The ability to discard body parts at a preferential locus of weakness is widespread across the Metazoans' Tree of Life and has received attention from ecological and behavioral perspectives. Still, in many cases, a clear understanding of its genetic, morphological, and anatomical pathways is lacking. Distinct terms (autotomy, autotilly, autospasy) have been used in the literature to describe the process of limb detachment, usually carrying in their meaning information regarding the mechanics involved in it, and appendotomy is the most general word to encompass all of them. Appendotomy is found early in the evolution of the Arthropoda lineage and varies among taxa. Spiders, for example, have four distinct pre-determined fracture lines on their exoskeleton, and little is known about the co-occurrence of these lines within spider species. In this study, we examine the appendotomy at the trochanter of spiders using light and scanning electron microscopy to reconstruct the evolution of this character across the spider's tree of life. We describe trochanter structures and correct previous misunderstandings on how the appendotomy at the trochanter occurs in spiders. Our data show a clear, preferred breakage plane on the spider trochanter and although we focused on this appendotomy, we investigated its concomitant occurrence with other fracture areas of the leg. We show that the proximal rim of the trochanter breaks during appendotomy, leaving fragments on the distal end of the coxal arthrodial membrane. We also present several new records of appendotomy among 127 spider families examined and reconstruct the ancestral state of this character. Due to these discoveries, we conclude that the term “coxa-trochanter” appendotomy is misleading, and we propose replacement by the term “trochanter appendotomy”.
So far, a full exocrine system survey exists for the major ant subfamilies but not yet for Pseudomyrmecinae. This study provides a morphological survey of the exocrine system in workers of Tetraponera ants using the large Tetraponera rufonigra and the smaller T. allaborans, T. penzigi and T. tessmanni. We found 20 glands of which the antennal bulb gland is a new exocrine structure in ants. The cardo base gland is well-developed in all species which is striking as this gland so far was mainly found in the subfamily Formicinae. Gland size is linked with worker size, in which larger workers clearly have more cells rather than bigger cells. A study of the exocrine system in other ant subfamilies often revealed differences that are relevant for species’ lifestyle and communication system. In spite of the numerous glands described in the present paper, almost nothing is known about their function in Tetraponera as surprisingly poor literature data exist on the communication system in this genus. Our study hopefully inspires researchers to perform bioassay experiments using gland extracts to fill this gap in the social biology of these ants.
Pycnogonids are a fascinating clade of marine epibenthic chelicerates that generally undergo indirect development, unlike all other chelicerates, where direct development prevails. Here we describe the first instar, known as the "protonymphon", of a species within the Phoxichilidiidae, namely Phoxichilidium quadradentatum Hilton, 1942a, using scanning electron microscopy (SEM). To date, the protonymphons of only four other species in this family have been described. Our morphological analysis places P. quadradentatum within the type 4 mode of development, hatching as a small larva that lacks attachment spines on the chelifores and has distal extension of the larval limbs. Based on this classification, P. quadradentatum most likely lives as an endoparasite of hydrozoans during its post-embryonic development, similar to Phoxichilidium femoratum.
Sea spiders (Pycnogonida) are benthic, marine chelicerates of shallow to deep water environments. They are mostly dioecious and engage in copulation that leads to external insemination, followed by brooding of large embryo masses by the male. In this study, we perform the first ultrastructural and elemental characterization of brooded embryos in pycnogonids. Scanning (SEM) and transmission electron microscopy (TEM) reveals the embryo masses to be covered by a contiguous extracellular matrix that consists of electron-dense fibers embedded in an electron-lucent medium. The matrix appears to be derived from the vitelline envelopes of individual embryos, thereby confirming recent hypotheses that the matrix is not a product of the male femoral glands. Elemental analysis using SEM-energy dispersive X-ray spectroscopy (EDS) reveals the vitelline envelope to contain high levels of C, O, and N with lesser amounts of Fe, Si, and Ni. The underlying embryos possess a separate fertilization membrane, which is devoid of ornamentation and has a relatively homogeneous, electron-opaque ultrastructure without distinct zonation or inclusions. The fertilization membrane contained C, O, and N as well as trace elements including Fe, Al, Au, Ca and P. The encapsulated embryo consists of numerous electron-dense yolk granules among other organelles. EDS of the embryos reveals high levels of C, O, and N, with trace amounts of Si, Au, Ni, P, and Zn. These results add new data for pycnogonid embryos, and with further investigations of additional species, may provide a wealth of information relevant for understanding more about the ecology, evolution, and systematics of this extraordinary marine taxon.
