Identification and Expression Patterns of Opsin Genes in Phortica okadai, the Only Confirmed Vector of Thelazia callipaeda in China

In China, Phortica okadai is the only established vector for Thelazia callipaeda and transmits infective larvae to various animals feeding on ocular secretions. Insect opsins are key components of the visual system and play essential roles in host location. However, the opsin repertoire and phylogenetic relationships in P. okadai remain unknown. Here, we identified five opsin genes from adult P. okadai genomic data and profiled their expression across developmental stages and tissues by real-time polymerase chain reaction. The results showed that four opsin genes (PoRh1, PoRh3, PoRh5, and PoRh6) were predominantly expressed in adult compound eyes and peaked during the adult stage, suggesting important roles in vision-dependent behaviors of adult P. okadai. These findings provide a foundation for elucidating the visual mechanisms and host-seeking behavior of P. okadai.