Vector Mosquito Larvae Research Articles

Comparative study on the larvicidal effect of some ciliated protists on Culex gelidus, Culex tritaeniorhynchus, and Aedes aegypti in Sri Lanka

Rice fields in Sri Lanka create suitable breeding places for vector mosquitoes. Such sites provide habitats for diversified naturally occurring microbiota. Ciliated protists, Zoothamnium sp., Chilodonella sp., and Vorticella microstoma are among such microbiota found in vector mosquito habitats especially in rice field habitats in Sri Lanka. The present study was carried out to determine the comparative larvicidal effect of these ciliated protists collected from naturally infested mosquito larvae in some rice-field habitats in Kurunegala, Sri Lanka, against vector mosquito larvae. Vector mosquito larvae, Culex tritaeniorhynchus, and Culex gelidus were reared in the laboratory from field-collected water samples while Aedes aegypti mosquito larvae were reared using egg sheets, for the laboratory bioassays. V. microstoma showed the potential for infection and mortality of Cx. tritaeniorhynchus larvae (71.33% ± 5.23). Results revealed a minimum of 1000V. microstoma is required to kill a single third instar larva of Cx. tritaeniorhynchus at 69.60 ± 2.40h of exposure. Cx. gelidus larvae showed 41.33% ± 3.43 mortality due to V. microstoma infestation. However, none of the ciliates were effective against Ae. aegypti larvae. Chilodonella sp. was very occasionally reported during this study hence was not possible to the mass rear for experimentations. This study concludes that V. microstoma is an effective ciliated parasite of Cx. tritaeniorhynchus larvae. Due to their effectiveness and eco-friendly nature, this species can be developed as an effective bio-controlling agent against Cx. tritaeniorhynchus mosquito species.

Design, synthesis, characterization and insecticidal screening of novel anthranilic diamides comprising acyl thiourea substructure.

Mosquito-borne pathogens constitute a major health problem worldwide. The extermination of the mosquito remains a significant issue in public health. Chemical insecticides have been used to control mosquitoes for decades. However, resistance has become a limiting factor for their control. The anthranilic diamide insecticides possess excellent insecticidal activities against Lepidoptera and its resistant strains by draining internal calcium stores on activating insect ryanodine receptors. However, the reports on the effect on mosquitoes are scarce and hence a series of novel anthranilic diamides comprising acyl thiourea substructure were synthesized and their insecticidal activities against three vector mosquito larvae namely, Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi were evaluated as per WHO protocol. Also investigated the morphological observations of treated larvae. Novel anthranilic diamides containing an acyl thiourea substructure were synthesized and structures were established by 1 H nuclear magnetic resonance (NMR), 13 C NMR, Fourier transform infrared (FTIR) and high-resolution mass spectrometry (HR-MS). Mosquito larvicidal activity of the title compounds 6-a-s revealed that compound 6-l exhibited marked larvicidal activities against C.quinquefasciatus and A.aegypti 3rd instar larvae with median lethal concentrations (LC50 ) values of 0.0044 mm and 0.0070 mm, respectively, for 48 hours of treatment. Compound 6-g exhibited larvicidal activity against An.stephensi with LC50 value of 0.0085 mm. Peculiar morphological alterations in the body of the treated larvae leading to death were observed on microscopic examination. Novel anthranilic diamides containing an acyl thiourea substructure were designed, synthesized and characterized. Their bioassay results demonstrated significant mosquito larvicidal activity with striking morphological alterations in the body, which should ensure forthcoming designs of highly active diamide derivatives as mosquito larvicides. © 2022 Society of Chemical Industry.

