Philornis downsi is a dipteran fly species known to parasitize passerine birds in the Neotropics. P. downsi is speculated to be a recently introduced species in Galápagos Islands, so it is important to understand its effects on the archipelago’s native and endemic avian species. Avian parasites and pathogens have been previously reported in the Galápagos, leading the Galápagos National Park and the Charles Darwin Foundation to focus efforts on the study and management of potential avian disease vectors. The main goal of this study was to determine whether P. downsi is a host for avian parasites and pathogens found in the Galápagos Islands. In Chapter I, I initially discuss introduced species as avian disease agents or vectors and highlight previous studies focused in Galápagos. Detailed background information on the life history and ecology of P. downsi is provided, followed by a review of the literature on insects as vectors of avian disease. In Chapter II, I report research conducted on P. downsi, assessing its capability of hosting avian parasites. Using molecular techniques, we tested P. downsi adults for haemosporidian parasites and Trypanosoma, as well as microfilarial nematodes, all parasites that have been described in Galápagos birds. We did not detect the presence of avian parasites of these genera, nor did we detect filarial nematodes; however, we did detect insect-specific trypanosomatids within P. downsi samples with a 0.90 overall prevalence. Our results suggest P. downsi is not a host of the avian parasites and pathogens for which I screened, indicating it is not a suitable vector; however, further research should be conducted. We recommend future studies to include testing of P. downsi larvae, an expanded geographical range for sample collection, and inclusion of other avian parasites and arboviruses
