Galapagos Species Checklist


Philornis downsi

Dodge & Aitken, 1968

Domain Eukaryota
Kingdom Animalia
Division Arthropoda
Class Insecta
Order Diptera
Suborder Brachycera
Family Muscidae
Genus Philornis

Philornis downsi  Dodge & Aitken, 1968

 

English common name: Ectoparasitic fly

Spanish common name: mosca parásita

Taxonomic comments: Syn: Philornis isla Couri 2000: 1.

Name status: Accepted name; taxon occurs in Galapagos.

Description: Similar in size and appearance to the common house fly, and usually dark in coloration. Male adults usually have yellow legs and eyes closer together, whereas females have darker legs. Female antenna plumose. Adult flies are free-ranging, eating fruits and nectar. They lay eggs in bird nests and the fly larvae feed on the blood and tissue of young chicks.

Larvae are free-living external parasites upon nestlings in bird nests (Dodge & Aitken 1968; Fessl et al. 2001), including Darwin’s finches.

Year of first record: 1964

Last updated: 24 Aug 2016

Origin

  • In
    Introduced
  • Na
    Native

  • Ac
    Accidental

    Taxon accidentally introduced, naturalized in the wild.

  • Cu
    Cultivated
  • Er
    Eradicated
  • Es
    Escaped
  • Ic
    Intercepted
  • AcQ
    Questionable Accidental
  • NaQ
    Questionable Native

Distribution

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Galapagos island groups: Floreana, Isabela, San Cristóbal, Santa Cruz, Santiago.

Present on 13 islands: Champion, Daphne Major, Fernandina, Floreana, Gardner (Floreana), Isabela, Marchena, Pinta, Pinzon, San Cristobal, Santa Cruz, Santa Fe, Santiago.

Preference for altitude zone in Galapagos: Dry zone-humid zone.

Native range: Known from Trinidad & Brasil, but the native range is likely to be wider.

Distribution classification: Eutropical.


Please be aware that this distribution map is automatically generated from database records (CDF and external specimens, literature records, and observations) and may not accurately reflect the currently-known distribution for all species.

General Ecology

Habitat preferences: Found in most habitat types in the Galapagos, from the arid lowland to humid highland zones.

Substrate or host preferences: Larval hosts are mainly passerine birds, but also include Culiciformes.

Trophic role: Pathogenous parasite (a parasite that causes diseases of its host).

Feeding type: Adults feed on fruit and nectar, and larvae are semi-hematophagous (blood and tissue feeding) parasites of birds.

Feeding preferences: Little is known about the feeding habits of adult flies. It is believed that they feed on fruits and nectar. In the laboratory they will feed on a variety of fruits and protein sources.

Reproductive biology: Females lay their eggs in birds’ nests on the nest material surface or on nestlings. Fly eggs have also been found on the nasal openings (nares) of nestlings. The eggs hatch after 1-2 days and 1st instar larvae feed within the nestlings’ nares. The 2nd and 3rd instar stages live in the nest base and emerge at night to feed on the blood and tissues of nestlings either externally or within the nares. Larvae pupate in the nest base after about 7 days, and emerge as flies approximately 14 days later. Genetic studies have shown that female flies can mate with up to 5 males, but mating has not been observed in the nests or anywhere else in the field.

Reproduction mode: Exclusively sexual (through production of gametes and fertilization).

Dispersal mechanism: Active dispersal.

Dispersal propagule: Philornis species are able to travel over large distances. In Galapagos, Philornis downsi are attracted to lights on tourist boats and may also have been dispersed by boats.

Galapagos associated species: Camarhynchus heliobates, Camarhynchus pallidus, Camarhynchus parvulus, Camarhynchus pauper, Camarhynchus psittacula, Certhidea olivacea, Coccyzus melacoryphus, Crotophaga ani, Dendroica petechia aureola, Geospiza fortis, Geospiza fuliginosa, Geospiza magnirostris, Geospiza scandens, Mimus melanotis, Mimus parvulus, Mimus trifasciatus, Myiarchus magnirostris, Pyrocephalus rubinus.

Natural enemies: In Galapagos four species of parasitic wasps have been reared from Philornis pupae (Spalangia endius, Brachymeria podagrica, B. cabira; and the eulophid Aprostocetus [Tetrastichinae]). There are no records of parasitoids of P. downsi in its native range; however, at least three species of wasps are known to parasitize Philornis species.

