Types Of Sensilla Research Articles

The Antennal Sensilla and Expression Patterns of Olfactory Genes in the Lower Termite Reticulitermes aculabialis (Isoptera: Rhinotermitidae).

The insect olfactory system plays pivotal roles in insect survival and reproduction through odor detection. Morphological and physiological adaptations are caste-specific and evolved independently in workers, soldiers, and reproductives in termites. However, it is unclear whether the olfactory system is involved in the division of labor in termite colonies. In the present study, the antennal sensilla of alates, workers, soldiers, nymphs, and larvae of the termite Reticulitermes aculabialis Tsai et Hwang ( Isoptera: Rhinotermitidae) were investigated. Transcriptomes were used to detect olfactory genes, and differential expression levels of olfactory genes were confirmed in various castes by qRT–PCR analysis. Nine types of sensilla were identified on the antennae of R. aculabialis, and soldiers possessed all 9 types. In 89,475 assembled unigenes, we found 16 olfactory genes, including 6 chemosensory protein (CSP) and 10 odorant-binding protein (OBP) genes. These OBP genes included 8 general odorant-binding protein genes (GOBPs) and 2 pheromone-binding protein-related protein (PBP) genes. Five CSP genes were more highly expressed in alates than in workers, soldiers, larvae, and nymphs, and the expression levels of CSP6 were significantly higher in nymphs. Seven GOBP and two PBP genes exhibited significantly higher expression levels in alates, and there were no significant differences in the expression levels of GOBP2 among workers, soldiers, alates, and larvae. These results suggest that alates, as primary reproductives, have unique expression patterns of olfactory genes, which play key roles in nuptial flight, mate seeking, and new colony foundation.

Ultrastructure of Antennal Sensory Organs in Nine Flesh Flies (Diptera: Sarcophagidae): New Insight into the Definition of Family Sarcophagidae

Simple SummaryThe antennal sensilla of species in all three subfamilies of Sarcophagidae are studied for the first time via scanning electron microscopy. The morphology, density, and distribution of each type are described for each species. A total of eight types of antennal sensilla (chaetic sensilla, setiferous plaques, pedicellar buttons, trichoid sensilla, basiconic sensilla, coeloconic sensilla, clavate sensilla, bottle-shaped sensilla) and sensory pits are found in both sexes. The existence of bottle-shaped sensilla in the sensory pits in all three subfamilies of the sarcophagid species suggests a potential synapomorphy of sarcophagids and a new morphological diagnosis character of the family Sarcophagidae.The antennae are the main olfactory organ of flies, playing key roles in their survival and the success of all life stages. Antennal ultrastructural morphology has been well described in the representative species of most calyptrate families, yet only a few studies have focused on Sarcophagidae species, those with ecological and medical relevance. Antennal morphology and the types, shapes, distribution, and density of the antennal sensilla of nine Sarcophagidae species are studied in detail with scanning electron microscopy, including Miltogramminae: Metopia campestris (Fallén) and Mesomelena mesomelaena (Loew), Paramacronychiinae: Agria mihalyii (Rohdendorf & Verves), Wohlfahrtia bella (Macquart), and W. magnifica (Schiner); Sarcophaginae: Sarcophaga (Parasarcophaga) albiceps Meigen, S. (Bercaea) africa (Wiedemann), S. (Boettcherisca) peregrina (Robineau-Desvoidy), and S. (Liosarcophaga) portschinskyi (Rohdendorf), covering all three subfamilies of this family. The morphology of the three segments of the antennae has been described. The scape has only one type of chaetic sensilla, while three subtypes of chaetic sensilla were detected on the pedicel. The postpedicel has four types of sensilla: trichoid sensilla, coeloconic sensilla, clavate sensilla, and three subtypes of basiconic sensilla. Bottle-shaped sensilla were observed in sensory pits on the postpedicel in all nine species. These sensilla have not been discovered in other calyptrate species, suggesting that they are a potential sarcophagid synapomorphy.

The Sensilla-Specific Expression and Subcellular Localization of SNMP1 and SNMP2 Reveal Novel Insights into Their Roles in the Antenna of the Desert Locust Schistocerca gregaria.

