See a magazine story about other ARS water-hyacinth research. (March 2000)

U.S. and Mexico Cooperating To Control Water-Hyacinth Infestation

Agricultural Research Service scientists are collaborating with Mexican researchers in an effort to curb the spread of the aquatic weed water-hyacinth--Eichhornia crassipes-- in Mexico's dikes, reservoirs and canals. The researchers have introduced two weevils and a moth as biological control agents that have proven to be successful in reducing water-hyacinth densities in the United States.

The two weevils--Neochetina bruchi and Neochetina eichhorniae--were first released in the United States in the early 1970s by Ted Center and other ARS scientists. Center, of ARS' Invasive Plant Research Laboratory in Ft. Lauderdale, Fla., currently leads ARS' involvement with this project in Mexico. Since then both weevils have been shown to suppress water-hyacinth mat expansion by causing the development of smaller, less intertwined mats which eventually led to significant declines in infestation levels.

This success and others like it in far-flung corners of the globe like South Africa, Malaysia and Egypt prompted Mexican researchers to introduce the weevils in infested irrigation systems in the state of Sinaloa, on the Pacific coast of Mexico. In western Sinaloa, water-hyacinth infestation has caused obstruction of canals, clogged ditches and other severe problems in 60 irrigation districts.

Researchers have recently found that the weevils have dramatically reduced water-hyacinth mats throughout Sinaloa's irrigation districts in two to three years, compared to three to 10 years in other areas. At a number of locations, biomass coverage was reduced from 90-100 percent to less than 5 percent. Adult females will chew a hole in the stem of a leaf to deposit a single egg. A single adult female weevil will lay more than 400 eggs during her lifetime.

The scientists also found that some weevils were infected with a microsporidian-like organism. These parasitic spores reduce the weevil's ability to lay eggs. Studies have shown that only 14 percent of infected females lay eggs compared to 100 percent of healthy females. This finding allowed researchers to eliminate infected breeding lines, which helped optimize the weevils' performance once released.

ARS is the chief scientific research agency in the U.S. Department of Agriculture.

Scientific contact: Ted D. Center, ARS Aquatic Plant Control Research Unit, Ft. Lauderdale, Fla., phone (954) 475-0541, fax (954) 476-9169, tcenter@saa.ars.usda.gov.