Host attraction and host feeding patterns indicate generalist feeding of Culex pipiens s.s. and Cx. torrentium

BACKGROUND

Mosquito host feeding patterns are an important factor of the species-specific vector capacity determining pathogen transmission routes. Culex pipiens s.s./Cx. torrentium are competent vectors of several arboviruses, such as West Nile virus and Usutu virus. However, studies on host feeding patterns rarely differentiate the morphologically indistinguishable females.

METHODS

We analyzed the host feeding attraction of Cx. pipiens and Cx. torrentium in host-choice studies for bird, mouse, and a human lure. In addition, we summarized published and unpublished data on host feeding patterns of field-collected specimens from Germany, Iran, and Moldova from 2012 to 2022, genetically identified as Cx. pipiens biotype pipiens, Cx. pipiens biotype molestus, Cx. pipiens hybrid biotype pipiens × molestus, and Cx. torrentium, and finally put the data in context with similar data found in a systematic literature search.

RESULTS

In the host-choice experiments, we did not find a significant attraction to bird, mouse, and human lure for Cx. pipiens pipiens and Cx. torrentium. Hosts of 992 field-collected specimens were identified for Germany, Iran, and Moldova, with the majority determined as Cx. pipiens pipiens, increasing the data available from studies known from the literature by two-thirds. All four Culex pipiens s.s./Cx. torrentium taxa had fed with significant proportions on birds, humans, and nonhuman mammals. Merged with the data from the literature from 23 different studies showing a high prevalence of blood meals from birds, more than 50% of the blood meals of Cx. pipiens s.s. were identified as birds, while up to 39% were human and nonhuman mammalian hosts. Culex torrentium fed half on birds and half on mammals. However, there were considerable geographical differences in the host feeding patterns.

CONCLUSIONS

In the light of these results, the clear characterization of the Cx. pipiens s.s./Cx. torrentium taxa as ornithophilic/-phagic or mammalophilic/-phagic needs to be reconsidered. Given their broad host ranges, all four Culex taxa could potentially serve as enzootic and bridge vectors.

Irrigation increases and stabilizes mosquito populations and increases West Nile virus incidence

Humans have greatly altered earth's terrestrial water cycle with the majority of fresh water being used for agriculture. Irrigation changes spatial and temporal water availability and alters mosquito abundance and phenology. Previous studies evaluating the effect of irrigation on mosquito abundance and mosquito-borne disease have shown inconsistent results and little is known about the effect of irrigation on variability in mosquito abundance. We examined the effect of irrigation, climate and land cover on mosquito abundance and human West Nile virus (WNV) disease cases across California. Irrigation made up nearly a third of total water inputs, and exceeded precipitation in some regions. Abundance of two key vectors of several arboviruses, including WNV, Culex tarsalis and the Culex pipiens complex, increased 17-21-fold with irrigation. Irrigation reduced seasonal variability in C. tarsalis abundance by 36.1%. Human WNV incidence increased with irrigation, which explained more than a third (34.2%) of the variation in WNV incidence among California counties. These results suggest that irrigation can increase and decouple mosquito populations from natural precipitation variability, resulting in sustained and increased disease burdens. Shifts in precipitation due to climate change are likely to result in increased irrigation in many arid regions which could increase mosquito populations and disease.

Mosquito prevalence, resting habitat preference, and Plasmodium infection status of anophelines in coastal Karnataka during the declining phase of malaria-an exploratory study

Malaria has a historical presence in the Dakshina Kannada (D.K.) and Udupi districts of Karnataka, India. To understand the potential involvement of anopheline fauna in malaria transmission, we conducted an exploratory entomological survey. The study is crucial given the decreasing malaria incidence in these districts in recent years. From September 2022 to August 2023, we collected indoor resting mosquitoes using a manual aspirator at 27 randomly chosen sites within three distinct resting habitats (human dwellings, cattle sheds, and construction sites) in the urban areas of Udupi and Dakshina Kannada districts. Mosquitoes were morphologically identified, and anopheline specimens were tested for the presence of malarial parasite by polymerase chain reaction (PCR) analysis. We collected a total of 1810 mosquitoes, comprising 21 species distributed across five genera. Culex emerged as the predominant genus, constituting 84.4% of the collected specimens, while Anopheles accounted for 5.4%. Among the observed species, Culex quinquefasciatus was predominant, comprising 77.9% of the mosquito specimens collected in this study. Two malaria vectors, An. stephensi and An. subpictus complex, constituted 16.3% and 1.0% of the total anophelines collected, respectively. None of the 96 female anophelines was tested positive for Plasmodium infection. Our findings suggest that Anopheles mosquitoes prefer resting in cattle sheds over human dwellings. While our study identified two malaria vectors, they were present at low densities. To gain a more comprehensive understanding of the dynamics of these vector mosquitoes, it is essential to conduct long-term surveillance to monitor their prevalence and role in malaria transmission.

