Functional dissection of mosquito humidity sensing reveals distinct Dry and Moist Cell contributions to blood feeding and oviposition.

Aedes aegypti mosquitoes are major vectors of dengue, chikungunya, and other arboviral diseases. Ae. aegypti's capacity to reproduce and to spread disease depends on the female mosquitoes' ability to obtain blood meals and find water-filled containers in which to lay eggs (oviposit). While humidity sensation (hygrosensation) has been implicated in these behaviors, the specific hygrosensory pathways involved have been unclear. Here, we establish the distinct molecular requirements and anatomical locations of Ae. aegypti Dry Cells and Moist Cells and examine their contributions to behavior. We show that Dry Cell and Moist Cell responses to humidity involve different ionotropic receptor (IR) family sensory receptors, with dry air-activated Dry Cells reliant upon the IR Ir40a, and humid air-activated Moist Cells upon Ir68a. Both classes of hygrosensors innervate multiple antennal sensilla, including sensilla ampullacea near the antennal base as well as two classes of coeloconic sensilla near the tip. Dry Cells and Moist Cells each support behaviors linked to mosquito reproduction but contribute differently: Ir40a-dependent Dry Cells act in parallel with Ir68a-dependent Moist Cells to promote blood feeding, while oviposition site seeking is driven specifically by Ir68a-dependent Moist Cells. Together these findings reveal the importance of distinct hygrosensory pathways in blood feeding and oviposition site seeking and suggest Ir40a-dependent Dry Cells and Ir68a-dependent Moist Cells as potential targets for vector control strategies.

4-Vinylanisole is an aggregation pheromone in locusts.

Locust plagues threaten agricultural and environmental safety throughout the world1,2. Aggregation pheromones have a crucial role in the transition of locusts from a solitary form to the devastating gregarious form and the formation of large-scale swarms3,4. However, none of the candidate compounds reported5-7 meet all the criteria for a locust aggregation pheromone. Here, using behavioural assays, electrophysiological recording, olfactory receptor characterization and field experiments, we demonstrate that 4-vinylanisole (4VA) (also known as 4-methoxystyrene) is an aggregation pheromone of the migratory locust (Locusta migratoria). Both gregarious and solitary locusts are strongly attracted to 4VA, regardless of age and sex. Although it is emitted specifically by gregarious locusts, 4VA production can be triggered by aggregation of four to five solitary locusts. It elicits responses specifically from basiconic sensilla on locust antennae. We also identified OR35 as a specific olfactory receptor of 4VA. Knockout of OR35 using CRISPR-Cas9 markedly reduced the electrophysiological responses of the antennae and impaired 4VA behavioural attractiveness. Finally, field trapping experiments verified the attractiveness of 4VA to experimental and wild populations. These findings identify a locust aggregation pheromone and provide insights for the development of novel control strategies for locusts.

Discrete roles of Ir76b ionotropic coreceptor impact olfaction, blood feeding, and mating in the malaria vector mosquito Anopheles coluzzii.

Anopheline mosquitoes rely on their highly sensitive chemosensory apparatus to detect diverse chemical stimuli that drive the host-seeking and blood-feeding behaviors required to vector pathogens for malaria and other diseases. This process incorporates a variety of chemosensory receptors and transduction pathways. We used advanced in vivo gene-editing and -labeling approaches to localize and functionally characterize the ionotropic coreceptor AcIr76b in the malaria mosquito Anopheles coluzzii, where it impacts both olfactory and gustatory systems. AcIr76b has a broad expression pattern in female adult antennal grooved pegs, coeloconic sensilla, and T1 and T2 sensilla on the labellum, stylets, and tarsi, as well as the larval sensory peg. AcIr76b is colocalized with the Orco odorant receptor (OR) coreceptor in a subset of cells across the female antennae and labella. In contrast to Orco and Ir8a, chemosensory coreceptors that appear essential for the activity of their respective sets of chemosensory neurons in mosquitoes, AcIr76b−/− mutants maintain wild-type peripheral responses to volatile amines on the adult palps, labellum, and larval sensory cone. Interestingly, AcIr76b−/− mutants display significantly increased responses to amines in antennal grooved peg sensilla, while coeloconic sensilla reveal significant deficits in responses to several acids and amines. Behaviorally, AcIr76b mutants manifest significantly female-specific insemination deficits, and although AcIr76b−/− mutant females can locate, alight on, and probe artificial blood hosts, they are incapable of blood feeding successfully. Taken together, our findings reveal a multidimensional functionality of Ir76b in anopheline olfactory and gustatory pathways that directly impacts the vectorial capacity of these mosquitoes.

