bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2021‒08‒22
eighteen papers selected by
Richard Halfpenny
Staffordshire University

  1. PLoS Negl Trop Dis. 2021 Aug 20. 15(8): e0009438
      BACKGROUND: Aedes (Stegomyia) albopictus (Skuse) impacts human outdoor activity because of its aggressive biting behavior, and as a major vector of mosquito-borne diseases, it is also of public health importance. Although most mosquito species exhibit crepuscular activity by primarily host seeking at dawn and dusk, Ae. albopictus has been traditionally characterized as a diurnal or day-biting mosquito. With the global expansion and increased involvement of Ae. albopictus in mosquito-borne diseases, it is imperative to elucidate the diel activity of this species, particularly in newly invaded areas.METHODOLOGY AND PRINCIPAL FINDINGS: Human sweep netting and carbon dioxide-baited rotator traps were used to evaluate the diel activity of Ae. albopictus in two study sites. Both trapping methods were used in New Jersey's Mercer County, USA (temperate/urban), while only human sweep netting was used in Florida's Volusia County, USA (subtropical/suburban). Human sweep netting was performed to determine adult mosquito activity at Sunrise, Solar Noon, Sunset, and Lunar Midnight. Because New Jersey is in a temperate area, diel activity was investigated during the early season (3-19 July), peak season (25 July-19 September), and late season (22 September- 22 October). Aedes albopictus showed the highest activity during peak and late seasons at Solar Noon (P < 0.05). At Sunrise and Sunset during the peak season, Ae. albopictus activity was similar. Lunar Midnight activity was significantly lower than Sunrise and Solar Noon (P < 0.05) but was similar to that of Sunset. In the late season, the highest activity was observed during Solar Noon while the least activity was observed during Sunrise and Lunar Midnight (P<0.05). Bottle rotator traps used in conjunction with the human sweep net technique exhibited similar results. Seasonal activity was not differentiated in Florida due to the consistent subtropical climate. The highest adult activity was observed at Sunrise using human sweep netting, but it was not significantly different from Solar Noon and Sunset. The lowest adult activity was observed at Lunar Midnight; however, it was not significantly different from Solar Noon and Sunset. These results provide evidence that the diel activity of Ae. albopictus, contrary to the common perception of its diurnal activity, is much more varied.
    CONCLUSION/SIGNIFICANCE: Involvement of Ae. albopictus in the transmission of debilitating mosquito-borne pathogens such as chikungunya, dengue, and Zika virus, coupled with its affinity to thrive in human peridomestic environments, substantiates that our findings have global implications in areas where Ae. albopictus populations established. It also highlights the importance of behavioral studies of vector species which will not only help mosquito control professionals plan the timing of their control efforts but also provides empirical evidence against conventional wisdoms that may unjustly persist within public health stewards.
  2. Parasit Vectors. 2021 Aug 18. 14(1): 413
      BACKGROUND: Dengue is a significant public health issue that is caused by Aedes spp. mosquitoes. The current vector control methods are unable to effectively reduce Aedes populations and thus fail to decrease dengue transmission. Hence, there is an urgent need for new tools and strategies to reduce dengue transmission in a wide range of settings. In this study, the Mosquito Home System (MHS) and Mosquito Home Aqua (MHAQ) formulations were assessed as commercial autodissemination traps in laboratory and small-scale field trials.METHOD: Multiple series of laboratory and small-scale field trials were performed to assess the efficacy of MHS and MHAQ exposed to Ae. aegypti. In the laboratory trials, various parameters such as fecundity, fertility, wing size, oviposition preferences, residual effects, and MHAQ transference to other containers through controlled experiments were tested. For small-scale field trials, the efficacy of the MHS and MHAQ approaches was determined to ascertain whether wild mosquitoes could transfer the MHAQ formulation from MHS stations to ovitraps.
    RESULTS: The data revealed that Ae. aegypti was highly susceptible to low concentrations of MHAQ formulations and had a residual effect of up to 3 months, with MHAQ exposure affecting fecundity, fertility, and mosquito wing size. In the oviposition studies, gravid females strongly preferred the hay infusion compared to tap water and MHAQ during egg-laying in the laboratory. Nevertheless, the use of commercial MHAQ by MHS was highly attractive in field settings compared to conventional ovitraps among local Aedes spp. mosquitoes. In addition, MHAQ horizontal transfer activities in the laboratory and small-scale field trials were demonstrated through larval bioassays. These findings demonstrated the potential of MHAQ to be transferred to new containers in each study site.
