Chikungunya, Zika, yellow fever, and dengue have reemerged and emerged as an important public health challenge worldwide as well in the Democratic Republic of the Congo (DRC) (1–3). These mosquito-borne viral diseases (MBVD) are mainly transmitted by Aedes mosquitoes. Aedes aegypti and Ae. albopictus are known to be the major vectors of most of the MBVD (4, 5). Multiple factors ranging from climatic, environmental, ecological, and socioeconomic factors exert influence over arbovirus vectors distribution and abundance (6, 7).

Mosquito immature stages are entirely aquatic and require water for their development. Various water-holding containers ranging from small to large and natural to manmade have been reported to support Aedes mosquito breeding. They include tires, flower pots, plastic or metal recipients, drains, swimming pools, storm water, flooding water, bamboo sticks, and plant axils (8–10). Moreover, any standing water body represents a potential mosquito breeding site. The quality of the water might selectively favor the development of larvae and pupae of some mosquitoes species and successful development into adult mosquitoes (11. The choice of breeding sites by mosquitoes is a key element for mosquito productivity, population survival, and dynamics (12).

The physicochemical characteristics of a mosquito breeding site express a significant influence on the immature stage of the mosquito life cycle and have important implications for mosquito control (9, 13). Some of these characteristics such as pH, salinity, dissolved oxygen (DO), and total dissolved solids (TDS) have been shown to influence the density of Ae. aegypti and Ae. albopictus (14, 15). These water characteristics affect some mosquito basic features such as survival, body size, and biting behavior which are linked to mosquito vectorial capacity, hence the magnitude and intensity of disease transmission. Indeed, the deficit of food supply in the stage of immature mosquito development leads to hatching of small mosquito adult body size and decrease in longevity (16). Habitually, the small female mosquitoes are more active in host seeking and blood feeding than the larger-size females probably due to limited energy stock to support egg maturation (17). Therefore, this behavior modification exposes hosts to high mosquito biting rates with possibility of pathogen transmission (17, 18). Thus, water availability and storage procedures greatly influence mosquito immature richness and MBVD risk occurrence (19).

The majority of large cities of DRC including Kinshasa are characterized by heterogeneous levels of urbanization and unequal levels of pollution. With the geographical expansion of chikungunya and dengue and repeated yellow fever outbreaks in DRC, there is a need to improve our understanding of the vector ecological factors (20–22). The physicochemical and environmental factors in mosquito breeding sites exert an effect on the density of mosquito larvae as well as on their detoxification enzyme activities. They can present an impact on insecticide resistance occurrence (23). It has been reported that the management of the pH of favored breeding sites could serve as a tool to control mosquito, and it can also assist the choice of biopesticides to use (24). Therefore, the good knowledge on Aedes breeding site physicochemical properties is critical in the design of effective vector interventions (25).

Not much data are currently available on the physicochemical characteristics of Aedes mosquito larval habitats in DRC. The present study assessed the physicochemical characteristics of Aedes water breeding habitats in the urban and suburban areas of Kinshasa, DRC.

A total of 438 water-breeding places were inspected. Of these, 273 contained mosquito larvae including 90 (32. 97%) tires, 56 (20.51%) plastic containers, 43 (15.82%) collections of stagnant and flooding water, 17 (6.23%) bamboo sticks, 16 (5.86%) tins, and 14 (5.13%) metal containers ( Table 1 ). Aedes spp. were found in 208 (76.19%) breeding sites; 79 (28.94%) breeding sites were positive for Culex spp.; 21 (7.69%) had Anopheles spp.; and three (1.09%) had Toxorhynchites mosquitoes. The co-occurrence of Aedes spp. and Culex spp. was recorded in 23 (8.42%) breeding sites, while in seven (2.56%) breeding sites, Aedes cohabited with Anopheles. Of 208 positive Aedes spp. habitats, Ae. albopictus were found in 140 (67.30%) sites and Ae. aegypti in 79 (37.98%) sites, while in 23 breeding habitats, the two species of Aedes were found together ( Table 2 ).

