Search

The Black Soldier Fly (BSF) is considered as the "crown jewel" of the insect feed industry and circular economy, significantly contributing to the 2030 Sustainable Development Goals by reducing carbon dioxide emissions and enabling circular management of organic waste, animal manure, and plant residues. Despite their industrial importance, limited knowledge about adult BSF biology has hindered optimal mass production. In this context, the present paper aims to explore the olfactory capabilities of both male and female BSF in response to various odorants commonly associated with organic decomposition in substrates suitable for mate encounters and egg laying. This will be achieved by performing electroantennographic recordings and scanning electron microscopy (SEM) observations on the antennal sensilla. Our results demonstrate for the first time the supposed olfactory capabilities of BSF antennae and present a first dataset of substances emitted by decaying organic matter detected by both male and female flies. Additionally, the current EAG recordings allowed comparisons with molecular data previously obtained through in silico and in vitro methods, highlighting the need for caution and strongly supporting a multidisciplinary approach as the best tool for investigating insect chemical ecology. These findings advance our understanding of BSF chemical ecology, which is crucial for effective reproduction and could significantly optimize global breeding systems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background: Insects detect odours using odorant receptors (ORs) expressed in olfactory sensory neurons (OSNs) in the antennae. Ecologically important odours are often detected by selective and abundant OSNs; hence, ORs with high antennal expression. However, little is known about the function of highly expressed ORs in beetles, since few ORs have been functionally characterized. Here, we functionally characterized the most highly expressed OR (ItypOR36) in the bark beetle Ips typographus L. (Coleoptera, Curculionidae, Scolytinae), a major pest of spruce. We hypothesized that this OR would detect a compound important to beetle fitness, such as a pheromone component. We next investigated the antennal distribution of this OR using single sensillum recordings (SSR) and in situ hybridization, followed by field- and laboratory experiments to evaluate the behavioural effects of the discovered ligand., Results: We expressed ItypOR36 in HEK293 cells and challenged it with 64 ecologically relevant odours. The OR responded exclusively to the monoterpene-derived ketone lanierone with high sensitivity. Lanierone is used in chemical communication in North American Ips species, but it has never been shown to be produced by I. typographus, nor has it been studied in relation to this species' sensory physiology. Single sensillum recordings revealed a novel and abundant lanierone-responsive OSN class with the same specific response as ItypOR36. Strikingly, these OSNs were co-localized in sensilla together with seven different previously described OSN classes. Field experiments revealed that low release rates of lanierone inhibited beetle attraction to traps baited with aggregation pheromone, with strongest effects on males. Female beetles were attracted to lanierone in laboratory walking bioassays., Conclusions: Our study highlights the importance of the so-called 'reverse chemical ecology' approach to identify novel semiochemicals for ecologically important insect species. Our discovery of the co-localization pattern involving the lanierone OSN class suggests organizational differences in the peripheral olfactory sense between insect orders. Our behavioural experiments show that lanierone elicits different responses in the two sexes, which also depend on whether beetles are walking in the laboratory or flying in the field. Unravelling the source of lanierone in the natural environment of I. typographus is required to understand these context-dependent behaviours., Competing Interests: Declarations. Ethics approval and consent to participate: Not applicable. Consent for publication: Not applicable. Competing interests: The authors declare that they have no competing interests., (© 2024. The Author(s).)

Bactrocera dorsalis is one of the major invasive pests worldwide. The acetic acid-enriched sweet bait trapping is an important method for monitoring and controlling this fly. Several studies showed that acetic acid is perceived by ionotropic receptors (IRs). Thus, we annotated 65 IR genes in the B. dorsalis genome. We also investigated the IRs involved in acetic acid perception in this fly by behavioral, electrophysiological, and molecular methods. As the results indicated, the antennae are the main olfactory organs to sense acetic acid. Among the antennal IRs showed acetic acid-induced expression profiles, IR8a was proven to perceive acetic acid by CRISPR/Cas9-mediated mutagenesis. Additionally, calcium imaging showed that IR64a and IR75a are potential acetic acid receptors respectively co-expressed with IR76b and IR8a. This study represents the first comprehensive characterization of IRs in B. dorsalis at the whole-genome level, revealing the significant role of IRs in acetic acid perception.

Understanding the maintenance of genetic variation in reproductive strategies and polymorphisms in the wild requires a comprehensive examination of the complex interactions between genetic basis, behaviour and environmental factors. We tested the association between three colour genotypes and variation in female pheromone signalling and male antennal morphology in the wood tiger moth (Arctia plantaginis). These moths have genetically determined white (WW, Wy) and yellow (yy) hindwings that are linked to mating success and fitness, with heterozygotes (Wy) having an advantage. We hypothesized that attractiveness and reproductive success are correlated, with Wy females being more attractive than the other two genotypes which could contribute to maintaining the polymorphism. Female attractiveness was tested by baiting traps with females of the three colour genotypes both in low- (i.e. field set-up) and in high-population density (i.e. large enclosure set-up). Male's ability to reach females was correlated to their own colour genotype and antennal morphology (length, area and lamellae count). Contrary to our prediction, morph-related reproductive success and attractiveness were not correlated. Heavier Wy females attracted a lower proportion of males compared to WW and yy females. Specifically, an increase in weight corresponded to a decreased Wy but increased yy female attractiveness. yy females were generally more attractive than others likely due to earlier pheromone release. In males, lamellae count and genetic colour morph were linked to the male's ability to locate females. Furthermore, male traits affected their ability to reach females in a context-specific way. Males with denser antennae (i.e. higher lamellae count) and white males reached the females faster than yellows in the enclosure, while yellow males located females faster than whites in the field. Our results indicate that higher yy female attractiveness was likely affected by the combined effect of early pheromone release, female weight and higher population density. Males' searching success was affected by morph-specific behavioural strategies and local population density. Ultimately, the combined effect of genotype-related pheromone signalling strategies of females together with environment-dependent male behaviour affect male response and potentially contribute to maintaining variation in fitness-related traits., (© 2024 The Author(s). Journal of Animal Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.)

Background: This study investigated the behavioral responses and toxicity of three basic amines: 1-methylpiperazine, 1-methylpyrrolidine, and triethylamine (TEA), compounds suggested previously to be anosmic in vapor exposures to caged mosquitoes., Results: These compounds showed repellency of Aedes aegypti mosquitoes, followed by flightlessness, knockdown, and paralysis, all increasing with exposure time and dosage. Electrophysiological experiments showed a blocking effect on nerve discharge of the Drosophila melanogaster larval central nervous system (CNS) with little evidence of hyperexcitation. Blockage of voltage-gated (Kv2) potassium channel currents under patch clamp occurred at similar concentrations. Involvement of K + channels in the action of basic amines was supported by behavior and CNS recordings of a Shaker Kv1 mutant exposed to TEA, where instead of blockage, a hyperexcitation of nerve firing was observed. Experiments on cockroach leg mechanoreceptors demonstrated neuronal excitation and on mosquito antennae strong electroantennogram (EAG) signals with an augmentation of blank air responses after a single puff of basic amine., Conclusions: The neurophysiological effects of basic amines are consistent with K + channel block, whereas the antennal EAG response was not obviously associated with anosmia. The low-dose effects of basic amines appear to be repellency and bradykinesia. Overall, the findings provide key insights into the mechanisms underlying the biological activity of basic amines. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a global pest that feeds on  > 350 plant species and causes major yield loses. Variation in the responses of S. frugiperda males to female sex pheromone compounds affects the detection, monitoring and management of the pest. We determined geographic variation in the responses of S. frugiperda males to four different doses of synthetic sex pheromone compounds using a gas chromatography-electroantennogram detector (GC-EAD). Furthermore, we disentangled regional populations into C- and R- mitotypes via molecular analysis of the cytochrome oxidase I gene, and measured their responses to the compounds. When comparing responses of males from Florida, Benin, Nigeria and Kenya, we found some regional differences in the responses of S. frugiperda males to the major compound, Z9-14:OAc and minor component Z9-12:OAc. However, we found no differences in male responses between the different African countries. All males showed significantly higher antennal responses to Z7-12:OAc than to E7-12:OAc. When comparing the mitotypes, we found that Florida R-type males showed higher responses to Z9-14:OAc, Z7-12:OAc and Z9-12:OAc than Benin R-type males, while C-type males from both regions responded equally to Z7-12:OAc. In addition, Florida R-type males showed higher responses to E7-12:OAc than Florida C-type males. Our study thus shows some differential physiological responses of S. frugiperda males towards the known sex pheromone compounds, including E7-12:OAc, but mostly in the different mitotypes. How these differences translate to field trap catches remains to be determined., (© 2024. The Author(s).)