Local environmental factors drive distributions of ecologically-contrasting mosquito species (Diptera: Culicidae)

Mosquitoes are important vectors of disease pathogens and multiple species are undergoing geographical shifts due to global changes. As such, there is a growing need for accurate distribution predictions. Ecological niche modelling (ENM) is an effective tool to assess mosquito distribution patterns and link these to underlying environmental preferences. Typically, macroclimatic variables are used as primary predictors of mosquito distributions. However, they likely undervalue local conditions and intraspecific variation in environmental preferences. This is problematic, as mosquito control takes place at the local scale. Utilising high-resolution (10 × 10 m) Maxent ENMs on the island of Bonaire as model system, we explore the influence of local environmental variables on mosquito distributions. Our results show a distinct set of environmental variables shape distribution patterns across ecologically-distinct species, with urban variables strongly associated with introduced species like Aedes aegypti and Culex quinquefasciatus, while native species show habitat preferences for either mangroves, forests, or ephemeral water habitats. These findings underscore the importance of distinct local environmental factors in shaping distributions of different mosquitoes, even on a small island. As such, these findings warrant further studies aimed at predicting high-resolution mosquito distributions, opening avenues for preventative management of vector-borne disease risks amidst ongoing global change and ecosystem degradation.

Characterization of mosquito host-biting networks of potential Rift Valley fever virus vectors in north-eastern KwaZulu-Natal province, South Africa

BACKGROUND

Rift Valley fever virus (RVFV) is a zoonotic mosquito-borne virus with serious implications for livestock health, human health, and the economy in Africa, and is suspected to be endemic in north-eastern KwaZulu-Natal (KZN), South Africa. The vectors of RVFV in this area are poorly known, although several species, such as Aedes (Neomelaniconion) mcintoshi, Aedes (Neomelaniconion) circumluteolus, Aedes (Aedimorphus) durbanensis, and Culex (Lasioconops) poicilipes may be involved. The aim of the study was to determine the vertebrate blood meal sources of potential RVFV mosquito vectors in north-eastern KZN and to characterize the host-biting network.

METHODS

Blood-fed mosquitoes were collected monthly from November 2019 to February 2023 using a backpack aspirator, CO2-baited Centers for Disease Control and Prevention (CDC) miniature light traps and tent traps, in the vicinity of water bodies and livestock farming households. The mosquitoes were morphologically identified. DNA was extracted from individual mosquitoes and used as templates to amplify the vertebrate cytochrome c oxidase I (COI) and cytochrome b (cytb) genes using conventional polymerase chain reaction (PCR). Amplicons were sequenced and queried in GenBank and the Barcode of Life Data systems to identify the vertebrate blood meal sources and confirm mosquito identifications. All mosquitoes were screened for RVFV using real time reverse transcription (RT)-PCR.

RESULTS

We identified the mammalian (88.8%) and avian (11.3%) blood meal sources from 409 blood-fed mosquitoes. Aedes circumluteolus (n = 128) made up the largest proportion of collected mosquitoes. Cattle (n = 195) and nyala (n = 61) were the most frequent domestic and wild hosts, respectively. Bipartite network analysis showed that the rural network consisted of more host-biting interactions than the reserve network. All mosquitoes tested negative for RVFV.

CONCLUSIONS

Several mosquito species, including Ae. circumluteolus, and vertebrate host species, including cattle and nyala, could play a central role in RVFV transmission. Future research in this region should focus on these species to better understand RVFV amplification.

An electropenetrography waveform library for the probing and ingestion behaviors of Culex tarsalis on human hands

Culex tarsalis Coquillett (Diptera: Culicidae) mosquitoes are capable of vectoring numerous pathogens affecting public and animal health. Unfortunately, the probing behaviors of mosquitoes are poorly understood because they occur in opaque tissues. Electropenetrography (EPG) has the potential to elucidate these behaviors by recording the electrical signals generated during probing. We used an AC-DC EPG with variable input resistors (Ri levels) to construct a waveform library for Cx. tarsalis feeding on human hands. Biological events associated with mosquito probing were used to characterize waveforms at four Ri levels and with two electrical current types. The optimal settings for EPG recordings of Cx. tarsalis probing on human hands was an Ri level of 107 Ohms using an applied signal of 150 millivolts alternating current. Waveforms for Cx. tarsalis included those previously observed and associated with probing behaviors in Aedes aegypti L. (Diptera: Culicidae): waveform families J (surface salivation), K (stylet penetration through the skin), L (types 1 and 2, search for a blood vessel/ingestion site), M (types 1 and 2, ingestion), N (type 1, an unknown behavior which may be a resting and digestion phase), and W (withdrawal). However, we also observed variations in the waveforms not described in Ae. aegypti, which we named types L3, M3, M4, and N2. This investigation enhances our understanding of mosquito probing behaviors. It also provides a new tool for the automated calculation of peak frequency. This work will facilitate future pathogen acquisition and transmission studies and help identify new pest and disease management targets.

