DNA barcode for the identification of the sand fly Lutzomyia longipalpis plant feeding preferences in a tropical urban environment

Identification of nectar sources foraged by female mosquitoes in Canada

For many mosquito species, the females must obtain vertebrate blood to complete a gonotrophic cycle. These blood meals are frequently supplemented by feeding on sugary plant nectar, which sustains energy reserves needed for flight, mating, and overall fitness. Our understanding of mosquito nectar foraging behaviors is mostly limited to laboratory experiments and direct field observations, with little research into natural mosquito-host plant relationships done in North America. In this study, we collected nectar-fed female mosquitoes over a 2-year period in Manitoba, Canada, and amplified a fragment of the chloroplast rbcL gene to identify the plant species fed upon. We found that mosquitoes foraged from diverse plant families (e.g., grasses, trees, ornamentals, and legumes), but preferred certain species, most notably soybean and Kentucky blue grass. Moreover, there appeared to be some associations between plant feeding preferences and mosquito species, date of collection, landscape, and geographical region. Overall, this study implemented DNA barcoding to identify nectar sources forage by mosquitoes in the Canadian Prairies.

Molecular detection of Wolbachia and Bartonella as part of the microbiome of phlebotomine sand flies from Chiapas, Mexico

Phlebotomine sand flies are dipterans of relevance due to their role as vectors of several pathogens worldwide. Bacteria in the gut of sand flies possibly affect their vectorial capacity and competence to transmit parasites. A retrospective study was performed in sand fly specimens that had previously been collected in four localities of the state of Chiapas during the period 2009-2011 to detect Wolbachia and Bartonella and their possible coinfection with Leishmania. For the molecular detection of bacteria, we used primers and conditions that had previously been reported. A total of 531 sand fly specimens of 10 species were analyzed. Four Wolbachia strains were detected in five sand fly species, showing a prevalence of 8.6%. All the Wolbachia strains had previously been reported in other taxa. In one sand fly species, we also detected a new lineage of Bartonella evidenced by a phylogenetic analysis. No sand fly specimens showed coinfections of these bacteria and Leishmania. The bacteria found in the phlebotomine sand flies are possibly transmitted by plant-mediated horizontal transmission and during blood meal feeding.

Next generation biosecurity: Towards genome based identification to prevent spread of agronomic pests and pathogens using nanopore sequencing

The unintentional movement of agronomic pests and pathogens is steadily increasing due to the intensification of global trade. Being able to identify accurately and rapidly early stages of an invasion is critical for developing successful eradication or management strategies. For most invasive organisms, molecular diagnostics is today the method of choice for species identification. However, the currently implemented tools are often developed for certain taxa and need to be adapted for new species, making them ill-suited to cope with the current constant increase in new invasive species. To alleviate this impediment, we developed a fast and accurate sequencing tool allowing to modularly obtain genetic information at different taxonomical levels. Using whole genome amplification (WGA) followed by Oxford nanopore MinION sequencing, our workflow does not require any a priori knowledge on the investigated species and its classification. While mainly focusing on harmful plant pathogenic insects, we also demonstrate the suitability of our workflow for the molecular identification of bacteria (Erwinia amylovora and Escherichia coli), fungi (Cladosporium herbarum, Colletotrichum salicis, Neofabraea alba) and nematodes (Globodera rostochiensis). On average, the pairwise identity between the generated consensus sequences and best GenBank BLAST matches was 99.6 ± 0.6%. Additionally, assessing the generated insect genomic dataset, the potential power of the workflow to detect pesticide resistance genes, as well as arthropod-infecting viruses and endosymbiotic bacteria is demonstrated.

Can floral nectars reduce transmission of Leishmania?

Background

Insect-vectored Leishmania are responsible for loss of more disability-adjusted life years than any parasite besides malaria. Elucidation of the environmental factors that affect parasite transmission by vectors is essential to develop sustainable methods of parasite control that do not have off-target effects on beneficial insects or environmental health. Many phytochemicals that inhibit growth of sand fly-vectored Leishmania—which have been exhaustively studied in the search for phytochemical-based drugs—are abundant in nectars, which provide sugar-based meals to infected sand flies.

Principle findings

In a quantitative meta-analysis, we compare inhibitory phytochemical concentrations for Leishmania to concentrations present in floral nectar and pollen. We show that nectar concentrations of several flowering plant species exceed those that inhibit growth of Leishmania cell cultures, suggesting an unexplored, landscape ecology-based approach to reduce Leishmania transmission.