    CONCLUSION: This study provided proof of principle for the autodissemination of MHAQ. Through further refinement, this technique and device could become an effective oviposition trap and offer an alternative preventive tool for vector control management.
    Keywords:  Autodissemination; Horizontal transfer; Inhibition emergences; Insect growth regulators; Vector control management
  3. J Am Mosq Control Assoc. 2021 Sep 01. 37(3): 169-171
      Ovitraps were set inside and outside of 15 households in December 2012 (dry season) and August 2013 (rainy season) in 2 communes (An Thanh and Phu Hoa) of Binh Duong Province in southern Vietnam. Eggs laid in the ovitraps were collected after 4 days, dried, and soaked in water. Hatched larvae were transferred to cups and reared to adulthood to identify the species. The rate of positive ovitraps did not differ between December and August for Aedes aegypti, but it was lower in December for Ae. albopictus. The number of eggs laid per ovitrap by Ae. aegypti did not differ between December and August, while that for Ae. albopictus decreased significantly in December in both communes. Moreover, Ae. albopictus laid eggs in ovitraps placed outside the households. Therefore, it is necessary for future studies to investigate whether the major source containers for oviposition had dried in the dry season or Ae. albopictus entered diapause, leading to these observations.
    Keywords:   Aedes aegypti ; Aedes albopictus ; Vietnam; ovitrap
  4. Parasit Vectors. 2021 Aug 16. 14(1): 405
      BACKGROUND: The exotic invasive tiger mosquito, Aedes albopictus, appeared in southern Switzerland in 2003. The spread of the mosquito has been surveyed constantly since then, and an integrated vector management (IVM) has been implemented to control its numbers. The control measures focus on the aquatic phase of the mosquito with removal of breeding sites and applications of larvicides in public areas whereas private areas are reached through extensive public information campaigns. Here, we evaluated the efficacy of the IVM.METHODS: Since all the municipalities with Ae. albopictus in southern Switzerland are currently implementing the IVM, Italian municipalities just across the Swiss-Italian border, where Ae. albopictus is present but no coordinated intervention programme is in place, served as control. Ovitraps and adult female traps were used to measure mosquito abundance in 2019. Generalised mixed-effects models were used to model the numbers of Ae. albopictus eggs and adult females collected. These numbers of Ae. albopictus eggs were compared to the numbers of eggs collected in 2012 and 2013 in a previous assessment of the IVM, using a hurdle model.
    RESULTS: Mean numbers of Ae. albopictus eggs and adult females in 2019 were consistently higher in the municipalities not following an IVM programme. In these municipalities, there were about four times (3.8) more eggs than in the municipalities implementing an IVM programme. Also, the numbers of eggs and adult females increased steadily from the beginning of the Ae. albopictus reproductive season, reaching a peak in August. In contrast, the increase in numbers of Ae. albopictus was much more contained in the municipalities implementing an IVM programme, without reaching an evident peak. Comparison with data from 2012 and 2013 indicates that the gap between intervention and non-intervention areas may have almost doubled in the past 6 years.
    CONCLUSIONS: The results of the survey strongly support the efficacy of the IVM programme implemented in southern Switzerland compared to municipalities without defined control measures. With the constant implementation of an IVM, it appears possible to contain the numbers of Ae. albopictus at a manageable level, reducing the nuisance for the human population and the risk of arbovirus epidemics.
    Keywords:  Aedes albopictus; Control measures; Gravid Aedes trap; Integrated vector management; Ovitrap; Surveillance
  5. J Travel Med. 2021 Aug 18. pii: taab130. [Epub ahead of print]
      BACKGROUND: In August 2020, in the context of COVID-19 pandemics, an autochthonous dengue outbreak was identified for the first time in Italy.METHODS: Following the reporting of the index case of autochthonous dengue, epidemiological investigation, vector control, and substances of human origin safety measures were immediately activated, according to the national arbovirus surveillance plan. Dengue cases were followed-up with weekly visits and laboratory tests until recovery and clearance of viral RNA from blood.