Establishing Colonies from Field-Collected Mosquitoes: Special Accommodations for Wild Strains

A researcher may have many reasons for wanting to establish new laboratory colonies from field-collected mosquitoes. In particular, the ability to study the diversity found within and among natural populations in a controlled laboratory environment opens up a wide range of possibilities for understanding how and why burdens of vector-borne disease vary over space and time. However, field-collected mosquitoes are often more difficult to work with than established laboratory strains, and considerable logistical challenges are involved in safely transporting field-collected mosquitoes into the laboratory. Here, we provide advice for researchers working with Aedes aegypti, Anopheles gambiae, and Culex pipiens, as well as notes on other closely related species. We provide guidance on each stage of the life cycle and highlight the life stages for which it is easiest to initiate new laboratory colonies for each species. In accompanying protocols, we provide methods detailing Ae. aegypti egg collection and hatching as well as how to transport larvae and pupae from the field.

Upscaling the production of sterile male mosquitoes with an automated pupa sex sorter

Effective mosquito population suppression has been repeatedly demonstrated in field trials through the release of male mosquitoes to induce sterile mating with wild females using the incompatible insect technique (IIT), the sterile insect technique (SIT), or their combination. However, upscaling these techniques requires a highly efficient and scalable approach for the sex separation of mass-reared mosquitoes to minimize the unintentional release of females, which can lead to either population replacement or biting nuisance, a major bottleneck up to now. Here, we report the successful development of an automated mosquito pupa sex sorter that can effectively separate large numbers of males from females for population suppression of Aedes aegypti, A. albopictus, and Culex quinquefasciatus. The male production capacity of the automated sex sorter was increased by ~17-fold compared with manual sex separation with the Fay-Morlan sorter and enabled one person to separate 16 million males per week. With ~0.5% female contamination, the produced males exhibited high flight ability and mating performance. The field trial demonstrates that the quality of A. albopictus males produced using the automated sex sorter is suitable for inducing population suppression. These results indicate that the automated sex sorter offers the potential to upscale IIT and SIT against mosquito vectors for disease control.

Application of circular statistics in temporal distribution of adult mosquitoes in Qingdao, Shandong Province, China, 2021-2023

BACKGROUND

Analyses of the temporal distribution of mosquitoes are presented in statistical charts, but it is difficult to prove in statistics whether differences in peak periods exist among different years or habitats. This study aimed to investigate the application of circular statistics in determining the peak period and a comparison of differences.

METHODS

Surveillance of adult mosquitoes was conducted twice a month by light traps in five different habitats from March to November for 3 years (2021-2023) in Qingdao, Shandong Province, China. The Kruskal-Wallis test was performed to determine the differences in mosquito density among different years and habitats. Circular statistics and line charts were employed to determine the peak period and a comparison of differences.

RESULTS

Among a total of 14,834 adult mosquitoes comprising five mosquito species from four genera, Culex pipiens pallens was dominant and accounted for 89.6% of the specimens identified. Aedes albopictus, Armigeres subalbatus, and Anopheles sinensis made up 5.7%, 4.2%, and 0.5%, respectively. Culex tritaeniorhynchus accounted for less than 0.1%. The mean mosquito density (females/trap night) for the trapping period was 10.3 in 2021, 5.6 in 2022, and 3.6 in 2023. Among five habitats, the highest mosquito density was 8.9 in livestock sheds, followed by 6.8 in parks, 5.9 in rural dwellings, 5.5 in urban dwellings, and 5.4 in hospitals. No statistically significant differences were found among different years (H = 1.96, d.f. 2, P = 0.376) and habitats (H = 0.45, d.f. 4, P = 0.978). Overall, the peak period of mosquito activity fell in the months from June to September. The peak period among 3 years differed significantly (F(2,7022) = 119.17, P < 0.01), but there were no statistically significant differences in peak period among different habitats (F(4,7020) = -159.09, P > 0.05).

CONCLUSION

Circular statistics could be effectively combined with statistical charts to elucidate the peak period of mosquitoes and determine the differences in statistics among different years and habitats. These findings will provide valuable information for mosquito control and public health management.

