Mechanosensory neurons control sweet sensing in Drosophila

Osiris gene family defines the cuticle nanopatterns of Drosophila

Nanostructures of pores and protrusions in the insect cuticle modify molecular permeability and surface wetting and help insects sense various environmental cues. However, the cellular mechanisms that modify cuticle nanostructures are poorly understood. Here, we elucidate how insect-specific Osiris family genes are expressed in various cuticle-secreting cells in the Drosophila head during the early stages of cuticle secretion and cover nearly the entire surface of the head epidermis. Furthermore, we demonstrate how each sense organ cell with various cuticular nanostructures expressed a unique combination of Osiris genes. Osiris gene mutations cause various cuticle defects in the corneal nipples and pores of the chemosensory sensilla. Thus, our study emphasizes on the importance of Osiris genes for elucidating cuticle nanopatterning in insects.

HisCl1 regulates gustatory habituation in sweet taste neurons and mediates sugar ingestion in Drosophila

Similar to other animals, the fly, Drosophila melanogaster, reduces its responsiveness to tastants with repeated exposure, a phenomenon called gustatory habituation. Previous studies have focused on the circuit basis of gustatory habituation in the fly chemosensory system1,2. However, gustatory neurons reduce their firing rate during repeated stimulation3, suggesting that cell-autonomous mechanisms also contribute to habituation. Here, we used deep learning-based pose estimation and optogenetic stimulation to demonstrate that continuous activation of sweet taste neurons causes gustatory habituation in flies. We conducted a transgenic RNAi screen to identify genes involved in this process and found that knocking down Histamine-gated chloride channel subunit 1 (HisCl1) in the sweet taste neurons significantly reduced gustatory habituation. Anatomical analysis showed that HisCl1 is expressed in the sweet taste neurons of various chemosensory organs. Using single sensilla electrophysiology, we showed that sweet taste neurons reduced their firing rate with prolonged exposure to sucrose. Knocking down HisCl1 in sweet taste neurons suppressed gustatory habituation by reducing the spike frequency adaptation observed in these neurons during high-concentration sucrose stimulation. Finally, we showed that flies lacking HisCl1 in sweet taste neurons increased their consumption of high-concentration sucrose solution at their first meal bout compared to control flies. Together, our results demonstrate that HisCl1 tunes spike frequency adaptation in sweet taste neurons and contributes to gustatory habituation and food intake regulation in flies. Since HisCl1 is highly conserved across many dipteran and hymenopteran species, our findings open a new direction in studying insect gustatory habituation.

Somatotopic organization among parallel sensory pathways that promote a grooming sequence in Drosophila

Mechanosensory neurons located across the body surface respond to tactile stimuli and elicit diverse behavioral responses, from relatively simple stimulus location-aimed movements to complex movement sequences. How mechanosensory neurons and their postsynaptic circuits influence such diverse behaviors remains unclear. We previously discovered that Drosophila perform a body location-prioritized grooming sequence when mechanosensory neurons at different locations on the head and body are simultaneously stimulated by dust (Hampel et al., 2017; Seeds et al., 2014). Here, we identify nearly all mechanosensory neurons on the Drosophila head that individually elicit aimed grooming of specific head locations, while collectively eliciting a whole head grooming sequence. Different tracing methods were used to reconstruct the projections of these neurons from different locations on the head to their distinct arborizations in the brain. This provides the first synaptic resolution somatotopic map of a head, and defines the parallel-projecting mechanosensory pathways that elicit head grooming.

Evolution of chemosensory tissues and cells across ecologically diverse Drosophilids

Chemosensory tissues exhibit significant between-species variability, yet the evolution of gene expression and cell types underlying this diversity remain poorly understood. To address these questions, we conducted transcriptomic analyses of five chemosensory tissues from six Drosophila species and integrated the findings with single-cell datasets. While stabilizing selection predominantly shapes chemosensory transcriptomes, thousands of genes in each tissue have evolved expression differences. Genes that have changed expression in one tissue have often changed in multiple other tissues but at different past epochs and are more likely to be cell type-specific than unchanged genes. Notably, chemosensory-related genes have undergone widespread expression changes, with numerous species-specific gains/losses including novel chemoreceptors expression patterns. Sex differences are also pervasive, including a D. melanogaster-specific excess of male-biased expression in sensory and muscle cells in its forelegs. Together, our analyses provide new insights for understanding evolutionary changes in chemosensory tissues at both global and individual gene levels.

Merkel cells and keratinocytes in oral mucosa are activated by mechanical stimulation

The detection of mechanical qualities of foodstuffs is essential for nutrient acquisition, evaluation of food freshness, and bolus formation during mastication. However, the mechanisms through which mechanosensitive cells in the oral cavity transmit mechanical information from the periphery to the brain are not well defined. We hypothesized Merkel cells, which are epithelial mechanoreceptors and important for pressure and texture sensing in the skin, can be mechanically activated in the oral cavity. Using live-cell calcium imaging, we recorded Merkel cell activity in ex vivo gingival and palatal preparations from mice in response to mechanical stimulation. Merkel cells responded with distinct temporal patterns and activation thresholds in a region-specific manner, with Merkel cells in the hard palate having a higher mean activation threshold than those in the gingiva. Unexpectedly, we found that oral keratinocytes were also activated by mechanical stimulation, even in the absence of Merkel cells. This indicates that mechanical stimulation of oral mucosa independently activates at least two subpopulations of epithelial cells. Finally, we found that oral Merkel cells contribute to preference for consuming oily emulsion. To our knowledge, these data represent the first functional study of Merkel-cell physiology and its role in flavor detection in the oral cavity.

Somatotopic organization among parallel sensory pathways that promote a grooming sequence in Drosophila

Mechanosensory neurons located across the body surface respond to tactile stimuli and elicit diverse behavioral responses, from relatively simple stimulus location-aimed movements to complex movement sequences. How mechanosensory neurons and their postsynaptic circuits influence such diverse behaviors remains unclear. We previously discovered that Drosophila perform a body location-prioritized grooming sequence when mechanosensory neurons at different locations on the head and body are simultaneously stimulated by dust (Hampel et al., 2017; Seeds et al., 2014). Here, we identify nearly all mechanosensory neurons on the Drosophila head that individually elicit aimed grooming of specific head locations, while collectively eliciting a whole head grooming sequence. Different tracing methods were used to reconstruct the projections of these neurons from different locations on the head to their distinct arborizations in the brain. This provides the first synaptic resolution somatotopic map of a head, and defines the parallel-projecting mechanosensory pathways that elicit head grooming.

