Ultraviolet inflorescence cues enhance attractiveness of inflorescence odour to Culex pipiens mosquitoes

Mosquito Floral Visitation and Pollination

We often consider mosquitoes through an 'anthropocentric lens' that disregards their interactions with non-human and non-pathogenic organisms, even though these interactions can be harnessed for mosquito control. Mosquitoes have been recognized as floral visitors, and pollinators, for more than a century. However, we know relatively little about mosquito-plant interactions, excepting some nutrition and chemical ecology-related topics, compared to mosquito-host interactions, and frequently use flawed methodology when investigating them. Recent work demonstrates mosquitoes use multimodal sensory cues to locate flowers, including ultraviolet visual cues, and we may underestimate mosquito pollination. This review focuses on current knowledge of how mosquitoes locate flowers, floral visitation assay methodology, mosquito pollination, and implications for technologies such as sterile male mosquito release through genetic control programs or Wolbachia infection.

Experiments and Analysis of Mosquito Flight Behaviors in a Wind Tunnel: An Introduction

Mosquitoes detect and navigate to important resources, like a host, using combinations of different sensory stimuli. The relative importance of the sensory cues can change as the mosquito gets closer to their target. Other factors, both internal and external, can also influence the mosquito behavior. A mechanistic understanding of these sensory stimuli, and how they impact mosquito navigation, can now be readily studied using wind tunnels and associated computer vision systems. In this introduction, we present a behavioral paradigm using a wind tunnel for flight behavior analysis. The wind tunnel's large size with its associated cameras and software system for analysis of the mosquito flight tracks can be sophisticated and sometimes cost-prohibitive. Nevertheless, the wind tunnel's flexibility in allowing the testing of multimodal stimuli and scaling of environmental stimuli makes it possible to reproduce conditions from the field and test them in the laboratory, while also allowing the observation of natural flight kinematics.

Chemical ecology of nectar-mosquito interactions: recent advances and future directions

Mosquitoes, males and females, rely on sugar-rich resources, including floral nectar as a primary source of sugar to meet their energy and nutritional needs. Despite advancements in understanding mosquito host-seeking and blood-feeding preferences, significant gaps in our knowledge of the chemical ecology mediating mosquito-nectar associations remain. The influence of such association with nectar on mosquito behavior and the resulting effects on their fitness are also not totally understood. It is significant that floral nectar frequently acts as a natural habitat for various microbes (e.g. bacteria and yeast), which substantially alter nectar characteristics, influencing the nutritional ecology of flower-visiting insects, such as mosquitoes. The role of nectar-inhabiting microbes in shaping the nectar-mosquito interactions remains, however, under-researched. This review explores recent advances in understanding the role of such multitrophic interactions on the fitness and life history traits of mosquitoes and outlines future directions for research toward their control as disease vectors.

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.

The paradox of plant preference: The malaria vectors Anopheles gambiae and Anopheles coluzzii select suboptimal food sources for their survival and reproduction

Anopheles gambiae and Anopheles coluzzii mosquitoes, two major malaria vectors in sub-Saharan Africa, exhibit selectivity among plant species as potential food sources. However, it remains unclear if their preference aligns with optimal nutrient intake and survival. Following an extensive screening of the effects of 31 plant species on An. coluzzii in Burkina Faso, we selected three species for their contrasting effects on mosquito survival, namely Ixora coccinea, Caesalpinia pulcherrima, and Combretum indicum. We assessed the sugar content of these plants and their impact on mosquito fructose positivity, survival, and insemination rate, using Anopheles coluzzii and Anopheles gambiae, with glucose 5% and water as controls. Plants displayed varying sugar content and differentially affected the survival, sugar intake, and insemination rate of mosquitoes. All three plants were more attractive to mosquitoes than controls, with An. gambiae being more responsive than An. coluzzii. Notably, C. indicum was the most attractive but had the lowest sugar content and offered the lowest survival, insemination rate, and fructose positivity. Our findings unveil a performance-preference mismatch in An. coluzzii and An. gambiae regarding plant food sources. Several possible reasons for this negative correlation between performance and preference are discussed.

