Control of the Invasive Parasitic Fly Philornis downsi

Control of the Invasive Parasitic Fly Philornis downsi

Finding methods 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.

Our 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 as a volunteer of the project " Finding Alternatives to Control the Invasive fly Philornis downsi ". Her undergraduate thesis focused on developing a method for...

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Alejandro Mieles


Alejandro started working for the CDF in 1999 as a volunteer. Following which he was awarded a grant from the CDF to carry out his undergraduate thesis on the impacts of a fire ant eradication...

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Courtney Pike


Denis Mosquera


Andrea Cahuana

Project Assistant

Andrea Cahuana has a Bachelor's Degree in Ecological Tourism and came to CDF in 2012 as a local volunteer while finishing her third level studies. She worked in the Herbarium, Botany area where she...

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Magally joined the project " Finding Alternatives to Control the Invasive fly Philornis downsi " in October 2018 and has quickly learned about the work that we are doing. She is helping with the...

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Joselyn Yar

Field Assistant

Joselyn Yar is from Ecuador and she is a permanent resident of the Galapagos Islands. She lives in Puerto Ayora on Santa Cruz Island. Joselyn first worked as a volunteer at the Charles Darwin...

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Project Details

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.

Philornis Downsi fly
Invasive parasitic fly Philornis Downsi. Photo by: Sam Rowley, CDF.

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 team in the field.
Project team checking traps in the field. Photo by: Liza Díaz Lalova, CDF.

Our main goal is to develop effective tools for the management of Philornis downsi to ensure the long-term conservation of Galapagos landbirds.

The specific objectives of our project are:

  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.

Our results

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).

Paola Lahuatte criando larvas de la mosca invasora Philornis downsi en el laboratorio de la FCD.
Paola Lahuatte analyzing larvae of the Philornis downsi fly in the CDF laboratory. Photo by: Liza Díaz Lalova, CDF.

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

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


The mission of the Charles Darwin Foundation and its Research Station is to tackle the greatest threats and challenges to Galapagos through scientific research and conservation action, in order to safeguard one of the world’s most important natural treasures.

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