Specificity within bird–parasite–parasitoid food webs: A novel approach for evaluating potential biological control agents of the avian vampire fly

Ismael E. Ramirez, Charlotte E. Causton, George A. Gutierrez, Denis A Mosquera, Paolo Piedrahita, George E. Heimpel

Research output: Contribution to journalArticlepeer-review


Quantitative food web analyses can provide insights into the specificity of consumers such as herbivores, parasites and parasitoids. Understanding such patterns can be useful in forecasting the potential benefits and risks of biological control agents being considered for introduction against invasive species. The avian vampire fly, Philornis downsi (Diptera: Muscidae), is a neotropical bird parasite that is invasive in the Galapagos Islands, where it is causing substantial mortality of endemic bird species. We used a novel in-field experimental food web approach within the native range of P. downsi in Ecuador to test the hypotheses that pupal parasitoids known to attack P. downsi specialize on members of the genus Philornis, which occur only in bird nests. We deployed pupae of non-Philornis fly species adjacent to bird nests to assess specificity of the parasitoids and used two indices to assess specificity: Resource Range (RR), which evaluates the breadth of host use, and Pair Difference Index (PDI), which evaluates interaction strength. The results revealed very strong compartmentalization within the guild of pupal fly parasitoids, with four species attacking only Philornis spp. Both specificity indices indicated significant levels of specificity towards the genus Philornis for two of these species: Conura annulifera and Trichopria sp. novus. We also assessed the specificity of the two dominant Philornis species attacking 11 bird species and preference of the two dominant parasitoid species for bird species. Although there was some significant preference for particular bird species by the Philornis spp., there was no indication that this drove specificity patterns by the parasitoids. Policy implications. Our results confirm previous laboratory studies indicating specificity by C. annulifera and support the hypothesis that this species would produce few, if any, nontarget impacts if released into Galapagos to suppress populations of the P. downsi. These results can inform an environmental risk assessment framework to guide governmental agencies in deliberation on potential field releases of parasitoids in the Galapagos Islands.

Original languageEnglish (US)
Pages (from-to)2189-2198
Number of pages10
JournalJournal of Applied Ecology
Issue number8
StatePublished - Aug 2022

Bibliographical note

Funding Information:
We thank Mauricio Torres and Gabriel Brito for field assistance, and the community of El Suspiro and the Rosales family for logistical support. We thank Dr. Bradley Sinclair from the Canadian National Collection of Insects & Canadian Food Inspection Agency for fly identification and ESPOL University for institutional support. We thank the INABIO and the Ecuadorian Ministry of the Environment for the granting of permits to work in the Loma Alta Ecological Reserve. We thank the Bell Museum, Galapagos Conservancy, the International Community Foundation (with a grant awarded by The Leona M. and Harry B. Helmsley Charitable Trust), National Geographic Foundation and the University of Minnesota for financial support. This publication is contribution number 2437 of the Charles Darwin Foundation for the Galapagos Islands. Open access funding enabled and organized by ProjektDEAL.

Publisher Copyright:
© 2022 The Authors. Journal of Applied Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.


  • Conura annulifera
  • Galapagos Islands
  • Island conservation
  • Philornis
  • Trichopria
  • enemy-free space
  • gap-laying
  • in-field technique
  • invasive species


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