Water quality characteristics of breeding habitats in relation to the density of Aedes aegypti and Aedes albopictus in domestic settings in Gampaha district of Sri Lanka

In spite of the unavailability of measures to target dengue control in human populations, the promising way of combating the disease is by controlling vector mosquito larvae and their breeding habitats. Water quality characteristics of the breeding habitats of dengue vectors are among the crucial parameters that determine the female mosquito's oviposition and breeding. Therefore, a cross-sectional study was conducted to investigate the habitat characteristics of dengue vector mosquitoes by assessing the water quality of positive breeding habitats using the weighted arithmetic water quality index (WQI). The present study was conducted in domestic areas of the selected medical officer of health areas of the Gampaha district, Sri Lanka, from 2017 to 2019. Water quality characteristics of breeding habituations were measured and analyzed. The relationship between water quality parameters in breeding habitats with the occurrence of mosquito species was assessed using Kruskal-Wallis one-way analysis of variance, followed by pairwise comparison using Dunn's test and Mann-Whitney U test at a 5% level of significance. This study revealed that the temperature of Aedes mosquito breeding water ranged between 25.3 and 39.8 °C, and bred at temperatures as high as 39.8 °C in discarded receptacles. The results indicated that Ae. aegypti was prominent in alkaline water ranging between 7.5 and 8.5 pH, whereas Ae. albopictus was abundant in water with a pH range of 6.5–7.5. Both species of Aedes inhabited waters of low turbidity and TDS level. Ae. aegypti and Ae. albopictus immatures were prominent in water where TDS levels ranged between 250 and 350 ppm. The mean conductivity in the mosquito breeding water was recorded as 228.3 ± 63.9 µs/cm. The study revealed that Aedes mosquitoes could breed in water with a mean dissolved oxygen level of 6.9 ± 0.7 mg/L, ranging between 6.35 ± 1.09 mg/L and 7.28 ± 0.26 mg/L. The water quality indices were calculated for the eight previously identified breeding habitat categories of Aedes mosquitoes.

Pathogenic fungi infection attributes of malarial vectors Anopheles maculipennis and Anopheles superpictus in central Iran

BackgroundDue to the effect of synthetic and commercial insecticides on non-target organisms and the resistance of mosquitoes, non-chemical and environmentally friendly methods have become prevalent in recent years. The present study was to isolate entomopathogenic fungi with toxic effects on mosquitoes in natural larval habitats.MethodsLarvae of mosquitoes were collected from Central, Qamsar, Niasar, and Barzok Districts in Kashan County, Central Iran by standard dipping method, from April to late December 2019. Dead larvae, live larvae showing signs of infection, and larvae and pupae with a white coating of fungal mycelium on the outer surface of their bodies were isolated from the rest of the larvae and sterilized with 10% sodium hypochlorite for 2 min, then washed twice with distilled water and transferred to potato-dextrose-agar (PDA) and water-agar (WA) media and incubated at 25 ± 2 °C for 3–4 days. Larvae and fungi were identified morphologically based on identification keys.ResultsA total of 9789 larvae were collected from urban and rural areas in Kashan County. Thirteen species were identified which were recognized to belong to three genera, including Anopheles (7.89%), Culiseta (17.42%) and Culex (74.69%). A total of 105 larvae, including Anopheles superpictus sensu lato (s.l), Anopheles maculipennis s.l., Culex deserticola, Culex perexiguus, and Culiseta longiareolata were found to be infected by Nattrassia mangiferae, Aspergillus niger, Aspergillus fumigatus, Trichoderma spp., and Penicillium spp. Of these, Penicillium spp. was the most abundant fungus isolated and identified from the larval habitats, while An. superpictus s.l. was the most infected mosquito species.ConclusionsBased on the observations and results obtained of the study, isolated fungi had the potential efficacy for pathogenicity on mosquito larvae. It is suggested that their effects on mosquito larvae should be investigated in the laboratory. The most important point, however, is the proper way of exploiting these biocontrol agents to maximize their effect on reducing the population of vector mosquito larvae without any negative effect on non-target organisms.