Females smell differently: characteristics and significance of the most common olfactory sensilla of female silkmoths.

In the silkmoth Bombyx mori, the role of male sensilla trichodea in pheromone detection is well established. Here we study the corresponding female sensilla, which contain two olfactory sensory neurons (OSNs) and come in two lengths, each representing a single physiological type. Only OSNs in medium trichoids respond to the scent of mulberry, the silkworm's exclusive host plant, and are more sensitive in mated females, suggesting a role in oviposition. In long trichoids, one OSN is tuned to (+)-linalool and the other to benzaldehyde and isovaleric acid, both odours emitted by silkworm faeces. While the significance of (+)-linalool detection remains unclear, isovaleric acid repels mated females and may therefore play a role in avoiding crowded oviposition sites. When we examined the underlying molecular components of neurons in female trichoids, we found non-canonical co-expression of Ir8a, the co-receptor for acid responses, and ORco, the co-receptor of odorant receptors, in long trichoids, and the unexpected expression of a specific odorant receptor in both trichoid sensillum types. In addition to elucidating the function of female trichoids, our results suggest that some accepted organizational principles of the insect olfactory system may not apply to the predominant sensilla on the antenna of female B. mori.

Asynchronous haltere input drives specific wing and head movements in Drosophila.

Halteres are multifunctional mechanosensory organs unique to the true flies (Diptera). A set of reduced hindwings, the halteres beat at the same frequency as the lift-generating forewings and sense inertial forces via mechanosensory campaniform sensilla. Though haltere ablation makes stable flight impossible, the specific role of wing-synchronous input has not been established. Using small iron filings attached to the halteres of tethered flies and an alternating electromagnetic field, we experimentally decoupled the wings and halteres of flying Drosophila and observed the resulting changes in wingbeat amplitude and head orientation. We find that asynchronous haltere input results in fast amplitude changes in the wing (hitches), but does not appreciably move the head. In multi-modal experiments, we find that wing and gaze optomotor responses are disrupted differently by asynchronous input. These effects of wing-asynchronous haltere input suggest that specific sensory information is necessary for maintaining wing amplitude stability and adaptive gaze control.

Insect pectinate antennae maximize odor capture efficiency at intermediate flight speeds.

Flying insects are known to orient themselves over large distances using minute amounts of odors. Some bear pectinate antennae of remarkable architecture thought to improve olfactory performance. The semiporous, multiscale nature of these antennae influences how odor molecules reach their surface. We focus here on the repeating structural building blocks of these antennae in Saturniid moths. This microstructure consists of one ramus or branch and its many hair-like sensilla, responsible for chemical detection. We experimentally determined leakiness, defined as the proportion of air going through the microstructure rather than flowing around it, by particle image velocimetry visualization of the flow around three-dimensional printed scaled-up mock-ups. The combination of these results with a model of mass transfer showed that most pheromone molecules are deflected around the microstructure at low flow velocities, keeping them out of reach. Capture is thus determined by leakiness. By contrast, at high velocities, molecular diffusion is too slow to be effective, and the molecules pass through the structure without being captured. The sensory structure displays maximal odor capture efficiency at intermediate flow speeds, as encountered by the animal during flight. These findings also provide a rationale for the previously described "olfactory lens," an increase in pheromone reception at the proximal end of the sensors. We posit that it is based on passive mass transfer rather than on physicochemical surface processes.

