News Release
November  9, 2007

UW scientists study life dance between parasitic wasps, caterpillars in Ecuador

There’s no parallel in the human world for the goings on in the species-rich tropical forest in Ecuador.

Among lush branches, vines, and leaves, camouflage experts become unwitting prey for flying species that have adapted to poisons capable of killing other organisms. In air usually dripping with mist or rain, flying assassins stalk the camouflaged and lay eggs within unwitting hosts. Offspring then hatch and munch away.

Scott Shaw in the University of Wyoming’s College of Agriculture loves this stuff.

Shaw, a professor in the Department of Renewable Resources specializing in insect biology and classification, and graduate student Drew Townsend are researching the mysteries of caterpillars and parasitic wasps. That relationship is being studied at the Yanayacu Biological Station and Center for Creative Studies on the eastern slopes of the Ecuadorian Andes. At 7,100 feet, the station encompasses nearly 5,000 acres of cloud forest and cattle pasture.

“It’s a high-elevation cloud forest with mists rising from the forest, or it is raining,” noted Shaw, who had studied parasitic wasps in Costa Rica. Shaw is also curator of the UW Insect Museum. “Yanayacu is a cool place to study. We have found many new species, and I feel like we are just getting started.”

The research is supported by a National Science Foundation grant with two professors from Tulane also interested in studying in Ecuador. The initial grant was funded three years ago and renewed this year.

“We picked the highlands of the Andes in eastern Ecuador because it is a hot spot for caterpillars and other organisms,” said Shaw. “There is a tremendous diversity of organisms – more than almost any other area along the equator.”

Caterpillars are the key herbivores in the forest and are oblivious to the poisons in the plants they eat. The wasps are the primary biological control that keeps the caterpillar population in balance. “They are shaping the distribution and abundance of caterpillars and therefore the plants,” said Shaw.

Yanayacu (http://yanayacu.org/) hosts researchers from around the world. Getting there is an adventure. “It’s a remote area, difficult to get to,” noted Shaw.

First-timers are given directions on the Web site. Get off the bus at Cosanga, and, if you want to make sure you’re on the right path, ask for directions at the restaurant in the center of town, La Enmita, which is right next to the only gas station. You’re about a mile’s walk from the station.

There are two to three employees working at the laboratory whose main function is setting up caterpillar rearing and the basic ecology.

Townsend has been there twice. “I’m extremely fortunate to have the opportunity I’ve been given,” the Mission, Texas, native said. “I love Ecuador, and when I tell people where I am studying, many are jealous. It’s one of the hot spots of diversity.”

Under Shaw’s tutelage, Townsend has standardized the caterpillar research. When research started, there was one plot. There are now 250 plots each 10 meters in diameter every 100 meters in altitude. Townsend and assistants determined the 30 plant groups common at various elevations. When five of the 30 genomes are found in a circle, a plot is created. Plants are recorded, and every leaf of every plant is examined for caterpillars. Each plot takes about three hours to record.

“We have a huge amount of data,” said Townsend. “We are not only getting biological inventory but also the density of caterpillars by plant and elevations. They are big-time herbivores.”

The food plants of the caterpillars are largely unknown. “We are learning a tremendous amount,” he noted. “Caterpillar diets are specific to a narrow range of plants.”

They are also munching on plants that have become chemically defended. “They are toxic or distasteful and not fed on much by other animals,” said Shaw. “But some insects have broken through that barrier. In a tropical cloud forest, caterpillars are the key group of herbivores on plants, and they are not eaten by frogs or birds. They get hammered by parasitic wasps. The wasps have broken through the chemical barrier and feed on the caterpillars.”

Caterpillars evolved their own defenses against other organisms – some have spines and some hairs that deter birds but not parasitic wasps.

Two types of wasps are targeted: Meteorus, a group already studied by Shaw, and Townsend is studying Aleiodes. Meteorus is easily recognized before it turns into an adult wasp. Aleiodes lays from one to 50 eggs inside a caterpillar and then mummifies its host.

The Yanayacu workers hang the caterpillars and plants in plastic bags on a clothesline inside an open shed. “We don’t know a heck of a lot more about the caterpillars than the wasps,” said Shaw. “We don’t know what the caterpillar will turn into, whether a butterfly or a moth. All caterpillars are photographed. If they are not parasitized, they are sent for categorization. The rates of parasitism are pretty high. We need 10 to 20 to get a few that emerge.”

In addition to finding new species, Shaw is attempting to theorize why some wasps lay one egg and another wasp lays many in their hosts.

“I have my suspicions,” he said. “The ones that attack the chemically defended caterpillars are solitary. It’s too risky to put lots of eggs in something potentially poisonous. It’s safer to put one egg in one caterpillar.”

Not so the gregarious wasps. “They attack either the really hairy or spiny caterpillars, good defenses against birds but inside they are probably OK to eat. It’s relatively safe for a wasp to put large numbers of eggs in large, hairy or spiny caterpillars,” noted Shaw.

On the Web:

http://uwadmnweb.uwyo.edu/UWRENEWABLE/Faculty/S_Shaw.asp

Contact: Steven L. Miller, Senior Editor
Phone: (307) 766-6342
E-mail: slmiller@uwyo.edu
Archived News Site http://uwadmnweb.uwyo.edu/UWAG/news.asp

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