Stable flies sense and behaviorally respond to the polarization of light

Insects use their polarization-sensitive photoreceptors in a variety of ecological contexts including host-foraging. Here, we investigated the effect of polarized light on host foraging by the blood-feeding stable fly, Stomoxys calcitrans, a pest of livestock. Electroretinogram recordings with chromatic adaptation demonstrated that the spectral sensitivity of stable flies resembles that of other calyptrate flies. Histological studies of the flies' compound eye revealed differences in microvillar arrangement of ommatidial types, assumed to be pale and yellow, with the yellow R7 and pale R8 photoreceptors having the greatest polarization sensitivity. In behavioural experiments, stable flies preferred to alight on horizontally polarized stimuli with a high degree of linear polarization. This preferential response disappeared when either ultraviolet (UV) or human-visible wavelengths were omitted from light stimuli. Removing specific wavelength bands further revealed that the combination of UV (330-400 nm) and blue (400-525 nm) wavelength bands was sufficient to enable polarized light discrimination by flies. These findings enhance our understanding of polarization vision and foraging behavior among hematophagous insects and should inform future trap designs.

Measuring Mosquito Spectral Sensitivity Using Electroretinograms

Mosquitoes use a variety of cues to locate resources in the world around them, including olfactory, thermal, and visual stimuli. Understanding how mosquitoes perceive these stimuli is important for understanding and investigating mosquito behaviors and mosquito ecology. Specifically, mosquito vision can be studied in many ways, including by using electrophysiological recordings from their compound eyes. Electroretinograms can be used to characterize the spectral sensitivity of a mosquito species, revealing the wavelengths of light they can perceive. Here, we provide details on how to perform and analyze these recordings.

Mosquito (Diptera: Culicidae) Vision and Associated Electrophysiological Techniques

Mosquitoes are considered the world's deadliest animal because of the pathogens they spread. Additionally, they are an unbearable nuisance in many areas. Visual stimuli play an important role in the mosquito life cycle, helping them find vertebrate hosts, floral nectar, and oviposition sites. Here, we review mosquito vision, including its influences on mosquito behavior, the photoreceptors involved, and mosquito spectral sensitivity, as well as provide an overview of techniques used for the analysis of mosquito vision, including electroretinograms, single-cell recordings, and the use of opsin-deficient mutants. We anticipate that this information will be useful for researchers studying mosquito physiology, evolution, ecology, and management.

Evaluation of the solar-powered Silver Bullet 2.1 (Lumin 8) light trap for sampling malaria vectors in western Kenya

BACKGROUND

Centers for Disease Control and Prevention (CDC) light traps are widely used for sampling mosquitoes. However, this trap, manufactured in the USA, poses challenges for use in sub-Saharan Africa due to procurement costs and shipping time. Traps that are equally efficient than the CDC light trap, but which are amenable for use in remote African settings and made in Africa, are desirable to improve local vector surveillance. This study evaluated a novel solar-powered light trap made in South Africa (Silver Bullet trap; SB), for its efficiency in malaria vector sampling in western Kenya.

METHODS

Large cage (173.7 m3) experiments and field evaluations were conducted to compare the CDC-incandescent light trap (CDC-iLT), CDC-UV fluorescent tube light trap (CDC-UV), SB with white diodes (SB-White) and SB with UV diodes (SB-UV) for sampling Anopheles mosquitoes. Field assessments were done indoors and outdoors following a Latin square design. The wavelengths and absolute spectral irradiance of traps were compared using spectrometry.

