Midgut microbial community of Culex quinquefasciatus mosquito populations from India

Isolation and identification of bacteria from the invasive pest Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) and evaluation of their biocontrol potential

As an alternative to chemical insecticides, gut bacteria of insects could be used to control insect pests. In this study, bacteria associated with Tuta absoluta, an invasive species that has developed resistance to chemical insecticides, were isolated, and their potential for pest control was investigated. We isolated 13 bacteria from larvae of the pest and identified the isolates on the basis of their morphological, physiological, biochemical, and molecular characteristics as Bacillus thuringiensis (Ta1-8), Staphylococcus petrasii (Ta9), Citrobacter freundii (Ta10), Chishuiella changwenlii (Ta11), Enterococcus casseliflavus (Ta12), and Pseudomonas tremae (Ta13). A laboratory screening test at 109 cfu/ml showed that B. thuringiensis (Bt) isolates caused more than 90% mortality after 3 days. Among the isolates, Bt-Ta1 showed the highest mortality in a short time. The LC50 and LC90 values for Bt-Ta1 were estimated to be 1.2 × 106 and 2 × 109 cfu/ml, respectively. Detailed characterization of Bt-Ta1 revealed that it is one of the serotypes effective on lepidopterans and contains the genes cry1Aa, cry2Aa, and vip3Aa, which encode lepidopteran toxic proteins. Bt-Ta1 isolate has been shown to have the potential to be used in the integrated management of Tuta absoluta.

Effects of seasonality and developed land cover on Culex mosquito abundance and microbiome diversity

The vectorial capacity of mosquitoes, which influences the dynamics of vector-borne disease transmission, is intricately linked to mosquito abundance and the composition and diversity of their associated microbiomes. However, the influence of environmental factors on mosquito populations and microbiome diversity remains underexplored. Here we examined the effects of seasonality and developed land cover on Culex mosquito abundance and bacterial diversity. Biweekly field sampling of female Culex mosquitoes was conducted using gravid and CDC light traps, spanning summer to autumn across varying developed land cover levels in two urban areas in Central Illinois. Mosquito abundance was assessed by the number of mosquitoes captured per trap night and compared across seasons and developed levels. The mean mosquito abundance for gravid and light traps was 12.96 ± 2.15 and 7.67 ± 1.44, respectively. Notably, higher levels of developed land cover exhibited higher Culex abundance than the low level for light traps, but no significant difference was found between summer and early autumn. In gravid traps, no significant differences were detected across seasons or developed levels. Microbial analysis of the mosquito microbiome revealed that Proteobacteria and Wolbachia, with a mean relative abundance of 80.77 and 52.66% respectively, were identified as the most dominant bacterial phylum and genus. Their relative abundance remained consistent across seasons and developed land cover levels, with negligible variations. Alpha diversity, as measured by observed species, Chao1, Shannon, and Simpson, showed slightly higher values in early-autumn compared to late-summer. A notable pattern of bacterial diversity, as indicated by all four diversity indexes, is evident across varying levels of land development. Significantly, high or intermediate developed levels consistently showed reduced alpha diversity when compared to the lower level. This underscores the pronounced impact of anthropogenic ecological disturbances in shaping mosquito microbiomes. Beta diversity analysis revealed no significant dissimilarities in bacterial community composition across seasons and developed levels, although some separation was noted among different levels of developed land cover. These findings highlight the significant role of environmental factors in shaping mosquito abundance and their associated microbiomes, with potential implications for the vectorial capacity in the transmission of vector-borne diseases.

Erwiniaceae bacteria play defensive and nutritional roles in two widespread ambrosia beetles

Ambrosia beetles are fungal-growing insects excavating galleries deep inside the wood. Their success as invaders increased scientific interest towards them. However, most studies on their microbiota targeted their fungal associates whereas the role of bacterial associates is understudied. To explore the role of abundant microbial associates, we isolated bacteria from active galleries of two widespread ambrosia beetles, Xylosandrus crassiusculus and X. germanus. These isolates were classified within the Erwiniaceae family and through a phylogenetic analysis including isolates from other insects we showed that they clustered with isolates obtained from ambrosia and bark beetles, including Erwinia typographi. The whole genome analysis of the isolate from active galleries of X. crassiusculus suggested that this bacterium plays both a nutritional role, by providing essential amino acids and enzymes for the hydrolysis of plant biomass, and a defensive role, by producing antibiotics. This defensive role was also tested in vitro against fungi, including mutualists, common associates, and parasites. The bacteria inhibited the growth of some of the common associates and parasites but did not affect mutualists. Our study supported the hypothesis of a mutualist role of Erwiniaceae bacteria in ambrosia beetles and highlighed the importance of bacteria in maintaining the symbiosis of their host with nutritional fungi.

Odour-mediated oviposition site selection in Aedes aegypti depends on aquatic stage and density

BACKGROUND

Olfaction plays an important role in the selection and assessment of oviposition sites by mosquitoes. Volatile organic compounds (VOCs) associated with potential breeding sites affect the behaviour of gravid mosquitoes, with VOCs from aquatic stages of conspecific mosquitoes influencing and regulating oviposition. The purpose of this study was to conduct a systematic analysis of the behavioural response of gravid Aedes aegypti to conspecific aquatic stage-conditioned water, to identify the associated bioactive VOCs and to determine how blends of these VOCs regulate oviposition site selection and stimulate egg-laying.

METHODS

Using a multi-choice olfactory oviposition assay, controlling for other sensory modalities, the responses of individual females to water conditioned with different densities of conspecific aquatic stages were assessed. The conditioned water samples from the most preferred density of each aquatic stage were subsequently compared to each other using the same oviposition assay and analysed using an analysis of variance (ANOVA) followed by a Tukey post-hoc test. Using combined gas chromatography and electroantennographic detection or mass spectrometry, bioactive VOCs from the preferred density of each aquatic stage were identified. Synthetic blends were prepared based on the identified ratios of bioactive VOCs in the aquatic stages, and then tested to determine the oviposition choice of Ae. aegypti in a dose-dependent manner, against a solvent control, using a dual-choice assay. This dataset was analysed using nominal logistic regression followed by an odds ratio comparison.

RESULTS

Gravid Ae. aegypti responded stage- and density-dependently to water conditioned with eggs, second- and fourth-instar larvae, and pupal exuviae, but not to water conditioned with pupae alone. Multi-choice assays demonstrated that gravid mosquitoes preferred to oviposit in water conditioned with fourth-instar larvae, over the other aquatic stage-conditioned water. Gravid Ae. aegypti were attracted, and generally stimulated, to oviposit in a dose-dependent manner to the individual identified synthetic odour blends for the different aquatic stages.

CONCLUSIONS

Intraspecific VOCs regulate oviposition site selection in Ae. aegypti in a stage- and density-dependent manner. We discuss the need for further studies to evaluate the identified synthetic blends to modulate the odour-mediated oviposition of Ae. aegypti under field conditions.

Bacterial Communities Associated with Houseflies (Musca domestica L.) Inhabiting Hospices in South Africa

Houseflies are alleged reservoirs as well as vectors of human and animal pathogens, including bacteria, because they frequently have contact with animal excreta and decaying organic substances. The rapid adaptation process of ingested microbes in the insect gut may involve gene transfer, including antibiotic resistance determinants among different bacterial strains. Six hundred and fifty-seven (n = 657) houseflies were collected from hospices and were identified morphologically and genetically using the 16S rRNA, CO1, and ITS2 barcoding genes. This study also characterized the bacterial communities harboured by the captured houseflies using 16S rRNA metabarcoding on the next-generation sequencing (NGS) platform and further sought to detect antibiotic resistance traits by using gene-specific PCR assays. Generated sequences for the targeted gene fragments matched with Musca domestica and all the sequences were deposited to the GenBank database. The 16S rRNA metabarcoding analysis revealed that the most abundant phyla detected with variable abundance observed among all the houseflies were Proteobacteria, followed by Firmicutes, and Bacteroidetes. Furthermore, the NGS data revealed the presence of multiple bacterial genera, including Providencia, Enterobacter, Dysgonomonas, Escherichia-Shigella, Klebsiella, Pseudomonas, and Streptococcus, which are known to harbour potentially pathogenic species of animals and humans. Antibiotic resistance genes detected from the housefly DNA in this study included ermB, tetA, blaSHV, and blaTEM. Moreover, these genes are associated with resistance to erythromycin, tetracycline, and beta-lactams antibiotics, respectively. The presence of bacterial pathogens and the detection of antibiotic resistance genes from the houseflies collected from the hospices indicates the possible health risk to patients in hospices and the surrounding community. Therefore, it is imperative to keep high standards of hygiene, food preparation, safety, and control of houseflies in hospices.

