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

Meligethinae has entirely become strictly anthophagous, also being called "pollen beetles", with all members (similar to 700 species) of this subfamily using pollen and other floral parts as food resources for their larvae and adults. In this study, we used light, fluorescence, and scanning electron microscopy (LM, FM, and SEM) to explore the fine morphological structure of the alimentary canal and Malpighian tubules of Meligethes (Odonthogethes) chinensis, a common Chinese pollen beetle associated with flowers of Rosaceae. The results show that the alimentary canal of M. (O.) chinensis is divided into three parts of foregut, midgut, and hindgut. The foregut is the shortest part and has no crop; the midgut is the widest part with numerous blunt-fingered gastric ceca; the front of the hindgut folds in a circle and then extends back to the anus. Six Malpighian tubules are attached to the colon to form a cryptonephridial system. We also provide a schematic color picture of the alimentary canal and Malpighian tubules in the hemocoelic cavity of the dissected M. (O.) chinensis. This study is the first to systematically study the general morphology of the alimentary canal and Malpighian tubules of Meligethinae, which can provide important support for subsequent anatomical and physiological studies of anthophagous beetles. 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.