RESUMO
Mosquitoes vector dangerous human diseases during blood feeding. Gustatory (taste) receptor neurons in the mosquito provide important chemical information including the nature and suitability of a potential host. Here we discuss the behavior, neurophysiology and molecular mechanisms associated with feeding in aedine mosquitoes, important vectors of emerging diseases including Zika fever, chikungunya and dengue fever. We describe how interactions between feeding stimulation and deterrency at the peripheral neural receptor level provide input to higher order neural processing centers affecting decisions to feed. A better understanding of gustatory mechanisms involved in the female's decision to bite will provide the framework for novel strategies aimed at preventing the spread of vector-borne disease.
Assuntos
Aedes/fisiologia , Infecções/transmissão , Insetos Vetores/fisiologia , Aedes/genética , Animais , Comportamento Alimentar , Humanos , Infecções/sangue , Proteínas de Insetos/genética , Proteínas de Insetos/metabolismo , Insetos Vetores/genética , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismoRESUMO
Female mosquitoes feed on blood from animal hosts to obtain nutritional resources used for egg production. These contacts facilitate the spread of harmful human diseases. Chemical repellents are used to disrupt mosquito host-seeking and blood-feeding behaviors; however, little is known about the gustatory sensitivity of mosquitoes to known repellents. Here, we recorded electrical responses from gustatory receptor neurons (GRNs) housed within the labellar sensilla of female Anopheles quadrimaculatus to N,N-diethyl-3-methylbenzamide (DEET), picaridin, IR3535, 2-undecanone, p-menthane-3,8-diol, geraniol, trans-2-hexen-1-ol, quinine, and quinidine. A bitter-sensitive GRN responded to all tested repellents and quinine, a known feeding deterrent. Responses of the bitter-sensitive neuron to quinine and an isomer, quinidine, did not differ. Delayed bursts of electrical activity were observed in response to continuous stimulation with synthetic repellents at high concentrations. Electrophysiological recordings from bitter-sensitive GRNs associated with mosquito gustatory sensilla represent a convenient model to evaluate candidate repellents.
Assuntos
Anopheles/efeitos dos fármacos , Anopheles/fisiologia , Repelentes de Insetos/farmacologia , Animais , Células Quimiorreceptoras/efeitos dos fármacos , Células Quimiorreceptoras/fisiologia , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Feminino , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , PaladarRESUMO
Three gustatory receptor neurons were characterized for contact chemoreceptive sensilla on the labella of female yellow-fever mosquitoes, Aedes aegypti. The neuron with the smallest amplitude spike responded to the feeding deterrent, quinine, as well as N,N-diethyl-3-methylbenzamide and other insect repellents. Two other neurons with differing spikes responded to salt (NaCl) and sucrose. This is the first report of a gustatory receptor neuron specific for insect repellents in mosquitoes and may provide a tool for screening chemicals to discover novel or improved feeding deterrents and repellents for use in the management of arthropod disease vectors.
Assuntos
Aedes/efeitos dos fármacos , Repelentes de Insetos/farmacologia , Aedes/fisiologia , Animais , Células Quimiorreceptoras/efeitos dos fármacos , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Feminino , Cloreto de Sódio/farmacologia , Sacarose/farmacologiaRESUMO
An unsaturated hydroxy-ester pheromone was isolated from the headspace and feces of male Diaprepes abbreviatus, identified, and synthesized. The pheromone, methyl (E)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate, was discovered by gas chromatography-coupled electroantennogram detection (GC-EAD), and identified by gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR). The synthesis yielded an 86:14 mixture of methyl (E)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate (active) and methyl (Z)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate (inactive), along with a lactone breakdown product. The activity of the synthetic E-isomer was confirmed by GC-EAD, GC-MS, NMR, and bioassays. No antennal response was observed to the Z-isomer or the lactone. In a two-choice olfactometer bioassay, female D. abbreviatus moved upwind towards the synthetic pheromone or natural pheromone more often compared with clean air. Males showed no clear preference for the synthetic pheromone. This pheromone, alone or in combination with plant volatiles, may play a role in the location of males by female D. abbreviatus.
