A general theory for host seeking decisions in mosquitoes

We develop a theory for host seeking decisions in mosquitoes that explicitly considers the tradeoffs mosquitoes face in allocation to somatic and gametic function. Specifically, we consider conditions under which mosquitoes should seek out nectar and blood hosts upon encountering host odours. Results from development of a dynamic model that considers free and crop energy states suggest that mosquitoes should seek out blood hosts under a wide variety of conditions but that decisions to seek nectar depends upon crop volume, concentration and free energy. This pattern arises because mosquitoes carrying large crop loads are constrained in their ability to obtain large blood meals due to space limitations in the abdomen. The predicted patterns of behaviour are supported by published observations of mosquito behaviour.     

Bird hosts, blood parasites and their vectors--associations uncovered by molecular analyses of blackfly blood meals

The level of host specificity of blood-sucking invertebrates may have both ecological and evolutionary implications for the parasites they are transmitting. We used blood meals from wild-caught blackflies for molecular identification of parasites and hosts to examine patterns of host specificity and how these may affect the transmission of avian blood parasites of the genus Leucocytozoon . We found that five different species of ornithophilic blackflies preferred different species of birds when taking their blood meals. Of the blackflies that contained avian blood meals, 62% were infected with Leucocytozoon parasites, consisting of 15 different parasite lineages. For the blackfly species, there was a significant association between the host width (measured as the genetic differentiation between the used hosts) and the genetic similarity of the parasites in their blood meals. The absence of similar parasite in blood meals from blackflies with different host preferences is interpreted as a result of the vector–host associations. The observed associations between blackfly species and host species are therefore likely to hinder parasites to be transmitted between different host-groups, resulting in ecologically driven associations between certain parasite lineages and hosts species.     

Unbiased Characterization of Anopheles Mosquito Blood Meals by Targeted High-Throughput Sequencing

Understanding mosquito host choice is important for assessing vector competence or identifying disease reservoirs. Unfortunately, the availability of an unbiased method for comprehensively evaluating the composition of insect blood meals is very limited, as most current molecular assays only test for the presence of a few pre-selected species. These approaches also have limited ability to identify the presence of multiple mammalian hosts in a single blood meal. Here, we describe a novel high-throughput sequencing method that enables analysis of 96 mosquitoes simultaneously and provides a comprehensive and quantitative perspective on the composition of each blood meal. We validated in silico that universal primers targeting the mammalian mitochondrial 16S ribosomal RNA genes (16S rRNA) should amplify more than 95% of the mammalian 16S rRNA sequences present in the NCBI nucleotide database. We applied this method to 442 female Anopheles punctulatus s. l. mosquitoes collected in Papua New Guinea (PNG). While human (52.9%), dog (15.8%) and pig (29.2%) were the most common hosts identified in our study, we also detected DNA from mice, one marsupial species and two bat species. Our analyses also revealed that 16.3% of the mosquitoes fed on more than one host. Analysis of the human mitochondrial hypervariable region I in 102 human blood meals showed that 5 (4.9%) of the mosquitoes unambiguously fed on more than one person. Overall, analysis of PNG mosquitoes illustrates the potential of this approach to identify unsuspected hosts and characterize mixed blood meals, and shows how this approach can be adapted to evaluate inter-individual variations among human blood meals. Furthermore, this approach can be applied to any disease-transmitting arthropod and can be easily customized to investigate non-mammalian host sources.     

Dynamics of Vector-Host Interactions in Avian Communities in Four Eastern Equine Encephalitis Virus Foci in the Northeastern U.S.

