Types Of Sensilla Research Articles

Morphology of the Mouthparts of Ladybeetle Vibidia duodecimguttata (Coleoptera: Coccinellidae), with Emphasis on Their Sensilla

Mouthparts are the feeding organs of insects, which play vital roles in the feeding process. The morphology of insect mouthparts has greatly evolved according to different foods and feeding habits. Therefore, studying the structure of the mouthparts is the key to understanding their feeding mechanisms. Vibidia duodecimguttata is an important biological control agent for powdery fungus. In this study, the fine morphology of the mouthpart of V. duodecimguttata was studied by scanning electron microscopy. The basic components of mouthpart of V. duodecimguttata are similar to those of other ladybeetles, while the specific morphology of each part is different. In total, six kinds of sensilla were identified on mouthpart, and twelve types of sensilla were divided according to their morphology, length and distribution. In addition, two kinds of glandular structures were also found, namely perforated plates and cuticular pores. Finally, the morphological differences between mycetophagous and other feeding habits ladybeetles were compared, and the function of each kind of sensilla was discussed, which may establish a solid foundation for further understanding of the feeding mechanism of ladybirds.

Morphology and distribution of antennal sensilla of Plautia stali (Hemiptera: Pentatomidae)

AbstractIn this study, the morphology and distribution of antennal sensilla of male and female adults of Plautia stali were investigated using scanning electron microscopy. In both sexes, the antennae of P. stali were composed of a scape, two‐segmented pedicels (P1 and P2) and two‐segmented flagellomeres (F1 and F2). There were no differences in the overall length and shape between males and females. Four basic types of sensilla (s. trichodea, s. basiconica, s. chaetica and s. coeloconica) were identified in each sex. Sensilla basiconica and s. chaetica were further divided into four and two subtypes, respectively. Among the sensilla, s. trichodea and s. basiconica subtype 4 were multiporous, indicating that these two types are involved in olfactory functions. There was an apical pore on the tip of s. basiconica subtypes 2 and 3, suggesting that they have contact chemosensory function. There was no pore on the cuticular surface of the other types of sensilla, suggesting that these types may be mechano‐, thermo‐ or hygroreceptors. Sexual dimorphism was not evident in the distribution of the four types of sensilla, although there were variations in the number and distribution of sensilla along with the antennae in both sexes. This study reveals information regarding the sensory function of each type of sensillum in P. stali.

Scanning of antennae and maxillary palps of anthropophilic Aedes aegypti and ornithophilic Culex pipiens as potential arbovirus vectors

Background and Aim: Efficient mosquito vectors are required to persist and propagate arthropod-borne diseases that seriously affect impoverished populations worldwide. Mosquito sensilla plays a crucial role in host-seeking and disease transmission to humans. This study aimed to distinguish between the several types of sensilla found on the antennae and maxillary palps of Culex pipiens and Aedes aegypti, matching this diversity with host preference and disease transmission. Materials and Methods: Overall, 1300 mosquitoes were collected and examined using dissection and light microscopy. Scanning electron microscopy was used to identify and describe the diverse types of sensilla found on the antennae and maxillary palps of C. pipiens and A. aegypti. Results: In total, 900 C. pipiens and 400 A. aegypti mosquitoes were identified. The antennae and maxillary palps of C. pipiens and A. aegypti carry both sensilla trichoidea and sensilla chaetica. The C. pipiens antenna has long and short grooved peg sensilla, whereas A. aegypti lacks long pegs and expresses only occasional short pegs. The maxillary palps express Capitate pegs in both mosquito species and exclusively show sensilla campaniform in A. aegypti. Conclusion: The lack of long-grooved pegs and the presence of few short pegs, along with campaniform sensilla, limit the host range of A. aegypti and reduce its susceptibility to many infections, unlike C. pipiens. Keywords: Aedes aegypti, Culex pipiens, Scanning electron microscopy, Sensilla.