Assuntos
Atrativos Sexuais/análise , Atrativos Sexuais/síntese química , Gorgulhos/metabolismo , Animais , Fezes/química , Feminino , Masculino , Atrativos Sexuais/biossíntese , Atrativos Sexuais/farmacologia , Comportamento Sexual Animal/efeitos dos fármacosRESUMO
Ticks use chemical and thermal signals emitted by humans and other vertebrates to locate suitable hosts for a blood meal. Here, we study the behavior of black-legged Ixodes scapularis and the lone star ticks Amblyomma americanum exposed to heat sources held at temperatures near those of vertebrate hosts (32 °C). First, we used a locomotion compensator to test behavioral responses of ticks to an infrared light emitting diode (LED). The servosphere allowed us to measure parameters such as velocity, acceleration, linearity, and orientation. Then a heating element (Peltier) located in one of the extremes of a double-choice vertical rod (flying T), was employed to observe upward movement of the ticks toward such a heat source. While both species oriented toward the LED, only lone star ticks were attracted to the Peltier element while climbing upward. In conclusion, we showed that heat attracted ticks from short distances up to several centimeters on a the servosphere, and those responses differed between the two species of ticks on the flying T. We discuss our results in the context of the ecology of both tick species and their potential in tick survey and management.
RESUMO
Field and laboratory-choice experiments were conducted to understand aspects of host plant orientation by the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in Virginia. In laboratory bioassays, L. decemlineata oriented to volatiles emitted by potato, Solanum tuberosum L., foliage over both tomato, Lycopersicon esculentum L., and eggplant, Solanum melongena L., foliage, and eggplant over tomato foliage, all of which had been mechanically damaged. Field choice tests revealed more L. decemlineata adults, larvae, and egg masses on eggplant than on tomato. In other experiments, counts of live L. decemlineata on untreated paired plants and counts of dead beetles on imidacloprid-treated plants did not differ between potato and eggplant. L. decemlineata was significantly attracted to eggplant over both tomato and pepper. To determine whether feeding adults affected orientation to host plants, an imidacloprid-treated eggplant or potato plant was paired with an untreated eggplant or potato plant covered in a mesh bag containing two adult male beetles. Significantly more adults were attracted to eggplant with feeding male beetles paired with another eggplant than any other treatment combination. These results indicate that the presence of male L. decemlineata on plants affects host plant orientation and suggests that the male-produced aggregation pheromone may be involved.
Assuntos
Besouros/patogenicidade , Plantas/classificação , Plantas/parasitologia , Solanum tuberosum/parasitologia , Ração Animal , Animais , Interações Hospedeiro-Parasita , Masculino , Odorantes , Solo/análise , Solanum melongena/parasitologiaRESUMO
Mosquitoes use chemical cues to modulate important behaviors such as feeding, mating, and egg laying. The primary chemosensory organs comprising the paired antennae, maxillary palps and labial palps are adorned with porous sensilla that house primary sensory neurons. Dendrites of these neurons provide an interface between the chemical environment and higher order neuronal processing. Diverse proteins located on outer membranes interact with chemicals, ions, and soluble proteins outside the cell and within the lumen of sensilla. Here, we review the repertoire of chemosensory receptors and other membrane proteins involved in transduction and discuss the outlook for their functional characterization. We also provide a brief overview of select ion channels, their role in mammalian taste, and potential involvement in mosquito taste. These chemosensory proteins represent targets for the disruption of harmful biting behavior and disease transmission by mosquito vectors.
RESUMO
Nepeta essential oil (Neo; catnip) and its major component, nepetalactone, have long been known to repel insects including mosquitoes. However, the neural mechanisms through which these repellents are detected by mosquitoes, including the yellow fever mosquito Aedes aegypti (L.), an important vector of Zika virus, were poorly understood. Here we show that Neo volatiles activate olfactory receptor neurons within the basiconic sensilla on the maxillary palps of female Ae. aegypti. A gustatory receptor neuron sensitive to the feeding deterrent quinine and housed within sensilla on the labella of females was activated by both Neo and nepetalactone. Activity of a second gustatory receptor neuron sensitive to the feeding stimulant sucrose was suppressed by both repellents. Our results provide neural pathways for the reported spatial repellency and feeding deterrence of these repellents. A better understanding of the neural input through which female mosquitoes make decisions to feed will facilitate design of new repellents and management strategies involving their use.
