Trichoid Sensilla Research Articles

Comparison of the antennal sensilla of females of four fig-wasps associated with Ficus auriculata

A comparison was performed of the antennal sensilla of females of four chalcid wasp species Ceratosolen emarginatus Mayr, 1906, Sycophaga sp., Philotrypesis longicaudata Mayr, 1906, and Sycoscapter roxburghi Joseph, 1957, which are specific and obligatory associated with Ficus auriculata (Lour, 1790). The four species exhibit different oviposition strategies in the fig ovules where their offspring hatch and develop. Antennal sensilla morphology was evaluated using scanning electron microscopy. Females of the four species present 11 morphologically similar types of sensilla: trichoid sensilla, sensilla obscura, chaetica sensilla 1 and 2, which all have mechanosensory functions; uniporous basiconic sensilla, which are presumably contact chemosensilla; basiconic capitate peg sensilla, coeloconic sensilla 1, multiporous basiconic and placoid sensilla, which may be regarded as olfactory sensilla, and coeloconic sensilla 2 and 3, which are presumed to be proprioreceptors or pressure receptors. The four species have significant differences in the abundance and arrangement of trichoid sensilla and chaetica sensilla 1 on the flagellum. The coeloconic sensilla and sensilla obscura only occur on the antennae of C. emarginatus that enter figs. The chemosensilla which are presumably involved in host discrimination, i.e., basiconic sensilla, multiporous placoid sensilla and basiconic capitate peg sensilla, are similar in shape and configuration, although they present some differences in abundance. These findings provide practical information on the adaptations of fig wasps and the relationship between multisensory antennae and functions in fig wasp behaviour.

Structure of antennal sensilla in the caddisfly genus Rhyacophila pictet (Trichoptera, Rhyacophilidae)

Microstructure and distribution of sensilla were studied in 25 species of caddisflies of the family Rhyacophilidae for the first time. Comparative analysis allowed 13 sensilla types to be identified in members of this family: long grooved trichoid, curved trichoid, chaetoid, mushroom-like pseudoplacoid, forked pseudoplacoid, leaf-like pseudoplacoid, dissected pseudoplacoid, multiforked pseudoplacoid, styloconic, auricillic, coronal, basiconic sensilla, and Bohm’s bristles. The largest variations were found in the pseudoplacoid sensilla. Dissected, leaflike, auricillic, and multiforked sensilla were discovered in the order Trichoptera for the first time. Curved trichoid sensilla can be grouped or assembled into sensory fields. The total number of sensilla per antennal segment decreases towards the antenna apex. Data on the structural diversity of sensilla in groups of fast-evolving species suggest the participation of sensilla structures in the speciation processes.

Male antenna morphology and its effect on scramble competition in false garden mantids.

Well-developed antennae are crucial for many insects, but especially for scramble competitors, who race to find their mates using female sex cues. In these systems, the ability of males to locate females quickly is thought to be under strong selection. A rarely tested assumption is that males with more sensory structures are able to locate females faster. In the present study, we used the false garden mantid Pseudomantis albofimbriata to investigate male antennal morphology and its effect on male efficiency in finding a mate. We used scanning electron microscopy to describe the major sensilla types and their arrangement along the length of male antennae. We also conducted field enclosure trials relating male antennal morphology to scramble competition in this system. We identified six different types of antennal sensilla (cheatic, trichoid, basiconic, grooved peg, ceolocapitular and campaniform) on male P. albofimbriata antennae. As expected, males who had more trichoid sensilla located females quicker than did males with fewer sensilla. Results of the current study suggest that antenna morphology plays a significant role in mate location and hence scramble competition in the P. albofimbriata mating system.

Electrophysiological Recording from Drosophila Trichoid Sensilla in Response to Odorants of Low Volatility.

Insects rely on their sense of smell to guide a wide range of behaviors that are critical for their survival, such as food-seeking, predator avoidance, oviposition, and mating. Myriad chemicals of varying volatilities have been identified as natural odorants that activate insect Olfactory Receptor Neurons (ORNs). However, studying the olfactory responses to low-volatility odorants has been hampered by an inability to effectively present such stimuli using conventional odor-delivery methods. Here, we describe a procedure that permits the effective presentation of low-volatility odorants for in vivo Single-Sensillum Recording (SSR). By minimizing the distance between the odor source and the target tissue, this method allows for the application of biologically salient but hitherto inaccessible odorants, including palmitoleic acid, a stimulatory pheromone with a demonstrated effect on ORNs involved in courtship and mating behavior1. Our procedure thus affords a new avenue to assay a host of low-volatility odorants for the study of insect olfaction and pheromone communication.