RESULTS

The odds of catching a released Anopheles in the large cage experiments with the SB-UV under ambient conditions in the presence of a CDC-iLT in the same system was three times higher than what would have been expected when the two traps were equally attractive (odds ratio (OR) 3.2, 95% confidence interval CI 2.8-3.7, P < 0.01)). However, when the white light diode was used in the SB trap, it could not compete with the CDC-iLT (OR 0.56, 95% CI 0.48-0.66, p < 0.01) when the two traps were provided as choices in a closed system. In the field, the CDC and Silver Bullet traps were equally effective in mosquito sampling. Irrespective of manufacturer, traps emitting UV light performed better than white or incandescent light for indoor sampling, collecting two times more Anopheles funestus sensu lato (s.l.) (RR 2.5; 95% CI 1.7-3.8) and Anopheles gambiae s.l. (RR 2.5; 95% 1.7-3.6). Outdoor collections were lower than indoor collections and similar for all light sources and traps.

CONCLUSIONS

The solar-powered SB trap compared well with the CDC trap in the field and presents a promising new surveillance device especially when charging on mains electricity is challenging in remote settings.

Sleep: An Essential and Understudied Process in the Biology of Blood-Feeding Arthropods

Understanding the biology of blood-feeding arthropods is critical to managing them as vectors of etiological agents. Circadian rhythms act in the regulation of behavioral and physiological aspects such as blood feeding, immunity, and reproduction. However, the impact of sleep on these processes has been largely ignored in blood-feeding arthropods, but recent studies in mosquitoes show that sleep-like states directly impact host landing and blood feeding. Our focus in this review is on discussing the relationship between sleep and circadian rhythms in blood-feeding arthropods along with how unique aspects such as blood gluttony and dormancy can impact sleep-like states. We highlight that sleep-like states are likely to have profound impacts on vector-host interactions but will vary between lineages even though few direct studies have been conducted. A myriad of factors, such as artificial light, could directly impact the time and levels of sleep in blood-feeding arthropods and their roles as vectors. Lastly, we discuss underlying factors that make sleep studies in blood-feeding arthropods difficult and how these can be bypassed. As sleep is a critical factor in the fitness of animal systems, a lack of focus on sleep in blood-feeding arthropods represents a significant oversight in understanding their behavior and its role in pathogen transmission.

A synthetic lure for Anopheles gambiae (Diptera: Culicidae) based on the attractive plant Parthenium hysterophorus

Sugar is the sole diet for male mosquitoes and a complementary meal for females. Searching for natural sources of sugar is mediated by semiochemicals. Floral nectars, extra floral nectaries, damaged tissues of plants and rotten fruits are the most common sources of sugar in nature. I provide laboratory evidence of the high attraction of Parthenium hysterophorus L., a weed that grows in tropical climates, to Anopheles gambiae Giles. This study has tried to identify the chemicals which might be involved in the chemical attraction of A. gambiae to this plant. Using quantitative GC-MS analysis, α-pinene, camphene, 1-octen-3-ol, β-pinene, cis-β-ocimene, bornyl acetate, α-caryophyllene, hexadecanoic acid, and α-linolenic acid were identified as the main constituents of P. hysterophorus volatiles. Successive olfactory assays helped a better understanding of the more attractive chemicals of P. hysterophorus to A. gambiae which was the basis for testing a possible synthetic blend. Olfactory experiments proved this synthetic blend to be as attractive as Parthenium intact plants for A. gambiae. A minimal blend, consisting of only α-pinene, camphene, and cis-β-ocimene, was also produced and laboratory experiments indicated its relative attraction for A. gambiae. This blend can be tested in the attractive toxic sugar bait stations for sampling, surveillance, or control programs of mosquitoes in tropical Africa, where A. gambiae sensu stricto transfer malaria among residents.

Effects of Color and Light Intensity on the Foraging and Oviposition Behavior of Culex pipiens biotype molestus Mosquitoes

Mosquitoes are the most important vector of arboviruses; thus, controlling mosquito population is a key point for controlling these diseases. Two major factors that influence mosquito population size are the availability of blood hosts and suitable oviposition sites. Behavioral mechanisms by which Culex pipiens biotype molestus mosquitoes locate their hosts or oviposition sites are influenced by physical and chemical factors. The present study evaluated the impact of the colors (for human eyes) red, green, blue and yellow in combination with different light intensities on preferences for oviposition and foraging sites under laboratory conditions. We identified the color red as the overall favored color for both target behaviors, which was only surpassed by black as the foraging stimulus. Altogether, we described two new inexpensive and simple bioassays, which can be used as a mosquito-tracking method for behavioral tests and as an oviposition trap to monitor Culex pipiens biotype molestus populations.

