Population dynamics of an invasive bird parasite, Philornis downsi (Diptera: Muscidae), in the Galapagos Islands

A study on the invasive parasitic fly, Philornis downsi, in the Galápagos Islands reveals that female flies can persist even when bird hosts are scarce, challenging previous assumptions about their population dynamics. The research, conducted between 2012 and 2014 at dry lowland and humid highland sites on Santa Cruz Island, found that female flies remained active year-round, with a significant proportion inseminated and gravid, indicating continuous breeding cycles. Male fly catch rates declined outside bird breeding seasons, suggesting host availability is a key regulator of their population. Overall, fly numbers were higher in drier habitats, potentially due to greater host or resource availability. The study also suggests that P. downsi populations are multivoltine and governed by simple density dependence, with female numbers likely regulated by the availability of bird nests with nestlings. These findings highlight the vulnerability of already threatened Galápagos bird species, which may be further exacerbated by unknown reservoir hosts or behavioral changes in the parasite.

Causton, C. E., Moon, R. D., Cimadom, A., Boulton, R. A., Cedeño, D., Lincango, M. P., Tebbich, S., & Ulloa, A. (2019). Population dynamics of an invasive bird parasite, Philornis downsi (Diptera: Muscidae), in the Galapagos Islands. Plos One, 14(10), e0224125. https://doi.org/10.1371/journal.pone.0224125