Ultrastructure of the excretory organs of Bombus morio (Hymenoptera: Bombini): bee without rectal pads

Fipronil exposure compromises respiration and damages the Malpighian tubules of the stingless bee Partamona helleri Friese (Hymenoptera: Apidae)

Fipronil has been widely used in agriculture and forestry in Brazil to control several pests. However, this insecticide may be hazardous to non-target organisms, including stingless bees, which are essential pollinators of crops and natural environments. Here, we investigated the effect of 24-h acute oral exposure to LC₅₀ of fipronil on the Malpighian tubules of the stingless bee Partamona helleri (Friese). Insecticide exposure decreases the respiration rate of forager bees, and the Malpighian tubules are severely affected, as shown by the epithelial architecture disorganization, loss of cytoplasmic content, degradation of the brush border, and nuclear pyknosis. In addition, fipronil ingestion increases the number of Malpighian cells positive for peroxidase, LC3, cleaved caspase-3, and JNK. However, Notch and ERK1/2-positive cells decrease in the exposed bees. These changes in the signaling proteins indicate an increase in oxidative stress, autophagy and apoptosis, and impairment of cell recovery. Overall, our results demonstrate the toxicological effects of fipronil on a stingless bee, which compromises the physiology of this important pollinator.

Histomorphology of the Malpighian Tubules and the Chemical Composition of the Spherocrystals in the Tubule Epithelial Cells of Adult Leptophyes albovittata (Kollar, 1833) (Orthoptera, Tettigoniidae)

In insects, the number, cytological and histological structures, and the spherocrystals of the Malpighian tubules (MTs) can vary considerably in different insect groups. These differences are considered important because they can be used as taxonomic characters. For this purpose, the ultrastructure of the MT epithelial cells in Leptophyes albovittata (Kollar, 1833) (Orthoptera, Tettigoniidae) was examined by light microscopy, scanning electron microscopy, and transmission electron microscopy. The wall of each tubule consists of a single layer of cells. These cells have round-shaped nuclei. Two different cell types were demonstrated in the tubule cell. These are cells that have electron-dense cytoplasm and electron-lucent cytoplasm. It was observed that the cytoplasm of these cells has many spherocrystals. The chemical composition of the spherocrystals was found to be high in carbon, phosphorus, and manganese in tubule cells.

Transmission Electron Microscopy as a Tool to Study the Toxicological Effects of Thiamethoxam in Workers of Atta sexdens (Myrmicinae, Attini)

Thiamethoxam is a neonicotinoid that has been used to control insect pests. The literature reports a few behavioral studies evaluating the toxic effect of thiamethoxam in ants; however, there are scarce studies at the cellular level. The present research evaluated the effects of thiamethoxam in labial (LG) and mandibular glands (MG), fat bodies (FB), and Malpighian tubules (MT) of workers of Atta sexdens, using transmission electron microscopy. The duct and secretory cells of LG were profoundly affected, then the production of saliva can be compromised, as well as its quality and subsequent use. In MG, reservoir and canaliculi cells presented slight alterations; however, MG secretory cells presented vacuoles containing lamellar structures, increased lipid production, and a large amount of mitochondria, which may lead to organ's malfunctioning. The FB cell alterations do not seem enough to cause significant changes that lead to cell death. Prominent changes in MT, such as loss of the electron-dense concentric ring, increased smooth endoplasmic reticulum, loss of basal infolds, vacuoles containing mineralized granules, and lamellar structures associated with mitochondria, suggest that their excretory function is compromised. In conclusion, thiamethoxam acts not only in the nervous system but also contributes to systemic toxicity on the target organism.