    RESULTS: The primary dengue case was identified in a young woman, who developed fever after returning from Indonesia to northern Italy, on July 27, 2020. She spent the mandatory quarantine for COVID-19 at home with relatives, six of whom developed dengue within two weeks. Epidemiological investigation identified further five autochthonous dengue cases among people who lived or stayed near the residence of the primary case. The last case of the outbreak developed fever on September 29, 2020. Dengue cases had a mild febrile illness, except one with persistent asthenia and myalgia. DENV-1 RNA was detected in blood and/or urine in all autochthonous cases, up to 35 days after fever onset. All cases developed IgM and IgG antibodies which cross-reacted with West Nile virus (WNV) and other flaviviruses. Sequencing of the full viral genome from blood samples showed over 99% nucleotide identity with DENV-1 strains isolated in China in 2014-2015; phylogenetic analysis classified the virus within Genotype I. Entomological site inspection identified a high density of A. albopictus mosquitoes, which conceivably sustained local DENV-1 transmission. Aedes koreicus mosquitoes were also collected in the site.
    CONCLUSIONS: Areas in Europe with high density of Aedes mosquitoes should be considered at risk for dengue transmission. The presence of endemic flaviviruses, like WNV, might pose problems in the laboratory diagnosis.
    Keywords:  A. albopictus; Aedes koreicus; DENV; follow-up; saliva; surveillance; urine
  6. Rev Inst Med Trop Sao Paulo. 2021 ;pii: S0036-46652021000100235. [Epub ahead of print]63 e64
      Infections caused by arboviruses that have mostly impacted the Brazilian morbidity and mortality are caused by the same vector, Aedes aegypti. Preventive actions related to the vector are the most effective strategies in the prevention and control of these diseases. This study aimed to associate the knowledge on the vector that transmits dengue, Zika and chikungunya with the sociodemographic and behavioral preventive practices towards Aedes aegypti in the municipality of Tangara da Serra, Mato Grosso State, in the Brazilian Legal Amazon. A probabilistic urban population sampling was obtained by clusters: census sectors and households. The sample size calculation considered 10% of loss and a 1.5 design effect. This is a cross-sectional research carried out through a household survey in February and March 2018. There were 583 participants. The study variables were knowledge on the vector, sociodemographic characteristics and preventive practices related to the vector. The statistical analysis was based on a bivariate analysis and Poisson multiple regressions. Inadequate or insufficient knowledge on the vector Aedes aegypti remained associated with education in the categories illiterate (p<0.001) and 8 years of study or less (p<0.001), in addition to not adopting practices of capping and cleaning the water tank (p=0.002) and not using insecticides at home (p=0.007). It is concluded that there is a need for health communication actions that consider characteristics the population, especially the level of education and previous knowledge on the vector, allowing a dialogical approach and enabling the community participation in preventive practices and control of the vector Aedes aegypti .
  7. Rev Inst Med Trop Sao Paulo. 2021 ;pii: S0036-46652021000100232. [Epub ahead of print]63 e60
      The majority of malaria cases in South America occur in rural areas of the Amazon region. Although these areas have a significant impact on malaria cases, few entomological studies have been carried out there. This study aimed to describe entomological parameters in settlements in Rondonia State, Brazil. Collections of anopheles were carried out using the Protected Human Attraction Technique (PHAT). The risk and the potential for malaria transmission were assessed using the human biting rate (HBR), the sporozoite rate (SR) and the entomological inoculation rate (EIR). The results confirmed that Nyssorhynchus darlingi is the predominant species in the two studied locations. Although settlement in the two study sites has occurred at different times, the species richness found was low, showing that environmental changes caused by anthropological actions have probably favor the adaptation of Ny. darlingi species. From the total of 615 anopheline mosquitoes assessed, seven (1.1%) were positive for Plasmodium sp. infections. The EIR revealed that Ny. darlingi contributes to malaria transmission in both locations, as it was responsible for 0.05 infectious bites in humans at night in the old settlement and 0.02 in the recent occupation. In the two study sites, the biting occurred more frequently at dusk. Nyssorhynchus darlingi was prevalent in areas of recent colonization but, even when present in a low density, this species could maintain the transmission of malaria in the older settlement. The entomological information obtained in this study is important and may aid the selection of vector control actions in these locations.
