Gravid Female Mosquitoes Research Articles

Effects of Xenorhabdus and Photorhabdus bacterial metabolites on the ovipositional activity of Aedes albopictus

AbstractViral diseases like yellow fever, dengue, and Zika have an alarming impact on public health. These diseases can be transmitted by Aedes mosquito species, such as Ae. albopictus, which is now found in many countries outside its original range. Xenorhabdus and Photorhabdus spp. are enteric bacterial symbionts of insect-preying nematodes and are known to produce an array of natural products with various activities including larvicidal activity. In this study, the effects of natural products produced by four Xenorhabdus and one Photorhabdus bacteria on the ovipositional behavior of Ae. albopictus mosquitoes were assessed. Utilizing a binary choice assay in insect cages, gravid female mosquitoes were presented with two oviposition cups containing water supplemented with varying concentrations of bacterial supernatants (50–1% concentrations) versus control medium. After 72 h, the eggs deposited on filter papers were counted. The oviposition attractant index (OAI) feature of the bacterial supernatant was evaluated using the number of eggs laid in the cups. Notably, all tested supernatants exhibited concentration-dependent deterrence of oviposition. Xenorhabdus cabanillasii displayed the strongest deterrent effect, inhibiting egg-laying at 50–5% concentrations (OAI: − 0.87 to − 0.35), followed by X. nematophila (50–10%, OAI: − 0.82 to − 0.52). Xenorhabdus szentirmaii, X. doucetiae, and P. kayaii showed significant deterrence at ≥ 20% concentrations. Using promoter exchange mutants generated by the easyPACId approach, fabclavine from X. szentirmaii was identified as the bioactive compound with evident deterrent effects. Such deterrents targeting egg-laying could be valuable for controlling populations by disrupting their breeding in suitable habitats.

Fish microbiota repel ovipositing mosquitoes.

The mere presence of predators causes prey organisms to display predation-avoidance strategies. Predator presence is often communicated through predator-released chemical signals. Ovipositing female mosquitoes of several species are repelled by unknown signals released from larvivorous fish. It was previously suggested that in many cases, a predator's microbiota plays an important role in the release of these signals; however, this mechanism is still poorly understood. In this study, we looked into the effects of the microbiota originating from the larvivorous Gambusia affinis (Baird and Girard) on the oviposition behaviour of gravid female mosquitoes. We used fish with altered microbiota and bacterial isolates in a set of outdoor mesocosm experiments to address this aim. We show that interference with the fish microbiota significantly reduces fish's repellent effect. We further show that the bacterium Pantoea pleuroti, isolated from the skin of the fish, repels oviposition of Culex laticinctus Edwards and Culiseta longiareolata Macquart mosquitoes similarly to the way in which live fish repel them. Our results highlight the importance of bacteria in the interspecies interactions of their hosts. Furthermore, this finding may lead to the development of an ecologically friendly mosquito repellent, that may reduce the use of larvivorous fish for mosquito control.

Current evidences of the efficacy of mosquito mass-trapping interventions to reduce Aedes aegypti and Aedes albopictus populations and Aedes-borne transmission.

Over the past decades, several viral diseases transmitted by Aedes mosquitoes-dengue, chikungunya, Zika-have spread outside of tropical areas. To limit the transmission of these viruses and preserve human health, the use of mosquito traps has been developed as a complement or alternative to other vector control techniques. The objective of this work was to perform a systematic review of the existing scientific literature to assess the efficacy of interventions based on adult mosquito trap to control Aedes population densities and the diseases they transmit worldwide. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a systematic review was conducted using the PubMed and Scopus databases. Among the 19 selected papers, lethal ovitraps were used in 16 studies, host-seeking female traps in 3 studies. Furthermore, 16 studies focused on the control of Ae. aegypti. Our review showed great heterogeneity in the indicators used to assess trap efficacy: e.g., the number of host-seeking females, the number of gravid females, the proportion of positive containers, the viral infection rate in female mosquitoes or serological studies in residents. Regardless of the type of studied traps, the results of various studies support the efficacy of mass trapping in combination with classical integrated vector control in reducing Aedes density. More studies with standardized methodology, and indicators are urgently needed to provide more accurate estimates of their efficacy. This review highlights gaps in the demonstration of the efficacy of mass trapping of mosquitoes in reducing viral transmission and disease. Thus, further large-scale cluster randomized controlled trials conducted in endemic areas and including epidemiological outcomes are needed to establish scientific evidence for the reduction of viral transmission risk by mass trapping targeting gravid and/or host-seeking female mosquitoes.