Anatomy and histology of the alimentary canal of larvae and adults of Chrysoperla externa (Hagen, 1861) (Neuroptera: Chrysopidae)

The larvae of the lacewing Chrysoperla externa are important predators with the potential to be used in the biological control in agriculture. Although some studies provide important data on the gut morphology in lacewings, they are limited to few species. This study describes the anatomy and histology of the alimentary canal in the predatory larvae and herbivorous adult of C. externa. In larvae, the crop is the larger part of the foregut and it is connected to the midgut by the stomodeal valve. The midgut is an enlarged sac-like organ. At the mid-hindgut transition, there are eight Malpighian tubules. The hindgut is a non-functional vestigial region in the larvae. In adults, the crop has a diverticulum associated with large tracheal trunks, a conic proventriculus with sclerotized lips followed by an elongated tubular midgut. Histological analyses of larval and adult midgut show the presence of a single-layered epithelium with columnar cells with well-developed brush border, nests of regenerative cells, and a peritrophic matrix lining the midgut lumen. The hindgut in adults has an epithelium with cubic cells lined by a thin cuticular intima and rectal pads in the rectum. These data are discussed in comparison with the digestive tract in other Chrysopidae.

Aquaporin expression in the alimentary canal of the honey bee Apis mellifera L. (Hymenoptera: Apidae) and functional characterization of Am_Eglp 1

Aquaporins (AQP) are a family of plasma membrane proteins responsible for water transport through cell membranes. They are differentially expressed in different parts of the alimentary canal of insects where they regulate water transport. These proteins have been studied in detail in some insects, but few data are available for aquaporins of the honey bee, Apis mellifera. We used quantitative PCR to study the expression of six putative aquaporin genes in forager honey bees. We found differential expression of all putative AQP genes in crop, midgut, ileum, rectum and Malpighian tubules. We found the entomoglyceroporin Am_Eglp 1 expressed at extremely high levels in the midgut. We performed a functional characterization of Am_Eglp 1 using heterologous expression in Xenopus laevis oocyte followed by water uptake assays. Our results confirmed that the Am_Eglp 1 gene encodes a functional water transporter. This study shows that all putative honey bee aquaporin genes have complex expression patterns in the digestive and excretory organs of honey bee workers. Our results suggest that Am_Eglp 1 is the principal water transporter in the midgut of A. mellifera workers.

Ultrastructure of the rectum of the soil-spraying larva in Bittacus cirratus (Mecoptera: Bittacidae)

The larvae of Bittacidae have an interesting behavior of spraying soil particles on their body surface through the anus. However, the hindgut specialization associated with this behavior has rarely been studied hitherto. Here, we investigated the fine structure of the larval rectum in the hangingfly Bittacus cirratus Tjeder using light and transmission electron microscopy. The results show that the larvae of B. cirratus have a tubular rectum without rectal pads or papillae. The rectum consists of well-developed visceral muscle layers, a non-cellular basal lamina, a single-layer epithelium with a cuticular intima, and a central lumen. The folded rectal epithelium consists of two types of flattened epithelial cells: electron-dense type I cells and electron-lucent type II cells. The apical and basal plasma membranes are infolded and are associated with mitochondria in the epithelial cells. The epithelial cells are held by septate and scalariform junctions. The lateral cell membranes are combined with mitochondria among type I cells and generate mitochondria-scalariform junction complexes. These features suggest that the epithelial cells are active in water and ion reabsorption. We conclude that the absence of rectal pads or papillae and the presence of developed circular muscles are likely morphological adaptations of these larvae to the soil-spraying behavior.

Excretion in the mother's body: modifications of the larval excretory system in the viviparous dermapteran, Arixenia esau

The vast majority of Dermaptera are free-living and oviparous, i.e., females lay eggs within which embryonic development occurs until the larva hatches. In contrast, in the epizoic dermapteran Arixenia esau, eggs are retained within mother's body and the embryos and first instar larvae develop inside her reproductive system. Such a reproductive strategy poses many physiological challenges for a mother, one of which is the removal of metabolic waste generated by the developing offspring. Here, we examine how the Arixenia females cope with this challenge by analyzing features of the developing larval excretory system. Our comparative analyses of the early and late first instar larvae revealed characteristic modifications in the cellular architecture of the Malpighian tubules, indicating that these organs are functional. The results of the electron probe microanalyses suggest additionally that the larval Malpighian tubules are mainly involved in maintaining ion homeostasis. We also found that the lumen of the larval alimentary track is occluded by a cellular diaphragm at the midgut-hindgut junction and that cells of the diaphragm accumulate metabolic compounds. Such an organization of the larval gut apparently prevents fouling of the mother's organism with the offspring metabolic waste and therefore can be regarded as an adaptation for viviparity.