Assuntos
Aedes/efeitos dos fármacos , Ciclopentanos/farmacologia , Repelentes de Insetos/farmacologia , Nepeta/química , Óleos Voláteis/farmacologia , Neurônios Receptores Olfatórios/efeitos dos fármacos , Pironas/farmacologia , Sensilas/efeitos dos fármacos , Aedes/fisiologia , Animais , Monoterpenos Ciclopentânicos , Feminino , Maxila/efeitos dos fármacos , Maxila/fisiologia , Neurônios Receptores Olfatórios/fisiologia , Sensilas/fisiologiaRESUMO
A recently synthesized kairomone blend, based on the volatiles produced by potato (Solanum spp.) plants, has been demonstrated to be attractive to both adult and larval stages of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). It was subsequently formulated in a viscous inert carrier for field applications and showed potential for aggregating beetles in treated areas of the field. We investigated effects of this kairomone formulation on the potato aphid, Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae). The response of both winged and wingless adults to natural potato foliage and synthetic kairomone was tested in a Y-tube olfactometer. Aphid response to untreated potato foliage, foliage treated with the kairomone blend, and foliage treated with blank inert carrier also was tested in petri dishes. In addition, aphid densities on field plots treated with kairomone and blank inert carrier were compared with the control plots. The untreated potato foliage was found to be attractive to wingless, but not winged, potato aphids. In the olfactometer, the foliage treated with synthetic Colorado potato beetle kairomone was not attractive to either winged or wingless aphids. In petri dishes, aphids avoided leaflets treated with both kairomone formulation and its blank carrier. There was no statistical difference between any treatments compared in the field.
Assuntos
Afídeos , Comportamento Animal/efeitos dos fármacos , Solanum tuberosum , Animais , Afídeos/virologia , Besouros , Feromônios/farmacologia , Extratos Vegetais/farmacologia , Folhas de Planta , Densidade Demográfica , Solanum tuberosum/parasitologia , Solanum tuberosum/virologiaRESUMO
We recorded electrical responses from sensory cells associated with gustatory sensilla on the labella of female Anopheles quadrimaculatus Say to salt, sucrose, quinine (a feeding deterrent), and the insect repellent, N,N-diethyl-3-methylbenzamide (DEET). A salt-sensitive cell responded to increasing concentrations of sodium chloride. A second cell was activated by increasing sucrose concentrations, while quinine, DEET, or a mixture of quinine + DEET elicited spike activity from a third cell, an apparent bitter- or deterrent-sensitive cell. Both quinine and DEET suppressed activity of the sugar-sensitive cell; sucrose suppressed activity of the bitter- or deterrent-sensitive cell. These results demonstrate separate gustatory pathways for a feeding stimulant and aversive contact cues mediated through distinct sensory inputs on the labellum. This sensory appendage may serve as a useful target to disrupt feeding behavior in this and other anopheline species, which transmit diseases like malaria to human populations.
RESUMO
Chemical repellents are used to decrease contacts between insect disease vectors and their hosts, thus reducing the probability of disease transmission. The molecular mechanisms by which repellents have their effects are poorly understood and remain a controversial topic. Here, we present recent results of studies aimed at a more thorough understanding of the mode of action of repellents and discuss the implications of these findings for future research and development of novel or improved repellents.
Assuntos
Agentes de Controle Biológico , Controle de Doenças Transmissíveis , Repelentes de Insetos/uso terapêutico , Insetos Vetores/fisiologia , Transtornos do Olfato/prevenção & controle , Animais , Humanos , Insetos Vetores/efeitos dos fármacosRESUMO
This multi-author paper reviews current work by USDA-ARS scientists in the field of chemical ecology. Work with pheromones, the discovery and development of the codling moth kairomone, studies on insect-plant interactions and chemically mediated tritrophic plant-insect interactions have led to practical methods for control of important insect pests.
Assuntos
Ecologia , Insetos/fisiologia , Desenvolvimento Vegetal , Projetos de Pesquisa , United States Department of Agriculture , Animais , Besouros/química , Besouros/fisiologia , Interações Hospedeiro-Parasita , Himenópteros/química , Himenópteros/fisiologia , Insetos/química , Mariposas/química , Mariposas/fisiologia , Plantas/parasitologia , Estados UnidosRESUMO
Electrophysiological recording of action potentials from sensory neurons of mosquitoes provides investigators a glimpse into the chemical perception of these disease vectors. We have recently identified a bitter sensing neuron in the labellum of female Aedes aegypti that responds to DEET and other repellents, as well as bitter quinine, through direct electrophysiological investigation. These gustatory receptor neuron responses prompted our sequencing of total mRNA from both male and female labella and tarsi samples to elucidate the putative chemoreception genes expressed in these contact chemoreception tissues. Samples of tarsi were divided into pro-, meso- and metathoracic subtypes for both sexes. We then validated our dataset by conducting qRT-PCR on the same tissue samples and used statistical methods to compare results between the two methods. Studies addressing molecular function may now target specific genes to determine those involved in repellent perception by mosquitoes. These receptor pathways may be used to screen novel repellents towards disruption of host-seeking behavior to curb the spread of harmful viruses.