Spatial distribution and environmental correlations of Culex pipiens pallens (Diptera: Culicidae) in Haidian district, Beijing

Culex pipiens pallens Coquillett, 1898 (Diptera: Culicidae) was the dominant health threat to mosquito species in Beijing, and it is important to unravel the spatial distribution and environmental correlations of Cx. pipiens pallens in Beijing. 3S technology methods and spatial statistics were used to clarify the distribution pattern. Subsequently, linear and spatial regression were performed to detect the environmental factors linked with the density of Cx. pipiens pallens. The same "middle peak" spatial distribution pattern was observed for Cx. pipiens pallens density at the community, subdistrict, and loop area levels in our study area. In addition, there were various correlated environmental factors at the community and subdistrict scales. At the community scale, the summary values of the Modified Normalized Difference Water Index (MNDWI) in 2 km buffer zone (MNDWI_2K) were negatively correlated, and the summary values of Normalized Difference Built-up Index (NDBI) in 800 m buffer zone (NDBI_800) was positively correlated to the Cx. pipiens pallens density. However, the summary values of Normalized Difference Vegetation Index and Nighttime Light Index significantly affected Cx. pipiens pallens density at the subdistrict scale. Our findings provide insight into the spatial distribution pattern of Cx. pipiens pallens density and its associated environmental risk factors at different spatial scales in the Haidian district of Beijing for the first time. The results could be used to predict the Cx. pipiens pallens density as well as the risk of lymphatic filariasis (LF) infection, which would help implement prevention and control measures to prevent future risks of biting and LF transmission in Beijing.

Taking it with a grain of salt: tolerance to increasing salinization in Culex pipiens (Diptera: Culicidae) across a low-lying delta

BACKGROUND

Salinity, exacerbated by rising sea levels, is a critical environmental cue affecting freshwater ecosystems. Predicting ecosystem structure in response to such changes and their implications for the geographical distribution of arthropod disease vectors requires further insights into the plasticity and adaptability of lower trophic level species in freshwater systems. Our study investigated whether populations of the mosquito Culex pipiens, typically considered sensitive to salt, have adapted due to gradual exposure.

METHODS

Mesocosm experiments were conducted to evaluate responses in life history traits to increasing levels of salinity in three populations along a gradient perpendicular to the North Sea coast. Salt concentrations up to the brackish-marine transition zone (8 g/l chloride) were used, upon which no survival was expected. To determine how this process affects oviposition, a colonization experiment was performed by exposing the coastal population to the same concentrations.

RESULTS

While concentrations up to the currently described median lethal dose (LD50) (4 g/l) were surprisingly favored during egg laying, even the treatment with the highest salt concentration was incidentally colonized. Differences in development rates among populations were observed, but the influence of salinity was evident only at 4 g/l and higher, resulting in only a 1-day delay. Mortality rates were lower than expected, reaching only 20% for coastal and inland populations and 41% for the intermediate population at the highest salinity. Sex ratios remained unaffected across the tested range.

CONCLUSIONS

The high tolerance to salinity for all key life history parameters across populations suggests that Cx. pipiens is unlikely to shift its distribution in the foreseeable future, with potential implications for the disease risk of associated pathogens.

Effect of textile colour on vector mosquito host selection: a simulated field study in Mali, West Africa

BACKGROUND

The effect of clothing colour on the biting rates of different vector mosquito species is not well understood. Studies under tropical field conditions are lacking. This study aimed to determine the influence of clothing colours on mosquito biting rates in rural and suburban settings in West Africa.

METHODS

We performed a simulated field study in a suburban and a rural site in Mali using Mosquito-Magnet traps utilizing CO2 and other attractants, which were covered with black, white, and black/white striped textile sheets covers. These targets operated continuously for 10 consecutive days with bright nights (around full moon) and 10 consecutive days with dark nights (around new moon). Trapped mosquitoes were collected and catch rates counted hourly. Mosquitoes were morphologically identified to the species complex level (Anopheles gambiae s.l. and Culex pipiens s.l.) or species level (Aedes aegypti). A subset of Anopheles specimens were further identified by molecular methods.

RESULTS

Under bright-night conditions, An. gambiae s.l. was significantly more attracted to black targets than to white and striped targets; during dark nights, no target preference was noted. During bright nights, Cx. pipiens s.l. was significantly more attracted to black and striped targets than to white targets; a similar trend was noted during dark nights (not significant). For day-active Ae. aegypti, striped targets were more attractive than the other targets and black were more attractive than white targets.

CONCLUSIONS

The study firstly demonstrated that under field conditions in Mali, West Africa, mosquito catch rates were influenced by different clothing colours, depending on mosquito species and light conditions. Overall, light colours were least attractive to host-seeking mosquitoes. Using white or other light-coloured clothing can potentially reduce bite exposure and risk of disease transmission in endemic tropical regions.

