Sugar Feeding Patterns for Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae) Mosquitoes in South Texas

Sugar Detection in Mosquitoes via Anthrone Tests

Adult mosquitoes feed on plant sugar, frequently in the form of floral nectar. However, because of spatial and temporal variation in this behavior, as well as to the predilection of most mosquitoes to alter their behavior in the presence of a researcher, observing mosquito nectar feeding and similar behaviors directly in real time is not always feasible. In this protocol, I describe methods for hot and cold anthrone tests, which can be used to quantify the degree to which mosquito sugar feeding occurs in nature.

Mosquito Pollination and Sugar Detection Methods: An Overview

The interactions between mosquitoes and plants and, particularly, between mosquitoes and plant sugars from flowers and other structures are often overlooked and are vastly underresearched compared to mosquito-vertebrate or mosquito-pathogen interactions. Given the importance of mosquito nectar-feeding behavior, as well as its impact on vectorial capacity and its implications for vector suppression, a better understanding of mosquito-plant interactions is needed. Direct observation of mosquitoes visiting plants to obtain sugar and other nutrients can be difficult because females may leave flowers to seek a blood meal from the observer, but this can be overcome with the right experimental procedures. This article discusses methods for the detection of sugar in mosquitoes and for assessing mosquito pollination.

Unveil the sugar diet and associated environmental compounds in the crop of the mosquito Culex pipiens

Culex pipiens (Linnaeus, 1758) mosquitoes search plant sources of sugars to cope with the energetic demand of various physiological processes. The crop as part of the digestive system is devoted to the storage of sugar-based meal obtained from various nectars sources. The profiling of sugars and metabolites in the Culex pipiens' crop is scarce, and only few studies used Liquid Chromatography - Mass Spectrometry (LC-MS), which provides broad detection for biomonitoring environmental substances and even contaminants in the sugar diet of mosquitoes populations. Therefore, sugar and metabolite profiling were performed on crops obtained from mosquitoes exposed to plant nectar under laboratory or natural conditions by Ultra High-Performance LC-MS (UHPLC-MS). This method allowed us a precise quantitative and qualitative identification of sugar diet and associated environmental compounds in the crop of the mosquito C. pipiens. Under laboratory condition, mosquitoes were allowed to feed on either glucose solution, commercially-available flowers or field collected flowers. In addition, we collected mosquitoes from the field to compare those crop metabolomes with metabolome patterns occurring after nectar feeding in the lab. The sugar quantities and quality obtained from the crops of mosquitoes collected in the field were similar to those crops obtained from mosquitoes that fed on commercially-available flowers and from field collected flowers with a limit of detection of 10 μg/L for sucrose, glucose and sucrose. Next to sugar compounds, we identified 2 types of amino acids, 12 natural products, and 9 pesticides. Next to the diversity of sugar compounds, we could confirm that secondary metabolites and environmental pollutants are typically up taken from floral nectar sources by C. pipiens. The in-depth knowledge on mosquito-plant interactions may inspire the development and further optimization of mosquito trap systems and arboviral surveillance systems.

Automated analysis of feeding behaviors of females of the mosquito Aedes aegypti using a modified flyPAD system

Mosquitoes present a global health challenge due to their ability to transmit human and animal pathogens upon biting and blood feeding. The investigation of tastants detected by mosquitoes and their associated feeding behaviors is needed to answer physiological and ecological questions that could lead to novel control methods. A high-throughput system originally developed for research in fruit flies feeding behavior, the flyPAD, was adapted and tested for behaviors associated with the interaction or consumption of liquid diets offered to females of the mosquito Aedes aegypti Liverpool strain. Females were given water, sucrose solution and sheep blood in choice and non-choice assays. The volume ingested was evaluated with fluorescein. The placement of the system on a heated surface allowed blood consumption, and without females puncturing a membrane. The flyPAD system recorded nine feeding behavioral variables, of which the number of sips and number of activity bouts correlated with meal volume ingested for both sucrose solution and blood. The adaptation to mosquitoes of the flyPAD system differentiated feeding behavior variables between two feeding deterrents, capsaicin, and caffeine. The flyPAD has potential to quickly assess diverse tastants in both sucrose and blood and may contribute to characterizing more precisely their mode of action.