Scanning electron microscopic studies on antenna of Hemipyrellia ligurriens (Wiedemann, 1830) (Diptera: Calliphoridae)—A blow fly species of forensic importance

Blow flies (Diptera: Calliphoridae) are one of the foremost organisms amongst forensic insects to colonize corpses shortly after death, thus are of immense importance in the domain of forensic entomology. The blow fly Hemipyrellia ligurriens (Wiedemann, 1830) (Diptera: Calliphoridae) is considered as a forensically important fly species globally and is also known for its medical and veterinary importance. In the present study, we report for the first time scanning electron microscopic studies on the morphology of sensilla of antenna of adult male and female of H. ligurriens is with profound importance in better understanding of the insect morphology from forensic entomological perspective, and also could aid in proper identification of the species from other calliphorid flies. The structural peculiarities observed in the (i) antenna of H. ligurriens with three segments- scape, pedicel and flagellum with dorso-laterally placed arista (ii) densely covered microtrichia and most abundant trichoid sensilla identified on the antenna (iii) observation of only one type of sensilla, chaetic sensilla (ChI) on the scape (iv) two types of chaetic sensilla (ChI and ChII) and styloconic sensilla on the pedicel (v) the flagellum with three types of sensilla- trichoid, basiconic and coeloconic sensilla (vi) Basiconic sensilla with multiporous surfaces with characteristic olfactory function. Moderate sexual dimorphism in the width of the flagellum, the females with wider flagella than the males, bear significance to the fact that they bear more multi-porous sensilla than the males, thus suffice their need to detect oviposition sites. Significant difference was observed in the length and width of coeloconic sensilla between the two sexes, the females showed bigger coeloconic sensilla, suggesting their function in oviposition site detection and successful colonization in corpses.

Molecular basis for the behavioral effects of the odorant degrading enzyme Esterase 6 in Drosophila

Previous electrophysiological and behavioural studies implicate esterase 6 in the processing of the pheromone cis-vaccenyl acetate and various food odorants that affect aggregation and reproductive behaviours. Here we show esterase 6 has relatively high activity against many of the short-mid chain food esters, but negligible activity against cis-vaccenyl acetate. The crystal structure of esterase 6 confirms its substrate-binding site can accommodate many short-mid chain food esters but not cis-vaccenyl acetate. Immunohistochemical assays show esterase 6 is expressed in non-neuronal cells in the third antennal segment that could be accessory or epidermal cells surrounding numerous olfactory sensilla, including basiconics involved in food odorant detection. Esterase 6 is also produced in trichoid sensilla, but not in the same cell types as the cis-vaccenyl acetate binding protein LUSH. Our data support a model in which esterase 6 acts as a direct odorant degrading enzyme for many bioactive food esters, but not cis-vaccenyl acetate.

A new genus and species of Lasiopteridi (Diptera, Cecidomyiidae) on Haplopappus foliosus (Asteraceae) from Chile

A new genus and species of gall midge, Haplopappusmyia gregaria, is described and illustrated (larva, pupa, male, and female). This species induces apical galls on Haplopappus foliosus (Asteraceae), an endemic shrub from central Chile. The specimens were collected at La Ligua Municipality, Petorca Province, Valparaiso region, Chile, during spring of 2011–2014. This area corresponds to one of the fifth Mediterranean Matorral biome, considered among Earth's biodiversity hotspots. The new genus is characterized by presenting lateral margin of antennal scape with a mesal reentrance; four-segmented palpus, one-toothed tarsal claws, R5 straight, reaching C anterior to wing apex; male seventh and eighth tergites lacking sclerotization mesally, beyond proximal margin; presence of trichoid sensilla on the abdominal terga and sterna of both sexes, protrusible ovipositor with elongate fused cerci, and larva with 4 pairs of setose terminal papillae.

Morphology of the Antenna of Hermetia illucens (Diptera: Stratiomyidae): An Ultrastructural Investigation.

