January 30, 2020 – In the mangrove trees of the Galapagos Islands lives a highly specialized finch, aptly named the mangrove finch. This bird is one of 17 species known as Darwin’s finches, each filling a different niche on different islands. Once abundant, the mangrove finch is now extinct across much of its former range, with only about 100 mangrove finches remaining in the wild, found in only one isolated location. What in the world happened?
Philornis downsi, an Invasive Bird-Parasitic Fly
The fly, also known as the vampire fly, lays its eggs in nests, and the resulting young maggots use the nestling birds for their blood meals, causing high mortality in chicks.
Researchers believe the vampire fly was unintentionally transported to the island sometime before the mid-1960s. Since then, it has thrived and become a destructive, invasive species on the islands, especially to Darwin’s finches.
Now, Morris Animal Foundation-funded researchers at the University of Minnesota, in collaboration with the Charles Darwin Foundation, are in a race against time. They are working on a biological control strategy that just might save the mangrove finch from extinction and protect other Galapagos Island birds impacted by the vampire fly.
Wasp Comes to the Rescue
“Philornis downsi exists naturally on the Ecuadorian mainland,” said Dr. George Heimpel, researcher at the University of Minnesota and primary investigator on the project. “One insect that keeps Philornis downsi in check and from seriously impacting bird species on the mainland is a specialized wasp whose larvae seem to feed exclusively on the pupa of this parasitic fly.”
Dr. Heimpel believes this specialized wasp may be a solution to restore ecological health to the islands and help save the finches. But first, he and his team are studying the wasp’s behaviors and habits to ensure its suitability for release in the Galapagos Islands. While they hope the wasp will take care of the overabundance of vampire flies, they also have to make sure that the wasp will not prey on any other native species.
“Scientists today better understand the risks of using biological control agents and my team has spent years studying the vampire fly and its natural enemies,” said Dr. Heimpel. “Our goal is not to eradicate the fly from the Galapagos Islands, but to safely bring the pests to a low, manageable level so it does not cause extensive and irreversible harm to the native birds.”
Biological Control – Now and Then
In the last century or so, biological control measures have had some disastrous consequences with introduced species becoming invasive species themselves. Some of the most notorious failures include the introduction of cane toads in 1935 in Australia to control destructive beetles in sugarcane crops, and similarly the introduction of mongoose in Hawaii in 1880s to control rats in cane fields. Both these species may have addressed perceived problems in the short term but they also severely impacted native species and drastically changed the balance of nature. Very little scientific thought went into these early biocontrol releases.
Thankfully, science has come a long way since then. Identifying and fully vetting risk before introducing one species to control another species takes years of research and a thoughtful and careful approach. And today, in addition to using biological controls to protect agricultural commodities, researchers are using this strategy to save species from extinction.
“Thanks to advances in science and careful risk assessment, there have been hundreds of successes using biological control strategies to save animal and plant species,” said Dr. Heimpel. “One recent success right here in the Galapagos Islands was the deliberate release of a beetle to help control cottony cushion scale, an exotic plant pest believed to have first arrived in the islands in the 1980s. Cottony cushion scale eventually got out of control and began attacking and killing native plants.”
Dr. Heimpel emphasizes that it took years of research and local cooperation to make sure releasing a specialized beetle that preyed on the scale was the right solution at the right time. And it was. The beetle completely resolved the problem and saved island-endemic plants from sharp declines and even extinction. Included in the list of plant species affected were the mangrove trees and habitat for Darwin’s mangrove finches.
“Cottony cushion scale has not been wiped out in the Galapagos Islands,” said Dr. Heimpel. “But it remains in check, thanks to release of the beetle. This is a great example of how a biological control, when carefully studied and planned, can have a huge impact in saving native and endemic species from population decline or even extinction.”
Hope for Galapagos Island Birds
In the short term, researchers are using a noninvasive pesticide to control the vampire fly in Darwin’s finch nests while controlled laboratory studies of its enemy, the parasitic wasp, are underway. While the pesticide strategy works well, it is labor intensive and expensive to maintain for the long haul. Dr. Heimpel is hoping the wasp will be a long-term solution, restoring health to the Galapagos Island ecosystem.
“On its current course, even with some interventions, the mangrove finch is at risk of extinction in the next decade or two,” said Dr. Heimpel. “As a scientist, I want to make sure that these and other Galapagos Island birds live thousands of years beyond my lifetime. And so far, our studies suggest the specialized wasp that preys on the vampire flies may be a viable long-term solution. But we have a few years of more study to ensure this is the right strategy before introducing the wasps on the islands. We want to make sure this strategy is both safe and effective for the birds and other native species."