Assuntos
Aedes/fisiologia , RNA Mensageiro/química , RNA Mensageiro/genética , Análise de Sequência de RNA/métodos , Aedes/genética , Animais , Células Quimiorreceptoras/fisiologia , Fenômenos Eletrofisiológicos , Feminino , Insetos Vetores/genética , Insetos Vetores/fisiologia , MasculinoRESUMO
Female yellow-fever mosquitoes, Aedes aegypti, are obligate blood-feeders and vectors of the pathogens that cause dengue fever, yellow fever and Chikungunya. This feeding behavior concludes a series of multisensory events guiding the mosquito to its host from a distance. The antennae and maxillary palps play a major role in host detection and other sensory-mediated behaviors. Compared to the antennae, the maxillary palps are a relatively simple organ and thus an attractive model for exploration of the neuromolecular networks underlying chemo- and mechanosensation. In this study, we surveyed the expressed genetic components and examined their potential involvement with these sensory modalities. Using Illumina sequencing, we identified the transcriptome of the maxillary palps of physiologically mature female Ae. aegypti. Genes expressed in the maxillary palps included those involved in sensory reception, signal transduction and neuromodulation. In addition to previously reported chemosensory genes, we identified candidate transcripts potentially involved in mechanosensation and thermosensation. This survey lays the groundwork to explore sensory networks in an insect appendage. The identification of genes involved in thermosensation provides prospective molecular targets for the development of chemicals aimed at disrupting the behavior of this medically important insect.
Assuntos
Aedes/genética , Aedes/fisiologia , Sensação/genética , Animais , Sequência de Bases , Feminino , Expressão Gênica , Dados de Sequência Molecular , Neurotransmissores , Análise de Sequência de Proteína , Olfato/genética , Paladar/genética , Sensação Térmica/genética , Tato/genéticaRESUMO
The yellow-fever mosquito Aedes aegypti is a major vector of human diseases, such as dengue, yellow fever, chikungunya and West Nile viruses. Chemoreceptor organs on the labella and tarsi are involved in human host evaluation and thus serve as potential foci for the disruption of blood feeding behavior. In addition to host detection, these contact chemoreceptors mediate feeding, oviposition and conspecific recognition; however, the molecular landscape of chemoreception in these tissues remains mostly uncharacterized. Here we report the expression profile of all putative chemoreception genes in the labella and tarsi of both sexes of adult Ae. aegypti and discuss their possible roles in the physiology and behavior of this important disease vector.
Assuntos
Aedes/genética , Olfato/genética , Paladar/genética , Aedes/fisiologia , Animais , Células Quimiorreceptoras , Extremidades , Comportamento Alimentar , Feminino , Expressão Gênica , Insetos Vetores , MasculinoRESUMO
The interactions between insect repellents and the olfactory system have been widely studied, however relatively little is known about the effects of repellents on the gustatory system of insects. In this study, we show that the gustatory receptor neuron (GRN) located in the medial styloconic sensilla on the maxillary palps of gypsy moth larvae, and known to be sensitive to feeding deterrents, also responds to the insect repellents DEET, IR3535, and picaridin. These repellents did not elicit responses in the lateral styloconic sensilla. Moreover, behavioral studies demonstrated that each repellent deterred feeding. This is the first study to show perception of insect repellents by the gustatory system of a lepidopteran larva and suggests that detection of a range of bitter or aversive compounds may be a broadly conserved feature among insects.
Assuntos
Comportamento Animal/efeitos dos fármacos , DEET/farmacologia , Repelentes de Insetos/farmacologia , Mariposas/fisiologia , Piperidinas/farmacologia , Propionatos/farmacologia , Animais , Comportamento Animal/fisiologia , LarvaRESUMO
The tropical root weevil Diaprepes abbreviatus is a major pest of multiple crops in the Caribbean Islands and has become a serious constraint to citrus production in the United States. Recent work has identified host and conspecific volatiles that mediate host- and mate-finding by D. abbreviatus. The interaction of light, color, and odors has not been studied in this species. The responses of male and female D. abbreviatus to narrow bandwidths of visible light emitted by LEDs offered alone and in combination with olfactory stimuli were studied in a specially-designed multiple choice arena combined with a locomotion compensator. Weevils were more attracted to wavelengths close to green and yellow compared with blue or ultraviolet, but preferred red and darkness over green. Additionally, dim green light was preferred over brighter green. Adult weevils were also attracted to the odor of its citrus host + conspecifics. However, the attractiveness of citrus + conspecific odors disappeared in the presence of a green light. Photic stimulation induced males but not females to increase their speed. In the presence of light emitted by LEDs, turning speed decreased and path straightness increased, indicating that weevils tended to walk less tortuously. Diaprepes abbreviatus showed a hierarchy between chemo- and photo-taxis in the series of experiments presented herein, where the presence of the green light abolished upwind anemotaxis elicited by the pheromone + host plant odor. Insight into the strong responses to visual stimuli of chemically stimulated insects may be provided when the amount of information supplied by vision and olfaction is compared, as the information transmission capacity of compound eyes is estimated to be several orders of magnitude higher compared with the olfactory system. Subordination of olfactory responses by photic stimuli should be considered in the design of strategies aimed at management of such insects.
