What a stinker

 作者:阴捣逃     |      日期:2019-02-26 05:07:04
By Andy Coghlan A MOUTHFUL of rancid wax lies in store for insect pests that have a taste for tomatoes. The wax, which is similar to the coating on a species of wild tomato, could be used to keep cultivated varieties of the fruit free from blemishes. Martha Mutschler, professor of plant breeding at Cornell University in Ithaca, New York, discovered the waxy substances after noticing the hardiness of Lycopersicon pennellii, a wild tomato that grows throughout the US. “She noticed that none of these tomatoes growing wild had the usual blemishes and wormholes seen on their commercial relatives,” says Bruce Ganem, the chemist who analysed the waxy coatings. Ganem found that the wax contains a variety of glycolipids—large molecules built up from fat and sugar units. As the glycolipids in the wax biodegrade, short fatty acids that are repellent to insects slowly detach from the sugar scaffold. “It has the same effect on the insects as when humans smell rancid butter,” says Ganem. “You don’t want to try it again.” Ganem says that the natural coating is too complex to manufacture commercially. He made synthetic analogues that were simpler and cheaper but just as effective by swapping the natural glucose scaffold for glycerol, a simpler molecule which accommodates three instead of five fatty acids. The fatty acids released include butyric acid, which makes rancid butter smell. But the fatty acids are released so gradually from the wax, and in such small quantities, that only insect pests can smell them. Field experiments at Cornell show that the larvae affected include the tomato fruitworm (Helicoverpa zea) and the beet armyworm (Spodoptera exigua),