Background

Eastern equine encephalitis (EEE) virus (Togaviridae, Alphavirus) is a highly pathogenic mosquito-borne zoonosis that is responsible for occasional outbreaks of severe disease in humans and equines, resulting in high mortality and neurological impairment in most survivors. In the past, human disease outbreaks in the northeastern U.S. have occurred intermittently with no apparent pattern; however, during the last decade we have witnessed recurring annual emergence where EEE virus activity had been historically rare, and expansion into northern New England where the virus had been previously unknown. In the northeastern U.S., EEE virus is maintained in an enzootic cycle involving the ornithophagic mosquito, Culiseta melanura, and wild passerine (perching) birds in freshwater hardwood swamps. However, the identity of key avian species that serve as principal virus reservoir and amplification hosts has not been established. The efficiency with which pathogen transmission occurs within an avian community is largely determined by the relative reservoir competence of each species and by ecological factors that influence contact rates between these avian hosts and mosquito vectors.

Methodology and principle findings

Contacts between vector mosquitoes and potential avian hosts may be directly quantified by analyzing the blood meal contents of field-collected specimens. We used PCR-based molecular methods and direct sequencing of the mitochondrial cytochrome b gene for profiling of blood meals in Cs. melanura, in an effort to quantify its feeding behavior on specific vertebrate hosts, and to infer epidemiologic implications in four historic EEE virus foci in the northeastern U.S. Avian point count surveys were conducted to determine spatiotemporal host community composition. Of 1,127 blood meals successfully identified to species level, >99% of blood meals were from 65 avian hosts in 27 families and 11 orders, and only seven were from mammalian hosts representing three species. We developed an empirically informed mathematical model for EEE virus transmission using Cs. melanura abundance and preferred and non-preferred avian hosts. To our knowledge this is the first mathematical model for EEE virus, a pathogen with many potential hosts, in the northeastern U.S. We measured strong feeding preferences for a number of avian species based on the proportion of mosquito blood meals identified from these bird species in relation to their observed frequencies. These included: American Robin, Tufted Titmouse, Common Grackle, Wood Thrush, Chipping Sparrow, Black-capped Chickadee, Northern Cardinal, and Warbling Vireo. We found that these bird species, most notably Wood Thrush, play a dominant role in supporting EEE virus amplification. It is also noteworthy that the competence of some of the aforementioned avian species for EEE virus has not been established. Our findings indicate that heterogeneity induced by mosquito host preference, is a key mediator of the epizootic transmission of vector-borne pathogens.

Conclusion and significance

Detailed knowledge of the vector-host interactions of mosquito populations in nature is essential for evaluating their vectorial capacity and for assessing the role of individual vertebrates as reservoir hosts involved in the maintenance and amplification of zoonotic agents of human diseases. Our study clarifies the host associations of Cs. melanura in four EEE virus foci in the northeastern U.S., identifies vector host preferences as the most important transmission parameter, and quantifies the contribution of preference-induced contact heterogeneity to enzootic transmission. Our study identifies Wood Thrush, American Robin and a few avian species that may serve as superspreaders of EEE virus. Our study elucidates spatiotemporal host species utilization by Cs. melanura in relation to avian host community. This research provides a basis to better understand the involvement of Cs. melanura and avian hosts in the transmission and ecology of EEE virus and the risk of human infection in virus foci.     

Innate preference or opportunism: mosquitoes feeding on birds of prey at the Southeastern Raptor Center

The amplification of mosquito‐borne pathogens is driven by patterns of host use by vectors. While each mosquito species is innately adapted to feed upon a particular group of hosts, this “preference” is difficult to assess in field‐based studies, because factors such as host defenses and spatial and temporal overlap of mosquitoes and hosts affect which host animals actually get bitten. Here we examined patterns of host use by mosquitoes feeding on caged raptors at a rehabilitation and education center for birds of prey in Alabama, U.S.A. PCR‐based techniques were used to determine the host species fed upon. Of 19 raptor species at the facility, seven were found to be fed upon by mosquitoes. Feeding indices and linear regression indicated that no species or family of raptor were significantly preferred over another (R²=0.46). Relative abundance adjusted for bird size explained a statistically significant amount of the variation in relative host use (R²=0.71), suggesting that bird size is an important component of host selection by mosquitoes. These findings support the hypothesis that traits of host animals drive patterns of host use by mosquitoes in nature, an interaction that leads to amplification of mosquito‐borne viruses.     

