Prevalence and seasonality of Ascogregarina culicis (Apicomplexa: Lecudinidae) in natural populations of Aedes aegypti (Diptera: Culicidae) from temperate Argentina

Ascogregarina infections from South America were recently documented in Brazil and Argentina. The aim of this study was to report our recent findings on the prevalence and seasonality of Ascogregarina culicis in Aedes aegypti adults from temperate Argentina. Between December 2003 and May 2005, 391 females of Ae. aegypti were captured in two areas of Greater Buenos Aires. Overall prevalence of A. culicis was 21.2% (83/391), and a significant difference was observed between both areas (28.4% vs. 8%). Infected Ae. aegypti were found from November to May, with highest values in March (24-37%). Parasite prevalence and host abundance showed similar seasonal patterns. Our observations suggest a widespread infestation of A. culicis among Ae. aegypti populations from temperate Argentina.     

Effects of AeDNV infection on Aedes aegypti lifespan and reproduction

The effects of Aedes Densovirus (AeDNV) infections on survival, fertility, fecundity and vertical transmission in Aedes aegypti (Diptera: Culicidae) were measured in laboratories in Kiev, Ukraine and Colorado, USA and incorporated into a predictive model of the effects of AeDNV on vector capacity. Adult lifespan and daily survival were reduced in AeDNV infected mosquitoes. This effect was dependent on the dose of the virus. Infected females had decreased fecundity. The oviposition rate was less in infected females and the hatch rate declined in eggs laid by infected females. The amounts of AeDNV in infected females and the infection rate of their offspring were measured with real-time PCR. The average filial transmission rate was 70% and larval infection rates from infected females varied between 42 and 62%. Vertically infected larvae, and individual eggs contained 1 × 10⁵ AeDNV genome equivalents (geq). Modeling the effects of AeDNV infection on Ae. aegypti populations suggested a large decrease in the numbers of eggs, larvae, pupae, and adults arising from infected mothers and suggested that AeDNV treatment of larvae could cause up to a 76% reduction of infectious mosquito days.     

三色迷彩油添加避蚊胺对白纹伊蚊驱避效果的实验室评价

参照中华人民共和国国家标准GB/T 17322.10-1998和《军队特需药品研发勤务技术指导原则(试行)》规定的测试方法,测试了避蚊胺和水溶性二氧化钛处理迷彩油(CFP)对白纹伊蚊Aedes albopictus的驱避效果,为研发我军专用的防蚊虫迷彩油提供依据。结果表明:在3种颜色迷彩油中加入DEET后,不影响DEET的驱蚊效果;添加不同浓度DEET对蚊虫的驱避效果差异显著,20%DEET和25%DEET+迷彩油对白纹伊蚊的平均防护时间均达到或超过10 h,达到《军队特需药品研发勤务技术指导原则(试行)》规定的标准,15%DEET+迷彩油平均防护时间不足10 h,未达《军队特需药品研发勤务技术指导原则(试行)》规定的标准。研究表明:将适量DEET与迷彩油混合涂抹于皮肤可能作为演习或战时的伪装和防蚊的一种有效的综合保护措施。     

Aquatic effect duration study of Cry4 toxin with immunoassay and Aedes aegypti larval biotest

Bacillus thuringiensis subsp. israelensis (Bti) preparations are widely used for culicid larvae. There is no suitable commercially available analytical method for Cry4 toxin as active ingredient in Bti preparations. To overcome this limitation, an enzyme-linked immunosorbent assay (ELISA) was developed for quantitative determination of Cry4 toxin allowing a limit of detection (LOD) of ～2 ng ml^?1 in water. Preconcentration of aqueous samples by lyophilisation resulted in low but reproducible recoveries (25.7±6.8%), and the practical LODs for Bti preparations VECTOBAC WDG granulate and VECTOBAC 12 AS suspension were found to be ～170 ng ml^?1 and ～900 ng ml^?1, respectively. ELISA determinations indicated a rapid decay in detectable concentrations of VECTOBAC WDG applied at 400 ng ml^?1 concentration in surface water: detected concentrations decreased by 18% and 44% in 4 days in water collected from two locations, and dropped below LOD afterwards. Larval mortality of Aedes aegypti indicated a continuous decrease even thereafter. Thus, quantitative Cry4 toxin detection facilitates proper timing and frequency of treatments to achieve optimal efficacy.     

