Darwin's finches face a deadly new invader, but scientists are tracing its tracks

Comprehensive genetic analysis has shed new light on the spread of an invasive, blood-sucking fly, which poses a devastating threat to the iconic Darwin’s finches of the Galápagos Islands.

The larvae of the parasitic avian vampire fly (Philornis downsi) feed on the blood and tissue of developing chicks, often killing 100 per cent of the brood. First discovered in nests in 1997, the fly has become one of the most serious threats to the survival of Darwin's finches.

New Macquarie University-led research, just published in the journal Molecular Ecology, uses genomic evidence to uncover how the parasite spreads between islands, providing vital information for efforts to control its impact across the archipelago.

The avian vampire fly has been recorded on 15 islands of the Galápagos and attacks many species of the finches, which famously helped naturalist Charles Darwin deduce how species evolve and adapt to their environments.

To investigate how the invader has established and spread, PhD student Abbie Hay and Associate Professor Rachael Dudaniec from Macquarie’s School of Natural Sciences together with other collaborators analysed flies collected from five major Galápagos islands and from mainland Ecuador, where the parasite is native. By sequencing and comparing the genomes of flies collected from the different islands, the researchers were able to trace patterns of directional movement, and genetic diversity.

“This is the first study to reveal genetic migration pathways of the vampire fly across the Galápagos archipelago,” said Dr Dudaniec.

The findings revealed genetic divergence between mainland and Galápagos vampire fly populations and identified the island of San Cristóbal – the closest island to the Ecuadorian mainland and historically the first docking point for cargo vessels – as a likely point of entry and source population.

“Our results suggest that the fly may be travelling from the mainland to San Cristóbal with human assistance, and from there to other islands through a combination of human activity and natural dispersal,” said Dr Dudaniec.

Island species are particularly susceptible to invasive parasites and pathogens. Having evolved in relative isolation, many lack the defences needed to withstand newly introduced threats.

“By identifying which populations are genetically connected, we can better understand where flies may be coming from and where control efforts could have the greatest impact,” said Dr Dudaniec.

The study builds on more than two decades of research into interactions between the avian vampire fly and Darwin's finches, led by Professor Sonia Kleindorfer, now based at the University of Vienna.

“Our findings are critical for prioritising islands for control strategies that will reduce the impact of the vampire fly on the finches and other vulnerable endemic birds,” said Dr Dudaniec.

Beyond the Galápagos, the findings highlight the value of genomic approaches for tracking biological invasions and informing conservation strategies in vulnerable island ecosystems.