That chick’s survival would have sustained the 100 individual mangrove finches left on this planet. Previously an important and treasured evidence to the theory of evolution, this finch along with the medium tree finch are critically endangered (McNew and Clayton 2017). The reason? Those seemingly harmless flies. Although they might look like your common house fly, Philornis downsi are invasive parasitic flies. Accidentally carried over by humans on a boat in the 1960s, the larvae of Philornis are wreaking havoc on the ecosystem by feeding on the blood of baby finches and other songbirds, killing them before they are even able to get out of the nest. This introduced parasitism is killing at least 20 other bird species. Without these birds who serve as essential pollinators, a lot of flora will also start to collapse, and then the fauna who depends on the flora will follow.
Adult female Philornis fly © Henri Herrera, Charles Darwin Foundation.
During my trip to the Galápagos, I got to visit Santa Cruz Island where the Charles Darwin Research Station is located and chat with Paola about this devastating problem. Paola told me she had always wanted to work in the Galápagos because of its history with Darwin and the theory of evolution. But what inspired her to take on the Philornis project was her drive to help the vulnerable organisms who can’t speak for themselves.
Image © Juan Manuel Garcia, Charles Darwin Foundation..
Right now, she is working to implement the sterile insect technique, a popular method for controlling invasive species in which sterile males are released in the wild to compete for mates and result in no fertilization, meaning no more next generations. But in order to set this in motion, Paola and her team of researchers need to accomplish two goals:
- investigate what factors Philornis need to mate and
- being able to breed enough of these blood-sucking fly larvae in the lab.
Image © Juan Manuel Garcia, Charles Darwin Foundation.
Neither are easy tasks but luckily, years of failed and successful studies have contributed to this research project to get us close. Countless field surveys and experiments have been conducted to elucidate the very specifics of when and where do Philornis mate, what attracts Philornis, and the life cycle of Philornis. And in 2016, Paola collected eggs from captured Philornis females and cultivated a novel Philornis breeding method that allows larvae which wouldn’t survive without live hosts to be able to do so in the lab.
Field collection © Liza Diaz Lalova, Charles Darwin Foundation.
However, those flies can’t reproduce in the lab so Paola and her team are working hard to be able to complete the whole life cycle in the lab and mass breed Philornis. As Paola indicates, “this fly is very complicated, and we don’t have much information about it.” So for the sterile insect technique to be utilized, even more information needs to be collected.
Images © Juan Manuel Garcia, Charles Darwin Foundation.
Alongside trying to achieve the sterile insect technique on Philornis, Paola and her team are also currently working on a biological control. That is to introduce an enemy for Philornis.
One of the first responses to Philornis management was to retrieve infested nests and isolate the fly to study in the lab. Amongst these nests, another group of researchers observed that wasps were also emerging from the samples. Looking closer, they discovered that these Conura annulifera wasps were parasites to the parasitic fly! This excitingly led to many experiments in the field and the lab to see if the wasp would only parasitize Philornis by exposing it to five other species. The hit was positive: out of the different species of flies the Conura wasp was subjected to, it only laid eggs in Philornis.