As holometabolous insects, ladybird beetles display marked morphological differences between the larval and adult stages. However, the larvae and adults of Chilocorus rubidus share the same diet, and no prior study has compared their mouthparts. In this study, scanning electron microscopy (SEM) was used to examine the ultramorphology of mouthparts and associated sensilla in both adults and larvae of C. rubidus. The results showed that the mouthparts of C. rubidus are of the typical biting-chewing type, and their basic composition of the mouthparts are conserved between larvae and adults. However, the specific morphological characteristics of each mouthpart component varies among different larval instars and between larvae and adults, particularly from the 4th instar to the adult stage. The mandibles of larvae bear bifid incisors, whereas those of adults are unidentate. Additionally, the maxilla and labium exhibit distinct structural differences between the two stages. Six types of sensilla and two types of glandular structures were identified on the adult mouthparts, among which sensilla campaniformia (Sca), sensilla coleconica (Sco), perforated plates (Pp), and cuticular pores (Cp) were absent in the larval stage. The number of all sensillum types gradually increased from the larval to adult stage, especially for the sensory fields on the top of labial palpi and maxillary palpi. In particular, sensilla styloconica II are observed on the tip of labial palpi of ladybird beetles for the first time. These results provide a theoretical basis for understanding the biological control potential of this species.
Sexually dimorphic coloration is common in Lepidoptera. In addition to differences in pigmentation, Lepidopterans also exhibit sexually dimorphic structural coloration. Lycaenidae are unique among Lepidoptera due to the presence of a multilayer pepper-pot photonic structure located within the body of their cover scales. While sexually dimorphic pepper-pot structures in Lycaenidae have previously been observed between male blue scales and female melanic scales, the nature of sexually dimorphic photonic structures within non-pigmented scales has yet to be examined in detail. In this study, we examined the morphology and reflective capabilities of cover scales from the sexually dimorphic postdiscal forewing region of summer form Celastrina neglecta (W. H. Edwards, 1862) (Lycaenidae: Polyommatinae) specimens to determine the basis of sexually dimorphic structural coloration in the species. Wing region and single-scale reflectance were compared based on spectrometry. Scale morphology was compared based on scanning electron, transmission electron, and light microscopy. Wing region analyses revealed that males and females possess statistically different wing region reflectance. Males exhibit high reflectance of violet (400-450 nm) and low reflectance in the 451-750 nm range, while females exhibit lower reflectance of violet and higher reflectance in the 451-750 nm range. Single-scale analyses revealed both blue and clear cover scales in the region of interest. While male and female scales exhibit similar reflective properties, females possess more clear scales in the dimorphic region than males. Morphological analyses indicate that the ridges and cross-ribbing of clear scales are more densely packed than their blue counterparts. Additionally, blue scales exhibit a fully developed pepper-pot photonic structure within the scale lumen, while clear scales possess irregular photonic structures that are frequently absent from the scale lumen.
Inadequate research on polymorphism and functional adaptations of sensilla in social aphids hinders elucidation of the sensory basis underlying their caste differentiation and host specialization. This study employed scanning electron microscopy to investigate and compare the key sensilla traits on the sensory appendages across castes of the social aphid Pseudoregma bambucicola. Eight morphological types encompassing 16 subtypes of sensilla were identified. Antennae possess the most diverse sensilla, including 8 types and 11 subtypes. Five SB-1 sensilla are consistently distributed at the antennal apex. The ultimate rostral segment uniquely harbors ST-3, SB-2, and SB-3. AS are found exclusively along the subcostal vein of the forewings in alate females. Sch-1 is restricted to articular junctions. The first tarsomere bears CS, while SB-1 is present on the second tarsomere. Notably, the sensilla types differ between alate and apterous morphs. Statistical analysis also revealed significant differences in key functional sensilla traits across castes of P. bambucicola. Specifically, the abundance and length of ST-1, the volume of SB-1, and the area of RMPS differed significantly between the An/As and soldier/nymph caste pairs. The caste- and tissue-specific distribution and variation of sensilla traits in P. bambucicola may arise from the intrinsic biology, ecological adaptation, and distinct functional demands of each caste. This study provides a comprehensive map of sensilla types and distribution in a social aphid, establishing a morphological framework for future research on the communication of social information.