The Ultramorphology and Sexual Dimorphism of Antennae and Sensilla in the Pale Grass Blue, Pseudozizeeria maha (Lepidoptera: Lycaenidae).

The pale grass blue, Pseudozizeeria maha, is a small lycaenid butterfly widely distributed across Asia. Due to its exclusively diurnal lifestyle and conspicuous sexual dimorphism in wing coloration, vision has traditionally been regarded as the primary sensory system driving various behaviors. However, non-visual sensory systems related to sex-specific behavioral responses, such as antennae, have received far less attention. This study investigated the morphological characteristics and sensilla types of the antennae in adult P. maha using scanning electron microscopy, with a focus on potential sexual dimorphism. The antennae of adult P. maha are clavate, with no significant sexual differences in overall morphology. Six types of antennal sensilla were identified: Böhm bristles, sensilla squamiformia, sensilla trichodea, sensilla chaetica, sensilla basiconica, and sensilla coeloconica, with no sexual dimorphism observed in their morphological types or dimensions. Remarkably, the sensilla coeloconica exhibit significant sexual dimorphism, with a more prominent presence in females. This finding suggests that female P. maha may rely more on olfactory cues for some sex-specific behaviors, such as oviposition site selection.

An Examination of the Antennal Sensilla of the Oligophagous Moth Species Dioryctria sylvestrella (Lepidoptera: Pyralidae)

Dioryctria sylvestrella (Lepidoptera: Pyralidae) is a destructive borer pest on Korean pine (Pinus koraiensis) indigenous to northeastern China. The antennal sensilla of D. sylvestrella were examined by scanning electron microscopy to understand the behavioral ecology of this insect pest. Both the male and female antennae are filiform, and each consists of a scape, a pedicel, and a flagellum. D. sylvestrella is characterized by sexual dimorphism. Only the male antennae present two deeply grooved thumblike protuberances on the crest surfaces of their fourth and fifth flagellomeres, respectively. These structures have never been reported for any other Pyralidae. Eight different types of sensilla with unique bioecological functions were detected on the antennae of both sexes. There may be structure–location–function relationships for these sensilla, and most of them are involved in communication between the insect and the host plant, mate detection, and oviposition site selection.

Functional Characterization of Peripheral Neurons and a Receptor Recognizing Sex Pheromones in Hyphantria cunea (Erebidae).

Hyphantria cunea (Lepidoptera: Erebidae) is difficult and costly to control as a quarantine pest found globally. Sex pheromone trapping is an effective measure for its population monitoring and control; however, the peripheral neural mechanism of sex pheromone recognition in H. cunea remains unclear. An electrophysiological analysis showed that both male and female moths of H. cunea responded to four components of sex pheromones and the responses of male moths were stronger than those of the female moths. We identified three types of trichoid sensilla (ST) responsive to sex pheromones using the single sensillum recording technique. Each type was involved in recognizing 9R, 10S-epoxy-1, Z3, Z6-heneicosatriene (1, Z3, Z6-9S, 10R-epoxy-21Hy). Four peripheral neurons involved in the olfactory encoding of sex pheromones were identified. Four candidate pheromone receptor (PR) genes, HcunPR1a, HcunPR1b, HcunPR3, and HcunPR4, were screened by transcriptome sequencing. All of them were highly expressed in the antennae of males, except for HcunPR4, which was highly expressed in the antennae of females. Functional identification showed that HcunPR1a responded to sex pheromone. Other HcunPRs were not functionally identified. In summary, neurons involved in sex pheromone recognition of H. cunea were located in the ST, and HcunPR1a recognized secondary pheromone components 1, Z3, Z6-9S, 10R-epoxy-21Hy. Interestingly, PRs that recognize the main components of the sex pheromone may be located in an unknown branch of the olfactory receptor and merit further study. Our findings provide a better understanding of the peripheral neural coding mechanism of type II sex pheromones, and HcunPR1a may provide a target for the subsequent development of highly effective and specific biopesticides for H. cunea.

Morphological characterization and distribution of antennal sensilla of Spodoptera frugiperda (Lepidoptera: Noctuidae) using scanning electron microscopy.