Honey-baited FTA cards in box gravid traps for the assessment of Usutu virus circulation in mosquito populations in Germany

Usutu virus (USUV) is becoming increasingly important to veterinary and human health in Germany. USUV has been implicated in mass die-off events of birds, especially of blackbirds (Turdus merula), and has experienced significant range expansion in the years since its first detection in 2010. Current detection methods rely primarily on dead bird surveillance or mass mosquito collection using CO2 as the main attractant. Dead bird surveillance can result in detection of disease circulation past the point at which control efforts would be most impactful. Vector surveillance offers the opportunity to detect disease circulation before significant outbreaks occur. However, current methods result in collections of extremely large numbers of predominantly nulliparous female mosquitoes who have not yet taken a blood meal. This study sought to test whether box gravid traps could successfully trap USUV infected gravid Culex mosquitoes, and if viral RNA could be successfully transferred and stabilised on an FTA card. During the month of August 2020, 18 Reiter-Cummings style box gravid traps with honey-baited FTA cards were set in a region of known USUV circulation around the southern border of Hesse, Germany. Four 48-hour trapping rounds were conducted. All mosquitoes and FTA cards were collected and stored during transport to the laboratory on dry ice. Samples and FTA cards were then transferred and stored in a freezer at -5 °C until identification. Identification was carried out on a chill plate before being sent with overnight courier in a styrofoam box with cooling elements for virus detection with a modified generic flavivirus RT-PCR. Mosquitoes were separated into pools by trap, date, species and feeding status. 2003 mosquitoes were caught in four rounds of trapping, 1834 or 88% of which were female Culex mosquitoes used for examination. 13 pools of mosquitoes and four FTA cards tested positive for USUV. No positive FTA cards were found in traps with positive mosquitoes and no positive mosquitoes were found in traps with positive FTA cards. Although fewer FTA cards than expected returned a positive result, this may have been a result of the extreme conditions experienced in the field and highlights the need to establish the temperature and humidity boundaries such a collection method can withstand. Box gravid traps however, provided a highly effective and targeted approach for capturing gravid female Culex mosquitoes, the most appropriate subpopulation for testing for USUV. Additionally, the simplicity and effectiveness of this trapping and surveillance method make it an attractive option for use as an early warning system, including for large scale surveillance programmes.

"Assessment of Water Preferences by Gravid Female Mosquitoes in the Selection of Oviposition Sites"

"Assessment of Water Preferences by Gravid Female Mosquitoes in the Selection of Oviposition Sites"

Small-scale field assessment against the dengue vector Aedes aegypti using the auto-dissemination approach in an urban area of Vientiane, Lao PDR.

