Caterpillars Use Their Poop to Trick Plants
Caterpillars that munch on corn leaves have developed a clever way to get the most nutrients from their meals.
Caterpillars that munch on corn leaves have developed a clever way to get the most nutrients from their meals: They use their poop to trick the plants into lowering their defenses.
Scientists at Pennsylvania State University recently discovered that fall armyworm caterpillars (Spodoptera frugiperda) can send chemical signals to plants through their poop, or frass.
"It turns out that the caterpillar frass tricks the plant into sensing that it is being attacked by fungal pathogens," study co-author Dawn Luthe, a professor of plant stress biology at Pennsylvania State University, said in a statement. [In Photos: Animals That Mimic Plants]
Corn plants can deal with only one kind of attack at a time, so while a corn plant is dealing with the perceived "fungal infection," the caterpillar is left to feast on the plant's leaves. Normally, a plant will recognize chemical signatures from insect secretions, which helps the plant know when to raise its defenses. In many cases, this includes producing a biochemical that repels herbivores, such as insects.
But chemical signals from the caterpillar's poop act as crafty diversions, the researchers said.
"The plant perceives that it is being attacked by a pathogen and not an insect, so it turns on its defenses against pathogens, leaving the caterpillar free to continue feeding on the plant," Swayamjit Ray, a doctoral student in plant biology at Penn State and co-author of the paper, said in a statement. "It is an ecological strategy that has been perfected over thousands of years of evolution."
Caterpillars usually feed on the leaves in the confined whorls of corn plants. The critters typically defecate in the crevasses where the leaves meet the stalk, the researchers said.
Scientists studied the biochemical relationship between fall armyworm caterpillar frass and a plant's defensive mechanisms by performing two tests. In the first test, the scientists applied frass extract to the leaves of some corn plants and compared caterpillar growth of those that fed on treated leaves with those that munched on untreated leaves.
The second test involved measuring how frass-treated corn leaves affected defensive performance on plants exposed to a fungal pathogen - in this case, spores of a fungus that causes blight in corn (Cochliobolus heterostrophus). The scientists observed that, initially, proteins in the frass activated an insect defense in the plant, but over time, as the corn plants were exposed to more of the protein, the plants' defenses became altered and instead began to recognize the frass protein as a fungal pathogen instead of an insect waste product. This caused the plant to defend itself against what it saw as a fungal threat instead of an insect threat.
While this may not be good news for plants suffering from a caterpillar infestation, the researchers think it may be possible to isolate the specific components in caterpillar poop that heighten a plant's defenses against pathogens. If this is the case, the scientists said, farmers could one day develop an organic and sustainable pesticide to prevent infection and disease in crops.
The findings were published online Aug. 26 in the Journal of Chemical Ecology.
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Fall armyworm larvae are voracious feeders on leaves in the confined whorls of corn plants, and by necessity the insects defecate nearby in the crevasses where the leaves meet the stalks.
Insects and other creepy crawlies may be tiny, but their lineages are mighty, finds a new study that determined the common ancestor of mites and insects existed about 570 million years ago. The study, published in the latest issue of the journal Science, presents an evolutionary timeline that settles many longstanding uncertainties about insects and related species. It found that true insects first emerged about 479 million years ago, long before dinosaurs first walked the Earth. Co-author Karl Kjer, a Rutgers entomologist, explained that mites are arthropods, a group that's distantly related to insects. Spiders and crustaceans are also arthropods.
Spiders such as the huntsman spider can, like mites, trace their lineages back to about 570 million years ago, according to the new study. The researchers believe that the common ancestor of mites, spiders and insects was a water-dweller.
Millipedes, such as the one shown here, as well as centipedes are known as myriapods. The most recent common ancestor of myriapods and crustaceans lived about 550 million years ago. Again, this "mother of many bugs" would have been a marine dweller. Kjer explained, "You can't really expect anything to live on land without plants, and plants and insects colonized land at about the same time, around 480 million years ago. So any date before that is a sea creature." Moving forward in time, the most common ancestor of millipedes and centipedes existed a little over 400 million years ago. The leggy body plan has proven to be extremely successful.
"This is an early insect that evolved before insects had wings," Kjer said. Its ancestry goes back about 420 million years. The common ancestor of silverfish living today first emerged about 250 million years ago. Dinosaurs and the earliest mammals likely would have then seen silverfish very similar to the ones that are alive now.
Dragonflies and damselflies have family histories that go back about 406 million years. Kjer said that such insects looked differently then, however. "For example," he said, "they had visible antennae." Their distant ancestors were among the first animals on earth to fly.
"Parasitic lice are interesting, because they probably needed either feathers or fur," Kjer said. As a result, they are the relative newbies to this list. Nonetheless, the researchers believe it is possible that ancestors of today's lice were around 120 million years ago, possibly living off of dinosaurs and other creatures then.
Crickets, katydids and grasshoppers had a common ancestor that lived just over 200 million years ago, and a stem lineage that goes back even further to 248 million years ago. A trivia question might be: Which came first, these insects or grass? The insects predate the grass that they now often thrive in.
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Dinosaur Era fossils sometimes include what researchers call "roachoids," or wing impressions that were made by ancestors to today's roaches, mantids (like the praying mantis) and termites. "Some cockroaches are actually more closely related to termites than they are to other cockroaches," Kjer said, explaining that this makes tracing back their lineages somewhat confusing. He and his colleagues determined that the stem lineage goes back about 230 million years, while the earliest actual cockroach first emerged around 170 million years ago.
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Termites and cockroaches have a tightly interwoven family history. Termites similar to the ones we know today were around 138 million years ago. Now we often think of termites as pests, but they are good eats for many different animals, which back in the day would have included our primate ancestors.
Flies like houseflies that often buzz around homes belong to the order Diptera, which has a family tree that goes back 243 million years ago. The most recent common ancestor for modern flies lived about 158 million years ago, according to the study. There is little doubt that the earliest humans, and their primate predecessors, had to contend with pesky flies and all of the other insects mentioned on this list. All of these organisms are extremely hardy. The researchers determined that, in the history of our planet, there has only been one mass extinction event that had much impact on insects. It occurred 252 million years ago (the Permian mass extinction), and even it set the stage for the emergence of flies, cockroaches, termites and numerous other creepy crawlies.