Sexual dimorphism of Dyschiriini (Coleoptera, Carabidae): Comparative morphological SEM study of palpi sensilla and its possible role in intraspecific chemical communication.

Sexual dimorphism in Dyschiriini (Coleoptera, Carabidae) consists of the presence of an autapomorphic sensory area in apical palpomeres of males, here named as Male Palpi Sensory Area (MPSA). In this work, microstructure of palpi, with focus on MPSA, is characterized and formally described using Scanning Electron Microscopy (SEM). Interspecific variability among 13 species and three subgenera of Dyschirius Bonelli, 1810 and one species of Reicheiodes Ganglbauer, 1891 is assessed. Palpi of studied Dyschiriini presented up to 4 sensilla classes (coeloconica, basiconica, digitiformia, trichodea) in both sexes, while males had one more class (sensilla placodea) found grouped in MPSA. Measurements of sensilla and MPSA are provided. Differences among taxa corresponded to development grade of MPSA and its number of sensilla placodea. The MPSA of Dyschirius (Dyschirius) thoracicus Rossi, 1790 were clearly different to the rest of the studied subgenera and species of Dyschirius and Reicheiodes, whose MPSA were similar and had slight intraspecific variability. We suggest that function of MPSA is likely detection of female pheromones, which would evidence chemical communication between sexes. We hypothesize that evolution of MPSA could be related to burrowing habits of Dyschiriini and its possible sexual behavior in soil tunnels. Study of MPSA may help to elucidate phylogenetic relationships among members of the tribe.

Anatomy and ultrastructural details of the eye of the passalid beetle Ceracupes yui Okano 1988 (Scarabaeoidea; Passalidae).

One of the least studied eyes of any beetle taxon are those of the scarabaeoid family Passalidae. Some members of this family of around 600 species worldwide are known to have superposition eyes (Aceraius grandis; A. hikidai) while others have apposition eyes (Cylindrocaulus patalis; Ceracupes yui). In C. yui of nearly 3 cm body length (this paper) the retinal layer is very thin and occupies approximately half of an ommatidium's total length, the latter amounting to 284 and 266 µm in the respective dorsal and ventral eye regions. The two eye regions are almost completely separated by a prominent cuticular canthus, a feature usually associated with the presence of a tracheal tapetum, a clear-zone between dioptric and light-perceiving structures and a regular array of smooth facets. In C. yui the facets are smooth (but not very regular) and a tracheal tapetum and a clear-zone are absent. The rhabdoms, formed by 8-9 retinula cells, are complicated, multilobed structures with widths and lengths of around 15 and 80 µm, respectively. The combination of some superposition and mostly apposition eye features, e.g., extensive corneal exocones, relatively small number of ommatidia, absence of a clear-zone and tracheal bush, suggest an adaptation of this species' eye to the fossorial lifestyle of C. yui, and, thus, a manifestation of the passalid eye's plasticity.

The ultrastructure of the spermatheca of Mordellistena brevicauda (Coleoptera, Tenebrionoidea) and the associated bacterial cells.

The ultrastructural study on the female reproductive system of the beetle M. brevicauda (Mordellidae) confirmed the positive correlation between the length of the sperm and the size of the female seminal receptacle (Spermatheca). The spermatheca of the species is characterized by an apical bulb-like structure where the spermathecal duct forms numerous folds filled with sperm. At this level many bacterial cells are present intermingled with the duct folds. Some are organized in large structures, such as bacteriomes, while other are single bacteriocytes. The latter are often found near the basal lamina of duct epithelium. In addition, some bacteria are visible in the cytoplasm of the duct epithelial cells. Interestingly, bacterial cells have never been observed in the duct lumen. The possible function of the bacterial cells is discussed.

Biology of Callistethus plagiicollis (Coleoptera: Scarabaeoidea: Rutelinae) and comparative morphology of its larvae.