Autofluorescent Biomolecules in Diptera: From Structure to Metabolism and Behavior

Light-based phenomena in insects have long attracted researchers’ attention. Surface color distribution patterns are commonly used for taxonomical purposes, while optically-active structures from Coleoptera cuticle or Lepidoptera wings have inspired technological applications, such as biosensors and energy accumulation devices. In Diptera, besides optically-based phenomena, biomolecules able to fluoresce can act as markers of bio-metabolic, structural and behavioral features. Resilin or chitinous compounds, with their respective blue or green-to-red autofluorescence (AF), are commonly related to biomechanical and structural properties, helpful to clarify the mechanisms underlying substrate adhesion of ectoparasites’ leg appendages, or the antennal abilities in tuning sound detection. Metarhodopsin, a red fluorescing photoproduct of rhodopsin, allows to investigate visual mechanisms, whereas NAD(P)H and flavins, commonly relatable to energy metabolism, favor the investigation of sperm vitality. Lipofuscins are AF biomarkers of aging, as well as pteridines, which, similarly to kynurenines, are also exploited in metabolic investigations. Beside the knowledge available in Drosophila melanogaster, a widely used model to study also human disorder and disease mechanisms, here we review optically-based studies in other dipteran species, including mosquitoes and fruit flies, discussing future perspectives for targeted studies with various practical applications, including pest and vector control.

UV Light-Emitting-Diode Traps for Collecting Nocturnal Biting Mosquitoes in Urban Bangkok

Simple Summary

This study was conducted to evaluate the efficacy of six ultraviolet light-emitting diodes (UV-LED) traps and a fluorescent light trap for sampling urban nocturnal mosquitoes. Results demonstrated that the fluorescent light trap outperformed all the UV-LED traps throughout the 72 sampling nights and between wet and dry seasons. Among the UV-LED traps, the LED375 trapped the highest number of mosquitoes. Additional field trials are needed to validate these findings in different ecological settings.

Abstract

Well-designed surveillance systems are required to facilitate a control program for vector-borne diseases. Light traps have long been used to sample large numbers of insect species and are regarded as one of the standard choices for baseline insect surveys. The objective of this study was to evaluate the efficacy of six ultraviolet light-emitting diodes and one fluorescent light for trapping urban nocturnal mosquito species within the Kasetsart University (KU), Bangkok. Ultraviolet light-emitting diodes (UV-LEDs), (LED365, LED375, LED385, LED395, and LED405) and a fluorescent light were randomly assigned to six different locations around the campus in a Latin square design. The traps were operated continuously from 18:00 h to 06:00 h throughout the night. The traps were rotated between six locations for 72 collection-nights during the dry and wet seasons. In total, 6929 adult mosquitoes were caught, with the most predominant genus being Culex, followed by Aedes, Anopheles, Armigeres and Mansonia. Among the Culex species, Culex quinquefasciatus (n = 5121: 73.9%) was the most abundant followed by Culex gelidus (n = 1134: 16.4%) and Culex vishnui (n = 21: 0.3%). Small numbers of Aedes, Armigeres, and Anopheles mosquitoes were trapped [Aedes albopictus (n = 219: 3.2%), Aedes pocilius (n = 137: 2.0%), Armigeres subalbatus (n = 97: 1.4%), Anopheles vagus (n = 70: 1.0%), Aedes aegypti (n = 23: 0.3%)]. There were 2582 specimens (37.2%) captured in fluorescent light traps, whereas 942 (13.6%), 934 (13.5%), 854 (12.3%), 820 (11.8%), and 797 (11.5%) were captured in the LED375, LED405, LED395, LED365, and LED385 traps, respectively. None of the UV-LED light traps were as efficacious for sampling nocturnal mosquito species as the fluorescent light trap. Among the five UV-LED light sources, LED375 trapped the greatest number of mosquitoes. Additional field trials are needed to validate these findings in different settings in order to substantially assess the potential of the LEDs to trap outdoor nocturnal mosquitoes.