The overall trends of physicochemical characteristics of the positive breeding habitats were significantly different from the ones without mosquito larvae ( Table 3 ). Using Dunn’s multiple-comparison test as post-hoc test, the median of DO was significantly higher in water breeding sites of Aedes (1.0) compared to Culex mosquitoes (0.8), p = 0.0001. Respectively, the means of conductivity (228.5), TDS (112.5), turbidity (19.5), and salinity (0.115) in water breeding sites of Aedes were significantly lower than in Culex (555.0, 267.0, 55.0, and 0.29) with p < 0.05. The pH in the Aedes breeding site (6.76) was higher than in Anopheles (6.58) with p = 0.0002. The patterns of physicochemical characteristics favoring different mosquito occurrence are summarized in Figure 2 .

The percentage of DO in Aedes breeding habitats ranged from 0.5 to 2.6. The medians of DO, pH, conductivity, salinity, TDS, and turbidity as well as temperature of Aedes breeding habitats are provided in Table 4 . Ae. aegypti and Ae. albopictus were found breeding in water sites with related properties as regards turbidity, salinity, pH, TDS, DO, conductivity, and temperature levels ( Table 5 ). Compared to suburban areas, the median of conductivity in urban areas was 236 vs. 228, U = 5088, p = 0.7118; TDS (109.5 vs. 114.5, U = 5141, p = 0.8059) and salinity (0.12 vs. 0.115, U = 5084, p = 0.7046). The median of temperature was significantly high in urban areas (29.82) than in suburban areas 29.60, U = 4319, p = 0.0298 ( Table 6 ). Some of these physicochemical parameters varied significantly according to the larval habitat types. A high percentage of DO was recorded in tin (1.2) and tire (1.05) and lower % DO in stagnant water (0.7) and sewage pit (0.65); U p = 0.0014. The salinity was high in bamboo sticks (0.31) and lower in tin (0.04), p = 0.0001. The trends of different physicochemical parameters of the different breeding Aedes habitats are summarized in Table 7 .

In simple linear regression, the larval density in Aedes breeding habitats showed a positive relationship with TDS (r₍₂₀₆₎ = 0.23; p = 0.001), conductivity (r₍₂₀₆₎ = 0.23; p = 0.001), salinity (r₍₂₀₆₎ = 0.23; p = 0.001), and temperature (r₍₂₀₆₎ = 0.138; p = 0.04) ( Table 8 ). In the multiple linear regression model (r₍₂₀₂₎ = 0.30, p = 0.002), salinity (r = 0.23, p = 0.001) and DO = 0.138, p = 0.047) adjusted to temperature, pH, and turbidity were positively associated with larval density ( Table 9 ).

The present study addressed the association between physicochemical properties of Aedes mosquito habitats in urban and suburban areas of Kinshasa. Infestation with Ae. albopictus and Ae. aegypti accounted for the over three-quarters of the breeding sites. Ae. aegypti and Ae. albopictus bred in water sites with closely related turbidity, pH, TDS, DO, conductivity, and temperature levels. However, these Aedes species preferred less turbid waters with moderate salinity and moderate DO. The findings of this study revealed differences in some parameters such as TDS, DO, conductivity, turbidity, and salinity according to the level of urbanization and habitant types, either natural or artificial. This is contrary to the findings from Zanzibar in Tanzania where the presence of immature Ae. aegypti was not linked significantly to any physicochemical characteristics of water breeding habitats (31).

Indeed, Kinshasa is characterized by uncontrolled and heterogeneous urbanization levels, poor environmental hygiene, multiple soil erosion, and recently multiple floodings (26, 27, 32). These conditions create suitable mosquito breeding habitats. The quality of water within these habitats varies in terms of their physicochemical characteristics which can promote or limit the proliferation of some Aedes species. The physicochemical parameters of Ae. aegypti and Ae. albopictus breeding site water were similar in regard to turbidity, pH, salinity, chloride, and phosphate levels (24).

