Ultramorphological and molecular characteristics of the larval stages of the horse nasal-myiasis fly, Rhinoestrus sp. (Diptera: Oestridae) from Mongolian horse in China.

The research article focuses on the study and analysis of the larvae of Rhinoestrus sp., a fly responsible for causing severe nasal myiasis in horses and potentially humans. The study also explores the project’s possible economic impact.

Research and Analysis Method

• The ultrastructure of the larval stages of Rhinoestrus sp. obtained from a Mongolian horse was studied under light and scanning electron microscopy to understand its characteristics better.
• The analysis was focused on the structure of the anterior and posterior regions, and the spines of the third segment.
• Ten specimens were analyzed for each stage of the larval development.
• In addition to this, 34 third-instar (the last stage before the larvae metamorphose into pupae) larvae of Rhinoestrus sp. were put through molecular characterization using polymerase chain reaction (PCR).

Genetic Sequencing and Phylogenetic Relationships

• The study also involved sequencing part of the mitochondrial cytochrome oxidase subunit I gene (COXI) of Rhinoestrus sp.
• Based on COXI gene sequences from 12 oestrid species available in GenBank, phylogenetic relationships for Rhinoestrus sp. obtained from Mongolian horses were reconstructed.
• Both intra- and interspezies variations in nucleotide sequences were analyzed.

Findings and Conclusion

• The study found that the cephalopharyngeal skeleton of immature Rhinoestrus sp. larvae consists of “H”-shaped hypopharyngeal sclerites and “Y”-shaped pharyngeal sclerites.
• There was a consistent number and placement of pairs of papillary sensillae in the larvae’s cephalic region across all three instars. However, two pairs of verruciform sensillae were found in the third-instar larvae which was not found in other instars.
• When comparing COXI sequences, the researchers found that the Rhinoestrus sp. larvae collected from Mongolian horses were separable from Cephenemyia sp., R. phacochoeri, and R. usbekistanicus.
• The findings also suggested that the samples closely resembled, but were not the same as, Rhinoestrus purpureus, hinting towards the possibility of the existence of a new species. Further studies are needed to confirm it.
• Moreover, the pairs of verruciform sensilla present in the third-instar larvae resembled those found in Oestrus ovis and Pharyngomyia picta.