Sex pheromones, which consist of multiple components in specific ratios promote intraspecific sexual communications of insects. Plutella xylostella (L.) is a worldwide pest of cruciferous vegetables, the mating behavior of which is highly dependent on its olfactory system. Long trichoid sensilla on male antennae are the main olfactory sensilla that can sense sex pheromones. However, the underlying mechanisms remain unclear. In this study, 3 sex pheromone components from sex pheromone gland secretions of P. xylostella female adults were identified as Z11-16:Ald, Z11-16:Ac, and Z11-16:OH in a ratio of 9.4 : 100 : 17 using gas chromatography - mass spectrometry and gas chromatography with electroantennographic detection. Electrophysiological responses of 581 and 385 long trichoid sensilla of male adults and female adults, respectively, to the 3 components were measured by single sensillum recording. Hierarchical clustering analysis showed that the long trichoid sensilla were of 6 different types. In the male antennae, 52.32%, 5.51%, and 1.89% of the sensilla responded to Z11-16:Ald, Z11-16:Ac, and Z11-16:OH, which are named as A type, B type, and C type sensilla, respectively; 2.93% named as D type sensilla responded to both Z11-16:Ald and Z11-16:Ac, and 0.34% named as E type sensilla were sensitive to both Z11-16:Ald and Z11-16:OH. In the female antennae, only 7.53% of long trichoid sensilla responded to the sex pheromone components, A type sensilla were 3.64%, B type and C type sensilla were both 0.52%, D type sensilla were 1.30%, and 1.56% of the sensilla responded to all 3 components, which were named as F type sensilla. The responding long trichoid sensilla were located from the base to the terminal of the male antennae and from the base to the middle of the female antennae. The pheromone mixture (Z11-16:Ald : Z11-16:Ac : Z11-16:OH = 9.4 : 100 : 17) had a weakly repellent effect on female adults of P. xylostella. Our results lay the foundation for further studies on sex pheromone communications in P. xylostella., (© 2024 Institute of Zoology, Chinese Academy of Sciences.)

The recognition of cerambycids as frequent and damaging invaders led to an increase in the interest in the chemical ecology of the group with the identification of pheromones and pheromone-like attractants for well over 100 species. Pheromone components of the Cerambycidae are often phylogenetically conserved, with a single compound serving as a pheromone component for several related species. In the subfamily Lamiinae, the compound 2-(undecyloxy)ethanol (monochamol) has been identified as an aggregation-sex pheromone for several species of the genus Monochamus. In other species, including Monochamus maculosus Haldeman, field trials have demonstrated that monochamol is a pheromone attractant, but at that point it was still unknown as to whether it was a pheromone for this species. Here we report the identification, and laboratory and field trials of a pheromone component produced by adult male M. maculosus. Chemical analyses of headspace volatile collections sampled from field collected beetles of both sexes revealed the presence of one male-specific compound that was identified as 2-(undecyloxy)ethanol. Electroantennography analyses showed that monochamol elicited responses from the antennae of female beetles. Traps baited with monochamol in the field captured M. maculosus adults of both sexes corroborating the identification of monochamol as the sex-aggregation pheromone of this species. The attractivity of monochamol to adult M. maculosus in our field trapping experiment was synergized by the addition of the host volatile α-pinene., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Sclerodermus cereicollis is a European flat wasp ectoparasitoid of some longhorn beetle species. This species is important as a suitable biological control agent against xylophagous pests. To better understand its chemical ecology, the ultrastructure of the antennal sensilla of the adult was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The sensilla are located mainly in the ventro-medial side of the antennae. We report a clearly sexual dimorphism with respect to antennae length, and to types, number, and distribution of chemosensilla. The antennae in males are significantly longer than those of females. We describe in detail the external and internal structure of different chemoreceptors represented by sensilla placodea, long sensilla basiconica, multiporous sensilla chaetica, grooved sensilla ampullacea, uniporous grooved sensilla chaetica. The potential involvement of the different kinds of chemoreceptors in inter- (mainly sexual recognition and social behavior-kin recognition) or intra-specific communication (mainly host selection) is discussed on the basis of behavioral and electrophysiological investigations performed on other parasitoid species belonging to the same family. Other sensilla with morphology that is not consistent with that of chemoreceptors are represented by grooved pegs, coeloconic pegs, trichoid sensilla. Such detailed ultrastructural investigation of the flagellar chemoreceptors of S. cereicollis, clarifying the number of chemosensory neurons innervating the different sensilla, is crucial for further electrophysiological investigations on this important species. RESEARCH HIGHLIGHTS: Evident sexual dimorphism concerning antennae length, type, number, and distribution of chemosensilla. Long sensilla basiconica (LSB) present only in females could play a role in host location and/or maternal care. Multiporous sensilla chaetica (MSC), significantly longer and mostly represented in males, could play a role in the perception of sexual pheromones. Detailed ultrastructural study is crucial for electrophysiological investigations on this important species., (© 2024 Wiley Periodicals LLC.)

There is a growing interest in the effects of climate warming on olfaction, as temperature may affect this essential sense. In insects, the response of the olfactory system to developmental temperature might be mediated by body size or mass because body size and mass are negatively affected by developmental temperature in most ectotherms. We tested this hypothesis of a mass-mediated effect of developmental temperature on olfaction in the moth Spodoptera littoralis. We measured the olfactory sensitivity of male to female sex pheromone and five plant odors using electroantennography. We compared males reared at an optimal temperature (25 °C with a daily fluctuation of ±5 °C) and at a high temperature (33 ± 5 °C) close to the upper limit of S. littoralis. On average, the olfactory sensitivity of males did not differ between the two developmental temperatures. However, our analyses revealed an interaction between the effects of developmental temperature and body mass on the detection of the six chemicals tested. This interaction is explained by a positive relationship between antennal sensitivity and body mass observed only with the high developmental temperature. Our results show that the effect of developmental temperature may not be detected when organism size is ignored., (© 2024. The Author(s).)

Odour processing exhibits multiple parallels between vertebrate and invertebrate olfactory systems. Insects, in particular, have emerged as relevant models for olfactory studies because of the tractability of their olfactory circuits. Here, we used fast calcium imaging to track the activity of projection neurons in the honey bee antennal lobe (AL) during olfactory stimulation at high temporal resolution. We observed a heterogeneity of response profiles and an abundance of inhibitory activities, resulting in various response latencies and stimulus-specific post-odour neural signatures. Recorded calcium signals were fed to a mushroom body (MB) model constructed implementing the fundamental features of connectivity between olfactory projection neurons, Kenyon cells (KC), and MB output neurons (MBON). The model accounts for the increase of odorant discrimination in the MB compared to the AL and reveals the recruitment of two distinct KC populations that represent odorants and their aftersmell as two separate but temporally coherent neural objects. Finally, we showed that the learning-induced modulation of KC-to-MBON synapses can explain both the variations in associative learning scores across different conditioning protocols used in bees and the bees' response latency. Thus, it provides a simple explanation of how the time contingency between the stimulus and the reward can be encoded without the need for time tracking. This study broadens our understanding of olfactory coding and learning in honey bees. It demonstrates that a model based on simple MB connectivity rules and fed with real physiological data can explain fundamental aspects of odour processing and associative learning., Competing Interests: MP, AW, BR, MG No competing interests declared, (© 2024, Paoli et al.)