Larvae of the beetle subfamily Rutelinae are poorly described in the literature. Notably, the morphology of the larvae of Callistethus plagiicollis Fairmaire has not previously been analyzed. Here, we report for the first time that these larvae feed on the tubers and roots of Gastrodia elata Blume, an important traditional Chinese herbal medicine, which causes a reduction in the yield and economic value of G. elata. We employed scanning electron microscopy and light microscopy to investigate the morphology and occurrence regularity of egg, larvae, pupae, and adult specimens of C. plagiicollis collected from the G. elata planting base in Guizhou Province, China, with a focus on the ultrastructure of mature larvae. The results revealed one generation of C. plagiicollis per year in the study area and three instar stages of larvae. Mature larvae were identified by the following characteristics: raster without palidia with a large number of hamate setae, antennal apex containing seven sensilla basiconica, larval haptomerum containing eight sensilla styloconica and four enlarged heli, and seven longitudinally arranged stridulatory teeth on the stipes of the maxilla. The combination of scanning electron and light microscopy effectively revealed the difference between membranous and sclerotized structures, ensuring accurate identification of C. plagiicollis larvae. By determining the feeding characteristics and occurrence regularity of C. plagiicollis, this study has implications for improved pest management in G. elata crops. RESEARCH HIGHLIGHTS: We identified C. plagiicollis as a new pest of G. elata, a traditional Chinese medicine Scanning electron and light microscopy were combined to analyze the morphology of the mature larvae of C. plagiicollis for the first time We determined the feeding characteristics and occurrence regularity of C. plagiicollis, which can be used to develop effective pest management strategies.

A study on the aerodynamic behaviors learned from microscopy imaging of beetle corrugated hindwing.

Beetle hindwings have the unique advantages of lightweight and high strength, which play a key role in flight. In this study, the beetle hindwings were cut along the chordal direction, then the first groove microstructure of different vein cross sections was investigated using the 3D microscope system and the laser scanning confocal microscope. It was found that the position of the first groove relative to the entire chordal cross section of the wing gradually moves backward, which has an effect on the flying aerodynamic behaviors of the beetle. Next, three corrugated airfoils learned from the microscopy imaging of the ladybird beetle hindwing were designed. Then, aerodynamic behaviors were calculated by the ANSYS Fluent software, and it was confirmed that the position of the first groove microstructure affects the aerodynamic performance of the airfoil. For further study, the influence of corrugated structural and motion parameters on the aerodynamic, 2D 'simplified' airfoil models with triangular wave airfoil models (TWA models) was developed and studied. RESEARCH HIGHLIGHTS: The position of the first groove microstructure affects the aerodynamic performance of the airfoil. The pressure difference of different corrugation patterns shows significantly asymmetric during the upstroke and downstroke. The aerodynamic is optimal of 2D-TWA models, when the number of corrugations is five, the corrugation is right angle, and the flapping frequency is 75 Hz.

The sperm structure of Clinidium canaliculatum (Costa): A contribution to the systematic position of Rhysodidae (Coleoptera: Carabidae).

The systematic position and the phylogenetic relationship of Rhysodidae members is still debated, with some authors considering the group as a separate family of Adephaga, while for others they could be a subfamily of Carabidae. The group have morphological traits quite different from Carabidae and an aberrant behaviour compared to ground beetles being not predaceous. The sperm ultrastructure of C. canaliculatum was studied comparatively with other species of beetles, Carabidae in particular. The results indicate that the sperm structure of this species is similar to that of the Carabinae species. As in these species, C. canaliculatum has sperm conjugates with an apical conical cap protecting the heads and the initial region of flagella. This sperm appearance is also shared by another species of Rhysodidae, Omoglymmius hamatus. The material of the apical cap consists of an electron-dense material with a peculiar outer net configuration. Many species of Carabidae, however, can present a different type of sperm conjugation, the spermatostyle: a long rod-like structure where the individual sperms have only the most apical part inserted in the cortical area and the flagella are completely free. C. canaliculatum sperm are endowed with a mono-layered acrosome, a nucleus of variable shape along its length, a flagellum consisting of a typical axoneme 9 + 9+2, provided with 16 protofilaments in the tubular wall of accessory tubules, two asymmetric mitochondrial derivatives with the left one larger than the opposite one, and the right accessory body elongated and larger than the opposite one. These sperm characteristics, which are shared also by another member of the group, suggest the demotion of the family Rhysodidae to the subfamily Rhysodinae within Carabidae, a result also supported by recent molecular data.

Observations on the ultrastructure of the oral appendages of Glenea cantor Fabricius (Coleoptera: Lamiinae).