Lymantria juglandis Chao, 1984 is an important arboreal defoliator, yet the immature morphology has remained poorly documented despite its ecological importance. In this study, the egg and early larval stages of L. juglandis were described using light microscopy and scanning electron microscopy to clarify diagnostic characters and developmental adaptations. The hemispherical egg exhibits a finely reticulated chorion composed of contiguous polygonal cells with numerous aeropyles at ridge intersections. First-instar larvae bear dense verrucae and two distinct types of setae: elongated barbed setae with extended socket bases and spiniform setae with a subbasal bulbous process, features likely functioning in mechanical and chemical defense. Crochet number increases progressively during larval development, from four in the first instar to ∼12 in the second and ∼32 with a median process in the third, reflecting enhanced grasping ability and substrate adaptation. These morphological features provide new diagnostic evidence for Lymantria and advance comparative and functional interpretations of early developmental stages within Lymantriinae.
The majority of species in the genus Bodilus (Aphodiinae, Aphodiini) are coprophagous, playing a crucial role in maintaining the cleanliness of the natural environment. However, compared with adults, research on the larvae of this group is significantly insufficient. In light of this, the present study focused on the larvae of Bodilus gregarius and used scanning electron microscopy (SEM) to provide the first detailed description of the ultrastructural features of larvae at different instars. It was found that the larvae of B. gregarius have three instars. After comparing the ultrastructures of the head, mouthparts, and anal sternite among larvae of different instars, it was revealed that the number of microsensilla at the tips of the antennae, the sensory spines attached to the anterior end of the hypopharynx, as well as setae on the frontal region of the head, labrum, and the raster of the anal sternite in the second- and third-instar larvae were much more numerous than those in the first-instar larvae. Meanwhile, the morphology of the stridulatory teeth differs among larvae of different instars, and only the third-instar larvae have an "X"-shaped depression on the surface of the labrum. The findings of this study not only provide effective data for the taxonomic research of larvae in the genus Bodilus but also offer fundamental data for revealing the evolution of morphological characteristics and ecological adaptability of small dung beetles.
Superposition compound eyes are a hallmark of many nocturnal beetles and moths and represent a major evolutionary innovation for dim-light. Although their optical organization has been extensively documented, the developmental processes underlying their assembly remain poorly understood. Here, we traced the morphogenesis of the compound eyes in the diamondback moth Plutella xylostella from the prepupal stage to adult emergence using transmission electron microscopy. Early ommatidia adopt an apposition-like arrangement, with crystalline cones in direct contact with distal retinulae. The retinulae subsequently undergo coordinated proximal displacement, while secondary pigment cells expand into the intervening space, forming a pigment-free clear zone. The tracheal tapetum develops via distal extension of numerous tracheoles between adjacent retinulae, developing in close synchrony with the formation of the clear zone. The rhabdom elongation proceeds in a distinct distal-to-proximal sequence, and corneal nipples appear prior to deposition of fibrous corneal lamellae. These observations demonstrate that the superposition eyes of P. xylostella arise through stepwise modification of an apposition-like developmental framework rather than through the formation of entirely novel structures, supporting the view that evolutionary innovation in insect compound eyes primarily results from modification of conserved developmental programs.
Establishing the taxonomic identity of newly-discovered populations of Aegla Leach (1820) has become more challenging due to the increasing number of cryptic and new species described, some of which have limitations in the morphological characters used. Recent studies have proposed additional characters, but these are still insufficient to accommodate the morphological diversity of aeglids, especially those from the speciose Upper Paraná River region (clade C), where most of the recently described species are found. This work aims to investigate morphological variation in the fifth pereopod of male of Aegla in both phylogenetic and ontogenetic contexts, using scanning electron microscopy (SEM). In addition to searching for new morphological characters useful in the differentiation of Aegla species, we also identified the setal types present on the entire fifth pereopod. Most of the setae on the fifth pereopod in Aegla are denticles and setules of the serrate setal type, with uniform serrated morphology and setulae, with bilateral denticles and elongated dorsal setulae. Distinct setal patterns were found in aeglid clades A, C and E, with no clear geographic correlation, suggesting that these differences may be related to ecological specializations rather than geographic distribution. Quantitative analysis of different size classes revealed variation in the number and distribution of setae, with progressive increases suggesting ontogenetic trends. The sexual tubes exhibited the two clear morphotypes for each population described in the literature ("long/narrow" and "short/wide"), but with morphological transition occurring during ontogeny in Aegla jacutinga, suggesting caution in describing this character in other species without the maturity stage being reported.
