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Simple Summary: The capture and transport of pheromone odorants to olfactory sensory neurons (OSNs) via the surfaces of thousands of antennal sensory hairs of male moths are the first and requisite steps that permit olfaction and upwind flight orientation to females to occur. Our investigations of the male pheromone-sensitive sensory hairs (trichoid sensilla) from five moth species using atomic force microscopy (AFM) revealed differences in the densities, heights and depths of pores and ridges involved in pheromone odorant capture and transport. Measurements of electrical surface potentials across sensilla in our study suggests that there is a heterogeneity in the distribution of surface lipids between ridges, pores and inter-ridge areas that likely facilitate the capture and transport of pheromone odorants to OSNs. Controlled heating of sensilla revealed that heating did not melt or change the shapes of small lipid exudates residing within the pores or of large exudates completely covering the pores. These results suggest that such exudates are crystalline wax blooms that comprise a different form of lipid than the free lipid monolayer that covers the rest of these olfactory hairs. The surfaces of trichoid sensilla on male moth antennae have been sculpted over evolutionary time to capture pheromone odorant molecules emitted by the females of their species and transport the molecules in milliseconds into the binding protein milieu of the sensillum lumen. The capture of pheromone molecules likely has been optimized by the topographies and spacings of the numerous ridges and pores on these sensilla. A monolayer of free lipids in the outer epicuticle covers the sensillar surfaces and must also be involved in optimal pheromone odorant capture and transport. Using electro-conductive atomic force microscopy probes, we found that electrical surface potentials of the pores, ridges and flat planar areas between ridges varied in consistent ways, suggesting that there is a heterogeneity in the distribution of surface lipid mixtures amongst these structures that could help facilitate the capture and transport of pheromone molecules down through the pores. We also performed experiments using peak force atomic force microscopy in which we heated the sensilla to determine whether there is a temperature-related change of state of some of the surface lipid exudates such as the prominent domes covering many of the pores. We found that these exudates were unaffected by heating and did not melt or change shape significantly under high heat. Additionally, we measured and compared the topographies of the trichoid sensilla of five species of moths, including the distributions, spacings, heights and diameters of ridges, pores and pore exudates. [ABSTRACT FROM AUTHOR]

The effect of Tagetes minuta oil on the morphology of Aphis craccivora is reported in the scanning electron microscopy (SEM). Results showed that, flagellar segments of antenna treated with T. minuta showed filamentous and knotted without losing the setae after 96 h of treatment. The sensilla (Type I and II) showed remarkable deformation, reduction in the length and width. Morphometric measurements also helped to identify the deformed sensilla on cuticle and antenna. Type I and antennal sensilla reduced its length by 30% and type II sensilla by 42%. The breadth of type I and II sensilla also reduced by 35%. [ABSTRACT FROM AUTHOR]

The surfaces of trichoid sensilla on male moth antennae have been sculpted over evolutionary time to capture pheromone odorant molecules emitted by the females of their species and transport the molecules in milliseconds into the binding protein milieu of the sensillum lumen. The capture of pheromone molecules likely has been optimized by the topographies and spacings of the numerous ridges and pores on these sensilla. A monolayer of free lipids in the outer epicuticle covers the sensillar surfaces and must also be involved in optimal pheromone odorant capture and transport. Using electro-conductive atomic force microscopy probes, we found that electrical surface potentials of the pores, ridges and flat planar areas between ridges varied in consistent ways, suggesting that there is a heterogeneity in the distribution of surface lipid mixtures amongst these structures that could help facilitate the capture and transport of pheromone molecules down through the pores. We also performed experiments using peak force atomic force microscopy in which we heated the sensilla to determine whether there is a temperature-related change of state of some of the surface lipid exudates such as the prominent domes covering many of the pores. We found that these exudates were unaffected by heating and did not melt or change shape significantly under high heat. Additionally, we measured and compared the topographies of the trichoid sensilla of five species of moths, including the distributions, spacings, heights and diameters of ridges, pores and pore exudates.

Trichoid sensilla are the most common mechanoreceptors in insects; depending on their distribution, they can act as either exteroceptors or proprioceptors. In this study, the internal structure of the trichoid sensillum from Nilaparvata lugens was studied, using focused ion beam scanning electron microscopy (FIB-SEM). We reconstructed a three-dimensional (3D) model derived from the FIB-SEM data set. The model displayed characteristic mechanosensory sensilla components, including a hair inserted in the socket, a dendrite going through the laminated cuticle, and an electron-dense tubular body at the dendrite terminal. The detailed 3D model showed the relationship between the microtubules within the tubular body and those outside of the tubular body. We also found an autocellular junction in the tormogen cell, indicating that the tormogen cell grows around the dendrite sheath to form a hollow column shape during sensilla morphogenesis. [ABSTRACT FROM AUTHOR]