Agonistic behaviors are crucial and ubiquitous among animals for the competition of limited resources. Although the study of aggression has been a popular topic, plenty of studies focused on model organisms, and typically on crayfish and lobsters for crustaceans. Variations of the agonistic behaviors and the underpinning eliciting cues of other crustaceans therefore have not been fully explored. In the present study, we targeted Stenopus, a genus of shrimp-like crustaceans that displays prominent agonistic behaviors when encountering conspecifics of the same sex owing to their monogamous social structure. Using S. hispidus (Olivier, 1811) and S. cyanoscelis (Goy, 1984) as representatives, we characterized their agonistic behaviors and fighting pattern, conducted experiments to investigate the contribution of visual, olfactory and tactile cues to inducing aggression, and examined the effects of antennal and antennular ablation on their agonistic interactions. A total of seven agonistic behaviors were documented, where antennal entwining and tactile contact is the major driver and seemingly important cue, respectively, in inducing agonistic behaviors in Stenopus. Although ablation of antennae and antennules did not inhibit fighting, behavioral changes, such as the prolonged agonistic interactions and the delayed establishment of dominance were observed, suggesting a reduction of aggressiveness. A comparison of agonistic behaviors with other crustaceans showed that certain features appeared to be unique or distinct in Stenopus, including the potential functional overlap of antennae and antennules, a higher aggressiveness of the fighting behaviors, and the exhibition of crouching behavior by submissive individuals. The present study provides a crucial background understanding for subsequent research on Stenopus and paves the way for its establishment as another crustacean model for studying aggression., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Mosquito-borne diseases affect hundreds of millions of people annually and disproportionately impact the developing world 1,2 . One mosquito species, Aedes aegypti, is a primary vector of viruses that cause dengue, yellow fever and Zika. The attraction of Ae. aegypti female mosquitos to humans requires integrating multiple cues, including CO 2 from breath, organic odours from skin and visual cues, all sensed at mid and long ranges, and other cues sensed at very close range 3-6 . Here we identify a cue that Ae. aegypti use as part of their sensory arsenal to find humans. We demonstrate that Ae. aegypti sense the infrared (IR) radiation emanating from their targets and use this information in combination with other cues for highly effective mid-range navigation. Detection of thermal IR requires the heat-activated channel TRPA1, which is expressed in neurons at the tip of the antenna. Two opsins are co-expressed with TRPA1 in these neurons and promote the detection of lower IR intensities. We propose that radiant energy causes local heating at the end of the antenna, thereby activating temperature-sensitive receptors in thermosensory neurons. The realization that thermal IR radiation is an outstanding mid-range directional cue expands our understanding as to how mosquitoes are exquisitely effective in locating hosts., (© 2024. The Author(s).)

The antennal sensilla play an important role in many behavioral activities of insects. The fungivorous beetle Triplax ainonia Lewis (Erotylidae) is an important pest which prefers to feed on Pleurotus mushrooms. In order to clarify the types, number, and distribution of the antennal sensilla of male and female T. ainonia, scanning electron microscopy was used. The results showed that there were five sensillum types on the antennae of adults male and female, including Böhm's bristles (BB), sensilla chaetica (three subtypes: SC 1, SC 2, and SC 3), sensilla basiconica (three subtypes: SB 1, SB 2, and SB 3), sensilla trichodea (ST), and sensilla styloconica (SS). Among all the sensilla, the number of SB 2 was the most abundant in both sexes. We found that there was no sexually dimorphic in the sensillum types, but there were differences in the number, lengths, and diameters of some sensilla between males and females. Based on the information of the morphology and distribution of the sensilla, the potential functions of the antennal sensilla of T. ainonia adults were discussed. The results of this study provide a basis for further study on the behavioral ecology and electrophysiology of the fungivore beetles of the Erotylidae., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Hou et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

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., Competing Interests: Competing interests statement:P.A.G. is an inventor on patent WO2017196861A1 (WIPO PCT; pending; inventors: Z. Knecht, P. Garrity, L. Ni). “Methods for modulating insect hygro and/or thermosensation.” This patent proposes using ionotropic receptors as targets to disrupt hygrosensation and thermosensation in insects.

Signal theory predicts organisms should evolve signals that are conspicuous to intended receivers in natural signalling environments. Cleaner shrimps remove ectoparasites from reef fish clients and many signal their intent to clean by whipping long, white antennae. As white is a reliably conspicuous colour in aquatic environments, we hypothesized that selection has acted to increase broad-spectrum antennal reflectance in cleaners. Using scanning electron microscopy, optical models and reflectance measurements, we found that the antennae in three obligate cleaner species from two families (Palaemonidae and Lysmatidae) had thick (∼6 µm) chitinous layers or densely packed high refractive index spheres (300-400 nm diameter), which models show increase reflectance (400-700 nm). Two facultative and non-cleaning species had no visible antennae ultrastructure beyond the chitinous exoskeleton. Antennae reflectance was significantly higher in obligate cleaners than in facultative and non-cleaning species. Our results suggest that some obligate cleaners may have evolved ultrastructures that increase the conspicuousness of their antennae as signals., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

The major and possibly only component of the sex attractant pheromone of the moth Hemileuca nevadensis (Lepidoptera: Saturniidae) from southern California was determined to be (E10,Z12)-hexadecadienal (E10,Z12-16:Ald). Detectable quantities of the analogs (E10,Z12)-hexadecadien-1-yl acetate (E10,Z12-16:Ac) and (E10,Z12)-hexadecadien-1-ol (E10,Z12-16:OH) were also present in solvent extracts of sex pheromone glands, and stimulated male antennae in coupled gas chromatography-electroantennogram detector (GC-EAD) assays. GC-EAD traces from solid phase microextraction (SPME) wipe samples of sex pheromone glands of calling females confirmed the presence of E10,Z12-16:Ald and traces of E10,Z12-16:OH on the gland surface, but E10,Z12-16:Ac was not detected. Despite evidence for the presence of all three compounds in extracts, behavioral responses to synthetic compounds in the field suggested that only E10,Z12-16:Ald is required for optimal attraction., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Global climate change disrupts key ecological processes and biotic interactions. The recent increase in heatwave frequency and severity prompts the evaluation of physiological processes that ensure the maintenance of vital ecosystem services such as pollination. We used experimental heatwaves to determine how high temperatures affect the bumblebees' ability to detect floral scents. Heatwaves induced strong reductions in antennal responses to floral scents in both tested bumblebee species ( Bombus terrestris and Bombus pascuorum ). These reductions were generally stronger in workers than in males. Bumblebees showed no consistent pattern of recovery 24 h after heat events. Our results suggest that the projected increased frequency and severity of heatwaves may jeopardize bumblebee-mediated pollination services by disrupting the chemical communication between plants and pollinators. The reduced chemosensitivity can decrease the bumblebees' abilities to locate food sources and lead to declines in colonies and populations.

Chemical, electrophysiological, and field trapping experiments were carried out to identify the female-produced sex pheromone of the asparagus moth, Parahypopta caestrum, a very serious pests of asparagus cultivations in southern Europe. Gas chromatography coupled with mass spectrometry and electroantennogram detection (GC-MS-EAD) analysis of hexane and solid-phase microextraction (SPME) extracts of sex pheromone glands of calling females consistently detected four compounds eliciting EAG responses in male moth antennae. According to their GC retention times, mass spectra, and comparative EAG analyses with reference standards, these EAD-active compounds were identified as (Z)-9-tetradecenol (Z9-14:OH), (Z)-5-tetradecenyl acetate (Z5-14:Ac), (Z)-7-tetradecenyl acetate (Z7-14:Ac), and (Z)-9-tetradecenyl acetate (Z9-14:Ac), respectively. In the SPME extracts from the head-space of individual abdominal tips, Z9-14:Ac, Z5-14:Ac, Z7-14:Ac, and Z9:14 OH were detected in the ratio of 82:9:5:4. In EAG dose-response experiments, Z9-14:Ac was the strongest antennal stimulant at different doses tested. In field trapping experiments, Z9-14:Ac, Z7-14:Ac, and Z5-14:Ac proven to be essential for male attraction and a their 85:5:10 blend loaded onto green rubber septum dispensers was significantly more effective than single-, two-, and any other three-component blend of these compounds. The addition of Z9-14:OH to the optimal blend resulted in a significant reduction of male catches. The attractive blend here identified allowed for an effective and accurate monitoring of P. caestrum flight activity in southern Italy., (© 2024. The Author(s).)