Similar to findings from other studies, containers expressed differences in water physicochemical profile and urbanization considerably accelerates the larval development rate and survival time of adult of Ae. albopictus, with a positive effect on vector capacity (17). The anthropogenic Ae. aegypti prefers clean water found in various types of peridomestic containers while Ae. albopictus prefers natural containers or outdoor manmade habitats containing abundant amounts of organic debris (19). The temperature, DO, and pH of breeding site water have differences between endemic and non-endemic areas (33). The physicochemical and biological markers of mosquito larval habitats help in mapping of areas suitable for breeding and distribution for targeting surveillance and controlling activities (17, 34).

Reports from different environments show a relationship between physicochemical characteristics of immature habitats and container types. However, differences in some parameters could be linked to the nature of the container, either natural or artificial, and water source (19, 35, 36). In the current study, various natural and artificial breeding habitats of immature mosquitoes were explored and grouped according to their materials made. They exhibited a significant difference in their physicochemical properties. The concentration of TDS and the levels of turbidity and conductivity were low in tin and plastic container. The non-household locations, as well as non-disposable containers, should be targeted in the standard control activities of mosquito-borne viral diseases (37), contrary to findings from Tanzania where the presence of immature Ae. aegypti was not linked significantly to any physicochemical characteristics of water breeding habitats (31). In other studies, it was reported that the selection of breeding sites depends on the volume and size of the water surface and the type of material of which they are made (38.). Aedes mosquito prefers materials which are made from cement, metal, soil, ceramics, and plastic (36, 39.). In a study in Kolkata, India, plastic containers were reported as the most productive habitats for Aedes species (35). The populations of immature mosquitoes growing in ground pools are exposed to diverse factors of death, natural enemies compared to those in water-filled containers in which the growth is restricted by food availability (38).

Although in simple linear regression, larval density showed a positive relationship with the temperature, concentration of TDS, conductivity, and salinity, in multiple linear regression analysis, only salinity and DO adjusted to temperature, pH, and turbidity were associated with increasing larval density. This observation was in agreement with findings from a study in Egypt (40). It was also reported from Iran that DO presents a significant impact on larval density (41). The salinity is another parameter that can promote or limit the growth of larvae (40–43). Temperature affects the degree of evapotranspiration, and therefore, it acts on the water salinity (43). Water temperature is a crucial parameter for mosquito metabolism and development (17, 38, 44). In other studies, the breeding site characteristics of Ae. albopictus showed a negative correlation of the larval density with turbidity and conductivity but a positive correlation with pH and DO (40, 42, 43, 45). Water pH and turbidity in the current study seemed to decrease larval density, but the association was not significant. Similar findings have been reported from a study in Iran (44).

The current study showed that the salinity and percentage of DO exert influence on the distribution of Aedes mosquito occurrence, survival, and abundance. Other parameters such temperature, acidity or alkalinity, and turbidity indirectly influence Aedes mosquito proliferation. Environment factors such urbanization and the nature of breeding habitat affect these physicochemical parameters. The findings of this study can assist in designing control activities of Aedes-borne diseases by targeting areas suitable for breeding.

The original contributions presented in the study are included in the article/ Supplementary Material . Further inquiries can be directed to the corresponding author.

KM designed the study, conducted the fieldwork, performed the statistical analysis, and prepared the manuscript for publication. RW, PM, and SIK assisted in the study design. DE, MB, and JZ participated in the fieldwork. LM and GM critically read the manuscript for publication. All authors contributed to the article and approved the submitted version.

KM is a recipient of a PhD scholarship from the Government of the United Republic of Tanzania through the World Bank (WB-ACE II Grant PAD1436, IDA credit 5799-TZ) to the SACIDS Africa Centre of Excellence for Infectious Diseases at the Sokoine University of Agriculture.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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