Blood feeding habits of mosquitoes: hardly a bite in South America

Mosquito blood feeding plays a key role in epidemiology. Despite its importance and large number of studies worldwide, less attention has been paid in South America. We summarized some general concepts and methodological issues related to the study of mosquito blood feeding habits, and compiled and analyzed all published information regarding the subject in the continent until 2020. Available literature comprised 152 scientific studies, that pursued different approaches: human landing catches (102 studies), baited trap (19), and blood meal analyses of collected specimens (38). Among the latter, 23 used serological and 15 molecular techniques. Species most frequently studied were those incriminated in malaria transmission, whereas relevant vectors such as Aedes aegypti, Ae. albopictus, and Haemagogus janthinomys were surprisingly neglected. Brazil was the leading country both in number of works and species studied. For over 70% of the species and three out of 13 South American countries there is no single information on mosquito blood feeding habits. Data from baited traps included 143 mosquito species, 83.9% of which were attracted to humans, either exclusively (10.5%) or in combination with other vertebrates (73.4%). Host blood identification of field collected specimens provided data on 102 mosquito species, and 60.8% of these fed on humans (55.9% combined with other vertebrates). Only 17 of the 73 species assessed by both methods yielded similar feeding patterns. Finally, supplementary tables are provided in a comprehensive summary of all information available and information gaps are highlighted for future research in the continent.

The Floral Signals of the Inconspicuous Orchid Malaxis monophyllos: How to Lure Small Pollinators in an Abundant Environment

Simple Summary

Malaxis monophyllos is an ephemeral orchid with very small, greenish flowers, whose pollination system remains vague. Therefore, the authors aimed to identify the flower’s features, including its anatomical micro and ultrastructure as well as scent biochemistry, which are involved in attracting pollinators. In this paper, the authors established the variety of emissions of M. monophyllos volatile compounds, with a high proportion of aldehydes and aliphatic alcohols, listed as chemicals that induce a pronounced reaction in Diptera. Second, the entire M. monophyllos labellum exhibits metabolic and secretory activity, which can be related to both emission of volatiles and visual attractants but also to the nutritional reward for pollinators. All these flower features indicated that its pollination system is dedicated to dipterans, with few signaling modalities corresponding to deceptive species (brood site and food decoy) but also referring to rewarding ones (nutritional secretion, fungus/microbe reward). This research reveals a few new issues in M. monophyllos pollination biology that provides new scientific areas for in-depth insights in the future.

Abstract

Many orchid species have evolved complex floral signals to ensure pollination efficiency. Here, the authors combined analyses of anatomical flower structure with analyses of the volatile composition and flower-visiting insects’ behaviour, as well as characterised features that can attract pollinators of the inconspicuous orchid Malaxis monophyllos. During field observations, the authors found that only small Diptera (e.g., mosquitos, drosophilids, fungus gnats) visit and are interested in the flowers of M. monophyllos, which was reflected in the characterised flower features that combine well with the pollination system, which engages dipterans. Analyses of the M. monophyllos floral scent revealed substantial concentrations of aliphatic compounds, e.g., 1-octen-3-ol and 1-octanol, which condition the mushroom-like scent and a substantial fraction of alkanes, some of which have been previously described as sex mimicry and aggregation pheromones in orchids’ deceptive systems. The labellum anatomical structure exhibits a highly diverse cell cuticle surface and pronounced metabolic and secretory activity of the epidermal and subepidermal cells from all parts of the labellum. Moreover, our study provides evidence for the subsequent decoys of M. monophyllos flowers, including visual signals, such as raphides located on the labellum margin and the rewarding ones connected with lipid secretion limited to the area behind the column. Taking an integrative approach to studying M. monophyllos pollination biology, the authors provide new insight into its previously vague pollination strategies and provide evidence for complex floral signal operation in luring potential pollinators. The synergistic effect of M. monophyllos flowers’ volatile and visual signals, together with additional rewarding for nectar/fungus/microbe-feeding pollinators, requires further detailed investigation that will be invaluable in explaining the evolution of Diptera-specific pollination systems in orchids.