Sex pheromones are considered to play critical roles in partner communication of most parasitic Hymenoptera. However, the identification of sex pheromone components remains limited to a few families of parasitoid wasps. In this study, we functionally characterized a candidate sex pheromone component in Microplitis mediator (Hymenoptera: Braconidae), a solitary parasitoid of Noctuidae insects. We found that the body surface extract from female wasps could significantly stimulate courtship behavior of males. Gas chromatography-electroantennographic detection (GC-EAD) analysis revealed that a candidate semiochemical from extract triggered significant electrophysiological response of antennae of males. By performing gas chromatography-mass spectrometer (GC-MS) measurement, GC-EAD active compound was identified as n-octyl acrylate, a candidate sex pheromone component in female M. mediator. In electroantennogram (EAG) tests, antennae of male wasps showed significantly higher electrophysiological responses to n-octyl acrylate than those of females. Y-tube olfactometer assays indicated that male wasps significantly chose n-octyl acrylate compared with the control. Furthermore, male wasps showed a remarkable preference for n-octyl acrylate in a simulated field condition behavioral trial; simultaneously, n-octyl acrylate standard could also trigger significant courtship behavior in males. We propose that n-octyl acrylate, as a candidate vital sex pheromone component, could be utilized to design behavioral regulators of M. mediator to implement the protection and utilization of natural enemies., (© 2023 Institute of Zoology, Chinese Academy of Sciences.)

To probe its environment, the flying insect controllably flexes, twists, and maneuvers its antennae by coupling mechanical deformations with the sensory output. We question how the materials properties of insect antennae could influence their performance. A comparative study was conducted on four hawkmoth species: Manduca sexta, Ceratomia catalpae, Manduca quinquemaculata, and Xylophanes tersa. The morphology of the antennae of three hawkmoths that hover while feeding and one putatively non-nectar-feeding hawkmoth (Ceratomia catalpa) do not fundamentally differ, and all the antennae are comb-like (i.e., pectinate), markedly in males but weakly in females. Applying different weights to the free end of extracted cantilevered antennae, we discovered anisotropy in flexural rigidity when the antenna is forced to bend dorsally versus ventrally. The flexural rigidity of male antennae was less than that of females. Compared with the hawkmoths that hover while feeding, Ceratomia catalpae has almost two orders of magnitude lower flexural rigidity. Tensile tests showed that the stiffness of male and female antennae is almost the same. Therefore, the differences in flexural rigidity are explained by the distinct shapes of the antennal pectination. Like bristles in a comb, the pectinations provide extra rigidity to the antenna. We discuss the biological implications of these discoveries in relation to the flight habits of hawkmoths. Flexural anisotropy of antennae is expected in other groups of insects, but the targeted outcome may differ. Our work offers promising new applications of shaped fibers as mechanical sensors. STATEMENT OF SIGNIFICANCE: Insect antennae are blood-filled, segmented fibers with muscles in the two basal segments. The long terminal segment is muscle-free but can be flexed. Our comparative analysis of mechanical properties of hawkmoth antennae revealed a new feature: antenna resistance to bending depends on the bending direction. Our discovery replaces the conventional textbook scenario considering hawkmoth antennae as rigid rods. We showed that the pectinate antennae of hawkmoths behave as a comb in which the bristles resist bending when they come together. This anisotropy of flexural resistance offers a new mode of environmental sensing that has never been explored. The principles we found apply to other insects with non-axisymmetric antennae. Our work offers new applications for shaped fibers that could be designed to sense the flows., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

The representation of odors in the locust antennal lobe with its >2,000 glomeruli has long remained a perplexing puzzle. We employed the CRISPR-Cas9 system to generate transgenic locusts expressing the genetically encoded calcium indicator GCaMP in olfactory sensory neurons. Using two-photon functional imaging, we mapped the spatial activation patterns representing a wide range of ecologically relevant odors across all six developmental stages. Our findings reveal a functionally ring-shaped organization of the antennal lobe composed of specific glomerular clusters. This configuration establishes an odor-specific chemotopic representation by encoding different chemical classes and ecologically distinct odors in the form of glomerular rings. The ring-shaped glomerular arrangement, which we confirm by selective targeting of OR70a-expressing sensory neurons, occurs throughout development, and the odor-coding pattern within the glomerular population is consistent across developmental stages. Mechanistically, this unconventional spatial olfactory code reflects the locust-specific and multiplexed glomerular innervation pattern of the antennal lobe., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

While the neural basis of age-related decline has been extensively studied, 1 , 2 , 3 less is known about changes in neural function during the pre-senescent stages of adulthood. Adult neural plasticity is likely a key factor in social insect age polyethism, where individuals perform different tasks as they age and divide labor in an age-dependent manner. 4 , 5 , 6 , 7 , 8 , 9 Primarily, workers transition from nursing to foraging tasks, 5 , 10 become more aggressive, and more readily display alarm behavior 11 , 12 , 13 , 14 , 15 , 16 as they get older. While it is unknown how these behavioral dynamics are neurally regulated, they could partially be generated by altered salience of behaviorally relevant stimuli. 4 , 6 , 7 Here, we investigated how odor coding in the antennal lobe (AL) changes with age in the context of alarm pheromone communication in the clonal raider ant (Ooceraea biroi). 17 Similar to other social insects, 11 , 12 , 16 older ants responded more rapidly to alarm pheromones, the chemical signals for danger. Using whole-AL calcium imaging, 18 we then mapped odor representations for five general odorants and two alarm pheromones in young and old ants. Alarm pheromones were represented sparsely at all ages. However, alarm pheromone responses within individual glomeruli changed with age, either increasing or decreasing. Only two glomeruli became sensitized to alarm pheromones with age, while at the same time becoming desensitized to general odorants. Our results suggest that the heightened response to alarm pheromones in older ants occurs via increased sensitivity in these two core glomeruli, illustrating the importance of sensory modulation in social insect division of labor and age-associated behavioral plasticity., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Anopheles coluzzii (Coetzee & Wilkerson) and its sibling species Anopheles gambiae s.s. (Giles) are highly anthropophilic and among the major malaria vectors in sub-Saharan Africa. Mosquitoes use various senses to find hosts, but rely primarily on olfaction. Therefore, the mosquito olfactory system has been studied extensively, including a variety of studies comparing chemosensory gene expression between An. coluzzii and its zoophilic sibling species Anopheles quadriannulatus (Theobald). These studies revealed species-specific chemosensory gene expression in the antennae and maxillary palps, which raised the question of a potential role for the palps in determining species-specific host preferences. To answer this question, we mechanically ablated the antennae, maxillary palps, and labella, and ran both control and ablated mosquitoes through a dual-port olfactometer. While we aimed to identify the organs responsible for vertebrate host choice, the ablated mosquitoes exclusively responded to human odor, so we were unable to do so. However, we were able to refine our understanding of the roles of these organs in host-seeking activation (leaving the release cage) as well as odor response (entering an odor port). As expected, the antennae are the most important organs to both behaviors: activation was roughly halved and vertebrate odor response was abolished in antennae-ablated mosquitoes. Maxillary palp ablation had little impact on activation, but reduced odor response to a similar degree as the exclusion of CO2. Finally, while labellar ablation dramatically reduced activation (probably associated with the inability to feed), it had little impact on odor response, suggesting that any labellar role in host choice is likely not olfactory., (© The Author(s) 2024. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Background: The Asian tiger mosquito, Aedes albopictus, is a competent vector for the spread of several viral arboviruses including dengue, chikungunya, and Zika. Several vital mosquito behaviors linked to survival and reproduction are primarily dependent on a sophisticated olfactory system for semiochemical perception. However, a limited number of studies has hampered our understanding of the relationship between the A. albopictus acute olfactory system and the complex chemical world., Results: Here, we performed a qRT-PCR assay on antennae from A. albopictus of differing sex, age and physiological states, and found that AalbOr10 was enriched in blood-fed female mosquitoes. We then undertook single sensillum recording to de-orphan AalbOr10 using a panel of physiologically and behaviorally relevant odorants in a Drosophila 'empty neuron' system. The results indicated that AalbOr10 was activated by seven aromatic compounds, all of which hampered egg-laying in blood-fed mosquitoes. Furthermore, using a post-RNA interference oviposition assay, we found that reducing the transcript level of AalbOr10 affected repellent activity mediated by 2-ethylphenol at low concentrations (10 -4 vol/vol). Computational modeling and molecular docking studies suggested that hydrogen bonds to Y68 and Y150 mediated the interaction of 2-ethylphenol with AalbOr10., Conclusion: We reveal a potential link between aromatics-induced oviposition repellency behaviors and a specific odorant receptor in A. albopictus. Our findings provide a foundation for identifying active semiochemicals for the monitoring or controlling of mosquito populations. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

