Darwin’s finches deploy pesticides to combat blood-sucking maggots

Darwin’s finches deploy pesticides to combat blood-sucking maggots

Several species of Galapagos finch are in serious danger from a deadly nest parasite.

But there may be a simple and ingenious solution, according to new research

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It was the sight of Galapagos finches pulling frayed fibres from a washing line that gave University of Utah biologist Sarah Knutie the idea for an ingenious experiment. If she provided the birds with nest material laced with a pesticide, would they use it to line their nests and would the chemical protect against the larva of the invasive botfly Philornis downsi? Photograph: Sarah Knutie/University of Utah

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It’s not a pretty sight, but it’s important that we don’t look away. Philornis downsi is a serious threat to most of the 14 species of Darwin’s finch (species that have been acting as avian evangelists for evolution since the 1930s). The adult fly lays its eggs in a nest and the larvae feed on the nestlings, sucking their blood and boring into their flesh. The first official account of the fly in the Galapagos was in 1997, but it’s probably been around for longer. The larvae have a devastating effect on reproductive fitness, in some cases causing all chicks to die. Photograph: PLoS ONE

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At a study site on the central Galapagos island of Santa Cruz, researchers put out dispensers loaded with cotton. Several species of Darwin’s finch (including the medium ground finch, small ground finch, small tree finch and vegetarian finch) were happy to use the material to line their nests, report Sarah Knutie and her colleagues in Current Biology. Half of the dispensers contained cotton laced with the pesticide permethrin. The other half acted as controls, with the cotton treated with water. Photograph: Sarah Knutie/University of Utah

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The researchers located 26 nests in the vicinity of the dispensers. Of these 13 contained the treated cotton and nine contained the untreated cotton. The other four nests were cotton-free. Nests with experimental cotton had around half the number of parasites (15, on average) compared to controls . The more experimental cotton, the fewer the parasites. “Of the eight nests that contained at least one gram of experimental cotton, seven had no parasites and the eighth had only four parasites,” they write in Current Biology. Photograph: Sarah Knutie/University of Utah

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In a separate experiment, also in the Current Biology paper, Knutie and colleagues demonstrate that permethrin-treated nests produce significantly more fledglings. “Self-fumigation may thus be a viable approach for combating P. downsi in the nests of Darwin’s finches,” they write. This may be particularly helpful in the case of the mangrove finch, the most critically endangered of Darwin’s finches with only around 100 individuals left. “Sixty cotton dispensers could treat this entire population.” Photograph: Michael Dvorak/PLoS ONE

This article was written by Henry Nicholls for The Guardian.

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