Sensory signals of unloading in insects are tuned to distinguish leg slipping from load variations in gait: experimental and modeling studies.

In control of walking, sensory signals of decreasing forces are used to regulate leg lifting in initiation of swing and to detect loss of substrate grip (leg slipping). We used extracellular recordings in two insect species to characterize and model responses to force decrements of tibial campaniform sensilla, receptors that detect forces as cuticular strains. Discharges to decreasing forces did not occur upon direct stimulation of the sites of mechanotransduction (cuticular caps) but were readily elicited by bending forces applied to the leg. Responses to bending force decreases were phasic but had rate sensitivities similar to discharges elicited by force increases in the opposite direction. Application of stimuli of equivalent amplitude at different offset levels showed that discharges were strongly dependent upon the tonic level of loading: firing was maximal to complete unloading of the leg but substantially decreased or eliminated by sustained loads. The contribution of cuticle properties to sensory responses was also evaluated: discharges to force increases showed decreased adaptation when mechanical stress relaxation was minimized; firing to force decreases could be related to viscoelastic "creep" in the cuticle. Discharges to force decrements apparently occur due to cuticle viscoelasticity that generates transient strains similar to bending in the opposite direction. Tuning of sensory responses through cuticular and membrane properties effectively distinguishes loss of substrate grip/complete unloading from force variations due to gait in walking. We have successfully reproduced these properties in a mathematical model of the receptors. Sensors with similar tuning could fulfil these functions in legs of walking machines.NEW & NOTEWORTHY Decreases in loading of legs are important in the regulation of posture and walking in both vertebrates and invertebrates. Recordings of activities of tibial campaniform sensilla, which encode forces in insects, showed that their responses are specifically tuned to detect force decreases at the end of the stance phase of walking or when a leg slips. These results have been reproduced in a mathematical model of the receptors and also have potential applications in robotics.

Evaluation of force feedback in walking using joint torques as "naturalistic" stimuli.

Control of adaptive walking requires the integration of sensory signals of muscle force and load. We have studied how mechanoreceptors (tibial campaniform sensilla) encode "naturalistic" stimuli derived from joint torques of stick insects walking on a horizontal substrate. Previous studies showed that forces applied to the legs using the mean torque profiles of a proximal joint were highly effective in eliciting motor activities. However, substantial variations in torque direction and magnitude occurred at the more distal femorotibial joint, which can generate braking or propulsive forces and provide lateral stability. To determine how these forces are encoded, we used torque waveforms of individual steps that had maximum values in stance in the directions of flexion or extension. Analysis of kinematic data showed that the torques in different directions tended to occur in different ranges of joint angles. Variations within stance were not accompanied by comparable changes in joint angle but often reflected vertical ground reaction forces and leg support of body load. Application of torque waveforms elicited sensory discharges with variations in firing frequency similar to those seen in freely walking insects. All sensilla directionally encoded the dynamics of force increases and showed hysteresis to transient force decreases. Smaller receptors exhibited more tonic firing. Our findings suggest that dynamic sensitivity in force feedback can modulate ongoing muscle activities to stabilize distal joints when large forces are generated at proximal joints. Furthermore, use of "naturalistic" stimuli can reproduce characteristics seen in freely moving animals that are absent in conventional restrained preparations.NEW & NOTEWORTHY Sensory encoding of forces during walking by campaniform sensilla was characterized in stick insects using waveforms of joint torques calculated by inverse dynamics as mechanical stimuli. Tests using the mean joint torque and torques of individual steps showed the system is highly sensitive to force dynamics (dF/dt). Use of "naturalistic" stimuli can reproduce characteristics of sensory discharges seen in freely walking insects, such as load transfer among legs.