  8. Elife. 2021 Aug 17. pii: e69630. [Epub ahead of print]10
      The potential for adaptive evolution to enable species persistence under a changing climate is one of the most important questions for understanding impacts of future climate change. Climate adaptation may be particularly likely for short-lived ectotherms, including many pest, pathogen, and vector species. For these taxa, estimating climate adaptive potential is critical for accurate predictive modeling and public health preparedness. Here, we demonstrate how a simple theoretical framework used in conservation biology-evolutionary rescue models-can be used to investigate the potential for climate adaptation in these taxa, using mosquito thermal adaptation as a focal case. Synthesizing current evidence, we find that short mosquito generation times, high population growth rates, and strong temperature-imposed selection favor thermal adaptation. However, knowledge gaps about the extent of phenotypic and genotypic variation in thermal tolerance within mosquito populations, the environmental sensitivity of selection, and the role of phenotypic plasticity constrain our ability to make more precise estimates. We describe how common garden and selection experiments can be used to fill these data gaps. Lastly, we investigate the consequences of mosquito climate adaptation on disease transmission using Aedes aegypti-transmitted dengue virus in Northern Brazil as a case study. The approach outlined here can be applied to any disease vector or pest species and type of environmental change.
    Keywords:  adaptation; climate change; ecology; evolutionary rescue; mosquito; pest; vector
  9. J Am Mosq Control Assoc. 2021 Sep 01. 37(3): 119-124
      The aim of this study was to consolidate mosquito information for 13 counties west of San Antonio, Bexar County, Texas, and to create a species checklist for future regional studies. The resulting checklist established a baseline for local mosquito-borne disease surveillance and can serve as a resource for public health officials. The 13 counties in this region were Bandera, Edwards, Kendall, Kerr, Kimble, Kinney, Maverick, Medina, Real, Sutton, Uvalde, Val Verde, and Zavala counties. To develop the checklist, county-level mosquito species data were extracted from 38 peer-reviewed publications and government documents, university reference collections, private collections, and the Texas Department of State Health Services' historical collection data. These data were combined with author field collections to create a comprehensive species list. Overall, 339 county-level records were documented through field studies with a total of 36 species representing 8 genera confirmed as being present in this region. An additional 14 species listed in historical surveillance records were not collected during this study.
    Keywords:  Culicidae; geographic distribution; surveillance
  10. J Insect Physiol. 2021 Aug 16. pii: S0022-1910(21)00105-0. [Epub ahead of print] 104295
      The mosquito microbiome is critical to multiple facets of their biology, including larval development and disease transmission. For mosquitoes that reside in temperate regions, periods of diapause are critical to overwintering survival, but how the microbiome impacts this state is unknown. In this study, we compared the midgut microbial communities of diapausing and non-diapausing Culex pipiens and assessed how a reduced midgut microbiome influences diapause preparation. High community variability was found within and between non-diapausing and diapausing individuals, but no specific diapause-based microbiome was noted. Emergence of adult, diapausing mosquitoes under sterile conditions generated low bacterial load (LBL) lines with nearly a 1000-fold reduction in bacteria levels. This reduction in bacterial content resulted in significantly lower survival of diapausing females after two weeks, indicating acquisition of the microbiome in adult females is critical for survival throughout diapause. LBL diapausing females had high carbohydrate levels, but did not accumulate lipid reserves, suggesting an inability to process ingested sugars necessary for lipid accumulation. Expression patterns of select genes associated with mosquito lipid metabolism during diapause showed no significant differences between LBL and control lines, suggesting transcriptional changes may not underlie impaired lipid accumulation. Overall, a diverse, adult-acquired microbiome is critical for diapause in C. pipiens to process sugar reserves and accumulate lipids that are necessary to survive prolonged overwintering.
    Keywords:  Culex pipiens; dormancy; lipid levels; metabolism; microbiome
  11. J Am Mosq Control Assoc. 2021 Sep 01. 37(3): 161-163
      Mosquito larvae were collected in the urban area of the city of Culiacan, Sinaloa, in September of 2020. The immature stages were placed in emergence containers and fed with Aedes aegypti larvae. The adults that emerged from the immature stages were mounted on insect pins and characterized based on their morphology. The species corresponded morphologically to Toxorhynchites moctezuma, making this the first report of the species for the state of Sinaloa, Mexico. Similarities and morphological variations are discussed with previous analysis for this species.