Volatile sex pheromones are vital for sexual communication between males and females. Females of the American cockroach, Periplaneta americana, produce and emit two sex pheromone components, periplanone-A (PA) and periplanone-B (PB). Although PB is the major sex attractant and can attract males, how it interacts with PA in regulating sexual behaviors is still unknown. In this study, we found that in male cockroaches, PA counteracted PB attraction. We identified two odorant receptors (ORs), OR53 and OR100, as PB/PA and PA receptors, respectively. OR53 and OR100 were predominantly expressed in the antennae of sexually mature males, and their expression levels were regulated by the sex differentiation pathway and nutrition-responsive signals. Cellular localization of OR53 and OR100 in male antennae further revealed that two types of sensilla coordinate a complex two-pheromone-two-receptor pathway in regulating cockroach sexual behaviors. These findings indicate distinct functions of the two sex pheromone components, identify their receptors and possible regulatory mechanisms underlying the male-specific and age-dependent sexual behaviors, and can guide novel strategies for pest management., (© 2024. Science China Press.)

Behavioural regulation in insect societies remains a fundamental question in sociobiology. In hymenopteran societies, the queen plays a crucial role in regulating group behaviour by affecting individual behaviour and physiology through modulation of worker gene expression. Honey bee (Apis mellifera) queens signal their presence via queen mandibular pheromone (QMP). While QMP has been shown to influence behaviour and gene expression of young workers, we know little about how these changes translate in older workers. The effects of the queen pheromone could have prolonged molecular impacts on workers that depend on an early sensitive period. We demonstrate that removal of QMP impacts long-term gene expression in the brain and antennae in foragers that were treated early in life (1 day post emergence), but not when treated later in life. Genes important for division of labour, learning, chemosensory perception and ageing were among those differentially expressed in the antennae and brain tissues, suggesting that QMP influences diverse physiological and behavioural processes in workers. Surprisingly, removal of QMP did not have an impact on foraging behaviour. Overall, our study suggests a sensitive period early in the life of workers, where the presence or absence of a queen has potentially life-long effects on transcriptional activity., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Background: Tandem running is a recruitment method found in some species of ants where one ant follows another ant to reach a destination having maintained a physical contact with its antennae, throughout the journey. It is considered that the exchange of information regarding the destination among the nestmates happened during the process of tandem running. We examined the impact of restricting antennal movement on tandem running by using Diacamma indicum, a tandem-running ponerine ant by following 480 tandem runs across 9 treatment colonies and comparing it with 10 control relocating colonies., Result: Though all the 19 colonies relocated successfully, treatment colonies took significantly longer time to do so. Restricted antennal movement did not influence the ability to become tandem leaders, initiate tandem runs or the work organization significantly. However, antennae-restricted ants performed fewer tandem runs and took significantly longer time. Followers with single or both antennae-restriction performed significantly higher number of interruptions and the alignment between the leader and follower was impacted as antenna-restricted followers subtended a greater angle and walked more to the side of the leader as compared to the control followers., Conclusion: This study showed unhindered movement of the followers' antennae is important for tandem-running ants. In the next step, to gain a comprehensive understanding of this recruitment method, it is essential to individually delineate different sensory modalities., (© 2024. The Author(s).)

Sex pheromone analogs have high structural similarity to sex pheromone components. They also play a role in studying many agricultural pests. In our study, (Z, Z, Z)-3,6,9-nonadecadiene (Z3Z6Z9-19:Hy) was successfully synthesized, which is an analogue to 1 of 2 sex pheromone components of Ectropis grisescens Warren (Z, Z, Z)-3,6,9-octadecatriene (Z3Z6Z9-18:Hy), and it showed potential inhibition in experiments. In the electroantennogram test, Z3Z6Z9-19:Hy showed a dose-dependent response, and only measured half the response of Z3Z9-6,7-epo-18:Hy. However, the compound significantly reduced positive response of E. grisescens males by up to 70% in the Y-tube olfactometer. Furthermore, in the wind tunnel, it significantly inhibited all types of behavioral responses. The percentage of moths contacting the pheromone odor source was reduced even at the lowest dose tested. In silico study afterward, molecular docking results showed affinity between Z3Z6Z9-19:Hy and sensory neuron membrane protein 1. Our study revealed the potential of Z3Z6Z9-19:Hy as a sex pheromone inhibitor, which would provide new tools for monitoring and mating disruption of E. grisescens., (© The Author(s) 2024. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

The orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), is a significant wheat pest in the Prairie Provinces of Canada and northern regions of the USA. Wheat phenology plays a critical role in wheat midge oviposition. We hypothesized that S. mosellana oviposition behaviour is influenced by volatile organic compounds (VOCs) emitted by wheat at two adjacent wheat growth stages: preanthesis and postanthesis. A higher number of S. mosellana eggs laid on preanthesis than postanthesis spikes in an oviposition choice experiment using the susceptible spring wheat cultivar 'Roblin'. In preanthesis, wheat emitted higher amounts of Z-3-hexenyl acetate (Z3-06:OAc) than at the postanthesis stage. Higher amounts of methyl ketones such as 2-tridecanone, 2-pentadecanone, and 2-undecanone were emitted by wheat in the postanthesis stage and these VOCs were sensitive to S. mosellana antennae used in the Gas Chromatography-Electroantennographic Detection. Females were attracted to synthetic Z3-06:OAc but were deterred by 2-tridecanone relative to the solvent control in the vertical Y-tube olfactometer. 2-Undecanone and 2-pentadecanone did not show any attractiveness or deterrence. In a no-choice oviposition experiment, fewer eggs were laid in preanthesis wheat exposed to a synthetic VOC blend of Z3-06:OAc, 2-undecanone, 2-tridecanone, and 2-pentadecanone at the concentrations released by postanthesis spikes. This study shows that the reduction of Z3-06:OAc, in the VOC mix, and possibly the increase in 2-tridecanone, are likely responsible for the reduction in oviposition on postanthesis wheat. These results elucidate for the first time the role of specific VOCs mediating S. mosellana oviposition in preanthesis and postanthesis wheat., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The detection of magnetic fields by animals is known as magnetoreception. The ferromagnetic hypothesis explains magnetoreception assuming that magnetic nanoparticles are used as magnetic field transducers. Magnetite nanoparticles in the abdomen of Apis mellifera honeybees have been proposed in the literature as the magnetic field transducer. However, studies with ants and stingless bees have shown that the whole body of the insect contain magnetic material, and that the largest magnetization is in the antennae. The aim of the present study is to investigate the magnetization of all the body parts of honeybees as has been done with ants and stingless bees. To do that, the head without antennae, antennae, thorax, and abdomen obtained from Apis mellifera honeybees were analyzed using magnetometry and Ferromagnetic Resonance (FMR) techniques. The magnetometry and FMR measurements show the presence of magnetic material in all honeybee body parts. Our results present evidence of the presence of biomineralized magnetite nanoparticles in the honeybee abdomen and, for the first time, magnetite in the antennae. FMR measurements permit to identify the magnetite in the abdomen as biomineralized. As behavioral experiments reported in the literature have shown that the abdomen is involved in magnetoreception, new experimental approaches must be done to confirm or discard the involvement of the antennae in magnetoreception., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Huanglongbing (HLB), a devastating citrus disease caused by Candidatus Liberibacter asiaticus, is efficiently vectored by the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). Tamarixia radiata (Waterston) plays a crucial role as an ectoparasitoid, preying on D. citri nymphs. By collecting and identifying headspace volatiles from fifth instar nymphs of D. citri using a gas chromatograph-mass spectrometer (GC-MS), we obtained a collection of 9 volatile compounds. These compounds were subsequently chosen to investigate the electrophysiological and behavioral responses of female T. radiata. At a concentration of 10 μg/μl, 9 compounds were compared with cis-3-hexen-1-ol (control), resulting in trans-2-nonenal inducing the highest relative electroantennogram (EAG) value, followed by hexanal, heptanal, n-heptadecane, tetradecanal, n-tetradecane, n-pentadecane, 1-tetradecanol, and 1-dodecanol. The top 5 EAG responses of female T. radiata to these compounds were further investigated through EAG dose-response experiments. The results showed positive dose-responses as concentrations increased from 0.01 to 10 μg/μl. In Y-tube olfactometer bioassays, female T. radiata exhibited a preference for specific compounds. They were significantly attracted to tetradecanal at a concentration of 10 µg/µl and trans-2-nonenal at 0.01 µg/µl, while no significant attraction was observed toward hexanal, heptanal, or n-heptadecane. Our report is the first to demonstrate that volatiles produced by D. citri nymphs attract T. radiata, which suggests that this parasitoid may utilize nymph volatiles to locate its host., (© The Author(s) 2024. Published by Oxford University Press on behalf of Entomological Society of America.)