Mosquito species composition and phenology (Diptera,Culicidae) in two German zoological gardens imply different risks of mosquito‐borne pathogen transmission

Due to their large diversity of potential blood hosts, breeding habitats, and resting sites, zoological gardens represent highly interesting places to study mosquito ecology. In order to better assess the risk of mosquito‐borne disease‐agent transmission in zoos, potential vector species must be known, as well as the communities in which they occur. For this reason, species composition and dynamics were examined in 2016 in two zoological gardens in Germany. Using different methods for mosquito sampling, a total of 2,257 specimens belonging to 20 taxa were collected. Species spectra depended on the collection method but generally differed between the two zoos, while species compositions and relative abundances varied seasonally in both of them. As both sampled zoos were located in the same climatic region and potential breeding sites within the zoos were similar, the differences in mosquito compositions are attributed to immigration of specimens from surrounding landscapes, although the different sizes of the zoos and the different blood host populations available probably also have an impact. Based on the differences in species composition and the various biological characteristics of the species, the risk of certain pathogens to be transmitted must also be expected to differ between the zoos.     

Mosquito bloodmeal preferences in two zoological gardens in Germany

Because they provide a high density and diversity of vertebrate species, small water pools and shaded environments, zoological gardens offer ideal living conditions for numerous mosquito species. Depending on their host preferences and vector competencies, these species may be able to transmit pathogens between native and non‐adapted exotic blood host species, thereby causing morbidity and mortality among valuable zoo animals. To determine the extent to which native mosquito species feed on captive and wild animals, as well as on humans, in two German zoological gardens, mosquitoes were collected over two seasons by trapping and aspirating. A total of 405 blood‐fed specimens belonging to 16 mosquito taxa were collected. Genetic bloodmeal analysis revealed 56 host species, mainly representing mammals of the zoo animal population, including exotic species previously not known as blood hosts of the mosquito species collected. These results indicate opportunistic feeding patterns with low host‐specificity in the analysed mosquitoes, although these could be grouped, according to their bloodmeals, into ‘amphibian‐’, ‘non‐human mammal‐’ and ‘non‐human mammal and human‐’ feeding species. As the blood‐feeding preferences of vector‐competent mosquito species are major determinants of vector capacity, information on the blood‐feeding behaviour of mosquitoes in zoos is crucial to the success of targeted vector management.     

Predicting the Mosquito Species and Vertebrate Species Involved in the Theoretical Transmission of Rift Valley Fever Virus in the United States

Rift Valley fever virus (RVFV) is a mosquito-borne virus in the family Bunyaviridiae that has spread throughout continental Africa to Madagascar and the Arabian Peninsula. The establishment of RVFV in North America would have serious consequences for human and animal health in addition to a significant economic impact on the livestock industry. Published and unpublished data on RVFV vector competence, vertebrate host competence, and mosquito feeding patterns from the United States were combined to quantitatively implicate mosquito vectors and vertebrate hosts that may be important to RVFV transmission in the United States. A viremia-vector competence relationship based on published mosquito transmission studies was used to calculate a vertebrate host competence index which was then combined with mosquito blood feeding patterns to approximate the vector and vertebrate amplification fraction, defined as the relative contribution of the mosquito or vertebrate host to pathogen transmission. Results implicate several Aedes spp. mosquitoes and vertebrates in the order Artiodactyla as important hosts for RVFV transmission in the U.S. Moreover, this study identifies critical gaps in knowledge which would be necessary to complete a comprehensive analysis identifying the different contributions of mosquitoes and vertebrates to potential RVFV transmission in the U.S. Future research should focus on (1) the dose-dependent relationship between viremic exposure and the subsequent infectiousness of key mosquito species, (2) evaluation of vertebrate host competence for RVFV among North American mammal species, with particular emphasis on the order Artiodactyla, and (3) identification of areas with a high risk for RVFV introduction so data on local vector and host populations can help generate geographically appropriate amplification fraction estimates.     

