Dengue cases and Aedes aegypti indices in Trinidad, West Indies

This study was conducted to determine whether any relationships exist between Aedes aegypti indices, dengue seroprevalence and dengue transmission in County Victoria, Trinidad, West Indies. The cardinal points surveillance method was used to evaluate 50 suspected dengue fever (DF) cases. Thirty-three (33) confirmed DF cases were fully investigated within 48 h of clinical diagnosis. Using retrospective data collected during the previous year (2003-2004) and study data, key premises and key containers were determined. Ninety-two percent of the houses were considered key premises, and 66% (22/33) of the houses with dengue positive cases harboured Ae. aegypti immature stages. These results showed that significantly (P < 0.001) more adults (1050 vs 493) and immatures were collected during dengue case investigations than during routine inspection and treatment cycles. In addition, when the DF diagnosis was made the pupae per person rates increased from 0.65 to 1.35 with significantly (P < 0.001) larger numbers of Ae. aegypti females emerging daily, increasing from 221 to 472.5. That is, the mosquito density required for DF transmission may be high for Trinidad given the high seroprevalence rates (94% among pregnant women). These results suggest that dengue transmission occurs, not at a fixed entomologic figure/quantity but rather at a variable level based on numerous factors including seroprevalence, mosquito density and climate. These findings have implications for effective programs: by combining cardinal points and the key premises approaches; vector control programs can now target the most productive containers in key premises thus reducing dengue transmission levels.     

Oviposition behaviour and parity rates of Aedes aegypti collected in sticky traps in Trinidad, West Indies

The oviposition behaviour of Aedes aegypti was studied using sticky traps (ST), double sticky traps (DST) and standard ovitrap traps in urban St. Augustine and rural Tamana, Trinidad, West Indies. In St. Augustine three traps were deployed in 10 houses for 10 weeks while in Tamana traps were similarly deployed (10 houses for 10 weeks). At each house one ovitrap, one ST and one DST were placed using the criteria established for ovitrap placement. The results showed large numbers of adults collected, 3602 collected in DSTs and 1,670 adults collected in STs. In addition, >9000 immatures were collected in the DST vs >7000 in the STs. Over the 10 weeks 517 Ae. aegypti eggs were collected from ovitraps from Tamana and 3252 eggs from St. Augustine. Most of the females collected were parous (99%) with many older females collected e.g. 7 pars collected in both Tamana and St. Augustine. A major finding of the study was the observation of the “death stress oviposition” behaviour displayed among Ae. aegypti females captures in the sticky traps. This is the first report of this behaviour in the field and may well explain the collection of large numbers of immatures found in the ST and DSTs. The results of this study are discussed in the context of developing surveillance and control strategies, especially for reducing man-vector contact.     

Impact of pre-seasonal focal treatment on population densities of the mosquito Aedes aegypti in Trinidad, West Indies: A preliminary study

A new pre-seasonal focal treatment strategy against Aedes aegypti L. (Diptera: Culicidae) mosquitoes is described for the first time. It was evaluated for 25 weeks using ovitraps, and larval and pupal surveys in the townships of Curepe (treated) and St. Joseph (untreated), Trinidad, West Indies. Both townships were similar with respect to number of houses, size of human populations, the number of Ae. aegypti infested houses and containers. In March 2003, a total of 9403 containers were inspected, of which 1.4% in Curepe (63/4499) and 1.3% in St. Joseph (64/4904) were positive for Ae. aegypti immature stages. Curepe had a lower percentage (12.7%) of the main type of breeding container present (small miscellaneous containers) than St. Joseph (28.1%). Following focal treatment during the month of April (2-3 weeks before the onset of the rainy season), the Ae. aegypti population declined significantly (P > 0.01) from a Breteau index (BI; proportion of containers positive for larvae and pupae) of 19.0 to a minimum of 6.0 and a pupae/person index (PI) of 1.23 to a minimum of 0.35 in May, while in the untreated town of St. Joseph, the BI steadily increased from 23 to 38 and the PI rose from 0.96 to 2.00 in August. Similar declines in other measures of population density (the number of positive houses and number of eggs collected in ovitraps) were observed in Curepe, while St. Joseph maintained PI of >1.50 and BI of >28. Furthermore, the Curepe Ae. aegypti population did not return to pre-treatment levels until 9-11 weeks after treatment, far beyond the 6 weeks normally expected during vector suppression campaigns. The results suggest that timely application of pre-seasonal focal treatment with temephos together with standard control measures, such as source reduction of the most productive containers, can reduce the Breteau index to <5 and the pupae/person index to <0.71 (i.e., below the suggested dengue transmission thresholds for Trinidad), and extend the duration of vector suppression.     