Giant steps: adhesion and locomotion in theraphosid tarantulas.

Theraphosid tarantulas are large spiders that bear dense hairy adhesive pads on the distal parts of their legs: scopula and claw tufts. These structures allow them to climb on vertical smooth surfaces and contribute to prey capture. While adult females and juveniles remain most of the time in their burrows, adult males actively walk searching for females during the reproductive period. Adhesion and locomotion thus play important roles in the ecology and reproduction of these animals. In this paper, we review the current state of the knowledge on adhesion and locomotion in tarantulas, focusing on functional and evolutionary morphology.

Role of legs and foot adhesion in salticid spiders jumping from smooth surfaces.

Many spiders and insects can perform rapid jumps from smooth plant surfaces. Here, we investigate how jumping spiders (Pseudeuophrys lanigera and Sitticus pubescens) avoid slipping when accelerating. Both species differed in the relative contribution of leg pairs to the jump. P. lanigera accelerated mainly with their long third legs, whereas their short fourth legs detached earlier. In contrast, S. pubescens accelerated mainly with their long fourth legs, and their short third legs detached earlier. Because of the different orientation (fourth-leg tip pointing backward, third-leg tip pointing forward), the fourth-leg tarsus pushed, whereas the third-leg tarsus pulled. High-speed video recordings showed that pushing and pulling was achieved by different attachment structures. In P. lanigera, third-leg feet made surface contact with setae on their distal or lateral claw tuft, whereas fourth-leg feet engaged the proximal claw tuft, and the distal tuft was raised off the ground. S. pubescens showed the same division of labour between proximal and distal claw tuft for pushing and pulling, but the claw tuft contact lasted longer and was more visible in the fourth than in the third legs. Experimental ablation of claw tufts caused accelerating spiders to slip, confirming that adhesion is essential for jumps from smooth substrates.

A spider in motion: facets of sensory guidance.

Spiders show a broad range of motions in addition to walking and running with their eight coordinated legs taking them towards their resources and away from danger. The usefulness of all these motions depends on the ability to control and adjust them to changing environmental conditions. A remarkable wealth of sensory receptors guarantees the necessary guidance. Many facets of such guidance have emerged from neuroethological research on the wandering spider Cupiennius salei and its allies, although sensori-motor control was not the main focus of this work. The present review may serve as a springboard for future studies aiming towards a more complete understanding of the spider's control of its different types of motion. Among the topics shortly addressed are the involvement of lyriform slit sensilla in path integration, muscle reflexes in the walking legs, the monitoring of joint movement, the neuromuscular control of body raising, the generation of vibratory courtship signals, the sensory guidance of the jump to flying prey and the triggering of spiderling dispersal behavior. Finally, the interaction of sensors on different legs in oriented turning behavior and that of the sensory systems for substrate vibration and medium flow are addressed.

Mechanosensory interactions drive collective behaviour in Drosophila.

Collective behaviour enhances environmental sensing and decision-making in groups of animals. Experimental and theoretical investigations of schooling fish, flocking birds and human crowds have demonstrated that simple interactions between individuals can explain emergent group dynamics. These findings indicate the existence of neural circuits that support distributed behaviours, but the molecular and cellular identities of relevant sensory pathways are unknown. Here we show that Drosophila melanogaster exhibits collective responses to an aversive odour: individual flies weakly avoid the stimulus, but groups show enhanced escape reactions. Using high-resolution behavioural tracking, computational simulations, genetic perturbations, neural silencing and optogenetic activation we demonstrate that this collective odour avoidance arises from cascades of appendage touch interactions between pairs of flies. Inter-fly touch sensing and collective behaviour require the activity of distal leg mechanosensory sensilla neurons and the mechanosensory channel NOMPC. Remarkably, through these inter-fly encounters, wild-type flies can elicit avoidance behaviour in mutant animals that cannot sense the odour--a basic form of communication. Our data highlight the unexpected importance of social context in the sensory responses of a solitary species and open the door to a neural-circuit-level understanding of collective behaviour in animal groups.

