Got Lygus? You may indeed, without knowing it. Sampling alfalfa, cotton or even roadside vegetation with a sweep net will tell the tale quickly.
Research under way at the Texas A&M University System Agricultural Research and Extension Center in Lubbock is geared toward finding out more about lygus bugs and their potential impact on cotton.
“Lygus are an unknown quantity here,” said Megha Parajulee, a Texas Agricultural Experiment Station entomologist. “They can damage cotton by feeding on young squares. In 2002, we began a study to determine which species of Lygus are common here and which host plants they prefer during their life cycle.”
The study has revealed two species of lygus bugs in a 25-county survey area around Lubbock: pale legume bugs and Western tarnished plant bugs. The latter is more numerous and can pose a threat to cotton if its preferred food plants are not abundant.
“In our species survey we determined that Lygus prefer to live in and feed on flixweed and mustard from mid-March through mid-April,” Parajulee said. “Then they move into alfalfa, pigweed and Russian thistle. They overwinter here in alfalfa and pigweed.
“They are opportunistic feeders. We believe they prefer these hosts plants over cotton, but there is a June through September window when they will move into cotton and feed on squares, blooms and bolls if they are forced to. That window closes after cotton plants attain about 350 heat units. The bolls then harden and become impenetrable to lygus bugs.”
Lygus feeding can cause cotton plants to abort squares and small bolls, or stain and reduce the amount of lint. This damage means fewer dollars for farmers at harvest and in the market place.
“Lygus populations on the South Plains have been pretty static for several years,” said James Leser, a Texas Cooperative Extension cotton entomologist who works with Parajulee in this research. “Lygus and fleahopper damage was especially high in 1999, but has generally been much lower and spotty during the last six years. In 1999, combined damage from Lygus and fleahoppers averaged about 12 percent, and control costs added up to more than $7 million.”
Lygus are difficult to control, often requiring two or more expensive applications, Leser said.
“Another species of Lygus is a real threat to cotton in the southeastern United States now that the boll weevil and bollworm have been taken out of the picture through eradication programs and by planting Bollgard cotton,” Leser said. “The resulting reduction in sprays for these two pests has allowed Lygus infestations to reach damaging levels. I think they are becoming more noticeable in the Texas High Plains because we, too, are eliminating boll weevils and reducing bollworm infestations.
“But more importantly, our producers read about the eastern Lygus problems and assume they will have similar problems. Thus far this has not been the case.”
By studying the host plants that lygus bugs prefer, their feeding behavior and patterns of movement, scientists hope to develop tools farmers can use to protect their cotton.
“We also are evaluating methods for sampling and detecting Lygus in the field. If we can combine accurate sampling with knowledge of how and when they move and feed, we may be able to control them before they move into cotton,” Parajulee said. “We are also evaluating host plants in the lab to see which ones Lygus favor for reproduction. And we are evaluating cotton varieties for Lygus resistance and tolerance in the field as well as in the lab.”
Knowing which varieties are more tolerant to lygus bug feeding damage and when bolls become safe from the damage may help researchers develop solid thresholds for spray treatments.
“All current treatment thresholds are from Arizona,” Leser said. “It will be helpful to have treatment thresholds for Texas and to know which insecticides and doses will work best here. We are also looking for a simple, hand-held tool producers can use to gauge boll hardness in the field so they can tell when Lygus are no longer a threat.”
The researchers are also studying how irrigation regimes may affect Lygus populations.
As the researchers gather more information about Lygus, they will step up their education campaign with area farmers. Leser's weekly “Focus on Entomology” electronic newsletter provides information about many important insect pests. Lygus will also be a featured topic in an ongoing series of Crop Production Guides Leser and other scientists are compiling. Extension's integrated pest management agents also provide lygus bug information to producers.
“Focus on Entomology” is available weekly during the cotton growing season on the Internet at http://lubbock.tamu.edu/focus/.
“This is a team effort that combines applied research with a strong Extension component,” Parajulee said. “We hope one day to have more solid information about Lygus than questions.”
The Plains Cotton Growers, Cotton Incorporated and the Texas Department of Agriculture fund their research.