The efficacy of Ximenia americana plant mediated silver nanoparticles against dengue vector mosquito larvae [Aedes (Stegomyia) aegypti (Linnaeus, 1762) (Diptera: Culicidae)

Nanotechnology is an emerging technology and day to day expanding its roots of knowledge to various branches of Science and fulfilling human conveniences. To manage vector populations, new tools have been emerging through nanotechnology. Nanoparticles possess peculiar toxicity mechanisms due to surface volume ratio, and this may actively contribute to their excellent larvicidal potential against Aedes aegypti mosquito. Dengue is a mosquito borne disease and making major public health issue worldwide. Aedes (Stegomyia) aegypti (Linnaeus, 1762) prefers to bread in artificial containers, and anti-larval measures with Ximenia americana L. (Olacaceae) leaf mediated silver nanoparticles (AgNPs) proves to be a potential substitute for the existing organophosphorus insecticides like temephos, malathion and fenthion etc., for mosquito control programme. Larvae were exposed to varying concentrations of plant extracts and synthesized silver nanoparticles for 24 hours. From the results, it was found that plant extracts showed moderate larvicidal effects (LC50 at 179.87 and LC90 at 376.77 ppm) but, the synthesized silver nanoparticles had found to be toxic to larvae at LC50 (0.63 ppm) and LC90 (1.20 ppm). This research highlighted that, the Ximenia americana leaf mediated AgNPs are an efficient and eco-friendly agents against Ae. aegypti mosquito, though the laboratory studies have shown the promising results, yet their efficacy in the field is to be tested for effective mosquito larval control.

Naturally Occurring Microbiota in Dengue Vector Mosquito Breeding Habitats and Their Use as Diet Organisms by Developing Larvae in the Kandy District, Sri Lanka.

Naturally occurring microbiota in mosquito larval habitats are among biotic factors which affect the population dynamics of developing larvae. Many microbiota species serve as food items for vector mosquito larvae, and food limitations within habitats adversely affect larval survival, developmental rate, adult fitness, and thereby vector competence. Therefore, identification of microbiota as associates with larvae reveals their relationship between each other as parasites, pathogens, epibionts, or diet organisms. Analysis of associated microbiota species in the dengue vector larval breeding habitats (n = 40) and the mosquito larval gut content were conducted in Kandy District in Sri Lanka. Study revealed that a total of 22 microbiota species belong to nine phyla (Amoebozoa, Bacillariophyta, Ciliophora, Chlorophyta, Sarcodina, Cyanobacteria/Cyanophyta, Euglenozoa, Ochrophyta/Heterokontophyta, and Rotifera) were encountered from different Ae. aegypti mosquito breeding habitats while 26 microbiota species that belonged to ten phyla were recorded from Ae. albopictus mosquito breeding habitats with one additional phylum Arthropoda. Considering Ae. aegypti breeding habitats, only Philodina citrina in low roof gutters existed as constant species. Considering Aedes albopictus breeding habitats, Volvox aureus in plastic containers, Lecane luna in coconut shells, Phacus pleuronectes in concrete slabs, and Pinnularia sp. in tree holes existed as constant species. The rest of the microbiota existed as common or accidental/rare species in a variety of habitat types. The Shannon-Weiner diversity (21.01 and 19.36) and gamma diversity (eight and eight) of the microbiota associated with Ae. aegypti and Ae. albopictus larvae, respectively, in ponds were found to be higher than other types of breeding habitats recorded during the study. Twelve microbiota species were recorded from larval gut analysis as food organisms of both species of mosquito larvae. However, the distribution of gut microbiota species differed between Ae. aegypti and Ae. albopictus (Chi − square = 21.294, P = 0.002). Identification of microbiota as food items of vector mosquito larvae led to a focus on larval food limitation by introducing food competitors, which could be a potential additional tool for integrated vector control approaches within the country.

Comparative study on larvicidal activity of green synthesized silver nanoparticles and Annona glabra (Annonaceae) aqueous extract to control Aedes aegypti and Aedes albopictus (Diptera: Culicidae)