Interindividual variation among Culex pipiens larvae in terms of thermal response

This study aims to determine the phenological characteristics of thermal responses in the larvae of a Culex pipiens complex field population at the individual level under the influence of thermal regime of its habitat. The analysis is based on a structured population model quantifying the thermal responses of development time and survival under variable conditions and characterising the variety between the larvae (interindividual variety). During the study performed in Turkish Thrace on a monthly basis between May 2021 and June 2022, a total of 3744 larvae were reared as peer larval cohorts and 2330 larvae as siblings in artificial containers to be fully exposed to the natural thermal condition that was recorded hourly. The development process of larvae was monitored daily from egg to adult. As a result, a total of 4788 adult mosquitoes emerged, with a development period ranging from 8 to 52 days in the females and 7 to 50 days in the males, and the survival rate was found to range from 0% to 100%. Both parameters varied by month and individuals, and the variations manifested itself, particularly in the colder periods. The results indicate that the variation between the individuals in terms of thermal response in the larvae of C. pipiens, along with the thermal acclimation ability, appears to be fate determinant in resisting fluctuating thermal regimes, surviving in concurrent climate change and adapting to new conditions with modifications in the seasonal phenology, such as maintaining reproductive dynamics throughout the winter thanks to global warming.

Broadscale spatial synchrony in a West Nile virus mosquito vector across multiple timescales

Insects often exhibit irruptive population dynamics determined by environmental conditions. We examine if populations of the Culex tarsalis mosquito, a West Nile virus (WNV) vector, fluctuate synchronously over broad spatial extents and multiple timescales and whether climate drives synchrony in Cx. tarsalis, especially at annual timescales, due to the synchronous influence of temperature, precipitation, and/or humidity. We leveraged mosquito collections across 9 National Ecological Observatory Network (NEON) sites distributed in the interior West and Great Plains region USA over a 45-month period, and associated gridMET climate data. We utilized wavelet phasor mean fields and wavelet linear models to quantify spatial synchrony for mosquitoes and climate and to calculate the importance of climate in explaining Cx. tarsalis synchrony. We also tested whether the strength of spatial synchrony may vary directionally across years. We found significant annual synchrony in Cx. tarsalis, and short-term synchrony during a single period in 2018. Mean minimum temperature was a significant predictor of annual Cx. tarsalis spatial synchrony, and we found a marginally significant decrease in annual Cx. tarsalis synchrony. Significant Cx. tarsalis synchrony during 2018 coincided with an anomalous increase in precipitation. This work provides a valuable step toward understanding broadscale synchrony in a WNV vector.

Exposure to Zika and chikungunya viruses impacts aspects of the vectorial capacity of Aedes aegypti and Culex quinquefasciatus

Zika (ZIKV) and chikungunya (CHIKV) are arboviruses that cause infections in humans and can cause clinical complications, representing a worldwide public health problem. Aedes aegypti is the primary vector of these pathogens and Culex quinquefasciatus may be a potential ZIKV vector. This study aimed to evaluate fecundity, fertility, survival, longevity, and blood feeding activity in Ae. aegypti after exposure to ZIKV and CHIKV and, in Cx. quinquefasciatus exposed to ZIKV. Three colonies were evaluated: AeCamp (Ae. aegypti-field), RecL (Ae. aegypti-laboratory) and CqSLab (Cx. quinquefasciatus-laboratory). Seven to 10 days-old females from these colonies were exposed to artificial blood feeding with CHIKV or ZIKV. CHIKV caused reduction in fecundity and fertility in AeCamp and reduction in survival and fertility in RecL. ZIKV impacted survival in RecL, fertility in AeCamp and, fecundity and fertility in CqSLab. Both viruses had no effect on blood feeding activity. These results show that CHIKV produces a higher biological cost in Ae. aegypti, compared to ZIKV, and ZIKV differently alters the biological performance in colonies of Ae. aegypti and Cx. quinquefasciatus. These results provide a better understanding over the processes of virus-vector interaction and can shed light on the complexity of arbovirus transmission.

Evaluation of the vector competence for Batai virus of native Culex and exotic Aedes species in Central Europe

BACKGROUND

Batai virus (BATV) is a zoonotic arbovirus of veterinary importance. A high seroprevalence in cows, sheep and goats and infection in different mosquito species has been observed in Central Europe. Therefore, we studied indigenous as well as exotic species of the genera Culex and Aedes for BATV vector competence at different fluctuating temperature profiles.

