The diversity of trypanosomatids in Culicoides biting midges in the Eastern Baltic region

Culicoides (Diptera, Ceratopogonidae) biting midges serve as vectors of viruses, bacteria, filaria, and protozoans, such as dixenous avian blood parasites (Trypanosomatidae). Additionally, these insects can harbour insect-specific flagellates-monoxenous trypanosomatids-which are generally considered harmless commensals; however, in certain cases, they can increase mortality or reduce the fitness of their insect hosts. Recent studies indicate that the prevalence of trypanosomatids in wild-caught biting midges can reach up to 11.1%, while in experimentally infected individuals, infection rates can be even higher. This study explores the diversity of trypanosomatids detected in Culicoides biting midges worldwide and supplements current knowledge with new records of avian Trypanosoma occurrence in these insects from the Curonian Spit, Lithuania. Wild-caught biting midges collected in 2020-2022 using UV light traps were tested for the presence of trypanosomatids using polymerase chain reaction (PCR)-based methods. Both morphological and molecular methods were used for Culicoides species identification. Four species of Trypanosoma were determined in biting midges belonging to eight different species. Avian trypanosomes from the T. bennetti group, T. avium, and T. culicavium were detected in C. pallidicornis/subfascipennis, C. segnis, C. kibunensis, C. festivipennis, C. pictipennis, C. duddingstoni, C. impunctatus, and biting midges of the C. obsoletus group. Additionally, mammal-infecting Trypanosoma from the T. theileri group were detected in C. pictipennis. Monoxenous Herpetomonas ztiplika and Sergeia podlipaevi were found in C. obsoletus group, C. segnis, C. pallidicornis/subfascipennis, C. kibunensis, C. pictipennis, C. festivipennis, and C. impunctatus biting midges as well. This study reports, for the first time, the presence of avian Trypanosoma in C. duddingstoni females and also reviews previous research data on the prevalence of both monoxenous and dixenous trypanosomatids in different Culicoides species. Our results enhance the understanding of trypanosomatid diversity in Culicoides biting midges and update the list of Culicoides species that should be considered in research on their role as potential vectors of avian Trypanosoma.