The present study reports mosquito larvicidal potential of green synthesized silver nanoparticles by using Annona glabra leaves (An-AgNPs). Synthesized An-AgNPs were characterized by Ultraviolet-Visible spectroscopy (UV-VIS), Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS) technique and Fourier transform infrared spectroscopy (FTIR). Colur change from pale yellow to brick red of the plant extract and AgNO3 solution indicated the formation of An-AgNPs initially. Surface Plasmon Resonance (SPR) band at 435 nm in the UV-Vis confirmed the formation of An-AgNPs. SEM images showed that An-AgNPs were spherical in shape. FTIR proved that An-AgNPs were functionalized with biomolecules in A. glabra leaves. Based on DLS analysis the average size range of synthesized An-AgNPs was determine to be 10–100 nm and 100–1000 nm.Third instar larvae of dengue vector mosquitoes, Aedes aegypti and Aedes albopictus were subjected to larvicidal bioassays in a range of concentrations of An-AgNPs and A. glabra crude aqueous leaf extract (2–10 mg/L). An-AgNPs exhibited very high larvicidal activity against dengue vector mosquito larvae; LC50 value for Ae. aegypti at 24 h exposure to An-AgNPs (Plant extract: AgNO3 1 : 10) 5.29 mg/L; An-AgNPs (Plant extract: AgNO3 2 : 10) 2.43 mg/L while LC50 value for Ae. albopictus at 24 h exposure to An-AgNPs (Plant extract: AgNO31:10) 3.02 mg/L; An-AgNPs (Plant extract: AgNO3 2:10) 2.51 mg/L. LC50 values obtained for A. glabra leaf extract tested against Ae. aegypti and Ae. albopictus are 5.94 mg/L and 5.00 mg/L respectively at 24-hour exposure. This study further revealed that Ae. albopictus is more susceptible than to Ae. aegypti to a given concentration of An-AgNPs and to crude aqueous leaf extract of A. glabra. Larvicidal effect of An-AgNPs is superior to the crude aqueous leaf extract of A. glabra. An-AgNPs is a potent larvicide for dengue vector control.

Distinct navigation behaviors in Aedes, Anopheles and Culex mosquito larvae.

Mosquitoes spread deadly diseases that impact millions of people every year. Understanding mosquito physiology and behavior is vital for public health and disease prevention. However, many important questions remain unanswered in the field of mosquito neuroethology, particularly in our understanding of the larval stage. In this study, we investigate the innate exploration behavior of six different species of disease vector mosquito larvae. We show that these species exhibit strikingly different movement paths, corresponding to a wide range of exploration behaviors. We also investigated the response of each species to an appetitive food cue, aversive cue or neutral control. In contrast to the large differences in exploration behavior, all species appeared to gather near preferred cues through random aggregation rather than directed navigation, and exhibited slower speeds once encountering food patches. Our results identify key behavioral differences among important disease vector species, and suggest that navigation and exploration among even closely related mosquito species may be much more distinct than previously thought.

Laboratory and semi-field evaluations on lethal and residual effects of temephos and pyriproxyfen insecticides to control malaria mosquito larvae, Anopheles stephensi Liston

BackgroundThe application of insecticides against vector mosquito larvae is a crucial step to control human malaria. Insecticide resistance is a major impediment to vector control strategies. The main aim of this study was to conduct laboratory and semi-field evaluations on lethal and residual effects of temephos and pyriproxyfen insecticides against malaria mosquito larvae, Anopheles stephensi.MethodsBoth susceptibility test and residual bioassay were performed to assess the lethal concentrations of each insecticide on 50% (LC50) of the IV instars larval populations and their activity periods according to standard protocols of WHO. Nine and eleven different concentrations with two sets of control in each case were applied for temephos and pyriproxyfen, respectively. Data were analyzed using probit analysis and SPSS software.ResultsThe LC50 and LC90 for temephos and pyriproxyfen under laboratory conditions were 0.4 and 0.63, and 1.69 × 10-4 and 4.036 × 10-4 ppm, respectively. Although the field strain of An. stephensi larvae was completely susceptible to pyriproxyfen, there was noticeable resistance (8% mortality at the diagnostic dose) to temephos in Nikshahr County, Southeast Iran. This is the first report of resistance to temephos for this malaria main vector in Iran. Depending on the applied variable doses, the residual effects of temephos and pyriproxyfen under semi-field conditions lasted maximally for 3 and 10 weeks, respectively.ConclusionThe high lethal and residual effects of pyriproxyfen on mosquito larvae confer an unprecedented opportunity in vector control operations leading to elimination of malaria in Iran.