Population dynamics of mosquito-borne disease: persistence in a completely heterogeneous environment

We investigate the persistence of a mosquito-borne disease (malaria) in a system where mosquitoes and hosts are grouped in patches containing any number of individuals. A mosquito from any one of vector patches can bite, and take blood meals, in any one of m host patches. We confirm our earlier result (C. Dye and G. Hasibeder, 1986, Trans. R. Soc. Trop. Med. Hyg. 80, 69-77) that nonhomogeneous host selection by mosquitoes leads to basic reproductive rates (which measure the persistence of infection in the system) greater than or equal to those obtained under uniform host selection. We find, in addition, that strong associations between particular groups of mosquitoes and hosts lead to still higher basic reproductive rates. Exacting fieldwork would be required to find out how much higher.     

Vector-Host Interactions of Culiseta melanura in a Focus of Eastern Equine Encephalitis Virus Activity in Southeastern Virginia

Eastern equine encephalitis virus (EEEV) causes a highly pathogenic mosquito-borne zoonosis that is responsible for sporadic outbreaks of severe illness in humans and equines in the eastern USA. Culiseta (Cs.) melanura is the primary vector of EEEV in most geographic regions but its feeding patterns on specific avian and mammalian hosts are largely unknown in the mid-Atlantic region. The objectives of our study were to: 1) identify avian hosts of Cs. melanura and evaluate their potential role in enzootic amplification of EEEV, 2) assess spatial and temporal patterns of virus activity during a season of intense virus transmission, and 3) investigate the potential role of Cs. melanura in epidemic/epizootic transmission of EEEV to humans and equines. Accordingly, we collected mosquitoes at 55 sites in Suffolk, Virginia in 2013, and identified the source of blood meals in engorged mosquitoes by nucleotide sequencing PCR products of the mitochondrial cytochrome b gene. We also examined field-collected mosquitoes for evidence of infection with EEEV using Vector Test, cell culture, and PCR. Analysis of 188 engorged Cs. melanura sampled from April through October 2013 indicated that 95.2%, 4.3%, and 0.5% obtained blood meals from avian, mammalian, and reptilian hosts, respectively. American Robin was the most frequently identified host for Cs. melanura (42.6% of blood meals) followed by Northern Cardinal (16.0%), European Starling (11.2%), Carolina Wren (4.3%), and Common Grackle (4.3%). EEEV was detected in 106 mosquito pools of Cs. melanura, and the number of virus positive pools peaked in late July with 22 positive pools and a Maximum Likelihood Estimation (MLE) infection rate of 4.46 per 1,000 mosquitoes. Our findings highlight the importance of Cs. melanura as a regional EEEV vector based on frequent feeding on virus-competent bird species. A small proportion of blood meals acquired from mammalian hosts suggests the possibility that this species may occasionally contribute to epidemic/epizootic transmission of EEEV.     

Host selection by Anopheles arabiensis and An. quadriannulatus feeding on cattle in Zimbabwe

In the Zambezi valley, mosquito females of the Anopheles gambiae Giles complex (Diptera: Culicidae) were collected from a hut containing pairs of cattle distinguishable by known DNA markers. DNA was extracted from the blood-fed mosquito abdomens and primer sets for ungulate and mosquito DNA loci were used to identify the mosquito sibling species and individual host source(s) of their bloodmeals. The 67 mosquitoes comprised a mixture of An. arabiensis Patton (31%) and An. quadriannulatus Theobald (69%). DNA from one or both of the cattle present in the hut was detected in 91% of samples. When the hut contained an adult and a calf, the percentage of bloodmeals from the adult, the calf and adult + calf were 58%, 27% and 15%, respectively; the trend towards meals from the adult host was consistent but not always significant. When the pair of cattle comprised two adults of roughly equal size and age, then mosquitoes generally showed no significant bias towards feeding from one individual. There was no significant difference in the pattern of host selection made by An. arabiensis and An. quadriannulatus but the former had a significantly higher percentage (20%) of mixed meals than An. quadriannulatus (9%). These two members of the An. gambiae complex appear to be less selective in their choice of cattle hosts compared to day-active Diptera such as tsetse and Stomoxys, possibly because the hosts are generally asleep when Anopheles are active and there is therefore less selective pressure to adapt to host defensive behaviour. The slight bias of Anopheles towards older and/or larger cattle may be related to the host's larger surface area.     