Invasion Ecology

Invasion risk score: Extreme risk.

Form of introduction: Accidentially introduced.

Impact in Galapagos: At least 16 endemic bird species, one native, and one introduced specie are attacked by P. downsi. The fly’s impact on birds is a serious threat especially to vulnerable and declining species. Philornis downsi parasitism has already been implicated in the decline of endemic, critically endangered species such as the mangrove finch (Camarhynchus heliobates) and the medium tree finch (C. pauper).
In addition to direct mortality (sometimes up to 100% of hatchlings in a nest die from parasitism), studies have confirmed that surviving birds have reduced life expectancy due to deformed beaks, reduced growth rates, and anaemia. Philornis has a greater impact on bird species with small clutch sizes, e.g. tree finch species, than species with bigger clutch sizes.

Related species impact: Philornis species affect at least 115 species of bird, particularly in the neotropics. Larvae of the genus Philornis reside in bird nests and may feed on either nestling feces (coprophagous scavengers), the blood of nestlings (semi-hematophagous parasites), or on nestling tissue and fluid (subcutaneous parasites).

Management

Control history in Galapagos: At this point in time, there are no known techniques to effectively mitigate the threat of P. downsi. In spite of considerable efforts by the Charles Darwin Foundation (CDF) and collaborators there are still substantial gaps in the understanding of the life history and ecology of P. downsi, which has prevented the development of methods to control the fly. Because of this, an international workshop was held by the Galapagos National Park Directorate (GNPD) and CDF in February 2012 to bring together local and international experts to find a solution for the management of P. downsi. Control options that are being investigated include mass trapping using lures, biological control, and spot treatments of nests with low risk pesticides.