The distinctive bionomics of Aedes aegypti populations in Africa

Aedes aegypti is the primary vector of dengue, chikungunya, and Zika viruses of medical importance. Behavioral and biological attributes contribute to its vectorial capacity. The mosquito domestic form, which resides outside Africa (Ae. aegypti aegypti (Aaa)), is considered to breed in artificial containers in and around homes and preferentially feeds on human blood but commonly indulges in a plant diet. Potential divergence in these attributes, in sub-Saharan Africa (SSA) where Aaa coexists with the forest ecotype (Ae. aegypti formosus), should impact the vectoring ability and hence disease epidemiology. A summary of current knowledge on Ae. aegypti blood feeding, oviposition, and plant-feeding habits among SSA populations is provided in comparison with those in different geographies, globally. Emphasis is placed on improved understanding of the connection between changing subspecies adaptation in these traits and arbovirus disease risk in SSA in response to climate change and increasing urbanization, with the ultimate use of this information for effective disease control.

Natural sugar feeding rates of Anopheles mosquitoes collected by different methods in western Kenya

Attractive targeted sugar baits (ATSBs) are a potential vector control tool that exploits the sugar-feeding behaviour of mosquitoes. We evaluated the sugar-feeding behaviour of Anopheles mosquitoes as part of baseline studies for cluster randomised controlled trials of ATSBs. Mosquitoes were collected indoors and outdoors from two villages in western Kenya using prokopack aspirations, malaise tent traps and ultraviolet (UV) light traps. Individual mosquitoes were subjected to the cold anthrone test to assess the presence of sugar. Overall, 15.7% of collected mosquitoes had fed on natural sugar sources. By species and sex, the proportion sugar-fed was 41.3% and 27.7% in male and female Anopheles funestus, 27.2% and 12.8% in male and female An. arabiensis, and 9.7% and 8.3% in male and female An. coustani, respectively. Sugar-feeding was higher in unfed than blood-fed mosquitoes and higher in male than gravid mosquitoes. Anopheles mosquitoes obtained sugar meals from natural sources during all physiological stages, whether they rest indoors or outdoors. These findings offer a potential avenue to exploit for the control of mosquitoes, particularly with the advent of ATSBs, which have been shown to reduce mosquito densities in other regions.

The MosHouse® Trap: Evaluation of the Efficiency in Trapping Sterile Aedes aegypti Males in Semi-Field Conditions

Arbovirus diseases, such as dengue, chikungunya, and Zika, are important public health problems. Controlling the major vector, Aedes aegypti, is the only approach to suppressing these diseases. The surveillance of this mosquito species needs effective collecting methods. In this study, a simple MosHouse sticky trap was evaluated in a semi-field condition. Our results demonstrated the efficiency of this trap in collecting Ae. aegypti males, and no significant difference (p > 0.05) in the numbers of males was detected when compared with the widely used BG- Sentinel trap. However, there were significantly lower numbers of females (p < 0.05) collected using the MosHouse trap when compared to the BG-Sentinel trap. We also found a significant difference (p < 0.05) in the collected numbers between irradiated and non-irradiated males. More irradiated males were collected in the MosHouse traps. The improvement of male collection was achieved with the addition of a sugar stick and sticky flags. Significantly higher numbers of males were collected in the MosHouse trap with sticky flags compared to the original one when they were released independently of females, but both were collected in higher numbers when they were released together (p < 0.05). In conclusion, our experiments demonstrated that the MosHouse trap could sample Ae. aegypti, especially males, as efficiently as the established BG-Sentinel trap, while the cost was more than 50 times lower, showing the potential of the MosHouse trap for improved Ae. aegypti male and female surveillance with very large numbers of traps at affordable costs. In addition, significantly (p < 0.001) increased male sampling was achieved by adding an external sticky flag on the MosHouse trap, providing an avenue for further development of the novel male-trapping strategy.