Diverse mechanisms of taste coding in Drosophila

Taste systems encode chemical cues that drive vital behaviors. We have elucidated noncanonical features of taste coding using an unconventional kind of electrophysiological analysis. We find that taste neurons of Drosophila are much more sensitive than previously thought. They have a low spontaneous firing frequency that depends on taste receptors. Taste neurons have a dual function as olfactory neurons: They are activated by most tested odorants, including N,N-diethyl-meta-toluamide (DEET), at a distance. DEET can also inhibit certain taste neurons, revealing that there are two modes of taste response: activation and inhibition. We characterize electrophysiological OFF responses and find that the tastants that elicit them are related in structure. OFF responses link tastant identity to behavior: the magnitude of the OFF response elicited by a tastant correlated with the egg laying behavior it elicited. In summary, the sensitivity and coding capacity of the taste system are much greater than previously known.

Insect transient receptor potential vanilloid channels as potential targets of insecticides

Chordotonal organs are miniature sensory organs present in insects. Chordotonal organs depend on transient receptor potential (TRP) channels. Transient receptor potential vanilloid (TRPV) channels are the only TRPs identified that can act as targets of insecticides. By binding with TRPV channels, insecticides targeting the chordotonal organs trigger the inflow of calcium ions, resulting in abnormal function of the chordotonal organ to achieve the goal of eliminating pests. TRPV channels are highly expressed in various developmental stages and tissue parts of insects and play an important role in the whole life history of insects. In this review, we will discuss the structure and types of TRPV channels as well as their genetic relationships in different species. We also systematically reviewed the recent progress of TRPV channels as insecticide targets, demonstrating that TRPV channels can be used as the target of new high-efficiency insecticides.

Intake of caffeine containing sugar diet remodels gut microbiota and perturbs Drosophila melanogaster immunity and lifespan

The diet-microbiome-immunity axis is one among the many arms that draw up the "we are what we intake" proclamation. As such, studies on the effect of food and beverage intake on the gut environment and microbiome and on modulating immunological responses and the host's susceptibility to pathogens are on the rise. A typical accompaniment in different sustenance we consume on daily basis is the trimethylxanthine alkaloid caffeine. Being a chief component in our regular aliment, a better understanding of the effect of caffeine containing food and beverages on our gut-microbiome-immunity axis and henceforth on our health is much needed. In this study, we shed more light on the effect of oral consumption of caffeine supplemented sugar diet on the gut environment, specifically on the gut microbiota, innate immunity and host susceptibility to pathogens using the Drosophila melanogaster model organism. Our findings reveal that the oral intake of a dose-specific caffeine containing sucrose/agarose sugar diet causes a significant alteration within the fly gut milieu demarcated by microbial dysbiosis and an elevation in the production of reactive oxygen species and expression of immune-deficiency (Imd) pathway-dependent antimicrobial peptide genes. The oral intake of caffeine containing sucrose/agarose sugar diet also renders the flies more susceptible to bacterial infection and shortens their lifespan in both infection and non-infection settings. Our findings set forth additional insight into the potentiality of diet to alter the gut milieu and highlight the importance of dietary control on health.

Characterization, expression, and functional analysis of TRPV genes in cotton aphid, Aphis gossypii Glover

Transient receptor potential vanilloid (TRPV) channels have been found to be the molecular target of afidopyropen, a novel insecticide that is highly effective in controlling Aphis gossypii Glover in the field. However, the TRPV genes of A. gossypii has not yet been characterized. In this study, two TRPV genes of A. gossypii (AgNan and AgIav) were cloned and their expression levels were determined by quantitative real-time PCR (RT-qPCR). The deduced amino acids of AgNan and AgIav contain all conserved domains of TRPV and share very high amino acid identity with other insect TRPVs. AgNan and AgIav expressed in all developmental stages and their expression can be induced by afidopyropen in a dose- and time-dependent manner. Moreover, we found that silencing of AgNan and AgIav by RNA interference resulted in a significant mortality increase of adult A. gossypii compared to the control, which was even higher than 93 % at five days after feeding with dsAgIav, suggesting that knockdown of AgNan and AgIav have great effects on the survival of A. gossypii. The results of this study would be helpful for determining the reasonable use of afidopyropen in the integrated pest management programs of A. gossypii and provide useful information for further functional study of TRPVs in insects.

Chemosensory Coding in Drosophila Single Sensilla

The chemical senses-smell and taste-detect and discriminate an enormous diversity of environmental stimuli and provide fascinating but challenging models to investigate how sensory cues are represented in the brain. Important stimulus-coding events occur in peripheral sensory neurons, which express specific combinations of chemosensory receptors with defined ligand-response profiles. These receptors convert ligand recognition into spatial and temporal patterns of neural activity that are transmitted to, and interpreted in, central brain regions. Drosophila melanogaster provides an attractive model to study chemosensory coding because it possesses relatively simple peripheral olfactory and gustatory systems that display many organizational parallels to those of vertebrates. Moreover, nearly all peripheral chemosensory neurons have been molecularly characterized and are accessible for physiological analysis, as they are exposed on the surface of sensory organs housed in specialized hairs called sensilla. Here, we briefly review anatomical, molecular, and physiological properties of adult Drosophila olfactory and gustatory systems and provide background to methods for electrophysiological recordings of ligand-evoked activity from different types of chemosensory sensilla.

Molecular sensors in the taste system of Drosophila

BACKGROUND

Most animals, including humans and insects, consume foods based on their senses. Feeding is mostly regulated by taste and smell. Recent insect studies shed insight into the cross-talk between taste and smell, sweetness and temperature, sweetness and texture, and other sensory modality pairings. Five canonical tastes include sweet, umami, bitter, salty, and sour. Furthermore, other receptors that mediate the detection of noncanonical sensory attributes encoded by taste stimuli, such as Ca²⁺, Zn²⁺, Cu²⁺, lipid, and carbonation, have been characterized. Deorphanizing receptors and interactions among different modalities are expanding the taste field.

METHODS

Our study explores the taste system of Drosophila melanogaster and perception processing in insects to broaden the neuroscience of taste. Attractive and aversive taste cues and their chemoreceptors are categorized as tables. In addition, we summarize the recent progress in animal behavior as affected by the integration of multisensory information in relation to different gustatory receptor neuronal activations, olfaction, texture, and temperature. We mainly focus on peripheral responses and insect decision-making.

CONCLUSION

Drosophila is an excellent model animal to study the cellular and molecular mechanism of the taste system. Despite the divergence in the receptors to detect chemicals, taste research in the fruit fly can offer new insights into the many different taste sensors of animals and how to test the interaction among different sensory modalities.