Post-embryonic development of the Malpighian tubules in Apis mellifera (Hymenoptera) workers: morphology, remodeling, apoptosis, and cell proliferation

The honeybee Apis mellifera has ecological and economic importance; however, it experiences a population decline, perhaps due to exposure to toxic compounds, which are excreted by Malpighian tubules. During metamorphosis of A. mellifera, the Malpighian tubules degenerate and are formed de novo. The objective of this work was to verify the cellular events of the Malpighian tubule renewal in the metamorphosis, which are the gradual steps of cell remodeling, determining different cell types and their roles in the excretory activity in A. mellifera. Immunofluorescence and ultrastructural analyses showed that the cells of the larval Malpighian tubules degenerate by apoptosis and autophagy, and the new Malpighian tubules are formed by cell proliferation. The ultrastructure of the cells in the Malpighian tubules suggest that cellular remodeling only occurs from dark-brown-eyed pupae, indicating the onset of excretion activity in pupal Malpighian tubules. In adult forager workers, two cell types occur in the Malpighian tubules, one with ultrastructural features (abundance of mitochondria, vacuoles, microvilli, and narrow basal labyrinth) for primary urine production and another cell type with dilated basal labyrinth, long microvilli, and absence of spherocrystals, which suggest a role in primary urine re-absorpotion. This study suggests that during the metamorphosis, Malpighian tubules are non-functional until the light-brown-eyed pupae, indicating that A. mellifera may be more vulnerable to toxic compounds at early pupal stages. In addition, cell ultrastructure suggests that the Malpighian tubules may be functional from dark-brown-eyed pupae and acquire greater complexity in the forager worker bee.

Post-embryonic changes in the hindgut of honeybee Apis mellifera workers: Morphology, cuticle deposition, apoptosis, and cell proliferation

In insects, the hindgut is a homeostatic region of the digestive tract, divided into pylorus, ileum, and rectum, that reabsorbs water, ions, and small molecules produced during hemolymph filtration. The hindgut anatomy in bee larvae is different from that of adult workers. This study reports the morphological changes and cellular events that occur in the hindgut during the metamorphosis of the honeybee Apis mellifera. We describe the occurrence of autophagosomes and the ultrastructure of the epithelial cells and cuticle, suggesting that cuticular degradation begins in prepupae, with the cuticle being reabsorbed and recycled by autophagosomes in white- and pink-eyed pupae, followed by the deposition of new cuticle in light-brown-eyed pupae. In L5S larvae and prepupae, the hindgut undergoes cell proliferation in the anterior and posterior ends. In the pupae, the pylorus, ileum, and rectum regions are differentiated, and cell proliferation ceases in dark-brown-eyed pupae. Apoptosis occurs in the hindgut from the L5S larval to the pink-eyed pupal stage. In light-brown- and dark-brown-eyed pupae, the ileum epithelium changes from pseudostratified to simple only after the production of the basal lamina, whereas the rectal epithelium is always flattened. In black-eyed pupae, ileum epithelial cells have large vacuoles and subcuticular spaces, while in adult forager workers these cells have long invaginations in the cell apex and many mitochondria, indicating a role in the transport of compounds. Our findings show that hindgut morphogenesis is a dynamic process, with tissue remodeling and cellular events taking place for the formation of different regions of the organ, the reconstruction of a new cuticle, and the remodeling of visceral muscles.

Histological and ultrastructural features of the rectum in Poecilimon cervus Karabağ, 1950 (Orthoptera: Tettigoniidae)

The morphology and ultrastructure of the rectum in Poecilimon cervus Karabağ, 1950 (Orthoptera, Tettigoniidae) were analyzed by light microscope, scanning (SEM) and transmission electron microscopes (TEM). The rectum is the final part of the digestive tract that plays an important role in water reabsorption in insects and so provides osmoregulation. In the transverse sections, six rectal pads and columnar epithelium can be distinguished. The cuticular intima lines the lumen at the apical side of the epithelium. In the cytoplasm, there are numerous mitochondria, some endocytic vesicles, secreting vesicles whose sizes differ according to the area in the cell, and a nucleus with globular in shape. With this study, we aimed to demonstrate the ultrastructure of the rectum of P. cervus and differences or similarities of with other species.