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U researchers in front of a large white fabric used to catch caddisflies.

U research associate Roger Blahnik and graduate student Desiree Robetson, members of Raph Holzenthal's research team, capture caddisflies with black light and a white sheet strung between two treees.

Caddisfly catchers

By Jennifer Amie

From eNews, September 15, 2005

Caddisflies are found in nearly every type of stream, pond, or lake, but few people--aside from flyfishing fans--are familiar with these insects. " Adult flies are nocturnal and very secretive during the day," explains Ralph Holzenthal, University of Minnesota professor of entomology.

Caddisflies, like other species of insects such as mayflies and stoneflies are sensitive to particular types and levels of pollutants in the water they inhabit. In any river or stream, a population drop in one species may indicate a problem with water quality and may point to which contaminant is the culprit. In the United States and Europe, biomonitoring programs that track changes in insect populations are commonly used to evaluate water quality. In some parts of the world, however, such programs are difficult to implement--no matter how ecologically important the region is or what environmental threats it faces--because it is impossible to monitor populations of species that science has yet to discover.

One such place is southeastern Brazil, which contains some of the most endangered ecosystems in South America. Bounded by three mountain ranges and home to Brazil's largest cities--including Rio de Janeiro and S?o Paulo--the area contains remnants of the once vast Atlantic rainforest, as well as rare sections of interior dry land forests known as cerrado. While much is known about the health of these terrestrial ecosystems, little is known about the condition of the watershed that sustains them and their neighboring communities.

For the past nine years, Holzenthal has been working to remedy this as part of a massive effort to discover and identify caddisfly populations throughout the Central and South American neotropics. Holzenthal and his team have spent up to two months each year trekking through forests, wading in streams, and setting up shop on riverbanks in Brazil, as well as establishing research programs in Costa Rica, Nicaragua, Venezuela, Peru, Bolivia, and Chile.

"We're at the forefront of discovering biodiversity--out in the trenches, out in the field," says Holzenthal. He and his team begin work before dusk by stringing an ordinary white bedsheet between two trees near the bank of a river. They mount a black light tube, powered by a 12-volt car battery, above the sheet and turn it on when the sun goes down. The light attracts flying insects to the sheet, where the researchers pluck off the caddisflies, capturing them in jars.

"There is a certain urgency to the work because the Atlantic forest is being lost to development. Only 5 percent of the original forest remains," says Holzenthal.

"It's extremely important to know what is there and where it is," says Holzenthal. "Southeastern Brazil, for example, is important from a biological, ecological, and conservation perspective. There is a certain urgency to the work because the Atlantic forest is being lost to development. Only 5 percent of the original forest remains."

Holzenthal's documentation of insect populations in the intact sections of the forest can be used as a yardstick to measure species loss in developed areas. But loss of habitat is not the only threat to a region whose watershed is beset by pesticide, herbicide, and fertilizer runoff; contamination from untreated sewage; siltation from logging; chemical pollutants; and, in some places, acid rain.

"Aquatic habitats are particularly impacted by human use," says graduate student Desiree Robertson, a member of the research team. "They're like the sewers of the landscape if they're not treated properly."

Conservation measures and environmental protection are critical throughout the neotropics, and both aims are aided by the type of research Holzenthal's team does. "Conservation without documentation is incomplete," says Roger Blahnik, another member of the team. "With limited resources, how do you select and prioritize what to conserve? You need to know what's out there."

Aquatic creature

Like their close relatives moths and butterflies, caddisfly larvae have the ability to produce silk. Net-spinning caddisflies spin silk nets that they place into the water to harvest bits of algae, plankton, and plant material for food. They also use the silk to bind together grains of sand and organic material, which they fashion into little shelters.

In some places in South America, up to 75 percent of the caddisflies collected by the research team turn out to be species previously unknown to science. When the team started work in Brazil in 1996, only 125 species had been recorded in the region. To date, the researchers have recorded 525 additional species.

"Before we collected in Brazil, no one knew that there were 650 species of caddisflies still hanging on after 500 years of European habitation in the region," says Holzenthal.

The collected flies and larvae are carefully prepared as museum specimens. "At the University of Minnesota, we've built one of the world's best collections of caddisflies," says Holzenthal, who is also director of the University's insect museum at the Bell Museum of Natural History. The collection features a fully accessible database, illustrations of the insects, and specimens that are well-labeled and carefully maintained.

"If this taxonomy is done well," says Holzenthal, "it has a certain immutability. It becomes part of the timeless record of life on Earth."