Odorant binding protein 69a connects social interaction to modulation of social responsiveness in Drosophila.

Living in a social environment requires the ability to respond to specific social stimuli and to incorporate information obtained from prior interactions into future ones. One of the mechanisms that facilitates social interaction is pheromone-based communication. In Drosophila melanogaster, the male-specific pheromone cis-vaccenyl acetate (cVA) elicits different responses in male and female flies, and functions to modulate behavior in a context and experience-dependent manner. Although it is the most studied pheromone in flies, the mechanisms that determine the complexity of the response, its intensity and final output with respect to social context, sex and prior interaction, are still not well understood. Here we explored the functional link between social interaction and pheromone-based communication and discovered an odorant binding protein that links social interaction to sex specific changes in cVA related responses. Odorant binding protein 69a (Obp69a) is expressed in auxiliary cells and secreted into the olfactory sensilla. Its expression is inversely regulated in male and female flies by social interactions: cVA exposure reduces its levels in male flies and increases its levels in female flies. Increasing or decreasing Obp69a levels by genetic means establishes a functional link between Obp69a levels and the extent of male aggression and female receptivity. We show that activation of cVA-sensing neurons is sufficeint to regulate Obp69a levels in the absence of cVA, and requires active neurotransmission between the sensory neuron to the second order olfactory neuron. The cross-talk between sensory neurons and non-neuronal auxiliary cells at the olfactory sensilla, represents an additional component in the machinery that promotes behavioral plasticity to the same sensory stimuli in male and female flies.

Numerical analysis of conduction velocity/path relationships in a crustacean sensory neuron.

Experimental observations of the axonal conduction velocities of sensory neurons associated with near-field sensilla on the cephalothorax of the crayfish Procambarus clarkii indicate that neurons supplying sensilla farther from their connections with the central nervous system exhibit higher overall impulse conduction velocities. The conduction velocity/distance relationship is best described by an exponentially rising, asymptotic curve. A numerical model for regional variations in impulse conduction velocity in these sensory neurons was developed, based upon neuronal morphological metrics and physiological data. The predicted relationship between conduction velocity and length of conduction pathway in the model was compared to experimental data from 88 sensory neurons associated with thoracic near-field receptor sensilla, in which both the mean conduction velocity and the length of the conduction pathway for each neuron were known. Curves fitted to the conduction velocity versus distance relationship in the two cases were similar, although not congruent. Chi-square statistics comparing the curves predict that the curves are similar at the 0.005 probability level, suggesting that the numerical model's variations in axonal morphology can satisfactorily account for the observed conduction velocity-distance relationship in these sensory neurons.

Detection of heliothine sex pheromone components in the Australian budworm moth, Helicoverpa punctigera: electrophysiology, neuroanatomy, and behavior.

This study examined electrophysiological responses of the Australian budworm moth Helicoverpa punctigera, to heliothine sex pheromone components, via single sensillum recordings (SSR), and examined male neuroanatomy using confocal microscopy and 3D imaging tools. We found that male H. punctigera have three distinct regions of the macroglomerular complex (MGC) in the antennal lobe. Male antennae have only two functional types of sensilla trichoidea (A and C) and type A sensilla contain an olfactory sensory neuron (OSN) that responds to the major sex pheromone component (Z)-11-hexadecenal (Z11-16:Ald) with axons projecting to the cumulus of the macroglomerular complex (MGC) in the antennal lobe. Type C sensilla contained large-spiking receptor neurons which responded primarily to (Z)-9-tetradecenal (Z9-14:Ald) and to a lesser degree to (Z)-11-hexadecenol (Z11-16:OH). These were co-compartmentalized with small-spiking receptor neurons in type C sensilla which responded strongly to Z9-14:Ald and (Z)-9-hexadecenal (Z9-16:Ald), and to a lesser degree to (Z)-11-hexadecenyl acetate (Z11-16:OAc) and Z11-16:OH. Axons from the two co-localized neurons in Type C sensilla projected to the two small MGC units, the dorsomedial anterior and dorsomedial posterior, respectively. In wind tunnel assays, the addition of Z9-16:Ald to an otherwise attractive blend completely shut down male H. punctigera upwind flight.