Odor-mediated response of gravid Aedes aegypti to mosquito-associated symbiotic bacteria

Complex oviposition decisions allow gravid Aedes aegypti mosquitoes to select suitable sites for egg-laying to increase the probability that their progeny will thrive. The bacterial communities present in larval niches influence mosquito oviposition behavior, and gravid mosquitoes transmit key microbial associates to breeding sites during oviposition. Our study evaluated whether symbiotic Klebsiella sp., which are strongly associated with mosquitoes, emit volatiles that affect mosquito oviposition decisions. Dual-choice behavioral assays demonstrated that volatile organic compounds emitted by Klebsiella sp. induce a preference in oviposition decisions by Ae. aegypti. Bacterial headspace volatiles were sampled by solid-phase microextraction, and subsequent combined gas chromatography and electroantennogram detection analysis, revealed that the antennae of gravid females detect two compounds present in the Klebsiella sp. headspace. These compounds were identified by gas chromatography and mass spectrometry as 2-ethyl hexanol and 2,4-di‑tert-butylphenol. The binary blend of these compounds elicited a dose-dependent egg-laying preference by gravid mosquitoes. We propose that bacterial symbionts, which are associated with gravid mosquitoes and may be transferred to aquatic habitats during egg-laying, together with their volatiles act as oviposition cues indicating the suitability of active breeding sites to conspecific females.

Midguts of Culex pipiens L. (Diptera: Culicidae) as a potential source of raw milk contamination with pathogens

Despite their importance, only few studies focused on the mosquitoes borne microbial diseases, especially bacterial and fungal diseases, their vectorial capacity toward microorganisms, and their important role in raw milk contamination with pathogens in some unsanitary dairy farms. In Egypt, where Culex pipiens is the historical main vector of lymphatic filariasis, only few studies discussed the isolation of pathogens from the midguts of different stages of C. pipiens. This study aims to isolate and identify the pathogenic symbiotic microorganisms inside the midgut of adult female C. pipiens as well as investigate its ability to transmit their midgut pathogens to raw milk. A total of 750 field strain C. pipiens larvae of the second and third larval instars were collected from ponds water around the livestock farms in Mariotteya, Giza, Egypt, for microbial pathogen isolation and identification. All collected larval instars were transported to the laboratory at the Research and Training Center on Vectors of Diseases (RTC), Ain Shams University, where they were maintained for further studies. Six groups of C. pipiens were tested for the incidence of various pathogenic microorganisms in their midguts and their possibility to contaminate commercial sterilized milk. Traditional PCR assays and sequencing method detected and identified 16srRNA genes of the predominant hemolytic isolates from milk and midguts of female C. pipiens. The phylogenetic analyses of the obtained isolates were performed based on NCBI data. Three strains of Bacillus anthracis strain CPMESA 2021, Staphylococcus warneri strain CPSAME 2021, and Bacillus cereus strain CPSEMA 2021, which represent most food pathogens, were found in the midguts of C. pipiens and were submitted to the GenBank database with the accession numbers OK585071, OK576651, and OK585052, respectively. The isolation of these strains from mosquitoes raises contemporary issues concerning milk safety, such as bacterial isolates, the degree of the vectorial capacity of mosquitoes, milk production and processing conditions, and human pathogenicity. Such serious issues need further investigation.

The influence of culture-dependent native microbiota in Zika virus infection in Aedes aegypti

Background

Emerging and re-emerging vector-borne diseases (VBDs) pose a recurring threat to tropical countries, mainly due to the abundance and distribution of the Aedes aegypti mosquito, which is a vector of the Zika, dengue, chikungunya, and yellow fever arboviruses.

Methods

Female 3–5 day-old Ae. aegypti were distributed into two experimental groups: group I—survey of cultivable bacteria; sucrose group: fed only on sucrose, i.e., non-blood-fed (UF); blood-fed group: (i) fed with non-infected blood (BF); (ii) fed with blood infected with the Zika virus (BZIKV); (iii) pretreated with penicillin/streptomycin (pen/strep), and fed with non-infected blood (TBF); (iv) pretreated with pen/strep and fed blood infected with ZIKV, i.e., gravid with developed ovaries, (TGZIKV); group II—experimental co-infections: bacteria genera isolated from the group fed on sucrose, i.e., non-blood-fed (UF).

Results

Using the cultivable method and the same mosquito colony and ZIKV strain described by in a previous work, our results reveled 11 isolates (Acinetobacter, Aeromonas, Cedecea, Cellulosimicrobium, Elizabethkingia, Enterobacter, Lysinibacillus, Pantoea, Pseudomonas, Serratia, and Staphylococcus). Enterobacter was present in all evaluated groups (i.e., UF, BF, BZIKV, TBF, and TGZIKV), whereas Elizabethkingia was present in the UF, BZIKV, and TBF groups. Pseudomonas was present in the BZIKV and TBF groups, whereas Staphylococcus was present in the TBF and TGZIKV groups. The only genera of bacteria that were found to be present in only one group were Aeromonas, Lysinibacillus, and Serratia (UF); Cedacea, Pantoea and Acinetobacter (BF); and Cellulosimicrobium (BZIKV). The mosquitoes co-infected with ZIKV plus the isolates group fed on sucrose (UF) showed interference in the outcome of infection.

Conclusions

We demonstrate that the distinct feeding aspects assessed herein influence the composition of bacterial diversity. In the co-infection, among ZIKV, Ae. aegypti and the bacterial isolates, the ZIKV/Lysinibacillus–Ae. aegypti had the lowest number of viral copies in the head-SG, which means that it negatively affects vector competence. However, when the saliva was analyzed after forced feeding, no virus was detected in the mosquito groups ZIKV/Lysinibacillus–Lu. longipalpis and Ae. aegypti; the combination of ZIKV/Serratia may interfere in salivation. This indicates that the combinations do not produce viable viruses and may have great potential as a method of biological control.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05160-7.

Characterization of midgut microbiome of Anopheles stephensi Liston

BACKGROUND & OBJECTIVES

Anopheles stephensi is an important vector of malaria in South East Asia. The abundance and diversity of gut microbiota in the disease vectors affect their development, digestion, metabolism and immunity. The immatures of An. stephensi engulf microbes from their aquatic environment. The present study investigates midgut microbiota of wild and laboratory populations and compares it with their habitat bacterial diversity to study transstadial transmissibility.

METHODS

The gut microbes from immatures, adults and water samples were cultured at ambient conditions on different media. The colony and biochemical characteristics, and 16S rRNA gene sequencing of gut microbes were studied.

RESULTS

Altogether, 298 bacterial isolates were characterized as 21 genera belonging to four major Phyla viz., Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria. In the field population-1, Proteobacteria and Firmicutes accounted for 49% and Actinobacteria constituted 51% of the bacterial isolates. In field population-2, Bacteroidetes and Firmicutes accounted for 99% of the isolates. In the laboratory populations, Firmicutes constituted 77%, while Proteobacteria 23% of the isolates. Additionally, 9 genera occurred in the breeding habitats, 13 in the larval midgut, 6 in pupal midgut, 9 in male midgut and 10 in the female midgut.

