USDA sends in wasps to save water supply

In Mexico, the tall, bamboo-like plants are known as el ladron de agua, or the "water thief." And for good reason.

The giant reed, also known as carrizo cane or Spanish reed, grows in dense thickets all along the Rio Grande and often siphons off large quantities of water from the river, according to experts. The plant, imported from the Mediterranean in the 1500s, frequently chokes off waterways, depletes water availability, destabilizes river banks and crowds out native plants, researchers say.

To tackle the invasive plant, the U.S. Department of Agriculture is about to unleash an army of tiny, reed-eating wasps.

Next month, scientists with the USDA's Agricultural Research Service will release wasps - each about 1/16th of an inch long - over a particularly reed-heavy area of the Rio Grande in Laredo. Because these wasps feed only on the giant reed, they will likely prove to be an effective weapon in the effort to slow down reed growth, said John Goolsby, research entomologist for the Beneficial Insects Research Unit at the USDA in Weslaco.

The wasps "weaken the plants, making them small and brittle," Goolsby said. As the reeds die off, water availability in the river will improve and native plants will return, researchers predict.

And more water from the river's upper reaches will make it down to the Rio Grande Valley, experts predict.

"We know drought returns pretty frequently here and so we want to conserve more water," Goolsby said. "The cane absorbs a significant amount of water ... and the cane reaches huge proportions above Laredo."

Reducing the cane's stranglehold on the Rio Grande near Laredo will free up more water for farmers and irrigators in this region, Goolsby said.

Scientists will study the wasp's impact on the giant reed, and the amount of water saved, over the next year.

USDA scientists have been studying these wasps, along with other insects that feed on giant reed, since 2001. They've found that the wasp is an ideal biological-control agent because it won't harm any native plants or crops - just the giant reed, Goolsby said.

Researchers in Cuernavaca in the state of Morelos, Mexico, also are planning a wasp release on the Mexican side of the Rio Grande Basin, officials said.

Local water officials are so hopeful about the results of this study that they've contributed funds for it -    the Rio Grande Regional Water Planning Group, the Irrigation District Managers' Association, Valley Agricultural Research and Development Corp., the Rio Grande Regional Water Authority and local utilities granted a total of $5,000.

"We're very happy to see it ... hopefully it will accomplish something," said Jo Jo White, manager of Hidalgo and Cameron County Irrigation District No. 9 in Mercedes. White is co-chairman of the water-planning group's Aquatic Weed Task Force, which has tackled other weed problems in the Rio Grande.

White said he expected seeing results - and more water in the Rio Grande - would take time.

"Natural control is long term," he said.

The task force and the regional water planning group, with state and federal funding, previously employed Mother Nature in attacking other invasive plants in the river. In the 1990s, two plants - hydrilla, which grows thickly underwater, and water hyacinth, which coats the water's surface - became a big problem in the Rio Grande, officials said. Hydrilla acted as a sponge, sucking up the river's available water, and water hyacinth contributed to its evaporation.

In 2003, officials introduced sterile grass carp into the river to feed on hydrilla, and started using herbicides on water hyacinth. The strategies worked - within a few months, a 260-acre stretch of the river contained half the hydrilla it had when the carp were introduced. A year later, the hydrilla had all but disappeared.

These plants aren't completely gone, but are better controlled, White said.

"They're not near as menacing as they were 10 years ago," he said.

If the hydrilla problem worsens again, the carp might have to be reintroduced, White said. Some have been caught or captured by their natural predators, he said.

Now, scientists are hoping to cut down on another pest before it further depletes the water supply.

"We're being proactive as scientists, trying to solve these problems in advance," Goolsby said.

Melissa McEver covers health and environment issues for Valley Freedom Newspapers. She is based in Harlingen and you can reach her at (956) 430-6252.