水稻种植区疟疾媒介环境生产力与地面植被覆盖的关系

本文选择了肯尼亚Mwea水稻种植区中Kangichiri、Kiuria和Rurumi3个村庄-农田交错地区为观察区,分析并比较了2种卫星数据对水稻种植区疟疾媒介分布的指示情况。首先运用2005年7月获取的Quickbird(分辨率0.6m)和Ikonos(分辨率4m)卫星数据在ErdasImagineV8.7中生成观察区的地面植被覆盖图;并于2005年的7月至2006的7月观察相应地区地面蚊虫消长情况。通过对观察区的卫星数据的最大似然法监测分类,并于分类后对每一田块与灌溉渠道都用Arc Info9.1进行栅格矢量化处理(每一栅格设置唯一的标识)。所有调查的蚊虫滋生点,依照水稻的生育期的不同分为6层进行分析。然后将经差分GPS定位的每一处水稻田及按蚊产卵点都叠加到该地区的卫星底层数据上,并对不同的水体、水稻生育期、调查地点的蚊虫滋生情况进行了方差分析。结果显示,由于Ikonos只有可见光和近红外光谱分辨能力,单一的Ikonos卫星数据难以区分不同样点和分层的生境,而QuickBird具有全光谱分辨能力,可区分所有的稻田生境。因此,可根据QuickBird0.6m卫星数据的土地利用和覆盖指数和阿拉伯按蚊滋生点幼虫的增殖特性,在当地建立和应用媒介综合防治系统(IVM-Integrated Vector Management)。     

苏丹瓦乌地区蚊媒密度监测及其影响因素分析

为明确任务区蚊媒种类、密度及其与环境因素的关系,笔者采用人诱法和容器指数法对苏丹瓦乌地区蚊媒的成虫和幼虫开展了密度监测。结果表明,在瓦乌维和任务区,主要蚊种为淡色库蚊、冈比亚按蚊和阿拉伯按蚊,由旱季进入雨季,蚊虫组成由单一的淡色库蚊变化为3种蚊虫共存的状态。其中阿拉伯按蚊偏好于干燥环境,而冈比亚按蚊则选择湿润环境。同时研究发现,按蚊幼虫选择弱酸性、低盐度、较清澈的积水孳生,水藻和植物有利于其孳生繁衍。库蚊则选择酸性、较浑浊的积水进行孳生。按蚊幼虫的孳生特点和成虫的活动生态特点,为开展任务区疟疾防治工作提供了基础资料和技术支持。     

微小按蚊复合体Rdna-ITS2序列差异及遗传多态性研究

本研究对我国微小按蚊广西、云南、海南 6个地理株和越南Caonguen株rDNA ITS2PCR扩增片段和序列差异作分析 ,获得基因片段总长为 5 6 1bp～ 5 6 3bp ,发现地理株间ITS2序列差异程度不同 ,分析表明元江株为微小按蚊C型 ;其余 6个地理株为A型。应用限制性内切酶Sau96Ⅰ对微小按蚊复合体rDNA ITS2PCR扩增片段作酶切分型 ,结果同样显示两型差异 ,从而简化微小按蚊复合体分类方法     

广西部分地区蚊虫种类及分布的抽样调查研究

为了解广西蚊种类及分布的动态,按中泰科技合作协议,于广西南宁市郊、龙胜县、桂平县及环江县开展了本项工作。从蚊虫孳生地采集蚊幼虫并带回实验室饲养,分别制备蚊幼虫、幼虫蜕皮、蛹皮、成蚊及雄蚊尾器标本并进行鉴定。采集到308只标本,共查见7属20种蚊虫,结果表明广西主要的能传播疾病的蚊媒如中华按蚊、嗜人按蚊、致倦库蚊、三带喙库蚊、白纹伊蚊等依然存在,提示主要蚊媒孳生条件没有消失;此外结果显示风景区内白纹伊蚊是主要的优势蚊种,如何防治白纹伊蚊的吸血骚扰是提高旅游质量的重要环节。     

