Semester of Graduation
Master of Science (MS)
The Dipteran family Tabanidae is among the most diverse families of insects that is comprised of approximately 144 genera with 4455 described species (Pape et al. 2011). Members of the family Tabanidae have been studied for well over 100 years in Louisiana. Hine (1906, 1907) conducted the first surveys of the members of the tabanid family and noted the presence of 14 species. Jones and Bradley (1923) supplemented Hine’s observations with their own inventory of horse flies across four parishes and found an additional 14 species that were not recorded by Hine. Subsequently, Tidwell (1970, 1973) conducted a survey of horse flies of Louisiana and constructed dichotomous keys for identification of 87 species across eleven genera. Leprince et al. (1991) completed a survey of horse flies captured in mixed bottomland hardwood regions in St. Landry Parish and Lafourche Parish and reported the seasonal abundances of 14 species found within the two study locations. While these surveys yielded valuable information, there has been no comprehensive survey of horse flies along the Louisiana coast. The purpose of this study was to establish inventories of the horse flies of tidal marshes of Louisiana which range from freshwater to the high salinity zones. The study was initiated to describe the spatial and temporal occurrence of the greenhead horse fly, Tabanus nigrovittatus and potential sibling species relations along coastal Louisiana using morphometric techniques, DNA barcoding methods, and phylogenetic trees. Monthly adult tabanid collections were made with canopy traps in tidal marshes of Barataria Bay in Plaquemines Parish and Caillou Bay in Terrebonne Parish in intermediate (~3ppt), brackish (~8ppt), and saltmarsh (~16ppt) locations. Three species of tabanids (T. acutus, T. hinellus and C. flavidus) were collected along with T. nigrovittatus within the estuaries. Specimens of T. acutus were collected primarily during crespuscular and nocturnal hours. Population abundance of the different Tabanus species varied among salinity zones. The number of collected specimens of T. hinellus decreased with increasing salinity while specimens of the T. nigrovittatus complex were collected at both High and Low salinities sites, dependent upon the estuary and time. In addition to seasonal distribution data, genetic barcoding of the four species was completed. The cytochrome oxidase I (CO1) subunit was found to be the locus with the highest resolution power to make species-level designations. Previously unidentified larvae and males were successfully matched to the genetic sequences of morphologically identified females of the different species. The T. nigrovittatus complex populations were bivoltine through multiple seasons. Then, T. nigrovittatus complex specimens collected from early and late season and from the different salinity zones were used to measure the genetic diversity within the T. nigrovittatus complex by using morphometrics and phylogenetic analysis. The morphometric analyses showed that total body length of specimens of the T. nigrovittatus complex were higher in the first generation of the year compared to the second. Phylogenetic analysis of the T. nigrovittatus complex showed that there are three clades of greenheads in the estuaries of Louisiana among the salinity zones. One of the clades was found in High salinity zones and was genetically similar to T. nigrovittatus specimens from Massachusetts. A second clade was native to the lower salinity zones. Additionally, flies from the third clade fit the description of T. conterminus. The findings from this study provide more insight into the T. nigrovittatus complex along the Gulf Coast that includes the addition of T. conterminus. The species identity of the freshwater member of the T. nigrovittatus complex remains to be determined.
Davis, Darrius M., "Understanding the Horse Fly Species and Species Relations of the Tabanus nigrovittatus Complex Along Coastal Louisiana" (2022). LSU Master's Theses. 5639.