Photos

Literature

  • Causton, C.E., Peck, S. B., Sinclair, B. J., Roque-Albelo, L., Hodgson, C. J. & B. Landry. (2006) Alien insects: threats and implications for the conservation of the Galapagos Islands. Annals of the Entomological Society of America, 99(1), 121-143.
  • Causton, C.E., Sevilla, C. (2008) Latest Records of Introduced Invertebrates in Galapagos and Measures to control them. Galapagos Report 2006-2007, CDF, GNP and INGALA, Puerto Ayora, Galapagos, Ecuador, p. 142-145.
  • 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. In: Galapagos Report 2011-2012. GNPS, GCREG, CDF and GC. Puerto Ayora, Galápagos, Ecuador.
  • Causton, C.E., Cunninghame, F. & Tapia, W. (2013) Manejo del parásito aviar Philornis downsi en las islas Galápagos: Un plan de acción colaborativo y estratégico. En: Galapagos Report 2011-2012. GNPS, GCREG, CDF and GC. Puerto Ayora, Galapagos, Ecuador.
  • Couri, M. S., Tavares, M. T. & Stenzel, R. R. (2006) Parasitoidism of chalcidid wasps (Hymenoptera: Chalcididae) on Philornis sp. (Diptera: Muscidae). Brazilian Journal of Biology 66:553-557.
  • Cunninghame, F., Ortiz-Catedral, L. & Fessl, B. (2012) Landbird Conservation Plan: Strategies for Reversing the Decline of passerine birds on the Galapagos Islands. Technical Report, CDF and GNPD.
  • Cunninghame, F., Ortiz-Catedral, L. & Fessl, B. (2012) Plan para la conservación de aves terrestres: Estrategias para revertir la disminución de las aves paseriformes en las Islas Galápagos. Informe Tecnico, CDF and GNPD.
  • Dudaniec, R.Y., Kleindorfer, S. & Fessl, B. (2006) Effects of the introduced ectoparasite Philornis downsi on haemoglobin level and nestling survival in Darwin’s Small Ground Finch (Geospiza fuliginosa). Austral Ecology (2006) 31, 88–94, doi:10.1111/j.1442-9993.2006.01553.x
  • Dudaniec, R.Y., Fessl, B. & Kleindorfer, S. (2007) Interannual and interspecific variation in intensity of the parasitic fly, Philornis downsi, in Darwin’s finches. Biological Conservation 30: 325-323.
  • Dudaniec, R.Y., Gardner, M.G. & Kleindorfer, S. (2007) Isolation, characterization and multiplex polymerase chain reaction of novel microsatellite loci for the avian parasite Philornis downsi (Diptera: Muscidae). Molecular Ecology Notes (2007), doi: 10.1111/j.1471-8286.2007.01900.x
  • Dudaniec, R.Y., Gardner, M.G. & Kleindorfer, S. (2009) Offspring genetic structure reveals mating and nest infestation behaviour of an invasive parasitic fly (Philornis downsi) of Galápagos birds. Biol. Invasions, DOI 10.1007/s10530-009-9464-x.
  • Dvorak, M., Fessl, B., Nemeth, E., Kleindorfer, S.M., & Tebbich, S. (2012) Distribution and abundance of Darwin ́s Finches and other land birds on Santa Cruz Island Galapagos: evidence for declining populations. Oryx 46:78-86
  • Fessl, B., Kleindorfer, S. & Tebbich, S. (2006) An experimental study on the effects of an introduced parasite in Darwin’s finches. Biological Conservation 127(1): 55-61.
  • Fessl, B., Young, H. G., Young, R. P., Rodríguez-Matamoros, J., Dvorak, M. & Tebbich, S. (2010) How to save the rarest Darwin’s finch from extinction: the mangrove finch on Isabela Island. Philosophical Transactions of the Royal Society of London, Series B: Biological Sciences 365:1019–1030.
  • Fessl, B., Tebbich, S. (2002) Philornis downsi - a recently discovered parasite on the Galápagos archipelago - a threat to Darwin's finches? Ibis 144: 445-451.
  • Fessl, B., Couri, M.S. & Tebbich, S. (2001) Philornis downsi Dodge & Aitken, new to the Galapagos Islands
    (Diptera, Muscidae).
    Studia Dipterologic 8: 317-322.
  • Fessl, B., Sinclair, B.J. & Kleindorfer, S. (2006) The life-cycle of Philornis downsi (Diptera: Muscidae) parasitizing Darwin’s finches and its impacts on nestling survival. Parasitology 133: 739–747, doi:10.1017/S0031182006001089
  • Galligan, T.H., Kleindorfer, S. (2009) Naris and beak malformation caused by the parasitic fly, Philornis downsi (Diptera: Muscidae), in Darwin's small ground finch, Geospiza fuliginosa (Passeriformes: Emberizidae). Biological Journal of the Linnean Society 98: 577-585.
  • Huber, S.K. (2008) Effects of the introduced parasite Philornis downsi on nestling growth and mortality in the medium ground finch (Geospiza fortis). Biological Conservation 141: 601-609.
  • Jiménez-Uzcátegui, G., Wiedendfeld, D.A. (2005) Philornis downsi ectoparasite: wild birds affected and distribution in Galápagos. XIX Annual Meeting of the Society Conservancy Biology. Universidade de Brasília. Brasilia DF, Brazil, pp. 103.
  • Koop, J. A. H., Huber, S. K., Laverty, S. M. & Clayton, D. H. (2011) Experimental demonstration of the fitness consequences of an introduced parasite of Darwin’s finches. PLoS ONE, 6(5):e19706, doi: 10.1371/journal.pone.0019706.
  • O'Connor, J.A., Sulloway, F.J., Robertson, J. & Kleindorfer, S. (2009) Philornis downsi parasitism is the primary cause of nestling mortality in the critically endangered Darwin's medium tree finch (Camarhynchus pauper). Biodiversity Conservation DOI 10.1007/s10531-009-9740-1
  • Sinclair, B.J., Peck, S.B. (2005) An annotated checklist of the Diptera of the Galápagos Archipelago (Ecuador). Charles Darwin Research Station, unpublished, 64 pp.
  • Tavares, M.T., Stenzel, R.R. (2006) Parasitoidism of chalcidid wasps (Hymenoptera: Chalcididae) on Philornis sp. (Diptera: Muscidae). Brazilian Journal of Biology 66:553-557.
  • Wiedenfeld, D.A., Jiménez-Uzcátegui, G., Fessl, B., Kleindorfer, S. & Valarezo, J.C. (2007) Distribution of the introduced parasitic fly Philornis downsi (Diptera, Muscidae) in the Galapagos Islands. Pacific Conservation Biology 13(1): 14-19.