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a globally significant agricultural pest, causing severe damage to corn production in China. Chemical odor-based trapping is a major approach for FAW control, making it essential to understand the FAW antennal sensillum types to enhance development of effective chemical odor attractants. In this study, we comprehensively examined the antennal sensilla types of FAW, identifying eight types and two subtypes, including Böhm's bristles, sensilla trichoidea, sensilla chaetica (I and II), sensilla coeloconica, sensilla styloconica, sensilla squamiformia (I and II), sensilla auricillica, and sensilla basiconica. Sensilla chaetica II, and sensilla squamiformia II are reported for the first time for FAW in this study. Detailed low-voltage field emission scanning electron microscope (LVSEM) images and descriptions are provided for each sensillum type. This study provides the morphological information to aid in conducting antennal sensillum neurophysiological tests on FAW. RESEARCH HIGHLIGHTS: The types of sensilla of fall armyworm were examined, identifying eight types and two subtypes, including Böhm's bristles, sensilla trichoidea, sensilla chaetica (I and II), sensilla coeloconica, sensilla styloconica, sensilla squamiformia (I and II), sensilla auricillica, and sensilla basiconica. Detailed low-voltage field emission scanning electron microscope images and descriptions were provided for each sensillum type.

Sensillar Ultrastructure of the Antennae and Maxillary Palps of the Warble Fly Oestromyia leporina (Pallas, 1778) (Diptera: Oestridae).

Despite the development of molecular techniques, morphological phylogeny still remains integral in underpinning the relationship between some clades of Calyptratae, especially the ones with fast radiation, such as those in Oestridae (Diptera: Brachycera), yet few synapomorphy has been proposed for adults in this family. Using scanning electron microscopy, we investigated the morphological structure and ultrastructure of the antennae and maxillary palps of adult Oestromyia leporina (Hypodermatinae, Oestridae). One type of trichoid sensillum (Tr), three types of basiconic sensilla (Ba I, Ba II, and Ba III), one type of coeloconic sensillum (Co I), and one type of clavate sensillum (Cl) were found on the antennal postpedicel. Surprisingly, this species has the most complex types of sensilla on the maxillary palps that have been reported in Calyptratae so far, with two types of coeloconic sensilla (Co II and Co III) and two types of mechanoreceptors. We then identified three common characteristics on the arista of Oestridae (Hypodermatinae, Oestrinae, Gasterophilinae and Cuterebrinae) that are potential synapomorphies. These characteristics indicate the value of the morphology of maxillary palps and aristae in taxonomy studies of Calyptratae.

Ultrastructure and distribution of antennal sensilla of parasitic wasp, Cotesia gregalis (Hymenoptera: Braconidae).

Cotesia gregalis Yang et Wei (Hymenoptera: Braconidae) is a gregarious koinobiont endoparasitic wasp attacking the larvae of fall webworm, Hyphantria cunea, an important invasive insect pest in China. To better understand the parasitic wasps' mating and parasitic behaviors, we examined the morphology of the antennae of adult C. gregalis, as well as the type, number, and distribution of antennal sensilla, via scanning electron microscopy. The antennae of female and male C. gregalis are filiform and comprise a scape, pedicel, and 16 flagellomeres. The female antennae are significantly shorter than those of male. A total of nine morphological types of antennal sensilla (mechanoreceptor and chemoreceptor) are presented in both sexes, including four mechanoreceptors (sensilla chaetica [two subtypes], sensilla trichodea and Böhm bristles); five chemoreceptors (sensilla basiconica [two subtypes], sensilla placodea, sensilla styloconica, and sensilla coelocapitula). There is no difference in the type and distribution of antennal sensilla between males and females, but the number and length of some antennal sensilla show sexual dimorphism. The functional morphology of the sensilla of C. gregalis is discussed by comparison with other parasitic wasps. These findings provide foundation for further research on the chemical communication and host localization mechanisms of C. gregalis. RESEARCH HIGHLIGHTS: The first report of morphology and distribution pattern of the antennal sensilla in C. gregalis is discussed. A total of seven main types and nine antennal sensilla subtypes are observed in male and female C. gregalis. The type and distribution of antennal sensilla in males and females are identical; however, the number and length of certain antennal sensilla show sexual dimorphism.

