大气气溶胶对北京杨树人工林生态系统生产力的影响

大气气溶胶可以影响到达地面的太阳辐射，进而影响植物光合作用和生态系统生产力，乃至区域上的碳收支。为探究北京地区气溶胶对杨树人工林生态系统生产力的影响，利用2006—2009年北京大气气溶胶数据结合北京大兴杨树人工林涡度相关系统监测的辐射、碳通量等数据，分析了气溶胶对散射辐射、光能利用效率(LUE)、生态系统初级生产力(GPP)的影响，并利用通径分析方法探究了气溶胶和生态环境因子对GPP的直接和间接影响。结果表明，北京市气溶胶光学厚度(AOD)具有明显的季节变化特征：春、夏两季大于秋、冬季，夏季气溶胶光化学厚度最大。大气气溶胶显著影响了地表辐射组分以及温度、湿度环境因子，随着AOD从0增大到3,总辐射减小了43.63%,散射辐射增加132.26%,散射辐射比例增大了2.55倍，而相对湿度增大48.52%,日温差增大3℃左右。当生态系统受水分胁迫时，气溶胶对生态系统生产力无显著影响，当生态系统处于非水分胁迫时，杨树人工林生态系统光能利用效率和生产力随着气溶胶浓度增大先增大后减小，当AOD为1.0—1.6时，GPP维持在较高的水平，当AOD>2.5时，GPP显著减小且小于背景气溶胶(A...     

冬季PM2.5的气象影响因素解析

气象因素能够显著影响PM_(2.5)浓度,可减轻或加剧城市空气污染,尤其是在雾霾严重的冬季。同时由于城市间污染物排放强度和扩散条件的差异,雾霾的发生往往具有较强的区域性。选择了石家庄、西安、北京、太原、广州5个不同污染区域的典型城市,首先分析多个气象因子与PM_(2.5)浓度的关系,进而研究气象因素对PM_(2.5)浓度变异解释度的差异,以及气象因子对PM_(2.5)浓度影响的相对重要性,进一步对比分析气象因素对PM_(2.5)浓度影响在不同污染程度的城市之间的差异,解析了不同城市的主要气象影响因素和气象因素的综合影响程度。研究结果表明:(1)气象条件与PM_(2.5)日浓度显著相关,且在不同污染程度的城市与PM_(2.5)浓度相关的气象因子不同。与石家庄冬季PM_(2.5)浓度相关的气象因素为相对湿度、平均风速;与西安PM_(2.5)浓度相关的主要气象因素为相对湿度、平均风速和最大持续风速;与北京PM_(2.5)浓度相关的主要气象因素相对湿度、日均温度、平均风速、最大持续风速和最低温;与太原PM_(2.5)浓度相关的主要气象因素为日均温、相对湿度、平均风速、最高温、最低温和最大持续风速;与广州PM_(2.5)浓度相关的主要气象因素为相对湿度、平均风速、最高温和降雨量。(2)PM_(2.5)浓度越高的地区,气象因素能够解释的PM_(2.5)浓度变异越小。严重污染区的石家庄气象因素多元回归分析的R~2为0.27,重污染区的西安气象因素多元回归分析R~2为0.29,中污染区的北京气象因素多元回归分析R~2为0.46,污染地区的太原气象因素多元回归分析R~2为0.67。研究结果揭示了不同城市的主要气象影响因素及其综合影响程度,可为城市PM_(2.5)控制和预测精度提高提供理论参考,并为区域生态环境规划和城市协调发展提供科学依据。     

阿拉伯海区域气溶胶时空动态变化及海域叶绿素a浓度特征

基于2003—2017年的MODIS/Aqua气溶胶和海洋叶绿素a浓度遥感数据资料,分析了阿拉伯海域气溶胶光学厚度(AOD)的时空动态变化及海域叶绿素a浓度(Chl-a)特征,并探讨了该海域气溶胶和海洋叶绿素a浓度的关系。结果表明:阿拉伯海区域AOD和Chl-a的空间分布都呈现出显著的季节性变化,且总体呈现出由近岸向外海逐渐降低的特征,其大小和分布受到陆源沙尘影响显著;海域AOD夏季高于春季,冬季高于秋季,15年间海域AOD整体呈现增加趋势,其中东部海域增加较明显,北部海域无显著变化;海域Chl-a秋冬季明显高于春夏季,变异性较高;由春冬季AOD与Chl-a的相关系数分析发现,二者相关性在阿拉伯海西北部区域显著性相关,且呈现出由北向南、由近海岸向外海区逐渐减弱的趋势。     

