Coextinction dilemma in the Galápagos Islands: Can Darwin's finches and their native ectoparasites survive the control of the introduced fly Philornis downsi?

1. The survival of parasites is threatened directly by environmental alter- ation and indirectly by all the threats acting upon their hosts, facing coextinction.
2. The fate of Darwin’s finches and their native ectoparasites in the Galapagos Islands is uncertain because of an introduced avian parasitic fly, Philornis downsi, which could potentially drive them to extinction.
3. We documented all known native ectoparasites of Darwin’s finches. Thir- teen species have been found: nine feather mites, three feather lice and one nest mite. No ticks or fleas have been recorded from them yet.
4. Management options being considered to control P. downsi include the use of the insecticide permethrin in bird nests which would not only kill the invasive fly larvae but the birds’ native ectoparasites too.
5. Parasites should be targeted for conservation in a manner equal to that of their hosts. We recommend steps to consider if permethrin-treated cotton sta- tions are to be deployed in the Galapagos archipelago to manage P. downsi.