Functional Morphology and Ultrastructure of the Peripheral Antennal Sensillar System of Graphosoma italicum (Müller, 1766) (Insecta: Hemiptera: Pentatomidae).

The antennae of the shield bug Graphosoma italicum (Müller, 1766) were examined through scanning and transmission electron microscopy to reveal their general morphology, as well as the antennal sensilla's distribution, size, and ultrastructure of their dendrites and function. The antennae comprise five antennomeres (one scape, two pedicels, and two flagellomeres). Different lengths of chaetic mechanosensilla (Ch1-Ch4) exist on all antennomeres, and several highly sensitive campaniform sensilla are embedded in the exoskeleton and measure cuticular strain. One pair of peg sensilla, the typical proprioceptive, is only on the proximal edge of the first pedicel and directed to the distal edge of the scapus. The antennal flagellum possesses two subtypes of trichoid and basiconic sensilla, each with one type of coeloconic olfactory sensilla. The distinctive characteristics of G. italicum are also apparent in two subtypes of coeloconic sensilla embedded in different cavities on both antennomeres of the flagellum, probably with a thermo-hypersensitive function. All studied morphological types of the sensilla and their function were supported by ultrastructural elements. The long and thin trichoid sensilla type 2 (TrS2) with an olfactive function was the most abundant sensilla localized on both flagellomeres. The peripheral antennal sensilla system consists of six main types of sensilla divided into twelve subtypes.

Identification of chemosensory genes and antennal sensilla in Nassophasis sp. (Coleoptera: Rhynchophorinae)

Phytophagous insects rely on plant volatiles to select and locate hosts for feeding or reproduction and their olfactory system is essential for detecting plant volatiles. The stem-boring pest, Nassophasis sp. damages Dendrobium and causes economic losses. Currently, there are no effective methods for its control. However, understanding the morphological and molecular basis of its olfactory system may identify new pathways for their management and control. In this study, we observed the stemborer's antennal sensilla using scanning electron microscopy, and transcriptome sequencing was undertaken to annotate and analyze its chemosensory genes. Results showed that the antennal morphology is similar between males and females, with five types of antennal sensilla observed: sensilla chaetica (SC), sensilla trichodea (ST), sensilla brush (SB), sensilla basiconica (SBA) and sensilla gemmiformium (SG). Sexual dimorphism was not observed in sensilla type, but in the length of SBA and SG. A total of 70 olfactory-related genes were annotated, including 16 odorant binding proteins (OBP), 5 chemosensory proteins (CSPs), 26 olfactory receptors (ORs), 9 gustatory receptors (GRs), 10 ionotropic receptors (IRs), and 4 sensory neuron membrane proteins (SNMPs). Most genes were highly expressed and 14 of these genes were only expressed in the head, and 7 genes in the abdomen. This study provides a theoretical basis for the olfactory perception of Nassophasis sp. and a scientific basis for developing new pest control strategies.

Comparative SEM Study of Sensilla and Tyloid Structures in the Antennae of Vespinae (Hymenoptera: Vespidae).