Olfactory Receptor Neurons for Plant Volatiles and Pheromone Compounds in the Lucerne Weevil, Sitona discoideus.

Antennal olfactory receptor neurons (ORNs) for pheromone-related and plant volatile compounds were identified and characterized in the lucerne weevil, Sitona discoideus (Gyllenhal), using the single sensillum recording technique. Our study using five pheromone-related compounds and 42 plant volatile compounds indicates that S. discoideus have highly specialized ORNs for pheromone and plant volatile compounds. Different groups of ORNs present in both males and females of S. discoideus were highly sensitive to 4-methylheptane-3,5-dione (diketone) and four isomers (RR, RS, SR and SS) of 5-hydroxy-4-methylheptan-3-one, respectively. Our results also indicate that male S. discoideus, using the sensory input from antennal ORNs, can distinguish both diketone and the RR-isomer from others, and RS- and SS-isomers from others, although it was unclear if they can distinguish between RS-isomer and SS-isomer, or between diketone and the SR-isomer. It also appeared that female S. discoideus could distinguish between RS-isomer and SS-isomers. The antennae of S. discoideus thus contain sex-specific sets of ORNs for host- and non-host plant volatile compounds. Both sexes of S. discoideus have highly sensitive and selective ORNs for some green-leaf volatiles, such as (Z)-3-hexenol and (E)-2-hexenal. In contrast, male antennae of S. discoideus house three distinct groups of ORNs specialized for myrcene and (E)-ß-ocimene, 2-phenylethanol, and phenylacetaldehyde, respectively, whereas female antennae contain three groups of ORNs specialized for (±)-linalool and (±)-α-terpineol, myrcene and (E)-ß-ocimene, (±)-1-octen-3-ol, and 3-octanone. Our results suggest that S. discoideus use a multi-component pheromone communication system, and a sex-specific set of ORNs with a narrow range of response spectra for host-plant location.

The pleiotropic effects of Innexin genes expressed in Drosophila glia encompass wing chemosensory sensilla.

The neuroanatomy of Drosophila wing chemosensilla and the analysis of their sensory organ precursor cell lineage have demonstrated that they are surprisingly related to taste perception. The microarchitecture of wing bristles limits the use of electrophysiology methods to investigate wing chemosensory mechanisms. However, by monitoring the fluorescence of the complex calcium/GCaMP, calcium flux triggered upon tastant stimulation was observed within sensilla aligned along the wing anterior nerve. This string of fluorescent puncta was impaired in wings of Innexin 2 (Inx2) mutant flies; although it is unclear whether the Innexin proteins act at the level of the wing imaginal disc, adult wing and/or at both levels. Glial cells known to shelter Innexin(s) expression have no documented role in adult chemosensory sensilla. Our data suggest that Innexin(s) are likely required for the maturation of functional wing chemosensilla in adulthood. The unexpected presence of most Innexin transcripts in adult wing RNAseq data set argues for the expression of Innexin proteins in the larval imaginal wing disc that are continued in wing chemosensilla at adulthood. OPEN PRACTICES: This article has earned an Open Data badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available as supporting materials and includes the electronic lab notebook. Learn more about the Open Practices badges from the Center for Open Science: https://osf.io/tvyxz/wiki.

Identification of the origin of force-feedback signals influencing motor neurons of the thoraco-coxal joint in an insect.

