Their Love Tunes Differ From Mainland Cousins : ‘Sweet Nothings’ of Hawaiian Fruit Flies

Fruit flies sing love songs to put each other in the mood to mate, but the tunes crooned by Hawaiians of the spemetro bullcies are far different from their mainland cousins’, scientists have found.

The biologists said they had discovered Hawaiian fruit flies have completely different rhythms, frequencies and even different ways of producing sounds in courting rituals than are found in mainland species that resemble the islanders’ ancestors.

Ronald R. Hoy, a professor of neurobiology at Cornell University in Ithaca, N.Y., who led the study reported recently in the journal Science, said he first got the idea to study the Hawaiian flies’ songs during a television program that showed male insects beating their wings in an unusual way during courtship.

“I said, ‘Boy, I bet that sounds neat,’ ” Hoy said in a telephone interview.

‘Intimate Whispers’

Most fruit flies’ songs are only audible with ultra-sensitive microphones that pick up a special type of sound undetected by ordinary equipment for recording human speech or music.

“These are intimate whispers,” Hoy said, made by males that are only a fraction of an inch from female fruit flies.

The Hawaiian fruit flies have become classic subjects for other types of evolutionary studies, Hoy said, but until his research, no one had studied the Hawaiian fruit flies’ unique love tunes.

Along with two co-workers, Hoy found that one group of Hawaiian fruit flies is able to make “clicky” noises at a frequency 10 times higher than any sound found in continental fruit flies--or any flies at all. Unrelated insects such as cicadas and katydids can make clicks, but the sound has never been heard in any fly the researchers said.

Hoy said in a telephone interview that the first time he heard the click-song he “was shocked, totally shocked.”

Another group of species sings a complex song with a repeating phrase of two rhythms--two to seven pulses with distinctive pauses in between followed by a trill. The other two groups of songs Hoy identified are “purrs” and “hums,” with one of the purring species making the sound by vibrating its abdomen, rather than its wings.

Hoy said the males do their crooning to females no more than a body length away. In some species the male stands behind the female with his head under a female’s wings while he sings.

The researchers recorded the romantic melodies with a special microphone in a fruit fly honeymoon suite the size of a drinking cup, then played the sounds into an oscilloscope, which made a graph if them.

Hoy said to a human, the amplified sounds resemble growls and purrs of dogs and cats, or, in the case of the click-song, the strumming of the teeth of a plastic comb.

The courtship songs, along with visual displays and odors, are believed to be part of the complex signals that help the fruit flies identify suitable mates and prevent them from mating with a fly of another species.

The more than 500 species of fruit flies--known to scientists as Drosophila --have long fascinated naturalists and evolutionary biologists.

As early as 1910 a scientist described the startlingly different fruit flies that evolved on the islands in an explosion of species analogous to the blossoming of Darwin’s finches in the Galapagos Islands.

“In a sense the Hawaiian Drosophila is a replay of that on a much grander scale,” Hoy said.