How to turn on a firefly

The flashing of fireflies on a hot summer's night is a wonderful site and one that has intrigued scientists for decades. The effect depends on precisely timed and patterned flashes that last just a few hundred milliseconds. The flashes let potential mates know exactly who has the glowing report and is a major part of courtship.

Barry Trimmer of Tufts University and colleagues have now discovered that the almost ubiquitous chemical messenger nitric oxide (NO) may also play a critical role in the switching on and off of the insects' flashes of brilliance. Light production involves an adenosine triphosphate- and oxygen-dependent luciferin-luciferase reaction that takes place in the firefly lantern. The bug's light is, the team has found, jump-started by an influx of oxygen. This triggers the enzyme-driven reaction within cells in the firefly lantern to produce the insect's characteristic glow.

The researchers suggest that NO transmits the neural message that corresponds to "start flashing" from cells at the ends of branching air ducts - trachea - in the firefly lantern to energy-releasing mitochondria that surround the lantern's light-producing organs. The mitochondria, Trimmer explains, are thought to act as gatekeepers controlling the flow of oxygen into the light-production units. The team proposes that NO actually inhibits mitochondrial oxygen respiration, which leads to a sharp increase in oxygen levels in the light-producing cells, turning the flash on. Conversely, the production of light then quenches the reaction by inhibiting NO and switching off the glow.

Intriguingly, while the glow of Photinus fireflies speaks only of love, the females of the Photuris species also use their glow to lure unsuspecting Photinus males, which they then devour. Who said love is blind?

Science, 2001, 292, 2486^*

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