RNAi knock-downs support roles for the mucin-like (AeIMUC1) gene and short-chain dehydrogenase/reductase (SDR) gene in Aedes aegypti susceptibility to Plasmodium gallinaceum

The mosquito midgut represents the first barrier encountered by the Plasmodium parasite (Haemosporida: Plasmodiidae) when it is ingested in blood from an infected vertebrate. Previous studies identified the Aedes aegypti (L.) (Diptera: Culicidae) mucin-like (AeIMUC1) and short-chain dehydrogenase/reductase (SDR) genes as midgut-expressed candidate genes influencing susceptibility to infection by Plasmodium gallinaceum (Brumpt). We used RNA inference (RNAi) by double-stranded RNA (dsRNA) injections to examine ookinete survival to the oocyst stage following individual gene knock-downs. Double-stranded RNA gene knock-downs were performed 3 days prior to P. gallinaceum infection and oocyst development was evaluated at 7 days post-infection. Mean numbers of parasites developing to the oocyst stage were significantly reduced by 52.3% in dsAeIMUC1-injected females and by 36.5% in dsSDR-injected females compared with females injected with a dsβ-gal control. The prevalence of infection was significantly reduced in dsAeIMUC1- and dsSDR-injected females compared with females injected with dsβ-gal; these reductions resulted in a two- and three-fold increase in the number of uninfected individuals, respectively. Overall, these results suggest that both AeIMUC1 and SDR play a role in Ae. aegypti vector competence to P. gallinaceum.     

Chikungunya virus impacts the diversity of symbiotic bacteria in mosquito vector

Mosquitoes transmit numerous arboviruses including dengue and chikungunya virus (CHIKV). In recent years, mosquito species Aedes albopictus has expanded in the Indian Ocean region and was the principal vector of chikungunya outbreaks in La Reunion and neighbouring islands in 2005 and 2006. Vector‐associated bacteria have recently been found to interact with transmitted pathogens. For instance, Wolbachia modulates the replication of viruses or parasites. However, there has been no systematic evaluation of the diversity of the entire bacterial populations within mosquito individuals particularly in relation to virus invasion. Here, we investigated the effect of CHIKV infection on the whole bacterial community of Ae. albopictus. Taxonomic microarrays and quantitative PCR showed that members of Alpha‐ and Gammaproteobacteria phyla, as well as Bacteroidetes, responded to CHIKV infection. The abundance of bacteria from the Enterobacteriaceae family increased with CHIKV infection, whereas the abundance of known insect endosymbionts like Wolbachia and Blattabacterium decreased. Our results clearly link the pathogen propagation with changes in the dynamics of the bacterial community, suggesting that cooperation or competition occurs within the host, which may in turn affect the mosquito traits like vector competence.     

Tree-hole breeding mosquitoes in Israel

A survey was conducted to evaluate the number of tree-hole breeding mosquito species and their distribution in the six principal woodland types in Israel. Out of approximately 3,000 mature trees examined, only 38 contained holes that retained water for extended periods of time, and breeding mosquitoes were observed in 27 of them. Two specialized tree-hole breeders, Aedes pulchritarsis Rondani and Aedes geniculatus Oliver, were found breeding at several sites in northern Israel, always at locations 500 m above sea level (a.s.l) and with high annual precipitation. Aedes albopictus Skuse which, in Israel, is known as an opportunistic container breeder, was found in this study to have adapted remarkably well to breeding in tree holes and was found in most forest types investigated and in most tree species which had adequate tree holes. Two other species, Culiseta annulata Schrank and Culex pipiens Linnaeus instars, were found in one of the tree holes, but did not survive to reach maturity.     