Simple SummaryThe desert locust, Schistocerca gregaria, can form gigantic swarms of millions of individuals that devastate the vegetation of invaded landscapes. Locust food search, reproduction, and aggregation behaviors are triggered and controlled by complex olfactory signals. Insects detect odorants through different types of olfactory sensilla on the antenna that house olfactory sensory neurons and associated support cells, both of which express the proteins required for olfactory signaling. Among these proteins, two members of the CD36 lipid transporter/receptor family, named sensory neuron membrane proteins 1 and 2 (SNMP1 and SNMP2), are indicated to be of vital importance. Towards a better understanding of the role of the two SNMPs in the olfactory system of S. gregaria, we have analysed their antennal topography and subcellular localization using specific antibodies. The results indicate sensilla type- and cell type-specific distribution patterns of the SNMP proteins. SNMP1 was located in the receptive dendrites of subpopulations of olfactory sensory neurons as well as in the microvilli of associated support cells, suggesting a dual function of this protein, both in olfactory signal detection and in sensillum lymph maintenance, respectively. In contrast, SNMP2 was found solely in support cells and their microvilli membranes, suggesting a role limited to sensillum lymph recovery processes. Insect olfactory sensilla house olfactory sensory neurons (OSNs) and supports cells (SCs). The olfactory sensory processes require, besides the odorant receptors (ORs), insect-specific members of the CD36 family, named sensory neuron membrane proteins (SNMPs). While SNMP1 is considered to act as a coreceptor in the OR-mediated detection of pheromones, SNMP2 was found to be expressed in SCs; however, its function is unknown. For the desert locust, Schistocerca gregaria, we previously visualized mRNA for SNMP1 in OSNs and SNMP2 mRNA in cells associated with OSN clusters. Towards an understanding of their functional implication, it is imperative to explore the cellular and the subcellular localization the SNMP proteins. Therefore, we have generated polyclonal antibodies against SNMP1 and SNMP2 and used fluorescence immunohistochemistry (FIHC) to visualize the SNMP proteins. We found SNMP1 in the somata and respective dendrites of all OSNs in trichoid sensilla and in subsets of OSNs in basiconic sensilla. Notably, SNMP1 was also detected in SCs of these sensilla types. In contrast, SNMP2 protein was only visualized in SCs of basiconic and coeloconic sensilla, but not of trichoid sensilla. Exploring the subcellular localization by electron microscopy using anti-SNMP1-ab and anti-SNMP2-ab revealed an immunogold labelling of SC microvilli bordering the sensillum lymph. Together our findings suggest a dual role of SNMP1 in the antenna of S. gregaria, in some OSN subpopulations in odor detection as well as in functions of some SCs, whereas the role of SNMP2 is limited to the functions of support cells.

Comparative morphology of part of the integumental fine structure of two Erythroneurine species: Singaporashinshana (Matsumura, 1932) and Empoascanarasipra Dworakowska, 1980 (Hemiptera, Cicadellidae, Typhlocybinae).

This study describes the fine structure of the mouthparts, antennae, forewings, and brochosomes of two leafhopper species belonging to the typhlocybine tribe Erythroneurini collected from the Karst area of Guizhou Province, southern China: Singaporashinshana, which prefers woody dicot hosts, and Empoascanarasipra, which feeds on grasses. As in other leafhoppers, the piercing-sucking mouthparts consist of a conical labrum, a cylindrical three-segmented labium, and a slender stylet fascicle. The labrum of both species has no sensilla and the labium has several common types of sensilla, but the two species differ in the numbers, types, and distribution of sensilla and in other aspects of the surface sculpture of the mouthparts. The stylet fascicle has distinctive dentition on both the maxillary and mandibular stylets. The antennae of the two species differ in several respects, including the sensilla and sculpture of the scape, pedicel, and flagellum, as well as the degree of sub-segmentation of the flagellum. Except for the variable scaly structure and rounded protrusions on the surface of S.shinshana, the fine structure of the forewing surfaces of the two species are similar to those of other leafhoppers. Only small spherical brochosomes were found on the body surface of S.shinshana and E.sipra. Similar studies of additional erythroneurine species are needed to determine whether differences in mouthpart and antennal fine structure may reflect adaptation to different host plant.