The honeybee waggle dance has been widely studied as a communication system, yet we know little about how nestmates assimilate the information needed to navigate toward the signaled resource. They are required to detect the dancer's orientation relative to gravity and duration of the waggle phase and translate this into a flight vector with a direction relative to the sun 1 and distance from the hive. 2 , 3 Moreover, they appear capable of doing so from varied, dynamically changing positions around the dancer. Using high-speed, high-resolution video, we have uncovered a previously unremarked correlation between antennal position and the relative body axes of dancer and follower bees. Combined with new information about antennal inputs 4 , 5 and spatial encoding in the insect central complex, 6 , 7 we show how a neural circuit first proposed to underlie path integration could be adapted to decoding the dance and acquiring the signaled information as a flight vector that can be followed to the resource. This provides the first plausible account of how the bee brain could support the interpretation of its dance language., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Insect antennae facilitate the nuanced detection of vibrations and deflections, and the non-contact perception of magnetic or chemical stimuli, capabilities not found in mammalian skin. Here, we report a neuromorphic antennal sensory system that emulates the structural, functional, and neuronal characteristics of ant antennae. Our system comprises electronic antennae sensor with three-dimensional flexible structures that detects tactile and magnetic stimuli. The integration of artificial synaptic devices adsorbed with solution-processable MoS 2 nanoflakes enables synaptic processing of sensory information. By emulating the architecture of receptor-neuron pathway, our system realizes hardware-level, spatiotemporal perception of tactile contact, surface pattern, and magnetic field (detection limits: 1.3 mN, 50 μm, 9.4 mT). Vibrotactile-perception tasks involving profile and texture classifications were accomplished with high accuracy (> 90%), surpassing human performance in "blind" tactile explorations. Magneto-perception tasks including magnetic navigation and touchless interaction were successfully completed. Our work represents a milestone for neuromorphic sensory systems and biomimetic perceptual intelligence., (© 2024. The Author(s).)

Aquatic insects represent a great portion of Arthropod diversity and the major fauna in inland waters. The sensory biology and neuroanatomy of these insects are, however, poorly investigated. This research aims to describe the antennal sensilla of nymphs of the stonefly Dinocras cephalotes using scanning electron microscopy and comparing them with the adult sensilla. Besides, central antennal pathways in nymphs and adults are investigated by neuron mass-tracing with tetramethylrhodamine, and their brain structures are visualized with an anti-synapsin antibody. No dramatic changes occur in the antennal sensilla during nymphal development, while antennal sensilla profoundly change from nymphs to adults when switching from an aquatic to an aerial lifestyle. However, similar brain structures are used in nymphs and adults to process diverging sensory information, perceived through different sensilla in water and air. These data provide valuable insights into the evolution of aquatic heterometabolous insects, maintaining a functional sensory system throughout development, including a distinct adaptation of the peripheral olfactory systems during the transition from detection of water-soluble chemicals to volatile compounds in the air. From a conservation biology perspective, the present data contribute to a better knowledge of the biology of stoneflies, which are very important bioindicators in rivers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: Electroantennography (EAG) is a basic neuroscientific tool that is widely used to measure olfactory responses in insects. It is particularly adapted to probing the olfactory systems of non-model insect species in chemical ecology and evolutionary biology. As currently practiced, EAG measures have varying degrees of correlation with olfactory responses, especially for insects whose olfactory sensory neurons (OSNs) are arranged in zones on the antennae. This limitation was shown to be partly due to the fact that only a single antennal position was recorded., New Methods: We describe a setup using triple electroantennography (EAG 3 ), whereby three antennal positions are recorded simultaneously. The spatial arrangement of the electrodes ensures the mechanical stability of the assembly. The EAG 3 detector was coupled to a gas chromatograph (GC-EAD 3 ), customized using a Dean's switch to improve the EAG signals by chopper modulation. EAG 3 signals were analysed through a current point model to estimate olfactory responses across the antenna., Results: Recordings were performed on Tephritidae and Drosophila species, which have antennae of different shapes and sizes. We confirmed that the spatio-temporal pattern of antennal activation was stimulus dependent and allowed us to quantify the antennal olfactory response., Comparisons With Existing Method: Compared to typical single-probe EAG, we show that EAG 3 improves response quantification and increases the range of compounds for which a sensory response is detected., Conclusions: Our EAG 3 setup is an original low-cost and easy-to-use method. It offers a useful bridge between comprehensive neurophysiological investigations and the broader themes explored in chemical ecology., Competing Interests: Declaration of Competing Interest The authors declare no competing interests., (Copyright © 2023. Published by Elsevier B.V.)

Overall body proportions and relative limb length are highly characteristic for most insect taxa. In case of the legs, limb length has mostly been discussed with regard to parameters of locomotor performance and, in particular cases, as an adaptation to environmental factors or to the mating system. Here, we compare three species of stick and leaf insects (Phasmatodea) that differ strongly in the length ratio between antennae and walking legs, with the antennae of Medauroidea extradentata being much shorter than its legs, nearly equal length of antennae and legs in Carausius morosus, and considerably longer antennae than front legs in Aretaon asperrimus. We show that that relative limb length is directly related to the near-range exploration effort, with complementary function of the antennae and front legs irrespective of their length ratio. Assuming that these inter-species differences hold for both sexes and all developmental stages, we further explore how relative limb length differs between sexes and how it changes throughout postembryonic development. We show that the pattern of limb-to-body proportions is species-characteristic despite sexual dimorphism, and find that the change in sexual dimorphism is strongest during the last two moults. Finally, we show that antennal growth rate is consistently higher than that of front legs, but differs categorically between the species investigated. Whereas antennal growth rate is constant in Carausius, the antennae grow exponentially in Medauroidea and with a sudden boost during the last moult in Aretaon., (© 2022. The Author(s).)