METHODS

Field caught Culex pipiens biotype pipiens, Culex torrentium, Aedes albopictus and Aedes japonicus japonicus from Germany and Aedes aegypti laboratory colony were infected with BATV strain 53.3 using artificial blood meals. Engorged mosquitoes were kept under four (Culex species) or three (Aedes species) fluctuating temperature profiles (18 ± 5 °C, 21 ± 5 °C, 24 ± 5 °C, 27 ± 5 °C) at a humidity of 70% and a dark/light rhythm of 12:12 for 14 days. Transmission was measured by testing the saliva obtained by forced salivation assay for viable BATV particles. Infection rates were analysed by testing whole mosquitoes for BATV RNA by quantitative reverse transcription PCR.

RESULTS

No transmission was detected for Ae. aegypti, Ae. albopictus or Ae. japonicus japonicus. Infection was observed for Cx. p. pipiens, but only in the three conditions with the highest temperatures (21 ± 5 °C, 24 ± 5 °C, 27 ± 5 °C). In Cx. torrentium infection was measured at all tested temperatures with higher infection rates compared with Cx. p. pipiens. Transmission was only detected for Cx. torrentium exclusively at the highest temperature of 27 ± 5 °C.

CONCLUSIONS

Within the tested mosquito species, only Cx. torrentium seems to be able to transmit BATV if the climatic conditions are feasible.

Vector competence of Swedish Culex pipiens mosquitoes for Japanese encephalitis virus

BACKGROUND

Japanese encephalitis virus (JEV) is an emerging mosquito-borne Orthoflavivirus that poses a significant public health risk in many temperate and tropical regions in Asia. Since the climate in some endemic countries is similar to temperate climates observed in Europe, understanding the role of specific mosquito species in the transmission of JEV is essential for predicting and effectively controlling the potential for the introduction and establishment of JEV in Europe.

METHODS

This study aimed to investigate the vector competence of colonized Culex pipiens biotype molestus mosquitoes for JEV. The mosquitoes were initially collected from the field in southern Sweden. The mosquitoes were offered a blood meal containing the Nakayama strain of JEV (genotype III), and infection rates, dissemination rates, and transmission rates were evaluated at 14, 21, and 28 days post-feeding.

RESULTS

The study revealed that colonized Swedish Cx. pipiens are susceptible to JEV infection, with a stable infection rate of around 10% at all timepoints. However, the virus was only detected in the legs of one mosquito at 21 days post-feeding, and no mosquito saliva contained JEV.

CONCLUSIONS

Overall, this research shows that Swedish Cx. pipiens can become infected with JEV, and emphasizes the importance of further understanding of the thresholds and barriers for JEV dissemination in mosquitoes.

Evaluating the carnivorous efficacy of Utricularia aurea (Lamiales: Lentibulariaceae) on the larval stages of Anopheles stephensi, Culex quinquefasciatus, and Aedes aegypti (Diptera: Culicidae)

The emergence of insecticide resistance in mosquitoes necessitates the exploration and validation of sustainable biological strategies for controlling mosquitoes in their natural habitats. We assessed the predatory effect of Utricularia aurea Lour (Lamiales: Lentibulariaceae), an aquatic carnivorous plant found in the Indian subcontinent, Japan, and Australia, on 4 instars of Anopheles stephensi Liston, Culex quinquefasciatus Say, and Aedes aegypti Linn (Diptera: Culicidae), in the laboratory and field settings. In the laboratory setting, predation of larvae by U. aurea was highest during the first hour when it predated 45%, 61%, and 58% of first instars of An. stephensi, Cx. quinquefasciatus, and, Ae. aegypti, respectively, and, within 12 h, U. aurea preyed upon ~95% of the first, second, and third instars of the 3 mosquito species, ~80% of the fourth instars of An. stephensi and Ae. aegypti, and ~60% of fourth instars of Cx. quinquefasciatus. The predatory effect of U. aurea varied with mosquito species and instar. Broadly, predation risk declined with the increase of the instar size. In the field setting, at the end of 16 days, U. aurea predated 76% and 71% of the immature An. stephensi and Ae. aegypti, respectively. Our findings suggest U. aurea can be utilized as a potential biocontrol agent for controlling mosquito larvae in natural habitats; however, the current claim warrants additional investigations in a variety of natural habitats.

Vegetation structure drives mosquito community composition in UK's largest managed lowland wetland

PURPOSE

The rising burden of mosquito-borne diseases in Europe extends beyond urban areas, encompassing rural and semi-urban regions near managed and natural wetlands evidenced by recent outbreaks of Usutu and West Nile viruses. While wetland management policies focus on biodiversity and ecosystem services, few studies explore the impact on mosquito vectors.

METHODS

Our research addresses this gap, examining juvenile mosquito and aquatic predator communities in 67 ditch sites within a South England coastal marsh subjected to different wetland management tiers. Using joint distribution models, we analyse how mosquito communities respond to abiotic and biotic factors influenced by wetland management.

