The other footprint we leave behind. the environmental emergency to save darwin's finches

Right now, imagine you’re not sitting staring at this screen. Instead, put yourself in the shoes of a field scientist stationed in the Galápagos Islands. You’re trekking over lava-formed terrain worn down by the developing vegetation on the belly of the seahorse-shaped Isabela Island. There’s not really a trail so you’re avoiding branches while swatting away flies that are landing on your face. Finally, using your handy binoculars, you spot your first sample site: a mangrove finch nest. As you carefully climb up to reach the nest, you fear bad news. There are no chirps and no chirps mean there are no healthy chicks. And you’re right, there are none. What you find is a dead nestling and not even needing to look closer, you also see an abundance of larvae feeding of it.

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.

Salvador Cazar, a biologist who now leads life-changing expeditions around the Galapagos as a naturalist, remarks that

“the worse trend for island ecosystems right now is invasive species.”

So, it comes as no surprise that controlling the Philornis fly is of utmost importance in the Galápagos. And that is exactly what researcher Paola Lahuatte is doing.

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:

  1. investigate what factors Philornis need to mate and
  2. 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.

Finding a way to mass breed Philornis in the lab is needed for the sterile insect technique used to mitigate the damages of invasive species.

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.

Song birds of the Galápagos. Although Philornis larvae poses the highest mortality on Darwin's finches, it is also affecting eight other Galápagos bird species. Images by Vicki Deng.

Right now, researchers excitedly have two very close solutions to managing the Philornis population. However, more experiments are needed to ensure these measures are effective and will not further damage the ecosystem. Although everyone is urgent for a solution to this invasive species, it is important to assess how we will potentially change the environment and can cause further damage. Before releasing a bunch of sterile Philornis males, experiments need to be conducted to ensure they are actually sterile. Before releasing a bunch of Conura wasps, Paola is working to bring the wasps to a quarantine lab in the Galápagos and see how it interacts with endemic species.

As evident with our scientists finding solutions to solve this problem, we have the ability to manage and potentially reverse the anthropogenic damage to ecosystems. However, despite our victories here, we are reminded that we are the cause of these damages and we might inflict even more damage. And these damages are not just because of one specific isolated action.

Even in the highly protected Galápagos, artifacts of past and current anthropogenic threat remains. Pictured left is a mitigating solution to the invasive rat problem on the Islands.

Images by Vicki Deng.

When invasive species are established, they are proliferative. But before that step, they are faced with many challenges in survival. In our story here, Philornis were carried over with trade goods. But for them to be the damaging creature they are today, more anthropogenic factors come into play. In 1982 and 1997, climate change resulted in an extreme El Niño that bought plenty of rain to flourish the flora and fauna. This provided the perfect condition and ample sustenance for the flies to proliferate.

Therefore, we need to be wary of the many footprints we leave behind and how much power we have over our ecosystem. As we scroll through the news, we are informed about the dangerous carbon emissions and increased plastic waste. However, our impact on the environment is also the little critters that we accidentally give free rides across oceans that destroys once pristine ecosystems. As we have seen time and time again, our environment suffers from the unforeseen magnitude of impact we leave behind. As such, it is so important that today, we learn to strengthen our conservation and sustainability efforts.

-- Vicki Deng