UW develops economical way of controlling grasshoppers on rangeland

2013-06-05T03:30:00Z UW develops economical way of controlling grasshoppers on rangelandBy Sue Roesler, Farm & Ranch Guide Farm and Ranch Guide
June 05, 2013 3:30 am  • 

A group of scientists at the University of Wyoming have developed a cheaper, more efficient and environmentally safer strategy to reduce grasshopper populations on rangeland.

There are more than 400 species of grasshoppers, according to Douglas Smith, a doctorate graduate student at UW who was part of the team, adding that grasshoppers increase rangeland productivity through nutrient cycling, and are important food resources for numerous insects.

“There are a lot of good grasshoppers,” Smith said. For instance, the snakeweed grasshopper only eats a type of forbe (known as a weed) that is not a nutritional forage for livestock to consume.

However, of these 400, about 10-15 are the type of pests which can multiply to population densities that can devastate and severely consume rangeland forage.

“Healthy rangeland is vital to livestock grazing,” said Smith, adding that destructive grasshopper populations need to be controlled. “Managing the forage loss due to grasshoppers is also important to the livelihood of producers who ranch on the rangelands, wildlife forage, and wildlife habitat.”

Most ranchers control the problem with a full rate of insecticides, applying up to 100 percent of the infested area, Smith said. But a new methodology of controlling grasshoppers was developed that not only works but decreases costs to ranchers.

“The USDA typically treats grasshopper outbreaks when densities exceed 9 grasshoppers per square meter. But, confusingly, most treatments for grasshopper control are between 11 and 22 grasshoppers per square yard,” Smith said.

So UW scientists knew a different approach was necessary.

Smith grew up in Casper, Wyo., and received his bachelors and masters degree in entomology at UW.

“I was interested in insects and I actually wanted to become a fly fisherman,” he said. Instead, Smith ended up working in private industry as an entomologist on the East Coast.

His former advisor at UW, Alex Latchininsky, asked Smith to join a team of scientists working with the Reduced Agent Area Treatment (RAAT) methodology of grasshopper management and Smith decided to go for his doctorates in RAAT.

“I was intrigued with the methodology, and I wanted to work with grasshoppers,” Smith said, adding the RAAT strategy was initially developed at UW.

The traditional treatment where full rate of broad spectrum insecticides are applied to 100 percent of the infested area ends up killing all grasshoppers and beneficial insects, he said, adding the group of UW scientists knew a 100 percent kill was not the answer to saving rangeland.

For the past 10 years in the U.S., grasshopper management practices have utilized the RAAT methodology with the use of an insect growth regulator (diflubenzuron) as the main agent. It is a slow way to kill the grasshoppers as it takes from seven to 10 days for the grasshoppers to go through the molt stage.

“The growth regulator disrupts the way grasshoppers molt,” Smith said.

Grasshoppers are highly mobile and for that reason, have been difficult to control. They will molt through several stages before reaching the adult grasshopper form. Interrupting this molting cycle kills them, Smith said.

The UW scientists, of which Smith was a team member, found a different way to eradicate grasshoppers that devastated rangeland under the RAAT methodology.

They treated grasshoppers in a smaller area and reduced the amount of insecticide from the high rate of 4 ounces to the low rate of 1 ounce.

Under the trial, the RAAT treatment tried treating swaths that were about 100 feet wide with insecticide alongside untreated swaths up to 200 feet wide.

And they used a much lower rate of insecticide.

“Our research found that by reducing the amount of insecticide as well as the area receiving the insecticide, the efficacy of control was not diminished,” Smith said.

In addition, the untreated swaths provided a refuge for many non-target fauna and natural enemies of grasshoppers.

“We found if you need to protect 10,000 acres of rangeland, you only need to treat up to 5,000 acres,” he said.

RAATs also resulted in higher bird populations in treated areas, compared to traditional methods of control. The growth regulator was not toxic to the birds, but only affected the growth of molts.

As such, this method of application to control grasshopper outbreaks was included as an option in the Environmental Impact Statement for USDA-APHIS, and is being used by the USDA and by producers on rangeland in Wyoming, North Dakota, South Dakota, Montana, Utah, California and Nevada.

Smith said they did the trial with many ranchers in these states. They went out in the spring and scouted for grasshoppers with the Weed and Pest Control and offered ranchers the growth regulator at little or no cost.

“A lot of private landowners used it,” he said.

RAAT methodology with the growth regulators was especially desired by ranchers for alfalfa hay as it is a high value crop.

This method was also introduced internationally and is being used in Africa, Australia, and in Central Asian countries, Smith said.

“We were really proud of developing this. I wasn’t alone in this. There was a whole team of scientists working on it,” he said.

As a result of his work, Smith received the $32,000 Lloyd/Kumar Graduate Fellowship in Entomology that honors longtime entomologists Jack Lloyd and Rabinder Kumar. The fellowship supports graduate student education and helps train future entomologists.

In addition, Smith received the prestigious International Integrated Pest Management Award of Excellence at the International IPM Symposium in Memphis, Tenn., last year.

“Not many graduate students are recognized for their research with such a prestigious award of international scope,” Latchininsky says.

Smith is only the second recipient of the Lloyd/Kumar award, says John Tanaka, head of the Department of Ecosystem Science and Management. The first award was in 2010. Entomology faculty members recommend the recipient with Tanaka having the final decision.

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