Significance

If nectar compounds are as effective against parasites in the sand fly gut as predicted from experiments in vitro, strategic planting of antiparasitic phytochemical-rich floral resources or phytochemically enriched baits could reduce Leishmania loads in vectors. Such interventions could provide an environmentally friendly complement to existing means of disease control.

Leishmania parasites infect over a million people each year—including over 200,000 infections with deadly visceral leishmaniasis—resulting in a greater health burden than any human parasite besides malaria. Leishmania infections of humans are transmitted by blood-feeding sand flies, which also consume floral nectar. Nectar contains many chemicals that inhibit Leishmania growth and are candidate treatments for infection of humans. However, these same compounds could also reduce infection in nectar-consuming sand flies. By combining existing data on the chemistry of nectar and sensitivity of Leishmania to plant compounds, we show that some floral nectars contain sufficient chemical concentrations to inhibit growth of insect-stage Leishmania. Our results suggest that consumption of these nectars could reduce parasite loads in sand flies and transmission of parasites to new human hosts. In contrast to insecticide-based methods of sand fly control, incorporation of antiparasitic nectar sources into landscapes and domestic settings could benefit public health without threatening beneficial insects. These findings suggest an unexplored, landscape-based approach to reduce transmission of a major neglected tropical disease worldwide.

Behavioural responses of Phlebotomus duboscqi to plant-derived volatile organic compounds

Phlebotomine sand flies are vectors of Leishmania parasites that cause leishmaniases. Both sexes of sand flies feed on plants primarily for sugars, although the chemical cues that mediate attraction to host plants remain largely unknown. Previously, using coupled gas chromatography-mass spectrometry, the authors identified several volatile organic compounds (VOCs) common to preferred host plants for selected Afrotropical sand flies from the Fabaceae family. Of the identified volatiles, the significance of the monoterpenes linalool oxide, ocimene and p-cymene and the benzenoid m-cresol, p-cresol in sand fly behaviour is unknown. In olfactometer assays, the authors tested these compounds singly and in blends for their attractiveness to Phlebotomus duboscqi, cutaneous leishmaniasis vector in Kenya. In dose-response assays, single compounds increased the responses of males and females over controls, but their optimum attractive doses varied between the sexes. Two five-component blends, referred to as Blend-f and Blend-m for females and males respectively, were formulated and tested in dose-response assays against 1-octen-3-ol (positive control). The results of the present study showed that males and females were significantly attracted to varying levels of the two blends. In pairwise assays, the authors evaluated the most attractive of these blends to each sex (i.e., Blend Am for male against Blend Bf for female), revealing that males were attracted to both blends at varying levels, whereas females were indifferent. The study's results demonstrate that plant-derived VOCs can be exploited for sand fly management.

Plant sugar feeding patterns of wild-caught Aedes aegypti from dengue endemic and non-endemic areas of Kenya

A fundamental understanding of plant sugar feeding behaviour in vector populations can lead to the development of ecologically effective vector monitoring and control strategies. Despite previous studies on mosquito-plant interactions, relatively few have been conducted on the dengue vector Aedes aegypti (Diptera: Culicidae). The authors studied Ae. aegypti-plant interactions at two sites of varying dengue endemicity in Kenya: Kilifi (endemic) and Isiolo (non-endemic). Using chemical and molecular assays [DNA barcoding targeting the chloroplast ribulose-1,5 bisphosphate carboxylase/oxygenase large chain (rbcL) gene], the authors show that at the two sites plant feeding in this mosquito species: (a) varies by sex and season; (b) results in the acquisition of diverse sugars, and (c) is associated with diverse host plants in the families Fabaceae, Malvaceae, Poaceae and Rosaceae. These results reveal insights into the plant sugar feeding patterns of wild-caught Ae. aegypti and provide a baseline for future studies on the olfactory basis for host plant attraction for the development of vector monitoring and control tools.

DNA barcoding of Lutzomyia longipalpis species complex (Diptera: Psychodidae), suggests the existence of 8 candidate species

The sand fly Lutzomyia (L.) longipalpis has been implicated as the primary vector of Leishmania infantum, the causative agent of visceral leishmaniasis VL. In addition, it has been associated with atypical cutaneous leishmaniasis transmission in the Neotropic and Central America, respectively. The existence of a L. longipalpis complex species has been suggested with important implications for leishmaniasis epidemiology; however, the delimitation of species conforming it remains a topic of controversy. The DNA Barcoding Initiative based on cox1 sequence variation was used to identify the MOTUs in L. longipalpis including previously described L. pseudolongipalpis. The genetic variation was analyzed based on tree and distance methods. Fifty-five haplotypes were obtained from 103 sequences which were assigned to MOTUs, with a clear separation and a high correspondence of individuals to the groups. Maximum likelihood and Bayesian phylogenetic analysis showed eight MOTUs (100% bootstrap) with high genetic divergence (12.6%). Data obtained in the present study suggest that L. longipalpis complex consists of at least 8 lineages that may represent species. It would be desirable perform additional morphological and molecular analysis of L. longipalpis from Colosó (Caribbean ecoregion) considering that specimens from that area were grouped with L. pseudolongipalpis one of the complex species previously described from Venezuela, which has not been registered in Colombia.