Bionomics of Aedes aegypti subpopulations (Diptera: Culicidae) from Misiones Province, northeastern Argentina

Life statistics of four Aedes aegypti subpopulations from the subtropical province of Misiones were studied during autumn and winter, under semi-natural conditions, coming from the localities of Posadas (SW), San Javier (SE), Bernardo de Irigoyen (NE) and Puerto Libertad (NW). The eastern subpopulations are geographically separated by the central mountain system of the province from the western subpopulations. High percentages of larval and pupal survival (97-100%) were recorded, and no significant differences were detected among the four subpopulations. Larvae and pupae lasted approximately 8 days to complete their development, no significant differences being detected among the four subpopulations studied. Sex ratio recorded did not differ significantly from 1:1. Male longevity did not show difference among the different subpopulations, but female longevity was remarkably different among the four subpopulations (F = 16.27; d.f. = (3;8); P = 0.0009), ranging among 11.45 days for San Javier and 57.87 days for Posadas. Fecundity also varied considerably among subpopulations, the greatest number (307.44 eggs/female) being recorded for Posadas (F = 4.13; d.f. = (3;8); P = 0.04). Ae. aegypti females of the western subpopulations lived longer than the eastern subpopulations studied, therefore, the risk of dengue outbreak would be greater on the Misiones Province border with Paraguay.     

Culture-dependent and culture-independent characterization of microorganisms associated with Aedes aegypti (Diptera: Culicidae) (L.) and dynamics of bacterial colonization in the midgut

In this work we show that the lumen of Aedes aegypti midgut is highly colonized by bacteria that were identified by culture-dependent and culture-independent methods. rDNA sequences obtained were compared with those from GenBank and the main bacterial genera identified were: Serratia, Klebsiella, Asaia, Bacillus, Enterococcus, Enterobacter,Kluyvera and Pantoea. All genera were identified in midgut except Enterobacter that was observed only in eggs. Asaia and Pantoea were also identified in eggs and ovary, respectively. In addition two yeast genera were observed in A. aegypti: Pichia isolated from midgut and Candida identified in midgut and ovary. The genus Serratia was dominant in all isolation assays representing 54.5% of the total of microorganisms. Thirty-nine and 24 bacterial clones were successfully obtained from midguts 24 and 48 h after blood feeding (ABF), respectively. The majority of clones obtained were from Serratia sp. (48.7% and 50% for 24 and 48 h ABF, respectively). Light microscopy showed that bacteria were located preferentially in the posterior midgut, around the blood meal and associated with peritrophic matrix. Scanning electron microscopy images showed a high number of bacteria in midgut during blood digestion and the peak of bacterial enumeration was reached 48 h ABF, stage in which lumen was almost totally occupied by bacteria that were also interacting with epithelial microvilli. Our results show the dynamics of microbial colonization and their distribution in midgut during blood digestion.     

Indirect effects of cigarette butt waste on the dengue vector Aedes aegypti (Diptera: Culicidae)

Despite major insecticide-based vector control programs, dengue continues to be a major threat to public health in urban areas. The reasons for this failure include the emergence of insecticide resistance and the narrowing of the spectrum of efficient products. Cigarette butts (CBs), the most commonly discarded piece of waste, also represent a major health hazard to human and animal life. CBs are impregnated with thousands of chemical compounds, many of which are highly toxic and none of which has history of resistance in mosquitoes. This study was performed to examine whether exposure to CB alters various biological parameters of parents and their progeny. We examined whether the mosquito changes its ovipositional behaviors, egg hatching, reproductive capacity, longevity and fecundity in response to CB exposure at three different concentrations. Females tended to prefer microcosms containing CBs for egg deposition than those with water only. There were equivalent rates of eclosion success among larvae from eggs that matured in CB and water environments. We also observed decreased life span among adults that survived CB exposure. Extracts of CB waste have detrimental effects on the fecundity and longevity of its offspring, while being attractive to its gravid females. These results altogether indicate that CB waste indirectly affect key adult life traits of Aedes aegypti and could conceivably be developed as a novel dengue vector control strategy, referring to previously documented direct toxicity on the larval stage. But this will require further research on CB waste effects on non-target organisms including humans.     