Ultrastructure of sensilla on the antennae and maxillary palpi of the human-biting black flies, Simulium nigrogilvum and Simulium umphangense, (Diptera: Simuliidae) in Thailand

Antennae and maxillary palpi are the most important sensory organs involved in the behaviors of black flies. The ultrastructure of sensilla on these sensory appendages of two human-biting black fly species, Similium nigrogilvum and Simulium umphangense, was studied for the first time. Wild adult females of both species were collected in Umphang District, Tak Province, western Thailand. The morphology and distribution of sensilla were examined using scanning electron microscopy. Overall, the morphology of the antennae and maxillary palpi and distribution of sensilla are similar in the two species. Four major types of sensilla were found on the antennae of both species: sensilla basiconica (three subtypes), coeloconica, chaetica (four subtypes), and trichodea. However, sensilla basiconica subtype IV are only present on the antennal surface of S. nigrogilvum. Sensilla trichodea are the most abundant among the four types of sensilla that occur on the antennae of both species. Significant differences in the length of the antennae (scape and flagellomere IX), length of the maxillary palpi (whole and palpal segments I, III, IV and V), and the length and basal width of four sensilla types (trichodea, chaetica, basiconica, and coeloconica) were found. In addition, two types of sensilla were observed on the maxillary palpi: sensilla chaetica (three subtypes) and bulb-shaped sensilla. Differences were observed in the numbers of bulb-shaped sensilla in the sensory vesicles of S. nigrogilvum and S. umphangense. The findings are compared with the sensilla of other insects, and the probable functions of each sensillum type are discussed. The anatomical data on sensory organs derived from this study will help to better understand black fly behavior.

Functional Morphology of Sensory Organs of the House Cricket, Acheta domesticus (L.): A Morphological and Physiological Investigation

Insects have paired antennae that bear many sensory organs or sensilla. These sensilla allow them to gather information about olfactory, gustatory, and mechanosensory environmental cues. Both antennae of male and female house crickets, Acheta domesticus, bear approximately 200 segments. The first aim of this study was to morphologically characterize the sensillum types on the antennae. Scanning and transmission electron microscopy studies revealed that each antennal segment bears seven sensillum types. Four types have external morphological features suggestive of olfactory sensilla, namely an abundance of cuticular pores. Two of these types resemble short to medium‐sized pegs, a third resembles a short peg with longitudinal ridges or “fingers,” while a fourth resembles a short peg recessed in a deep pit. Each antenna also bears two sensillum types devoid of external cuticular pores, suggestive of a mechanosensory function. One of these types is a long hair‐like sensillum with conspicuous ridges, while the other is a small circular depression on the antennal surface. Another medium‐sized sensillum bears diagonal circular ridges and a single apical pore, indicative of a gustatory function.The second aim of this study was to determine which odorants elicited positive or negative anemotaxis (orientation toward or away from a food source, respectively), suggestive of possible food lures or repellents. Odorants permeate through the environment and bind to receptor sites in olfactory neurons. Once these molecules bind, chemical signals are converted to electrical ones. Olfactory signals are then transmitted to higher‐order olfactory processing centers in the insect’s brain. Depending on the odorant, this may trigger a behavioral response(s). Odorants may be used to detect and identify food, mating partners, and avoidance of predators. Previous studies in the lab have focused on odorants associated with some fruits, vegetables, and proteins. In this study, we tested some odorants associated with amines derived from ammonia. We hypothesized that such odorants would elicit negative anemotaxis. We carried out each experiment over a 24‐hour period in plastic bins. We found that the crickets elicited positive anemotaxis to the odorants tested, leading us to reject our hypothesis. These findings are important as house crickets are pests and known to contaminate food sources. This finding raises concerns about foodborne illnesses associated with microbial pathogens and can create health concerns especially in developing countries. The results of this study may prove to be helpful in the suggestion of lures as effective biocontrol measures against pests.

Antennal Sensilla in Vespidae: A Comparison Between a Diurnal and a Nocturnal Polistinae Wasp.

Social wasps have a widespread Neotropical distribution and are important pollinators and biological control agents for pest insects. The foraging activity of wasps is influenced by biotic and abiotic factors that are detected by the antennal sensilla that vary according to species, sex, caste, and environmental conditions. This study compares the types and quantities of antennal sensilla with a scanning electron microscope between the nocturnal Apoica flavissima and the diurnal Polistes simillimus wasps. Six types of sensilla were found in the antennae of both species: placoid, coeloconic, basiconic-type 1, basiconic-type 2, trichoid-type 1, and trichoid-type 2. Sensilla chaetica were found only in the scape and pedicel of A. flavissima. In the nocturnal wasp, there are 19,132.27 ± 1,247.72 sensilla in the left and 17,746.46 ± 1,477.46 in the right antennae, whereas in the diurnal wasp 14,936.72 ± 1,271.69 in the left and 16,090.82 ± 1,345.3 in the right antennae. A. flavissima has a longer antennal length and number of sensilla than P. simillimus. The higher number of antennal sensilla in the nocturnal wasp is not linked with the antennal size. The association of antennal sensilla functions with ecological and behavioral factors of A. flavissima and P. simillimus are discussed.