An Analysis of a Dengue Outbreak at a Large Hospital and Epidemiological Evidence for Nosocomial Dengue.

Reports on dengue outbreaks at hospitals are extremely rare. Here the authors analyze a dengue outbreak at the Teaching Hospital-Kandy (THK), Sri Lanka. Our hypothesis was that the present outbreak of dengue was due to nosocomial infections. Our objectives were to illustrate epidemiological evidence for nosocomial dengue infections among THK workers and comparison of dengue incidence of hospital workers of wards that treat dengue patients with workers of other wards, to ascertain whether most nosocomial dengue incidences occur closer to where dengue patients are treated and vector larvae were detected, and to draw the attention of the medical community to the significance of hospital outbreaks, making suggestions on how to improve dengue preventive work at the THK. We calculated weekly dengue incidences for the hospital workers and for the surrounding Kandy district population, plotted epicurves, and compared them. We also compared these with the temporal changes of numbers of patients who were admitted for other illnesses and then diagnosed with dengue and the numbers of containers with vector mosquito larvae found on hospital premises. Dengue incidence of the hospital workers for the 24-week study period (2388 per 100000 population) was significantly high when compared to incidence of the district (151 per 100000 population). Peaks of dengue incidence in hospital workers, the numbers of patients hospitalized for other illnesses contracting dengue, and numbers of containers with vector larvae occurred in the same week. The peak dengue incidence of the Kandy district happened six weeks later. There was no evidence to indicate blood contact causing dengue among hospital workers. The outbreak was controlled while dengue was rising in the district. This evidence indicates a probable nosocomial dengue outbreak. This outbreak adversely affected hospital workers, patients, and the community. We propose some measures to prevent such outbreaks.

A potent larvicidal agent against Aedes aegypti mosquito from cardanol.

Cardanol is a constituent of Cashew Nut Shell Liquid that presents larvicidal activity against Aedes aegypti. The isolation of cardanol is somewhat troublesome, however, in this work we describe an efficient and inexpensive method to obtain it as a pure material. The compound was used as starting material to make chemical transformation leading to saturated cardanol, epoxides and, halohydrins. These derivatives were tested for toxicity against Aedes aegypti larvae. The results showed that iodohydrins are very promising compounds for making commercial products to combat the vector mosquito larvae presenting a LC50 of 0.0023 ppm after 72 h of exposure.

Chitosan/Interfering RNA Nanoparticle Mediated Gene Silencing in Disease Vector Mosquito Larvae

Chitosan/Interfering RNA Nanoparticle Mediated Gene Silencing in Disease Vector Mosquito Larvae

Chitosan/interfering RNA nanoparticle mediated gene silencing in disease vector mosquito larvae.

Vector mosquitoes inflict more human suffering than any other organism-and kill more than one million people each year. The mosquito genome projects facilitated research in new facets of mosquito biology, including functional genetic studies in the primary African malaria vector Anopheles gambiae and the dengue and yellow fever vector Aedes aegypti. RNA interference- (RNAi-) mediated gene silencing has been used to target genes of interest in both of these disease vector mosquito species. Here, we describe a procedure for preparation of chitosan/interfering RNA nanoparticles that are combined with food and ingested by larvae. This technically straightforward, high-throughput, and relatively inexpensive methodology, which is compatible with long double stranded RNA (dsRNA) or small interfering RNA (siRNA) molecules, has been used for the successful knockdown of a number of different genes in A. gambiae and A. aegypti larvae. Following larval feedings, knockdown, which is verified through qRT-PCR or in situ hybridization, can persist at least through the late pupal stage. This methodology may be applicable to a wide variety of mosquito and other insect species, including agricultural pests, as well as other non-model organisms. In addition to its utility in the research laboratory, in the future, chitosan, an inexpensive, non-toxic and biodegradable polymer, could potentially be utilized in the field.