BackgroundIn Lao PDR, dengue fever is the most important vector borne disease and vector control remains the principal method to fight against Aedes aegypti the primary transmitter mosquito species. Vector control management programs need new strategies in addition to conventional larviciding and adulticiding interventions in the country. In this study, we examined the In2Care® Mosquito Trap’s efficacy using insecticide auto-dissemination strategy. The insecticide pyriproxyfen, present in powder form inside the trap station, contaminates the body of gravid female mosquitoes visiting the traps and is later on disseminated via the mosquitoes in breeding sites surrounding the traps. We tested the attractiveness of the Traps, their efficacy to reduce the larval and adult abundance, and the impact on emergence rates. Specifically, we tested if the servicing interval of the In2Care® Mosquito Trap could be extended to 12 weeks.MethodsTwo black plastic ovitrap buckets and two BG® sentinel traps were placed in the premises of the Science campus of Vientiane Capital located in an urban area to measure weekly the larval and adult relative abundance of Aedes mosquitoes from 2017 to 2019. Twenty-five In2Care® Mosquito Traps were evenly distributed in this area and two studies of 12 weeks were implemented during January and April 2018 and, July to October 2018 (dry and rainy season, respectively). Every 2 weeks, water samples from 5 In2Care® Traps were randomly selected and tested at the laboratory with Ae. aegypti larvae to measure the larval and pupal mortality. The relative abundance of Aedes mosquitoes in the BG traps® with the presence of In2Care® Traps in 2018, was compared with the surveillance results obtained in 2017 and 2019 without In2Care® Traps. Every week, water samples from the ovitrap buckets were tested for Emergence Inhibition (EI).ResultsThe In2Care® Traps were very attractive to gravid Ae. aegypti mosquitoes specifically during the rainy seasons with 96% of the traps colonized with larvae/pupae within four weeks. The bioassays showed 100% mortality in the water samples from the traps during the twelve weeks studies showing the good efficacy over time of the pyriproxyfen without additional servicing in the 12 week period. In addition, the larvicide was successfully disseminated into the ovitrap buckets placed in the treated area where 100% of EI during all weeks of intervention was measured. There was no significant effect of the treatment on adult abundance reduction in the treated area, probably due to recolonization of adult mosquitoes surrounding the field experiment.ConclusionsThe observed potential of the In2Care® Mosquito Trap using the auto-dissemination strategy could lead to the use of this new tool in combination with conventional control methods against Dengue vectors in urban tropical areas. Large scale field trials should be implemented in Lao PDR to prove its efficacy for Public Health programs.

Functional disruption of transferrin expression alters reproductive physiology in Anopheles culicifacies.

BackgroundIron metabolism is crucial to maintain optimal physiological homeostasis of every organism and any alteration of the iron concentration (i.e. deficit or excess) can have adverse consequences. Transferrins are glycoproteins that play important role in iron transportation and have been widely characterized in vertebrates and insects, but poorly studied in blood-feeding mosquitoes.ResultsWe characterized a 2102 bp long transcript AcTrf1a with complete CDS of 1872bp, and 226bp UTR region, encoding putative transferrin homolog protein from mosquito An. culicifacies. A detailed in silico analysis predicts AcTrf1a encodes 624 amino acid (aa) long polypeptide that carries transferrin domain. AcTrf1a also showed a putative N-linked glycosylation site, a characteristic feature of most of the mammalian transferrins and certain non-blood feeding insects. Structure modelling prediction confirms the presence of an iron-binding site at the N-terminal lobe of the transferrin. Our spatial and temporal expression analysis under altered pathophysiological conditions showed that AcTrf1a is abundantly expressed in the fat-body, ovary, and its response is significantly altered (enhanced) after blood meal uptake, and exogenous bacterial challenge. Additionally, non-heme iron supplementation of FeCl3 at 1 mM concentration not only augmented the AcTrf1a transcript expression in fat-body but also enhanced the reproductive fecundity of gravid adult female mosquitoes. RNAi-mediated knockdown of AcTrf1a causes a significant reduction in fecundity, confirming the important role of transferrin in oocyte maturation.ConclusionAll together our results advocate that detailed characterization of newly identified AcTrf1a transcript may help to select it as a unique target to impair the mosquito reproductive outcome.

Rapid assessment of West Nile virus circulation in a German zoo based on honey-baited FTA cards in combination with box gravid traps