New tools for Aedes control: mass trapping

Aedes aegypti, the main vector of dengue, chikungunya, and Zika viruses uses artificial containers around homes to undergo immature development, making household-level detection and control extremely difficult in large urban areas. Mass trapping is an emerging methodology to control container-Aedes species such as Aedes aegypti and Aedes albopictus because effective traps for adult stages of these mosquitoes were developed recently. There are three main approaches to mass-trapping these mosquitoes: 1) Pull (attract/kill), 2) push (repel)-pull (attract/kill), and 3) pull (attract/contaminate/infect)-push (fly away). Effective mass-trapping depends on trap quality (capture efficiency, sturdiness, frequency of servicing), trap density and areal coverage, community involvement, and safety. Recent studies showed that Ae. aegypti populations can be sustainably controlled by mass trapping, although more area-wide studies showing effectiveness at preventing disease are needed for all trapping systems. Cost-effectiveness studies are needed for all emerging Aedes control approaches.

A next-generation (DNA) sequencing (NGS)-based method for identifying the sources of sugar meals in mosquito vectors of West Nile virus in Israel

Mosquitoes of the genus Culex comprise important vectors of pathogenic arboviruses in our region, including West Nile and Rift Valley Fever viruses. To improve our understanding of the epidemiology and transmission dynamics of arboviruses, we need to study the behavior and ecology of their vectors. The feeding patterns of the vector mosquitoes can be very useful in determining how and where to focus control efforts. For example, determining the preferred blood hosts of the females can assist in the implementation of potentially efficacious strategies for focused control of mosquito females. Determining the plants from which both sexes derive their sugar meals can comprise the initial step towards the formulation of efficient lures for trapping mosquitoes. In the past, plant meal identification was based mainly on chemical detection of fructose and microscopical observations of cellulose particles in mosquito guts. More recent studies have utilized DNA barcoding capable of identifying plant food sources. In the current study, we identify multiple plant species from which large numbers of mosquitoes obtained their sugar meals in one experimental procedure. We employed next generation DNA sequencing to sequence the chloroplast specific plant genes atpB and rbcL.

Sugar prevalence in Aedes albopictus differs by habitat, sex and time of day on Masig Island, Torres Strait, Australia

Background

Sugar feeding is a fundamental behaviour of many mosquito species. For Aedes albopictus, an important vector of dengue virus and chikungunya virus, little is known about its sugar-feeding behaviour, and no studies have been conducted on this in the southern hemisphere. This knowledge is pivotal for determining the potential of attractive targeted sugar baits (ATSBs) to control this important vector.

Methods

The prevalence of sugar was assessed in 1808 Ae. albopictus from Masig Island, Torres Strait, Australia collected between 13 and 25 March 2020. Fructose presence and content in field-collected Ae. albopictus were quantified using the cold anthrone assay.

Results

Significantly more male (35.8%) than female (28.4%) Ae. albopictus were sugar fed. There was a significant interaction between sex and time of day on the probability of capturing sugar-fed Ae. albopictus. For both sexes, fructose prevalence and content were higher in mosquitoes caught in the morning than in the afternoon. Female Ae. albopictus collected in the residential habitat were significantly more likely to be sugar fed than those collected in the woodland habitat.

Conclusions

These findings provide baseline information about the sugar-feeding patterns of Ae. albopictus and provide essential information to enable an assessment of the potential of ATSBs for vector suppression and control on Masig Island, with relevance to other locations where this species occurs.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05020-w.

Highlights of Medical Entomology, 2020

Medical Entomology as a field is inherently global - thriving on international and interdisciplinary collaborations and affected dramatically by arthropod and pathogen invasions and introductions. This past year also will be remembered as the year in which the SARS-CoV-2 COVID-19 pandemic affected every part of our lives and professional activities and impacted (or changed, sometimes in good ways) our ability to collaborate and detect or respond to invasions. This incredible year is the backdrop for the 2020 Highlights in Medical Entomology. This article highlights the broad scope of approaches and disciplines represented in the 2020 published literature, ranging from sensory and chemical ecology, population genetics, impacts of human-mediated environmental change on vector ecology, life history and the evolution of vector behaviors, to the latest developments in vector surveillance and control.