Insects use their antennae to smell odors, 1 , 2 detect auditory cues, 3 , 4 and sense mechanosensory stimuli such as wind 5 and objects, 6 , 7 , 8 frequently by combining sensory processing with active movements. Genetic access to antennal motor systems would therefore provide a powerful tool for dissecting the circuit mechanisms underlying active sensing, but little is known about how the most genetically tractable insect, Drosophila melanogaster, moves its antennae. Here, we use deep learning to measure how tethered Drosophila move their antennae in the presence of sensory stimuli and identify genetic reagents for controlling antennal movement. We find that flies perform both slow adaptive movements and fast flicking movements in response to wind-induced deflections, but not the attractive odor apple cider vinegar. Next, we describe four muscles in the first antennal segment that control antennal movements and identify genetic driver lines that provide access to two groups of antennal motor neurons and an antennal muscle. Through optogenetic inactivation, we provide evidence that antennal motor neurons contribute to active movements with different time courses. Finally, we show that activation of antennal motor neurons and muscles can adjust the gain and acuity of wind direction encoding by antennal displacement. Together, our experiments provide insight into the neural control of antennal movement and suggest that active antennal positioning in Drosophila may tune the precision of wind encoding., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Odour plumes in the wild are spatially complex and rapidly fluctuating structures carried by turbulent airflows 1-4 . To successfully navigate plumes in search of food and mates, insects must extract and integrate multiple features of the odour signal, including odour identity 5 , intensity 6 and timing 6-12 . Effective navigation requires balancing these multiple streams of olfactory information and integrating them with other sensory inputs, including mechanosensory and visual cues 9,12,13 . Studies dating back a century have indicated that, of these many sensory inputs, the wind provides the main directional cue in turbulent plumes, leading to the longstanding model of insect odour navigation as odour-elicited upwind motion 6,8-12,14,15 . Here we show that Drosophila melanogaster shape their navigational decisions using an additional directional cue-the direction of motion of odours-which they detect using temporal correlations in the odour signal between their two antennae. Using a high-resolution virtual-reality paradigm to deliver spatiotemporally complex fictive odours to freely walking flies, we demonstrate that such odour-direction sensing involves algorithms analogous to those in visual-direction sensing 16 . Combining simulations, theory and experiments, we show that odour motion contains valuable directional information that is absent from the airflow alone, and that both Drosophila and virtual agents are aided by that information in navigating naturalistic plumes. The generality of our findings suggests that odour-direction sensing may exist throughout the animal kingdom and could improve olfactory robot navigation in uncertain environments., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Insect antennae are hollow, blood-filled fibers with complex shape. Muscles in the two basal segments control antennal movement, but the rest (flagellum) is muscle-free. The insect can controllably flex, twist, and maneuver its antennae laterally. To explain this behavior, we performed a comparative study of structural and tensile properties of the antennae of Periplaneta americana (American cockroach), Manduca sexta (Carolina hawkmoth), and Vanessa cardui (painted lady butterfly). These antennae demonstrate a range of distinguishable tensile properties, responding either as brittle or strain-adaptive fibers that stiffen when stretched. Scanning electron microscopy and high-speed imaging of antennal breakup during stretching revealed complex coupling of blood pressure and cuticle deformation in antennae. A generalized Lamé theory of solid mechanics was developed to include the force-driven deformation of blood-filled antennal tubes. We validated the theory against experiments with artificial antennae with no adjustable parameters. Blood pressure increased when the insect inflated its antennae or decreased below ambient pressure when an external tensile load was applied to the antenna. The pressure-cuticle coupling can be controlled through changes of the blood volume in the antennal lumen. In insects that do not fill the antennal lumen with blood, this blood pressure control is lacking, and the antennae react only by muscular activation. We suggest that the principles we have discovered for insect antennae apply to other appendages that share a leg-derived ancestry. Our work offers promising new applications for multifunctional fiber-based microfluidics that could transport fluids and be manipulated by the same fluid on demand. STATEMENT OF SIGNIFICANCE: Insect antennae are blood-filled, segmented fibers with muscles in the two basal segments. The long terminal segment is muscle-free but can be flexed. To explain this behavior, we examined structure-function relationships of antennae of cockroaches, hawkmoths, and butterflies. Hawkmoth antennae behaved as brittle fibers, but butterfly and cockroach antennae showed strain-adaptive behavior like fibers that stiffen when stretched. Videomicroscopy of antennal breakup during stretching revealed complex coupling of blood pressure and cuticle deformation. Our solid mechanics model explains this behavior. Because antennae are leg-derived appendages, we suggest that the principles we found apply to other appendages of leg-derived ancestry. Our work offers new applications for multifunctional fiber-based microfluidics that could transport fluids and be manipulated by the fluid on demand., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Animals perceive their surroundings using various modalities of sensory inputs to guide their locomotion. Nocturnal insects such as crickets use mechanosensory inputs mediated by their antennae to orient in darkness. Spatial information is acquired via voluntary antennal contacts with surrounding objects, but it remains unclear whether the insects modulate behaviors mediated by other sensory organs based on that information. Crickets exhibit escape behavior in response to a short air puff, which is detected by the abdominal mechanosensory organs called cerci and is perceived as a 'predator approach' signal. We placed objects of different shapes at different locations with which the cricket actively made contact using its antennae. We then examined the effects on wind-elicited escape behavior. The crickets changed their movement trajectory in response to nearby objects such as walls so that they could avoid collision with these obstacles even during the cercal-mediated behavior. For instance, when a wall was placed in front of the crickets so that it was detected by one antenna, the escape trajectory in response to a stimulus from behind was significantly biased toward the side opposite the wall. Even when the antenna on the free side without the wall was ablated, this collision avoidance was also observed, suggesting that the mechanosensory inputs from one antennae detecting an object edge would be sufficient to perceive the location of obstacle in front. This study demonstrated that crickets were able to use the spatial information acquired with their antennal system to modify their behavior mediated by other sensory organs., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2022. Published by The Company of Biologists Ltd.)

Ongoing neural activity has been observed across several brain regions and is thought to reflect the internal state of the brain. Yet, it is important to understand how ongoing neural activity interacts with sensory experience and shapes sensory representations. Here, we show that the projection neurons of the fruit fly antennal lobe exhibit spatiotemporally organized ongoing activity. After repeated exposure to odors, we observe a gradual and cumulative decrease in the amplitude and number of calcium events occurring in the absence of odor stimulation, as well as a reorganization of correlations between olfactory glomeruli. Accompanying these plastic changes, we find that repeated odor experience decreases trial-to-trial variability and enhances the specificity of odor representations. Our results reveal an odor-experience-dependent modulation of ongoing and sensory-evoked activity at peripheral levels of the fruit fly olfactory system., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

When flies explore their environment, they encounter odors in complex, highly intermittent plumes. To navigate a plume and, for example, find food, they must solve several challenges, including reliably identifying mixtures of odorants and their intensities, and discriminating odorant mixtures emanating from a single source from odorants emitted from separate sources and just mixing in the air. Lateral inhibition in the antennal lobe is commonly understood to help solving these challenges. With a computational model of the Drosophila olfactory system, we analyze the utility of an alternative mechanism for solving them: Non-synaptic ("ephaptic") interactions (NSIs) between olfactory receptor neurons that are stereotypically co-housed in the same sensilla. We find that NSIs improve mixture ratio detection and plume structure sensing and do so more efficiently than the traditionally considered mechanism of lateral inhibition in the antennal lobe. The best performance is achieved when both mechanisms work in synergy. However, we also found that NSIs decrease the dynamic range of co-housed ORNs, especially when they have similar sensitivity to an odorant. These results shed light, from a functional perspective, on the role of NSIs, which are normally avoided between neurons, for instance by myelination., Competing Interests: The authors have declared that no competing interests exist.

Most animals survive and thrive due to navigational behavior to reach their destinations. In order to navigate, it is important for animals to integrate information obtained from multisensory inputs and use that information to modulate their behavior. In this study, by using a virtual reality (VR) system for an insect, we investigated how the adult silkmoth integrates visual and wind direction information during female search behavior (olfactory behavior). According to the behavioral experiments using a VR system, the silkmoth had the highest navigational success rate when odor, vision, and wind information were correctly provided. However, the success rate of the search was reduced if the wind direction information provided was different from the direction actually detected. This indicates that it is important to acquire not only odor information but also wind direction information correctly. When the wind is received from the same direction as the odor, the silkmoth takes positive behavior; if the odor is detected but the wind direction is not in the same direction as the odor, the silkmoth behaves more carefully. This corresponds to a modulation of behavior according to the degree of complexity (turbulence) of the environment. We mathematically modeled the modulation of behavior using multisensory information and evaluated it using simulations. The mathematical model not only succeeded in reproducing the actual silkmoth search behavior but also improved the search success relative to the conventional odor-source search algorithm., Competing Interests: MY, HO, KH, DK, SS No competing interests declared, (© 2021, Yamada et al.)