RESULTS

Of the 12 mosquito species identified, Culiseta annulata (Usutu virus vector) and Culex pipiens (Usutu and West Nile virus vector) constitute 47% of 6825 larval mosquitoes. Abundant predators include Coleoptera (water beetles) adults, Corixidae (water boatmen) and Zygoptera (Damselfy) larvae. Models reveal that tier 3 management sites (higher winter water levels, lower agricultural intensity) associated with shade and less floating vegetation are preferred by specific mosquito species. All mosquito species except Anopheles maculipennis s.l., are negatively impacted by potential predators. Culiseta annulata shows positive associations with shaded and turbid water, contrary to preferences of Corixidae predators.

CONCLUSIONS

Tier 3 areas managed for biodiversity, characterised by higher seasonal water levels and reduced livestock grazing intensity, provide favourable habitats for key mosquito species that are known vectors of arboviruses, such as Usutu and West Nile. Our findings emphasise the impact of biodiversity-focused wetland management, altering mosquito breeding site vegetation to enhance vector suitability. Further exploration of these trade-offs is crucial for comprehending the broader implications of wetland management.

Genetic and behavioral differences between above and below ground Culex pipiens bioforms

Efficiency of mosquito-borne disease transmission is dependent upon both the preference and fidelity of mosquitoes as they seek the blood of vertebrate hosts. While mosquitoes select their blood hosts through multi-modal integration of sensory cues, host-seeking is primarily an odor-guided behavior. Differences in mosquito responses to hosts and their odors have been demonstrated to have a genetic component, but the underlying genomic architecture of these responses has yet to be fully resolved. Here, we provide the first characterization of the genomic architecture of host preference in the polymorphic mosquito species, Culex pipiens. The species exists as two morphologically identical bioforms, each with distinct avian and mammalian host preferences. Cx. pipiens females with empirically measured host responses were prepared into reduced representation DNA libraries and sequenced to identify genomic regions associated with host preference. Multiple genomic regions associated with host preference were identified on all 3 Culex chromosomes, and these genomic regions contained clusters of chemosensory genes, as expected based on work in Anopheles gambiae complex mosquitoes and in Aedes aegypti. One odorant receptor and one odorant binding protein gene showed one-to-one orthologous relationships to differentially expressed genes in A. gambiae complex members with divergent host preferences. Overall, our work identifies a distinct set of odorant receptors and odorant binding proteins that may enable Cx. pipiens females to distinguish between their vertebrate blood host species, and opens avenues for future functional studies that could measure the unique contributions of each gene to host preference phenotypes.

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.

Bamboo stumps that are artificially in use put pressure on dengue and chikungunya vector control in Dhaka city, Bangladesh

BACKGROUND OBJECTIVES

Aedes aegypti and Ae. albopictus mosquitoes breed in natural and artificial containers, and they transmit dengue and chikungunya. A study was conducted to identify the contribution of bamboo stumps to these disease vectors that were used in the flower garden as pillars to hold the bamboo flex fence.

METHODS

Two sizes of whole bamboo were used to hold fences around gardens at Dhaka University, Bangladesh, and were painted red and green. Mosquito larvae and pupae were collected from bamboo stumps between July and August, and vectors were identified up to the species level. The data were analyzed using the STATA/MP 14.2 version.

RESULTS

83.5% and 0.2% were Ae. albopictus and Ae. aegypti, respectively, and the remaining were Culex and Ar-migeres species. Ae. albopictus, Ae. aegypti, and both species-positive bamboo stumps were 46.9, 0.7, and 47.1%, respectively. 54.5% of the bamboo stumps had at least one mosquito species. The average stump depth for Aedes positive stumps (mean=11.7 cm, SE = 0.5) was significantly (p <0.001) higher than the Aedes negative stumps (mean = 9.5 cm, SE = 0.4). 53.8% and 38.0% stumps were found Aedes positive on the ground and upper sides of fences, respectively, and found significant (p<0.01) differences between both sides. A zero-inflated negative binomial count model is significant at a 5% level of significance, χ2(4) = 11.8, p = 0.019 (<0.05) for Ae. albopictus. Stump depth is found to have a significant positive effect on the number of Aedes-positive stumps.

INTERPRETATION CONCLUSION

Artificially used natural containers are adding pressure to current mosquito control activities as mosquitoes are breeding on them, which needs additional attention.