The olfactory gating of visual preferences to human skin and visible spectra in mosquitoes

Mosquitoes track odors, locate hosts, and find mates visually. The color of a food resource, such as a flower or warm-blooded host, can be dominated by long wavelengths of the visible light spectrum (green to red for humans) and is likely important for object recognition and localization. However, little is known about the hues that attract mosquitoes or how odor affects mosquito visual search behaviors. We use a real-time 3D tracking system and wind tunnel that allows careful control of the olfactory and visual environment to quantify the behavior of more than 1.3 million mosquito trajectories. We find that CO₂ induces a strong attraction to specific spectral bands, including those that humans perceive as cyan, orange, and red. Sensitivity to orange and red correlates with mosquitoes’ strong attraction to the color spectrum of human skin, which is dominated by these wavelengths. The attraction is eliminated by filtering the orange and red bands from the skin color spectrum and by introducing mutations targeting specific long-wavelength opsins or CO₂ detection. Collectively, our results show that odor is critical for mosquitoes’ wavelength preferences and that the mosquito visual system is a promising target for inhibiting their attraction to human hosts.

Vision in mosquitoes plays a critical but understudied role in their attraction to hosts. Here, the authors show that encounter with an attractive odor gates the mosquito attraction to specific colors, especially the long wavelengths reflected from human skin. Filtering the long wavelengths reflected from the human skin or knocking-out the ability for the mosquito to detect the wavelengths, suppressed their attraction. This work transforms our understanding of mosquito vision from the conventional view that vision does little in mediating mosquito-host interactions, to the recognition that vision plays a critical role.

Artificial Light as a Modulator of Mosquito-Borne Disease Risk

Light is a fundamental cue regulating a host of biological responses. The artificial modification thereof demonstrably impacts a wide range of organisms. The use of artificial light is changing in type, extent and intensity. Insect vector-borne diseases remain a global scourge, but surprisingly few studies have directly investigated the interactions between artificial light and disease vectors, such as mosquitoes. Here we briefly overview the progress to date, which highlights that artificial light must be considered as a modulator of mosquito-borne disease risk. We discuss where the mechanisms may lie, and where future research could usefully be directed, particularly in advancing understanding of the biological effects of the light environment. Further understanding of how artificial light may modulate mosquito-borne disease risk may assist in employing and redesigning light regimes that do not increase, and may even mitigate, already significant disease burdens, especially in the developing world.

Semi-field evaluation of novel chemical lures for Aedes aegypti, Culex quinquefasciatus, and Anopheles minimus (Diptera: Culicidae) in Thailand

BACKGROUND

Entomological surveillance is an important means of assessing the efficacy of insect vector management programs and estimating disease transmission thresholds. Among baited traps, Biogents' BG-Sentinel (BGS) trap baited with BG-Lure is considered to have the most similar outcome to, and be a possible replacement for, human-landing catches for the epidemiologically relevant monitoring of adult Aedes aegypti and Culex quinquefasciatus. In contrast to the BGS trap, the Black Hole ultraviolet (UV) light trap, which is widely used to catch nocturnal flying insects, is not baited with synthetic human odor-mimicking lures.

METHODS

We evaluated the L-lactic acid-based Kasetsart University (KU)-lures nos. 1-6 as novel candidate chemical lures for the diurnal species Ae. aegypti and the nocturnal species Cx. quinquefasciatus using two commercial traps (the BGS trap and the Black Hole UV light trap) in a semi-field screen (SFS) house. Firstly, we optimized the dose of each KU-lure in an SFS house (140 m3). Secondly, six different candidate KU-lures were screened by comparing their percent attraction using a single discriminating dose (0.5 g). Finally, we evaluated the synergism of the KU-lures selected in this way with commercially available traps.

