Arthropod Structure & Development最新文献

Aquatic insects represent a great portion of Arthropod diversity and the major fauna in inland waters. The sensory biology and neuroanatomy of these insects are, however, poorly investigated. This research aims to describe the antennal sensilla of nymphs of the stonefly Dinocras cephalotes using scanning electron microscopy and comparing them with the adult sensilla. Besides, central antennal pathways in nymphs and adults are investigated by neuron mass-tracing with tetramethylrhodamine, and their brain structures are visualized with an anti-synapsin antibody. No dramatic changes occur in the antennal sensilla during nymphal development, while antennal sensilla profoundly change from nymphs to adults when switching from an aquatic to an aerial lifestyle. However, similar brain structures are used in nymphs and adults to process diverging sensory information, perceived through different sensilla in water and air. These data provide valuable insights into the evolution of aquatic heterometabolous insects, maintaining a functional sensory system throughout development, including a distinct adaptation of the peripheral olfactory systems during the transition from detection of water-soluble chemicals to volatile compounds in the air. From a conservation biology perspective, the present data contribute to a better knowledge of the biology of stoneflies, which are very important bioindicators in rivers.

The large abundance of termites is partially achieved by their defensive abilities. Stylotermitidae represented by a single extant genus, Stylotermes, is a member of a termite group Neoisoptera that encompasses 83% of termite species and 94% of termite genera and is characterized by the presence of the frontal gland. Within Neoisoptera, Stylotermitidae represents a species-poor sister lineage of all other groups. We studied the structure of the frontal, labral and labial glands in soldiers and workers of Stylotermes faveolus, and the composition of the frontal gland secretion in S. faveolus and Stylotermes halumicus. We show that the frontal gland is a small active secretory organ in soldiers and workers. It produces a cocktail of monoterpenes in soldiers, and some of these monoterpenes and unidentified proteins in workers. The labral and labial glands are developed similarly to other termite species and contribute to defensive activities (labral in both castes, labial in soldiers) or to the production of digestive enzymes (labial in workers). Our results support the importance of the frontal gland in the evolution of Neoisoptera. Toxic, irritating and detectable monoterpenes play defensive and pheromonal functions and are likely critical novelties contributing to the ecological success of these termites.

A particularly conspicuous morphological feature in chalcidoid wasps are strikingly modified legs present in both males and females. It evolved convergently multiple times on either fore or hind legs implying strong evolutionary pressure and a prominent function in the wasps’ life history. We investigate the external and internal morphology of the modified legs of five species of chalcidoid wasps representing four families (Ooderidae, Heydeniidae, Chalcididae, and Leucospidae), using light microscopy, scanning electron microscopy and micro computed tomography. We aimed to identify shared characteristics as well as differences between genera/species, leg pairs and sexes and to draw first conclusions about the shared or different functions. All species and sexes share the same general leg morphology, with enlarged femur, curved tibia and a huge flexor tibiae muscle. However, there are also genus/species-specific differences such as distinctive spine-like setae on the femur of Oodera spp., or leg pair-specific differences in the position of the extensor tibiae muscle. Shared characteristics imply a common primary function in which strong forces are required to pull the tibia against the femur while differences imply different secondary functions. Both primary and secondary functions have yet to be revealed beyond informed speculations.

The Trichoptera, holometabolous aquatic insects found worldwide except in Antarctica, exhibit a unique feature in their sperm, which are solely nucleated (eupyrene). Current knowledge on Trichoptera sperm is limited to Old World species. To enhance our understanding of their reproductive biology and contribute to systematic discussions, we describe the male reproductive system and spermatozoa of Smicridea (Rhyacophylax) iguazu Flint, 1983 (Hydropsychidae). This species lacks seminal vesicles, possesses piriform to oval-shaped testes with spermatozoa grouped in apical bundles and dense filamentous material filling other areas. The vasa deferentia are long and a pair of elongated accessory glands displays distinct proximal and distal regions. The relatively short (∼40 μm) spermatozoa are nucleated, aflagellated, and immobile. Further research could explore variations and assess the taxonomic utility of these features for genus identification within Hydropsychidae.

A remarkable characteristic of katydids (Orthoptera, Tettigoniidae) is the elongated ovipositor, which is associated with oviposition behavior. The high degree of complexity of both sclerites and muscles arrangement of the ovipositor, is only similar to the ovipositor of Hymenoptera. Here we describe the morphology of the ovipositor within Tettigoniidae, and add descriptions of known oviposition behavior. Fifteen skeletal structures can be recognized, of these, three pairs of muscles are new while nine pairs were already described in the literature. The new muscles are ap2vf, anterior projection of second valvifer; bcov, blade complex of the ovipositor; and dbl, dorsal blade. The morphology of the ovipositor blade complex (bcov), the shape of the first valvifer (1vf), posterior intervalvular sclerite (piv), tergite IX (T9), anterior projection of the second valvifer (ap2vf), and the second valvifer (2vf), and their related muscles affect oviposition in Tettigoniidae. This contribution helps to understand katydid's oviposition behavior. Additionally, the new descriptions help in the search for new characters in Tettigoniidae.

