The ecology and taxonomy of the louse flies (Diptera: Hippoboscidae) and their role as vectors of avian disease

Vectors play a major role in the transmission of disease, and anthropogenic changes leading to shifts in parasite ranges, phenology and host associations can modify the risk of disease outbreaks. The Hippoboscidae are a family of Dipteran ectoparasites of birds (louse or flat flies) and mammals (keds) that are known to vector diseases. The last major United Kingdom (UK) studies of these flies took place in the 1950’s and 1960’s, and some aspects of their taxonomy remain confused. Avipoxvirus (APV) is mechanically vectored by a range of arthropods, and causes seasonal outbreaks of avian pox in Dunnocks Prunella modularis which peak when most arthropod vectors are most active.

Data from over 4300 Hippoboscids, collected by citizen scientists, as part of my “Mapping the UK’s Flat Flies Project”, are used throughout this thesis to update our knowledge of their ecology, and avian pox is used as a model for exploring disease transmission.

I begin by attempting to resolve the confusion around the species in the genus Ornithomya by focusing on Ornithomya fringillina, using both morphometric analysis and DNA sequences to show that it has several morphotypes, and is arguably the same species as the North American species O. bequaerti. Additionally, I include a cytochrome c oxidase subunit I (COX1) DNA sequence for Pseudolynchia garzettae, which like many Hippoboscids has no previously published DNA sequences available to help with identification by “DNA barcoding”.

Secondly, I describe the current biogeography and host associations of the UK Hippoboscidae. I provide evidence that three species, previously known only as vagrants, Ornithomya biloba, Pseudolynchia canariensis and P. garzettae, are now breeding here. I show major polewards range expansion of O. avicularia and O. fringillina, and range contraction of O. chloropus at the southern part of its range, since the 1960’s, and explore the increasingly complex network of interactions between the Hippoboscidae and their host species which could facilitate the spread of disease.

I then switch my focus to the epidemiology of APV in Dunnocks, using data from a 15 year study of Dunnocks in my garden on Exmoor, to explore survival rates, the seasonality of the disease and to estimate its incubation period, from the timing of the growth of primary feathers in Dunnock fledglings. Finally, I combine these results with those from DNA sequencing, and the phenology of Hippoboscids on Dunnocks, to conclude that APV is probably mechanically vectored by Hippoboscidae, and propose the use of Hippoboscidae as a non-invasive method for monitoring disease in wild bird populations.