Using scanning electron microscopy, we examined the gross and ultrastructure morphology of the mandibles, labial palpi, and mandibular palpi of adult male and female Glenea cantor beetles. The morphology of these parts, both in their gross and ultrastructure, varied significantly between males and females. The lengths of the mandible, labial palpi, and mandibular palpi were clearly noticeably longer in females than in men, which is mostly related to the oviposition mechanism. In terms of the ultrastructural morphology of the mandibles, labial palpi, and mandibular palpi, seven types of sensilla were found on these parts: sensilla twig basiconica (STB I, II, III, and IV), sensilla chaetica (Scheme IV and V), Böhm's bristles (Bb), sensilla placodea (SP), sensilla trichodea (ST II), sensilla plate (SP), sensilla coeloconica (SC), and sensilla campaniformia (SCa). Females have significantly more ST I and Scheme III on their mandibles than males. The mechanical sensors SCh and Bb, olfactory sensor ST II, taste sensor STB IV, and carbon dioxide sensor and temperature and humidity sensors SC, SP, and SCa were much more developed on the labial and maxillary palpi of females compared to those of males, which further clarified the significance of the oral appendages in oviposition behavior. These findings will advance information-based technique design and the creation of information-based pest control strategies by assisting in our understanding of the host preference and oviposition behavior of adult G. cantor. RESEARCH HIGHLIGHTS: The external morphology and distribution of the oral appendages of Glenea cantor between sexes has been researched through scanning electron microscopy (SEM) for the first time. Several significant differences between males and females have been found by analyzing the oral appendages of G. cantor with SEM. The differences in the structure of oral appendages of G. cantor between sexes reflect functional differences in reproductive behaviors.

Morphology of male and female reproductive systems in the ground beetle Apotomus and the peculiar sperm ultrastructure of A. rufus (P. Rossi, 1790) (Coleoptera, Carabidae).

Relatively few studies have focused on evolutionary losses of sexually selected male traits. We use light and electron microscopy to study the male and female reproductive anatomy of Apotomus ground beetles (Coleoptera, Carabidae), a lineage that we reconstruct as likely having lost sperm conjugation, a putative sexually selected trait. We pay particular attention to the structure of the testes and spermatheca. Both of these organs share a strikingly similar shape-consisting of long blind canals arranged into several concentric overlapping rings measuring approximately 18 mm and 19.5 mm in total length, respectively. The similarity of these structures suggests a positive evolutionary correlation between female and male genital organs. Males are characterized by unifollicular testes with numerous germ cysts, which contain 64 sperm cells each, and we record a novel occurrence of sperm cyst "looping", a spermatogenic innovation previously only known from some fruit fly and Tenebrionid beetle sperm. The sperm are very long (about 2.7 mm) and include an extraordinarily long helicoidal acrosome, a short nucleus, and a long flagellum. These findings confirm the structural peculiarity of sperm, testis, and female reproductive tract (FRT) of Apotomus species relative to other ground beetles, which could possibly be the result of shifts in sexual selection.

Novel flight style and light wings boost flight performance of tiny beetles.

Flight speed is positively correlated with body size in animals1. However, miniature featherwing beetles can fly at speeds and accelerations of insects three times their size2. Here we show that this performance results from a reduced wing mass and a previously unknown type of wing-motion cycle. Our experiment combines three-dimensional reconstructions of morphology and kinematics in one of the smallest insects, the beetle Paratuposa placentis (body length 395 µm). The flapping bristled wings follow a pronounced figure-of-eight loop that consists of subperpendicular up and down strokes followed by claps at stroke reversals above and below the body. The elytra act as inertial brakes that prevent excessive body oscillation. Computational analyses suggest functional decomposition of the wingbeat cycle into two power half strokes, which produce a large upward force, and two down-dragging recovery half strokes. In contrast to heavier membranous wings, the motion of bristled wings of the same size requires little inertial power. Muscle mechanical power requirements thus remain positive throughout the wingbeat cycle, making elastic energy storage obsolete. These adaptations help to explain how extremely small insects have preserved good aerial performance during miniaturization, one of the factors of their evolutionary success.

Cytoplasmic incompatibility in the semivoltine longicorn beetle Acalolepta fraudatrix (Coleoptera: Cerambycidae) double infected with Wolbachia.