The mouthparts and sensilla of the adult tomato leafminer moth, Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae)

In this study, investigation of the morphology and distribution of mouthpart sensilla in the adult tomato leafminer moth, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae), using a scanning electron microscope (SEM) is performed. SEM studies examining the mouthparts of Gelechiidae have been noted to be rare; moreover, there have been few investigations on the sensory structures of adult T. absoluta, despite the fact that it is an important pest. In adult T. absoluta, mouthpart structures include the labrum, maxillae comprising two maxillary galeae that form a proboscis, two maxillary palps, and two labial palps. Mandibles were not observed in all studied specimens (30 adults). The proboscis resembles that in other lepidopterous insects and is 1.48 ± 0.08 mm long. Its outer surface is covered with lamellar scales, dense microtrichia, and four sensillum types, that are, aporous sensilla chaetica, uniporous sensilla chaetica, uniporous sensilla styloconica, and aporous sensilla squamiformia. Uniporous sensilla basiconica were also found on the internal face of the proboscis. The labial palps are three-segmented and are known to bear three types of sensilla: squamiformia (present on all three segments), campaniformia, and coeloconica. In this study, we focus on the functional importance of the morphology and distribution of sensilla campaniformia on these labial palps.

Characterization of Antennal Chemosensilla and Associated Chemosensory Genes in the Orange Spiny Whitefly, Aleurocanthus spiniferus (Quaintanca).

The insect chemosensory system plays an important role in many aspects of insects’ behaviors necessary for their survival. Despite the complexity of this system, an increasing number of studies have begun to understand its structure and function in different insect species. Nonetheless, the chemosensory system in the orange spiny whitefly Aleurocanthus spiniferus, as one of the most destructive insect pests of citrus in tropical Asia, has not been investigated yet. In this study, the sensillum types, morphologies and distributions of the male and female antennae of A. spiniferus were characterized using scanning electron microscopy. In both sexes, six different sensilla types were observed: trichodea sensilla, chaetica sensilla, microtrichia sensilla, coeloconic sensilla, basiconic sensilla, and finger-like sensilla. Moreover, we identified a total of 48 chemosensory genes, including 5 odorant-binding proteins (OBPs), 12 chemosensory proteins (CSPs), 3 sensory neuron membrane proteins (SNMPs), 6 odorant receptors (ORs), 8 gustatory receptors (GRs), and 14 ionotropic receptors (IRs) using transcriptome data analysis. Tissue-specific transcriptome analysis of these genes showed predominantly expression in the head (including antennae), whereas CSPs were broadly expressed in both head (including the antennae) and body tissue of adult A. spiniferus. In addition, the expression profiling of selected chemosensory genes at different developmental stages was examined by quantitative real time-PCR which was mapped to the transcriptome. We found that the majority of these genes were highly expressed in adults, while AspiORco, AspiGR1, AspiGR2, and AspiIR4 genes were only detected in the pupal stage. Together, this study provides a basis for future chemosensory and genomic studies in A. spiniferus and closely related species. Furthermore, this study not only provides insights for further research on the molecular mechanisms of A. spiniferus-plant interactions but also provides extensive potential targets for pest control.

Functional analysis of pheromone receptor repertoire in the fall armyworm, Spodoptera frugiperda.