Avian haematozoan parasites and their associations with mosquitoes across Southwest Pacific Islands

The degree to which haematozoan parasites can exploit a range of vectors and hosts has both ecological and evolutionary implications for their transmission and biogeography. Here we explore the extent to which closely related mosquito species share the same or closely related haematozoan parasites, and examine the overlap in parasite lineages with those isolated from avian hosts, Zosterops species, sampled across the same study sites. Mosquito samples were collected and analysed (14 species, n = 804) from four islands in Vanuatu and the main island of New Caledonia. Using polymerase chain reaction, 15.5% (14/90) of pooled mosquito (thoracic) samples showed positive amplifications. Subsequent phylogenetic analysis of the cytochrome b gene identified four genetically distinct Plasmodium and two Haemoproteus lineages from these samples, five of which were identical to parasite lineages (n = 21) retrieved from the avian hosts. We found that three Plasmodium lineages differing by a maximum of 0.9% sequence divergence were recovered from different species and genera of mosquitoes and two Haemoproteus lineages differing by 4.6% sequence divergence were carried by 10 distantly related (11-21% divergent) mosquito species. These data suggest a lack of both cospeciation and invertebrate host conservatism. Without experimental demonstration of the transmission cycle, it is not possible to establish whether these mosquitoes are the biological vectors of isolated parasite lineages, reflecting a limitation of a purely polymerase chain reaction-based approach. Nonetheless, our results raise the possibility of a new transmission pathway and highlight extensive invertebrate host shifts in an insular mosquito-parasite system.     

Host reproductive phenology drives seasonal patterns of host use in mosquitoes

Seasonal shifts in host use by mosquitoes from birds to mammals drive the timing and intensity of annual epidemics of mosquito-borne viruses, such as West Nile virus, in North America. The biological mechanism underlying these shifts has been a matter of debate, with hypotheses falling into two camps: (1) the shift is driven by changes in host abundance, or (2) the shift is driven by seasonal changes in the foraging behavior of mosquitoes. Here we explored the idea that seasonal changes in host use by mosquitoes are driven by temporal patterns of host reproduction. We investigated the relationship between seasonal patterns of host use by mosquitoes and host reproductive phenology by examining a seven-year dataset of blood meal identifications from a site in Tuskegee National Forest, Alabama USA and data on reproduction from the most commonly utilized endothermic (white-tailed deer, great blue heron, yellow-crowned night heron) and ectothermic (frogs) hosts. Our analysis revealed that feeding on each host peaked during periods of reproductive activity. Specifically, mosquitoes utilized herons in the spring and early summer, during periods of peak nest occupancy, whereas deer were fed upon most during the late summer and fall, the period corresponding to the peak in births for deer. For frogs, however, feeding on early- and late-season breeders paralleled peaks in male vocalization. We demonstrate for the first time that seasonal patterns of host use by mosquitoes track the reproductive phenology of the hosts. Peaks in relative mosquito feeding on each host during reproductive phases are likely the result of increased tolerance and decreased vigilance to attacking mosquitoes by nestlings and brooding adults (avian hosts), quiescent young (avian and mammalian hosts), and mate-seeking males (frogs).     