Springtails are notable for their jumping apparatus and latch-mediated spring mechanism. The challenge, in the light of the tiny size and rapid movement of these organisms, has been to understand the morphological intricacies of this spring system. This study takes an approach that integrates SEM, MicroCT, cLSM and high-speed video recordings to understand the composition and functionality of the jumping apparatus in Megalothorax minimus (Neelipleona), Dicyrtomina ornata and Dicyrtomina minuta (Symphypleona). We focus on reconstructing, describing, and understanding the functioning of structures such as basal plates, musculature and furca. The dimensions of the jumping apparatus in Dicyrtomina and Megalothorax differ significantly from those in elongated springtails. A hypothesis of functional coherence between taxa, based on muscle connections and basal plates, is postulated. High-speed video recordings provide information on: 1) furca release timing and function during jumping and self-righting; 2) performance properties of manubrium, dens and mucro in interaction with the ground and in take-off; 3) possible pre-release furca moves. The study underscores the need for further research employing a variety of visualization methods in order to explore additional aspects such as retinaculum unlatching and furca flexion/extension muscles.

The parasitoid Torymus sinensis (Hymenoptera: Torymidae) has been successfully used in Italy since 2005 for biological control of the invasive cynipid Dryocosmus kuriphilus (Hymenoptera: Cynipidae), highly destructive for the economically relevant Castanea sativa (Fagales: Fagaceae). In order to investigate the morphological aspects related to sensorial behavior, a fine morphology study of the antennae and their sensilla was conducted by scanning electron microscopy on both sexes of T. sinensis. The antennae, composed of a scape, a pedicel and a flagellum with ten flagellomeres, had chaetic sensilla of six subtypes, placoid sensilla of three subtypes, trichoid sensilla, sensilla with a roundish grooved tip, and coeloconic sensilla. The chaetic sensilla of the first three subtypes were found in the scape and in the pedicel, and those of the last three subtypes, together with trichoid, roundish grooved tip and coeloconic sensilla, were found only on flagellomeres. Sexual dimorphism was detected in the morphology of the proper pedicel and the flagellum, and in the presence and distribution of the sensilla and their subtypes. The morphological aspects of the antenna of T. sinensis and of its sensilla were compared with those found in the family Torymidae and in other families of the extremely diverse superfamily Chalcidoidea.

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.

The complete larval development of Peltogaster lineata Shiino, 1943 (Rhizocephala: Peltogastridae), including five nauplii and one cypris stage, is described and illustrated using SEM. The development took 3.5–4 days at a water temperature of 22–23 °C. Peltogaster lineata has the peltogastrid type of development. Nauplii possess a large and clearly reticulated flotation collar, six pairs of dorsal shield setae with the U-shaped second pair, long segmented frontolateral horns each with two subterminal setae, and a long seta at the antennal basis. The attachment disc in female cyprids has a flap-like extension at the posterior margin. Cyprids of both sexes possess two sensory setae at the attachment disc. The large male aesthetasc is unilobed, the female subterminal aesthetasc terminates into two thin long filamentous processes. Larvae of P. lineata have distinctly visible nauplius eyes.

The genera Eumerus and Merodon (Syrphidae: Merodontini) form together the most speciose grouping of hoverflies in the Palaearctic Region. However, little is known about the morphology and biology of their larvae. The few larvae of Eumerus and Merodon that have been uncovered are phytophagous in underground organs of plants (some Eumerus and all Merodon) or saprophagous in a variety of plants' parts (the reminder of Eumerus). In this study, the second larval stage (L2) of Eumerus lyneborgi Ricarte & Hauser, 2020 and both the larva (L2) and puparium of Merodon constans (Rossi, 1794) are described for the first time. Larvae of E. lyneborgi were found in a decaying stem of Cyphostemma juttae (Dinter & Gilg) Desc., 1960 (Vitaceae) in Namibia (Africa), while larvae of M. constans were collected in bulbs of Leucojum vernum Linnaeus, 1753, (Amaryllidaceae) in France (Europe). Morphology of the immature forms was studied by observation and imaging with stereomicroscopy and scanning electron microscopy. The head skeleton of E. lyneborgi larvae was found to be of the filter feeding type, i.e., in accordance with a saprophagous trophic regime, while that of M. constans was typically phytophagous. Variability in certain characters of the M. constans early stages is described and discussed in relation to the adult form and molecular information published in literature. An updated identification key to all known third larval stages/puparia of Merodon is provided.