Pheromone-binding proteins (PBPs) are believed to be involved in the recognition of semiochemicals. In the present study, western blot analysis, fluorescence-binding characteristics and immunolocalization of CmedPBP4 from the rice leaffolder, Cnaphalocrocis medinalis, were investigated. Western blot analysis revealed that CmedPBP4 showed obvious antenna-specific expression patterns in female and male antenna, and made a clearly different sex-biased expression. Immunocytochemical labeling revealed that CmedPBP4 showed specific expression in the trichoid sensilla. Competitive fluorescence binding assays indicated that CmedPBP4 could selectively recognize three sex pheromone components (Z13-18:Ac, Z11-16:Al and Z13-18:OH) and eleven rice plant volatiles, including cyclohexanol, nerolidol, cedrol, dodecanal, ionone, (−)-α-cedrene, (Z)-farnesene, β-myrcene, R-(+)-limonene, (−)-limonene, and (+)-3-carene. Meanwhile the CmedPBP4 detection of sex pheromones and host odorants was pH-dependent. Our results, for the first time, provide further evidence that trichoid sensilla might be play an important role in detecting sex pheromones and host plant volatiles in the C. medinalis moth. Our systematic studies provided further detailed evidence for the function of trichoid sensilla in insect semiochemical perception. [ABSTRACT FROM PUBLISHER]

Insects have evolved sophisticated olfactory reception systems to sense exogenous chemical signals. Odorant receptors (ORs) on the membrane of chemosensory neurons are believed to be key molecules in sensing exogenous chemical cues. ORs in different species of insects are diverse and should tune a species to its own specific semiochemicals relevant to their survival. The orthopteran insect, locust ( Locusta migratoria ), is a model hemimetabolous insect. There is very limited knowledge on the functions of locust ORs although many locust OR genes have been identified in genomic sequencing experiments. In this paper, a locust OR, LmigOR3 was localized to neurons housed in trichoid sensilla by in situ hybridization. LmigOR3 was expressed as a transgene in Drosophila trichoid olfactory neurons (aT1) lacking the endogenous receptor Or67d and the olfactory tuning curve and dose-response curves were established for this locust receptor. The results show that LmigOR3 sensitizes neurons to ketones, esters and heterocyclic compounds, indicating that LmigOR3 is a broadly tuned receptor. LmigOR3 is the first odorant receptor from Orthoptera that has been functionally analyzed in the Drosophila aT1 system. This work demonstrates the utility of the Drosophila aT1 system for functional analysis of locust odorant receptors and suggests that LmigOR3 may be involved in detecting food odorants, or perhaps locust body volatiles that may help us to develop new control methods for locusts. [ABSTRACT FROM AUTHOR]

Sensing physical properties of liquids, such as viscosity, is of great significance for both biological organisms and industrial applications. For terrestrial organisms feeding on liquids, such as honey bees that forage nectar, sensing viscosity may help to determine the quality of food sources. Previous experiments showed that honey bees exhibit strong preferences for less viscous nectar; however, the physical mechanism underlying how they perceive viscosity remains unexplored. In this study, we propose that the western honey bee ( Apis mellifera L.) is capable of distinguishing viscosity using the slender trichoid sensilla emerging from a ball and socket-like joint on the proboscis. Observations of the trichoid sensilla using transmission electron microscopy reveal physical characteristics that are typical of mechanosensory structures. Additionally, we found that bees actively alter the rate at which they feed based on the liquid's viscosity and not its sugar content, hinting at their sensing of viscosity. Through mathematical modeling, we found that the sensitivity of the biological viscometer was determined by its length, and the optimal sensitivity for a western honey bee occurs when the tongue interacts with nectar with a viscosity of 4.2 mPa·s, coinciding with the viscosities typically found in the wild. Our findings broaden insights into how honey bees adapt to varying-viscosity nectar from the perspective of mechanical sensing, and how the bee-flower partnership may be based around the optimal nectar viscosity for feeding. By understanding how bees may sense viscosity at the micrometer scale, we may motivate new technologies for micro-viscometers., (© 2022 IOP Publishing Ltd.)

Abstract: After injury many arthropods are able to regenerate lost body parts and their innervation. Here, regeneration was studied in the desert locust Schistocerca gregaria after amputation of the midleg tibia and tarsus in the first larval instar. A regenerate was formed first in the third larval instar and it increased in size with each larval moult. The regenerate was always unsegmented and remained much shorter than the intact leg parts. The growth rate was initially rather high and decreased thereafter to that of intact parts. The amputation also influenced the growth rate of proximal leg parts (femur and trochanter) resulting in shortened leg segments. The regenerate carried many sense organs like trichoid sensilla and canal sensilla. The primary mechanosensory neurons of the trichoid sensilla projected somatotopically into the mesothoracic ganglion. A comparison of these projections from intact leg segments and regenerates showed a regrow into the target neuropil areas and a restoration of the somatotopy. Intact sensilla on the injured leg and regenerated sensilla expanded their central projections lateral-medially. [Copyright &y& Elsevier]

