommon infectious disease.The research of endosymbionts of Aedes albopictus is helpful for finding new technologies to prevent and control the Dengue fever.In this study,the distribution and seasonal changes of Aedes albopictus in Guangdong Province was investigated by three methods.Molecular biology technology was used to detect the Wolbachia in Aedes albopictus collected from different cities.The effects of the Wolbachia on the biological characteristics and drug resistance of Aedes albopictus were also studied.The main findings are as follows:1.Population density of Aedes albopictus from 2007 to 2017 in Guangdong provinceThe population density of Aedes albopictus was monitored twice monthly in 21 cities from 2007 to 2017 by these methods of Brett’s index method,mosquito trap ovitrap index and mosquito trap lamp method.The results showed that Aedes albopictus was distributed around in Guangdong province,and the population density in summer and fall were significantly higher than in spring and winter.The Brettu index(BI)was used to evaluate the density of larvae,a total of 9,506,102 households were surveyed,the mean BI value was 2.94,which was lower than the epidemic threshold of 5.The Mosquito Ovitrap index(MOI)used to monitor the mosquito density of adults,a total of 1,428,078 effective mosquito-eating devices were deployed,the mean MOI value was 4.98,which was lower than the epidemic threshold value of 5.Mosquito lamp method was also used to monitor the density of mosquito adults,a total of 82,019 mosquito traps were effectively deployed,the overall Aedes mosquito density was 0.21(only/light/night).The results showed that BI varied the most throughout the study period,followed by the mosquito trap lamp method.MOI has the smallest fluctuation.Then,the three methods have different sensitivities for monitoring in different environments.BI is the most sensitive in rural residential areas,and MOI and Aedes Mosquito density calculated by the mosquito trap lamp method were the highest in the parks.2.Wolbachia infection in Aedes albopictus in Guangdong ProvinceThese 936 male and 919 female were infected with Wolbachia among 3,780 Aedes albopictus samples.The infection rate of Wolbachia in total Aedes albopictus samples was 49.07 %.The infection rates of Wolbachia in female and male were 49.52%,48.62%,respectively.From 2015 to 2017,the Wolbachia infection rates in Aedes albopictus were 39.13%,48.97%,and 59.13%,respectively.The Wolbachia infection rate in Aedes albopictus in Guangdong were increased with the time,and the infection rates and trends were different among different cities.Based on these results,we speculated that the Wolbachia infection rate was affected by many factors,and it was not directly related to the fluctuation of the mosquito density.3.Evolutionary relationship of Wolbachia Strains in Aedes albopictus in Guangdong ProvinceThe Wolbachia strains isolated from Aedes albopictus in different areas and the corresponding evolutionary relationships were analyzed.The results of wsp gene sequences showed that a total of 222 sequences were divided into two evolutionary branches of two strains,namely B super group of Pip strains and A super group of AlbA strains,respectively.The dominant Wolbachia strain was B super group Pip strain,which infected in both male and female Aedes albopictus in 21 cities.The Wolbachia which belong to A super group AlbA strain,infected parts of Aedes albopictus in 7 cities,including female mosquitoes from Yunfu,Dongguan,Shantou,Chaozhou,Guangzhou,male mosquitoes from Yangjiang,and female and male mosquitoes from Zhongshan.The MLST gene combined with the sequences of wsp gene showed that the Wolbachia strains of Aedes albopictus mainly belong to the B super group,including female and male Aedes albopictus in 21 cities;a few belong to the A super group,including the Aedes albopictus from Guangzhou,Chaozhou,Jieyang and Foshan.4.Effect of Wolbachia on biological characteristics of Aedes albopictusEffect of B super group Pip strain Wolbachia on the growth and development of Aedes albopictus were studied and analyzed.The results showed that the duration of the egg-adult development of the positive population was shorter than that of the negative population.The egg-adult survival rate of the positive population was lower than that of the negative population.The female-male ratio of the positive population was lower than that of the negative population,whereas the pre-spawning period was significantly longer than the negative population.According to the analysis of the life table parameters at a specific time of the population,the life span of the negative population was longer than that of the positive population,and the average female egg production was higher than that of the positive population.The intrinsic rate of growth and the limit growth rate of the positive population were higher than that of the negative population.5.Effect of Wolbachia on pesticide resistance of Aedes albopictusPesticide resistance levels of B super group Pip strain Wolbachia positive Aedes albopictus populations and negative populations were determined.The results showed that the lethal rates of the five chemicals(beta-cypermethrin,permethrin,deltamethrin,malathion,and prochloraz)on positive populations were 97.88%,75.56%,86.67%,88.89%,and 91.11%,respectively.The lethal rates of adult mosquitoes in the negative population were 98.89%,56.67%,81.11%,87.78%,and 86.67%,respectively.Both populations were resistant to permethrin and potentially resistant to deltamethrin,malathion,and propoxur.The mortality rate of the positive population to these chemical was higher than that of the negative population,which indicated that Wolbachia positive populations were more sensitive to the above-mentioned chemical then the Wolbachia negtive populations.The median lethal concentrations(LC50)of Wolbachia positive mosquito larva of beta-cypermethrin,permethrin,deltamethrin,disulfuron,and chlorpyrifos were 0.0563 mg/L,0.0518 mg/L,0.055 mg/L,and 0.0076 mg/L,1.5487 mg/L,respectively.Compared with the susceptible population,the resistance levels of Wolbachia positive mosquitoes to the above 5 insecticides were determined as sensitive,sensitive,low-resistance,sensitive and sensitive,respectively.The results showed that Wolbachia changed the resistance level of Aedes albopictus adults and larva to common insecticides,making Aedes albopictus more sensitive against pyrethroids,carbamates,and organophosphate insecticides. |