    Keywords:   Toxorhynchites moctezuma ; Distribution; Mexico; Sinaloa; morphology
  12. Zoonoses Public Health. 2021 Aug 16.
      Mosquitoes are important biological vectors of pathogens and species identification in all life stages is the first step for effective monitoring and control of mosquito-borne diseases. Molecular methods for species identification have been developed over the last years to overcome the limitations of the taxonomic identification based on morphology. DNA barcoding, using a fragment of the mitochondrial cytochrome oxidase I (COI) gene, can be used for species identification but a reliable and comprehensive reference database of verified sequences is required. In this study, we aimed to generate a DNA barcode reference library for the identification of mosquito species from Portuguese mosquito fauna, including most relevant vector species. Mosquitoes captured under the National Vector Surveillance Program (REVIVE) were processed for DNA extraction, COI gene fragment amplification and sequencing. Nighty-eight barcode sequences were obtained, representing 26 species and 6 genera. Sequences were submitted to GenBank and BOLD and were used for validation of phenetic classification. Barcode Index Number (BIN) assignment and Automatic Barcode Gap Discovery (ABGD) were used and clustered COI sequences into twenty-five molecular operational taxonomic units (MOTUs). This is the first comprehensive study that combines morphological and molecular identification of most mosquito species present in Portugal aiming to offer a reliable framework for mosquito species identification.
    Keywords:  DNA barcoding; Portugal; culicidae; cytochrome oxidase I (COI); mosquito surveillance; species identification
  13. J Am Mosq Control Assoc. 2021 Sep 01. 37(3): 172-174
      Twelve experimental pools (30 cm width × 30 cm depth) around a large stormwater management pond (SWMP) were used to test the hypothesis that small puddles of water similar to animal hoofprints or other irregularities support more abundant and diverse mosquito populations due to having fewer insect predators. Six of the 12 pools were connected to the SWMP by a deep channel (7 cm wide × 10 cm depth × 50 cm length). Mosquito larvae and potential predators were sampled weekly over 16 wk in the summer. More mosquito larvae were found in the isolated pools than in connected pools or in the pond itself (U = 5.5, z = 2.002, P = 0.045). The observed differences between isolated and connected pools are presented and results discussed in terms of SWMP design.
    Keywords:  Culicidae; hoof prints; mosquito larvae; pools; stormwater management ponds
  14. Afr Health Sci. 2020 Dec;20(4): 1601-1609
      Background: Dengue fever (DF) is currently widespread in tropical and sub-tropical countries. Among the triggers of epidemic include urbanization and internal migrations. Within the past few years, there have been DF outbreaks in Tanzania. Although Pwani region is among the predicted risk areas for the DF, there is insufficient data about people's knowledge, attitude and practices towards prevention of DF in their settings. Therefore, the aim of this study was to assess knowledge, attitude and practices about DF among adults in Pwani region in Tanzania.Methods: The cross-sectional study conducted in Mkuranga District, Pwani region in Tanzania. We used face-to-face interviews to collect data. The main analytical procedure was descriptive using frequencies.
    Results: The majority, 97.7%, were aware of DF. Nevertheless, almost 80% had a low knowledge on symptoms, transmission and vector control measures. Furthermore, less than 20% had positive attitude towards dengue fever prevention, severity of the illness and health seeking behavior.
    Conclusion: Lack of enough knowledge and positive attitude about disease transmission, symptoms and preventive measures put the population at high risk of contracting the disease. There is need to create and improve friendly, correct and simple information, education and education messages for the rural populations.
    Keywords:  Attitude; Dengue; knowledge; practice; rural
  15. J Am Mosq Control Assoc. 2021 Sep 01. 37(3): 175-178
      Anopheles darlingi is considered the main vector of malaria in the Neotropical region, so knowledge of its distribution in the Americas is highly relevant for the design of strategies for prevention and control of the illness. In Mexico, An. darlingi was recorded for the first time in 1943, and currently its distribution covers the states of Campeche, Chiapas, Quintana Roo, and Tabasco. In this study, new distribution data and observations of the abundance of An. darlingi in 14 localities of Quintana Roo, southeastern Mexico, are presented.
    Keywords:  Anophelinae; malaria; vectors
  16. Sci Rep. 2021 Aug 16. 11(1): 16540
      Malaria risk is highly heterogeneous. Understanding village and household-level spatial heterogeneity of malaria risk can support a transition to spatially targeted interventions for malaria elimination. This analysis uses data from cross-sectional prevalence surveys conducted in 2014 and 2016 in two villages (Megiar and Mirap) in Papua New Guinea. Generalised additive modelling was used to characterise spatial heterogeneity of malaria risk and investigate the contribution of individual, household and environmental-level risk factors. Following a period of declining malaria prevalence, the prevalence of P. falciparum increased from 11.4 to 19.1% in Megiar and 12.3 to 28.3% in Mirap between 2014 and 2016, with focal hotspots observed in these villages in 2014 and expanding in 2016. Prevalence of P. vivax was similar in both years (20.6% and 18.3% in Megiar, 22.1% and 23.4% in Mirap) and spatial risk heterogeneity was less apparent compared to P. falciparum. Within-village hotspots varied by Plasmodium species across time and between villages. In Megiar, the adjusted odds ratio (AOR) of infection could be partially explained by household factors that increase risk of vector exposure, such as collecting outdoor surface water as a main source of water. In Mirap, increased AOR overlapped with proximity to densely vegetated areas of the village. The identification of household and environmental factors associated with increased spatial risk may serve as useful indicators of transmission hotspots and inform the development of tailored approaches for malaria control.