The fall armyworm, Spodoptera frugiperda (J. E. Smith), is a polyphagous moth species that is spreading all around the globe. It uses (Z)-9-tetradecenyl acetate (Z9-14:Ac) and (Z)-7-dodecenyl acetate (Z7-12:Ac) (100:3.9) as essential sex pheromone components. However, our understanding of the molecular basis of pheromone detection of S. frugiperda is still incomplete. Herein, we identified six PRs, i.e. SfruOR6, 11, 13, 16, 56, and 62, by transcriptome sequencing. Subsequently, we heterologously expressed them in Drosophila OR67d neurons and determined their response spectra with a large panel of sex pheromones and analogs. Among them, SfruOR13-expressing neurons strongly respond to the major sex pheromone component Z9-14:Ac, but also comparably to (Z,E)-9,12-tetradecadienyl acetate (Z9,E12-14:Ac) and weakly to (Z)-9-dodecenyl acetate (Z9-12:Ac). Both SfruOR56 and SfruOR62 are specifically tuned to the minor sex pheromone component Z7-12:Ac with varying intensities and sensitivities. In addition, SfruOR6 is activated only by Z9,E12-14:Ac, and SfruOR16 by both (Z)-9-tetradecenol (Z9-14:OH) and (Z)-9-tetradecenal (Z9-14:Ald). However, the OR67d neurons expressing SfruOR11 remain silent to all compounds tested, a phenomenon commonly found in the OR11 clade of Noctuidae species. Next, using single sensillum recording, we characterized four sensilla types on the antennae of males, namely A, B, C and D types that are tuned to the ligands of PRs, thereby confirming that S. frugiperda uses both SfruOR56 and SfruOR62 to detect Z7-12:Ac. Finally, using wind tunnel assay, we demonstrate that both Z9,E12-14:Ac and Z9-14:OH act as antagonists to the sex pheromone. We have deorphanized five PRs and characterized four types of sensilla responsible for the detection of pheromone compounds, providing insights into the peripheral encoding of sex pheromones in S. frugiperda.

Morphological characterization and sexual dimorphism of the antennal sensilla in Bactericera gobica Loginova (Hemiptera: Psyllidae)-a scanning and transmission electron microscopic study.

Bactericera gobica is the major pest of Goji berry plants and causes severe damage. Psyllids mainly use the antennal sensilla to recognize olfactory cues necessary to find host plants and mates. However, the structure and function of the antenna and the antennal sensilla of B. gobica remains previously unexplored. Here, we identify the external and internal morphology of the antennal sensilla of B. gobica using both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). We found seven types of sensilla on the filiform antennae, including apical setae (LAS, SAS), sensilla basiconica (SB1, SB2), sensilla campaniform (SCA), sensilla chaetica (ChS1, ChS2), cavity sensilla (CvS1, CvS2), antennal rhinaria (AR1, AR2), and sensilla trichodea (ST). Five of these sensilla types—apical setae, sensilla basiconica, sensilla chaetica, cavity sensilla, and antennal rhinaria—may have olfactory functions based on their porous surfaces and internal dendritic outer segments (DOS). We also found several differences between the two sexes of B. gobica in the sensilla array and internal structure. ChS and DOS in the protrusions of AR were more abundant in males than females. Altogether, we comprehensively revealed the fine structure and probable function of B. gobica antennae and identified differences in the distribution and structure between psyllid sexes. Our findings provide important insights for future studies on defining the olfactory function of psyllid antenna using electrophysiological methods.

Scanning Electron Microscopic Analysis of Antennal Sensilla and Tissue-Expression Profiles of Chemosensory Protein Genes in Ophraella communa (Coleoptera: Chrysomelidae).

Simple SummaryLeaf beetle Ophraella communa is considered an effective biocontrol agent against the common ragweed Ambrosia artemisiifolia. However, there are no studies that assess the antennal sensilla and chemosensory proteins expression profiles of O. communa. In this study, the types and morphology of sensilla on the antennae were examined by scanning electron microscopy (SEM). The results showed that there are six types of sensilla (sensilla trichodea, sensilla chaetica, sensilla basiconica, sensilla styloconica, sensilla coeloconica, and Böhm bristles) distributed on the antennae. We also found that the expression levels of five chemosensory proteins in male and female antennae were higher than those in other tissues by quantitative real-time polymerase chain reaction. Our results lay the foundation for interpreting the olfactory functions of adult O. communa.Ophraella communa is an efficient biocontrol agent used against the invasive weed Ambrosia artemisiifolia. It is an herbivorous insect that feeds on specific plants; the olfactory functions of this insects plays an important role in their search for host plants. There are no reports on O. communa sensilla types, morphology, or chemosensory protein (CSP) genes. In this study, we observed the external structure and distribution of antennal sensilla in adult O. communa antennae by scanning electron microscopy; moreover, we cloned 11 CSPs (CSP1–CSP11) and elucidated their tissue-expression profiles using quantitative real-time polymerase chain reaction. Six types of sensilla were identified: sensilla trichodea (including two subtypes), sensilla chaetica, sensilla basiconica (including two subtypes), sensilla styloconica, sensilla coeloconica, and Böhm bristles. Both male and female antennae had all six types of sensilla, and no sexual dimorphism was noted in sensillar types or distribution. We also found that the expression levels of CSP2, CSP3, CSP4, CSP6, and CSP7 in male and female antennae were higher than those in other tissues, which suggests that these five CSPs may be related to olfactory function in O. communa. Ultimately, our results lay the foundation for interpreting the olfactory functions of adult O. communa.