INTERPRETATION & CONCLUSION

This is a unique study on diversity of microbiota of An. stephensi from breeding water, developmental stages and adults. Different culture media used enhanced the isolation of diverse bacteria. The presence of Micrococcus and Leucobacter in different life stages indicates their adaptation in An. stephensi as symbionts which need further evaluation for their role in paratransgenesis.

Microbiomes of Blood-Feeding Arthropods: Genes Coding for Essential Nutrients and Relation to Vector Fitness and Pathogenic Infections. A Review

BACKGROUND

Blood-feeding arthropods support a diverse array of symbiotic microbes, some of which facilitate host growth and development whereas others are detrimental to vector-borne pathogens. We found a common core constituency among the microbiota of 16 different arthropod blood-sucking disease vectors, including Bacillaceae, Rickettsiaceae, Anaplasmataceae, Sphingomonadaceae, Enterobacteriaceae, Pseudomonadaceae, Moraxellaceae and Staphylococcaceae. By comparing 21 genomes of common bacterial symbionts in blood-feeding vectors versus non-blooding insects, we found that certain enteric bacteria benefit their hosts by upregulating numerous genes coding for essential nutrients. Bacteria of blood-sucking vectors expressed significantly more genes (p < 0.001) coding for these essential nutrients than those of non-blooding insects. Moreover, compared to endosymbionts, the genomes of enteric bacteria also contained significantly more genes (p < 0.001) that code for the synthesis of essential amino acids and proteins that detoxify reactive oxygen species. In contrast, microbes in non-blood-feeding insects expressed few gene families coding for these nutrient categories. We also discuss specific midgut bacteria essential for the normal development of pathogens (e.g., Leishmania) versus others that were detrimental (e.g., bacterial toxins in mosquitoes lethal to Plasmodium spp.).

Multi-Omic Analysis of Symbiotic Bacteria Associated With Aedes aegypti Breeding Sites

Mosquito breeding sites are complex aquatic environments with wide microbial diversity and physicochemical parameters that can change over time during the development of immature insect stages. Changes in biotic and abiotic conditions in water can alter life-history traits of adult mosquitos but this area remains understudied. Here, using microbial genomic and metabolomics analyses, we explored the metabolites associated with Aedes aegypti breeding sites as well as the potential contribution of Klebsiella sp., symbiotic bacteria highly associated with mosquitoes. We sought to address whether breeding sites have a signature metabolic profile and understand the metabolite contribution of the bacteria in the aquatic niches where Ae. aegypti larvae develop. An analysis of 32 mosquito-associated bacterial genomes, including Klebsiella, allowed us to identify gene clusters involved in primary metabolic pathways. From them, we inferred metabolites that could impact larval development (e.g., spermidine), as well as influence the quality assessment of a breeding site by a gravid female (e.g., putrescine), if produced by bacteria in the water. We also detected significant variance in metabolite presence profiles between water samples representing a decoupled oviposition event (oviposition by single females and manually deposited eggs) versus a control where no mosquito interactions occurred (PERMANOVA: p < 0.05; R² = 24.64% and R² = 30.07%). Five Klebsiella metabolites were exclusively linked to water samples where oviposition and development occurred. These data suggest metabolomics can be applied to identify compounds potentially used by female Ae. aegypti to evaluate the quality of a breeding site. Elucidating the physiological mechanisms by which the females could integrate these sensory cues while ovipositing constitutes a growing field of interest, which could benefit from a more depurated list of candidate molecules.

Native Wolbachia influence bacterial composition in the major vector mosquito Aedes aegypti

Bacterial species that inhabit mosquito microbiota play an essential role in determining vector competence. In addition to critical factors such as host genotype, feeding habit and geography, intracellular endosymbiont Wolbachia pipientis modulates microbial composition considerably. In the present study, we assessed the midgut bacterial diversity of Aedes aegypti mosquitoes that is either naturally carrying Wolbachia (wAegB⁺) or antibiotic cured (wAegB^-) through a culture-independent approach. Towards this, 16S rRNA gene libraries were constructed from midgut bacterial DNA of laboratory-reared larvae and adult female mosquitoes fed with sugar or blood. Among them 33 genera comprising 65 distinct species were identified, where > 75% of bacterial taxa were commonly shared by both groups (wAegB⁺ and wAegB^-), implying a subtle shift in the bacterial composition influenced by Wolbachia. Though the change was mostly restricted to minimally represented species, predominant taxa were observed unaltered except for certain genera. While Serratia sp. was abundant in Wolbachia carrying mosquitoes, Pseudomonas sp. and Acinetobacter sp. were predominant in Wolbachia free mosquitoes. This result demonstrates the influence of Wolbachia that could modulate the colonization of certain resident bacterial taxa through competitive interactions. Overall, this study shed more light on the impact of wAegB in altering the gut microbiota of Ae. aegypti mosquito, which might challenge host fitness and vector competence.

Insect vectors' saliva and gut microbiota as a blessing in disguise: probability versus possibility

Drawing of host blood is a natural phenomenon during the bite of blood-probing insect vectors. Along with the blood meal, the vectors introduce salivary components and a trail of microbiota. In the case of infected vectors, the related pathogen accompanies the aforementioned biological components. In addition to Anopheles gambiae or Anopheles stephensi, the bites of other nonmalarial vectors cannot be ignored in malaria-endemic regions. Similarly, the bite incidence of Phlebotomus papatasi cannot be ignored in visceral leishmaniasis-endemic regions. Even the chances of getting bitten by uninfected vectors are higher than the infected vectors. We have discussed the probability or possibility of uninfected, infected, and/or nonvector's saliva and gut microbiota as a therapeutic option leading to the initial deterrent to pathogen establishment.

Description of the ovarian microbiota of Aedes aegypti (L) Rockefeller strain

Aedes aegypti is one of the vectors responsible for transmitting the viruses that cause dengue, Zika and chikungunya in the human population. Mosquitoes have bacterial communities in different organs, mainly in the midgut, but to a lesser extent in their reproductive organs, such as the ovaries, where replication and vertical transmission is decisive for dengue virus. These bacteria also influence metabolic and physiological processes such as ingestion and digestion of blood. In this study, aerobic bacterial communities associated with ovaries of A. aegypti Rockefeller strain were determined, describing their potential function during ovocitary development. The groups of mosquitoes were separated into three treatments: diet with 10% sugar solution, diet with blood supply, and blood feeding combined with tetracycline. The ovaries were extracted from the mosquitoes, and then put in enriched culture media (blood and nutritive agar) by direct inoculation, for subsequent isolation and macroscopic and microscopic characterization of the colonies. The taxonomic determination of bacterial isolates was achieved by sequence analysis of the 16S rRNA gene. A higher bacterial load was observed in the sugar feeding group (6 × 10³ CFU/ml) in contrast to the group fed only with blood, with and without an antibiotic (4.03-4.04 × 10³CFU/ml; 4.85-5.04 × 10³CFU/ml). As a result, a total of 35 colonies were isolated, of which 80% were gram-negative and 20% gram-positive; 72% were lactose negative and 8% lactose positive. Of the total bacteria, 83% had gamma hemolysis, 17% alpha hemolysis, and none presented beta hemolysis. After phenotypic and biochemical characterization, 17 isolates were selected for molecular identification. Only phyla Actinobacteria and Proteobacteria were found. Bacteria associated with ovaries of A. aegypti were mainly identified as belonging to the Serratia and Klebsiella genera. Some bacteria (Serratia marcescens, Pantoea dispersa and Klebsiella oxytoca) have wide biotechnological potential due to their entomopathogenic power and their bioactivity against different pathogens.