基于克里金插值的白纹伊蚊空间分布研究

研究使用克里金(Kriging)模型在诱蚊诱卵器法中预测非监测点的白纹伊蚊Aedes albopictus丰度的可行性,用以识别白纹伊蚊高密度区域,为制定蚊虫防控措施提供依据.本次在约60000 m2研究区域内设置了132个诱蚊诱卵器监测点,于2020年7月28日至10月6日每周监测1次,统计诱蚊诱卵器指数和卵粒数等.通过计算增量空间自相关来评估白纹伊蚊数量是否存在空间自相关;计算局部Moran's I(Local Moran's I)用以分析是否存在具有统计意义的聚集、冷点和空间异常值的点.采用ArcGIS 10.8软件的地统计学分析扩展模块的经验贝叶斯克里金模型进行蚊密度的空间插值.本次研究共回收有效诱蚊诱卵器1308只,阳性424只,平均诱蚊诱卵器指数为32.42.每个监测点10次监测合计捕获的卵粒数增量空间自相关分析显示,全局空间自相关峰值半径(Z值最大)为62 m,Moran's I指数为0.067,Z值为2.995 (P＜0.05);局部自相关分析结果显示研究区域呈现出西南角的白纹伊蚊密度较低,其中有3个高密度的异常点;东侧蚊密度较高,其中也有数个低密度的异常点.本次研究显示克里金模型可用于诱蚊诱卵器法监测;在本次研究区域内,白纹伊蚊密度东部高于西部,通过经验贝叶斯克里金模型能有效识别白纹伊蚊高密度区域,为制定高效的防控策略提供依据.     

与大劣按蚊先天免疫相关丝氨酸蛋白酶的克隆及分析

目的克隆及分析与先天免疫相关的大劣按蚊差异基因。方法利用抑制性消减杂交 （ suppression subtractive hybridization, SSH）方法克隆大劣按蚊差异基因，并对与先天免疫相关的差异基因（文中命名为T6基因）进行生物信息学分析及半定量实验，分析约氏疟原虫感染前后其转录的变化，探讨它与按蚊抗疟原虫感染的先天免疫反应的关系。结果目前克隆的差异基因包含以下几类：①与先天免疫相关的酶类；②与能量代谢有关的酶：③与信号传递和调节有关的因子。对与先天免疫相关的分子进行的半定量实验表明，大劣按蚊T6基因的转录与感染疟原虫相关。结论本研究成功地克隆了与先天免疫相关的大劣按蚊差异基因，进一步的实验分析提示该基因可能与按蚊抗约氏疟原虫感染的黑化反应相关。     

埃及伊蚊腺苷脱氨酶相关基因的鉴定和表达分析

为了筛选和鉴定埃及伊蚊全基因组中腺苷脱氨酶相关基因,并分析其在蚊虫不同发育时期、雌蚊不同组织中的表达差异,本文运用模式昆虫黑腹果蝇Dm-ADA基因的ADA结构域序列在NCBI埃及伊蚊全基因组数据库中筛选并鉴定埃及伊蚊ADA相关基因,采用ExPASy在线相关工具包分析其理化性质和结构域,运用Signal P4.0预测信号肽,结合使用Gene Doc和Mega6.0软件包进行同源性比对和构建系统进化树构建。首先提取埃及伊蚊不同发育时期(卵、Ι~Ⅳ龄幼虫、蛹、未吸血雌蚊、雄蚊)、雌蚊不同组织(唾液腺、中肠、脂肪体和卵巢)RNA并逆转录为cDNA,利用荧光实时定量PCR(qRT-PCR)方法对埃及伊蚊不同发育时期和雌蚊不同组织表达谱进行相对定量分析。结果显示,从埃及伊蚊全基因组中获得3条具有完整开放阅读码框的ADA相关基因(Aa-ADAL、Aa-ADGF-A、Aa-ADGF-B);尽管不同物种ADA基因家族成员间相似性较低,但8个酶活性位点高度保守。Aa-ADAL在2龄幼虫期(7.88)、卵巢(8.05)高表达;Aa-ADGF-A在3龄幼虫期(7.25)高表达;Aa-ADGF-B在雌蚊唾液腺(10.07)显著高表达。经分析,2条属于ADA2/ADGF亚家族,1条属于ADAL亚家族。     

融合脑电特征的弹性网特征选择和分类

脑机接口系统的核心问题之一是信号分类。本文针对脑电信号的异构融合特征的分类问题提出了一种新方法:封装式弹性网特征选择和分类。首先,对预处理后的脑电(EEG)信号联合应用时域统计、功率谱、共空间模式和自回归模型方法提取高维异构融合特征。其次,采用封装方式进行特征选择:对训练数据采用弹性网罚逻辑回归拟合模型,通过坐标下降法估计模型参数,运用10倍交叉验证选择出最优特征子集。最后采用已训练的最优模型对测试样本进行分类。实验中采用国际BCI竞赛Ⅳ的EEG数据,结果表明,该方法适用于高维融合特征的最优特征子集选择问题,对于EEG信号的识别不仅效果好、速度快,而且能够选出与分类更相关的子集,获得相对简单的模型,平均测试正确率达到了81.78%。     