This study investigates the distribution, morphology, and potential functions of antennal sensilla in various wasp species, including Dolichovespula flora, D. intermedia, Vespula structor, Vl. vulgaris, Provespa barthelemyi, Vespa bicolor, V. ducalis, V. mocsaryana, and V. velutina var. nigothorax. The study thoroughly analyzes the antennal structure of these species, representing all four genera of the yellow-jacket and hornet subfamily Vespinae. Using scanning electron microscopy (SEM), the study identifies a total of nineteen types of sensilla, including sensilla trichodea (ST-I, ST-II, ST-III), sensilla campaniform (SCF-I, SCF-II, SCF-III), pit organs (SCO-I, SCO-II, and SA), sensilla placodea (SP-I, SP-II), sensilla chaetica (SCH-I, SCH-II), sensilla basiconica (SB-I, SB-II), sensilla agmon (SAG-I, SAG-II), and sensilla coelocapitular (SCA). Additionally, tyloids were observed in the males of seven species, except for Vl. structor and Vl. vulgaris. The study provides insights into these sensilla types' morphology, abundance, and distribution. It discusses the variations in sensilla morphology among different species and the presence of gender-specific sensilla. This study provides new data about the morphology and distribution patterns of sensilla and tyloid.

Ultrastructure of the antennal sensilla of the praying mantis Creobroter nebulosa Zheng (Mantedea: Hymenopodidae).

The praying mantis Creobroter nebulosa Zheng (Mantedea: Hymenopodidae) is an insect that has medicinal and esthetical importance, and being a natural enemy for many insects, the species is used as a biological control agent. In this publication, we used scanning electron microscopy (SEM) to study the fine morphology of antennae of males and females of this species. The antennae of both sexes are filiform and consist of three parts: scape, pedicel, and flagellum (differing in the number of segments). Based on the external morphology and the sensilla distribution, the antennal flagellum is could be divided into five regions. Seven sensilla types and eleven subtypes of sensilla were observed: grooved peg sensillum (Sgp), Bohm bristles (Bb), basiconic sensillum (Sb), trichoid sensillum (StI, StII), campaniform sensillum (Sca), chaetic sensillum (ScI, ScII, ScIII), and coeloconic sensillum (ScoI, ScoII). In Mantodea, the ScoII is observed for the first time, and it is located on the tip of the flagellum. The external structure and distribution of these sensilla are compared to those of other insects and possible functions of the antennal sensilla are discussed. The males and females of the mantis could be distinguished by the length of antennae and number of Sgp. Males have antennae about 1.5 times longer and have significantly larger number of Sgp compared to females. The sexual difference in distribution of the Sgp suggests that this type of sensilla may play a role in sex-pheromones detection in mantis.

Two sex pheromone receptors for sexual communication in the American cockroach.

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.

Ultrastructure of the sensilla on the larval antennae and mouthparts of Chilo infuscatellus (Snellen, 1890) (Lepidoptera: Crambidae)

The sugarcane shoot borer Chilo infuscatellus (Snellen, 1890) is a major sugarcane pest in Lepidoptera, but little information is available on its larval ultrastructure. Here, the sensilla of the antennae and mouthparts of the mature larva of C. infuscatellus were investigated using scanning electron microscopy. The antenna is three-segmented and possesses two types of sensilla, as well as three sensilla basiconica and two sensilla chaetica on the apical surface of the middle pedicel; three sensilla basiconica on the apex of the distal flagellum. The mandibulate mouthparts consist of a labrum, a pair of mandibles, a pair of maxillae, a labium, and a hypopharynx. The labrum possesses six pairs of sensilla chaetica; the membranous epipharynx bears three pairs of flattened sensilla chaetica, three pairs of epipharyngeal sensilla, and a pair of oval sensilla digitiformia. The mandible is equipped with two sensilla chaetica on the posterolateral surface. The maxillae are well developed, each formed by a cardo, a stipes, a galea and a two-segmented maxillary palp. Each galea carries six sensilla basiconica and two large sensilla styloconica. The maxillary palp is furnished with 9 sensilla basiconica, one sensillum digitiformium and one sensillum placodeum on the distal segment. On the labium, each labial palp has a sensillum chaeticum with apical bifurcation and a thick sensillum styloconicum. This paper briefly discusses the possible function of sensilla on antennae and mouthparts.

Morphological and genetic differences in legs of a polygamous beetle between sexes, Glenea cantor (Coleopter: Cerambycidae: Lamiinae).