Effect of niloticin,a protolimonoid isolated from Limonia acidissima L. (Rutaceae) on the immature stages of dengue vector Aedes aegypti L. (Diptera: Culicidae)

The aim of the present study was to evaluate the mosquitocidal activity of fractions and a compound niloticin from the hexane extract of Limonia acidissima L. leaves on eggs, larvae and pupae of Aedes aegypti L. (Diptera: Culicidae). In these bioassays, the eggs, larvae and pupae were exposed to concentrations of 2.5, 5.0, 7.5 and 10.0 ppm for fractions and 0.5, 1.0, 1.5 and 2.0 ppm for compound. After 24 h, the mortality was assessed and the LC₅₀ and LC₉₀ values were calculated for larvae and pupae. Per cent ovicidal activity was calculated for eggs after 120 h post treatment. Among the sixteen fractions screened, fraction 8 from the hexane extract of L. acidissima generated good mosquitocidal activity against Ae. aegypti. The LC₅₀ and LC₉₀ values of fraction 8 were 4.11, 8.04 ppm against Ae. aegypti larvae and 4.19, 8.10 ppm against Ae. aegypti pupae, respectively. Further, the isolated compound, niloticin recorded strong larvicidal and pupicidal activities. The 2 ppm concentration of niloticin showed 100% larvicidal and pupicidal activities in 24 h. The LC₅₀ and LC₉₀ values of niloticin on Ae. aegypti larvae were 0.44, 1.17 ppm and on pupae were 0.62, 1.45 ppm, respectively. Niloticin presented 83.2% ovicidal activity at 2 ppm concentration after 120 h post treatment and niloticin exhibited significant growth disruption and morphological deformities at sub lethal concentrations against Ae. aegypti. The structure of the isolated compound was identified on the basis of single XRD and spectral data (¹H NMR and ¹³C NMR) and compared with literature spectral data. The results indicate that niloticin could be used as a potential natural mosquitocide.     

Spatial analysis of Aedes aegypti immatures in Northern Argentina: Clusters and temporal instability

The objective of this study was to analyze the spatio-temporal patterns of Aedes aegypti immatures based on four entomological surveys that inspected over 6000 households in a large neighborhood of the city of Clorinda between 2007 and 2008. Global and local spatial point pattern analyses of immature presence or absence, habitat quality (estimated using a previously obtained statistical model) and pupal production were performed. Global analyses showed aggregation of both infestation and habitat quality up to 10 times bigger than previously described, ranging from 150 to 400 m between surveys. Pupal production was also clustered but at smaller scales than infestation presence/absence. The location of the clusters was temporally unstable between surveys. There was no spatial structure related to the control strategy; lots treated with temephos and lots uninspected (i.e., closed or refusing) were randomly distributed. These results suggest a combination of exogenous (the aggregation of better quality habitats) and endogenous (dispersal) processes explaining the observed patterns of larger-scale infestation. A spatial targeting strategy at the neighborhood scale would not be as cost-effective in Clorinda as in other sites where stable smaller-scale clusters permit the identification of key premises.     

Activities of naphthoquinones against Aedes aegypti (Linnaeus, 1762) (Diptera: Culicidae), vector of dengue and Biomphalaria glabrata (Say, 1818), intermediate host of Schistosoma mansoni

Larvicidal (against Aedes aegypti Linnaeus, 1762) and molluscicidal (against Biomphalaria glabrata Say, 1818) activities of several natural and synthetic naphthoquinones were measured, with significant results. The best larvicidal compound is 3-bromojuglone, while the better molluscicides are 2-bromo- and 3-bromo-5-acetoxy-1,4-naphthoquinones together with the 3-bromo-5-methoxy derivative. The present results reinforce the potential use of substituted hydroxyquinones, their salts and halogenated quinones as very promising compounds against 4th instar larves of Aedes aegypti, the vector of dengue and against adult snail of Biomphalaria glabrata.     