A dedicate sensorimotor circuit enables fine texture discrimination by active touch

Active touch facilitates environments exploration by voluntary, self-generated movements. However, the neural mechanisms underlying sensorimotor control for active touch are poorly understood. During foraging and feeding, Drosophila gather information on the properties of food (texture, hardness, taste) by constant probing with their proboscis. Here we identify a group of neurons (sd-L neurons) on the fly labellum that are mechanosensitive to labellum displacement and synapse onto the sugar-sensing neurons via axo-axonal synapses to induce preference to harder food. These neurons also feed onto the motor circuits that control proboscis extension and labellum spreading to provide on-line sensory feedback critical for controlling the probing processes, thus facilitating ingestion of less liquified food. Intriguingly, this preference was eliminated in mated female flies, reflecting an elevated need for softer food. Our results propose a sensorimotor circuit composed of mechanosensory, gustatory and motor neurons that enables the flies to select ripe yet not over-rotten food by active touch.

Sugar sensation and mechanosensation in the egg-laying preference shift of Drosophila suzukii

The agricultural pest Drosophila suzukii differs from most other Drosophila species in that it lays eggs in ripe, rather than overripe, fruit. Previously, we showed that changes in bitter taste sensation accompanied this adaptation (Dweck et al., 2021). Here, we show that D. suzukii has also undergone a variety of changes in sweet taste sensation. D. suzukii has a weaker preference than Drosophila melanogaster for laying eggs on substrates containing all three primary fruit sugars: sucrose, fructose, and glucose. Major subsets of D. suzukii taste sensilla have lost electrophysiological responses to sugars. Expression of several key sugar receptor genes is reduced in the taste organs of D. suzukii. By contrast, certain mechanosensory channel genes, including no mechanoreceptor potential C, are expressed at higher levels in the taste organs of D. suzukii, which has a higher preference for stiff substrates. Finally, we find that D. suzukii responds differently from D. melanogaster to combinations of sweet and mechanosensory cues. Thus, the two species differ in sweet sensation, mechanosensation, and their integration, which are all likely to contribute to the differences in their egg-laying preferences in nature.

TRPV channel nanchung and TRPA channel water witch form insecticide-activated complexes

We have previously shown that insect vanilloid-type transient receptor potential (TRPV) channels Nanchung (Nan) and Inactive (Iav) form complexes, which can be over-stimulated and eventually silenced by commercial insecticides, afidopyropen, pymetrozine and pyrifluquinazon. Silencing of the TRPV channels by the insecticides perturbs function of the mechano-sensory organs, chordotonal organs, disrupting sound perception, gravitaxis, and feeding. In addition to TRPV channels, chordotonal organs express an ankyrin-type transient receptor potential (TRPA) channel, Water witch (Wtrw). Genetic data implicate Wtrw in sound and humidity sensing, although the signaling pathway, which links Wtrw to these functions has not been clearly defined. Here we show that, in heterologous system, Nan and Wtrw form calcium channels, which can be activated by afidopyropen, pymetrozine and an endogenous agonist, nicotinamide. Analogous to Nan-Iav heteromers, Nan forms the main binding interface for afidopyropen, whereas co-expression of Wtrw dramatically increases its binding affinity. Pymetrozine competes with afidopyropen for binding to Nan-Wtrw complexes, suggesting that these compounds have overlapping binding sites. Analysis of Drosophila single-nucleus transcriptomic atlas revealed co-expression of nan and wtrw in audio- and mechanosensory neurons. The observation that Nan can form insecticide-sensitive heteromers with more than one type of TRP channels, raises a possibility that Nan may partner with some other TRP channel(s). In addition, we show that Wtrw can be activated by plant-derived reactive electrophiles, allyl isothiocyanate and cinnamaldehyde, defining new molecular target for these repellents.

History of Drosophila neurogenetic research in South Korea

Neurogenetic research using the Drosophila model has immensely expanded around the world. Likewise, scientists in South Korea have leveraged the advantages of Drosophila genetic tools to understand various neurobiological processes. In this special issue, we will overview the history of Drosophila neurogenetic research in South Korea that led to significant discoveries and notably implications. We will describe how Drosophila system was first introduced to elevate neural developmental studies in 1990s. Establishing Drosophila-related resources has been a key venture, which led to the generation of over 100,000 mutant lines and the launch of the K-Gut initiative with Korea Drosophila Research Center (KDRC). These resources have supported the pioneer studies in modeling human disease and understanding genes and neural circuits that regulate animal behavior and physiology.

Protocol for binary food choice assays using Drosophila melanogaster

Food preference is a fundamental behavior for animals to choose nutritious foods while rejecting foods containing toxins. Here, we describe binary food choice assays using Drosophila melanogaster, which are straightforward approaches for the characterization of two-way choice tastants. We detail the preparation of flies and dye-containing food, followed by the binary-choice feeding assays and the determination of the preference index (PI). This protocol is simple, sensitive, and reproducible in qualitatively detecting attractive or aversive characteristics toward any two-way choice tastants.

For complete details on the use and execution of this protocol, please refer to Aryal et al. (2022).

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Protocol for qualitatively analyzing food preferences in Drosophila

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A simple, sensitive, and reproducible binary food choice assay

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Determination of preference index using dye-containing foods

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Appropriate for any behavioral taste analysis of fly models

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Drosophila melanogaster Chemosensory Pathways as Potential Targets to Curb the Insect Menace

Simple Summary

The perception and processing of chemosensory stimuli are indispensable to the survival of living organisms. In insects, olfaction and gustation play a critical role in seeking food, finding mates and avoiding signs of danger. This review aims to present updated information about olfactory and gustatory signaling in the fruit fly Drosophila melanogaster. We have described the mechanisms involved in olfactory and gustatory perceptions at the molecular level, the receptors along with the allied molecules involved, and their signaling pathways in the fruit fly. Due to the magnifying problems of disease-causing insect vectors and crop pests, the applications of chemosensory signaling in controlling pests and insect vectors are also discussed.

Abstract

From a unicellular bacterium to a more complex human, smell and taste form an integral part of the basic sensory system. In fruit flies Drosophila melanogaster, the behavioral responses to odorants and tastants are simple, though quite sensitive, and robust. They explain the organization and elementary functioning of the chemosensory system. Molecular and functional analyses of the receptors and other critical molecules involved in olfaction and gustation are not yet completely understood. Hence, a better understanding of chemosensory cue-dependent fruit flies, playing a major role in deciphering the host-seeking behavior of pathogen transmitting insect vectors (mosquitoes, sandflies, ticks) and crop pests (Drosophila suzukii, Queensland fruit fly), is needed. Using D. melanogaster as a model organism, the knowledge gained may be implemented to design new means of controlling insects as well as in analyzing current batches of insect and pest repellents. In this review, the complete mechanisms of olfactory and gustatory perception, along with their implementation in controlling the global threat of disease-transmitting insect vectors and crop-damaging pests, are explained in fruit flies.