Force feedback from Campaniform sensilla (CS) on insect limbs helps to adapt motor outputs to environmental conditions, but we are only beginning to reveal the neural control mechanisms that mediate these influences. We studied CS groups that affect control of the thoraco-coxal joint in the stick insect Carausius morosus by applying horizontal and vertical forces to the leg stump. Motor effects of ablation of CS groups were evaluated by recording extracellularly from protractor (ProCx) and retractor (RetCx) nerves. Extracellular recordings showed that the effects of stimulating the sensilla were consistent with their broad ranges of directional sensitivity: for example, RetCx firing in response to posterior bending could be reduced by ablating several groups of trochanteral CS, whereas ablation of tibial and femoral sensilla had little effect. In contrast, ProCx motor neuron activity upon anteriorly directed stimuli was affected mainly by ablating a single CS group (G2). Dye fills of trochanteral, femoral and tibial CS groups with fluorescent dyes revealed a common projection pattern with little group specificity. These findings support the idea that the influences of CS feedback are determined by the activities of pre-motor interneurons, facilitating fast and task-dependent adaptation to changing environmental conditions.

Hearing in caterpillars of the monarch butterfly (Danaus plexippus).

Many species of caterpillars have been reported to respond to sound, but there has been limited formal study of what sounds they hear, how they hear them and how they respond to them. Here, we report on hearing in caterpillars of the monarch butterfly (Danaus plexippus). Fourth and fifth instar caterpillars respond to sounds by freezing, contracting, and flicking their thorax in a vertical direction. Behavioural responses were evoked by sound frequencies between 50 and 900 Hz, with best sensitivity at 100-200 Hz. The lowest mean threshold was 79 dB SPL (particle velocity 605 µm s-1) at 150 Hz. When presented with a repeated 200 Hz sound tone, caterpillars habituate by no longer responding. A series of ablation experiments confirmed that the primary sensory receptors are a pair of long hairs, called trichoid sensilla, located on the upper prothorax. These sensilla are ∼450 µm long, rest in a socket and are innervated by a single bipolar sensory neuron. Removal of these setae reduced responses significantly compared with controls. Other setae contributed minimally to hearing in response to 200 Hz tones, and tubercles and prothoracic shields played no apparent role in sound reception. We propose that hearing functions to prevent attacks by aerial insect predators and parasitoids, which produce flight sounds in the frequency range to which the caterpillars are sensitive. This research lays the foundation for further investigations on the function and evolution of hearing in caterpillars, and has significance for the conservation of threatened monarch butterfly larvae living near noisy urban environments and roadways.

The contribution of gustatory input to larval acceptance and female oviposition choice of potential host plants in Papilio hospiton (Géné).

The Lepidopteran Papilio hospiton uses only plants belonging to the Apiaceae and the Rutaceae families as hosts. Both adult females and larvae are equipped with gustatory receptor neurons (GRNs) capable of detecting sugars, bitters and salts, thus providing information for evaluating the chemical composition of the plant. Since the activation of these neurons may affect insect behavior, the aim of this study were: (a) to study the gustatory sensitivity of both females and larvae to the sap of two Apiaceae, Foeniculum vulgare (fennel) and Daucus carota (carrot), that are not used as host plants; (b) to cross-compare the spike activity evoked from these two plants with that evoked by Ferula communis (ferula), the host plant preferred by ovipositing females of P. hospiton and where the larvae perform best; (c) finally, to confirm that the gustatory system can provide the central nervous system with the necessary information to evaluate differences between plant saps. The results show that: (a) fennel and carrot both evoke a higher neural activity from the bitter-sensitive neurons and lower from the sugar-sensitive neurons with respect to ferula, in both adult females and larvae; (b) on the basis of the different patterns of neural activity generated in tarsal, lateral and medial sensilla by fennel and carrot versus ferula, both adult and larvae possess enough information to discriminate among these plants; (c) adult females of P. hospiton lay eggs where the larvae have the greatest growth success and this confirms the importance of taste sensitivity in host plants selection.