The black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), is a relevant species in waste and pest management, but is also of forensic and medical importance. A scanning electron microscopy (SEM) investigation of the antennae of both sexes of H. illucens is presented here for the first time. The antenna is composed of three regions: the scape, the pedicel, and the flagellum. The first two regions are single segments, whereas the third region, the longest one, is composed of eight flagellomeres. The scape and pedicel have microtrichia, chaetic sensilla, and rounded perforations. The flagellum is covered by different microtrichia, the morphology of which is described in detail. Two types of sensory pit are found on flagellomeres 1 to 6. An oval depression with trichoid sensilla extends from flagellomeres 4 to 6. On both sides of flagellomere 8 is a lanceolate depression covered by hair-like microtrichia. Morphometric and morphological analyses revealed some sex-related differences. The results of the SEM investigations are compared with those obtained on other species of the family Stratiomyidae and other brachyceran Diptera. The possible role of sensilla in sensory perception is also discussed in comparison with nondipteran species.

Synthetic blend of larval frass volatiles repel oviposition in the invasive box tree moth, Cydalima perspectalis

Insects find their oviposition sites using visual, contact and olfactory cues. Volatile stimuli emitted by an intact or herbivore-occupied host plant, non-host plants or the herbivore itself can all influence the final decision of females concerning where to lay eggs. Volatile substances surrounding larval excreted pellets, i.e., frass of the invasive box tree moth (Cydalima perspectalis Walker) were collected, and the physiological activity was investigated by coupled gas chromatographic–electroantennographic detection. Based on structural elucidation, two aromatic derivates and one terpene alcohol were identified to be physiologically active on the antennae of the adults: guaiacol, (±)-linalool and veratrol. For all compounds, antennal responses were found to be dose dependent with EAG amplitudes being the highest at the highest dose levels. Females were also more sensitive to all three compounds compared to males. Single sensillum recordings on mated female antennae revealed that these frass compounds triggered 22% of the tested olfactory sensory neurons housed in trichoid sensilla. Behavioral bioassays indicated that the blend of these compounds had an oviposition-repellent effect on conspecific females: individuals laid significantly fewer eggs on boxwood plants equipped with dispensers loaded with the synthetic blend compared to those treated with natural frass or the control plants. This difference likely originated from the measured rapid changes in the volatile profile of larval excrement when exposed to the air at room temperature. Our findings have the potential to unravel the complex ecology of this invasive moth species characterized by rapid range expansion and extensive damage in Europe.

Morphological Characteristics of Terminalia of the Wasp-Mimicking Fly, Stomorhina discolor (Fabricius).

Stomorhina discolor (Fabricius), a species of blow fly that mimics wasps, is distributed worldwide, but detailed information about characteristics of its adult terminalia is incomplete. To help fill this gap in the information, the morphology of adult stages of S. discolor was investigated using light microscopy and scanning electron microscopy. Observations using the light microscope revealed unique characteristics of the male genitalia that are markedly different from other blow fly species. More morphological detail, including observation of several sensilla (e.g., sensilla trichoid and sensilla basiconica) along the male terminalia and female ovipositor, was seen under the scanning electron microscope. These details can be taxonomically valuable for identifying males and females of S. discolor and may help address matters concerning copulation in this species.

A comparison between the adult antennal sensilla of the cavernicolous stonefly Protonemura gevi and other epigean Protonemura species (Plecoptera: Nemouridae) in a biological context

SummaryIn the present paper we study the antennal sensilla of the unusual hypogean stonefly Protonemura gevi Tierno de Figueroa & López-Rodríguez, 2010 (Plecoptera: Nemouridae), comparing them with those of two epigean species of the genus Protonemura, P. alcazaba (Aubert, 1954) and P. meyeri (Pictet, 1842), with the aim to describe possible peculiarities. No differences exist in the types and morphology of antennal sensilla among the studied species and neither between sexes. The types of sensilla identified are long aporous trichoid sensilla with a tactile function, uniporous gustatory sensilla chaetica, multiporous sensilla basiconica (porous pegs) and sensilla coeloconica (digitated pegs), with a supposed olfactory function, and domes probably hosting aporous thermohygroreceptive pegs. These sensilla are very similar to those observed in other Plecoptera families and described in detail in Dinocras cephalotes (Curtis, 1827), thus suggesting a quite conserved sensory function for the antenna in the whole order, as it happens in other aquatic insects, such as Ephemeroptera and Odonata.

A broadly tuned odorant receptor in neurons of trichoid sensilla in locust, Locusta migratoria

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.