RESULTS

BGS traps baited with KU-lure no. 1 exhibited the greatest percent attraction for Ae. aegypti (29.5% ± 14.3%), whereas those baited with KU-lure no. 6 most strongly attracted Cx. quinquefasciatus (33.3% ± 10.7%). Interestingly, BGS traps treated with 10 g BG-Lure did not significantly attract more Ae. aegypti or Cx. quinquefasciatus than the untreated BGS traps. CO2 at a flow rate of 250 ml/min most strongly attracted both Ae. aegypti and Cx. quinquefasciatus (42.2% ± 14.2% and 75.1% ± 16.9%, respectively). BGS and Black Hole UV light traps with KU-lure no. 6 exhibited a stronger attraction for Cx. quinquefasciatus than untreated traps, and the percent attraction did not differ between the treated traps.

CONCLUSIONS

Synergistic effects of KU-lures nos. 1 and 6 with the mosquito traps were demonstrated for both the diurnal and nocturnal species in the SFS house assays. However, further studies are urgently needed for the development of species-specific lures to increase trap efficacy in the field for local vector mosquitoes in Thailand.

Effect of Incandescent Light on Collection of West Nile Virus Vectors Using CDC Miniature Light Traps in Northern Colorado

To evaluate whether the presence of clear incandescent light was attractive or refractive to host-seeking mosquitoes in northern Colorado, a Bayesian hierarchical model was created to measure differences in trap effectiveness based on presence or absence of phototactic cues. A total of eight CDC miniature light traps (with and without light) were set weekly across four locations in northern Colorado between Weeks 23 and 32 of year 2020. Culex mosquitoes (Diptera: Culicidae) accounted for 81% of all collections in this study with two vectors of West Nile virus being represented. The probability of catching both Culex tarsalis Coquillett and Culex pipiens Linnaeus was reduced when traps were equipped with light, but the difference was not statistically significant for Culex tarsalis. The clear reduction in the number of Culex pipiens caught when these traps were equipped with light indicates negative phototactic behavior and underestimation with current surveillance strategies. Removal of light from these traps may aid our understanding of these species' distribution within the environment, improve collection efficiency, and help guide implementation of targeted control measures used in public health mosquito control.

Transmitted Light as Attractant with Mechanical Traps for Collecting Nocturnal Mosquitoes in Urban Bangkok, Thailand

Mosquito surveillance is the cornerstone for determining abundance, species diversity, pathogen infection rates, and temporal and spatial distribution of different life stages in an area. Various methods are available for assessing adult mosquito populations, including mechanical trap devices using different forms of attractant cues (chemical and visual) to lure mosquitoes to the trap. So-called "light traps" use various electromagnetic wavelengths to produce a variety of visible spectral colors to attract adult mosquitoes. However, this type of trapping technology has not been widely used in Thailand. This study compared the efficacy of 4 light-emitting diodes (LEDs) (blue, green, yellow, and red) and 2 fluorescent (ultraviolet [UV] and white) lights for collecting mosquitoes in urban Bangkok. Using a Latin square experimental design, 6 light traps equipped with different lights were rotated between 6 trap site locations within the Kasetsart University (KU) campus. Each location received 6 replicate collections (6 consecutive trap-nights represented 1 replicate) over 36 collection nights for a total of 216 trap-nights. Traps were operated simultaneously (1800 to 0600 h), with captured mosquitoes removed at 3-h intervals. In total, 2,387 mosquitoes consisting of 11 species across 5 genera (Aedes, Anopheles, Armigeres, Culex, and Mansonia) were captured. Collectively, Culex species represented the predominant group sampled (2,252; 94.4%). The UV light source captured 1,544 (64.7%) of the total mosquitoes collected, followed by white 389 (16.3%), with the 4 LED sources collecting between 6.8% (blue) and 1.9% (yellow). Traps equipped with UV light were clearly the most effective for capturing nocturnally active mosquito species on the KU campus.