Neural signalling of gut mechanosensation in ingestive and digestive processes

Eating and drinking generate sequential mechanosensory signals along the digestive tract. These signals are communicated to the brain for the timely initiation and regulation of diverse ingestive and digestive processes - ranging from appetite control and tactile perception to gut motility, digestive fluid secretion and defecation - that are vital for the proper intake, breakdown and absorption of nutrients and water. Gut mechanosensation has been investigated for over a century as a common pillar of energy, fluid and gastrointestinal homeostasis, and recent discoveries of specific mechanoreceptors, contributing ion channels and the well-defined circuits underlying gut mechanosensation signalling and function have further expanded our understanding of ingestive and digestive processes at the molecular and cellular levels. In this Review, we discuss our current understanding of the generation of mechanosensory signals from the digestive periphery, the neural afferent pathways that relay these signals to the brain and the neural circuit mechanisms that control ingestive and digestive processes, focusing on the four major digestive tract parts: the oral and pharyngeal cavities, oesophagus, stomach and intestines. We also discuss the clinical implications of gut mechanosensation in ingestive and digestive disorders.

A neural circuit integrates pharyngeal sensation to control feeding

Swallowing is an essential step of eating and drinking. However, how the quality of a food bolus is sensed by pharyngeal neurons is largely unknown. Here we find that mechanical receptors along the Drosophila pharynx are required for control of meal size, especially for food of high viscosity. The mechanical force exerted by the bolus passing across the pharynx is detected by neurons expressing the mechanotransduction channel NOMPC (no mechanoreceptor potential C) and is relayed, together with gustatory information, to IN1 neurons in the subesophageal zone (SEZ) of the brain. IN1 (ingestion neurons) neurons act directly upstream of a group of peptidergic neurons that encode satiety. Prolonged activation of IN1 neurons suppresses feeding. IN1 neurons receive inhibition from DSOG1 (descending subesophageal neurons) neurons, a group of GABAergic neurons that non-selectively suppress feeding. Our results reveal the function of pharyngeal mechanoreceptors and their downstream neural circuits in the control of food ingestion.

Drosophila sensory receptors-a set of molecular Swiss Army Knives

Genetic approaches in the fruit fly, Drosophila melanogaster, have led to a major triumph in the field of sensory biology-the discovery of multiple large families of sensory receptors and channels. Some of these families, such as transient receptor potential channels, are conserved from animals ranging from worms to humans, while others, such as "gustatory receptors," "olfactory receptors," and "ionotropic receptors," are restricted to invertebrates. Prior to the identification of sensory receptors in flies, it was widely assumed that these proteins function in just one modality such as vision, smell, taste, hearing, and somatosensation, which includes thermosensation, light, and noxious mechanical touch. By employing a vast combination of genetic, behavioral, electrophysiological, and other approaches in flies, a major concept to emerge is that many sensory receptors are multitaskers. The earliest example of this idea was the discovery that individual transient receptor potential channels function in multiple senses. It is now clear that multitasking is exhibited by other large receptor families including gustatory receptors, ionotropic receptors, epithelial Na+ channels (also referred to as Pickpockets), and even opsins, which were formerly thought to function exclusively as light sensors. Genetic characterizations of these Drosophila receptors and the neurons that express them also reveal the mechanisms through which flies can accurately differentiate between different stimuli even when they activate the same receptor, as well as mechanisms of adaptation, amplification, and sensory integration. The insights gleaned from studies in flies have been highly influential in directing investigations in many other animal models.

The predatory bug Orius strigicollis shows a preference for egg-laying sites based on plant topography

Background

Oviposition site selection is an important factor in determining the success of insect populations. Orius spp. are widely used in the biological control of a wide range of soft-bodied insect pests such as thrips, aphids, and mites. Orius strigicollis (Heteroptera: Anthocoridae) is the dominant Orius species in southern China; however, what factor drives its selection of an oviposition site after mating currently remains unknown.

Methods

Here, kidney bean pods (KBPs) were chosen as the oviposition substrate, and choice and nonchoice experiments were conducted to determine the preferences concerning oviposition sites on the KBPs of O. strigicollis. The mechanism of oviposition behavior was revealed through observation and measurement of oviposition action, the egg hatching rate, and the oviposition time.

Results

We found that O. strigicollis preferred the seams of the pods for oviposition, especially the seams at the tips of the KBPs. Choice and nonchoice experiments showed that females did not lay eggs when the KBP tail parts were unavailable. The rates of egg hatching on different KBP parts were not significantly different, but the time required for females to lay eggs on the tip seam was significantly lower. Decreased oviposition time is achieved on the tip seam because the insect can exploit support points found there and gain leverage for insertion of the ovipositor.

Discussion

The preferences for oviposition sites of O. strigicollis are significantly influenced by the topography of the KBP surface. Revealing such behavior and mechanisms will provide an important scientific basis for the mass rearing of predatory bugs.

Behavioral and Genomic Sensory Adaptations Underlying the Pest Activity of Drosophila suzukii

Studying how novel phenotypes originate and evolve is fundamental to the field of evolutionary biology as it allows us to understand how organismal diversity is generated and maintained. However, determining the basis of novel phenotypes is challenging as it involves orchestrated changes at multiple biological levels. Here, we aim to overcome this challenge by using a comparative species framework combining behavioral, gene expression, and genomic analyses to understand the evolutionary novel egg-laying substrate-choice behavior of the invasive pest species Drosophila suzukii. First, we used egg-laying behavioral assays to understand the evolution of ripe fruit oviposition preference in D. suzukii compared with closely related species D. subpulchrella and D. biarmipes as well as D. melanogaster. We show that D. subpulchrella and D. biarmipes lay eggs on both ripe and rotten fruits, suggesting that the transition to ripe fruit preference was gradual. Second, using two-choice oviposition assays, we studied how D. suzukii, D. subpulchrella, D. biarmipes, and D. melanogaster differentially process key sensory cues distinguishing ripe from rotten fruit during egg-laying. We found that D. suzukii's preference for ripe fruit is in part mediated through a species-specific preference for stiff substrates. Last, we sequenced and annotated a high-quality genome for D. subpulchrella. Using comparative genomic approaches, we identified candidate genes involved in D. suzukii's ability to seek out and target ripe fruits. Our results provide detail to the stepwise evolution of pest activity in D. suzukii, indicating important cues used by this species when finding a host, and the molecular mechanisms potentially underlying their adaptation to a new ecological niche.