动态磁共振成像中利用时空滤波的非笛卡尔稀疏数据重建新算法

通过非笛卡尔稀疏采样,可以显著缩短磁共振成像数据采集时间,在动态磁共振中具有良好的应用前景.现有的动态图像重建算法主要利用信号在时间域上的相关性完成图像重建,对信号在空间域上的相关性探讨不足.本文提出利用时空滤波的非笛卡尔稀疏数据重建新算法,同时考虑采集信号在时间域和空间域上的相关性.对动态的磁共振数据在时间域上采用改进的Hanning滤波,以克服数据量的不足;在空间域上,引入高频增强约束以突出图像中的细节信息.仿真实验结果显示,该方法重建出时间分辨率良好、细节比较清晰的图像,实现了稀疏采集的非笛卡尔数据在k空间的重建.     

基于互信息与主成分分析的运动想象脑电特征选择算法

针对脑机接口中运动想象任务的特征选择问题,提出一种基于互信息与主成分分析的脑电特征选择算法。该算法融入类别信息,用不同运动想象类别条件下特征间的互信息矩阵之和取代传统主成分分析算法中的协方差矩阵,其特征向量表示新的主成分空间内各主成分的方向,特征值则作为评价准则判断主成分维数。对2005年国际BCI竞赛数据集,联合功率谱估计、连续小波变换、小波包分解、Hjorth参数四种方法进行特征提取,采用所提出的算法进行特征选择并与主成分分析算法对比,实验结果表明,所提出算法的降维效果更好,以支持向量机为分类器,相同维数的主成分,所得分类正确率更高。     

Characteristics of larval anopheline (Diptera: Culicidae) habitats in Western Kenya

A longitudinal survey of mosquito larval habitats was carried out in Asembo Bay, western Kenya, during the rainy season of 1998. All pools of standing water along a 700-m transect were sampled twice per week. For each habitat, eight environmental variables were recorded and a sample of anopheline larvae was collected for identification. In total, 1,751 Anopheles gambiae s.l. and 2,784 Anopheles funestus Giles were identified. Identification of An. gambiae s.l. by polymerase chain reaction (PCR) indicated that 240 (14.7%) were An. gambiae Giles and 858 (52.4%) were An. arabiensis Patton; PCR failed to identify 539 (32.9%) specimens. Repeated measures logistic regression analysis indicated that An. gambiae and An. arabiensis larvae were associated with small, temporary habitats with algae and little or no aquatic vegetation. Anopheles funestus larvae were associated with larger, semipermanent bodies of water containing aquatic vegetation and algae. Direct comparison of habitat characteristics associated with either An. gambiae or An. arabiensis revealed that algae were associated more commonly with habitats containing An. gambiae; no other differences were detected. Chi-square analysis indicated that these species were collected from the same habitat more frequently than would be expected by chance alone. Together, these results indicate that An. gambiae and An. arabiensis have similar requirements for the larval environment and that, at least in western Kenya, they do not segregate into separate habitats.     

Predators of Anopheles gambiae sensu lato (Diptera: Culicidae) larvae in wetlands, western Kenya: confirmation by polymerase chain reaction method

Polymerase chain reaction analysis was performed to determine whether mosquito predators in wetland habitats feed on Anopheles gambiae sensu lato (s.l.) larvae. Aquatic mosquito predators were collected from six wetlands near Lake Victoria in Mbita, Western Kenya. This study revealed that the whole positive rate of An. gambiae s.l. from 330 predators was 54.2%. The order of positive rate was the highest in Odonata (70.2%), followed by Hemiptera (62.8%), Amphibia (41.7%), and Coleoptera (18%). This study demonstrates that the polymerase chain reaction method can determine whether aquatic mosquito predators feed on An. gambiae s.l. larvae if the predators have undigested An. gambiae s.l. in their midgut or stomach.     

Evaluation of environmental data for identification of Anopheles (Diptera: Culicidae) aquatic larval habitats in Kisumu and Malindi, Kenya

This research evaluates the extent to which use of environmental data acquired from field and satellite surveys enhances predictions of urban mosquito counts. Mosquito larval habitats were sampled, and multispectral thermal imager (MTI) satellite data in the visible spectrum at 5-m resolution were acquired for Kisumu and Malindi, Kenya, during February and March 2001. All entomological parameters were collected from January to May 2001, June to August 2002, and June to August 2003. In a Poisson model specification, for Anopheles funestus Giles, shade was the best predictor, whereas substrate was the best predictor for Anopheles gambiae, and vegetation for Anopheles arabensis Patton. The top predictors found with a logistic regression model specification were habitat size for An. gambiae Giles, pollution for An. arabensis, and shade for An. funestus. All other coefficients for canopy, debris, habitat nature, permanency, emergent plants, algae, pollution, turbidity, organic materials, all MTI waveband frequencies, distance to the nearest house, distance to the nearest domestic animal, and all land use land cover changes were nonsignificant. MTI data at 5-m spatial resolution do not have an additional predictive value for mosquito counts when adjusted for field-based ecological data.     

