Pest In Rice Fields New To Country

Boris A. Castro, Schultz, Bruce

News Release Distributed 04/06/05

A maggot that wreaked havoc on several rice fields last year has been identified as a species previously found in Peru and Costa Rica.

The species, Hydrellia wirthi, is a fly identified recently by the Smithsonian Institution. It has been found in Louisiana and Texas.

"Based on available information, it is not possible to determine when and how this insect came to the United States," said LSU AgCenter entomologist Dr. Boris Castro.

The entomologist from the Smithsonian, Dr. Wayne Mathis, indicated the fly also is present in Colombia.

Castro said a common name will have to be agreed upon by the Entomological Society of America.

"We’ve suggested the name of South American rice miner," he said, explaining the insect is known as "the miner of rice" throughout South American countries.

In addition to agreeing on a name, scientific drawings of the insect are being made to help in its identification.

More information is needed about this insect’s distribution and habits, such as its overwintering sites, number of offspring per year and how far north it can survive, according to experts here.

It also will be important to find out the early signs of infestation, Castro said. By the time a plant shows obvious signs of dead leaves, it’s too late to use any chemicals. Worse yet, no insecticides are labeled for use against the pest.

"They may behave completely different from those in South America," Castro said.

A teleconference organized by the U.S. Department of Agriculture’s New Pest Advisory Group was held earlier this week to assess risks and delineate actions to take against this new pest in rice-growing areas.

As a result, a report from the group is being prepared, and a field survey is scheduled in all rice-producing areas of the United States to evaluate the insect’s distribution and abundance. Data obtained from field surveys will be instrumental to develop risk mapping and pathway analyses and for informed decisions to assist in development of action programs against this new insect pest.

The pest’s larvae attacked fields last year in Acadia, Vermilion, Jefferson Davis, St. Landry and Concordia parishes, Castro said, and Dr. Mo Way, Texas A&M entomologist, has found it in Texas rice fields on a smaller scale.

Over the past few years, experts originally believed the damage was being caused by another small fly called a rice leaf miner, which is a sporadic pest of rice in the United States.

The rice leaf miner produces larvae that burrow between the two layers of a plant’s leaf, Castro explained. On the other hand, the larvae of the newer pest, which are an eighth of an inch to a quarter-inch long, feed on a leaf’s edge and work down into the whorl of a seedling – where a plant’s leaves and stem emerges. It’s not unusual to find several larvae infesting one plant, he said.

Damage is severe, either killing the plant or retarding growth, Castro said, adding that it appears the new fly preys on late-planted rice.

The LSU AgCenter recommends planting rice between March 15 and April 20 in South Louisiana; the recommendation for North Louisiana is between April 5 and May 10.

This newer pest seemed to have struck in June and July, according to Castro, who said the first case this past summer was found in a field that was planted in May.

"The earlier you plant, the better," Castro said.

Farmer Ted Girouard of Kaplan lost a 51-acre field to the pest. Girouard said he lost that rice, which was planted in July, to the pest and that his remaining 130 acres yielded only 12 barrels an acre.


Contact:     Boris Castro at 578-7386 or

Writer:        Bruce Schultz at (337) 788-8821 or

4/22/2005 8:25:44 PM
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