Seasonal and nonseasonal dynamics of Aedes aegypti in Rio de Janeiro,Brazil: Fitting mathematical models to trap data

Mathematical models suggest that seasonal transmission and temporary cross-immunity between serotypes can determine the characteristic multi-year dynamics of dengue fever. Seasonal transmission is attributed to the effect of climate on mosquito abundance and within host virus dynamics. In this study, we validate a set of temperature and density dependent entomological models that are built-in components of most dengue models by fitting them to time series of ovitrap data from three distinct neighborhoods in Rio de Janeiro, Brazil. The results indicate that neighborhoods differ in the strength of the seasonal component and that commonly used models tend to assume more seasonal structure than found in data. Future dengue models should investigate the impact of heterogeneous levels of seasonality on dengue dynamics as it may affect virus maintenance from year to year, as well as the risk of disease outbreaks.     

Effect of temperature on life history traits during immature development of Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae) from Córdoba city,Argentina

We investigated how ambient temperature under fluctuating conditions affects the larval–pupal immature traits of Aedes aegypti and Culex quinquefasciatus mosquitoes from Córdoba city, Argentina, and established each species development threshold and physiological time. Based on life tables, three cohorts of each mosquito species were reared in the laboratory under small fluctuating temperatures conditions of 15.2 ± 1.7 °C, 17.9 ± 1.6 °C, 21.6 ± 0.7 °C and 25.3 ± 0.4 °C for Ae. aegypti, and 16.6 ± 1.7 °C, 18.7 ± 1.7 °C and 25.2 ± 0.3 °C for Cx. quinquefasciatus. Immature development time and survival values, and also thermal development threshold and physiological time were estimated. Development times of all larval and pupal stages of Ae. aegypti and Cx. quinquefasciatus were significantly affected by the rearing temperatures, decreasing when temperature increased. Mean Ae. aegypti total (larva + pupa) development time ranged from 21.9 to 8.6 days, at 15.2 and 25.3 °C, whereas, for Cx. quinquefasciatus varied between 23.5 to 9.2 days at 16.6 and 25.2 °C, respectively. Larval and pupal survival of both species was affected by different rearing temperatures, increasing in general as temperature increased. For Ae. aegypti the total immature survival ranged from 26% at 15.2 °C to 92% at 21.6 °C; however, temperature did not have significant effect on this variable. The total immature survival of Cx. quinquefasciatus was significantly and positively affected by temperatures, ranging from 32 to 88%, at 16.6 and 25.2 °C. The temperature development threshold and the physiological time estimated for Ae. aegypti and Cx. quinquefasciatus were 11.11 °C and 93.74 degree-days, and 10.96 °C and 136.87 degree-days, respectively. The results of the present study showed that temperature significantly affects the larval–pupal immature traits of these mosquito species of sanitary importance, from the central region of Argentina. All the parameters recorded are useful for the development of mosquito management models.     

Stormwater drains and catch basins as sources for production of Aedes aegypti and Culex quinquefasciatus

We present data showing that structures serving as drains and catch basins for stormwater are important sources for production of the mosquito arbovirus vectors Aedes aegypti and Culex quinquefasciatus in Mérida City, México. We examined 1761 stormwater drains – located in 45 different neighborhoods spread across the city – over dry and wet seasons from March 2012 to March 2013. Of the examined stormwater drains, 262 (14.9%) held water at the time they were examined and 123 yielded mosquito immatures. In total, we collected 64,560 immatures representing nine species. The most commonly encountered species were Cx. quinquefasciatus (n = 39,269) and Ae. aegypti (n = 23,313). Ae. aegypti and Cx. quinquefasciatus were collected during all 11 months when we found water-filled stormwater drains, and both were found in stormwater drains located throughout Mérida City. We also present data for associations between structural characteristics of stormwater drains or water-related characteristics and the abundance of mosquito immatures. In conclusion, stormwater drains produce massive numbers of Ae. aegypti and Cx. quinquefasciatus across Mérida City, both in the wet and dry seasons, and represent non-residential development sites that should be strongly considered for inclusion in the local mosquito surveillance and control program.     