BackgroundFor over a decade, monitoring of West Nile virus (WNV) in Germany has consisted of a bird monitoring programme as well as a mosquito-based surveillance programme employing CO2-baited encephalitis vector surveillance (EVS) traps for mass trapping and screening of mosquitoes. In contrast to the EVS traps, the Reiter/Cummings type box gravid trap collects gravid female mosquitoes, which have already taken a blood meal, increasing the likelihood of being infected with pathogens. The traps can be equipped with a honey-baited Flinders Technology Associates® (FTA) card to encourage sugar feeding by the trapped mosquitoes. FTA cards contain nucleic acid preserving substances, which prevent the degradation of viral RNA in the expectorated mosquito saliva and allows for testing the card for flavivirus RNA. This study aimed to assess the suitability of the method for WNV surveillance in Germany as an alternative to previous methods, which are expensive, time-consuming, and predominantly target host-seeking populations less likely to be infected with WNV.MethodsIn the Thüringer Zoopark Erfurt, snowy owls (Nyctea scandiaca) and greater flamingos (Phoenicopterus roseus) died of WNV infections in July and August 2020. In response, five Reiter/Cummings type box gravid traps were positioned during the daytime on the 10th, 13th, and 16th of September in five different locations. The FTA cards and mosquitoes in the chamber were collected, kept in a cool chain, and further processed for virus detection using a modified generic flavivirus reverse transcription PCR.ResultsA total of 15 trappings during September collected a total of 259 female mosquitoes, 97% of which were Culex pipiens sensu lato, as well as 14 honey-baited FTA cards. Eight mosquitoes tested PCR-positive for WNV. Four FTA cards tested PCR-positive for mosquito-borne flaviviruses, two of which were confirmed as WNV, and the remaining two confirmed as Usutu virus.ConclusionThe suitability of the FTA cards in preserving viral RNA in the field and rapid turnaround time from collection to result is combined with a simple, cost-effective, and highly specific trapping method to create an arbovirus surveillance system, which circumvents many of the difficulties of previous surveillance programmes that required the analysis of mosquitoes in the laboratory.Graphical

GRAVID INFUSION WATER COMPARISON FOR COLLECTION OF THE WEST NILE VIRUS VECTOR CULEX QUINQUEFASCIATUS SAY

Gravid traps are an important tool in mosquito surveillance for the collection of gravid female mosquitoes that can be screened for arboviruses. The type of infusion water used is vital in targeting certain mosquito species, especially the West Nile vector, Culex quinquefasciatus Say. The gold standard of infusions is a whey protein mixture but is expensive and time consuming to make. The current study compared a cattail infusion to whey protein to determine if it is as effective at collecting Cx. quinquefasciatus as the current standard. If as attractive, the cattail infusion could be a more economical and less time-consuming option for use in WNV surveillance. Three sites were used to evaluate the efficacy of cattail infusion water with whey protein mixture. Each site had a trap with 100% whey protein, one with 100% cattail infusion and one with 50% cattail water infusion. All 9 traps were operated for 24 hours for seven trap nights. Collected mosquitoes were identified, speciated, and physiological stage was assessed. There was no statistically significant difference in the total number of mosquitoes, gravid female, and total number of females amongst the three types of infusions, at any of the sites for the collection of Cx. quinquefasciatus. These results demonstrate that a cattail infusion can be used as a more economical and less labor-intensive alternative to whey protein for the collection of Cx. quinquefasciatus.

DEET and other repellents are inhibitors of mosquito odorant receptors for oviposition attractants

In addition to its primary function as an insect repellent, DEET has many “off-label” properties, including a deterrent effect on the attraction of gravid female mosquitoes. DEET negatively affects oviposition sites. While deorphanizing odorant receptors (ORs) using the Xenopus oocyte recording system, we have previously observed that DEET generated outward (inhibitory) currents on ORs sensitive to oviposition attractants. Here, we systematically investigated these inhibitory currents. We recorded dose-dependent outward currents elicited by DEET and other repellents on ORs from Culex quinquefasciatus, Aedes aegypti, and Anopheles gambiae. Similar responses were observed with other plant-derived and plant-inspired compounds, including methyl jasmonate and methyl dihydrojasmolate. Inward (regular) currents elicited by skatole upon activation of CquiOR21 were modulated when this oviposition attractant was coapplied with a repellent. Compounds that generate outward currents in ORs sensitive to oviposition attractants elicited inward currents in a DEET-sensitive receptor, CquiOR136. The best ligand for this receptor, methyl dihydrojasmolate, showed repellency activity but was not as strong as DEET in our test protocol.

Comparing Effectiveness of Hay Infusion and Sugar Fermentation Solution as Ovitrap's Attractans to Aedes aegypti