Tettigoniidae (katydids) represent an important group within Orthoptera and play significant ecological roles, such as serving as a key food source for insectivorous birds and contributing to nutrient cycling through their herbivorous feeding activities. However, detailed knowledge of their digestive tract structure, particularly in relation to physiological function, remains limited. The midgut is the primary site of nutrient digestion and absorption, and its cellular composition directly reflects the digestive strategies and adaptive characteristics of insects. In this study, the midgut morphology and epithelial organization of Ducetia japonica (Orthoptera: Tettigoniidae) were examined using light microscopy, laser scanning confocal microscopy, and transmission electron microscopy. Both light and confocal microscopy were employed to characterize overall tissue architecture, while transmission electron microscopy was used to investigate the ultrastructural features of the epithelial cells. The midgut consists of two bulbous gastric caeca and a tubular ventriculus, with the structure of the gastric caeca being similar to that of the ventriculus. Three types of epithelial cells were identified: columnar cells, endocrine cells, and regenerative cells. Columnar cells, which participate in digestion and absorption, exhibit prominent apocrine secretion, together with possible vesicle trafficking activity suggestive of exocytosis. Endocrine cells, located at the base of the epithelium, exhibit strong immunoreactivity against FMRFamide-related neuropeptides, suggesting their involvement in local paracrine regulation. Regenerative cells, also situated basally, function as intestinal stem cells capable of differentiating into new cells to replace aged or apoptotic cells. These findings provide a cellular and subcellular framework for understanding midgut function in D. japonica and contribute to comparative studies on digestive system evolution in Orthoptera.
The black soldier fly (BSF) Hermetia illucens is a cosmopolitan insect species distributed across five continents. This broad distribution suggests a high capacity to adapt its life history to diverse ecological niches. However, the developmental checkpoints that determine the transition to metamorphosis, as well as whether starvation induces a dormancy-like state and its underlying structural basis, remain unclear. In this study, we characterized the anatomical features, developmental timeline, starvation resistance, and developmental checkpoints of BSF. We identified a critical weight (CW) of 83 mg, above which larvae irreversibly committed to metamorphosis. Notably, larvae below the CW survived starvation for several months and immediately resumed growth and development upon re-feeding, indicating that they enter a starvation-induced quiescent state. Starvation caused severe atrophy of the fat body, whereas five days of re-feeding fully restored fat body morphology, suggesting that stored energy reserves are mobilized during starvation to support survival. These findings reveal a previously unrecognized dormancy-like strategy in BSF and suggest that this developmental plasticity facilitates colonization of environments with intermittent or seasonal food availability.
Miniaturization, egg parasitism, and the presence of anucleate neurons in adults can greatly affect the quantitative and qualitative characteristics of the central nervous system (CNS) during metamorphosis. Such features have already been shown for the brain of Megaphragma, but have not been examined for other parts of the nervous system. Using histological methods, confocal microscopy, and three-dimensional computer modeling, we describe the structure of the CNS during the pupal development of Megaphragma viggianii (Hymenoptera: Trichogrammatidae). The processes of compactization and oligomerization of the ganglia continue throughout development. The absolute volume of the CNS decreases from the prepupa to the adult by a factor of more than 5. The main reason for this is the reduction in the volume of the cell body rind due to the lysis of cell bodies and nuclei, which occurs in each ganglion of the CNS. In the pharate adult, the CNS consists of an average of 13 000 nerve cells, but only about 400 nuclei remain in adult. The main changes in the course of CNS development, including the lysis of neuron nuclei, occur in all ganglia almost synchronously. The results obtained expand our understanding of the development of the CNS in parasitoid wasps and the phenomenon of anucleate neurons.
Mayflies (Order: Ephemeroptera) are the most basally branching winged insect group within the Hexapoda. They have three life stages: an exclusively aquatic nymph stage, a sexually immature winged subimago, and a sexually mature winged imago. We conducted an ultrastructure study of the antennae of all three life stages of Coloburiscus humeralis using Scanning Electron Microscopy (SEM). Differences in the cuticular surface of their antennae were observed across the three life stages. Numerous sensilla were identified, including sensilla trichodea, sensilla basiconica, and sensilla coeloconica, known to have roles in chemoreception, mechanoreception, thermoreception, and hygroreception. The antennae of different life stages housed various types of sensilla, which are probably reflective of the changes in sensory modalities associated with the distinct environments they inhabit. Sexual dimorphism was observed between antennae of winged life stages, with some types of sensilla found exclusively on the antenna of the female subimagos and imagos, suggesting they may play a role in supporting female-specific olfactory behaviours. This research contributes to further understanding how insects with life stages that occupy different habitats fulfil various sensory tasks.