Sensilla of the Western Flower Thrips, Frankliniella occidentalis (Pergande) (Thysanoptera, Thripidae)

The sensilla of insects play important roles in odor, taste, the feeling environment, and some sensory functions, which are closely associated with insect host locating, feeding, habitat searching, courtship, mating, and oviposition. In this study, we used a scanning electron microscope to observe the external morphology of nymph and adult Frankliniella occidentalis sensilla on antennae, compound eyes, legs, mouthparts, wings and tail. The results show that three main types of sensilla are located on the antennae: sensilla trichodea, sensilla chaetica, and sensilla basiconica. Among them, sensilla trichodea are the most abundant, followed by sensilla chaetica. Sensilla basiconica on antennae are divided into seven sub-styles, including longer sensilla (L-sensilla basiconica, long sensilla basiconica), shorter sensilla (angle sensilla basiconica, bud sensilla basiconica), and thicker and bigger sensilla (stick sensilla basiconica, fork sensilla basiconica, and finger sensilla basiconica). Only two fork sensilla basiconica were found, located on the dorsal part of the first flagellum subsegment and the ventral part of the second flagellum subsegment, respectively. Seven sensillum types were found on the legs: sensilla trichodea, sensilla chaetica, sensilla basiconica, sensilla ear washing buob-shaped, mamillary sensilla, sensilla campaniform, and Böhm bristle. About 60% of them are sensilla chaetica. Only one sensillum type was found on compound eyes: sensilla chaetica. In addition, some sensillum types were also found on the mouthparts, wings and tail, respectively. In the study, we observed the type, morphology, and distribution of sensilla on antennae, legs, compound eyes, and other regions of nymph and adult F. occidentalis, forming a base for future electrophysiological and behavior experiments on F. occidentalis.

Scanning electron microscopy of cuticular sensory structures on the legs of Micronecta haliploides (Horvath, 1904) and Hydrometra greeni (Kirkaldy, 1898) (Hemiptera: Heteroptera)

Structures on the legs of two hemipteran bugs, Micronecta haliploides (Horvath, 1904) and Hydrometra greeni (Kirkaldy, 1898), belonging to family Micronectidae and Hydrometridae of two infra orders Nepomorpha and Gerromorpha, respectively were investigated using scanning electron microscopy. Both species have a distinctive leg structure bearing specialised cuticular sensory structures. In the study, the sensilla were classified into five basic types: sensilla trichoidea, sensilla basiconidea, sensilla placoidea, porous circular sensilla and sensilla bell mouthed. These sensilla were further differentiated on the basis of shape, size, number, flexibility and type of socket attached. A total of 26 types of sensilla in the legs of these two species were observed. M. haliploides showed 18 types of sensory structures and H. greeni 8 types. A specific morphological structure of the porous circular sensilla was observed and found to be unique.

Diversity and distribution patterns of antennal sensilla in Hydropsychidae (Insecta, Trichoptera)

Structure and distribution of antennal sensilla were studied in males of 19 species of the caddisfly family Hydropsychidae by using scanning electron microscopy (SEM). Eleven types of sensilla were found: long trichoid, chaetoid, thick chaetoid, curved trichoid, coronary, basiconic, styloconic and four types of pseudoplacoid sensilla (mushroom-like, auricillic, ribbed, and T-shaped). Thick chaetoid, ribbed pseudoplacoid, and T-shaped pseudoplacoid sensilla were found only in Macronematinae. The great diversity of pseudoplacoid sensilla originated from a mushroom-like type, which also has a variable structure. Basal flagellomeres in the majority of studied species are equipped with ventrally positioned sensory fields of curved trichoid sensilla. In contrast to Arctopsychinae and Hydropsychinae, the increased number of these sensilla in the fields was noted for Diplectroninae and Smicrideinae. Most Macronematinae show a reduction of sensory fields and a strongly decreased average number of curved trichoid sensilla on distal segments. The great differences found in the studied family probably indicate a rapid function-related evolution of the antennal sensory surface structures in the caddisfly family Hydropsychidae.