Wolbachia are obligatory endosymbiotic α-proteobacteria found in many arthropods. They are maternally inherited, and can induce reproductive alterations in the hosts. Despite considerable recent progress in studies on the associations between Wolbachia and various taxonomic groups of insects, none of the researches have revealed the effects of Wolbachia on longicorn beetles as the host insect. Acalolepta fraudatrix is a forest longicorn beetle that is distributed in East Asia. In this study, the relationship between Wolbachia and A. fraudatrix was investigated. Out of two populations of A. fraudatrix screened for Wolbachia using the genes ftsZ, wsp, and 16S rRNA, only one of the populations showed detection of all three genes indicating the presence of Wolbachia. Electron microscopy and fluorescent in situ hybridization also confirmed that the A. fraudatrix population was infected with Wolbachia. Sequencing the wsp genes derived from single insects revealed that two strains of Wolbachia coexisted in the insects based on the detection of two different sequences of the wsp gene. We designated these strains as wFra1 and wFra2. The bacterial titers of wFra1 were nearly 2-fold and 3-fold higher than wFra2 in the testes and ovaries, respectively. The two strains of Wolbachia in the insects were completely eliminated by rearing the insects on artificial diets containing 1% concentration of tetracycline for 1 generation. Reciprocal crosses between Wolbachia-infected and Wolbachia-uninfected A. fraudatrix demonstrated that only eggs produced by the crosses between Wolbachia-infected males and Wolbachia-uninfected females did not hatch, indicating that Wolbachia infecting A. fraudatrix causes cytoplasmic incompatibility in the host insect. This is the first report showing the effect of Wolbachia on reproductive function in a longicorn beetle, A. fraudatrix.

Angular distribution of luminescence dissymmetry observed from a random laser built upon the exocuticle of the scarab beetle Chrysina gloriosa.

We investigate the angular distribution of luminescence dissymmetry of random lasing in the mixture of rhodamine 6G and titanium dioxide nanoparticles upon a biocompatible natural material substrate, i.e., the elytron of the scarab beetle Chrysina gloriosa. We look into both green and gold-colored areas of the elytron that exhibit distinctly different circular dichroism properties. The fabricated sample asymmetrically emits both left- and right-handed circularly polarized light at 570 nm when pumped at 532 nm, depending on the direction of emission and the angle of the pump incidence. We characterize the light via measuring the angular distribution of its luminescence dissymmetry factor (g lum), which reaches an unusually high maximal value of 0.90 or -0.50 at some specific angle depending on the handedness of its polarization. This random laser source can be used in numerous potential optoelectronic applications which require light emission of distributed luminescence dissymmetry or of high luminescence dissymmetry.

Description of larval morphology and phylogenetic relationships of Heterotemna tenuicornis (Silphidae).

Providing clear and detailed morphological descriptions of endemic species in limited areas enables new knowledge of their biology and ecology to be obtained through citizen science. This information can be further used for their protection. Our study presents the first morphological description of the larvae of all three instars of Heterotemna tenuicornis (Brullé, 1836), an endemic species of the Canary Islands that, together with H. britoi García & Pérez, 1996 and H. figurata (Brullé, 1839), belongs to the peculiar genus Heterotemna Wollaston, 1864. Furthermore, we present the first sequences of two mitochondrial genes (COI, 16S) obtained from larval specimens, and cross reference them with sequences from an adult specimen. Phylogenetic analysis of molecular data placed the genus Heterotemna within the genus Silpha Linnaeus, 1758, suggesting paraphyly of Silpha. In our study, we underline the importance of using a combination of morphological description and molecular data, that can be used for barcoding developmental stages which could not otherwise be definitely associated.

Observation and analysis of diving beetle movements while swimming.

The fast swimming speed, flexible cornering, and high propulsion efficiency of diving beetles are primarily achieved by their two powerful hind legs. Unlike other aquatic organisms, such as turtle, jellyfish, fish and frog et al., the diving beetle could complete retreating motion without turning around, and the turning radius is small for this kind of propulsion mode. However, most bionic vehicles have not contained these advantages, the study about this propulsion method is useful for the design of bionic robots. In this paper, the swimming videos of the diving beetle, including forwarding, turning and retreating, were captured by two synchronized high-speed cameras, and were analyzed via SIMI Motion. The analysis results revealed that the swimming speed initially increased quickly to a maximum at 60% of the power stroke, and then decreased. During the power stroke, the diving beetle stretched its tibias and tarsi, the bristles on both sides of which were shaped like paddles, to maximize the cross-sectional areas against the water to achieve the maximum thrust. During the recovery stroke, the diving beetle rotated its tarsi and folded the bristles to minimize the cross-sectional areas to reduce the drag force. For one turning motion (turn right about 90 degrees), it takes only one motion cycle for the diving beetle to complete it. During the retreating motion, the average acceleration was close to 9.8 m/s2 in the first 25 ms. Finally, based on the diving beetle's hind-leg movement pattern, a kinematic model was constructed, and according to this model and the motion data of the joint angles, the motion trajectories of the hind legs were obtained by using MATLAB. Since the advantages of this propulsion method, it may become a new bionic propulsion method, and the motion data and kinematic model of the hind legs will be helpful in the design of bionic underwater unmanned vehicles.

