- News Home
17 April 2014 12:48 pm ,
Vol. 344 ,
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
- About Us
Caterpillars Sign Their Own Death Warrants
26 August 2010 2:00 pm
Riveting dramas play out daily on a nature preserve in southwestern Utah. A tobacco plant is quietly minding its own business when moth caterpillars attack, devouring its leaves. The plant sends out a chemical distress call to another insect species called "big-eyed bugs," which soon arrive on the scene to attack the caterpillars. Now, researchers have discovered that the alarm signal goes out at lightning speed—and in a strange twist, the caterpillars appear to help make the call.
Scientists have known for a long time that plants create complex, specific chemical signals that attract predators when they're under siege from herbivores. But those compounds take hours to a day for the plant to make. "It's day-old news," says study author Ian Baldwin, an ecologist at the Max Planck Institute for Chemical Ecology in Jena, Germany. After all, a predator wouldn't want to arrive only to find that the herbivores have already left. The new study, published tomorrow in Science, reveals a much faster distress call.
Silke Allmann, a graduate student in Baldwin's group, first got a hint of this signal when she was examining chemical analyses of green leafy volatiles (GLV), a group of chemicals that makes up the grassy smell of a fresh-cut lawn. Plants emit GLVs whenever they're damaged. But GLVs from tobacco plants come in two varieties, usually called the (Z)- and (E)-isomers. Allman discovered that when a plant is cut by, say, a lawnmower or a knife, it releases much more (Z)- than (E)-GLVs. But if a tobacco hornworm caterpillar (Manduca sexta) bites the leaf, (Z)- and (E)-compounds are released in equal amounts.
To see if this made a difference to predators, the researchers glued caterpillar eggs onto leaves and, next to them, dabbed a paste containing different mixtures of GLVs. The mixtures with more (E)-GLVs attracted more big-eyed bugs of the Geocori genus, which poked a hole in the eggs and ate the innards.
Allmann also looked for chemical reactions in the plant that would shift the ratio between different forms of the molecules, but she couldn't find any. So she wondered if enzymes from the caterpillar might cause the shift right after the plant releases its GLVs. Indeed, she found that caterpillar saliva converts the (Z)-version of one of the GLV molecules to the (E)-version. "That's where it got really weird," says Baldwin. "Why would a caterpillar do this to itself?" He speculates that the (E)-GLVs could help kill microbes in the caterpillars' gut.
The fact that the caterpillar's own spit helps sign its death warrant is a "weird and novel twist," says Jeffrey Conner, an ecological geneticist at Michigan State University's Kellogg Biological Station in Hickory Corners. Further experiments may turn up some reason why changing the mixture of plant compounds benefits the caterpillars, says Conner.