Ontogenetic Variations in the Sensory Organ Structure and Morphology on the Cephalic Appendages of Hermetia illucens (Diptera: Stratiomyidae) Larvae

The black soldier fly, Hermetia illucens (Linnaeus, 1758), is a globally recognized resource insect for waste bioconversion and sustainable resource provision. Understanding its larval sensory system is key to explaining feeding and environmental perception behaviors. This study used scanning and transmission electron microscopy to analyze the types, distribution, ultrastructure, and developmental consistency of sensilla on larval cephalic appendages. Five sensilla types were found on antennae, sensilla basiconica I–II, sensilla twig basiconica I–II, and sensilla campaniformia, each type comprising 2–6 sensilla. Mouthparts harbored ten types, including sensilla twig basiconica III–V, sensilla placodea, sensilla ligulate, sensilla digitiformia, sensilla trichodea, and sensilla chaetica I–III, with 2–9 sensilla per type. All sensilla showed constant numbers and positions throughout larval development. Ten sensillum types with cuticle pores were innervated by 2–6 sensory neurons, primarily suggesting chemoreceptors; these were concentrated at the tips of antennae and maxillary palps. Sensilla digitiformia on the palps possessed a non-porous cuticle and a single sensory cell, indicative of a thermo-/hygroreceptive role. Sensilla chaetica and trichodea, with non-porous cuticles and no dendrites, were mechanosensory. These results reveal the morphofunctional basis of larval sensation, supporting chemoreception studies and optimizing rearing via behavioral modulation.