Avoidance of the Plant Hormone Cis-Jasmone by Aedes aegypti Depends On Mosquito Age in Both Plant and Human Odor Backgrounds

Adults of many mosquito species feed on plants to obtain metabolic energy and to enhance reproduction. Mosquitoes primarily rely on olfaction to locate plants and are known to respond to a range of plant volatiles. We studied the olfactory response of the yellow fever mosquito Aedes aegypti to methyl jasmonate (MeJA) and cis-jasmone (CiJA), volatile compounds originating from the octadecanoid signaling pathway that plays a key role in plant defense against herbivores. Specifically, we investigated how Ae. aegypti of different ages responded to elevated levels of CiJA in two attractive odor contexts, either derived from Lima bean plants or human skin. Aedes aegypti females landed significantly less often on a surface with CiJA and MeJA compared to the solvent control, CiJA exerting a stronger reduction in landing than MeJA. Odor context (plant or human) had no significant main effect on the olfactory responses of Ae. aegypti females to CiJA. Mosquito age significantly affected the olfactory response, older females (7–9 d) responding more strongly to elevated levels of CiJA than young females (1–3 d) in either odor context. Our results show that avoidance of CiJA by Ae. aegypti is independent of odor background, suggesting that jasmonates are inherently aversive cues to these mosquitoes. We propose that avoidance of plants with elevated levels of jasmonates is adaptive to mosquitoes to reduce the risk of encountering predators that is higher on these plants, i.e. by avoiding ‘enemy-dense-space’.

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.

The impact of mating and sugar feeding on blood-feeding physiology and behavior in the arbovirus vector mosquito Aedes aegypti

BACKGROUND

Aedes aegypti mosquitoes are globally distributed vectors of viruses that impact the health of hundreds of millions of people annually. Mating and blood feeding represent fundamental aspects of mosquito life history that carry important implications for vectorial capacity and for control strategies. Females transmit pathogens to vertebrate hosts and obtain essential nutrients for eggs during blood feeding. Further, because host-seeking Ae. aegypti females mate with males swarming near hosts, biological crosstalk between these behaviors could be important. Although mating influences nutritional intake in other insects, prior studies examining mating effects on mosquito blood feeding have yielded conflicting results.

METHODOLOGY/PRINCIPAL FINDINGS

To resolve these discrepancies, we examined blood-feeding physiology and behavior in virgin and mated females and in virgins injected with male accessory gland extracts (MAG), which induce post-mating changes in female behavior. We controlled adult nutritional status prior to blood feeding by using water- and sugar-fed controls. Our data show that neither mating nor injection with MAG affect Ae. aegypti blood intake, digestion, or feeding avidity for an initial blood meal. However, sugar feeding, a common supplement in laboratory settings but relatively rare in nature, significantly affected all aspects of feeding and may have contributed to conflicting results among previous studies. Further, mating, MAG injection, and sugar intake induced declines in subsequent feedings after an initial blood meal, correlating with egg production and laying. Taking our evaluation to the field, virgin and mated mosquitoes collected in Colombia were equally likely to contain blood at the time of collection.

CONCLUSIONS/SIGNIFICANCE

Mating, MAG, and sugar feeding impact a mosquito's estimated ability to transmit pathogens through both direct and indirect effects on multiple aspects of mosquito biology. Our results highlight the need to consider natural mosquito ecology, including diet, when assessing their physiology and behavior in the laboratory.