Response of Culex pipiens pallens to Visual and Olfactory Stimuli from a Mosquito Trap

This study examined Culex pipiens pallens responses to different combinations of colors and chemicals employed via a mosquito trap under semifield conditions. Our results indicated that Cx. p. pallens has color and chemical concentration preferences. Culex p. pallens had a 38.0% greater response to white than black color treated traps. Further, Cx. p. pallens showed differences in olfactory attraction depending on the chemical and concentration. Culex p. pallens was 107.6% more attracted to traps employing 500 ppm ammonia than control (i.e., unscented). Similarly, Cx. p. pallens was 117.5%, 128.8%, and 140.3% more attracted to traps employing, respectively, 1,000, 10,000, and 20,000 ppm of ammonia hydrogen carbonate compared to controls. And the response to lactic acid showed that Cx. p. pallens was most attracted to concentrations of 100 and 500 ppm (135.7% and 142.9%, respectively) compared to controls.

Nectar-dwelling microbes of common tansy are attractive to its mosquito pollinator, Culex pipiens L

Background

There is widespread interkingdom signalling between insects and microbes. For example, microbes found in floral nectar may modify its nutritional composition and produce odorants that alter the floral odor bouquet which may attract insect pollinators. Mosquitoes consume nectar and can pollinate flowers. We identified microbes isolated from nectar of common tansy, Tanacetum vulgare, elucidated the microbial odorants, and tested their ability to attract the common house mosquito, Culex pipiens.

Results

We collected 19 microbial isolates from T. vulgare nectar, representing at least 12 different taxa which we identified with 16S or 26S rDNA sequencing as well as by biochemical and physiological tests. Three microorganisms (Lachancea thermotolerans, Micrococcus lactis, Micrococcus luteus) were grown on culture medium and tested in bioassays. Only the yeast L. thermotolerans grown on nectar, malt extract agar, or in synthetic nectar broth significantly attracted Cx. pipiens females. The odorant profile produced by L. thermotolerans varied with the nutritional composition of the culture medium. All three microbes grown separately, but presented concurrently, attracted fewer Cx. pipiens females than L. thermotolerans by itself.

Conclusions

Floral nectar of T. vulgare contains various microbes whose odorants contribute to the odor profile of inflorescences. In addition, L. thermotolerans produced odorants that attract Cx. pipiens females. As the odor profile of L. thermotolerans varied with the composition of the culture medium, we hypothesize that microbe odorants inform nectar-foraging mosquitoes about the availability of certain macro-nutrients which, in turn, affect foraging decisions by mosquitoes.

Artificial light and biting flies: the parallel development of attractive light traps and unattractive domestic lights

Light trapping is an important tool for monitoring insect populations. This is especially true for biting Diptera, where light traps play a crucial role in disease surveillance by tracking the presence and abundance of vector species. Physiological and behavioural data have been instrumental in identifying factors that influence dipteran phototaxis and have spurred the development of more effective light traps. However, the development of less attractive domestic lights has received comparatively little interest but could be important for reducing interactions between humans and vector insects, with consequences for reducing disease transmission. Here, we discuss how dipteran eyes respond to light and the factors influencing positive phototaxis, and conclude by identifying key areas for further research. In addition, we include a synthesis of attractive and unattractive wavelengths for a number of vector species. A more comprehensive understanding of how Diptera perceive and respond to light would allow for more efficient vector sampling as well as potentially limiting the risk posed by domestic lighting.

Not Just from Blood: Mosquito Nutrient Acquisition from Nectar Sources

Anthropophilic female mosquitoes are well known for their strong attraction to human hosts, but plant nectar is a common energy source in their diets. When sugar sources are scarce, female mosquitoes of some species can compensate by taking larger and more frequent blood meals. Male mosquitoes are exclusively dependent on plant nectar or alternative sugar sources. Plant preference is likely driven by an innate attraction that may be enhanced by experience, as mosquitoes learn to recognize available sugar rewards. Nectar-seeking involves the integration of at least three sensory systems: olfaction, vision and taste. The prevention of vector-borne illnesses, the determination of the mosquitoes' ecological role, and the design of efficient sugar-baited traps will all benefit from understanding the molecular basis of nectar-seeking.