辽宁省春季土壤相对湿度特征及影响因素

以辽宁地区为研究区域,利用2004—2013年3—5月辽宁省49个气象站的土壤参数数据和常规气象要素的日值数据、2004—2010年5月辽西地区农业气象试验站土壤水分数据以及辽宁省各地区土壤参数进行统计分析,采用相关分析、回归分析、因子分析、插值分析等统计方法,研究了辽宁省播种期土壤相对湿度特征及其与土壤性质、作物种类和气象因子的关系。结果表明:辽宁省春季土壤相对湿度逐年平均增加1.6%,东南部地区的土壤相对湿度通常高于辽宁省的西北部;全省大部分地区土壤田间持水量处于20%~25%;耕种作物后土壤相对湿度降低5.6%~36.4%;在不同气象要素中,土壤相对湿度与前期土壤相对湿度的相关性最大(0.48),与水汽压的相关性最小(-0.08)。土壤自身性质、耕种作物种类和不同气象因素对土壤相对湿度均有影响。在春播期土壤湿度预报中,应充分考虑这些要素带来的影响。     

大气颗粒物污染对土地覆盖变化的响应

土地利用-覆盖变化(LUCC)直接或间接影响颗粒物污染。了解颗粒物污染对LUCC的响应,对维护和改善生态环境具有重要的意义。基于卫星遥感技术,从广域的空间尺度分析颗粒物污染对LUCC的响应。使用MODIS数据分别提取与颗粒物污染相关性较高的城市用地、林地等土地利用类型,确定土地利用类型的变化趋势,利用长时间序列MODIS气溶胶光学厚度(AOD,Aerosol optical depth)产品分析颗粒物污染与土地利用类型的变化的相关性。以山东省青岛市、淄博市、济南市3个典型城市为例,研究了AOD随土地利用类型的变化趋势。同时,考虑并分析了颗粒物污染对土地利用变化响应的敏感性,以及城市区域变化对环境的影响。研究结果表明,不同的城市类型,由于决定环境变化主导因素的差异,颗粒物污染对LUCC的响应具有明显的差异。青岛市地区,由于受海洋影响显著,大气颗粒物污染与LUCC的相关性较低,如中度污染天气与林地的相关系数为-0.451;而淄博市和济南市的相关系数分别为-0.473、-0.507。     

胶蚧属昆虫的自然分布扩散及地理起源(半翅目:胶蚧科)

在对南亚、东南亚及邻近地区胶蚧属昆虫分布资料归纳的基础上,结合近年实地调查资料,提出了胶蚧属昆虫的自然分布、扩散路线及地理起源。结果如下:胶蚧属昆虫主要分布在南亚、东南亚及邻近地区,主要包括中国、印度、巴基斯坦、孟加拉国、尼泊尔、不丹、缅甸、泰国、老挝、越南、马来西亚、印度尼西亚、菲律宾、澳大利亚等地。胶蚧属昆虫有2个分布区,即南亚分布区和东南亚分布区。国际流域恒河、印度河、布拉马普特拉河、萨尔温江-怒江、澜沧江-湄公河、元江-红河及它们的部分支流是胶蚧属昆虫扩散的通道。南亚扩散路线以印度为中心,分别向北、向西和向东3个方向扩散;东南亚扩散路线以马来西亚为中心,向北扩散。胶蚧属昆虫有2个地理起源,南亚范围以印度为中心,东南亚范围内以马来西亚为中心。胶蚧属昆虫的寄主植物是其分布扩散的先决条件,气候条件是限制分布扩散的关键因子。     

澳门城市森林生态系统白蚁群落对气象温度敏感性评估（英文）

白蚁是热带亚热带生态系统非常重要的分解者,而且对环境变化敏感。全球气候变暖直接影响到生物多样性的变化,已成为世界最为关注的环境问题。为了阐述气象温度变化对白蚁群落的影响,本文利用主成分分析和典型相关分析,对澳门南亚热带城市森林生境约1年的白蚁发生情况与气象温度因素之间的关系进行了分析。研究结果显示,澳门白蚁群落与气象因素之间多不具有相关性,但其中白蚁物种丰富度和培菌性白蚁功能群丰富度与气象温度因素之间存在典型相关性;澳门南亚热带城市森林系统中,培菌性白蚁功能群的丰度与月均气温、月均最高气温、月均最低气温、月均地下10 cm土壤温度和月均最低表层水温负相关。本研究认为培菌性白蚁丰度对于南亚热带城市森林的气象温度具有作为指示生物的潜力。     