Naturally Occurring Microbiota Associated with Mosquito Breeding Habitats and Their Effects on Mosquito Larvae

Immature mosquitoes are aquatic, and their distribution, abundance, and individual fitness in a particular breeding habitat are known to be dependent on mainly three factors: biotic factors, abiotic factors, and their interaction between each other and with other associated taxa. Mosquito breeding habitats harbor a diversified naturally occurring microbiota assemblage, and the biota have different types of interactions with mosquito larvae in those habitats. Those interactions may include parasitism, pathogenism, predation, and competition which cause the mortality of larvae, natural reduction of larval abundance, or alterations in their growth. Many microbiota species serve as food items for mosquito larvae, and there are also some indigestible or toxic phytoplanktons to larvae. However, when there is coexistence or mutualism of different mosquito species along with associated microbiota, they form a community sharing the habitat requirements. With the available literature, it is evident that the abundance of mosquito larvae is related to the densities of associated microbiota and their composition in that particular breeding habitat. Potential antagonist microbiota which are naturally occurring in mosquito breeding habitats could be used in integrated vector control approaches, and this method rises as an ecofriendly approach in controlling larvae in natural habitats themselves. To date, this aspect has received less attention; only a limited number of species of microbiota inhabiting mosquito breeding habitats have been recorded, and detailed studies on microbiota assemblage in relation to diverse vector mosquito breeding habitats and their association with mosquito larvae are few. Therefore, future studies on this important ecological aspect are encouraged. Such studies may help to identify field characteristic agents that can serve as mosquito controlling candidates in their natural habitats themselves.

Natural Variation in Physicochemical Profiles and Bacterial Communities Associated with Aedes aegypti Breeding Sites and Larvae on Guadeloupe and French Guiana

Aedes aegypti develop in aquatic habitats in which mosquito larvae are exposed to physicochemical elements and microorganisms that may influence their life cycle and their ability to transmit arboviruses. Little is known about the natural bacterial communities associated with A. aegypti or their relation to the biotic and abiotic characteristics of their aquatic habitats. We characterized the physicochemical properties and bacterial microbiota of A. aegypti breeding sites and larvae on Guadeloupe and in French Guiana. In addition, we explored whether geographic location, the type of breeding site and physicochemical parameters influenced the microbiota associated with this mosquito species. We used large-scale 16S rRNA gene sequencing of 160 breeding sites and 147 pools of A. aegypti larvae and recorded 12 physicochemical parameters at the sampled breeding sites. Ordination plots and multiple linear regression were used to assess the influence of environmental factors on the bacterial microbiota of water and larvae. We found territory-specific differences in physicochemical properties (dissolved oxygen, conductivity) and the composition of bacterial communities in A. aegypti breeding sites that influenced the relative abundance of several bacteria genera (e.g., Methylobacterium, Roseoccocus) on the corresponding larvae. A significant fraction of the bacterial communities identified on larvae, dominated by Herbiconiux and Microvirga genera, were consistently enriched in mosquitoes regardless the location. In conclusion, territory-specific differences observed in the biotic and abiotic properties of A. aegypti breeding sites raise concern about the impact of these changes on pathogen transmission by different A. aegypti populations.

Tripartite interactions: Leishmania, microbiota and Lutzomyia longipalpis

The microbial consortium associated with sandflies has gained relevance, with its composition shifting throughout distinct developmental stages, being strongly influenced by the surroundings and food sources. The bacterial components of the microbiota can interfere with Leishmania development inside the sandfly vector. Microbiota diversity and host-microbiota-pathogen interactions regarding New World sandfly species have yet to be thoroughly studied, particularly in Lutzomyia longipalpis, the primary vector of visceral leishmaniasis in Brazil.The native microbiota of different developmental stages and physiological conditions of Lu. longipalpis (Lapinha Cave), was described by culturing and 16s rRNA gene sequencing. The 16s rRNA sequencing of culture-dependent revealed 13 distinct bacterial genera (Bacillus, Enterococcus, Erwinia, Enterobacter, Escherichia, Klebsiella, Lysinibacillus, Pseudocitrobacter, Providencia, Pseudomonas, Serratia, Staphylococcus and Solibacillus). The in vitro and in vivo effects of each one of the 13 native bacteria from the Lu. longipalpis were analyzed by co-cultivation with promastigotes of L.i. chagasi, L. major, L. amazonensis, and L. braziliensis. After 24 h of co-cultivation, a growth reduction observed in all parasite species. When the parasites were co-cultivated with Lysinibacillus, all parasites of L. infantum chagasi and L. amazonensis died within 24 hours. In the in vivo co-infection of L.chagasi, L. major and L. amazonensis with the genera Lysinibacillus, Pseudocitrobacter and Serratia it was possible to observe a significant difference between the groups co-infected with the bacterial genera and the control group.These findings suggest that symbiont bacteria (Lysinibacillus, Serratia, and Pseudocitrobacter) are potential candidates for paratransgenic or biological control. Further studies are needed to identify the nature of the effector molecules involved in reducing the vector competence for Leishmania.

According to the World Health Organization Leishmaniasis is the second parasitic disease that kills the most in the world; the first is malaria. Despite this, knowledge about the Leishmania parasite and its interaction with vertebrate hosts concerning the transmitting insect is still relatively fewer and fragmented. Studies on insects microbiota have great importance to obtain basic information. How a vector responds to the presence of different microorganisms and how they interact with various pathogens and may lead to the development of new strategies or tools that can be used to prevent or hinder the transmission of the protozoan by the vector insect. Considering the knowledge about the intestinal microbiota of sandflies, we aim to study the effect of bacterial isolates on Lu. longipalpis infection by different species of Leishmania, and it believed that these bacteria might influence the development of Leishmania, preventing, and hindering transmission, contributing to Leishmaniasis control strategies.

Molecular Characterization of Culturable Aerobic Bacteria in the Midgut of Field-Caught Culex tritaeniorhynchus, Culex gelidus, and Mansonia annulifera Mosquitoes in the Gampaha District of Sri Lanka

Background

Larval and adult mosquito stages harbor different extracellular microbes exhibiting various functions in their digestive tract including host-parasite interactions. Midgut symbiotic bacteria can be genetically exploited to express molecules within the vectors, altering vector competency and potential for disease transmission. Therefore, identification of mosquito gut inhabiting microbiota is of ample importance before developing novel vector control strategies that involve modification of vectors.

Method

Adult mosquitoes of Culex tritaeniorhynchus, Culex gelidus, and Mansonia annulifera were collected from selected Medical Officer of Health (MOH) areas in the Gampaha district of Sri Lanka. Midgut lysates of the field-caught non-blood-fed female mosquitoes were cultured in Plate Count Agar medium, and Prokaryotic 16S ribosomal RNA partial genes of the isolated bacteria colonies were amplified followed by DNA sequencing. Diversity indices were used to assess the diversity and richness of the bacterial isolates in three mosquito species. The distribution pattern of bacterial isolates between different mosquito species was assessed by Distance-Based Redundancy Analysis (dbRDA).

Results

A total of 20 bacterial species (Staphylococcus pasteuri, Bacillus megaterium, Staphylococcus cohnii, Pantoea dispersa, Staphylococcus chromogenes, Bacillus aquimaris, Staphylococcus arlettae, Staphylococcus sciuri, Staphylococcus warneri, Moraxella osloensis, Enterobacter sp., Klebsiella michiganensis, Staphylococcus hominis, Staphylococcus saprophyticus, Streptomyces sp., Bacillus niacin, Cedecea neteri, Micrococcus luteus, Lysinibacillus sphaericus, and Bacillus licheniformis) were identified. All of these species belonged to three phyla, Proteobacteria, Firmicutes, and Actinobacteria, out of which phylum Firmicutes (71.1%) was the most prominent. The least number of species was recorded from Actinobacteria. The relative distribution of midgut microbes in different mosquito species differed significantly among mosquito species (Chi-square, χ ² = 486.091; df = 36; P ≤ 0.001). Midgut microbiota of Cx. tritaeniorhynchus and Cx. gelidus indicated a similarity of 21.51%, while Ma. annulifera shared a similarity of 6.92% with the cluster of above two species. The gut microbiota of Cx. tritaeniorhynchus was also significantly more diverse and more evenly distributed compared to Ma. annulifera. Simpson's diversity, Margalef's diversity, and Menhinick's diversity indices were higher in Cx. gelidus. Of the recorded species, P. dispersa and strains of nonpathogenic species in Bacillaceae family (B. megaterium, B. niacini, B. licheniformis, and L. sphaericus) can be recommended as potential candidates for paratransgenesis.

