Larval and adult digestive tract of the carrion beetle Oxelytrum discicolle (Brullé, 1840) (Coleoptera: Silphidae)

The anatomy and histology of the midgut and Malpighian tubules of Copris felschei Reitter, 1892 (Coleoptera: Scarabaeidae)

Copris are part of the Scarabaeidae family of Coleoptera. Copris are dung beetles or coprophagous beetles. These insects are called tunnelers because they excavate channels in the substrate. They use dead organisms and non-living organic compounds as a nutrient source. By breaking down dead matter, they provide nutrients that are important to the environment and necessary for the survival of other organisms. No studies have yet examined the midgut structure and Malpighian tubules of Copris. Therefore, this study investigated the histo-anatomical structure of the midgut and Malpighian tubules of Copris felschei Reitter, 1892 (Coleoptera: Scarabaeidae) using light and scanning electron microscopy (SEM) in detail. The midgut of C. felschei represents the largest part of the alimentary canal. Muscle layers and a monolayer of cylindrical epithelium surround the midgut wall. A peritrophic membrane envelops food in the midgut lumen, and crystals were observed within the lumen. The surface of the midgut has regenerative crypts and tracheae. The Malpighian tubules are arranged in two pairs and connect proximally between the midgut and hindgut. The Malpighian tubules are composed of a single layer of cuboidal epithelium. Numerous balloon-like tracheae were observed interspersed between the midgut and Malpighian tubules. Light and SEM images of the tracheae reveal a spongy structure with hollow chambers. These findings are anticipated to advance future research and deepen our understanding of the alimentary canal in Coleoptera, particularly within the Scarabaeidae family.

Targeting Syntaxin 1A via RNA interference inhibits feeding and midgut development in Locusta migratoria

Syntaxin 1A (Syx1A) has diverse and indispensable functions in animals. Previous studies have mainly focused on the roles of Syx1A in Drosophila, and so how Syx1A operates during the development of other insects remains poorly understood. This study investigated whether disrupting LmSyx1A using RNA interference (RNAi) affects the growth and development of Locusta migratoria. LmSyx1A was expressed in all tissues tested, with the highest expression observed in the fat body. After 5th-instar nymphs were injected with double-stranded LmSyx1A (dsLmSyx1A), none of the nymphs were able to molt normally and all eventually died. The silencing of LmSyx1A resulted in the cessation of feeding, body weight loss, and atrophy of the midgut and gastric cecum in locusts. Hematoxylin and eosin (H&E) staining showed that the columnar cells in the midgut were severely damaged, with microvilli defects visible in dsLmSyx1A-injected nymphs. Secretory vesicles were observed with transmission electron microscopy (TEM). In addition, reverse transcription quantitative polymerase chain reaction (RT-qPCR) further indicates that silencing LmSyx1A repressed the expression of genes involved in the insulin/mammalian target of rapamycin (mTOR)-associated nutritional pathway. Taken together, these results suggest that LmSyx1A significantly affects the midgut cell layer of locust nymphs, which was partially associated with the downregulation of the insulin/mTOR-associated nutritional pathway. Thus, we argue that LmSyx1A is a suitable target for developing dsRNA-based biological pesticides for managing L. migratoria.

Microscopic analysis of the digestive and reproductive tracts of male Silpha obscura (Coleoptera: Silphidae)

Silpha obscura Linnaeus, 1758 (Coleoptera: Silphidae) is an omnivorous beetle species known for damaging agricultural crops, making it an important target for pest control strategies. Despite its impact, no studies have yet examined the anatomical and histological structures of the male digestive and reproductive tracts of S. obscura. Therefore, this study aimed to describe these structures in detail, which could provide insights into potential control methods. Twenty individuals were collected and histologically processed, with observations made using light microscopy. The digestive tract of S. obscura comprises 3 parts: a short foregut, a relatively long and wide midgut characterized by folds and numerous crypts of the blind intestine, and a narrow and elongated hindgut, which expands into the rectum. Malpighian tubules attach at the beginning of the hindgut, which continues with the ileum, colon, and rectum and ends at the anus. The male reproductive tract includes a pair of testes, a pair of efferent ducts (vas efferentia), a pair of deferent ducts (vas deferentia), a pair of seminal vesicles, 2 pairs of accessory glands, and the ductus ejaculatorius, which extends into the ejaculatorius bulbus. The reproductive tract terminates with the aedeagus. The testes consist of 2 lobes, each containing numerous follicles where spermatogenesis and spermiogenesis occur. This study provides detailed insights into the anatomy and histology of the digestive and male reproductive tracts of Silpha obscura. These findings may lead to new strategies for controlling this agricultural pest. Understanding these structures is crucial for further research.