应用遥感技术对福州上空气溶胶的研究

大气气溶胶光学厚度是影响空气质量的重要因素之一,利用MODIS遥感影像对福州市城市上空的气溶胶光学厚度进行反演,采用了6S大气辐射模式对红通道、蓝通道和2.1通道做敏感性试验,表明了福州适宜采用暗像元法反演气溶胶光学厚度.建立了利用MODIS影像对福州城市上空的气溶胶光学厚度进行遥感反演模式,并与同期福州市地面3个空气质量监测站的PM10浓度值进行比较.结果表明福州城市气溶胶光学厚度与PM10质量浓度存在着较高的相关性,城市上空气溶胶光学厚度高值区集中在市中心商业区和郊区的工业带区,低值区主要分布为较高海拔且高植被的山区,福州的地形不利于气溶胶颗粒的输出和转移.     

大气气溶胶增加对作物的影响研究进展

大气气溶胶是指悬浮在大气中的固态和液态颗粒物总称。近年来空气污染带来了一些区域大气气溶胶浓度上升明显,一定程度上对作物生长环境带来影响。国内外关于大气气溶胶增加可能对作物产生的影响表现在:(1)大气气溶胶增加会导致直接辐射减少,而散射辐射可能会有一定程度增加;散射辐射增加有利于一些作物整个冠层光合能力的提高。(2)大气气溶胶带来辐射的改变也会影响近地面小气候环境,尤其是大气昼夜温度变化,从而影响作物干物质积累;而辐射与温度的改变同时也会影响农田蒸散和最终水分利用效率。(3)大气气溶胶形成的干沉降会停留在叶片表面,减少光合有效辐射到达叶片的量,同时对作物叶片结构和功能产生直接影响。在总结国内外研究进展基础上,提出未来关于大气气溶胶增加对作物影响需要进一步明确大气气溶胶带来的作物生长环境改变对作物碳同化、积累和消耗的影响以及直接和散射辐射比例改变如何影响作物光合和蒸腾的相互关系,通过全面系统的研究大气气溶胶对作物产量形成的影响机制,提出有针对性的田间应对技术。     

气溶胶光学厚度和不透水地表覆盖度对城市热岛强度的影响——以关中地区为例

城市热岛效应（UHI）是人们最为关注的城市生态环境热点问题之一,城市热岛及其影响因子的研究对生态城市建设具有重要意义。利用城市热岛足迹（UHI FP）、局部G^*指数、Pearson相关系数以及气溶胶定量归因分析法研究了气溶胶光学厚度（AOD）和不透水地表覆盖度（ISP）对城市热岛的影响。研究结果表明：在2000-2018年间,关中地区西安及咸阳（西咸）城区的白天/夜晚城市热岛足迹均有显著增加,城市热岛效应逐年增强。西咸白天/夜晚城市热岛足迹范围比宝鸡市大,城市热岛现象更为明显。西咸城区夜晚热岛足迹范围内被地表温度（LST）高值所占据,夜晚城市热岛效应比白天更明显。宝鸡市虽然热岛足迹范围增减幅度不大,但足迹内白天/夜晚LST次热区面积逐渐增大,城市热岛效应日趋增强。西咸、宝鸡市城区的夜晚城市热岛强度（ΔT）与不透水地表覆盖度呈显著正相关关系,与城乡气溶胶光学厚度之差（ΔAOD）呈明显负相关性。西咸城乡ΔAOD为负,对城市热岛强度的平均贡献度为（0.41±0.14）℃;宝鸡市城乡ΔAOD为正,其平均贡献度为（-0.26±0.25）℃。综上所述,城市不透水地表面积的扩张会使城市热岛效应进一步加剧,西咸与宝鸡市城区气溶胶浓度的增加会抑制城市热岛的形成,但综合其他因子的影响作用,西咸与宝鸡市城市热岛强度仍在逐年增加。     