Cross-talk of insulin-like peptides, juvenile hormone, and 20-hydroxyecdysone in regulation of metabolism in the mosquito Aedes aegypti

Female mosquitoes feed sequentially on carbohydrates (nectar) and proteins (blood) during each gonadotrophic cycle to become reproductively competent and effective disease vectors. Accordingly, metabolism is synchronized to support this reproductive cyclicity. However, regulatory pathways linking metabolism to reproductive cycles are not fully understood. Two key hormones, juvenile hormone (JH) and ecdysteroids (20-hydroxyecdysone, 20E, is the most active form) govern female mosquito reproduction. Aedes aegypti genome codes for eight insulin-like peptides (ILPs) that are critical for controlling metabolism. We examined the effects of the JH and 20E pathways on mosquito ILP expression to decipher regulation of metabolism in a reproducing female mosquito. Chromatin immunoprecipitation assays showed genomic interactions between ilp genes and the JH receptor, methoprene-tolerant, a transcription factor, Krüppel homolog 1 (Kr-h1), and two isoforms of the ecdysone response early gene, E74. The luciferase reporter assays showed that Kr-h1 activates ilps 2, 6, and 7, but represses ilps 4 and 5 The 20E pathway displayed the opposite effect in the regulation of ilps E74B repressed ilps 2 and 6, while E74A activated ilps 4 and 5 Combining RNA interference, CRISPR gene tagging and enzyme-linked immunosorbent assay, we have shown that the JH and 20E regulate protein levels of all eight Ae. aegypti ILPs. Thus, we have established a regulatory axis between ILPs, JH, and 20E in coordination of metabolism during gonadotrophic cycles of Ae. aegypti.

Biological traits of wild-caught populations of Aedes aegypti in dengue endemic and non-endemic regions of Kenya

Variation in vector traits can modulate local scale differences in pathogen transmission. Here, we compared seasonal variation in the wing length (proxy for body size) and energy reserves of adult wild-caught Aedes aegypti populations from a dengue endemic (Kilifi) and non-endemic (Isiolo) area of Kenya. Vector sampling in the dengue endemic site was conducted during the dry and wet seasons. In the non-endemic area, it was limited to the dry season which characterizes this ecology where sporadic or no rainfall is commonplace during the year. We found variation by site in the body size of both sexes, with an overall smaller size of Ae. aegypti populations collected from Isiolo than those from Kilifi. Our results show that although total carbohydrates and lipids levels were highest in both sexes during the dry season, they were two-fold higher in males than females. However, we found weak correlations between body size and energy reserves for both sexes, with body size being more sensitive in identifying differences at a population level. These results provide insights into the determinants of the vectoring potential of Ae. aegypti populations in dengue endemic and non-endemic ecologies in Kenya.

Susceptibility of South Texas Aedes aegypti to Pyriproxyfen

Simple Summary

We evaluated the susceptibility of an Ae. aegypti strain from the Lower Rio Grande Valley (LRGV) of South Texas to the insect growth regulator pyriproxyfen. We observed a difference in the inhibition of emergence to the lowest doses of pyriproxyfen tested between our field strain and a susceptible strain. However, the doses used are 10 times lower from the recommended application of <50 ppb for vector control programs. Our results suggest that pyriproxyfen should be an effective active ingredient in the LRGV to help reduce Ae. aegypti populations in the LRGV.

Abstract

An integral part to integrated mosquito management is to ensure chemical products used for area-wide control are effective against a susceptible population of mosquitoes. Prior to conducting an intervention trial using an insect growth regulator, pyriproxyfen, in South Texas to control Aedes aegypti, we conducted a larval bioassay to evaluate baseline levels of susceptibility. We used seven serially-diluted doses ranging from 2.5 ppb to 6.3 × 10⁻⁴ ppb. We observed 100% inhibition emergence (IE) at even the lowest dose of 6.3 × 10⁻⁴ ppb in our susceptible reference colony of Ae. aegypti Liverpool. In our field strain of Ae. aegypti (F5 colonized from South Texas) we observed 79.8% IE at 6.3 × 10⁻⁴ ppb, 17.7% IE at 1.25 × 10⁻³ ppb, 98.7% IE at 1.25 × 10⁻² ppb, and 100% emergence inhibition for the remainder of the doses. Given that commercial pyriproxyfen products are labeled for doses ranging to 50 ppb, we conclude that the field population sampled by this study are susceptible to this insect growth regulator.

