Control of the Invasive Parasitic Fly Philornis downsi

Control of the Invasive Parasitic Fly Philornis downsi

Finding Alternatives to Control the Invasive fly Philornis downsi

This project is currently Active

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.

Research Team

Charlotte Causton

Principal Investigator

Charlotte has worked with the CDRS in different projects since 1997, including terrestrial invertebrate research programs. She has extensive experience developing methods for controlling invasive...

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Paola Lahuatte


Paola Lahuatte arrived in 2013 to work as a volunteer in the project about an invasive fly, Philornis downsi , which parasitizes and kills the chicks of Galapagos landbirds. She focused her Bachelor...

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Alejandro Mieles


Courtney Pike


Dennis Mosquera


Andrea Cahuana

Project Assistants

Magaly del Consuelo Infante


Project Details

In late 2017 and early 2018, two more landbird species in Galapagos were found to be hosts for the introduced parasitic fly, Philornis downsi: One is the Galapagos martin (Progne modesta), and the other is the Gray Warbler Finch (Certhidea fusca), identified by Sarah Knutie. This makes a total of 20 bird species whose conservation status is seriously affected by this invasive fly. These species also include 12 species of Darwin Finches. So, Philornis downsi is seriously affecting the survival of numerous species of landbirds, including the Mangrove Finch, which is critically endangered.

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 making a multi-institutional collaboration effort (currently including 22 institutions from 10 countries) to research this little-known fly’s biology and ecology. At the same time, researchers are seeking effective, environmentally-friendly control methods.

To identify methods to control this land-bird parasite, it is fundamental to maintain laboratory colonies of it. This has never been achieved before by researchers working with this species. Now CDF scientists have developed a method to raise these flies’ maggots, by devising a diet to replace the live bird hosts. They are working arduously to discover how to successfully raise adult flies of this species. Ironically, although the flies can survive harsh environmental and ecological conditions in Galapagos, their reproductive success in the laboratory is low, which suggests that they need certain special elements, which researchers are now working on. The most interesting preliminary findings include the discovery that birds’ odors stimulate flies to lay eggs. Researchers suspect that these odors may also play a key role in helping flies locate nests and maybe even breeding pairs. During the remaining months of 2018, the research team will be expanded to discover which odors are most appealing to these flies. Once this is known, some of these odors might potentially be used to trap flies in endangered land-bird nesting areas.

Keywords: Invasive, Diptera, parasite, control

Main Goal

Develop effective tools for the management of Philornis downsi to ensure the long-term conservation of Galapagos landbirds.

Specific Goals

  1. Understand the ecology and biology of Philornis downsi on the Galapagos Islands and mainland Ecuador
  2. Develop and test methods to control Philornis downsi in the nesting areas of the Mangrove Finch and other threatened bird species;
  3. Identify a chemical attractant or mixture of attractants for use in the management of Philornis downsi;
  4. Determine if the natural enemies of Philornis downsi and Philornis spp. found on continental Ecuador can be used in a biological control program in Galapagos;
  5. Evaluate the feasibility of using the Sterile Insect Technique to control Philornis downsi.

Results (final or preliminary)

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.

Bibliographical References

  • Fessl, B., Heimpel, G.E., & Causton, C.E. (2018). Invasion of an avian nest parasite, Philornis downsi, to the Galapagos Islands: colonization history, adaptations to novel ecosystems, and conservation challenges. Disease Ecology, Social and Ecological Interactions in the Galapagos Islands, 213-268.  Springer International Publishing AG. DOI 10.1007/978-3-319-65909-1_9
  • Ben-Yosef, M.S., Zaada, D.S.Y., Dudaniec, R.Y., Pasternak, Z., Jurkevitch, E., Smith, R.J., Causton, C. E., Lincango, M.P., Tobe, S.S., Mitchell, J.G., Kleindorfer, S.,  & Yuval, B. (2017). Host-specific associations among the microbiome of the parasitic fly Philornis downsi and Darwin’s finches. Molecular Ecology.  DOI: 10.1111/mec.14219
  • Bulgarella, M., Quiroga, M. A., Boulton, R. A., Ramírez, I. E., Moon, R. D., Causton, C. E., & Heimpel, G. E. (2017). Life Cycle and Host Specificity of the Parasitoid Conura annulifera  (Hymenoptera: Chalcididae), a Potential Biological Control Agent of Philornis downsi (Diptera: Muscidae) in the Galapagos Islands. Annals of the Entomological Society of
  • Cha D. H. , Mieles A. E., Lahuatte P., Cahuana, A., Lincango, M. P., Causton, C. E., Tebbich, S., Cimadom, A., & Teale, S. A. (2016). Identification and optimization of microbial attractants for Philornis downsi, an invasive fly parasitic on birds. Journal of Chemical Ecology.
  • Lahuatte, P. F., Lincango, M. P., Heimpel, G. E. & Causton, C. E. (2016). Rearing larvae of the avian nest parasite, Philornis downsi (Diptera: Muscidae), on chicken blood-based diets. Journal of Insect Science 16: 84: 1-7.
  • Lincango, P., Causton, C., Cedeño, D., Castañeda, J., Hillstrom, A. & Freund D. (2015). Interactions between the Avian Parasite, Philornis downsi (Diptera: Muscidae) and the Galapagos Flycatcher, Myiarchus magnirostris Gould (Passeriformes: Tyrannidae). Journal of Wildlife Diseases. 51: 907-910.
  • Bulgarella, M., Quiroga, M. A., Brito Vera, G. A., Dregni, J. S., Cunninghame, F., Mosquera Muñoz, D. A., Monje, L. D., Causton, C. E., & Heimpel, G. E. (2015). Philornis downsi (Diptera: Muscidae), an avian nest parasite invasive to the Galápagos Islands, in mainland Ecuador. Ann. Entomol. Soc. Am. 108: 242–250.
  • Causton, C. E. & Lincango, M. P. (2014). Review of chemical control methods for use against Philornis downsi in nests of threatened Galapagos birds, with an in-depth nontarget risk assessment of permethrin. Technical report No 1-2014. Charles Darwin Foundation for the Galapagos Islands. ISSN: 1390-6526.
  • Causton C. E., Cunninghame, F. & Tapia, W. (2013). Management of the avian parasite Philornis downsi in the Galapagos Islands: a collaborative and strategic action plan. Galapagos Report 2011-2012. GNPS, GCREG, CDF and GC. Puerto Ayora, Galapagos, Ecuador. Management of the avian parasite Philornis downsi in the Galapagos Islands


Galapagos Conservancy, International Community Foundation (with a grant awarded by The Leona M. and Harry B. Helmsley Charitable Trust), and Lindblad Expeditions - National Geographic Fund.

The “Charles Darwin Foundation for the Galapagos Islands”, in French “Fondation Charles Darwin pour les îles Galapagos”, Association International sans but lucratif (“AISBL”), has its registered office located at Drève du Pieuré 19, 1160 Brussels, and is registered under the trade registry of Brussels under the number 0409.359.103.

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