Metathoracic Glands of Scaptocoris castanea Perty, 1833 (Heteroptera: Cydnidae): Morphology and Volatilomic

The characteristic odor of Heteroptera is produced by metathoracic glands, which is poorly evaluated in the brown stink bug Scaptocoris castanea Perty, 1833 (Heteroptera: Cydnidae), an important agricultural pest. This study describes the anatomy, histology, and ultrastructure of the external scent efferent system, associated metathoracic gland, and volatile compounds produced. The external scent efferent system of S. castanea is ventrally located in the thorax, with an ovoid ostiole, a small and protruded peritreme, and an evaporatory area (evaporatorium) rich in mycoid microsculptures. The metathoracic glands have a secretory region with irregular tubules that open into a large reservoir. The secretory epithelium of the metathoracic gland has bicellular secretory units with globular and canaliculus cells. The globular cells are rich in rough endoplasmic reticulum, mitochondria, and secretory vesicles. The reservoir has a single layered cubic epithelium with apical surface lined by a thin cuticular intima, and cytoplasm rich in mitochondria, lysosomes, and secretory vesicles. The secretion of the metathoracic glands of S. castanea has 11 components, including aldehydes, alcohols, and hydrocarbons, with abundant (E)-2-decenal, 2-octenal, 2-hexenal, and 1-octen-3-yl acetate. This study fills an important gap in understanding defensive strategy in this agricultural pest.