Phylogeography of Recently Emerged DENV-2 in Southern Viet Nam

Revealing the dispersal of dengue viruses (DENV) in time and space is central to understanding their epidemiology. However, the processes that shape DENV transmission patterns at the scale of local populations are not well understood, particularly the impact of such factors as human population movement and urbanization. Herein, we investigated trends in the spatial dynamics of DENV-2 transmission in the highly endemic setting of southern Viet Nam. Through a phylogeographic analysis of 168 full-length DENV-2 genome sequences obtained from hospitalized dengue cases from 10 provinces in southern Viet Nam, we reveal substantial genetic diversity in both urban and rural areas, with multiple lineages identified in individual provinces within a single season, and indicative of frequent viral migration among communities. Focusing on the recently introduced Asian I genotype, we observed particularly high rates of viral exchange between adjacent geographic areas, and between Ho Chi Minh City, the primary urban center of this region, and populations across southern Viet Nam. Within Ho Chi Minh City, patterns of DENV movement appear consistent with a gravity model of virus dispersal, with viruses traveling across a gradient of population density. Overall, our analysis suggests that Ho Chi Minh City may act as a source population for the dispersal of DENV across southern Viet Nam, and provides further evidence that urban areas of Southeast Asia play a primary role in DENV transmission. However, these data also indicate that more rural areas are also capable of maintaining virus populations and hence fueling DENV evolution over multiple seasons.     

Endemic dengue associated with the co-circulation of multiple viral lineages and localized density-dependent transmission

Dengue is one of the most important infectious diseases of humans and has spread throughout much of the tropical and subtropical world. Despite this widespread dispersal, the determinants of dengue transmission in endemic populations are not well understood, although essential for virus control. To address this issue we performed a phylogeographic analysis of 751 complete genome sequences of dengue 1 virus (DENV-1) sampled from both rural (Dong Thap) and urban (Ho Chi Minh City) populations in southern Viet Nam during the period 2003-2008. We show that DENV-1 in Viet Nam exhibits strong spatial clustering, with likely importation from Cambodia on multiple occasions. Notably, multiple lineages of DENV-1 co-circulated in Ho Chi Minh City. That these lineages emerged at approximately the same time and dispersed over similar spatial regions suggests that they are of broadly equivalent fitness. We also observed an important relationship between the density of the human host population and the dispersion rate of dengue, such that DENV-1 tends to move from urban to rural populations, and that densely populated regions within Ho Chi Minh City act as major transmission foci. Despite these fluid dynamics, the dispersion rates of DENV-1 are relatively low, particularly in Ho Chi Minh City where the virus moves less than an average of 20 km/year. These low rates suggest a major role for mosquito-mediated dispersal, such that DENV-1 does not need to move great distances to infect a new host when there are abundant susceptibles, and imply that control measures should be directed toward the most densely populated urban environments.     

Genetic differentiation of the dengue vector, Aedes aegypti (Ho Chi Minh City, Vietnam) using microsatellite markers

Dengue haemorrhagic fever emerged in the 1950s and has become a major public health concern in most Asian countries. In Vietnam, little is known about the intraspecific variation of the vector and its consequences on vectorial capacity. Here we report the use of microsatellite markers to differentiate Aedes aegypti populations in Ho Chi Minh City, a typical, overcrowded Asian city. Six microsatellite loci, with 5-14 alleles per locus, were scored in 20 mosquito samples collected in 1998 in Ho Chi Minh City. We found substantial differentiation among Ae. aegypti populations from the outskirts, whereas populations from the centre of the city showed less differentiation. These results are consistent with the hypothesis that populations of Ae. aegypti in central Ho Chi Minh City are panmictic because there are abundant larval breeding sites and an abundance of humans for adults to feed upon. In contrast, populations on the outskirts become differentiated largely through the processes of genetic drift because larval breeding sites are not as abundant. These findings implicate human activities associated with urbanization, as factors shaping the genetic structure of Ae. aegypti populations.     