Enhancement of Temephos and Deltamethrin Toxicity by Petroselinum crispum Oil and its Main Constituents Against Aedes aegypti (Diptera: Culicidae)

Previous work presented the profound antimosquito potential of Petroselinum crispum essential oil (PEO) against either the pyrethroid-susceptible or resistant strains of Aedes aegypti. This plant oil also inhibited the activity of acetylcholinesterase and mixed-function oxidases significantly, thus suggesting its potential as a synergist for improving mosquitocidal efficacy of insecticidal formulations. This study investigated the chemical composition, larvicidal activity, and potential synergism with synthetic insecticides of PEO and its main compounds for the purpose of interacting with insecticide resistance in mosquito vectors. The chemical profile of PEO, obtained by GC-MS analysis, showed a total of 17 bioactive compounds, accounting for 99.09% of the whole oil, with the most dominant constituents being thymol (74.57%), p-cymene (10.73%), and γ-terpinene (8.34%). All PEO constituents exhibited promising larvicidal effects, with LC50 values ranging from 19.47 to 59.75 ppm against Ae. aegypti, in both the pyrethroid-susceptible and resistant strains. Furthermore, combination-based bioassays revealed that PEO, thymol, p-cymene, and γ-terpinene enhanced the efficacy of temephos and deltamethrin significantly. The most effective synergist with temephos was PEO, which reduced LC50 values to 2.73, 4.94, and 3.28 ppb against MCM-S, PMD-R, and UPK-R, respectively, with synergism ratio (SR) values of 1.33, 1.38, and 2.12, respectively. The best synergist with deltamethrin also was PEO, which reduced LC50 values against MCM-S, PMD-R, and UPK-R to 0.008, 0.18, and 2.49 ppb, respectively, with SR values of 21.25, 9.00, and 4.06, respectively. This research promoted the potential for using essential oil and its principal constituents as not only alternative larvicides, but also attractive synergists for enhancing efficacy of existing conventional insecticides.

Infrared light sensors permit rapid recording of wingbeat frequency and bioacoustic species identification of mosquitoes

Recognition and classification of mosquitoes is a critical component of vector-borne disease management. Vector surveillance, based on wingbeat frequency and other parameters, is becoming increasingly important in the development of automated identification systems, but inconsistent data quality and results frequently emerge from different techniques and data processing methods which have not been standardized on wingbeat collection of numerous species. We developed a simple method to detect and record mosquito wingbeat by multi-dimensional optical sensors and collected 21,825 wingbeat files from 29 North American mosquito species. In pairwise comparisons, wingbeat frequency of twenty six species overlapped with at least one other species. No significant differences were observed in wingbeat frequencies between and within individuals of Culex quinquefasciatus over time. This work demonstrates the potential utility of quantifying mosquito wingbeat frequency by infrared light sensors as a component of an automated mosquito identification system. Due to species overlap, wingbeat frequency will need to integrate with other parameters to accurately delineate species in support of efficient mosquito surveillance, an important component of disease intervention.

Differential effects of larval and adult nutrition on female survival, fecundity, and size of the yellow fever mosquito, Aedes aegypti

Background

The yellow fever mosquito, Aedes aegypti, is the principal vector of medically-important infectious viruses that cause severe illness such as dengue fever, yellow fever and Zika. The transmission potential of mosquitoes for these arboviruses is largely shaped by their life history traits, such as size, survival and fecundity. These life history traits, to some degree, depend on environmental conditions, such as larval and adult nutrition (e.g., nectar availability). Both these types of nutrition are known to affect the energetic reserves and life history traits of adults, but whether and how nutrition obtained during larval and adult stages have an interactive influence on mosquito life history traits remains largely unknown.

Results

Here, we experimentally manipulated mosquito diets to create two nutritional levels at larval and adult stages, that is, a high or low amount of larval food (HL or LL) during larval stage, and a good and poor adult food (GA or PA, represents normal or weak concentration of sucrose) during adult stage. We then compared the size, survival and fecundity of female mosquitoes reared from these nutritional regimes. We found that larval and adult nutrition affected size and survival, respectively, without interactions, while both larval and adult nutrition influenced fecundity. There was a positive relationship between fecundity and size. In addition, this positive relationship was not affected by nutrition.