Characterization of Mosquito Breeding Sites in and in the Vicinity of Tigray Microdams

Malaria vector control in Ethiopia has a history of more than 50 years, but malaria remains a major cause of morbidity and mortality in Ethiopia. Thus, targeting the control program on the larval stage is of paramount importance. This study aimed to characterize the aquatic habitats of vector mosquito larvae associated with micro-dams. Cross-sectional larval survey was conducted on six micro-dams in Tigray, Northern Ethiopia in 2005/06. The study area on each dam was divided into eight zones. Immature stages of mosquitoes were collected using standard dippers. The physico-chemical characteristics of the aquatic habitats were measured onsite. A total of 301 aquatic habitats were surveyed for mosquito larvae; in 32.56% (n=301) only Anopheles, in 27.91% only Culex, both genera were found mixed in 21.59% and no mosquito larvae were found in 17.94%. The findings depicted that dissolved oxygen (r = 0.34, p =0.04), pH (r = 0.35, p =0.03), conductivity (r = 0.36, p =0.03), vegetation (F = 3.54, p =0.002), microhabitat (F = 2.65, p =0.04), fauna and bottom surface of the water body were positively associated and important in explaining the presence and abundance of Culex. On the other hand, dissolved oxygen (r = 0.39, p =0.02), pH (r = 0.42, p =0.008), vegetation (F = 5.6, p =0.000), water transparency (F = 2.72, p =0.00), rainfall (F = 2.22, p = 0.027) and fauna were positively associated and important in explaining the presence and abundance of Anopheles. The findings of this study suggest that both biotic (vegetation and fauna) and abiotic (chemical and physical) factors play a significant role in larvae's habitat preference in both Culex and Anopheles.

Fire fighting truck-based emergency mosquito biolarviciding to prevent outbreaks of malaria and arboviral disease in Kabul, Afghanistan

Emergency control of disease vectors requires high efficacy, rapid reaction and safe use of biocides in order interrupt transmission cycles without harming humans, non-target animals and the environment. In countries with complex emergencies, air-borne large-scale vector control is often limited, or impossible, due to questionable security as well as military, safety, equipment, or logistical constraints. While facing a potential outbreak of malaria and dengue fever in the Kabul area, Afghanistan, combined with high abundance of anopheline and Culex mosquitoes, emergency mosquito larvae control with Bacillus thuringiensis var. israelensis (Bti) and methoprene were carried out. For the first time, larvicides were applied by using a modern fire fighting truck in combination with aerial imaging of potential breeding sites. Three treatments with 0.07 g a.i. sterilized, water-dispersible granular (WDG) Bti/m2 in combination with 0.0014 g a.i. methoprene/m2, or 0.07 g a.i. Bti/m2 alone, were conducted on July 29, August 29, and September 28, 2004, and significantly reduced larval indexes of 96.5 (P < 0.0001), 96.7 (P < 0.0001), and 97.6% (P < 0.0001) against anopheline, and 98.2 (P < 0.0001), 95.6 (P < 0.0001), and 96.2% (P < 0.0001) against Culex larvae, respectively. Before the larviciding campaigns started, up to 222.4 ± 32.0 mosquitoes were captured per standardized light trap per night. During May until October 2004, the following anopheline and Culex species were abundant: A. superpictus (29.3%), A. fluviatilis (17.0%), C. pipiens (15.2%), and C. pseudovishnui (38.5%). After biolarviciding, abundance of adult mosquitoes, as measured by light trap catches 20 days post-treatment, decreased significantly in Anopheles at 81.4 (P < 0.0001), 87.1 (P < 0.0001), and 78.2% (P = 0.01), and in part significantly in Culex for 75.2 (P < 0.0001), 78.3 (P < 0.0001), and 30.8% (P = 0.463), respectively. After the treatment, mosquito-associated annoyance complaints and disease transmission decreased markedly, and not a single confirmed case of malaria or arbovirosis was reported. It is concluded that biolarviciding using a fire fighting truck as the application device is a highly successful, rapid, and cost-effective method to control vector mosquito larvae, and to reduce human exposure to mosquito-borne diseases during complex emergency situations.