The legs of insects play an important role in their daily behaviour, especially reproduction. Entomologists have performed much research on the role of the leg in different behaviours of beetles, an important group in the insect family, but relatively little has been done to study the ultrastructure and transcriptome of their legs. Hence, we systematically studied the ultrastructure and gene expression of the leg of G. cantor, a polygynous beetle, and compared its male and female diversity. In this study, we found the fore-leg, mid-leg and hind-leg of the female were significantly longer than those of the male. From the perspective of intuitive structural differences, we also compared the ultrastructures of the adhesion structure (tarsal) of males and females. The tarsal functional structure of the adult leg mainly includes sensilla and an adhesion structure. The sensilla on the tarsal joint mainly include sensilla chaetica (SCh II, SCh III) and sensilla trichodea (ST II). The adhesion structure includes disc-shaped bristles (di), lanceolate bristles (la), serrated bristles (se), spatula-shaped bristles (spl) and mushroom-shaped bristles (mus). Although there was no significant difference in sensillum distribution or type between males and females, there were significant differences in the distribution and species of adhesion structures between the fore-leg, mid-leg, and hind-leg of the same sex and between males and females. Therefore, different adhesion structures play different roles in various behaviours of beetles. On the other hand, the transcriptome results of male and female legs were screened for a subset of olfaction- and mechanics-related genes. We discovered that the male leg showed upregulation of 1 odorant binding protein (OBP), 2 Olfactory receptors (ORs) and 2 Chemosensory proteins (CSPs). Meanwhile, the female leg showed upregulation of 3 OBPs, 1 OR, 1 Gustatory receptor (GR) and 3 Mechanosensitive proteins (MSPs). An in-depth examination of the ultrastructure and molecular composition of the legs can elucidate its function in the reproductive behavior of G. cantor. Moremore, this investigation will serve as a cornerstone for subsequent research into the underlying behavioral mechanisms.

Morphological characterization of antennal sensilla in Toxorhynchites theobaldi, Toxorhynchites violaceus, andLutziabigotiadults: a comparative study using scanning electron microscopy.

Some mosquitoes, including species of the genus Toxorhynchites, are known for actively preying on other mosquito larvae, making these predators valuable allies in the fight against vector-borne diseases. A comprehensive understanding of the anatomy and physiology of these potential biological control agents is helpful for the development of effective strategies for controlling vector populations. This includes the antennae, a crucial component in the search for hosts, mating, and selection of oviposition sites. This study utilized scanning electron microscopy to characterize the sensilla on the antennae of adult mosquitoes from two species that are exclusively phytophagous, including Toxorhynchites theobaldi and Toxorhynchites violaceus, as well asLutzia bigoti, which females are allegedly hematophagous. The types of sensilla in each species were compared, and five basic types of antennal sensilla were identified: trichoid, chaetic, coeloconic, basiconic, and ampullacea. The analysis also found that they were morphologically similar across the three species, regardless of feeding habits or sex. The identification and characterization of basic types of antennal sensilla in T. theobaldi, T. violaceus, andL. bigoti suggest that these structures, which play a crucial role in the behavior and ecology, have common functions across different mosquito species, despite differences in feeding habits or sex.

Females smell differently: characteristics and significance of the most common olfactory sensilla of female silkmoths.

In the silkmoth Bombyx mori, the role of male sensilla trichodea in pheromone detection is well established. Here we study the corresponding female sensilla, which contain two olfactory sensory neurons (OSNs) and come in two lengths, each representing a single physiological type. Only OSNs in medium trichoids respond to the scent of mulberry, the silkworm's exclusive host plant, and are more sensitive in mated females, suggesting a role in oviposition. In long trichoids, one OSN is tuned to (+)-linalool and the other to benzaldehyde and isovaleric acid, both odours emitted by silkworm faeces. While the significance of (+)-linalool detection remains unclear, isovaleric acid repels mated females and may therefore play a role in avoiding crowded oviposition sites. When we examined the underlying molecular components of neurons in female trichoids, we found non-canonical co-expression of Ir8a, the co-receptor for acid responses, and ORco, the co-receptor of odorant receptors, in long trichoids, and the unexpected expression of a specific odorant receptor in both trichoid sensillum types. In addition to elucidating the function of female trichoids, our results suggest that some accepted organizational principles of the insect olfactory system may not apply to the predominant sensilla on the antenna of female B. mori.