Dynamics of midgut microflora and dengue virus impact on life history traits in Aedes aegypti

Significant morbidity and potential mortality following dengue virus infection is a re-emerging global health problem. Due to the limited effectiveness of current disease control methods, mosquito biologists have been searching for new methods of controlling dengue transmission. While much effort has concentrated on determining genetic aspects to vector competence, paratransgenetic approaches could also uncover novel vector control strategies. The interactions of mosquito midgut microflora and pathogens may play significant roles in vector biology. However, little work has been done to see how the microbiome influences the host's fitness and ultimately vector competence. Here we investigated the effects of the midgut microbial environment and dengue infection on several fitness characteristics among three strains of the primary dengue virus vector mosquito Aedes aegypti. This included comparisons of dengue infection rates of females with and without their normal midgut flora. According to our findings, few effects on fitness characteristics were evident following microbial clearance or with dengue virus infection. Adult survivorship significantly varied due to strain and in one strain varied due to antibiotic treatment. Fecundity varied in one strain due to microbial clearance by antibiotics but no variation was observed in fertility due to either treatment. We show here that fitness characteristics of Ae. aegypti vary largely between strains, including varying response to microflora presence or absence, but did not vary in response to dengue virus infection.     

Surveillance of dengue fever cases using a novel Aedes aegypti population sampling method in Trinidad, West Indies: the cardinal points approach

A novel dengue surveillance method is described and used to evaluate 100 suspected dengue fever (DF) cases in county St. Patrick, Trinidad, West Indies. From the 30 confirmed DF cases fully investigated within 48 h of diagnosis, 63% (19/30 houses) of their homes were found harboring Aedes aegypti immature stages. Only houses at the four cardinal points of the index case rather than the entire neighborhood were investigated. The results showed significantly (P<0.001) more Ae. aegypti positive houses were observed to the east (P<0.04) and west (P<0.01) than to the north and south (P>0.9). In addition, from the 150 houses inspected a total of 474 artificial containers were inspected and treated, of which 20.8% (99) were infested with Ae. aegypti immature stages. More than 49% of the containers inspected were small miscellaneous containers, but they only produced 4.0% of the Ae. aegypti immatures, of which only 0.4% were pupae. Water tanks (41.7%), drums (40.4%) and buckets (24.2%) produced over 98% of the pupae. The results of this study imply that dengue vector control programs in Trinidad could increase their efficiency by applying the cardinal points surveillance approach during DF case investigations and concentrating their vector control measures on the most productive containers located at the east and west of the index cases.     

Growth and development of Aedes aegypti larvae at limiting food concentrations

Mosquitoes have a complex life-cycle with dramatic changes in shape, function, and habitat. Aedes aegypti was studied by growing individual larvae at different concentrations of a defined rich food source. At higher food concentrations, rate of larval growth was faster, but the time required for 4th instar larvae to molt into the pupal stage was unexpectedly extended. These opposite tendencies resulted in constant times from hatching to pupation and up to adult eclosion at permissive food concentrations. The results demonstrate that nutritional conditions of 4th instar larvae impact initiation of the first metamorphic molt.     

Effects of different temperature regimens on the development of Aedes aegypti (L.) (Diptera: Culicidae) mosquitoes

This study was conducted to determine the effects of increased water temperatures on the development of Aedes aegypti immatures under laboratory conditions in Trinidad, West Indies using temperature regulated water baths to cover a range of temperatures from 24–25 °C to 34–35 °C at a relative humidity of 80%. Two experiments were designed: (1) at constant temperature regimens and (2) under diurnal temperature regimens ranging from 24–25 °C to 34–35 °C. At 24–25 °C egg hatching success was 98% at 48 h, however at 34–35 °C egg hatching rates declined to 1.6% after 48 h. Ae. aegypti larvae reared under constant temperature regimens showed pupation on day 4 with highest pupation occurring at 30 °C (78.4%) However, under diurnal temperature regimens, pupation began on day 4 but only at the higher temperatures of 30–35 °C. Under diurnal temperature regimens ranging from 24 °C to 35 °C significantly more females emerged at higher temperatures, than males. In contrast, at constant temperatures of 24–35 °C no significant difference in M/F ratios were observed. The body size of Ae. aegypti reared at constant temperature regimens was significantly larger than males and females larvae reared under diurnal temperature regimens of 25–30 °C. The results of this study are discussed in the context of changing or increasing water temperatures, seasonal changes in vector populations and vector competence. Using these key factors control strategies are recommended to manage vector populations as expected increases in temperatures impact the Caribbean region.     