Dengue Hemorrhagic Fever (DHF) is still one of the major public health problems in the world and Indonesia. There are several methods of mosquito vector control, one of them is the use of ovitrap and the addition of attractants which is a compound that may attract gravid mosquitoes to lay eggs. Some examples of attractants are hay infusion and sugar fermentation solution. This research aimed to compare effectiveness of hay infusion and sugar fermentation solution as Aedes aegypti attractants. This research type was true experimental laboratory with complete randomized design which is divided into 3 groups of ovitrap containing aquades as control, 20% hay infusion and 20% sugar fermentation solution. Ovitraps with those attractants were put into a mosquito coop containing 25 gravid female mosquitoes. Mosquito’s eggs counting was done after 2 days with 9 times repetition. The data were then analyzed using Kruskal-Wallis and Mann-Whitney test. It was found that the difference of mosquito’s eggs number in the ovitrap containing the fermentation solution of sugar and hay infusion had a significance value of 0.000 (p> 0,05). It means that hay infusion is more effective compared with sugar fermentation. Keywords : DHF, ovitrap, attractant, hay infusion, sugar fermentation solution

Mosquito oviposition deterrents.

Mosquitoes are well-known vectors of disease and threaten the health of millions of people annually. While synthetic insecticides have been relied on to combat these diseases, insecticide resistance and environmental concerns have directed attention towards novel and more targeted mosquitocides derived from botanicals. Research on the activity of botanical derivatives has focused on mosquito larvae and adults with little attention given to their potential as oviposition deterrents against gravid female mosquitoes. This review explores the influence of chemical and biological factors on deterrence and examines issues relating to environmental persistence and non-target effects. With very few discoveries of new insecticide pathways, the answer to effective mosquito control may well reside within other ancient plant-based organisms that have co-resided and evolved with this ubiquitous pest.

The State of the Art of Lethal Oviposition Trap-Based Mass Interventions for Arboviral Control.

The intensifying expansion of arboviruses highlights the need for effective invasive Aedes control. While mass-trapping interventions have long been discredited as inefficient compared to insecticide applications, increasing levels of insecticide resistance, and the development of simple affordable traps that target and kill gravid female mosquitoes, show great promise. We summarize the methodologies and outcomes of recent lethal oviposition trap-based mass interventions for suppression of urban Aedes and their associated diseases. The evidence supports the recommendation of mass deployments of oviposition traps to suppress populations of invasive Aedes, although better measures of the effects on disease control are needed. Strategies associated with successful mass-trap deployments include: (1) high coverage (>80%) of the residential areas; (2) pre-intervention and/or parallel source reduction campaigns; (3) direct involvement of community members for economic long-term sustainability; and (4) use of new-generation larger traps (Autocidal Gravid Ovitrap, AGO; Gravid Aedes Trap, GAT) to outcompete remaining water-holding containers. While to the best of our knowledge all published studies so far have been on Ae. aegypti in resource-poor or tropical settings, we propose that mass deployment of lethal oviposition traps can be used for focused cost-effective control of temperate Ae. albopictus pre-empting arboviral epidemics and increasing participation of residents in urban mosquito control.

Efficacy of neem chippings for mosquito larval control under field conditions.

BackgroundAn in depth understanding of mosquito breeding biology and factors regulating population sizes is fundamental for vector population control. This paper presents results from a survey of mosquito breeding habitats and the efficacy of neem chippings as a potential larvicide that can be integrated in mosquito control on Nyabondo Plateau in western Kenya.ResultsSix main mosquito habitat types namely artificial ponds, abandoned fish ponds, active fish ponds, open drains, temporary pools and swamps were found in Nyabondo. Early anopheline instars were mainly recovered from temporary pools, artificial ponds and abandoned fish ponds. The mosquitoes collected were Anopheles gambiae sensu lato (35%), An. coustani (46%) and Culex spp (19%). Both early and late instar larvae of anopheline and culicine mosquitoes were more abundant in the controls than in the Bti and neem treated habitats. Within treated habitats, early instar anopheline mosquitoes were recovered more from habitats provided with neem and fish compared to Bti treated habitats. All treated habitats recorded higher numbers of early instar larvae than late instars or pupae, indicating that gravid female mosquitoes still oviposited within treated habitats.ConclusionsNeem chippings are a good tool for mosquito larval source management under field conditions. However, more research needs to be done to quantify the contribution of this tool to the overall mosquito borne disease transmission.