Mechanism for food texture preference based on grittiness

An animal's decision to accept or reject a prospective food is based only, in part, on its chemical composition. Palatability is also greatly influenced by textural features including smoothness versus grittiness, which is influenced by particle sizes. Here, we demonstrate that Drosophila melanogaster is endowed with the ability to discriminate particle sizes in food and uses this information to decide whether a food is appealing. The decision depends on a mechanically activated channel, OSCA/TMEM63, which is conserved from plants to humans. We found that tmem63 is expressed in a multidendritic neuron (md-L) in the fly tongue. Loss of tmem63 impairs the activation of md-L by mechanical stimuli and the ability to choose food based on particle size. These findings reveal the first role for this evolutionarily conserved, mechanically activated TMEM63 channel in an animal and provide an explanation of how flies can sense and behaviorally respond to the texture of food provided by particles.

The Crustacean Antennule: A Complex Organ Adapted for Lifelong Function in Diverse Environments and Lifestyles

AbstractThe crustacean first antenna, or antennule, has been an experimental model for studying sensory biology for over 150 years. Investigations have led to a clearer understanding of the functional organization of the antennule as an olfactory organ but also to a realization that the antennule is much more than that. Across the Crustacea, the antennules take on many forms and functions. As an example, the antennule of reptantian decapods has many types of sensilla, each with distinct structure and function and with hundreds of thousands of chemosensory neurons expressing hundreds of genes that code for diverse classes of receptor proteins. Together, these antennular sensilla represent multiple chemosensory pathways, each with its own central connections and functions. The antennule also has a diversity of sensors of mechanical stimuli, including vibrations, touch, water flow, and the animal's own movements. The antennule likely also detects other environmental cues, such as temperature, oxygen, pH, salinity, and noxious stimuli. Furthermore, the antennule is a motor organ-it is flicked to temporally and spatially sample the animal's chemo-mechanical surroundings-and this information is used in resolving the structure of chemical plumes and locating the odor source. The antennule is also adapted to maintain lifelong function in a changing environment. For example, it has specific secretory glands, grooming structures, and behaviors to stay clean and functional. Antennular sensilla and the annuli on which they reside are also added and replaced, leading to a complete turnover of the antennule over several molts. Thus, the antennule is a complex and dynamic sensory-motor integrator that is intricately engaged in most aspects of the lives of crustaceans.

Multisensory interactions regulate feeding behavior in Drosophila

The integration of two or more distinct sensory cues can help animals make more informed decisions about potential food sources, but little is known about how feeding-related multimodal sensory integration happens at the cellular and molecular levels. Here, we show that multimodal sensory integration contributes to a stereotyped feeding behavior in the model organism Drosophila melanogaster Simultaneous olfactory and mechanosensory inputs significantly influence a taste-evoked feeding behavior called the proboscis extension reflex (PER). Olfactory and mechanical information are mediated by antennal Or35a neurons and leg hair plate mechanosensory neurons, respectively. We show that the controlled delivery of three different sensory cues can produce a supra-additive PER via the concurrent stimulation of olfactory, taste, and mechanosensory inputs. We suggest that the fruit fly is a versatile model system to study multisensory integration related to feeding, which also likely exists in vertebrates.

Drosophila suzukii avoidance of microbes in oviposition choice

While the majority of Drosophila species lays eggs onto fermented fruits, females of Drosophila suzukii pierce the skin and lay eggs into ripening fruits using their serrated ovipositors. The changes of oviposition site preference must have accompanied this niche exploitation. In this study, we established an oviposition assay to investigate the effects of commensal microbes deposited by conspecific and heterospecific individuals and showed that the presence of microbes on the oviposition substrate enhances egg laying of Drosophila melanogaster and Drosophila biarmipes, but discourages that of D. suzukii. This result suggests that a drastic change has taken place in the lineage leading to D. suzukii in how females respond to chemical cues produced by microbes. We also found that hardness of the substrate, resembling that of either ripening or damaged and fermenting fruits, affects the response to microbial growth, indicating that mechanosensory stimuli interact with chemosensory-guided decisions to select or avoid oviposition sites.

Drosophila Mechanosensory Transduction

Mechanosensation in Drosophila relies on sensory neurons transducing mechanical stimuli into ionic currents. The molecular mechanisms of this transduction are in the process of being revealed. Transduction relies on mechanogated ion channels that are activated by membrane stretch or the tension of force-conveying tethers. NOMPC (no-mechanoreceptor potential C) and DmPiezo were put forward as bona fide mechanoelectrical transduction (MET) channels, providing insights into MET channel architecture and the structural basis of mechanogating. Various additional channels were implicated in Drosophila mechanosensory neuron functions, and parallels between fly and vertebrate mechanotransduction were delineated. Collectively, these advances put forward Drosophila mechanosensory neurons as cellular paradigms for mechanotransduction and mechanogated ion channel function in the context of proprio- and nociception as well as the detection of substrate vibrations, touch, gravity, and sound.

Visceral Mechano-sensing Neurons Control Drosophila Feeding by Using Piezo as a Sensor

Animal feeding is controlled by external sensory cues and internal metabolic states. Does it also depend on enteric neurons that sense mechanical cues to signal fullness of the digestive tract? Here, we identify a group of piezo-expressing neurons innervating the Drosophila crop (the fly equivalent of the stomach) that monitor crop volume to avoid food overconsumption. These neurons reside in the pars intercerebralis (PI), a neuro-secretory center in the brain involved in homeostatic control, and express insulin-like peptides with well-established roles in regulating food intake and metabolism. Piezo knockdown in these neurons of wild-type flies phenocopies the food overconsumption phenotype of piezo-null mutant flies. Conversely, expression of either fly Piezo or mammalian Piezo1 in these neurons of piezo-null mutants suppresses the overconsumption phenotype. Importantly, Piezo⁺ neurons at the PI are activated directly by crop distension, thus conveying a rapid satiety signal along the "brain-gut axis" to control feeding.

Neuronal Compartmentalization: A Means to Integrate Sensory Input at the Earliest Stage of Information Processing?