Relevance of differentiating between residential and non-residential premises for surveillance and control of Aedes aegypti in Rio de Janeiro, Brazil

Entomological surveys on Aedes aegypti (L.) often focus on residential premises, while ignoring non-residential premises. It has been proposed that the latter should be subject to specific monitoring strategies, since they have the potential to contribute a large proportion of the overall mosquito population. In this study, we used traps for ovipositing females to compare the levels of Ae. aegypti infestation in residential and non-residential premises and assess whether there was any evidence for a spatial association of infestation between non-residential premises and the surrounding homes. This information is important for designing specific surveillance programmes for these special sites and their surroundings. This study was conducted in three neighbourhoods of the city of Rio de Janeiro, Brazil, with distinct population densities, water services, dengue histories and vegetation coverage. Ae. aegypti abundance was measured using two types of traps (standard and sticky ovitraps) installed in five non-residential premises and 80 residential premises per neighbourhood. Mosquitoes were collected in the summer (January to March) and winter (June to September) of 2007. The distribution of captures per household per week did not differ significantly between the seasons, although larger numbers of eggs and adults were obtained during the summer. Most non-residential premises were not significantly more infested than homes, despite the larger quantities of containers. There were a few exceptions, including a transportation company, two recycling centres and a boat yard. These highly infested non-residential premises were also spatially associated with highly infested homes in the vicinity. Continuous monitoring with traps may be an effective way of evaluating non-residential premises as sources of dengue vectors for nearby communities.     

Laboratory and scaled up evaluation of cis-permethrin applied as a new ultra low volume formulation against Aedes aegypti (Diptera: Culicidae)

Ultra low volume (ULV) aerial spraying is a common methodology for spatial treatments for Aedes aegypti (L.) control. Previous studies from our laboratory indicated that the cis isomer of permethrin has an excellent efficacy for vector control, in particular for Triatoma infestans. It was of interest to determine the efficacy of this pure isomer in a ULV water-based formulation for adult A. aegypti control, since both vectors usually are found together in South America. A method is presented to make a quick measure at laboratory level of the knock down effect (KT50) of a new EC water-based formulation of cis-permethrin, in a small Peet Grady chamber of 0.34 m3, with a specially designed glass sprayer. A deltamethrin standard ULV formulation "CISLIN" was used for comparison. cis-Permethrin showed a significantly lower KT50 value than deltamethrin (7.50 and 9.65 min, respectively). When the mosquitoes were introduced into the chamber 10 min after spraying KT50 values were almost equal (15.59 and 15.88 min, respectively). In scaled up bioassays the ULV formulation of cis-permethrin showed 100% mortality of A. aegypti adult mosquitoes at the beginning of the treatment (t=0) and some mortality at 1h post treatment of freshly introduced mosquitoes. It was concluded that cis-permethrin could be an excellent tool for control of A. aegypti and other vectors of medical importance, with fewer side effects and better cost-effectiveness than with the cyanopyrethroids.     

Laboratory evaluation of aqueous leaf extract of Tephrosia vogelii against larvae of Aedes albopictus (Diptera: Culicidae) and non-target aquatic organisms

Mosquito control using insecticides has been the most successful intervention known to reduce malaria prevalence or incidence. However, vector control is facing a threat due to the emergence of resistance to synthetic insecticides. Insecticides of botanical origin may serve as suitable alternative biocontrol techniques in the future. In this research, the leaf aqueous leachate of Tephrosia vogelii was evaluated for its toxicity against larvae of the most invasive mosquito worldwide, Aedes albopictus (Diptera: Culicidae), and toward adults of the water flea, Daphnia magna (Cladocera: Crustacea) and Oreochromis niloticus, two non-target aquatic organisms that share the same ecological niche of A. albopictus. The leaf aqueous leachate of T. vogelii was evaluated against fourth-instar larvae, non-blood fed 3–5 days old laboratory strains of A. albopictus under laboratory condition. In addition, the objective of the present work was to study the environmental safety evaluation for aquatic ecosystem. Mortality was then recorded after 7 d exposure. The leaf aqueous leachate of T. vogelii showed high mosquitocidal activity against larvae of A. albopictus, with a LC₅₀ = 1.18 μg/mL. However, it had a remarkable acute toxicity also toward adults of the non-target arthropod D. magna, with a LC₅₀ = 0.47 μg/L and O. niloticus with a LC₅₀ = 5.31 μg/L. The present findings have important implications in the practical control of mosquito larvae in the aquatic ecosystem, as the medicinal plants studied are commonly available in large quantities. The extract could be used in stagnant water bodies for the control of mosquitoes acting as vector for many communicable diseases.