Morphological Description of the Three Larval Instars of Wohlfahrtia nuba (Diptera: Sarcophagidae)

Background: Accurate identification of the larval stages of Wohlfahrtia nuba, a flesh fly species within the Sarcophagidae family, is crucial in forensic and medical entomology. This species may contribute to estimating the postmortem interval (PMI) and is associated with causing myiasis in livestock and humans. The insufficient data regarding the morphology of the immature stages of W. nuba hinders the taxonomic identification of this species’ larvae in carcasses without raising adults. Therefore, this study provides a comprehensive examination of the morphological characteristics of three instars of W. nuba larvae using light microscopy. Methods: It includes an examination of the cephalopharyngeal skeleton, pseudocephalon, antennal complex, oral ridges, anterior spiracles and their papillae number and arrangement, thorax and abdomen spinulation, number and distribution of papillae around the entrance of the spiracular cavity and posterior spiracles. Result: The present study’s findings demonstrate the distinct morphological characteristics that differentiate the three larval instars, facilitating accurate identification and developmental staging. The three larval stages have two curved mouth hooks. A large median hook is absent. The labrum is a reduced structure exhibiting four highly sclerotized teeth between the mouth hooks. The dorsal arch is short, curved and does not extend to the parastomal sclerite. The anterior spiracles, located laterally on the first thoracic segment, exhibited variability in the number of papillae across the three instar larvae. The first larval instar exhibited a total of eight papillae, which increased to 10 in the second instar and reached 11 in the third instar. These papillae are arranged in a row resembling an arch. The spines encircling the cephalic collar are thin and set into 6-7 rows, separating the first segments of the thorax. The posterior spiracle contains two incomplete peritremes hidden in a deep cavity. It is characterized by a single aperture divided at its upper section and shielded by thin hair-like structures during the first larval instar. Each incomplete peritreme contained two slits for the second larval instar and three slits for the third larval instar. The peritreme lacks a ventral arch and the button is not easily noticeable. A ring of 12 cuticular papillae encircles the anal cavity. These data add new morphological features to differentiate between W. nuba larvae in clinical and forensic contexts. This will help with taxonomic and forensic species identification studies and benefit farmers and veterinarians.