High Dietary Niche Overlap Between Non-native and Native Ant Species in Natural Ecosystems

Ants represent a highly diverse and ecologically important group of insects found in almost all terrestrial ecosystems. A subset of ant species have been widely transported around the globe and invade many natural ecosystems, often out-competing native counterparts and causing varying impacts on recipient ecosystems. Decisions to control non-native ant populations require an understanding of their interactions and related impacts on native communities. We employed stable isotope analysis and metabarcoding techniques to identify potential dietary niche overlap and identify gut contents of 10 ant species found in natural ecosystems in Aotearoa New Zealand. Additionally, we looked at co-occurrence to identify potential competitive interactions among native and non-native ant species. Ants fed mainly across two trophic levels, with high dietary overlap. Relative to other ant species sampled, two non-native ant species, Linepithema humile and Technomyrmex jocosus, were found to feed at the lowest trophic level. The largest isotopic niche overlap was observed between the native Monomorium antarcticum and the invasive Ochetellus glaber, with analyses revealing a negative co-occurrence pattern. Sequence data of ant gut content identified 51 molecular operational taxonomic units, representing 22 orders and 34 families, and primarily consisting of arthropod DNA. Although we generally found high dietary overlap among species, negative occurrence between a dominant, non-native species and a ubiquitous native species indicates that species-specific interactions could be negatively impacting native ecosystems. Our research progresses and informs the currently limited knowledge around establishing protocols for metabarcoding to investigate ant diet and interactions between native and non-native ant species.

Afrotropical sand fly-host plant relationships in a leishmaniasis endemic area, Kenya

The bioecology of phlebotomine sand flies is intimately linked to the utilization of environmental resources including plant feeding. However, plant feeding behavior of sand flies remains largely understudied for Afrotropical species. Here, using a combination of biochemical, molecular, and chemical approaches, we decipher specific plant-feeding associations in field-collected sand flies from a dry ecology endemic for leishmaniasis in Kenya. Cold-anthrone test indicative of recent plant feeding showed that fructose positivity rates were similar in both sand fly sexes and between those sampled indoors and outdoors. Analysis of derived sequences of the ribulose-1,5-bisphosphate carboxylase large subunit gene (rbcL) from fructose-positive specimens implicated mainly Acacia plants in the family Fabaceae (73%) as those readily foraged on by both sexes of Phlebotomus and Sergentomyia. Chemical analysis by high performance liquid chromatography detected fructose as the most common sugar in sand flies and leaves of selected plant species in the Fabaceae family. Analysis of similarities (ANOSIM) of the headspace volatile profiles of selected Fabaceae plants identified benzyl alcohol, (Z)-linalool oxide, (E)-β-ocimene, p-cymene, p-cresol, and m-cresol, as discriminating compounds between the plant volatiles. These results indicate selective sand fly plant feeding and suggest that the discriminating volatile organic compounds could be exploited in attractive toxic sugar- and odor- bait technologies control strategies.

Plant feeding as an essential resource of sand flies, primary vectors of Leishmania parasites, is largely understudied for Afrotropical species. Here, we combined field ecology, biochemical, molecular and chemical approaches, to decipher plant feeding associations in field-collected sand flies from a dry ecology endemic for leishmaniasis in Kenya revealing i) similar rates of plant feeding among sand fly sexes sampled from indoor and outdoor environments, ii) Acacia plants in the family Fabaceae as those readily foraged on by sand fly species in Phlebotomus and Sergentomyia, iii) fructose as the common sugar in sand flies and leaves of selected plant species in the Fabaceae family, iv) compounds namely benzyl alcohol, (Z)-linalool oxide, (E)-β-ocimene, p-cymene, p-cresol, and m-cresol, as discriminating volatile organic compounds between volatiles of selected Fabaceae plants. The findings indicate selective sand fly plant feeding and suggest that the discriminating volatile organic compounds could be exploited in attractive toxic sugar- and odor-bait technologies for sand fly control.