Conclusion

The relative distribution of midgut microbes in different mosquito species differed significantly among the three studied adult mosquito species. The present data strongly encourage further investigations to explore the potential usage of these microbes through paratransgenic approach for novel eco-friendly vector control strategies.

The potential distribution and dynamics of important vectors Culex pipiens pallens and Culex pipiens quinquefasciatus in China under climate change scenarios: an ecological niche modelling approach

BACKGROUND

Intense studies have been carried out on the effects of climate change on vector-borne diseases and vectors. Culex pipiens pallens and Culex pipiens quinquefasciatus are two medically concerned mosquito species in temperate and tropical areas, which serve as important disease-transmitting pests of a variety of diseases. The ongoing geographical expansion of these mosquitoes has brought an increasing threat to public health.

RESULTS

Based on mosquito occurrence records and high-resolution environmental layers, an ecological niche model was established to model their current and future potential distribution in China. Our model showed that the current suitable area for Cx. p. pallens is distributed in the central, eastern and northern parts of China, while Cx. p. quinquefasciatus is distributed in vast areas in southern China. Under future climate change scenarios, both species are predicted to expand their range to varying degrees and RCP 8.5 provides the largest expansion. Northward core shifts will occur in ranges of both species. Environmental variables which have significant impact on the distribution of mosquitoes were also revealed by our model.

CONCLUSION

Severe habitat expansion of vectors is likely to occur in the future 21st century. Our models mapped the high-risk areas and risk factors which needs to be paid attention. The results of our study can be referenced in further ecological surveys and will guide the development of strategies for the prevention and control of vector-borne diseases. © 2020 Society of Chemical Industry.

Identification of symbiotic bacteria in the midgut of the medically important mosquito, Culiseta longiareolata (Diptera: Culicidae)

Objective

The potential use of symbiotic bacteria for the control of mosquito-borne diseases has attracted the attention of scientists over the past few years. Culiseta longiareolata is among the medically important mosquitoes that transmit a wide range of vector-borne diseases worldwide. However, no extensive studies have been done on the identification of its symbiotic bacteria. Given the role of this species in the transmission of some important diseases and its widespread presence in different parts of the world, including northwestern parts and the West Azerbaijan Province in Iran, a knowledge about the symbiotic bacteria of this species may provide a valuable tool for the biological control of this mosquito. Accordingly, the present study was conducted to isolate and identify the cultivable isolates bacterial symbionts of Culiseta longiareolata using 16S rRNA fragment analysis.

Results

The midguts of 42 specimens of Cs. longiareolata were dissected, and the bacteria were cultured on agar plates. After the purification of the bacterial colonies, 16srRNA region amplification and gene sequence analysis were performed, and the sequences were confirmed by biochemical methods. In the present study, 21 isolates belonging to the genera Acinetobacter, Aerococcus, Aeromonas, Bacillus, Carnobacterium, Klebsiella, Morganella, Pseudomonas, Shewanella and Staphylococcus were identified.

Multiple Factors Determine the Structure of Bacterial Communities Associated With Aedes albopictus Under Artificial Rearing Conditions

Insect symbionts are major manipulators of host’s behavior. Their effect on parameters such as fecundity, male mating competitiveness, and biological quality in general, can have a major influence on the effectiveness of the sterile insect technique (SIT). SIT is currently being developed and applied against human disease vectors, including Ae. albopictus, as an environment-friendly method of population suppression, therefore there is a renewed interest on both the characterization of gut microbiota and their exploitation in artificial rearing. In the present study, bacterial communities of eggs, larvae, and adults (both males and females) of artificially reared Ae. albopictus, were characterized using both culture-dependent and culture-independent approaches. Mosquito-associated bacteria corresponding to thirteen and five bacteria genera were isolated from the larval food and the sugar solution (adult food), respectively. The symbiont community of the females was affected by the provision of a blood meal. Pseudomonas and Enterobacter were either introduced or enhanced with the blood meal, whereas Serratia were relatively stable during the adult stage of females. Maintenance of these taxa in female guts is probably related with blood digestion. Gut-associated microbiota of males and females were different, starting early after emergence and continuing in older stages. Our results indicate that eggs contained bacteria from more than fifteen genera including Bacillus, Chryseobacterium, and Escherichia–Shigella, which were also main components of gut microbiota of female adults before and after blood feeding, indicating potential transmission among generations. Our results provided a thorough study of the egg- and gut-associated bacteria of artificially reared Ae. albopictus, which can be important for further studies using probiotic bacteria to improve the effectiveness of mosquito artificial rearing and SIT applications.

Bacterial symbionts in human blood-feeding arthropods: Patterns, general mechanisms and effects of global ecological changes

Due to their high impact on public health, human blood-feeding arthropods are one of the most relevant animal groups. Bacterial symbionts have been long known to play a role in the metabolism, and reproduction of these arthropod vectors. Nowadays, we have a more complete picture of their functions, acknowledging the wide influence of bacterial symbionts on processes ranging from the immune response of the arthropod host to the possible establishment of pathogens and parasites. One or two primary symbiont species have been found to co-evolve along with their host in each taxon (being ticks an exception), leading to various kinds of symbiosis, mostly mutualistic in nature. Moreover, several secondary symbiont species are shared by all arthropod groups. With respect to gut microbiota, several bacterial symbionts genera are hosted in common, indicating that these bacterial groups are prone to invade several hematophagous arthropod species feeding on humans. The main mechanisms underlying bacterium-arthropod symbiosis are discussed, highlighting that even primary symbionts elicit an immune response from the host. Bacterial groups in the gut microbiota play a key role in immune homeostasis, and in some cases symbiont bacteria could be competing directly or indirectly with pathogens and parasites. Finally, the effects climate change, great human migrations, and the increasingly frequent interactions of wild and domestic animal species are analyzed, along with their implications on microbiota alteration and their possible impacts on public health and the control of pathogens and parasites harbored in arthropod vectors of human parasites and pathogens.

Bacterial community composition in the salivary glands of triatomines (Hemiptera: Reduviidae)

Background

Chagas disease is caused by the parasite Trypanosoma cruzi and is transmitted through triatomines (Hemiptera: Reduviidae). In the last year, many studies of triatomine gut microbiota have outlined its potential role in modulating vector competence. However, little is known about the microbiota present in the salivary glands of triatomines. Bacterial composition of salivary glands in selected triatomine species was investigated, as well as environmental influences on the acquisition of bacterial communities.

Methodology/Principal findings

The diversity of the bacterial communities of 30 pairs of salivary glands of triatomines was studied by sequencing of the V1- V3 variable region of the 16S rRNA using the MiSeq platform (Illumina), and bacteria isolated from skin of three vertebrate hosts were identified based on 16S rRNA gene sequence analysis (targeting the V3–V5 region). In a comparative analysis of microbiota in the salivary glands of triatomine species, operational taxonomic units belonging to Arsenophonous appeared as dominant in Triatoma spp (74% of the total 16S coverage), while these units belonging to unclassified Enterobacteriaceae were dominant in the Rhodnius spp (57% of the total 16S coverage). Some intraspecific changes in the composition of the triatomine microbiota were observed, suggesting that some bacteria may have been acquired from the environment.

