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Deadly Seduction Filches Chemical Defense
2 September 1997 8:00 pm
For some female insects, males make a tasty treat after mating. Now scientists report in today's Proceedings of the National Academy of Sciences that in one species of firefly, females lure males of closely related species for another reason: to steal predator-repelling toxins.
When fireflies court, males flash patterns unique to their species, while females wait on perches and answer with a precisely timed response. More than 30 years ago, researchers discovered that females of the genus Photuris could lure males of another genus, Photinus, by faking their females' blinking patterns. Both types of fireflies contain chemicals that protect them from predators, but the predatory Photuris fireflies have only about one-third as much of the repellent compounds, called lucibufagens, as Photinus. That imbalance led Thomas Eisner, a chemical ecologist at Cornell University, to suspect that Photuris was stealing its protection from the gullible Photinus males.
To test the idea, Eisner and his colleagues collected larval Photuris and raised them in petri dishes. Without any other fireflies to devour, the Photuris larvae grew into adults without lucibufagens. These larvae were devoured when fed to hungry jumping spiders, a normal predator of fireflies, Eisner reports. But after a meal of Photinus males, other captive females had high levels of lucibufagens and were rejected by jumping spiders. The spiders also avoided Photuris females who were fed a solution containing lucibufagens.
While females use their charms to acquire lucibufagens, Eisner says it's not clear where male Photuris get theirs. Males will eat Photinus in the lab, but that hasn't been reported in the wild. Another mystery is where the hapless Photinus fireflies themselves get the lucibufagens, as they can't manufacture them. "It is entirely possible that they get it from feeding as larvae," Eisner says. But no one knows where Photinus larvae live or what they eat.
The self-defense ruse of female Photuris might be quite widespread. Many predatory species of Photuris live across the United States and South America, and all the females respond to the mating flashes of several other species--at least for meals. "Now we'll have to go back and look at our records" to find out if devoured males contained lucibufagen, says Jim Lloyd, an entomologist at the University of Florida in Gainesville.