In numerous peripheral sense organs, external stimuli are detected by primary sensory neurons compartmentalized within specialized structures composed of cuticular or epithelial tissue. Beyond reflecting developmental constraints, such compartmentalization also provides opportunities for grouped neurons to functionally interact. Here, the authors review and illustrate the prevalence of these structural units, describe characteristics of compartmentalized neurons, and consider possible interactions between these cells. This article discusses instances of neuronal crosstalk, examples of which are observed in the vertebrate tastebuds and multiple types of arthropod chemosensory hairs. Particular attention is paid to insect olfaction, which presents especially well-characterized mechanisms of functional, cross-neuronal interactions. These examples highlight the potential impact of peripheral processing, which likely contributes more to signal integration than previously considered. In surveying a wide variety of structural units, it is hoped that this article will stimulate future research that determines whether grouped neurons in other sensory systems can also communicate to impact information processing.

A fly rhodopsin sheds light on thermal taste

In their recent paper, Li and colleagues discover that cold food tastes less sweet to flies, in part by activating bitter sensory neurons through a rhodopsin-dependent mechanism [1]. This work establishes temperature as an important variable in understanding fly taste processing and adds diversity to the sensory roles for rhodopsin receptors.

Parallel Mechanosensory Pathways Direct Oviposition Decision-Making in Drosophila

Female Drosophila choose their sites for oviposition with deliberation. Female flies employ sensitive chemosensory systems to evaluate chemical cues for egg-laying substrates, but how they determine the physical quality of an oviposition patch remains largely unexplored. Here we report that flies evaluate the stiffness of the substrate surface using sensory structures on their appendages. The TRPV family channel Nanchung is required for the detection of all stiffness ranges tested, whereas two other proteins, Inactive and DmPiezo, interact with Nanchung to sense certain spectral ranges of substrate stiffness differences. Furthermore, Tmc is critical for sensing subtle differences in substrate stiffness. The Tmc channel is expressed in distinct patterns on the labellum and legs and the mechanosensory inputs coordinate to direct the final decision making for egg laying. Our study thus reveals the machinery for deliberate egg-laying decision making in fruit flies to ensure optimal survival for their offspring.

Pymetrozine inhibits reproductive behavior of brown planthopper Nilaparvata lugens and fruit fly Drosophila melanogaster

Pymetrozine is a promising chemical used to control brown planthopper, which developed resistance to imidacloprid and buprofezin in the past decade. Field efficacy indicates that pymetrozine can reduce the number of offsprings of brown planthopper, but the specific physiological mechanism is unknown. In this study, we systematically described the mating process of brown planthopper including 8 steps (abdominal vibration, following, positioning, wing extension, attempted copulation, copulation, terminated copulation and leaving) and explored the optimal mating time after adult eclosion (3-5 days) and observation time (30 mins). Also, behavioral data showed that pymetrozine can affect the mating behavior and female fecundity of brown planthopper and fruit fly. As one of the target genes for pymetrozine, Nanchung (Nan), the nan^36a mutant male courtship index, female receptivity and the number of offsprings were significantly decreased. Behavioral defects in nan^36a mutant flies can be rescued by expressed NlNan. Our results indicated that Nan plays essential roles in the mating behavior and female fecundity. These findings provide useful information for demonstrating that pymetrozine effectively reduce the reproduction of brown planthopper and contribute to our understanding of reproductive strategies controlled by pymetrozine in insects.

Temperature and Sweet Taste Integration in Drosophila

Sugar-containing foods offered at cooler temperatures tend to be less appealing to many animals. However, the mechanism through which the gustatory system senses thermal input and integrates temperature and chemical signals to produce a given behavioral output is poorly understood. To study this fundamental problem, we used the fly, Drosophila melanogaster. We found that the palatability of sucrose is strongly reduced by modest cooling. Using Ca²⁺ imaging and electrophysiological recordings, we demonstrate that bitter gustatory receptor neurons (GRNs) and mechanosensory neurons (MSNs) are activated by slight cooling, although sugar neurons are insensitive to the same mild stimulus. We found that a rhodopsin, Rh6, is expressed and required in bitter GRNs for cool-induced suppression of sugar appeal. Our findings reveal that the palatability of sugary food is reduced by slightly cool temperatures through different sets of thermally activated neurons, one of which depends on a rhodopsin (Rh6) for cool sensation.

Knockdown of TRPV Genes Affects the Locomotion and Feeding Behavior of Nilaparvata lugens (Hemiptera: Delphacidae)

The vanilloid-type transient receptor potential (TRPV) channel is reported to be the molecular target of the commercial insecticide pymetrozine, which specifically disrupts the feeding of plant sap-sucking insects. However, the functions of TRPV channels in plant sap-sucking insects have not been fully elucidated. In the present study, RNA interference was used to investigate the effects of the knockdown of TRPV genes (Nan and Iav) on the mortality, locomotion, and feeding behavior of an important plant-feeding insect pest in rice, the brown planthopper, Nilaparvata lugens. Injecting dsRNA of Nan and Iav into fourth-instar nymphs significantly knocked down the target genes. The injection of dsNan or dsIav did not affect any morphological phenotype (including leg extension) of N. lugens nymphs and adults. Knockdown of Nan or Iav resulted in significantly decreased climbing activity against top plants but did not influence the leg-griping strength of adults. Knockdown of Nan resulted in a significantly elevated mortality of N. lugens in the observation period of 7 d after injection, whereas no significant difference in survival rates 7 d after injection was found between dsIav-injected and dsGFP-injected insects. Electropenetrographic (EPG) recordings indicated that knockdown of Nan and Iav reduced the ingestion activity in the rice phloem tissues of N. lugens. Knockdown of Nan and Iav significantly reduced the amount of honeydew excreted by N. lugens. Our findings indicated a relationship between TRPV and N. lugens locomotion and feeding behavior, which may help to fully elucidate the functions of TRPV in insects.

The prandial process in flies

Feeding is fundamental to any heterotroph organism; in its role to quell hunger it overrides most other motivational states. But feeding also literally opens the door to harmful risks, especially for a saprophagous animal like Drosophila; ingestion of poisonous substrate can lead to irreversible damage. Thus feeding incorporates a series of steps with several checkpoints to guarantee that the ingestion remains beneficial and provides a balanced diet, or the feeding process is interrupted. Subsequently, we will summarize and describe the feeding process in Drosophila in a comprehensive manner. We propose eleven distinct steps for feeding, grouped into four categories, to address our current knowledge of prandial regulatory mechanisms in Drosophila.

