Wing vein shape signal in Culicoides oxystoma (Schultzei group) in Nigeria – Tool for discrimination (diptera: Ceratopogonidae) using geometric approach

Abstract Culicoides oxystoma , C. enderleini, C. schultzei and C. subschultzei belong to the Schultzei group of biting midges in the Order Diptera and are members of the Nematocera sub-order. They are vectors of economically important livestock diseases. Precise morphological identification for discrimination between members of the group has remained ambiguous and incoherent in literature, but necessary in entomologic evaluations of disease transmission and epidemiology in solving taxonomic challenges among groups. Wing phenotypes represent signaling patterns useful for classification of Culicoides in two vegetation zones (Ibadan, rainforest zone and Makurdi, Guinea savannah zone) of Nigeria. This study utilized landmark-based geometric morphometric approach in differentiating wing venation patterns of C. oxystoma, C. enderleini , C. schultzei and C. subschultzei, thus providing baseline data for classification of biting midges in Nigeria. The wing shape of C. oxystoma revealed specific variability with at least two morphologic variants that were hitherto unclassified. Landmarks on the first dorsal and cubital veins contributed 68% and 92% of all variations and distinguished C. oxystoma from others in the group; both shape and size elements were found responsible for species discriminations. Only one morpho-typic variant of C. schultzei was observed with predominance of ecotypes based on geographical location. A consistent morpho-geometry of wing venation found in C. schultzei suggested non-plasticity in morphology while C. enderleini demonstrated the widest variability. Based on landmarks and phylogenetic analyses, it is suggested that the Schultzei group of Culicoides (genus Latreille) in Nigeria be updated with a C. oxystoma subgenus.