Ultrastructure of the Sensilla on the Antennae and Mouthparts of Bean Weevils, Megabruchidius dorsalis (Coleoptera: Bruchinae).

Simple SummaryIn this paper, we used scanning electron microscopy (SEM) to describe the morphological types, number of sensilla, and their distributions on the antennae and mouthparts of both sexes of the bean weevil, Megabruchidius dorsalis (Coleoptera: Bruchinae). The results showed twelve subtypes on antennal sensilla and five types of sensilla on maxillary and labial palps. No sexual dimorphism in sensilla type was observed, but there were variations between male and female in the numbers and distribution along with the antennae. In addition, we discussed potential function related to structure, through comparisons with previous studies of bruchids and other insects. This information will support further studies of semiochemicals as effective biological controls of this pest.Megabruchidius dorsalis (Fåhraeus, 1839) (Coleoptera: Bruchinae) is an important pest that damages the seeds of Gleditsia L. (Fabaceae: Caesalpinioideae). This beetle searches for host plants with its sensory system. To further explore the mechanisms of host location and to understand the ultrastructure of M. dorsalis, we examined the morphology and distribution of its sensilla on the antennae and mouthparts of male and female adults, using scanning electron microscopy (SEM). Both male and female antennae are serrated and can be divided into scape, pedicel, and flagellum. There were seven types and eight subtypes of antennal sensilla, including Bőhm bristles (BB), two subtypes of sensilla trichoid (ST1, ST2), two subtypes of sensilla chaetica (SC1, SC2), four subtypes of sensilla basiconic (SB1, SB2, SB3, SB4), sensilla cavity (SCa), sensilla auricillica (SA), and sensilla gemmiformium (SG). Five types of maxillary and labial palp sensilla in the mouthparts were observed: sensilla chaetica (SC), sensilla trichoidea (ST), sensilla styloconica (SSt), sensilla coeloconica (SCo), and sensilla digitiform (SD). No sexual dimorphism in sensilla type was observed, but there were variations between males and females in the numbers and distribution along the antennae. There were more SA in males than in females, while the number of ST sensilla in the maxillary palps were lower in males than in females. ST1 were most abundant in both sexes. We discussed potential function related to structure via comparisons with previous investigations of bruchids and other insects. Our results provide a theoretical basis for further studies on sensory physiological function, using semiochemicals as effective biological controls of M. dorsalis.

Structure and distribution of antennal sensilla in Pseudosymmachia flavescens (Brenske) (Coleoptera: Scarabaeidae: Melolonthinae).

Morphology, microstructure, and distribution of antennal sensilla were compared between female and male Pseudosymmachia flavescens (Brenske) (Coleoptera: Scarabaeidae: Melolonthinae). Lamellate antennae of P. flavescens were shown to have typical scape, pedicel, and flagellum segments. The flagellum consists of a four-segmented funicle and a three-segmented club. The lengths of their pedicel and funicle were found to be similar in females and males. Distinct sexual differences were observed in the length of lamellar segments. Nine types/subtypes of sensilla were identified on the antennae of both sexes, including Böhm sensilla, sensilla trichodea, sensilla basiconica (SB), and two subtypes for sensilla chaetica, sensilla coeloconica, and sensilla placodea each. Olfactory sensilla (e.g., SB and placodea) are mainly located on three lamellar segments of the antennal club. Variation was also seen in abundance of various types of antennal sensilla, with males possessing significantly more sensilla than females. Sensilla placodea were the most abundant, and their number in males was twice of that in females, showing a clear sexual dimorphism. The difference in the distribution of sensilla placodea might reflect their roles in sexual chemical communication.