Management into the Development Strategies of Urbanizing Regions in Asia: Implications of Urban Function, Form, and Role

The way urbanization unfolds over the next few decades in the developing countries of Asia will have profound implications for sustainability. One of the more important opportunities is to guide urbanization along pathways that begin to uncouple these gains in well-being from rising levels of energy use. Increasing energy use for transport, construction, climate control in houses and offices, and industrial processes is often accompanied by increasing levels of atmospheric emissions that impact human health, ecosystem functions, and the climate system. Agriculture, forestry, and animal husbandry alter carbon stocks and fluxes as carbon dioxide, methane, and black carbon. In this article we explore how carbon management could be integrated into the development strategies of cities and urbanizing regions. In particular, we explore how changes in urban form, functions, and roles might alter the timing, aggregation, spatial distribution, and composition of carbon emissions. Our emphasis is on identifying system linkages and points of leverage. The study draws primarily on emission inventories and regional development histories carried out in the regions around the cities of Manila, Jakarta, Ho Chi Minh City, New Delhi, and Chiang Mai. We find that how urban functions, such as mobility, shelter, and food, are provided has major implications for carbon emissions, and that each function is influenced by urban form and role in distinct ways. Our case studies highlight the need for major "U-turns" in urban policy.     

Geographical determinants and environmental implications of livestock production intensification in Asia

Under growing and urbanizing demand, livestock production is rapidly evolving in South, East and South-east Asia, with both an increase of production and a shift to intensive production systems. These changes infer impacts on the environment, on public health and on rural development. Environmental impacts are mainly associated with a mismanagement of animal excreta, leading to pollution of surface water, ground water and soils by nutrients, organic matter, and heavy metals. In the framework of the Livestock Environment and Development Initiative, this research aims at assessing, on a regional scale, the impacts of livestock production on nutrient fluxes. Phosphate (P(2)O(5)) mass balances were chosen as an indicator and were calculated on the basis of spatially modelled livestock densities, estimated excretion values and crop uptake. The results show a strong West--East gradient regarding the distribution of monogastrics, with clear concentration in densely populated areas and around urban centres. P(2)O(5) overloads are estimated on 23.6% of the study area's agricultural land, mainly located in eastern China, the Ganges basin and around urban centres such as Bangkok, Ho Chi Minh City and Manila. On average, livestock manure is estimated to account for 39.4% of the agricultural P(2)O(5) supply (the remaining share being supplied by chemical fertilisers). Livestock is the dominant agricultural source of P(2)O(5) around urban centres and in livestock specialised areas (southern and north-eastern China), while chemical fertilisers are dominant in crop (rice) intensive areas.     

Trends in colorectal cancer incidence in Ho Chi Minh City,Vietnam (1996–2015): Joinpoint regression and age–period–cohort analyses

BackgroundLittle is known about the trends in colorectal cancer (CRC) in Vietnam. We aimed to investigate the trends in epidemiology and anatomical subsites of CRC in Ho Chi Minh City, Vietnam.MethodsBased on the Ho Chi Minh City Cancer Registry data during 1996–2015, we calculated the average annual percent changes (AAPCs) of the age-standardized incidence rates (ASRs) by sex, age groups, and anatomical subsites, using joinpoint regressions analysis. We further performed age–period–cohort (APC) analysis using the United States National Cancer Institute’s web-based statistical tool to explore the underlying reason for the incidence trend.ResultsOver 20 years the overall ASR of CRC increased from 10.5 to 17.9 per 100,000, a 1.7-fold increase. CRC incidence elevated more rapidly in men (AAPC 4.7, 95%CI 2.2–7.3) than in women (AAPC 2.6, 95%CI 0.6–4.8). The highest and lowest increasing rates of ASRs were observed in the 50–64-year-old age group (AAPC 5.3, 95%CI 2.8–7.9) and < 50-year-old age group (AAPC 1.1, 95%CI –0.7 to 2.9), respectively. Regarding subsites, rectal cancer had the highest rate of increase (AAPC 3.3, 95%CI 1.0–5.7). Furthermore, the APC analysis indicated significant increases in CRC incidence in birth cohorts after 1975 in both genders.ConclusionsThe CRC incidence in Ho Chi Minh City increased, with the more prominent rates being among men and older populations, in rectal subsites, and in people born after 1975. The upward trend of CRC incidence in Ho Chi Minh City may be due to the adoption of a westernized lifestyle.     

Molecular epidemiology of rabies in Vietnam

The present study was done to determine the molecular epidemiology of rabies virus (RV) in Vietnam. The nucleoprotein (N) and glycoprotein (G) genes of RVs were amplified from the brains of ten rabid dogs of Ho Chi Minh City, Vietnam. The nucleotide sequences of these genes were compared with those of other Asian strains to find the possible relationship among them. Phylogenetic analysis revealed that the Asian N gene segregated into three main branches, namely South-East Asia 1 (SEA 1), South-East Asia 2 (SEA 2) and Indian subcontinent (ISC) genotypes. The SEA 1 genotype comprised RVs from Malaysia, Vietnam and Thailand. The SEA 2 genotype contained strains from the Philippines, and the ISC genotype comprised strains from Sri Lanka and India. Phylogenetically G genes of RVs from Vietnam and Thailand were clustered together. Our study suggests that Vietnamese and Thai RVs are closely related and might have originated from a common ancestor.     