Olfaction is crucial in mediating various behaviors of social insects such as red imported fire ants, Solenopsis invicta Buren. Olfactory receptor (OR) complexes consist of odor-specific ORs and OR co-receptors (Orco). Orcos are highly conserved across insect taxa and are widely co-expressed with ORs. Odorant binding proteins (OBPs) can transport semiochemicals to ORs as protein carriers and thus constitute the first molecular recognition step in insect olfaction. In this study, three OBP genes highly expressed in S. invicta antenna, OBP1, OBP5, OBP6, and Orco were partially silenced using RNA interference (RNAi). RNAi SiOBP5- and Orco-injected ants showed significantly lower EAG (electroantennography) responses to fire ant alarm pheromones and the alkaloid, 2,4,6-trimethylpyridine than water- or GFP-injected ants 72 h post injection. Subsequent qRT-PCR analysis demonstrated that the transcript level of the OBP1, OBP5, OBP6, and Orco significantly decreased 72 h after ants were injected with dsRNAs; however, there were no transcript level or EAG changes in ants fed dsRNAs. Our results suggest that S. invicta Orco and SiOBP5 are crucial to fire ants for their responses to alarm pheromones. RNAi knocking down SiOBP5 can significantly disrupt alarm pheromone communication, suggesting that disrupting SiOBP5 and Orcos could be potentially useful in the management of red imported fire ants.

Olfaction is a crucial sensory modality underlying foraging, social and mating behaviors in many insects. Since the olfactory system is at the interface between the animal and its environment, it receives strong evolutionary pressures that promote neuronal adaptations and phenotypic variations across species. Hornets are large eusocial predatory wasps with a highly developed olfactory system, critical for foraging and intra-specific communication. In their natural range, hornet species display contrasting ecologies and olfactory-based behaviors, which might match to adaptive shifts in their olfactory system. The first olfactory processing center of the insect brain, the antennal lobe, is made of morphological and functional units called glomeruli. Using fluorescent staining, confocal microscopy and 3D reconstructions, we compared antennal lobe structure, glomerular numbers and volumes in four hornet species (Vespa crabro, Vespa velutina, Vespa mandarinia and Vespa orientalis) with marked differences in nesting site preferences and predatory behaviors. Despite a conserved organization of their antennal lobe compartments, glomeruli numbers varied strongly between species, including in a subsystem thought to process intraspecific cuticular signals. Moreover, specific adaptations involving enlarged glomeruli appeared in two species, V. crabro and V. mandarinia, but not in the others. We discuss the possible function of these adaptations based on species-specific behavioral differences., (© 2021. The Author(s).)

Long-term exposure to different types of chemicals is hazardous to human health. Di(2-ethylhexyl) phthalate (DEHP) could exert pleiotropic deleterious effects on nervous systems. Mono(2-ethylhexyl) phthalate (MEHP), as one of the most toxic metabolites of DEHP, may have similar effects on nervous systems. However, no effects of MEHP on neural circuits have been reported. To uncover the regulation of MEHP on neural transmission, the functional changes of neural excitability and synaptic plasticity of projection neurons (PNs) have been assessed. In the current study, we recorded the action potentials (APs), stimulate action potentials (sti-APs), mini excitement postsynaptic current (mEPSC), calcium currents, and sodium currents from PNs of isolated whole brain of Drosophila model utilizing patch clamp recordings. We found that MEHP-300 (at the concentration of 300 μM), but not MHEP-100 (at the concentration of 100 μM), significantly decreased the frequency and amplitude of APs. Besides, the amplitude and anti-amplitude of sti-APs were reduced with the application of MEHP-300. Meanwhile, MEHP-300 reduced the frequency of mEPSC, but not the amplitude. Furthermore, MEHP-300 reduced the peak current densities of sodium and calcium channels. Therefore, our results indicated that MEHP could alter the neural excitability and synaptic plasticity of PNs by inhibiting the ion channels activities, revealing the potential modulation of MEHP on neural transmission of PNs., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Members of numerous animal species show consistent inter-individual differences in behaviours, but the forces generating animal "personality" or individuality remain unclear. We show that experiences gathered solely from social conflict can establish consistent differences in the decision of male crickets to approach or avoid a stimulus directed at one antenna. Adults isolated for 48 h from a colony already exhibit behavioural differences. Prior to staging a single dyadic contest, prospective winners approached the stimulus whereas prospective losers turned away, as they did also after fighting. In contrast, adults raised as nymphs with adult males present but isolated from them as last instar nymphs, all showed avoidance. Furthermore, adults raised without prior adult contact, showed no preferred directional response. However, following a single fight, winners from both these groups showed approach and losers avoidance, but this difference lasted only one day. In contrast, after 6 successive wins or defeats, the different directional responses of multiple winners and losers remained consistent for at least 6 days. Correlation analysis revealed examples of consistent inter-individual differences in the direction and magnitude of turning responses, which also correlated with individual aggressiveness and motility. Together our data reveal that social subjugation, or lack thereof, during post-embryonic and early adult development forges individuality and supports the notion of a proactive-reactive syndrome in crickets., (© 2021. The Author(s).)

In insects the tactile sense is important for near-range orientation and is involved in various behaviors. Nocturnal insects, such as the stick insect Carausius morosus , continuously explore their surroundings by actively moving their antennae when walking. Upon antennal contact with objects, stick insects show a targeted front-leg movement. As this reaction occurs within 40 ms, descending transfer of information from the brain to the thorax needs to be fast. So far, a number of descending interneurons have been described that may be involved in this reach-to-grasp behavior. One of these is the contralateral ON-type velocity-sensitive neuron (cONv). cONv was found to encode antennal joint-angle velocity during passive movement. Here, we characterize the transient response properties of cONv, including its dependence on joint angle range and direction. As antennal hair field afferent terminals were shown to arborize close to cONv dendrites, we test whether antennal hair fields contribute to the joint-angle velocity encoding of cONv. To do so, we conducted bilateral extracellular recordings of both cONv interneurons per animal before and after hair field ablations. Our results show that cONv responses are highly transient, with velocity-dependent differences in delay and response magnitude. As yet, the steady state activity level was maintained until the stop of antennal movement, irrespective of movement velocity. Hair field ablation caused a moderate but significant reduction of movement-induced cONv firing rate by up to 40%. We conclude that antennal proprioceptive hair fields contribute to the velocity-tuning of cONv, though further antennal mechanoreceptors must be involved, too. NEW & NOTEWORTHY Active tactile exploration and tactually induced behaviors are important for many animals. They require descending information transfer about tactile sensor movement to thoracic networks. Here, we investigate response properties and afferent input to the identified descending interneuron cONv in stick insects. cONv may be involved in tactually induced reach-to-grasp movements. We show that cONv response delay, transient and steady state are velocity-dependent and that antennal proprioceptive hair fields contribute to the velocity encoding of cONv.

Essential oils of aromatic plants represent an alternative to classical pest control with synthetic chemicals. They are especially promising for the alternative control of stored product pest insects. Here, we tested behavioral and electrophysiological responses of the stored product pest Tribolium confusum , to the essential oil of a Brazilian indigenous plant, Varronia globosa, collected in the Caatinga ecosystem. We analyzed the essential oil by GC-MS, tested the effects of the entire oil and its major components on the behavior of individual beetles in a four-way olfactometer, and investigated responses to these stimuli in electroantennogram recordings (EAG). We could identify 25 constituents in the essential oil of V. globosa , with anethole, caryophyllene and spathulenole as main components. The oil and its main component anethole had repellent effects already at low doses, whereas caryophyllene had only a repellent effect at a high dose. In addition, the essential oil abolished the attractive effect of the T. confusum aggregation pheromone. EAG recordings revealed dose-dependent responses to the individual components and increasing responses to the blend and even more to the entire oil. Our study reveals the potential of anethole and the essential oil of V. globosa in the management of stored product pests.