Trogoderma granarium Everts, 1898 (Coleoptera: dermestidae) - a model species to investigate hastisetae functional morphology

Hastisetae are detachable setae typical of the larvae of Megatomine (Dermestidae). These setae are commonly recognized as contaminants of stored products and work and living environments. Exposure to hastisetae through direct contact, ingestion, and inhalation causes inflammation symptoms in human. For these setae, beyond the biomechanical defensive action, a possible secretory function has been recently hypothesized. Through an ultrastructural study of the insertion of hastisetae of Trogoderma granarium, performed integrating histology, SEM, and ion milling, the present paper reconsiders hastisetae morphological categorization and function. The results demonstrate, contrary to previous hypotheses, that hastisetae are not capable of any secretory activity and how these bristles cannot be considered as "true setae". The existence of a fully developed sensorial apparatus indicates that hastisetae belong to a unique type of highly modified mechanoreceptors.