  17. PLoS Comput Biol. 2021 Aug 19. 17(8): e1009287
      There is an abundance of malaria genetic data being collected from the field, yet using these data to understand the drivers of regional epidemiology remains a challenge. A key issue is the lack of models that relate parasite genetic diversity to epidemiological parameters. Classical models in population genetics characterize changes in genetic diversity in relation to demographic parameters, but fail to account for the unique features of the malaria life cycle. In contrast, epidemiological models, such as the Ross-Macdonald model, capture malaria transmission dynamics but do not consider genetics. Here, we have developed an integrated model encompassing both parasite evolution and regional epidemiology. We achieve this by combining the Ross-Macdonald model with an intra-host continuous-time Moran model, thus explicitly representing the evolution of individual parasite genomes in a traditional epidemiological framework. Implemented as a stochastic simulation, we use the model to explore relationships between measures of parasite genetic diversity and parasite prevalence, a widely-used metric of transmission intensity. First, we explore how varying parasite prevalence influences genetic diversity at equilibrium. We find that multiple genetic diversity statistics are correlated with prevalence, but the strength of the relationships depends on whether variation in prevalence is driven by host- or vector-related factors. Next, we assess the responsiveness of a variety of statistics to malaria control interventions, finding that those related to mixed infections respond quickly (∼months) whereas other statistics, such as nucleotide diversity, may take decades to respond. These findings provide insights into the opportunities and challenges associated with using genetic data to monitor malaria epidemiology.
  18. J Am Mosq Control Assoc. 2021 Sep 01. 37(3): 143-151
      The females of Mansonia are voraciously hematophagous. The spiracular apparatus of the immature, larval, and pupal forms is adapted to perforate submerged aquatic vegetation, from whose aeriferous aerenchyma they obtain the oxygen necessary for breathing. The proliferation of aquatic plants, in some cases linked to anthropic modifications that reduce water flow and/or increase organic matter content, may therefore contribute to the spread of these mosquitoes. This study aims to assess the presence of immature individuals of Mansonia in different aquatic plants of the Madeira River basin in 10 lentic and lotic environments and correlate their population density with abiotic factors such as water pH, dissolved O2, conductivity, and temperature. The sampling lasted from February 2016 to June 2018, a 29-month period during which 31,287 specimens belonging to the genus Mansonia were captured. Of the 12 species of macrophytes inspected, Eichhornia crassipes made up 70.1% of the samples. Lentic environments accounted for 58.9% of the samples and lotic environments for 41.1%. Immature individuals were most commonly found on Eichhornia crassipes, with this plant accounting for an average of 96.2% of all individuals, with a percentage ranging between 58.2% and 77.1% in different breeding areas. Only at the Foz do Igarapé Jirau site was a different distribution observed, with the number of aquatic plants more nearly equal: 83.3% of the larvae were found in Eichhornia crassipes, 9.2% in Ceratopteris pteridoides, 3.6% in E. azurea, 2.0% in Salvinia sp., and 1.9% in Pistia sp. The greatest richness was found in Iguapé do Raul. Concerning the larval/plant relationship, although less frequent, E. azurea had a higher larval density of Mansonia spp. It is important to emphasize that this finding may indicate a possible selection for this plant. Egg deposition by Mansonia spp. was more abundant in sample areas with Eichhornia crassipes and Pistia sp. The number of specimens collected was positively correlated with temperature, pH, and conductivity. These correlations showed a marked increase in the rainy season. Therefore, we were able to establish preliminary parameters of how environmental changes influence the ecology of this important genus of mosquitoes, the species of which are critical disease vectors.
    Keywords:   Mansonia ; Abiotic factors; Madeira River; macrophytes; mosquitoes