Mitigating Philornis Parasitism on the Ridgway?s Hawk: Mid- And Long-Term Control Methods

HAYES, C.; QUIROGA, M.; THORSTROM, R.; HAYES, T.; ANDERSON, D.

Santo Domingo

Conferencia; 4th Caribaea Initiative Research & Conservation Conference; 2019

Caribaea Initiative

Philornis (Diptera: Muscidae), is a genus of generalist parasitic flies that parasitize over 250 species of birds all over the Neotropics. Knowledge on the genus is limited to 28 of the approximately 50 described species and their effects on hosts vary from light to lethal; sometimes taking bird species to the border of extinction (i.e., parasitism of Mangrove Finch by Philornis downsi). This is also the case of the critically endangered Ridgway's Hawk (Buteo ridgwayi) where up to75% of nestlings may die due to parasitism of Philornis (mainly Philornis pici). Although some control methods are being developed to eradicate the human introduced P. downsifrom the Galápagos, differences in parasite and host biology required the development of unique control methods for Ridgway?s hawks in the Dominican Republic.We are currently investigating mid- and long-term control methods (MTM and LTM respectively) to minimize the impact of Philornis pici on Ridgway?s Hawks. As a MTM we are testing different low-toxicity insecticides and natural repellents that may keep larvae and adult flies away from nests and nestlings.Advances towardsLTM have been made by seeking biological control agents and attempting to reproduce P. pici?s life cycle in captivity; which will be key in allowing for the implementation of known control techniques like Sterile Male Release Technique. Predictive models of Philornis distribution are currently being built to detect suitable places for new hawk releases. Some aspects of life history traits and taxonomy of these parasites are under study as well.By using a slow release Permethrin formula (Permacap? 1%) applied to nest material at the incubation stage, we strongly reduced parasitic load of nestling. Resultsshowed that organic compounds like ?Bija? (Bixa orellana) could potentially be good repellents of P.pici since the majority of exposed flies (>78%) avoided it. Regarding LTM, over 500 flies were reared in our lab and survived up to 93 days, evidencing strong rearing capabilities.We also observed that Brachymeria podagrica, a generalist parasitic wasp, is abundant in the area and may act as a biological control agent. We confirmed that low temperatures (18°C) may delay Philornis? adults emergence up to 30 days, but is not lethal to the larvae. At the same time, we collected evidence that there are more than a single species of parasites affecting Ridgway?s hawks.Although most of our research is still in progress and more research is needed, our findings made available a highly efficient short-term control method for Philornis. It also provided vital information on different techniques with potential to control P. pici and other Philornis species in the mid- and long-term.