Sweet neurons inhibit texture discrimination by signaling TMC-expressing mechanosensitive neurons in Drosophila

Integration of stimuli of different modalities is an important but incompletely understood process during decision making. Here, we show that Drosophila are capable of integrating mechanosensory and chemosensory information of choice options when deciding where to deposit their eggs. Specifically, females switch from preferring the softer option for egg-laying when both options are sugar free to being indifferent between them when both contain sucrose. Such sucrose-induced indifference between options of different hardness requires functional sweet neurons, and, curiously, the Transmembrane Channel-like (TMC)-expressing mechanosensitive neurons that have been previously shown to promote discrimination of substrate hardness during feeding. Further, axons of sweet neurons directly contact axons of TMC-expressing neurons in the brain and stimulation of sweet neurons increases Ca²⁺ influx into axons of TMC-expressing neurons. These results uncover one mechanism by which Drosophila integrate taste and tactile information when deciding where to deposit their eggs and reveal that TMC-expressing neurons play opposing roles in hardness discrimination in two different decisions.

Mechanosensory circuits coordinate two opposing motor actions in Drosophila feeding

Mechanoreception detects physical forces in the senses of hearing, touch, and proprioception. Here, we show that labellar mechanoreception wires two motor circuits to facilitate and terminate Drosophila feeding. Using patch-clamp recordings, we identified mechanosensory neurons (MSNs) in taste pegs of the inner labella and taste bristles of the outer labella, both of which rely on the same mechanoreceptor, NOMPC (no mechanoreceptor potential C), to transduce mechanical deflection. Connecting with distinct brain motor circuits, bristle MSNs drive labellar spread to facilitate feeding and peg MSNs elicit proboscis retraction to terminate feeding. Bitter sense modulates these two mechanosensory circuits in opposing manners, preventing labellar spread by bristle MSNs and promoting proboscis retraction by peg MSNs. Together, these labeled-line circuits enable labellar peg and bristle MSNs to use the same mechanoreceptors to direct opposing feeding actions and differentially integrate gustatory information in shaping feeding decisions.

Softness sensing and learning in Drosophila larvae

Mechanosensation provides animals with important sensory information in addition to olfaction and gustation during feeding behavior. Here, we used Drosophila melanogaster larvae to investigate the role of softness sensing in behavior and learning. In the natural environment, larvae need to dig into soft foods for feeding. Finding foods that are soft enough to dig into is likely to be essential for their survival. We report that larvae can discriminate between different agar concentrations and prefer softer agar. Interestingly, we show that larvae on a harder surface search for a softer surface using memory associated with an odor, and that they evaluate foods by balancing softness and sweetness. These findings suggest that larvae integrate mechanosensory information with chemosensory input while foraging. Moreover, we found that the larval preference for softness is affected by genetic background.

Pymetrozine activates TRPV channels of brown planthopper Nilaparvata lugens

The commercial insecticide pymetrozine has been extensively used for brown planthopper control in East Asia. The transient receptor potential vanilloid (TRPV) channel, which consists of two proteins, Nanchung (Nan) and Inactive (Iav), has recently been shown to be the molecular target of pymetrozine in the fruit fly (Drosophila melanogaster) and pea aphid (Acyrthosiphon pisum). In this study, we characterized the Nan and Iav TRPV channel subunits of N. lugens and measured the action of pymetrozine on them. NlNan and NlIav are structurally similar to homologs from other insects. The expression pattern analysis of various body parts showed that NlNan and NlIav were both more abundantly expressed in antennae. When NlNan and NlIav were co-expressed in Xenopus laevis oocytes, they formed channels with high sensitivity to pymetrozine (EC₅₀ = 5.5 × 10^-8 M). Behavioral observation revealed that the gravitaxis defect in the fruit fly nan^36a mutant was rescued by ectopically expressed NlNan and the rescued behavior could be abolished by pymetrozine. Our results confirm that NlNan and NlIav co-expressed complexes can be activated by pymetrozine both in vitro and in vivo and provide useful information for future resistance mechanism studies.

A complex peripheral code for salt taste in Drosophila

Each taste modality is generally encoded by a single, molecularly defined, population of sensory cells. However, salt stimulates multiple taste pathways in mammals and insects, suggesting a more complex code for salt taste. Here, we examine salt coding in Drosophila. After creating a comprehensive molecular map comprised of five discrete sensory neuron classes across the fly labellum, we find that four are activated by salt: two exhibiting characteristics of ‘low salt’ cells, and two ‘high salt’ classes. Behaviorally, low salt attraction depends primarily on ‘sweet’ neurons, with additional input from neurons expressing the ionotropic receptor IR94e. High salt avoidance is mediated by ‘bitter’ neurons and a population of glutamatergic neurons expressing Ppk23. Interestingly, the impact of these glutamatergic neurons depends on prior salt consumption. These results support a complex model for salt coding in flies that combinatorially integrates inputs from across cell types to afford robust and flexible salt behaviors.

Salt is essential for our survival, but too much can kill us. Our taste system has therefore evolved two different pathways to help us maintain balance. Low concentrations (like the salt on our chips) activate a pathway that makes us want to eat. But high concentrations (like the salt in seawater) activate pathways that do the opposite.

The nervous system takes on the role of detecting salt and encoding the information in a way that the brain can use. One specific type of cell detects each of the four other tastes: sweet, bitter, sour, and umami. But salt, with its two sensing pathways, is the exception to this rule. Previous work has examined salt taste responses in flies, but the picture is incomplete.

In flies, one type of taste neuron uses a different signaling mechanism to the others, suggesting that it might play a special role. So here, Jaeger, Stanley et al. asked how fly sensory cells encode salt information for the brain, and what those unusual neurons are for.

Mapping the taste receptor neurons in the tongue-like structure of the fly, the proboscis, revealed that salt information is not restricted to one or two types of cell. In fact, all five types of neurons tested (covering more than 90% of all the taste neurons present in flies) responded to salt in some way. Of these, two ‘low salt’ cell types made the fly want to eat salt, and two ‘high salt’ cell types made the fly want to avoid it. One of these high salt cell types was the unusual taste neuron identified previously. Rather than always encoding high salt as 'bad', the message from this type of cell changed depending on the diet of the fly. Salt-deprived flies ignored the activity of that cell type altogether. This complex way of encoding taste allowed the fly to change its behavior depending on how much salt it needed.

This work opens new questions, like how do the fly's neuronal circuits process this complex salt code? And how do the ‘high salt’ cells achieve their negative effect only when the need for salt is low? Understanding more about this system could lead to a better understanding of why our own brains enjoy salty foods so much.

