Insects depend on complex sensory systems to detect food sources, locate mates, and navigate in the environment. In the smallest insects, miniaturization imposes major constraints on anatomy and physiology, but it remains poorly understood how this affects the structure and function of sensory systems, such as the sensilla on the mouthparts. The specific problem addressed in this study is how extreme miniaturization influences the diversity, distribution, and structural complexity of mouthpart sensilla in the minute parasitoid wasp Megaphragma viggianii Fusu, Polaszek & Polilov. Using scanning and volumetric electron microscopy, we show that despite its minute body length of 0.2–0.3 mm, M. viggianii possesses a set of 70 sensilla on its mouthparts, including four major types (chaetoid, basiconic, coeloconic, and campaniform). These wasps display no noticeable sexual dimorphism in the structure and distribution of their mouthpart sensilla, and the set of sensilla is generally identical in different individuals. Compared to larger Hymenoptera, M. viggianii exhibits a reduced number of sensilla, but maintains the same types of sensilla and their similar position, suggesting stable developmental and functional traits. These findings confirm that miniaturization does not reduce the diversity of the sensilla, but instead drives simplification at the structural level, while preserving their functional roles. These insights not only advance our understanding of insect sensory biology but also contribute to elucidating broader questions of evolutionary morphology and functional scaling of biological systems