Assuntos
Sinais (Psicologia) , Estimulação Luminosa , Olfato/fisiologia , Clima Tropical , Gorgulhos/fisiologia , Ar , Animais , Fenômenos Biomecânicos/efeitos dos fármacos , Citrus/química , Comportamento Alimentar/efeitos dos fármacos , Feminino , Luz , Locomoção/efeitos dos fármacos , Masculino , Orientação/efeitos dos fármacos , Olfato/efeitos dos fármacos , Compostos Orgânicos Voláteis/farmacologia , Gorgulhos/efeitos dos fármacosRESUMO
The yellow-fever mosquito, Aedes aegypti, infects a growing number of people every year with dengue, yellow fever and chikungunya viruses. Contact chemoreception in mosquitoes influences a number of behaviors including host-selection, oviposition and feeding. While these behaviors are in many instances well documented, the molecular mechanisms mediating them are not well understood. Here we report the results of sequencing total messenger RNA in the labella and tarsi of both male and female Ae. aegypti to reveal Gustatory Receptor (GR) gene expression profiles in these major gustatory appendages. Gene expression levels in each tissue were verified by RT-qPCR. We discuss potential functions for the GRs revealed here by considering homologous GRs in other insects. Specific GRs provide molecular targets for modification of gustatory-mediated behaviors in this important disease vector.
Assuntos
Dengue/transmissão , Proteínas de Drosophila/genética , Receptores de Superfície Celular/genética , Percepção Gustatória/genética , Transcriptoma , Febre Amarela/transmissão , Aedes/genética , Aedes/virologia , Infecções por Alphavirus/transmissão , Infecções por Alphavirus/virologia , Animais , Febre de Chikungunya , Dengue/virologia , Drosophila melanogaster/genética , Feminino , Insetos Vetores/genética , Masculino , Febre Amarela/virologiaRESUMO
Attraction of female Aedes aegypti mosquitoes to 1-octen-3-ol (octenol), CO2, lactic acid, or ammonia emitted by vertebrate hosts is not only contingent on the presence of odorants in the environment, but is also influenced by the insect's physiological state. For anautogenous mosquito species, like A. aegypti, newly emerged adult females neither respond to host odors nor engage in blood-feeding; the bases for these behaviors are poorly understood. Here we investigated detection of two components of an attractant blend emitted by vertebrate hosts, octenol, and CO2, by female A. aegypti mosquitoes using electrophysiological, behavioral, and molecular approaches. An increase in sensitivity of octenol olfactory receptor neurons (ORNs) was correlated with an increase in odorant receptor gene (Or) expression and octenol-mediated attractive behavior from day 1 to day 6 post-emergence. While the sensitivity of octenol ORNs was maintained through day 10, behavioral responses to octenol decreased as did the ability of females to discriminate between octenol and octenol + CO2. Our results show differing age-related roles for the peripheral receptors for octenol and higher order neural processing in the behavior of female mosquitoes.
RESUMO
The modulation of insect behavior for the purpose of controlling the spread of infectious diseases has been the task of a few insect repellents for which the mechanistic modes of action on odorant receptors (ORs) are unclear. Here, we study the effects of the repellents DEET and IR3535, and a novel OR co-receptor (Orco) agonist on odorant-evoked currents in Xenopus oocytes expressing two subtypes of Aedes aegypti ORs (AaORs). We show that DEET and IR3535 behave as insurmountable antagonists of ORs, and that modulation of OR activity is not restricted to antagonism and agonism, but also includes synergism. This knowledge of the molecular mechanisms underlying OR blockade, activation and hyperactivation will be fundamental to the development of novel strategies for the control of mosquito behavior.