Coat protein I genes are essential for the morphogenesis of the intestinal tract in Locusta migratoria

The coat protein I (COPI) complex is crucial in several significant physiological processes in eukaryotes. The assembly of COPI vesicles is initiated by the recruitment of adenosine diphosphate-ribosylation factor 1 (Arf1) to the membrane. Previous studies have primarily focused on the roles of COPI in yeast, humans, insects, and beyond Drosophila. However, the function of COPI during the development of insects remains largely unknown. In this study, we first identified eight COPI assembly genes, including α-, β-, β'-, γ-, δ-, ε-, ζ-COPI, and Arf1 in Locusta migratoria. Quantitative reverse-transcription polymerase chain reaction revealed that these genes were uniformly expressed in multiple tissues, including wing pads, leg, foregut, midgut, hindgut, and gastric cecum, and on all developmental days in 5th-instar nymphs. The injection of double-stranded RNAs (dsRNAs) against LmCOPI and LmArf1 induced high silencing efficiency in the 3rd- and 5th-instar nymphs. Locusts treated with dsLmCOPIs and dsLmArf1 exhibited feeding cessation, leading to 100 % mortality. LmCOPIs and LmArf1 knockdown resulted in midgut and gastric cecum atrophy. Histological observation and hematoxylin-eosin staining indicated that the midgut and gastric cecum exhibited deformed structures, with defective microvilli and midgut peritrophic matrix. These results suggest that LmCOPIs and LmArf1 significantly affect the intestinal tract morphogenesis in locust nymphs. Thus, COPI assembly genes are promising RNA interference targets for managing L. migratoria, reducing the dependence on chemical pesticides for pest control.

A beetle for prosecution: exogenous DNA detection from larval and adult gut of a Neotropical carrion beetle

The use of recovered DNA ingested by necrophagous or hematophagous insects has increased in forensic sciences, mainly with representatives of flies. However, some beetles are also important for medico-legal forensic entomology because they feed on carcasses until advanced decomposition. This study evaluated whether the Neotropical carrion beetle Oxelytrum discicolle (Silphidae) has the potential for the detection of exogenous DNA into the gut. The whole gut or the gut contents were extracted from O. discicolle larvae and adult previously fed on pig carcass. The pig DNA recovery rate was 33.3% in larvae and 25% in adults, indicating that the carrion beetle's gut may be useful for DNA identification of ingested food. Samples with the whole gut or only gut contents showed the same DNA recovery rate. Exogenous DNA from the whole gut was recovered from samples stored in ethanol at -20 ºC for 11 days, showing that samples of O. discicolle can be stored in the forensic laboratory without loss in DNA recovery rate.

Morphological Study of the Alimentary Canal and Malpighian Tubules in the Adult of the Pollen Beetle Meligethes (Odonthogethes) chinensis (Coleoptera: Nitidulidae: Meligethinae)

Meligethes (Odonthogethes) chinensis is a highly specialized species of Nitidulidae in China that takes pollen as its main food source, and its main host plant is Rubus idaeus L. (Rosaceae). In this study, the structural morphology of the alimentary canal and Malpighian tubules of adult M. (O.) chinensis was observed under light, fluorescence, and scanning electron microscopy. The alimentary canal of adult M. (O.) chinensis is divided into foregut, midgut, and hindgut. The foregut is the shortest and consists of the pharynx, esophagus, proventriculus, and cardiac valve. The midgut is a straight, distended, cylindrical, thin-walled tube. Numerous blunt-fingered gastric ceca are distributed irregularly throughout the midgut. The hindgut is subdivided into the ileum, colon, and rectum. The ileum is coiled. The colon gradually enlarges posteriorly. The rectum is thickly muscled and followed by a membranous structure. The openings of proximal Malpighian tubules are evenly inserted into the junction of the midgut and hindgut, and distal Malpighian tubules are evenly attached to the colon to form a cryptonephridial system. In this study, we also compare the structure and infer the function of the alimentary canal and Malpighian tubules among beetles, as well as discuss the evolutionary and taxonomical implications.