The proventriculus is a specialized foregut structure that is variably developed across insect taxa and is primarily responsible for mechanical breakdown. In the present study, we investigated the regional organization and ultrastructure of the proventriculus in the mole cricket Gryllotalpa orientalis Burmeister, 1838 (Orthoptera: Gryllotalpidae) using light, scanning, and transmission electron microscopy. The proventriculus is nearly spherical and exhibits a tripartite organization comprising anterior valvular structures, a median region equipped with robust cuticular teeth and barbated lobes, and a posterior cardiac valve. Histological examination revealed that the proventricular wall is composed of circular and longitudinal muscle layers, an epithelial lining, and a heavily sclerotized cuticular intima, a configuration commonly associated with solid-feeding insects. Ultrastructural analysis demonstrated abundant mitochondria in muscle cells, well-developed rough endoplasmic reticulum in epithelial cells, and numerous secretory vesicles localized in the subintimal region, suggesting active tissue metabolism and potential intimal renewal. These structural features are consistent with an enhanced capacity for mechanical breakdown of solid or abrasive food materials and may provide protection against abrasive soil particles in this fossorial, omnivorous species. Our findings provide new morphological data on the proventriculus of Gryllotalpidae and a comparative framework for digestive specialization in subterranean Orthoptera.
The adults of Bittacidae assume a unique mating posture, by which the male twists his abdomen about 180° to contact the female genitalia in a belly-to-belly position. The males have an extremely elongated penisfilum, which enters the slender spermathecal duct to accomplish insemination during copulation. However, the interaction of the male and female genitalia remains largely unknown in hangingflies. Here, the interaction of genital structures between the males and females was investigated for three species of Bittacidae. In the context of what we know of other related groups, this is suggestive of antagonistic coevolution between the spines on the male epandrial lobes and the female subgenital plate. The length of the male penisfilum is significantly correlated with that of the female spermathecal duct. The coevolution of genitalia is briefly discussed based on morphological traits.
Geometrid moths constitute the second-largest lineage in Lepidoptera, yet the ultrastructure of their compound eyes remains poorly understood. In this study, the compound eyes of four geometrid species, Pelagodes antiquadraria, Percnia giraffata, Percnia luridaria, and Abraxas suspecta, were examined comparatively using light and transmission electron microscopy to identify conserved structural features and interspecific variation. All four species possess superposition compound eyes with a uniform ommatidial organization that includes a corneal lens, a crystalline cone, a retinula with a fused rhabdom, two primary pigment cells, six secondary pigment cells, and a tracheal tapetum. The most striking interspecific difference is the number of retinula cells per ommatidium: 20 in P. antiquadraria and Per. giraffata, 19 in Per. luridaria, and 16 in A. suspecta, representing the highest number of retinula cells reported to date in Lepidoptera. These findings reveal previously unrecognized morphological diversity in geometrid compound eyes and suggest that variation in retinula cell number may be associated with species-specific visual requirements. This study provides new insights into the structural diversity and evolutionary adaptation of the visual system in nocturnal Lepidoptera.
The Tanyderidae are a small, ancient, poorly studied nematoceran family with 10 extant genera. А previous study found in the adults of Eutanyderus and Peringueomyina a full set of mouthparts (including mandibles) - a rare case among Diptera. The new study examined the mouthparts of adult Tanyderus, Araucoderus and Nothoderus using light and scanning electron microscopy. A full set of mouthparts, with no significant differences between sexes, was again found in all three genera. Three structural types were identified, suggesting as many feeding strategies among recent Tanyderidae. The genera form a series according to the degree of reduction of mandibles and other piercing structures. The well-developed toothed mandibles, hypopharynx, and laciniae were found only in both sexes of Tanyderus. Such a pattern has not previously been observed in males of any recent Nematocera. In the absence of live observations, the structure of these mouthparts suggests active penetration or laceration during feeding. Similar mouthparts, with both mandibles and hypopharynx toothed, are described, for the first time, in a female of Jurassic Protanyderus. For comparison, piercing mouthparts of two recent predaceous genera of Blephariceridae, Blepharicera and Liponeura, were examined. They showed numerous differences from the mouthparts of Tanyderus. Moreover, the mandibles, well-developed in the females, were absent in the males, suggesting sexual dimorphism in the feeding of these blepharicerids. Correlations between the structure of the mandibulate mouthparts, their sexual dimorphism, and the diet in lower Diptera are reviewed from the evolutionary perspective.