Entomological assessment in 'hotspots' of four lymphatic filariasis endemic districts, Central Nepal during post-MDA surveillance

BACKGROUND OBJECTIVES

Annual mass drug administration (MDA) is the main strategy to interrupt the transmission of lymphatic filariasis (LF) in the community. The main aim of monitoring the MDA program, for its effectiveness and interruption of LF is the post-MDA surveillance using antigen survey in children born after MDA. The latest technique of new research suggests that xenomonitoring is an effective tool for monitoring LF intervention. The objective of this study was to assess the W. bancrofti infection/or infectivity in vector mosquitoes by xenomonitoring during post-MDA surveillance.

METHODS

A descriptive cross-sectional study was conducted in the hotspots of selected four districts of Central Nepal. A gravid trap technique was used for sampling mosquitoes. Infection/or infectivity was determined via the dissection of vector mosquitoes. Anopheles, Aedes, Armigerus and Culex species were collected from hotspots of four endemic districts, two from the hilly region (Lalitpur and Dhading) and two from Terai region (Bara and Mahottari) of Central Nepal.

RESULTS

A total of 4450 mosquitoes belonging to four genera, Anopheles, Culex, Armigeres, and Aedes were collected from four hotspots. The distribution of Culex quinquefasciatus was found to be the highest, 88.9% (n=3955/4450) followed by Cx. vishnui (4.5%), Armigeres sp (5.8%), An. culicifascies (0.2%), Aedes spp (0.8%). The proportion of female mosquitoes trapped is significantly higher. A total of 3344 parous Cx. quinquefasciatus mosquitoes were dissected for any larval stage of W. bancrofti. We could not find any filarial infection in dissected mosquito samples.

INTERPRETATION CONCLUSION

We conclude that the gravid trap is an efficient tool for the collection of gravid Cx. quinquefasciatus mosquitoes for xenomonitoring studies of filariasis endemic regions. Vector composition indicated a maximum number of vector mosquitoes of lymphatic filariasis were trapped compared with the other three species. Distribution and density of Cx. quinquefasciatus was found highest in four hotspots of endemic districts. None of the Cx. quinquefasciatus dissected were found to be infected by larval forms of filaria. Since the low levels of infection persistence in the human population in these hot spots, vector infection and infectivity can't be ignored. Microscopic xenomonitoring at a low level of infection persistent is less likely to be efficient so molecular xenomonitoring along with a large sample should be required in each of the hot spots of the districts. Additionally, area is receptive so further vector control intervention should be required to reduce the risk of resurgence of infection.

Predators as biocontrol agents of mosquito larvae in small and large habitats in Chiang Mai, Thailand

Controlling mosquito-borne disease is a major global challenge due to the rise of insecticide-resistant mosquitoes. In response, we conducted a study in Chiang Mai Province, Thailand, which is one of the largest and the most popular cities for tourists in Southeast Asia, to explore the potential of local species as biological control agents for mosquito larvae. Mosquito larvae and aquatic predators were sampled from large and small habitats, while relevant physico-chemical parameters were measured. The study identified 560 predators and 1,572 mosquitoes, with most mosquito species belonging to the genus Culex. Additionally, the study identified 16 predator taxa, including four fish taxa and 12 taxa of predatory aquatic insects belonging to four orders: Coleoptera, Hemiptera, Odonata, and Diptera. The study found that several locally occurring predator species, namely Poecillia, Laccophilus, Lutzia, Toxorhynchites splendens, Agrionoptera, and Pseudarion, shared habitats with mosquitoes, indicating their potential as effective biological control agents for mosquito control. Conductivity, dissolved oxygen, and pH were the important physico-chemical parameters that affect both predators and mosquito larvae. Consequently, promoting native predators and reducing mosquito larvae through habitat management would be a sustainable and ecologically friendly approach in large habitats where it is not possible to remove mosquito oviposition sites. In smaller habitats, releasing local aquatic predators and removing oviposition sites may be a suitable strategy.

Suppression of the gene encoding PDZ domain-containing protein decreases cold tolerance and overwintering survival of the mosquito, Culex pipiens (Culicidae: Diptera)

In diapausing mosquitoes, cold tolerance and prolonged lifespan are important features that are crucial for overwintering success. In the mosquito Culex pipiens, we suggest that PDZ domain-containing protein (PDZ) (post synaptic density protein [PSD95], drosophila disc large tumor suppressor [Dlg1], and zonula occludens-1 protein [zo-1]) domain-containing protein is involved with these diapause features for overwintering survival in Culex mosquitoes. The expression level of pdz was significantly higher in diapausing adult females in the early stage in comparison to their nondiapausing counterparts. Suppression of the gene that encodes PDZ by RNA interference significantly decreased actin accumulation in the midgut of early-stage adult diapausing females. Inhibition of pdz also significantly reduced the survivability of diapausing females which indicates that this protein could play a key role in preserving the midgut tissues during early diapause.