Morphology and sensilla of the enigmatic Bhutan pine aphid Pseudessigella brachychaeta Hille Ris Lambers (Hemiptera: Aphididae) – A SEM study

The aphid tribe Eulachnini is unusual in being both diverse in species number and specializing on conifer hosts. The Bhutan pine aphid Pseudessigella brachychaeta Hille Ris Lambers, 1966; the only known species of its genus and native of the Himalayan region, displays characteristics of both the Palearctic genus Eulachnus and the Nearctic Essigella. Species of all three genera, as well as eulachnine Cinara subgenus Schizolachnus, share the same ecological niche, feeding almost exclusively on the needles of true pines. To obtain a better understanding of this enigmatic aphid and its biological context within the Eulachnini, we conducted a scanning electron microscopy study of the fine morphology and sensilla of the live-bearing and egg-laying forms of the species. The general morphology most resembles that of species of the genus Eulachnus but in detail Pseudessigella also displays unique features. Many types of sensilla, including coeloconic, campaniform, placoid and trichoid sensilla occur at different locations on the antennae, mouthparts, and legs. The rhinariolum on the second antennal segment is described and illustrated for the first time in Lachninae and a second rhinariolum-like sensillum, hitherto unknown in aphids, is also described on the second antennal segment. We discuss the morphological features of Pseudessigella and the distribution of antennal and labial sensilla with respect of their possible taxonomic and functional significance.

Morphological and electrophysiological analysis of tarsal sensilla in the medfly Ceratitis capitata (Wiedemann, 1824) (Diptera: Tephritidae)

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann, 1824) (Diptera: Tephritidae), is a polyphagous pest in horticulture, mainly targeting pomaceous and citrus fruits. To gain better knowledge about its chemosensory system related to taste, essential for behavioural strategies and localisation of host plants, we examined the tarsal external morphology by high-resolution scanning electron microscopy, focusing on sensilla. Numerous trichoid and chaetica sensilla, related to taste and mechanoreceptor systems, and other types of sensilla are present in tarsal segments. The responses of specific trichoid chemosensilla were also studied through electrophysiological experiments by stimulation with sodium chloride, fructose and four bitter stimuli. Electrophysiological data allowed us to distinguish three types of different neurons: high (“H”), middle (“M”) and small (“S”). Increasing concentrations of sodium chloride enhanced the activity of H cells, while fructose boosted M cells activity. On the contrary, S cells showed no increase in spike activity after stimulation with these substances. Bitter stimuli induced no significant response on these cells. Behavioural assays showed no statistical difference among the responses to sugars, bitter substances and citric acid. Our results on taste stimuli will be useful in increasing knowledge of Ceratitis chemoreception, fundamental in new integrated pest management.

Odorant Responses and Courtship Behaviors Influenced by at4 Neurons in Drosophila.

In insects, pheromones function as triggers to elicit complex behavior programs, such as courtship and mating behavior. In most species, the neurons tuned to pheromones are localized in a specific subset of olfactory sensilla located on the antenna called trichoid sensilla. In Drosophila there are two classes of trichoid sensilla, at1 sensilla that contain the dendrites of a single neuron that is specifically tuned to the male-specific pheromone 11-cis vaccenyl acetate (cVA), and at4 sensilla that contain three neurons with relatively poorly defined chemical specificity and function. Using a combination of odorant receptor mutant analysis, single sensillum electrophysiology and optogenetics, we have examined the chemical tuning and behavioral consequences of the three at4 olfactory neuron classes. Our results indicate that one class, Or65abc neurons, are unresponsive to cVA pheromone, and function to inhibit courtship behaviors in response to an unknown ligand, while the other two neuron classes, Or88a and Or47b neurons, are sensitive to a diverse array of fly and non-fly odors, and activation of these neurons has little direct impact on courtship behaviors.

Antennal sensilla morphology of Theocolax elegans (Westwood) (Hymenoptera: Pteromalidae), a larval parasitoid of the maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae)

The antennal sensilla of Theocolax elegans (Westwood) (Hymenoptera: Pteromalidae), a larval parasitoid of the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) were investigated using scanning electron microscopy. The antennal sensilla of female and male wasps appeared similar in shape and types. Antennal sensilla in female and male T. elegans were classified into four groups: basiconic capitate peg sensilla, chaetica sensilla (types 1–5), placoid sensilla and trichoid sensilla. Chaetica sensilla type 5 were found only on the female antenna. These four groups of antennal sensilla probably function as proprioceptors, hygro- and thermo- mechanoreceptors or contact chemoreceptors. The receptors are involved in host examination, host discrimination, host recognition and host location by female and male T. elegans.

