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Critter Chemistry

November 25, 2002

Wasps Use Plants to Send Mating Signals

Rebecca Rawls

Like many insects, male gall wasps use their sense of smell to find females to mate with. But the chemical signals that these tiny, flea-sized insects zero in on are not produced by receptive females. They come instead from the plants that these wasps feed on [Proc. Natl. Acad. Sci. USA, 99, 15486 (2002)].

University of Illinois, Urbana-Champaign, entomology assistant professor Lawrence M. Hanks, graduate student John F. Tooker, and organic chemistry professor Wilfried A. Koenig of the University of Hamburg, Germany, find that plant stems that contain larvae soon to emerge as female wasps produce a mix of enantiomers of volatile monoterpenes that differs from the mix produced by uninfested plant stems.

The study is the first to show that insects can exploit the chemical composition of plants for the purpose of locating mates, Hanks says.

Female gall wasps (shown) lay their eggs inside the stems of several species of perennial prairie plants, the researchers explain. When the eggs hatch, larvae feeding inside the stems caus- and -pinene, the researchers find. Months later, the male wasps emerge from the stems before the females do and use these altered ratios to locate stems containing females. Male wasps finding a stem with a 50:50 ratio of enantiomers "move on," Tooker says. "If they find a stem with a 70:30 or a 100:0 ratio, they will likely stay and find females emerging from it."

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