Comparative susceptibility to permethrin of two Anopheles gambiae s.l. populations from Southern Benin, regarding mosquito sex, physiological status, and mosquito age

To investigate what kind of mosquito sample is necessary for the determination of insecticide susceptibility in malaria vectors. Larvae and pupae of Anopheles gambiae s.l. (An. gambiae) mosquitoes were collected from the breeding sites in Littoral and Oueme departments. The Centers for Disease Control and Prevention (CDC) susceptibility tests were conducted on unfed male and female mosquitoes aged 2-5 days old. CDC susceptibility tests were also conducted on unfed, blood fed and gravid female mosquitoes aged 2-5 days old. These susceptibility tests were also conducted on unfed and blood fed female mosquitoes aged 2-5 days old and 20 days old. CDC biochemical assay using synergist was also carried out to detect any increase in the activity of enzyme typically involved in insecticide metabolism. Female An. gambiae Ladji and Sekandji populations were more susceptible than the males when they were unfed and aged 2-5 days old. The mortality rates of blood fed female An. gambiae Ladji and Sekandji populations aged 2-5 days old were lower than those obtained when females were unfed. In addition, the mortality rates of gravid female An. gambiae Ladji and Sekandji populations aged 2-5 days old were lower than those obtained when they were unfed. The mortality rate obtained when female An. gambiae Sekandji populations were unfed and aged 20 days old was higher than the one obtained when these populations were unfed and aged 2-5 days old. The results obtained after effects of synergist penicillin in beeswax on F1 progeny of An. gambiae Ladji populations resistant to permethrin showed that mono-oxygenases were involved in permethrin resistant F1 progeny from Ladji. The resistance is a hereditary and dynamic phenomenon which can be due to metabolic mechanisms like overproduction of detoxifying enzymes activity. Many factors influence vector susceptibility to insecticide. Among these factors, there are mosquito sex, mosquito age, its physiological status. Therefore, it is useful to respect the World Health Organization criteria in the assessment of insecticide susceptibility tests in malaria vectors. Otherwise, susceptibility testing is conducted using unfed female mosquitoes aged 3-5 days old. Tests should also be carried out at (25±2) °C and (80±10)% relative humidity.

RNAi-based demonstration of direct link between specific odorant receptors and mosquito oviposition behavior

The Southern house mosquito, Culex quinquefasciatus – a vector of West Nile virus – is equipped with 130 odorant receptors (ORs), which enable young females to locate plants and blood-meal sources and older females to find suitable sites for oviposition. In our attempts to de-orphanize ORs expressed in female antennae, we identified CquiOR37 and CquiOR99, which were narrowly tuned to two phenolic compounds, 4-methylphenol and 4-ethylphenol. When tested in the Xenopus oocyte recording system the observed EC50s for 4-methylphenol and 4-ethylphenol were 6.4 and 18.2 μM for CquiOR37 and 14.4 and 0.74 μM for CquiOR99 (goodness of fit, R2 = 0.88–0.99), respectively. Indoor behavioral assays demonstrated that gravid female mosquitoes laid significantly more eggs in water trays spiked with these compounds than in control water trays. Field studies with gravid traps corroborated that 4-ethylphenol is active in a wide range of doses from 0.1 to 10 μg/l, as required for practical applications. A dsRNA construct based on the two genes, CquiOR37/99-dsRNA was stable in pupa hemolymph for up to 3 h. Pupae injected with CquiOR37/99-dsRNA, β-galactosidase-dsRNA or water had more than 40% survival rate at the peak of oviposition (day-9). qPCR analysis showed individual variation, but significant mean reduction in CquiOR37 and CquiOR99 transcript levels in CquiOR37/99-dsRNA-treated mosquitoes. Water-injected females and those treated with the control gene laid significantly more eggs in trays containing 4-ethylphenol than in water trays, whereas CquiOR37/99-dsRNA-treated mosquitoes laid normal number of eggs, but could not discriminate treatment from control. This study linked for the first time specific receptors for 4-ethylphenol with increased oviposition in the important vector Cx. quinquefasciatus.

Color and Container Size Affect Mosquito (Aedes triseriatus) Oviposition

This investigation compared color and artificial container size as attractants for the gravid female Aedes triseriatus (Eastern Tree-hole Mosquito) oviposition site selection. Three colors (white, green, and black) were investigated in combination with two container sizes (3672 ml and 12,000 ml). Presence of mosquito larvae was used to determine percent occupancy of containers. Black containers were selected in 70% of trials, compared to 63% for green containers and 41% for white containers. Large containers were selected more frequently (72% of trials) than small containers (44% of trials). Results suggest that container size may serve as an important selective cue for A. triseriatus and may take precedence over color when gravid female mosquitoes are given the choice. Our results provide further insight into the complexity of cues that influence mosquito oviposition behavior.