Conclusions and significance

Our study revealed the presence of a low-diversity microbiota associated to the salivary glands of the evaluated triatomines. The predominant bacteria genera are associated with triatomine genera and the bacteria can be acquired in the environment in which the insects reside. Further studies are necessary to determine the influence of bacterial communities on vector competence.

Chagas disease is caused by the parasite Trypanosoma cruzi and is transmitted through triatomines (Hemiptera: Reduviidae). It is estimated that over 10 000 people die every year from clinical manifestations of Chagas disease, and more than 25 million people risk acquiring the disease per year. Vector control remains the most effective method to prevent infection. In previous studies, the microbiota affected vector competence, thereby highlighting its potential for vector control. In this study, we demonstrate the presence of cultivable and non-cultivable bacteria in the salivary glands of different species of triatomines. The predominant bacterial genera appear to be specific to certain triatomines, e.g., the operational taxonomic units belonging to Arsenophonus bacterial genus is associated with the Triatoma spp, while these units belonging to unclassified Enterobacteriaceae bacterial family are associated with the Rhodnius spp. The operational taxonomic units found in low relative abundance also varied between species of triatomines and their occurrence could be influenced by the environment in which insects reside as well as inter-bacterial modulation by species-specific manner.

Metagenome and Culture-Based Methods Reveal Candidate Bacterial Mutualists in the Southern House Mosquito (Diptera: Culicidae)

Mosquitoes are intensely studied as vectors of disease-causing pathogens, but we know relatively less about microbes that naturally reside in mosquitoes. Profiling resident bacteria in mosquitoes can help identify bacterial groups that can be exploited as a strategy of controlling mosquito populations. High-throughput 16S rRNA gene sequencing and traditional culture-based methods were used to identify bacterial assemblages in Culex quinquefasciatus Say (Diptera: Culicidae) in a tissue- and stage-specific design. In parallel, wild host Cx. quinquefasciatus was compared with our domestic strain. 16S rRNA genes survey finds that Cx. quinquefasciatus has taxonomically restricted bacterial communities, with 90% of its bacterial microbiota composed of eight distinctive bacterial groups: Nocardioidaceae (Actinomycetales), Microbacteriaceae (Actinomycetales), Flavobacteriaceae, Rhizobiales, Acetobacteraceae, Rickettsiaceae, Comamondaceae (Burkholderiales), and Enterobacteriaceae. Taking into account both metagenome- and culture-based methods, we suggest three bacterial groups, Acetobacteraceae, Flavobacteriaceae, and Enterobacteriaceae, as candidates for mutualists in Cx. quinquefasciatus. Members of these three bacterial families have been studied as mutualists, or even as symbionts, in other insect groups, so it is quite possible they play similar roles in mosquitoes.

Biodiversity and pathogenicity of bacteria associated with the gut microbiota of beet armyworm, Spodoptera exigua Hübner (Lepidoptera: Noctuidae)

In order to find an effective and environmentally friendly biocontrol agent against Spodoptera exigua, we isolated and identified a total of 15 different bacterial species belonging to phyla Firmicutes, Proteobacteria and Bacteroidetes. According to the phenotypic, genotypic and phylogenetic properties, bacterial isolates were identified as Bacillus cereus (Se1), Lysinibacillus macroides (Se2), Pseudomonas geniculata (Se3), Paenibacillus tylopili (Se4), Staphylococcus succinus (Se5), Acinetobacter soli (Se6), Chryseobacterium indologenes (Se7), Bacillus toyonensis (Se8), Serratia marcescens (Se9), Paenibacillus amylolyticus (Se10), Paenibacillus xylanexedens (Se11), Enterobacter ludwigii (Se12), Bacillus thuringiensis (Se13), Bacillus thuringiensis (Se14) and Lysinibacillus fusiformis (Se15). Screening of bacterial isolates for insecticidal potential was conducted at 10⁹ cfu ml^-1 bacterial concentration. The highest larvacidal effect was obtained with Bacillus thuringiensis Se13 with 100% mortality. In the dose response experiments performed with this bacterium, the median lethal concentration (LC₅₀) was estimated as 7.5 × 10⁴ cfu ml^-1 against 3rd instar larvae of the pest at 10 days post treatment. The median lethal time (LT₅₀) value of 10⁹ cfu ml^-1 bacterial concentration was also determined as 1.59 days. Phase-contrast and scanning electron microscope studies exhibited that B. thuringiensis Se13 produced different shape and size crystals (bipyramidal, cubic and spherical). Phylogenetic analysis of cry1 and cry2 gene content of this isolate displayed that B. thuringiensis Se13 had 99% homology with cry1Ac and cry2Aa, respectively. Finding from this study indicated that B. thuringiensis Se13 appears to be a promising microbial control agent for use against S. exigua.

High levels of local inter- and intra-host genetic variation of West Nile virus and evidence of fine-scale evolutionary pressures

West Nile virus (WNV; Flaviviridae, Flavivirus) has been endemic in New York State (NYS) since its 1999 introduction, yet prevalence in Culex mosquitoes varies substantially over small spatial and temporal scales. It is unclear if viral genetics plays a role in this variability, as genetic and phenotypic characterization on local scales has generally been lacking. In addition, intrahost diversity of circulating strains have not been fully characterized despite the documented role of minority variants in viral fitness and virulence. In an effort to characterize WNV variability within epidemiologically relevant scales, we performed phylogenetic analyses on NYS isolates from 1999 to 2012. In addition, we performed full-genome, deep-sequencing and genetic analyses on 15 WNV strains isolated in 2012 from Cx. pipiens in an endemic focus of Suffolk County, NY. Our results indicate continued evolution and seasonal maintenance in NYS, yet also widespread mixing and high levels of genetic diversity within geographic foci and individual seasons. Well supported local clusters with shared amino acid differences were identified and suggest local evolutionary pressures and the potential for phenotypic variability. Intrahost diversity of focal isolates was also high, with polymorphism at levels >1.0% identified in approximately 10% of the WNV genome. Although most minority mutations were unique, mutational hotspots shared among local isolates were identified, particularly in C, NS1 and NS2A genes. The most polymorphic region, positions 3198-3388 of the NS1 gene, was comprised predominately of non-synonymous mutations, suggesting a selective advantage for amino acid diversity in this region.

The microbiome composition of Aedes aegypti is not critical for Wolbachia-mediated inhibition of dengue virus

Background

Dengue virus (DENV) is primarily vectored by the mosquito Aedes aegypti, and is estimated to cause 390 million human infections annually. A novel method for DENV control involves stable transinfection of Ae. aegypti with the common insect endosymbiont Wolbachia, which mediates an antiviral effect. However, the mechanism by which Wolbachia reduces the susceptibility of Ae. aegypti to DENV is not fully understood. In this study we assessed the potential of resident microbiota, which can play important roles in insect physiology and immune responses, to affect Wolbachia-mediated DENV blocking.

Methodology/Findings

The microbiome of Ae. aegypti stably infected with Wolbachia strain wMel was compared to that of Ae. aegypti without Wolbachia, using 16s rDNA profiling. Our results indicate that although Wolbachia affected the relative abundance of several genera, the microbiome of both the Wolbachia-infected and uninfected mosquitoes was dominated by Elizabethkingia and unclassified Enterobacteriaceae. To assess the potential of the resident microbiota to affect the Wolbachia-mediated antiviral effect, we used antibiotic treatment before infection with DENV by blood-meal. In spite of a significant shift in the microbiome composition in response to the antibiotics, we detected no effect of antibiotic treatment on DENV infection rates, or on the DENV load of infected mosquitoes.