Attraction of mosquitoes to primate odours and implications for zoonotic Plasmodium transmission

Vector-borne diseases often originate from wildlife and can spill over into the human population. One of the most important determinants of vector-borne disease transmission is the host preference of mosquitoes. Mosquitoes with a specialised host preference are guided by body odours to find their hosts in addition to carbon dioxide. Little is known about the role of mosquito host preference in the spillover of pathogenic agents from humans towards animals and vice versa. In the Republic of Congo, the attraction of mosquitoes to primate host odours was determined, as well as their possible role as malaria vectors, using odour-baited traps mimicking the potential hosts of mosquitoes. Most of the mosquito species caught showed a generalistic host preference. Anopheles obscurus was the most abundant Anopheles mosquito, with a generalistic host preference observed from the olfactory response and the detection of various Plasmodium parasites. Interestingly, Culex decens showed a much higher attraction towards chimpanzee odours than to human or cow odours. Human Plasmodium parasites were observed in both human and chimpanzee blood, although not in the Anopheles mosquitoes that were collected. Understanding the role of mosquito host preference for cross-species parasite transmission provides information that will help to determine the risk of spillover of vector-borne diseases.     

“Show me which parasites you carry and I will tell you what you eat”, or how to infer the trophic behavior of hematophagous arthropods feeding on wildlife

Most emerging infectious diseases are zoonoses originating from wildlife among which vector‐borne diseases constitute a major risk for global human health. Understanding the transmission routes of mosquito‐borne pathogens in wildlife crucially depends on recording mosquito blood‐feeding patterns. During an extensive longitudinal survey to study sylvatic anophelines in two wildlife reserves in Gabon, we collected 2,415 mosquitoes of which only 0.3% were blood‐fed. The molecular analysis of the blood meals contained in guts indicated that all the engorged mosquitoes fed on wild ungulates. This direct approach gave only limited insights into the trophic behavior of the captured mosquitoes. Therefore, we developed a complementary indirect approach that exploits the occurrence of natural infections by host‐specific haemosporidian parasites to infer Anopheles trophic behavior. This method showed that 74 infected individuals carried parasites of great apes (58%), ungulates (30%), rodents (11%) and bats (1%). Accordingly, on the basis of haemosporidian host specificity, we could infer different feeding patterns. Some mosquito species had a restricted host range (An. nili only fed on rodents, whereas An. carnevalei, An. coustani, An. obscurus, and An. paludis only fed on wild ungulates). Other species had a wider host range (An. gabonensis could feed on rodents and wild ungulates, whereas An. moucheti and An. vinckei bit rodents, wild ungulates and great apes). An. marshallii was the species with the largest host range (rodents, wild ungulates, great apes, and bats). The indirect method substantially increased the information that could be extracted from the sample by providing details about host‐feeding patterns of all the mosquito species collected (both fed and unfed). Molecular sequences of hematophagous arthropods and their parasites will be increasingly available in the future; exploitation of such data with the approach we propose here should provide key insights into the feeding patterns of vectors and the ecology of vector‐borne diseases.     

Vertebrate-Aedes aegypti and Culex quinquefasciatus (Diptera)-arbovirus transmission networks: Non-human feeding revealed by meta-barcoding and next-generation sequencing