Time-Lapse Live-Cell Imaging Reveals Dual Function of Oseg4, Drosophila WDR35, in Ciliary Protein Trafficking

Cilia are highly specialized antennae-like organelles that extend from the cell surface and act as cell signaling hubs. Intraflagellar transport (IFT) is a specialized form of intracellular protein trafficking that is required for the assembly and maintenance of cilia. Because cilia are so important, mutations in several IFT components lead to human disease. Thus, clarifying the molecular functions of the IFT proteins is a high priority in cilia biology. Live imaging in various species and cellular preparations has proven to be an important technique in both the discovery of IFT and the mechanisms by which it functions. Live imaging of Drosophila cilia, however, has not yet been reported. Here, we have visualized the movement of IFT in Drosophila cilia using time-lapse live imaging for the first time. We found that NOMPB-GFP (IFT88) moves according to distinct parameters depending on the ciliary segment. NOMPB-GFP moves at a similar speed in proximal and distal cilia toward the tip (~0.45 μm/s). As it returns to the ciliary base, however, NOMPB-GFP moves at ~0.12 μm/s in distal cilia, accelerating to ~0.70 μm/s in proximal cilia. Furthermore, while live imaging NOMPB-GFP, we observed one of the IFT proteins required for retrograde movement, Oseg4 (WDR35), is also required for anterograde movement in distal cilia. We anticipate our time-lapse live imaging analysis technique in Drosophila cilia will be a good starting point for a more sophisticated analysis of IFT and its molecular mechanisms.

Auditory experience controls the maturation of song discrimination and sexual response in Drosophila

In birds and higher mammals, auditory experience during development is critical to discriminate sound patterns in adulthood. However, the neural and molecular nature of this acquired ability remains elusive. In fruit flies, acoustic perception has been thought to be innate. Here we report, surprisingly, that auditory experience of a species-specific courtship song in developing Drosophila shapes adult song perception and resultant sexual behavior. Preferences in the song-response behaviors of both males and females were tuned by social acoustic exposure during development. We examined the molecular and cellular determinants of this social acoustic learning and found that GABA signaling acting on the GABAA receptor Rdl in the pC1 neurons, the integration node for courtship stimuli, regulated auditory tuning and sexual behavior. These findings demonstrate that maturation of auditory perception in flies is unexpectedly plastic and is acquired socially, providing a model to investigate how song learning regulates mating preference in insects.

Heterogeneity in the Drosophila gustatory receptor complexes that detect aversive compounds

Animals must detect aversive compounds to survive. Bitter taste neurons express heterogeneous combinations of bitter receptors that diversify their response profiles, but this remains poorly understood. Here we describe groups of taste neurons in Drosophila that detect the same bitter compounds using unique combinations of gustatory receptors (GRs). These distinct complexes also confer responsiveness to non-overlapping sets of additional compounds. While either GR32a/GR59c/GR66a or GR22e/GR32a/GR66a heteromultimers are sufficient for lobeline, berberine, and denatonium detection, only GR22e/GR32a/GR66a responds to strychnine. Thus, despite minimal sequence-similarity, Gr22e and Gr59c show considerable but incomplete functional overlap. Since the gain- or loss-of-function of Gr22e or Gr59c alters bitter taste response profiles, we conclude a taste neuron’s specific combination of Grs determines its response profile. We suspect the heterogeneity of Gr expression in Drosophila taste neurons diversifies bitter compound detection, improving animal fitness under changing environmental conditions that present a variety of aversive compounds.

Taste sensilla are Drosophila sensory organs containing taste neurons, which have differential tuning for bitter compounds. Here, the authors systematically examine what combinations of gustatory receptor genes confer a specific taste response profile in different bitter taste neurons.

Sensory mutations in Drosophila melanogaster influence associational effects between resources during oviposition

Neighboring resources can affect insect oviposition behavior when the complexity of sensory information obscures information about host resource availability in heterogeneous resource patches. These effects are referred to as associational effects and are hypothesized to occur through constraints in the sensory processing of the insect during host search, resulting into suboptimal resource use. Because the possibilities to study these constraints on naturally occurring animals are limited, we instead used sensory mutants of Drosophila melanogaster to determine the importance of sensory information in the occurrence of associational effects. We found that oviposition was mainly governed by non-volatile chemical cues and less by volatile cues. Moreover, the loss of gustatory sensilla resulted in random resource selection and eliminated associational effects. In conclusion, our study shows that associational effects do not necessarily depend on constraints in the sensory evaluation of resource quality, but may instead be a direct consequence of distinctive selection behavior between different resources at small scales.

Neuromodulatory circuit effects on Drosophila feeding behaviour and metabolism

Animals have evolved to maintain homeostasis in a changing external environment by adapting their internal metabolism and feeding behaviour. Metabolism and behaviour are coordinated by neuromodulation; a number of the implicated neuromodulatory systems are homologous between mammals and the vinegar fly, an important neurogenetic model. We investigated whether silencing fly neuromodulatory networks would elicit coordinated changes in feeding, behavioural activity and metabolism. We employed transgenic lines that allowed us to inhibit broad cellular sets of the dopaminergic, serotonergic, octopaminergic, tyraminergic and neuropeptide F systems. The genetically-manipulated animals were assessed for changes in their overt behavioural responses and metabolism by monitoring eleven parameters: activity; climbing ability; individual feeding; group feeding; food discovery; both fed and starved respiration; fed and starved lipid content; and fed/starved body weight. The results from these 55 experiments indicate that individual neuromodulatory system effects on feeding behaviour, motor activity and metabolism are dissociated.

Afidopyropen: New and potent modulator of insect transient receptor potential channels

The commercial insecticides pymetrozine and pyrifluquinazon control plant-sucking pests by disturbing their coordination and ability to feed. We have previously shown that these compounds act by overstimulating and eventually silencing vanilloid-type transient receptor potential (TRPV) channels, which consist of two proteins, Nanchung and Inactive, that are co-expressed exclusively in insect chordotonal stretch receptor neurons. Here we show that a new insecticidal compound, afidopyropen, modulates chordotonal organs of American grasshoppers (Schistocerca americana) in the same fashion. Afidopyropen stimulated heterologously expressed TRPV channels from two different insect species - fruit fly (Drosophila melanogaster) and pea aphid (Acyrthosiphon pisum) - but did not affect function of the mammalian TRPV channel TRPV4. Activation of the insect TRPVs required simultaneous expression of both Nanchung and Inactive proteins. Tritium-labeled afidopyropen bound fruit fly TRPVs with higher affinity than pymetrozine and competed with pymetrozine for binding. Nanchung protein formed the main binding interface for afidopyropen, whereas co-expression of Inactive dramatically increased binding affinity. Another modulator of chordotonal organs, flonicamid, did not activate insect TRPV channels, nor did it compete with afidopyropen for binding, indicating that it has a different target site. These results define afidopyropen as a new, potent and specific modulator of insect TRPV channels, and provide insight into the unique binding mode of these compounds.