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Twenty Galapagos bird species, including 12 species of Darwin’s finches, are under threat from a parasitic fly, Philornis downsi. This fly was accidentally introduced to Galapagos and is seriously affecting the survivorship of several Galapagos birds including the critically endangered Mangrove Finch. Flies are adept at locating bird nests to lay their eggs. Once larvae hatch they feed on the blood of hatchlings, sometimes causing all of the chicks in a nest to die.
In order to reduce the impact of Philornis downsi on birds, CDF and the Galapagos National Park Directorate are overseeing a multi-institutional collaborative effort (now up to 22 institutions from ten countries) that is investigating the biology and ecology of this little-known fly, while simultaneously conducting research to find effective and environmentally friendly control methods.
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In 2018, two more landbird species in Galapagos were found to be hosts of the introduced parasitic fly, Philornis downsi: the endangered Galapagos Martin (Progne modesta), and the Gray Warbler Finch (Certhidea fusca) — reports by D. Anchundia and S. Knutie. This makes a total of 20 bird species that are affected by this invasive fly. Twelve of these species are Darwin’s finches. Philornis downsi is seriously affecting the survivorship of several of these species including the critically endangered Mangrove Finch.
These invasive flies are experts at locating birds’ nests to lay their own eggs. Once the maggots hatch, they feed off the blood of baby chicks, which sometimes kills the nest’s entire clutch. To reduce the impact of Philornis downsi on landbirds, the CDF and GNPD are coordinating a multi-institutional collaboration effort (currently including 22 institutions from 10 countries) to research the biology and ecology of this little-known fly. At the same time, researchers are researching effective, environmentally-friendly control methods.
Our main goal is to develop effective tools for the management of Philornis downsi to ensure the long-term conservation of Galapagos landbirds.
Year-round access to flies is critical to the development of control methods. This requires maintaining colonies of this bird parasite in the lab, something that has never been achieved before. CDF scientists have managed to develop a method for rearing fly larvae on a diet that replaces that of their living bird hosts, and are now working hard to figure out how to successfully get adult flies to breed in captivity. Together with collaborators from SUNY-ESF and Syracuse University, scientists have discovered that bird odors stimulate flies to lay eggs. The scientists suspect that the odors may also play a role in helping locate nests and perhaps even mates. Scientists are investigating whether these odors could be used as lures in trapping programs, either alone, or in combination with odors of fermenting fruit (fed on by adults) or odors emitted by the flies themselves (for example, pheromones).
Another potential control technique is called biological control. This method involves finding a natural enemy of the fly from its native range and introducing it to Galapagos to help reduce fly numbers. This type of control can be used only when it is shown that the natural enemy would not have any negative impacts on Galapagos species and ecosystems. Exploratory surveys on mainland Ecuador led by University of Minnesota and collaborators have found at least one potential biological control agent, a parasitic wasp, Conura anullifera. Studies will continue to determine whether its introduction would pose risks to Galapagos.
In the meantime, CDF landbird and Philornis teams are working with Galapagos National Park Directorate and scientists from the University of Vienna to develop methods for protecting the nests of the most endangered bird species.
Keywords: Invasive, Diptera, parasite, control
This work is carried out in collaboration with Galapagos National Park Directorate, Galapagos Biosecurity Agency (ABG), the Canadian National Collection of Insects, Arachnids and Nematodes (CNC) of Agriculture and Agri-Food Canada, Flinders University, Galapagos Science Center, Hebrew University of Jerusalem (Israel), Instituto Nacional de Biodiversidad, LECEN - ICIVET LITORAL (Argentina), International Atomic Energy Agency (IAEA), Macquarie University, University of Missouri - Saint Louis, SUNY-ESF, Syracuse University, Universidad Central del Ecuador, University of Connecticut, University of Guayaquil, University of Massachusetts – Dartmouth, University of Minnesota, University of Utah, University of Vienna, University of West Indies, University of Victoria of Wellington, and USDA-ARS/COPEG.