Nutrition, malnutrition, and leishmaniasis

Leishmaniasis is a vector-borne infectious disease with a long history of infecting humans and other animals. It is a known emerging or resurging disease. The host nutritional state has an indispensable role in defense against pathogens. The host defense system disorganization as a result of undernutrition is responsible for asymptomatic infections and even severe diseases. Host susceptibility and pathophysiologic severity to infection can be aggravated owing to undernourishment in a number of pathways, and infection also may aggravate preexisting poor nutrition or further increase host susceptibility. This study suggests that there may be some relationship between malnutrition and the endemicity of the parasite. The susceptibility to and severity of leishmanial infection can be altered by the body weight and serum levels of micronutrients. Nutrition not only affects the vulnerability of the host but also may affect the desire of sandfly to bite a specific host. Apart from host defense mechanism, nutritional stress also greatly influences vector competence and host-seeking behavior, especially during larvae development. The host and sandfly vector nutritional states could also influence the evolution of the parasite. It is essential to elucidate the roles that diets and nutrition play in the leishmanial life cycle. The aim of this article is to review the influences of nutrition and diets on the host susceptibility and severity of infection, preemptive and therapeutic strategy feedback, parasite evolution, and vector competence.

Development of a next generation DNA sequencing-based multi detection assay for detecting and identifying Leishmania parasites, blood sources, plant meals and intestinal microbiome in phlebotomine sand flies

Leishmaniasis is a disease caused by Leishmania parasites transmitted by phlebotomine sand flies (Diptera: Psychodidae). Human infections with different Leishmania species cause characteristic clinical manifestations; cutaneous or visceral leishmaniasis. Here we describe the development and application of a Miseq Next GenerationSequencing (NGS)-based Multi Detection Assay (MDA) designed to characterize metagenomics parameters pertinent to the sand fly vectors which may affect their vectorial capacity for Leishmania. For this purpose, we developed a MDA by which, DNA fragments were amplified through polymerase chain reactions (PCR) and then sequenced by MiSeq/NGS. PCR amplification was achieved using some published and some new primers designed specifically for identifying Leishmania spp. (ITS1), sand fly spp. (cytochrome oxidase I), vertebrate blood (Cytochrome b), plant DNA ribulose-1,5-bisphosphate carboxylase large subunit gene (rbcL), and prokaryotic micobiome (16 s rRNA). This MDA/NGS analysis was performed on two species of wild-caught sand flies that transmit different Leishmania spp. in two ecologically distinct, but geographically neighboring locations. The results were analyzed to identify, quantitate and correlate the measured parameters in order to assess their putative importance in the transmission dynamics of leishmaniasis.

Transmission blocking sugar baits for the control of Leishmania development inside sand flies using environmentally friendly beta-glycosides and their aglycones

Background

The sand fly Lutzomyia longipalpis is the main vector of American visceral leishmaniasis, a disease caused by parasites of the genus Leishmania. Adults of this insect feed on blood (females only) or sugar from plant sources, but their digestion of carbohydrates is poorly studied. Beta-glycosides as esculin and amygdalin are plant compounds and release toxic compounds as esculetin and mandelonitrile when hydrolyzed. Beta-glucosidase and trehalase are essential enzymes in sand fly metabolism and participate in sugar digestion. It is therefore possible that the toxic portions of these glycosides, released during digestion, affect sand fly physiology and the development of Leishmania.

Results

We tested the oral administration to sand flies of amygdalin, esculin, mandelonitrile, and esculetin in the sugar meal. These compounds significantly decreased the longevity of Lutzomyia longipalpis females and males. Lutzomyia longipalpis adults have significant hydrolytic activities against esculin and feeding on this compound cause changes in trehalase and β-glucosidase activities. Female trehalase activity is inhibited in vitro by esculin. Esculin is naturally fluorescent, so its ingestion may be detected and quantified in whole insects or tissue samples stored in methanol. Mandelonitrile neither affected the amount of sugar ingested by sand flies nor showed repellent activity. Our results show that mandelonitrile significantly reduces the viability of L. amazonensis, L. braziliensis, L. infantum and L. mexicana, in a concentration-dependent manner. Esculetin caused a similar effect, reducing the number of L. infantum and L. mexicana. Female L. longipalpis fed on mandelonitrile had a reduction in the number of parasites and prevalence of infection after seven days of infection with L. mexicana, either by counting in a Neubauer chamber or by qPCR assays.

Conclusions

Glycosides have significant effects on L. longipalpis longevity and metabolism and also affect the development of parasites in culture and inside the insect. These observations might help to conceptualize new vector control strategies using transmission blocking sugar baits.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3122-z) contains supplementary material, which is available to authorized users.