Extracellular electrophysiological recordings were made from individual type-A trichoid sensilla on the antenna of the female sphinx moth Manduca sexta. A single annulus of the antenna bears about 1,100 of these sensilla, and each is innervated by two olfactory receptor cells. We tested the responses of these receptor cells to a panel of 102 volatile compounds, as well as three plant-derived odor mixtures, and could discern three different functional types of type-A trichoid sensilla. One subset of receptor cells exhibited an apparently narrow molecular receptive range, responding strongly to only one or two terpenoid odorants. The second subset was activated exclusively by aromatics and responded strongly to two to seven odorants. The third subset had a broad molecular receptive range and responded strongly to odorants belonging to several chemical classes. We also found receptor cells that did not respond to any of the odorants tested but were spontaneously active. Certain odorants elicited excitatory responses in some sensilla but inhibitory responses in others, and some receptor cells were strongly excited by certain odorants but inhibited by others. Impregnation of groups of receptor cells in type-A trichoid sensilla with rhodamine-dextran demonstrated that their axons project mainly to the large female glomeruli of the antennal lobe. [ABSTRACT FROM AUTHOR]

We recorded the electrophysiological responses of individual olfactory receptor neurons in sensilla trichodea on the antennae of adult arctiid moths, Utetheisa ornatrix, to stimulation with volatiles associated with both sexes. All trichoid sensilla contain at least two receptor neurons, each with distinct action potential amplitudes and waveforms, that respond dichotomously to male and female odors. Although, neither female neuron responds to extracts of coremata or the male-produced pheromone hydroxydanaidal, they do respond in a gender-specific manner to the volatiles emanating from whole pupae, hemolymph, thoracic froth, and adult animals of several ages. Thoracic froth, which contains pyrrolizidine alkaloids, is thought to play a role in defense. Froth from moths reared on diets, with or without added pyrrolizidine alkaloids, were equally effective in eliciting gender-specific patterns of response. Male trichoid receptor neurons respond to these same materials with similar patterns of activation. These receptor neurons provide information about substances, which we have termed “gender odors,” that are persistently emitted by nearby animals. These substances do not appear to be the same as those already known to be involved in defense or the sexual dialog between individuals. [ABSTRACT FROM AUTHOR]

The cerci of the praying mantid, Archimantis brunneriana Sauss., are paired segmented sensory organs located at the tip of the abdomen. Basally the cercal segments are slightly flattened dorso-ventrally and are fused to such a degree that it is difficult to distinguish them. Distally the segments become progressively more flattened laterally and their boundaries become more obvious. Two types of sensilla are present on the cerci, trichoid sensilla and filiform sensilla. Trichoid hairs are longest on the medial side of the cerci and toward the cercal base. On the proximal cercal segments they are grouped toward the middle of each segment while they are more uniformly distributed on the distal segments. Filiform sensilla are found at the distal end of each segment except the last and are most abundant on the middle segments of the cercus. Both the number of cercal segments and the number of sensilla are variable. Trichoid hairs are highly variable in appearance from short and stout to long and thin. They arise from a raised base, have a fluted shaft, and some have a pore at the tip. They are innervated by from one to five dendrites, one of which is always considerably larger than the others. Some of the dendrites continue out into the shaft of the hair. Filiform hairs have fluted shafts and are mounted in a flexible membrane within a cuticular ring in a depression. They are innervated by a single large sensory neuron, the dendrite of which passes across a flattened area on the inner wall of the lumen of the hair. The dendritic sheath forms the lining of the ecdysial canal and is therefore firmly attached to the hair. The dendrite is attached to the sheath by desmosomes distally and is penetrated by projections of the sheath more proximally. A fibrous cap surrounds the dendrite and may hold it in place relative to the hair. The cercal receptor system of Archimantis is compared to those of cockroaches and crickets. [ABSTRACT FROM AUTHOR]

Many species of caterpillars have been reported to respond to sound, but there has been limited formal study of what sounds they hear, how they hear them and how they respond to them. Here, we report on hearing in caterpillars of the monarch butterfly ( Danaus plexippus ). Fourth and fifth instar caterpillars respond to sounds by freezing, contracting, and flicking their thorax in a vertical direction. Behavioural responses were evoked by sound frequencies between 50 and 900 Hz, with best sensitivity at 100-200 Hz. The lowest mean threshold was 79 dB SPL (particle velocity 605 μm s -1 ) at 150 Hz. When presented with a repeated 200 Hz sound tone, caterpillars habituate by no longer responding. A series of ablation experiments confirmed that the primary sensory receptors are a pair of long hairs, called trichoid sensilla, located on the upper prothorax. These sensilla are ∼450 µm long, rest in a socket and are innervated by a single bipolar sensory neuron. Removal of these setae reduced responses significantly compared with controls. Other setae contributed minimally to hearing in response to 200 Hz tones, and tubercles and prothoracic shields played no apparent role in sound reception. We propose that hearing functions to prevent attacks by aerial insect predators and parasitoids, which produce flight sounds in the frequency range to which the caterpillars are sensitive. This research lays the foundation for further investigations on the function and evolution of hearing in caterpillars, and has significance for the conservation of threatened monarch butterfly larvae living near noisy urban environments and roadways., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2019. Published by The Company of Biologists Ltd.)