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How roaches developed disgust at first bite

A change in taste cells makes glucose-baited traps repellent

BITTERSWEET German cockroaches have fought back against bait traps that pair sugar with poison. Over time, the insects have developed taste cells that register sugar as disgusting. 

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Cockroaches that don’t fall for traps’ sweet poisons have evolved taste cells that register sugar as bitter.

In certain groups of the widespread German cockroach (Blattella germanica), nerve cells that normally detect bitter, potentially toxic compounds now also respond to glucose, says entomologist Coby Schal of North Carolina State University in Raleigh. The “bitter” reaction suppresses the “sweet” response from other nerve cells, and the roach stops eating, Schal and his colleagues report in the May 24 Science.

Normally roaches love sugar. But with these populations, a dab of jelly with glucose in it makes them “jump back,” Schal says. “The response is: ‘Yuck! Terrible!’”

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