Functional characterization of a pheromone-binding protein from rice leaffolder Cnaphalocrocis medinalis in detecting pheromones and host plant volatiles.

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.

Antennal Sensillum Morphology and Electrophysiological Responses of Olfactory Receptor Neurons in Trichoid Sensilla of the Diamondback Moth (Lepidoptera: Plutellidae)

Abstract Plant chemical signals are important olfactory cues for the survival and reproduction of phytophagous insects. The diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae) is a Brassica spp. (Brassicales: Brassicaceae) specialist pest, with most of its life events occurring on Brassica spp. hosts. We conducted a scanning electron microscopy study on the morphology and distribution of antennal sensilla of male and female P. xylostella. Seven morphological types of sensilla were identified in the antennae of P. xylostella: 3 types of sensilla trichodea (Tr I, Tr II and Tr III), sensilla chaetica, sensilla coeloconica, sensilla auricillica and sensilla styloconica. One particular type of trichoid sensillum (Tr III) was present only in the males. The presence of numerous pores or deep longitudinal grooves on the surfaces of 5 morphological types of sensilla indicated that their major function is olfactory. Single sensillum recordings were also carried out on the trichoid sensilla of the fe...

Ultrastructural Morphology of the Antenna and Maxillary Palp of Sarcophaga tibialis (Diptera: Sarcophagidae).

A scanning electron microscopy investigation of the antenna and maxillary palp of the adult of Sarcophaga tibialis Macquart (Diptera: Sarcophagidae), a species of medical, veterinary, and forensic relevance, is presented for the first time. Adults of both sexes used in this study were obtained from larvae collected in a case of traumatic myiasis in a domestic cat in northern Italy. The antenna of S. tibialis is that typical of cyclorrhaphan Diptera, consisting of three segments: the scape, the pedicel, and the postpedicel, bearing the arista. The scape is covered by microtrichia and has a row of long chaetic sensilla. The pedicel is also covered by microtrichia and has three types of chaetic sensilla and a cluster of setiferous plaques. Trichoid, styloconic, clavate, and basiconic sensilla are distributed among the microtrichia on the postpedicel. Invaginated basiconic-like sensilla and olfactory pits are also present, the latter ones more numerous in the female. Our results are compared with those obtained for other calyptrate flies, mainly in the family Sarcophagidae. The data obtained may represent a basis for electrophysiological studies on the sensorial activity of the species related to the search for food sources, mates, and suitable larviposition sites, and for comparative morphological studies with other Diptera.

Morphology and Distribution of Antennal Sensilla of the Bean Bug Riptortus pedestris (Hemiptera: Alydidae).

The bean bug, Riptortus pedestris is a major pest of bean pods and some tree fruits in north-east Asian countries. Scanning electron microscopy was conducted to investigate the morphology and distribution of antennal sensilla of R. pedestris to help in understanding the sensory mechanisms of the bug. Average antennal lengths of male and female R. pedestris were 11.00 mm and 9.84 mm, respectively, consisting of four distinct segments, scape, pedicel, basiflagellum, and distiflagellum. Based on the gross appearance, the antennal sensilla were classified into four major types (trichodea, basiconica, chaetica, and coeloconica), which could be further classified into four trichoid, three basiconic, four chaotic, and two coeloconic subtypes, based on their size, tip shape, presence of socket, and surface structure. Among them, two subtypes of trichoid sensilla, all three subtypes of basiconic sensilla, four subtypes of chaetic sensilla and two subtypes of coeloconic sensilla had numerous pores along the surface, suggesting their olfactory function. Nine subtypes (2 trichoid, 1 basiconic, 4 chaetic, and 2 coeloconic subtypes) showed a distinct socket structure at the base. Among the four antennal segments, the distiflagellum possessed highest number of sensilla. Trichoid sensilla were most abundant, followed by basiconic, chaetic, and coeloconic sensilla. Each subtype of sensilla exhibited distinct distribution profile along the four antennal segments. Two subtypes of trichoid sensilla, one subtype of basiconic sensilla and one subtype of chaetica sensilla were distributed on scape, pedicel, and basiflagellum, whereas distribution of other subtypes of sensilla was confined to basiflagellum and distiflagellum. Microsc. Res. Tech. 79:501-511, 2016. © 2016 Wiley Periodicals, Inc.