An Asian ladybug with an appetite for bruised grapes has been spreading throughout the United States since 1988. Canadian researchers confirm that the foul-smelling chemicals that these bugs secrete can easily spoil an entire vintage. The researchers also describe a treatment that they’re investigating for such ladybug-tainted wine.

Chemists had suspected that the ladybugs’ recently identified stinky ingredients, called methoxypyrazines, were mingling with grape juice at harvest time, giving wine the taste and aroma of peanuts, bell peppers, and asparagus—a mixture unlikely to captivate oenophiles. Lesser quantities of the chemicals are also present in “green” wines made from immature fruit.

In an upcoming Vitis, researchers at Brock University in St. Catharines, Ontario, report finding that just 200 to 400 ladybugs (Harmonia axyridis) per metric ton of harvested grapes can foul a batch of wine. Depending on the bugs’ methoxypyrazine output, an infestation of as few as two beetles per grapevine can destroy the harvest, notes team leader Gary J. Pickering.

The Ontario group has now found a protein additive that binds with methoxypyrazines to create a substance that can be removed from a wine vat. The problem, Pickering explains, is getting the system to operate efficiently in the presence of wine’s alcohol and acidity—”quite an aggressive environment for a protein.” An effective methoxypyrazine-removal system could, however, salvage “millions of liters of green or bad vintages” in North America each year, Pickering says.

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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