Conclusions/Significance

Our findings indicate that stable infection with Wolbachia strain wMel produces few effects on the microbiome of laboratory-reared Ae. aegypti. Moreover, our findings suggest that the microbiome can be significantly altered without affecting the fundamental DENV blocking phenotype in these mosquitoes. Since Ae. aegypti are likely to encounter diverse microbiota in the field, this is a particularly important result in the context of using Wolbachia as a method for DENV control.

Dengue virus is transmitted by the mosquito Aedes aegypti and can cause dengue fever and dengue haemorrhagic fever in humans. The World Health Organization currently considers it as the most important mosquito-borne virus globally. One method to control dengue infection of Ae. aegypti is to infect the mosquito with a common bacterium, Wolbachia, which increases the mosquito’s resistance to dengue virus. The mechanism by which resistance to dengue virus occurs is not well understood. Here, we considered whether other bacteria that reside in the mosquito might affect the ability of Wolbachia to limit dengue virus infection. First, we assessed whether Wolbachia had an impact on the abundance of bacterial species present in Ae. aegypti, finding that it had minimal effects. Second, we altered the composition of the bacterial species present by treating Ae. aegypti with antibiotics, then examined whether this affected Wolbachia’s antiviral effect. We found that there was no difference in the susceptibility of the mosquitoes to dengue virus, regardless of antibiotic treatment. We therefore conclude that it is unlikely that there are specific resident bacteria required for the principal mechanism(s) by which Wolbachia reduces susceptibility of Ae. aegypti to dengue virus.

Comparative analysis of gut microbiota of mosquito communities in central Illinois

Background

The composition and structure of microbial communities that inhabit the mosquito midguts are poorly understood despite their well-documented potential to impede pathogen transmission.

Methodology/Principal findings

We used MiSeq sequencing of the 16S rRNA gene to characterize the bacterial communities of field-collected populations of 12 mosquito species. After quality filtering and rarefaction, the remaining sequences were assigned to 181 operational taxonomic units (OTUs). Approximately 58% of these OTUs occurred in at least two mosquito species but only three OTUs: Gluconobacter (OTU 1), Propionibacterium (OTU 9), and Staphylococcus (OTU 31) occurred in all 12 mosquito species. Individuals of different mosquito species shared similar gut microbiota and it was common for individuals of the same species from the same study site and collection date to harbor different gut microbiota. On average, the microbiota of Aedes albopictus was the least diverse and significantly less even compared to Anopheles crucians, An. quadrimaculatus, Ae. triseriatus, Ae. vexans, Ae. japonicus, Culex restuans, and Culiseta inornata. The microbial community of Cx. pipiens and Ae. albopictus differed significantly from all other mosquitoes species and was primarily driven by the dominance of Wolbachia.

Conclusion and significance

These findings expand the range of mosquito species whose gut microbiota has been characterized and sets the foundation for further studies to determine the influence of these microbiota on vector susceptibility to pathogens.

The microbial communities that reside in mosquito midguts can impact transmission of mosquito-borne pathogens. We used high throughput next generation sequencing to characterize the midgut microbial communities of 12 mosquito species collected in urban residential areas in Champaign County, Illinois. A total of 181 OTUs from 11 phyla and 66 families were identified. Although several bacterial taxa were shared between two or more mosquito species, there was remarkable individual differences in gut microbiota and it was common for individuals of different mosquito species to harbor similar gut microbiota. The microbiota of Ae. albopictus was the least diverse and significantly less evenly distributed compared to 7 of 11 mosquito species. The microbial community of Cx. pipiens and Ae. albopictus differed significantly from other mosquito species and was primarily dominated by Wolbachia. These findings improve current knowledge on the composition and structure of mosquito gut microbiota and provide the framework for understanding their contribution to individual variation in vector competence and potential application in disease control.

Diversity of Cultivable Midgut Microbiota at Different Stages of the Asian Tiger Mosquito, Aedes albopictus from Tezpur, India

Aedes aegypti and Ae. albopictus are among the most important vectors of arboviral diseases, worldwide. Recent studies indicate that diverse midgut microbiota of mosquitoes significantly affect development, digestion, metabolism, and immunity of their hosts. Midgut microbiota has also been suggested to modulate the competency of mosquitoes to transmit arboviruses, malaria parasites etc. Interestingly, the midgut microbial flora is dynamic and the diversity changes with the development of vectors, in addition to other factors such as species, sex, life-stage, feeding behavior and geographical origin. The aim of the present study was to investigate the midgut bacterial diversity among larva, adult male, sugar fed female and blood fed female Ae. albopictus collected from Tezpur, Northeastern India. Based on colony morphological characteristics, we selected 113 cultivable bacterial isolates for 16S rRNA gene sequence based molecular identification. Of the 113 isolates, we could identify 35 bacterial species belonging to 18 distinct genera under four major phyla, namely Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes. Phyla Proteobacteria and Firmicutes accounted for majority (80%) of the species, while phylum Actinobacteria constituted 17% of the species. Bacteroidetes was the least represented phylum, characterized by a single species- Chryseobacterium rhizoplanae, isolated from blood fed individuals. Dissection of midgut microbiota diversity at different developmental stages of Ae. albopictus will be helpful in better understanding mosquito-borne diseases, and for designing effective strategies to manage mosquito-borne diseases.

Gut microbiota of Busseola fusca (Lepidoptera: Noctuidae)

Busseola fusca (Fuller) (Lepidoptera: Noctuidae) is a stemborer pest that attacks maize (Zea mays) throughout sub-Saharan Africa. Genetically modified maize has been shown to be effective against B. fusca. However, resistance of B. fusca against Bt-maize has developed and spread throughout South Africa. Previous studies suggested that gut microbiota contribute to mortality across a range of Lepidoptera. To fully assess the role of microbiota within the gut, it is essential to understand the microbiota harboured by natural B. fusca populations. This study aimed to identify the gut-associated bacteria by 16S rRNA gene sequencing. A total of 78 bacterial strains were characterised from the midgut of B. fusca larvae that were collected from 30 sites across the maize producing region of South Africa. Molecular phylogenetic analyses revealed bacteria affiliated to Proteobacteria, Actinobacteria, and Firmicutes. Taxonomic distribution placed these isolates into 15 different genera representing 20 species. The majority of bacteria identified belong to the genera Bacillus, Enterococcus, and Klebsiella. The B. fusca gut represents an intriguing and unexplored niche for analysing microbial ecology. The study could provide opportunities for developing new targets for pest management and contribute to understanding the phenomenon of resistance evolution of this species.

Culex pipiens and Culex restuans mosquitoes harbor distinct microbiota dominated by few bacterial taxa

BACKGROUND

Mosquitoes host diverse microbial communities that influence many aspects of their biology including reproduction, digestion, and ability to transmit pathogens. Unraveling the composition, structure, and function of these microbiota can provide new opportunities for exploiting microbial function for mosquito-borne disease control.

METHODS

MiSeq® sequencing of 16S rRNA gene amplicons was used to characterize the microbiota of adult females of Culex pipiens L. and Cx. restuans Theobald collected from nine study sites in central Illinois.

RESULTS

Out of 195 bacterial OTUs that were identified, 86 were shared between the two mosquito species while 16 and 93 OTUs were unique to Cx. pipiens and Cx. restuans, respectively. The composition and structure of microbial communities differed significantly between the two mosquito species with Cx. restuans hosting a more diverse bacterial community compared to Cx. pipiens. Wolbachia (OTU836919) was the dominant bacterial species in Cx. pipiens accounting for 91% of total microbiota while Sphingomonas (OTU817982) was the dominant bacterial species in Cx. restuans accounting for 31% of total microbiota. Only 3 and 6 OTUs occurred in over 60% of individuals in Cx. pipiens and Cx. restuans, respectively. There was little effect of study site on bacterial community structure of either mosquito species.

CONCLUSION

These results suggest that the two mosquito species support distinct microbial communities that are sparsely distributed between individuals. These findings will allow investigations of the role of identified microbiota on the spatial and temporal heterogeneity in WNV transmission and their potential application in disease control.