Conclusions

These findings highlight how larval and adult nutrition differentially influence female mosquito life history traits, suggesting that studies evaluating nutritional effects on vectorial capacity traits should account for environmental variation across life stages.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12983-021-00395-z.

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.

Plant nutrient quality impacts survival and reproductive fitness of the dengue vector Aedes aegypti

BACKGROUND

In a recent study using DNA barcoding, we identified the plants fed upon by four Afro-tropical mosquito species that vector dengue, malaria, and Rift Valley fever. Herein, we have expanded on this study by investigating the role of three of the plants, Pithecellobium dulce (Fabaceae), Leonotis nepetifolia (Lamiaceae), and Opuntia ficus-indica (Cactaceae), on the survival, fecundity, and egg viability of the dengue vector Aedes aegypti.

METHODS

We tested these effects using females that received (i) an initial three rations of blood meals and (ii) no blood meal at all. Two controls were included: age-matched females fed on glucose solution with or without an initial blood meal and those fed exclusively on blood meals. Data were collected daily over a 30-day period. The amino acid contents of Ae. aegypti guts and their respective diets were detected by coupled liquid chromatography-mass spectrometry.

RESULTS

Females fed on P. dulce and an exclusively blood meal diet had a shorter survival than those fed on glucose. On the other hand, females fed on L. nepetifolia survived longer than those fed exclusively on blood meals, whereas those fed on O. ficus-indica had the shortest survival time. With an initial blood meal, females fed on L. nepetifolia laid 1.6-fold more eggs while those fed on the other diets laid fewer eggs compared to those fed exclusively on blood meals. Hatching rates of the eggs laid varied with the diet. Mass spectroscopic analysis of gut contents of mosquitoes exposed to the different diets showed qualitative and quantitative differences in their amino acid levels.

CONCLUSION

Our findings highlight the central role of plant nutrients in the reproductive fitness of dengue vectors, which may impact their disease transmission potential.

Sugar feeding patterns of New York Aedes albopictus mosquitoes are affected by saturation deficit, flowers, and host seeking

BACKGROUND

Sugar feeding is an important behavior which may determine vector potential of female mosquitoes. Sugar meals can reduce blood feeding frequency, enhance survival, and decrease fecundity, as well as provide energetic reserves to fuel energy intensive behaviors such as mating and host seeking. Sugar feeding behavior can be harnessed for vector control (e.g. attractive toxic sugar baits). Few studies have addressed sugar feeding of Aedes albopictus, a vector of arboviruses of public health importance, including dengue and Zika viruses. To address this knowledge gap, we assessed sugar feeding patterns of Ae. albopictus for the first time in its invasive northeastern USA range.

METHODOLOGY/PRINCIPAL FINDINGS

Using the cold anthrone fructose assay with robust sample sizes, we demonstrated that a large percentage of both male (49.6%) and female (41.8%) Ae. albopictus fed on plant or homopteran derived sugar sources within 24 hrs prior to capture. Our results suggest that sugar feeding behavior increases when environmental conditions are dry (high saturation deficit) and may vary by behavioral status (host seeking vs. resting). Furthermore, mosquitoes collected on properties with flowers (>3 blooms) had higher fructose concentrations compared to those collected from properties with few to no flowers (0-3).

CONCLUSIONS/SIGNIFICANCE

Our results provide the first evidence of Ae. albopictus sugar feeding behavior in the Northeastern US and reveal relatively high rates of sugar feeding. These results suggest the potential success for regional deployment of toxic sugar baits. In addition, we demonstrate the impact of several environmental and mosquito parameters (saturation deficit, presence of flowers, host seeking status, and sex) on sugar feeding. Placing sugar feeding behavior in the context of these environmental and mosquito parameters provides further insight into spatiotemporal dynamics of feeding behavior for Ae. albopictus, and in turn, provides information for evidence-based control decisions.