Thermal radiation management by natural photonic structures: Morimus asper funereus case.

Convective, conductive and radiative mechanisms of thermal management are extremely important for life. Photonic structures, used to detect infrared radiation (IR) and enhance radiative energy exchange, were observed in a number of organisms. Here we report on sophisticated radiative mechanisms used by Morimus asper funereus, a longicorn beetle whose elytra possess a suitably aligned array of lenslets and blackbodies. Additionally, a dense array of microtrichia hyperuniformly covers blackbodies and operates as a stochastic, full-bandgap, IR-photonic structure. All these features, whose characteristic dimensions cover a range from several hundred down to a few micrometres, operate synergistically to improve the absorption, emission and, possibly, detection of IR radiation. We present a morphological characterization of the elytron, thermal imaging measurements and a theoretical IR model of insect elytron, uncovering a synergistic operation of all structures.

Female calling, life cycle, and microstructures of the parasitic beetle Ripidius quadriceps Abeille de Perrin.

The precopulatory behaviour of the larviform females of Ripidius quadriceps Abeille de Perrin, 1872 is described. The calling posture of virgin females is documented. The cephalic morphology and microstructures are visualised using scanning electron microscopy, in particular the secretory pores in the cuticle of inflatable maxillary palps. An exhaustive overview of relevant publications revealed that the location of secretory pores on the head of females is unique within the order Coleoptera. Compared to other beetles with sedentary calling females, the calling phase of the short-lived and non-feeding female of Ripidius is exceptionally short. For bioassays, various traps using virgin females of Ripidius were tested. It is likely that the sedentary behaviour of the short-lived female combined with a unique morphology and priority for investing in reproduction is compensated for by the actively flying males with remarkably flabellate antennae. The life cycle of this species, including some of the exceptions recorded at the individual level, is discussed. Perspectives for a biological and morphological survey of this rarely collected western Palaearctic species are outlined. In addition, the calling behaviour, secretory sites and location of pheromone glands in females of Coleoptera producing long range pheromones is reviewed.

Crucial role of framework with cytoskeletal actin filaments for shaping microstructure of footpad setae in the ladybird beetle, Harmonia axyridis.

Insects that can walk on smooth surfaces have specialized structures, footpads, on their legs. Footpads play an important role in adhesion to the substrate surface. Although the morphology and function of footpads have been studied, the mechanism of their formation is still elusive. In the ladybird beetle (Harmonia axyridis), hairy footpads are present on the first and second tarsal segments of the legs. The footpads are covered with hundreds of hairs, i.e. setae, whose tips consist of four types: pointed, lanceolate, spatular, and discoidal. We examined the formation of the footpad during the pupal stage using immuno-staining and fluorescent-conjugated phalloidin staining. We found that a seta was composed of a shaft and a socket and some setae were accompanied by a neuron. By the mid-pupal stages, the shaft cells elongated to form a setal structure. Cytoskeletal actin bundles ramified to create a framework for the setal tip structure of the cells. We examined the effects of the application of cytochalasin D, which inhibits actin polymerization, on the formation of footpad setal structures. The results showed that the setal tips were deformed by the inhibition of actin polymerization. Our observations reveal that cytoskeletal actin filaments are involved in shaping the setae.

Morphological description of the third instar larva of Lasiotrichius succinctus hananoi (Sawada) (Coleoptera: Scarabaeidae: Cetoniinae: Trichiini), using scanning electron microscopy.

Cetoniinae is one of the showiest scarab groups, exhibiting bright-metallic body colors, and usually attract great attention from entomologists and amateur collectors. Larvae of Cetoniinae show dramatically diversity on morphology and living habits. Although being considered one of the best-studied groups of Scarabaeidae, larvae have been described for less than 5% species to the known Cetoniinae. In this study, the final instar larva of Lasiotrichius succinctus hananoi was described using scanning electron microscopy. The larvae are peculiar for bearing a haptomeral process dividing 10 spines into two groups: six on the left side, four on the right side, different from the previous descriptions on L. succinctus (Pallas, 1781). The morphological differences under SEM imply the further requirement of taxonomic revision in Lasiotrichius. Both advantage and disadvantage of SEM utilizing in larval descriptions were briefly discussed.