BackgroundAedes aegypti mosquito-borne viruses including Zika (ZIKV), dengue (DENV), yellow fever (YFV), and chikungunya (CHIKV) have emerged and re-emerged globally, resulting in an elevated burden of human disease. Aedes aegypti is found worldwide in tropical, sub-tropical, and temperate areas. The characterization of mosquito blood meals is essential to understand the transmission dynamics of mosquito-vectored pathogens.Methodology/principal findingsHere, we report Ae. aegypti and Culex quinquefasciatus host feeding patterns and arbovirus transmission in Northern Mexico using a metabarcoding-like approach with next-generation deep sequencing technology. A total of 145 Ae. aegypti yielded a blood meal analysis result with 107 (73.8%) for a single vertebrate species and 38 (26.2%) for two or more. Among the single host blood meals for Ae. aegypti, 28.0% were from humans, 54.2% from dogs, 16.8% from cats, and 1.0% from tortoises. Among those with more than one species present, 65.9% were from humans and dogs. For Cx. quinquefasciatus, 388 individuals yielded information with 326 (84%) being from a single host and 63 (16.2%) being from two or more hosts. Of the single species blood meals, 77.9% were from dogs, 6.1% from chickens, 3.1% from house sparrows, 2.4% from humans, while the remaining 10.5% derived from other 12 host species. Among those which had fed on more than one species, 11% were from dogs and humans, and 89% of other host species combinations. Forage ratio analysis revealed dog as the most over-utilized host by Ae. aegypti (= 4.3) and Cx. quinquefasciatus (= 5.6) and the human blood index at 39% and 4%, respectively. A total of 2,941 host-seeking female Ae. aegypti and 3,536 Cx. quinquefasciatus mosquitoes were collected in the surveyed area. Of these, 118 Ae. aegypti pools and 37 Cx. quinquefasciatus pools were screened for seven arboviruses (ZIKV, DENV 1–4, CHIKV, and West Nile virus (WNV)) using qRT-PCR and none were positive (point prevalence = 0%). The 95%-exact upper limit confidence interval was 0.07% and 0.17% for Ae. aegypti and Cx. quinquefasciatus, respectivelyConclusions/significanceThe low human blood feeding rate in Ae. aegypti, high rate of feeding on mammals by Cx. quinquefasciatus, and the potential risk to transmission dynamics of arboviruses in highly urbanized areas of Northern Mexico is discussed.     

Biogeographical patterns of blood parasite lineage diversity in avian hosts from southern Melanesian islands

Aim (1) To describe the species–area relationships among communities of Plasmodium and Haemoproteus parasites in different island populations of the same host genus (Aves: Zosterops). (2) To compare distance–decay relationships (turnover) between parasite communities and those with potential avian and dipteran hosts, which differ with respect to their movement and potential to disperse parasite species over large distances. Location Two archipelagos in the south‐west Pacific, Vanuatu and New Caledonia (c. 250 km west of Vanuatu) and its Loyalty Islands, with samples collected from a total of 16 islands of varying sizes (328–16,648 km²). Methods We characterized parasite diversity and distribution via polymerase chain reaction (PCR) from avian (Zosterops) blood samples. Bayesian methods were used to reconstruct the parasite phylogeny. In accordance with recent molecular evidence, we treat distinct mitochondrial DNA lineages as equivalent to species in this study. Path analysis and parasite lineage accumulation curves were used to assess the confounding effect of inadequate sampling on the estimation of parasite richness. Species–area and species–distance relationships were assessed using linear regression: distance–decay relationships were assessed using Mantel tests. Results Birds and mosquito species and Plasmodium lineages exhibited significant species–area relationships. However, Plasmodium lineages showed the weakest ‘species–area’ relationship; no relationship was found for Haemoproteus lineages. Avian species richness influenced parasite lineage richness more than mosquito species richness did. Within individual avian host species, the species–area relationship of parasites showed differing patterns. Path analysis indicated that sampling effort was unlikely to have a confounding effect on parasite richness. Distance from mainland (isolation effect) showed no effect on parasite richness. Community similarity decayed significantly with distance for avifauna, mosquito fauna and Plasmodium lineages but not for Haemoproteus lineages. Main conclusions Plasmodium lineages and mosquito species fit the power‐law model with steeper slopes than found for the avian hosts. The lack of species–distance relationship in parasites suggests that other factors, such as the competence of specific vectors and habitat features, may be more important than distance. The decay in similarity with distance suggests that the sampled Plasmodium lineages and their potential hosts were not randomly distributed, but rather exhibited spatially predictable patterns. We discuss these results in the context of the effects that parasite generality may have on distribution patterns.     