Survivorship of immature stages of Anopheles gambiae s.l. (Diptera: Culicidae) in natural habitats in western Kenya highlands

We examined the survivorship of Anopheles gambiae s.l. Giles (Diptera: Culicidae) larvae and habitat productivity in three major habitat types in the western Kenya highlands. The age-specific distribution was determined for larvae and pupae, and survivorship curves were constructed. Larval-to-pupal survivorship was 6.8% in drainage ditches, 4.3% in cow hoofprints, and 1.8% in disused goldmines, respectively. High mortality rates were observed in all developmental stages. The estimated daily survival rate was highest in drainage ditches (0.74), followed by cow hoofprints (0.71), and it was lowest in disused goldmines (0.62). Productivity of emerging An. gambiae adults was generally low in these larval habitats (1.35, 1.55, and 1.84 mosquitoes per m2 per wk in drainage ditches, disused goldmines, and cow hoofprints, respectively). In total, seven families of larval mosquito predators were identified from the larval habitats, including Hydrophilidae, Dytiscidae, Corixidae, Nepidae, Notonectidae, Belostomatidae, and Cordulidae. Predator density in disused goldmines was significantly higher than that of other habitat types. Determination of the relative importance of predation, habitat stability and food contents on natural mosquito habitat productivity would help to design cost-effective vector control methods specifically targeted at the productive habitats.     

Survivorship of Anopheles gambiae sensu stricto (Diptera: Culicidae) larvae in western Kenya highland forest

The western Kenya highland has been experiencing dramatic landuse changes in the past three decades. Landuse change has been hypothesized to be one of the mechanisms for malaria epidemics in African highlands because it can alter the physical and chemical characteristics of mosquito breeding habitats. One important landuse change in western Kenya highland is deforestation. The current study examined the effects of forestation or deforestation on the survivorship of Anopheles gambiae larvae and colonization of other aquatic insects in larval habitats in Kakamega forest (elevation 1,500-1,700 m above sea level), western Kenya. We found that the survivorship of An. gambiae larvae was reduced from 55 to 57% in habitats fully exposed to sunlight (open habitats) to 1-2% in habitats with full forest canopy coverage (forest habitats) and partial canopy coverage (forest edge habitats) in two out of three trials. The average daily water temperature of the open habitats was approximately 3-3.4 degrees C higher than the forest habitats. Insect species in the orders of Diptera, Coleoptera, and Odonata colonized the larval habitats, but the three habitat types differed greatly in the animal assemblage. Canonical correspondence analysis found that water temperature and amount of leaf litter were the significant variables associated with animal assemblages. Redundancy analysis revealed that openness and the presence of predatory animals were significantly related to An. gambiae survivorship. This result suggests that deforestation facilitates the survival of the immature stage of An. gambiae in the highland.     

Oviposition site preference and egg hatchability of Anopheles gambiae: effects of land cover types

We studied the oviposition site preference and egg hatchability of Anopheles gambiae Giles with water collected from farmlands, forests, and natural wetlands. Water types significantly affected oviposition preference. Mosquitoes deposited significantly more eggs in rainwater in both the dry and wet seasons than waters from forests and wetlands, suggesting that An. gambiae prefers water with few impurities for oviposition. In the dry season, An. gambiae females also deposited significantly more eggs in waters from farmlands than those from forests and natural wetlands, but these differences were not statistically significant during the wet season. In both indoor and natural conditions, egg mortality in natural wetland habitats was significantly higher than in farmland habitats. The average water temperature in natural wetland habitats was significantly lower than farmland habitats in the natural conditions, but it remained the same under indoor experimental conditions, suggesting that factors other than water temperature play an important role in egg hatchability. Together with the findings from previous studies on the effects of land cover on larval survivorship, our results support the hypothesis that variations in habitat conditions induced by different land cover types contribute to the heterogeneous spatial distribution of An. gambiae larvae in the western Kenya highland.     