The structure and morphogenic changes of antennae of Spilococcus alhagi (Hall) (Hemiptera: Coccoidea: Pseudococcidae) in different instars

To better understand the antennal morphology and sensilla distribution of Spilococcus alhagi (Hall) in different instars, the antennae are examined using light microscopy and scanning electron microscopy. The results show that the antennae of S. alhagi could be differentiated in different instars based on their stucture, number of flagellomere, and sensillar distribution. Functional antennae of S. alhagi appear in first instar nymphs, adult females, and adult males as many scale insects. The antennae of first-instar nymphs comprise six segments, and each antenna has 62–71 sensilla of eight types, including sensilla basiconica (SB), one type of sensilla trichoidea (ST1), two types of sensilla companiform (SCa, sSCa), two types of sensilla coeloconica (SCo1, SCo2) and two types of sensilla chaetica (SCh1, SCh2). The antennae of adult females have eight segments, but each antenna has 164–188 sensilla of the same eight types as the first instar nymphs. The antennae of adult males are more developed, and each antenna contains ten segments and 670–725 sensilla of eleven types, including knobbed seta sensilla (Ks), intersegmental sensilla (Ins), two types of sensilla trichoidea (ST1, ST2), two types of sensilla companiform (SCa, sSCa), two types of sensilla coeloconica (SCo1, SCo2) and three types of sensilla chaetica (SCh1, SCh2, bSCh). Of these, four types of sensilla, viz., Ks, ST2, Ins, bSCh are only observed on the antennae of adult males. The prepupa-like and pupa-like male nymphs both possess simplified antennae, and exhibit four types of sensilla (ST1, SCa, SCh1, SCh2). Based on these results, the morphogenic changes and potential functions of antennae of S. alhagi in different instars are discussed.

Morphology and distribution of sensilla on antennae and mouthparts of the adult bruchid beetles, Bruchidius coreanus (Coleoptera: Bruchidae).

Bruchidius coreanus is a serious pest on Gleditsia sinensis Lam during seed storage, causing significant losses to their yield in southwest China. To gain insight into their behavioral mechanisms, the external morphology, ultrastructure, and distribution of sensilla on antennae, maxillary palps, and labial palps of both male and female B. coreanus were observed using a scanning electron microscope. The results revealed that both male and female adults had serrated antennae comprising a scape, a pedicel, and nine flagellomeres (F1-F9). There were eight types and seven subtypes of antenna sensilla observed in both sexes, including Böhm sensilla (BS), two subtypes of sensilla chaetica (SC1 and SC2), two subtypes of sensilla trichodea (ST1 and ST2), three subtypes of sensilla basiconica (SB1, SB2, and SB3), sensilla auricillica (SA), sensilla styloconicum (SS), capitate pegs (CP), and sensilla cavity (SCa). The average length of BS and ST (ST1 and ST2) showed significant differences between males and females. Furthermore, the number of SC (SC1 and SC2), ST1, and SCa differed significantly between the sexes. Four types of sensilla were found on the maxillary palps and labial palps, with the length of ST on these palps significantly differing between males and females. Additionally, SS on male labial palps was significantly longer than in females. The number of SC significantly differed between the male and female maxillary palps and labial palps, while ST and SS showed significant differences in the maxillary palps. These findings will contribute to further electrophysiological recording and behavioral research. RESEARCH HIGHLIGHTS: The external morphology and distribution of various sensilla on the antennae, maxillary palps, and labial palps of Bruchidius coreanus were described. Eight types and seven subtypes of antenna sensilla were observed on the antennae, while four types of sensilla were observed on the maxillary palps and labial palps. The capitate pegs were found exclusively on the antennae of female B. coreanus.