Dynamic gut microbiome across life history of the malaria mosquito Anopheles gambiae in Kenya

The mosquito gut represents an ecosystem that accommodates a complex, intimately associated microbiome. It is increasingly clear that the gut microbiome influences a wide variety of host traits, such as fitness and immunity. Understanding the microbial community structure and its dynamics across mosquito life is a prerequisite for comprehending the symbiotic relationship between the mosquito and its gut microbial residents. Here we characterized gut bacterial communities across larvae, pupae and adults of Anopheles gambiae reared in semi-natural habitats in Kenya by pyrosequencing bacterial 16S rRNA fragments. Immatures and adults showed distinctive gut community structures. Photosynthetic Cyanobacteria were predominant in the larval and pupal guts while Proteobacteria and Bacteroidetes dominated the adult guts, with core taxa of Enterobacteriaceae and Flavobacteriaceae. At the adult stage, diet regime (sugar meal and blood meal) significantly affects the microbial structure. Intriguingly, blood meals drastically reduced the community diversity and favored enteric bacteria. Comparative genomic analysis revealed that the enriched enteric bacteria possess large genetic redox capacity of coping with oxidative and nitrosative stresses that are associated with the catabolism of blood meal, suggesting a beneficial role in maintaining gut redox homeostasis. Interestingly, gut community structure was similar in the adult stage between the field and laboratory mosquitoes, indicating that mosquito gut is a selective eco-environment for its microbiome. This comprehensive gut metatgenomic profile suggests a concerted symbiotic genetic association between gut inhabitants and host.     

Multiple choice: hemiparasite performance in multi‐species mixtures

Hemiparasitic plants have green leaves, but extract water and solutes from neighbouring plants. It is still poorly understood how different host plants in communities contribute to parasite performance, as species that are good hosts in single‐host experiments may not necessarily be preferred hosts in mixtures. We grew the root hemiparasite Rhinanthus alectorolophus (Orobanchaceae) together with each of 13 host species (experiment 1) and with 15 different four‐species mixtures of these hosts (experiment 2) that differed in the number of legumes and of host functional groups. Parasites profited from mixtures including more legumes and from mixtures including different host functional groups. Some host species and mixtures were very tolerant of parasitism and supported large parasites without being strongly suppressed in their own growth, but the suppression of a species in the single‐host experiment did not explain the suppression of a species in a host mixture. We thus calculated for each host species an index of the difference in suppression between the two experiments which may be related to host use in a mixture. Host quality (mean parasite biomass with a host species) in the single‐host experiment could explain 64% of the variation in parasite biomass with a host mixture when it was weighted by the proportion of the host species in the mixture without the parasite and by the suppression difference index. Our results suggest that plant species which are the best hosts in single‐host experiments are not always those used most strongly by a parasite growing with a mixture. Together with the finding that hemiparasites benefit from a mixed diet based on hosts from different functional groups this suggests that parasites prefer certain host species to obtain a mixed diet.     

Blood meal sources of mosquitoes captured in municipal parks in São Paulo,Brazil

The aim of this study was to investigate blood meal sources of mosquitoes captured in municipal parks in the city of São Paulo, Brazil, and to identify possible associations between mosquito species and their food preferences. Fourteen species of blood hosts of 510 engorged adult female mosquitoes were identified using PCR assays with a vertebrate‐specific primer set based on cytochrome b mitochondrial DNA of the following vertebrates: birds, dogs, cats, rodents, humans, and other primates. Mosquitoes were captured using a manual aspirator, CDC traps in the canopy, CDC traps at ground level, and Shannon traps. With the exception of cats, all other vertebrates were used as hosts by mosquitoes in the parks. Statistical analysis failed to show any trend toward association between most culicid species captured and the sources of blood meals. Instead, they revealed random patterns, indicating that the mosquitoes fed on the most abundant or convenient blood meal sources. Although feeding preferences were observed in two species (birds in the case of Cx. nigripalpus and dogs in the case of Cx. quinquefasciatus), our results highlight the opportunistic feeding habits of the female mosquitoes in this study.