First Report of Megaselia scalaris in Évora Region

Abstract

Introduction: Megaselia scalaris, commonly known as scuttle fly, is a polyphagous and synanthropic species with broad distribution and high ecological plasticity. Its presence has significant implications for public and animal health, food safety, forensic science, and beekeeping. Objective: To report, for the first time, the presence of M. scalaris in Évora Region. Materials and Methods: In October 2025, as part of an ongoing study in the south of Portugal, several samples of distinct swine muscles and arthritis liquid were inoculated in Plate Count Agar and Violet Red Bile Glucose culture media and incubated at 30°C for regular microbiological analyses. After a 72 hours incubation period, the plates were examined and several larvae were observed. The plates were maintained, allowing the observation and later identification of various developmental stages: larva, pupa, and adult. Morphological identification of the adult flies was performed, and molecular confirmation via PCR targeting the mitochondrial cytochrome oxidase subunit I (COI) gene is ongoing. Results and Discussion: During the macroscopic examination of the Petri dishes, unusual trails on the culture media and small moving larvae were detected. Under conventional light microscopy, the larvae exhibited an elongated, translucent body approximately 6 mm in length. Morphological evaluation of adult flies led to their putative identification as M. scalaris, based on the morpho-anatomical features, including size and colour; the shape and dimensions of the head and thorax; wing shape, size, and venation pattern, the specimens were identified as belonging to M. scalaris fly. To the best of our knowledge, this is the first report of M. scalaris in mainland Portugal, which is noteworthy, because of its importance in food contamination, myiases (intestinal, urogenital, ocular, vaginal, and cutaneous), and its role as a parasite and vector of pathogens affecting other arthropods, as Apis mellifera. Conclusions and Future Perspectives: The accidental observation of M. scalaris in Évora region highlights the need for continuous monitoring of the species. Future research should assess its distribution, pathogenic potential in public health, implications for food safety, and impact on apiculture. A molecular confirmation via PCR is currently underway, and it will be the first report of molecular identification of M. scalaris in Portugal.