Thanks to Brent Crane writing in the Elements section of the New Yorker’s website:
Five years ago, George Heimpel, an entomologist at the University of Minnesota, travelled to Trinidad in search of insect larvae. He was after several kinds in particular—Philornis downsi, a fly whose parasitic young feed on the hatchlings of tropical birds, and various minuscule wasp species whose own offspring feed on those of the fly.Heimpel hoped that the wasps might solve a problem on the Galápagos Islands, where Philornis has taken a severe toll on native fowl. Those hurt most by the fly, which was likely brought to the archipelago by people, are the Galápagos finches, the songbirds that provided Charles Darwin with some of the earliest evidence of evolution. Currently, eleven of the fourteen finch species are confirmed prey of Philornis larvae, which gorge on the young birds’ blood. With a mortality rate nearing a hundred per cent in some species, the chicks are dropping like, well, flies. The critically endangered mangrove finch is particularly imperilled: if Philornis isn’t stopped, the bird could disappear in a matter of decades, according to mathematical simulations from the University of Utah. It would be the first extinction to befall a Galápagos finch since humans came to the islands, in 1535.
Biological control—the practice of strategically using organisms to kill pests—has been common in agriculture since the nineteenth century, but it is relatively new to conservation. Among some scientists, it has a foul reputation. “In much the same way that the current public thinks that pesticide use is bad based on certain examples—like some of the effects of DDT, for example—a generation of conservation biologists simply were taught that biological control was bad, again based on a couple of examples that are real enough but a very small percentage of the over-all cases,” Roy Van Driesche, an entomologist at the University of Massachusetts, Amherst, told me recently. In the eighteen-eighties, for instance, mongooses were introduced to Hawaii; they gobbled up rats, their intended target, but also precious native fauna. Later, in 1935, Australia turned to the cane toad to eradicate two species of beetle that were ravaging the country’s sugarcane crop. The toad proliferated uncontrollably, pillaging the ecosystem without fixing the beetle problem. Several decades after that, European seed-head flies were brought to Montana to stamp out spotted knapweed. Their larvae proved irresistible to the local mice, many of which carried hantavirus; the mouse population flourished, as did the virus, and more than a hundred people were fatally infected.
Heimpel, a major proponent of biocontrol, stresses the datedness of these examples…
Read the whole story here.