Antennal morphology and sensilla of the predaceous ladybirds, Menochilus sexmaculatus and Propylea dissecta

Menochilus sexmaculatus and Propylea dissecta (Coleoptera: Coccinellidae) are predaceous ladybird beetles with immense biological control potential. The morphology of the antennae of the adults along with the diversity and distribution of sensilla were investigated using a scanning electron microscope as they are the main sensory organs involved in chemical communication, thermo-reception, materecognition, gustation, etc. The antennae of males and females in both species were clavate and consisted of three parts: scape, pedicel and a 9-segmented flagellum. The antennae of male and female P. dissecta were significantly longer than those of M. sexmaculatus despite their overall body size being smaller, probably due to the much longer F9 flagellomere in P. dissecta. Antennae of female ladybirds of both species exhibited sexual dimorphism in being longer than those of males. Scape was longer than other antennal parts in both species of ladybirds. There was a great diversity of sensilla with most of them on the ninth-flagellomere. We identified nine types of sensillum: chaetica, trichoidea, basiconica, Bohm bristles, campaniformia, placoidea, coeloconica, sporangia and styloconica. Coeloconica were restricted to flagellomere F8 in male P. dissecta and female M. sexmaculatus, respectively, indicating sexual dimorphism and male-related functions of this sensillum.

Morphology and distribution of antennal sensilla in adults of Xylotrechus quadripes.

Xylotrechus quadripes (Chevrolat) is the serious woodborer pest of arabica coffee (Coffea arabica L.). To further elucidate the behavior mechanism of the insect based on chemical odorant and to advance effective trapping methods, the typology, distribution, and abundance of antennal sensilla were investigated meticulously in both sexes of X. quadripes by scanning electron microscopy. The filiform antennae of both sexes are composed of 11 segments, namely the scape, pedicel, and nine flagellomeres (f1-9). Ten types (14 subtypes) of sensilla were identified morphologically: sensilla chaetica (three subtypes, Ch.1-3), sensilla basiconica (three subtypes, Ba.1-3), Böhm bristles (Bb), sensilla dentiform (De), sensilla trichodea (Tr), sensilla auricillica (Au), sensilla campaniformia (Ca), grooved peg sensilla (Gp), cuticular pores (Cp), and a newly observed sensillum, named sensilla cone (Cone). The sensilla were mainly distributed in flagellomeres, and the types and amounts increased in frequency from scape to the ninth flagellomere. The numbers of sensilla were the highest on the antennal dorsal side, while the lowest on the ventral side. The types of sensilla were the most abundant on the lateral side, and two sensilla basiconica (Ba.1-2) were found exclusively. The average number of Tr, Ba, and Au on the antenna of the males was significantly greater than females, while the Gp and Cp on the antenna of the females were significantly greater than males. Ca was exclusively occurred on the male antennae but was absent in females. This study discusses the putative functions of the antennal sensilla in adults of X. quadripes based on their characteristics in related species' sensilla, and these results provide an important foundation to clarify the ecological adaption, olfactory recognition mechanism, and to develop the chemical ecology control of X. quadripes.

Sexual dimorphism of antennal and ovipositor sensilla of Tetrastichus sp. (Hymenoptera: Eulophidae)

• Sensilla on antenna and ovipositor of Tetrastichus sp. were investigated. • Tetrastichus sp. has eight types of antennal sensilla and four types of ovipositor sensilla. • Types and distribution of antennal and ovipositor sensilla were discussed. • Tetrastichus sp. exhibits sexual dimorphism in the profiles of the antennal sensilla. Tetrastichus sp. (Hymenoptera: Eulophidae) is a primary parasitoid of the Metisa plana (Lepidoptera: Psychidae), an oil palm bagworm. The sensilla on the surface of the antenna and ovipositor of Tetrastichus sp. were examined using a scanning electron microscope. The antennae of both male and female Tetrastichus sp. are geniculate in shape and hinged at the scape-pedicel joint. The female antenna is about 200 µm longer than the male antenna. However, the male antenna has an additional flagellomere compared to the female antenna. In total, eight different types of antennal sensilla were observed on the antenna of Tetrastichus sp.: trichoid sensilla type 1, 2, 3, 4, placoid sensilla type 1 and 2, basiconic sensilla, and campaniform sensilla. The antenna of the female Tetrastichus sp. lacks placoid sensilla type 2 and campaniform sensilla. The distribution and abundance of the antennal sensilla were compared between the male and female Tetrastichus sp. and discussed. On the ovipositor stylet of Tetrastichus sp., coeloconic sensilla, styloconic sensilla and campaniform sensilla were observed. Trichoid sensilla were observed at the medial part of the distal extremity of the ovipositor.