Molecular characterization of midgut microbiota of Aedes albopictus and Aedes aegypti from Arunachal Pradesh, India

BACKGROUND

Microbiota inhabiting midguts of mosquitoes play a key role in the host - parasite interaction and enhance vectorial capacity of viral diseases like dengue and chikungunya fevers. Mosquito midgut is considered to be an important site for host-pathogen interaction and pathogen survival is thought to be an outcome of this interaction. In the present study we examined the bacterial community in the midgut of Aedes mosquitoes in Arunanchal Pradesh, India, a subtropical zone where dengue fever is reported to be emerging.

METHOD

Larvae and pupa of Aedes mosquitoes were collected from a biodiversity hotspot, Bhalukpong, Arunachal Pradesh, India. 16S rRNA gene sequences were used for identification of isolated bacterial population from each species of mosquitoes. We used various diversity indices to assess the diversity and richness of the bacterial isolates in both mosquito species.

RESULT

On the basis of 16S rRNA gene sequence analysis a total of 24 bacterial species from 13 genera were identified belonging to 10 families of four major phyla. Phylum Proteobacteria was dominant followed by Firmicutes, Bacteroidetes and Actinobacteria. The midgut bacteria belonging to the phylum Proteobacteria and Firmicutes were isolated from both Ae. albopictus and Ae. aegypti, whereas, bacteria belonging to phylum Bacteroidetes and Actinobacteria were isolated only from Ae. albopictus and Ae. aegypti respectively. Enterobacter cloacae was the dominant bacterial species in both Ae. albopictus (33.65%) and Ae. aegypti (56.45%). Bacillus aryabhattai (22.78%) was the second most common bacterial species in Ae. albopictus whereas, in Ae. aegypti the second most common bacterial species was Stenotrophomonas maltophilia (7.44%).

CONCLUSION

The family Enterobacteriaceae of phylum Proteobacteria was dominant in both species of Aedes mosquitoes. To the best of our knowledge, this is the first attempt to study midgut microbiota from a biodiversity hotspot in Northeastern India. Some bacterial genera Enterobacter and Acinetobacter isolated in this study are known to play important roles in parasite-vector interaction. Information on midgut microflora may lead towards the development of novel, safe, and effective strategies to manipulate the vectorial capacity of mosquitoes.

Exposure to West Nile Virus Increases Bacterial Diversity and Immune Gene Expression in Culex pipiens

Complex interactions between microbial residents of mosquitoes and arboviruses are likely to influence many aspects of vectorial capacity and could potentially have profound effects on patterns of arbovirus transmission. Such interactions have not been well studied for West Nile virus (WNV; Flaviviridae, Flavivirus) and Culex spp. mosquitoes. We utilized next-generation sequencing of 16S ribosomal RNA bacterial genes derived from Culex pipiens Linnaeus following WNV exposure and/or infection and compared bacterial populations and broad immune responses to unexposed mosquitoes. Our results demonstrate that WNV infection increases the diversity of bacterial populations and is associated with up-regulation of classical invertebrate immune pathways including RNA interference (RNAi), Toll, and Jak-STAT (Janus kinase-Signal Transducer and Activator of Transcription). In addition, WNV exposure alone, without the establishment of infection, results in similar alterations to microbial and immune signatures, although to a lesser extent. Multiple bacterial genera were found in greater abundance in WNV-exposed and/or infected mosquitoes, yet the most consistent and notable was the genus Serratia.

Evaluation of five antibiotics on larval gut bacterial diversity of Plutella xylostella (Lepidoptera: Plutellidae)

Larvae of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), have rich microbial communities inhabiting the gut, and these bacteria contribute to the fitness of the pest. In this study we evaluated the effects of five antibiotics (rifampicin, ampicillin, tetracycline, streptomycin sulfate and chloramphenicol) on the gut bacterial diversity of P. xylostella larvae. We screened five different concentrations for each antibiotic in a leaf disc assay, and found that rifampicin and streptomycin sulfate at 3 mg/mL significantly reduced the diversity of the bacterial community, and some bacterial species could be rapidly eliminated. The number of gut bacteria in the rifampicin group and streptomycin sulfate group decreased more rapidly than the others. With the increase of antibiotic concentration, the removal efficiency was improved, whereas toxic effects became more apparent. All antibiotics reduced larval growth and development, and eventually caused high mortality, malformation of the prepupae, and hindered pupation and adult emergence. Among the five antibiotics, tetracycline was the most toxic and streptomycin sulfate was a relatively mild one. Some dominant bacteria were not affected by feeding antibiotics alone. Denaturing gradient gel electrophoresis graph showed that the most abundant and diverse bacteria in P. xylostella larval gut appeared in the cabbage feeding group, and diet change and antibiotics intake influenced gut flora abundance. Species diversity was significantly reduced in the artificial diet and antibiotics treatment groups. After feeding on the artificial diet with rifampicin, streptomycin sulfate and their mixture for 10 days, larval gut bacteria could not be completely removed as detected with the agarose gel electrophoresis method.

The insect microbiome modulates vector competence for arboviruses

Diseases caused by arthropod-borne viruses (arboviruses), such as Dengue, West Nile, and Chikungunya, constitute a major global health burden and are increasing in incidence and geographic range. The natural microbiota of insect vectors influences various aspects of host biology, such as nutrition, reproduction, metabolism, and immunity, and recent studies have highlighted the ability of insect-associated bacteria to reduce vector competence for arboviruses and other pathogens. This reduction can occur through mechanisms, such as immune response activation, resource competition, or the production of anti-viral molecules. Studying the interactions between insect vectors and their microbiota is an important step toward developing alternative strategies for arbovirus transmission control.

Comparative assessment of the bacterial communities associated with Aedes aegypti larvae and water from domestic water storage containers

Background

Domestic water storage containers constitute major Aedes aegypti breeding sites. We present for the first time a comparative analysis of the bacterial communities associated with Ae. aegypti larvae and water from domestic water containers.

Methods

The 16S rRNA-temporal temperature gradient gel electrophoresis (TTGE) was used to identify and compare bacterial communities in fourth-instar Ae. aegypti larvae and water from larvae positive and negative domestic containers in a rural village in northeastern Thailand. Water samples were cultured for enteric bacteria in addition to TTGE. Sequences obtained from TTGE and bacterial cultures were clustered into operational taxonomic units (OTUs) for analyses.

Results

Significantly lower OTU abundance was found in fourth-instar Ae. aegypti larvae compared to mosquito positive water samples. There was no significant difference in OTU abundance between larvae and mosquito negative water samples or between mosquito positive and negative water samples. Larval samples had significantly different OTU diversity compared to mosquito positive and negative water samples, with no significant difference between mosquito positive and negative water samples. The TTGE identified 24 bacterial taxa, belonging to the phyla Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes and TM7 (candidate phylum). Seven of these taxa were identified in larval samples, 16 in mosquito positive and 13 in mosquito negative water samples. Only two taxa, belonging to the phyla Firmicutes and Actinobacteria, were common to both larvae and water samples. Bacilli was the most abundant bacterial class identified from Ae. aegypti larvae, Gammaproteobacteria from mosquito positive water samples, and Flavobacteria from mosquito negative water samples. Enteric bacteria belonging to the class Gammaproteobacteria were sparsely represented in TTGE, but were isolated from both mosquito positive and negative water samples by selective culture.

Conclusions

Few bacteria from water samples were identified in fourth-instar Ae. aegypti larvae, suggesting that established larval bacteria, most likely acquired at earlier stages of development, control the larval microbiota. Further studies at all larval stages are needed to fully understand the dynamics involved. Isolation of enteric bacteria from water samples supports earlier outcomes of E. coli contamination in Ae. aegypti infested domestic containers, suggesting the need to further explore the role of enteric bacteria in Ae. aegypti infestation.