SEM analysis of sensilla on the mouthparts and antennae of Asian larch bark beetle Ips subelongatus.

The Asian larch bark beetle, Ips subelongatus, is a severe pest of larches in Northeastern China. The gustatory and olfactory systems of I. subelongatus play important roles in host location, mating, and feeding. In this study, we examined the types, distributions, and abundances of various sensilla associated with the mouthparts and antennae of I. subelongatus using scanning electron microscopy (SEM). On the mouthparts, five types of sensilla are present: sensilla trichodea (S.t.1-3), sensilla chaetica (S.c.1-3), sensilla basiconica (S.b.1-2), sensilla twig basiconica (S.tb.1-3), and sensilla placodea (S.p). S.t.3 are the most abundant sensilla subtype on the mouthparts in both sexes, while S.b.1 are the least abundant. Most sensilla on the mouthparts are located on the maxillae and labium, and the apex of each maxillary and labial palp carry the same sensilla subtypes (S.b.2 and S.tb.1-3). However, the total number of sensilla on the apex of each maxillary palp is higher than that on the labial palp. On the antennae, five types of sensilla are present: sensilla trichodea (S.t.1-3), sensilla chaetica (S.c.1-2), sensilla basiconica (S.b.1-3), Böhm bristles (B.b), and sensilla coeloconica (S.co). Antennal sensilla are mostly situated on the anterior surface of the antennal club, particularly on the two dense sensory bands. S.b.1 are the most abundant sensilla subtype on the antennae in both sexes, while S.t.1 are the least abundant. No sexual dimorphism in sensilla type or distribution on the mouthparts or antennae is observed between the sexes of I. subelongatus. However, S.t.3 (on mouthparts) and S.c.1 (on antennae) were significantly more abundant in males than in females, while more S.t.1 (on mouthparts) were observed in females than in males. Finally, the putative functions of each kind of sensilla with respect to their fine structures, distributions, and abundances on the mouthparts and antennae are discussed.

Comparison of tarsal attachment in two closely related leaf beetle species.

Green dock beetles Gastrophysa viridula and Colorado potato beetles Leptinotarsa decemlineata having distinctly different body mass and gait habits were compared with respect to their tarsal morphology and attachment ability. The focus laid on shapes and dimensions of tenent setae related to the peeling line, i.e., the sum of widths of all thin-film elements participating in contact. High-speed rotation of the two leaf beetle species attached to the horizontal and vertical sides of a Plexiglass drum resulted in higher attachment forces of the heavier beetle species that has a larger number of tarsal setae and a larger peeling line length. However, normalizing the measured forces with the corresponding peeling line lengths led to a reversed relationship. This allowed us to assume that the design of adhesive setae in different leaf beetle species matches the requirements imposed by their habitats. In accordance with the theory of thin film peeling, tangential forces were found to be higher than normal forces. The attachment system of females was found to exhibit stronger functional efficiency, which can be correlated to the morphology of their setae.

Type and distribution of sensilla in the antennae of Euplatypus parallelus (F.) (Coleoptera: Curculionidea, Platypodinae).

Euplatypus parallelus (F.) (Coleoptera: Curculionidea) is the most destructive cosmopolitan insect pest of the Platypodinae. Pheromone-based luring agents are used currently in controlling bark beetle. Antennae are the primary insect organs sensing volatiles of host trees and pheromones of pioneer males. We studied the external morphology of antennae and the type, distribution, and the number of the beetle sensilla. Our results show E. parallelus have a geniculate antenna composed of 6 segments, namely the scape, 4-segmented funicle and club. Ninety-seven percent of the antennal sensors were distributed in the club, and 3% were distributed in the scape and funicle. 6 types of sensilla on the antennae were found, including sensilla trichodea (subtypes: STI, STII and STIII), sensilla basiconica (subtypes: SBI, SBII, SBIII and SBIV), sensilla chaetica (subtypes: SChI, SChII and SChIII), as well as sensilla coeloconica, sensilla campaniform and sensilla furcatea. There was no significant difference in the type, distribution and number of sensilla in males and females. No significant difference in the shape and distribution of antennae was found between sexes, but the length of antennae and the number of SChI, SChII, STI, SBI, SBIII and SBIV were significantly larger in females than males. We revealed the external cuticular structure of the antennae in E. parallelus, which can be used to guide future electrophysiological investigations to understand the ability of this beetle to detect semiochemicals.