Plant-feeding phlebotomine sand flies, vectors of leishmaniasis, prefer Cannabis sativa

Blood-sucking phlebotomine sand flies (Diptera: Psychodidae) transmit leishmaniasis as well as arboviral diseases and bartonellosis. Sand fly females become infected with Leishmania parasites and transmit them while imbibing vertebrates' blood, required as a source of protein for maturation of eggs. In addition, both females and males consume plant-derived sugar meals as a source of energy. Plant meals may comprise sugary solutions such as nectar or honeydew (secreted by plant-sucking homopteran insects), as well as phloem sap that sand flies obtain by piercing leaves and stems with their needle-like mouthparts. Hence, the structure of plant communities can influence the distribution and epidemiology of leishmaniasis. We designed a next-generation sequencing (NGS)-based assay for determining the source of sand fly plant meals, based upon the chloroplast DNA gene ribulose bisphosphate carboxylase large chain (rbcL). Here, we report on the predilection of several sand fly species, vectors of leishmaniasis in different parts of the world, for feeding on Cannabis sativa We infer this preference based on the substantial percentage of sand flies that had fed on C. sativa plants despite the apparent "absence" of these plants from most of the field sites. We discuss the conceivable implications of the affinity of sand flies for C. sativa on their vectorial capacity for Leishmania and the putative exploitation of their attraction to C. sativa for the control of sand fly-borne diseases.

Entomological signatures in honey: an environmental DNA metabarcoding approach can disclose information on plant-sucking insects in agricultural and forest landscapes

Honeydew produced from the excretion of plant-sucking insects (order Hemiptera) is a carbohydrate-rich material that is foraged by honey bees to integrate their diets. In this study, we used DNA extracted from honey as a source of environmental DNA to disclose its entomological signature determined by honeydew producing Hemiptera that was recovered not only from honeydew honey but also from blossom honey. We designed PCR primers that amplified a fragment of mitochondrial cytochrome c oxidase subunit 1 (COI) gene of Hemiptera species using DNA isolated from unifloral, polyfloral and honeydew honeys. Ion Torrent next generation sequencing metabarcoding data analysis assigned Hemiptera species using a customized bioinformatic pipeline. The forest honeydew honeys reported the presence of high abundance of Cinara pectinatae DNA, confirming their silver fir forest origin. In all other honeys, most of the sequenced reads were from the planthopper Metcalfa pruinosa for which it was possible to evaluate the frequency of different mitotypes. Aphids of other species were identified from honeys of different geographical and botanical origins. This unique entomological signature derived by environmental DNA contained in honey opens new applications for honey authentication and to disclose and monitor the ecology of plant-sucking insects in agricultural and forest landscapes.

Host plant forensics and olfactory-based detection in Afro-tropical mosquito disease vectors

The global spread of vector-borne diseases remains a worrying public health threat, raising the need for development of new combat strategies for vector control. Knowledge of vector ecology can be exploited in this regard, including plant feeding; a critical resource that mosquitoes of both sexes rely on for survival and other metabolic processes. However, the identity of plant species mosquitoes feed on in nature remains largely unknown. By testing the hypothesis about selectivity in plant feeding, we employed a DNA-based approach targeting trnH-psbA and matK genes and identified host plants of field-collected Afro-tropical mosquito vectors of dengue, Rift Valley fever and malaria being among the most important mosquito-borne diseases in East Africa. These included three plant species for Aedes aegypti (dengue), two for both Aedes mcintoshi and Aedes ochraceus (Rift Valley fever) and five for Anopheles gambiae (malaria). Since plant feeding is mediated by olfactory cues, we further sought to identify specific odor signatures that may modulate host plant location. Using coupled gas chromatography (GC)-electroantennographic detection, GC/mass spectrometry and electroantennogram analyses, we identified a total of 21 antennally-active components variably detected by Ae. aegypti, Ae. mcintoshi and An. gambiae from their respective host plants. Whereas Ae. aegypti predominantly detected benzenoids, Ae. mcintoshi detected mainly aldehydes while An. gambiae detected sesquiterpenes and alkenes. Interestingly, the monoterpenes β-myrcene and (E)-β-ocimene were consistently detected by all the mosquito species and present in all the identified host plants, suggesting that they may serve as signature cues in plant location. This study highlights the utility of molecular approaches in identifying specific vector-plant associations, which can be exploited in maximizing control strategies such as such as attractive toxic sugar bait and odor-bait technology.