Gravitraps for Management of Dengue Clusters in Singapore

Although Singapore has an intensive dengue control program, dengue remains endemic with regular outbreaks. We report development and use of a novel adult oviposition trap, the Gravitrap, in managing dengue cluster areas. The Gravitrap is a simple, hay infusion-filled cylindrical trap with a sticky inner surface to serve as an oviposition site for gravid female Aedes mosquitoes. Wire gauze fitted above the water level minimizes the risk of it being an unwanted breeding habitat. The Gravitrap was deployed in 11 dengue cluster areas throughout Singapore. Aedes aegypti was the predominant mosquito caught in the trap and some (5.73%) were found to be positive for dengue virus.

Reconsideration of Anopheles rivulorum as a vector of Plasmodium falciparum in western Kenya: some evidence from biting time, blood preference, sporozoite positive rate, and pyrethroid resistance

BackgroundAnopheles gambiae, An. arabiensis, and An. funestus are widespread malaria vectors in Africa. Anopheles rivulorum is the next most widespread species in the An. funestus group. The role of An. rivulorum as a malaria vector has not been fully studied, although it has been found to be a minor or opportunistic transmitter of Plasmodium falciparum.MethodsMosquitoes were collected indoors over a 12-hour period using a light source attached to a rotating bottle collector in order to determine peak activity times and to provide DNA for meal source identification. Gravid female mosquitoes were collected indoors via an aspirator to generate F1 progeny for testing insecticidal susceptibility. Blood meal sources were identified using a multiplexed PCR assay for human and bovine cytochrome-B, and by matching sequences generated with primers targeting vertebrate and mammalian cytochrome-B segments to the Genbank database.ResultsAnopheles rivulorum fed on human blood in the early evening between 18:00 and 20:00, when insecticide-treated bed nets are not in use, and the presence of Plasmodium falciparum sporozoites in 0.70% of the An. rivulorum individuals tested was demonstrated. Susceptibility to permethrin, deltamethrin, and DDT is higher in An. rivulorum (84.8%, 91.4%, and 100%, respectively) than in An. funestus s.s. (36.8%, 36.4%, and 70%, respectively), whereas mortality rates for propoxur and fenitrothion were 100% for both species. Resistance to pyrethroids was very high in An. funestus s.s. and the potential of the development of high resistance was suspected in An. rivulorum.ConclusionGiven the tendency for An. rivulorum to be active early in the evening, the presence of P. falciparum in the species, and the potential for the development of pyrethroid resistance, we strongly advocate reconsideration of the latent ability of this species as an epidemiologically important malaria vector.

Effect of the Volume of Organic Infusion Used in Gravid Traps for CollectingCulex quinquefasciatus(Diptera: Culicidae)

Traps that selectively collect gravid mosquitoes have advantages over other collection methods for the purpose of disease surveillance: they trap mosquitoes with a higher probability of carrying disease as they have blood fed on at least one occasion. Gravid traps typically use infusions of organic material to attract gravid mosquitoes, particularly Culex quinquefasciatus (Say). These infusions are heavy and have an unpleasant odor, presenting logistical difficulties for disease monitoring programs. Typically, gravid traps use 4 liters of infusion. The present trial compared the responses of gravid female mosquitoes to 2 and 4 liters of infusion to see if equivalent numbers of mosquitoes could be collected using the smaller volume. In an attempt to better understand the effects of volume of infusion on mosquito oviposition behavior, egg laying on the two volumes was also monitored. There was a significant difference between the mean numbers of egg rafts laid on 2 and 4 liters of infusion. However, the mean numbers of gravid Cu. quinquefasciatus collected in gravid traps with 2 and 4 liters were not significantly different. The results indicate that 2 liters can be used instead of 4 liters for gravid trapping, significantly reducing the cost and logistical difficulties associated with such efforts. The behavioral responses of gravid females to different volumes are also discussed.