Combining two teaching techniques for young children on Aedes aegypti control: effects on entomological indices in western Mexico

A study of the effect of educating four- to six-year-old children in mosquito control was recently conducted in a city in the state of Jalisco, western Mexico. Four neighborhood districts were selected. Children attending one kindergarten in each of two experimental districts were taught mosquito control with a video from the American Mosquito Control Association (AMCA), joined to the use of the AMCA Touch Table Technique. The entomological indices monitored in the study decreased significantly (P<0.05) in houses in the experimental districts, apparently because parents acted on the comments and suggestions of the children and eliminated or monitored containers used as oviposition sites by mosquitoes. Based on these results, combining both techniques for teaching children mosquito control is a potentially useful tool for control efforts in Mexico and other places in Latin America.     

Effect of dengue vector control interventions on entomological parameters in developing countries: a systematic review and meta-analysis

The aim of this review was to compare the effects of different dengue vector control interventions (i.e. biological control, chemical control, environmental management and integrated vector management) with respect to the following entomological parameters: Breteau index (BI), container index (CI), and house index (HI). We systematically searched PubMed, ISI Web of Science, Science Direct, the Dengue Bulletin of the World Health Organization and reference lists of retrieved articles on dengue vector control interventions in developing countries. We extracted data on the effectiveness of different dengue vector control interventions (defined as the relative reduction of an entomological measure caused by the intervention compared with the control or pre-intervention phase) and calculated a measure of combined relative effectiveness, with 95% confidence intervals (95% c.i.). We identified 56 publications covering 61 dengue vector control interventions. Integrated vector management was found to be the most effective method to reduce the CI, HI and BI, resulting in random combined relative effectiveness values of 0.12 (95% c.i. 0.02-0.62), 0.17 (95% c.i. 0.02-1.28) and 0.33 (95% c.i. 0.22-0.48), respectively. Environmental management showed a relatively low effectiveness of 0.71 (95% c.i. 0.55-0.90) for the BI, 0.49 (95% c.i. 0.30-0.79) for the CI and 0.43 (95% c.i. 0.31-0.59) for the HI. Biological control (relative effectiveness for the CI: 0.18) usually targeted a small number of people (median population size: 200; range 20-2500), whereas integrated vector management focused on larger populations (median: 12 450; range: 210-9 600 000). In conclusion, dengue vector control is effective in reducing vector populations, particularly when interventions use a community-based, integrated approach, which is tailored to local eco-epidemiological and sociocultural settings and combined with educational programmes to increase knowledge and understanding of best practice. New research should assess the density-dependent effectiveness of each control measure in order to estimate whether reducing vector numbers has an impact on dengue transmission when populations are at a critical threshold.     

Defence mechanisms against insecticides temephos and diflubenzuron in the mosquito Aedes caspius: the P-glycoprotein efflux pumps

P-glycoproteins (P-gps) are efflux transporters found in cells of a broad range of both procaryotic and eukaryotic taxa, whose action is to relieve the cells of multiple, structurally dissimilar, toxic compounds. The possible role of P-gps in defence against the insecticides temephos and diflubenzuron was investigated in the mosquito Aedes caspius (Pallas), also known as Ochlerotatus (Aedes) caspius (Diptera: Culicidae), and the genomic DNA sequences encoding for P-gp transporters were isolated to provide molecular instruments for future research into the expression and characterization of genes codifying for P-gps in this mosquito species. Mosquito larvae were treated with insecticides alone and in conjunction with a sublethal dose of the P-gp inhibitor verapamil. The inhibition of P-gps reduced the LD(50) values of temephos and diflubenzuron by factors of 3.5 and 16.4, respectively, suggesting the potential involvement of P-gps in insecticide defence. Using a polymerase chain reaction (PCR)-based approach, a 481-bp sequence was isolated. The inferred nucleotide sequence shows high homology with the C-terminal sequence of known P-gps. The isolation and characterization of a putative P-gp sequence from Ae. caspius is the first step towards a better molecular understanding of the role played by multidrug transporters in the defence against insecticides in this species. This knowledge may open the way to a novel control strategy based on the inhibition of pest defences. The beneficial consequences of the inhibition of efflux pumps in improving insecticide performance are discussed.