Ultrastructural Characterization of Developmental Stages and Head Sensilla in Portici okadai, Vector of Thelazia callipaeda

<i>Phortica okadai</i>, a vector of <i>Thelazia callipaeda</i>, is associated with an increasing incidence of thelaziasis. The complex habitat and chemosensory system of <i>P. okadai</i> are critical for its proliferation and expansion. However, ultrastructural data across developmental stages remain limited. This study used scanning electron microscopy to examine the ultrastructure of <i>P. okadai</i> developmental stages, with a focus on head sensilla. The results showed that the eggs of <i>P. okadai</i> are dark brown and cylindro-oval. The larvae are vermiform, divided into 11 segments. The pupae are marked by a conspicuous respiratory tubercle, and the posterior spiracle contains three distinct spiracular slits. Among five types of sensilla (trichoid, intermediate, chaetica, coeloconic, and basiconic), coeloconic, intermediate, and trichoid sensilla were predominantly found on the antennae, while basiconic and chaetica sensilla were distributed on both the antennae and the maxillary palps of <i>P. okadai</i>. The analysis revealed that the absence of dorsal appendages on the eggs distinguishes <i>P. okadai</i> from <i>D. melanogaster</i>. Males have longer antennae and exhibit sexual dimorphism in the length of sensilla (ChII, TB, and LB). This study provides the first comprehensive ultrastructural characterization of <i>P. okadai</i> developmental stages and head sensilla, laying a foundation for species identification and olfactory system research.