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Subject: Anatomy: Fly Tunes In to Cricket's Mating Call<By David Brown<
Date: Mon, 16 Nov 92 05:02:45 EST
Message-ID: <42.1992Nov16.050246@AmeriCast.com>

Anatomy: Fly Tunes In to Cricket's Mating Call<By David Brown<

In a remarkable example of "convergent evolution," a type of
parasitic fly that preys on crickets has developed hearing organs
that, in structure and function, are much more like its hosts'
than its brethren flies'.

The similarity in the design is curious because, in much of the
rest of their anatomy, flies and crickets bear little resem-
blance. Moreover, flies and mosquitoes communicate at much lower
frequencies and over much shorter distances than crickets. So why
would a fly evolve an ear that is specifically optimized to hear
singing crickets?

For the same reason as female crickets, according to a new study.
Male crickets chirp to attract mates. In some places, however,
they also attract pregnant female flies of the genus Ormia.
These parasitic creatures use the cricket suitors as a sort of
incubator, rewarding the singer by depositing a load of maggots
on or near him. The maggots burrow into the cricket and feed on
him, killing the host within days.  The flies emerge as mature
larvae.

But to locate the target cricket, the flies need the right equip-
ment. Scientists at Cornell University and the University of
Florida report in the current issue of Science that Ormia flies
have hearing organs that employ a "tympanal" membrane, or ear
drum. In this and numerous other engineering features, the organ
resembles a cricket ear rather than the typical fly ear, which
uses a feathery, antenna-like structure to detect sound. The
latter design is useful only for low-frequency, short-distance
hearing. It may serve mosquitoes and fruit flies well, but it's
not what Ormia needs to find its singing host in the high grass.

Using microelectrode detectors, the scientists further found that
the fly's ear is "tuned" to best detect sound in the 4-6 ki-
lohertz frequency range - exactly the peak of the male cricket's
song. - D.B.>02:44 11-16C9999-----

Copyright 1992, The Washington Post.  This story is from the
Washington Post's Capitol Edition On-Line and is not to be ar-
chived or redistributed.

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