Survivorship and distribution of immature Anopheles gambiae s.l. (Diptera: Culicidae) in Banambani village, Mali

We observed the survivorship and distribution of larvae and pupae of Anopheles gambiae s.l. Giles immature stages in three habitats (rock pools, swamp, and puddles) in Banambani village. Mali, West Africa, during the mid-rainy season of 2000. Horizontal life tables were constructed for immatures in the laboratory. Times spent in the various immature stages were determined, and laboratory survival was measured. Vertical life tables were obtained from each habitat. We found large day-to-day variation for age class composition within habitats across days. The swamp samples had small but statistically significant different distributions in some instar stages compared with rock pools and puddles as affected by precipitation history. There were obviously unstable age distributions in the swamp and puddles and to some extent in rock pools. There were more individuals in some later age classes than in earlier ones. The daily survival estimates using an exponential decay model were 0.807 in rock pools, 0.899 in the swamp, 0.818 in puddles, and 0.863 in the overall village. Possible reasons for the departure from stable age distribution were cannibalism, predation and other complex interactions, rainfall effects, sampling bias, and differences in physicochemical properties of the water in the habitats.     

Relationships between occurrence of Anopheles gambiae s.l. (Diptera: Culicidae) and size and stability of larval habitats

One potentially important target of malaria vector control is the immature stages of anopheline mosquitoes. To design efficient larval control methods, mechanisms regulating mosquito productivity in natural habitats must be understood. We examined the relationships between pupal occurrence of Anopheles gambiae s.l. and size and stability of larval habitats for a period of 1 yr in western Kenya. We also examined relationships between abundance of indoor resting anophelines and habitat availability. Habitat size was measured by the total water volume (cubic meters). Habitat stability was defined as the number of occurrences when water was continuously present in a habitat for 6 d. Pupal occurrence was indicated by the number of days that pupae were observed in a habitat during the study period. We found that habitat stability and pupal occurrence were positively correlated with habitat size. When habitat size fell below approximately 1 m3, habitat stability and pupal occurrence decreased rapidly. Habitat availability was significantly correlated with the density of indoor resting mosquitoes in houses near to larval sites. These results suggest that habitat size is an important determinant of habitat stability, pupal occurrence, and adult mosquito abundance.     

Larval habitat diversity and ecology of anopheline larvae in Eritrea

Studies on the spatial distribution of anopheline mosquito larvae were conducted in 302 villages over two transmission seasons in Eritrea. Additional longitudinal studies were also conducted at eight villages over a 24-mo period to determine the seasonal variation in anopheline larval densities. Eight anopheline species were identified with Anopheles arabiensis predominating in most of the habitats. Other species collected included: An. cinereus, An. pretoriensis, An. d'thali, An. funestus, An. squamosus, An. adenensis, and An. demeilloni. An. arabiensis was found in five of the six aquatic habitats found positive for anopheline larvae during the survey. Anopheles larvae were sampled predominantly from stream edges and streambed pools, with samples from this habitat type representing 91.2% (n = 9481) of the total anopheline larval collection in the spatial distribution survey. Other important anopheline habitats included rain pools, ponds, dams, swamps, and drainage channels at communal water supply points. Anopheline larvae were abundant in habitats that were shallow, slow flowing and had clear water. The presence of vegetation, intensity of shade, and permanence of aquatic habitats were not significant determinants of larval distribution and abundance. Larval density was positively correlated with water temperature. Larval abundance increased during the wet season and decreased in the dry season but the timing of peak densities was variable among habitat types and zones. Anopheline larvae were collected all year round with the dry season larval production restricted mainly to artificial aquatic habitats such as drainage channels at communal water supply points. This study provides important information on seasonal patterns of anopheline larval production and larval habitat diversity on a countrywide scale that will be useful in guiding larval control operations in Eritrea.     

Anopheles gambiae s.l. and Anopheles funestus mosquito distributions at 30 villages along the Kenyan coast

This study investigated whether Anopheles gambiae s.l. and Anopheles funestus Giles mosquito populations were distributed randomly among houses on the coast of Kenya. Sample means and variances of mosquitoes were estimated from bimonthly pyrethrum spray collections at 30 villages from July 1997 through May 1998. In total, 5,476 An. gambiae s.l. and 3,461 An. funestus were collected. The number of An. gambiae s.l. collected was highest in November/December and lowest in May. The number of An. funestus collected was highest during September/October and lowest during May. As the density of mosquitoes decreased, there was a tendency toward randomness in the distribution. The proportion of An. gambiae s.l. and An. funestus mosquitoes collected per house for each sampling period also showed patterns of clustering, with 80% of An. gambiae s.l. collected from <30% of the houses and 80% of An. funestus collected from <20% of the total houses. The total number of mosquitoes collected from any one house ranged from 0 to 121 for An. gambiae s.l. and from 0 to 152 for An. funestus. This coupled with the results of the variance to mean ratio plots suggests extensive clustering in the distribution of An. gambiae s.l. and An. funestus mosquito populations throughout the year along the coast of Kenya.