Effect of dust and anthropogenic aerosols on columnar aerosol optical properties over Darjeeling (2200 m asl), eastern Himalayas, India

Background

The loading of atmospheric particulate matter (aerosol) in the eastern Himalaya is mainly regulated by the locally generated anthropogenic aerosols from the biomass burning and by the aerosols transported from the distance sources. These different types of aerosol loading not only affect the aerosol chemistry but also produce consequent signature on the radiative properties of aerosol.

Methodology/Principal Findings

An extensive study has been made to study the seasonal variations in aerosol components of fine and coarse mode aerosols and black carbon along with the simultaneous measurements of aerosol optical depth on clear sky days over Darjeeling, a high altitude station (2200 masl) at eastern Himalayas during the year 2008. We observed a heavy loading of fine mode dust component (Ca²⁺) during pre-monsoon (Apr – May) which was higher by 162% than its annual mean whereas during winter (Dec – Feb), the loading of anthropogenic aerosol components mainly from biomass burning (fine mode SO₄ ²⁻ and black carbon) were higher (76% for black carbon and 96% for fine mode SO₄ ²⁻) from their annual means. These high increases in dust aerosols during pre-monsoon and anthropogenic aerosols during winter enhanced the aerosol optical depth by 25 and 40%, respectively. We observed that for every 1% increase in anthropogenic aerosols, AOD increased by 0.55% during winter whereas for every 1% increase in dust aerosols, AOD increased by 0.46% during pre-monsoon.

Conclusion/Significance

The natural dust transport process (during pre-monsoon) plays as important a role in the radiation effects as the anthropogenic biomass burning (during winter) and their differential effects (rate of increase of the AOD with that of the aerosol concentration) are also very similar. This should be taken into account in proper modeling of the atmospheric environment over eastern Himalayas.     

Prevalence of Antibodies against Avian Influenza A (H5N1) Virus among Cullers and Poultry Workers in Ho Chi Minh City, 2005

Background

Between 2003 and 2005, highly pathogenic avian influenza A (H5N1) viruses caused large scale outbreaks in poultry in the Ho Chi Minh City area in Vietnam. We studied the prevalence of antibodies against H5N1 in poultry workers and cullers who were active in the program in Ho Chi Minh City in 2004 and 2005.

Methodology/Principal Findings

Single sera from 500 poultry workers and poultry cullers exposed to infected birds were tested for antibodies to avian influenza H5N1, using microneutralization assays and hemagglutination inhibition assay with horse blood. All sera tested negative using microneutralization tests. Three samples showed a 1∶80 titer in the hemagglutination inhibition assay.

Conclusions/Significance

This study provides additional support for the low transmissibility of clade 1 H5N1 to humans, but limited transmission to highly exposed persons cannot be excluded given the presence of low antibody titers in some individuals.     

Temporal genetic variation in Aedes aegypti populations in Ho Chi Minh City (Vietnam)

Aedes aegypti, the main vector of dengue viruses in Asia, displays variation in population density over time. The larval habitats of this species being unevenly distributed and transient (depending on cycles of drought and flood), the forces generating temporal variation in gene frequencies in populations are studied. We sampled seven mosquito populations from Ho Chi Minh City (Vietnam) and its suburbs on five occasions between April 1999 and August 2000. We investigated genetic variation by studying isoenzyme and microsatellite polymorphism and susceptibility to a dengue 2 virus strain. Ae. aegypti populations collected during the dry season (January-April) showed genetic differentiation (F(ST) = 0.016, P < 10(-6) for isoenzymes) and showed more differentiated infection rates of the dengue 2 virus. The genetic structure of the population is less marked during the rainy season (F(ST) = 0.081, P < 10(-6)). Thus, environmental factors, such as rainfall and factors related to human activity, such as breeding site density and insecticide treatment, control the genetic structure of Ae. aegypti populations in the short term. The implications of studies of this kind for the design of future control programmes are discussed.