
Beet
Armyworms: What Do They Really Want?By Lupe Chavez October 17, 2001South Texas farmers face their share
of crop pests, with the beet armyworm on their least- wanted list.
Now, Agricultural Research Servicescientists are hot on the pests tiny tracks, looking at clues to help
control the critter. One important new clue is that beet armyworms grow bigger when they eat a
diet of pigweed--a crop weed--than when they eat cotton plants. The finding
suggests pigweed might have a constructive role, by diverting some of the
armyworms from cotton. Shoil Greenberg and Thomas Sappington, ARS entomologists at the
Kika de la Garza Subtropical Agricultural
Research Center in Weslaco, Texas, cooperating with Tong-Xian Liu at the
Texas Agricultural Experiment
Station, also at Weslaco, study this cotton pest extensively. Armyworms
quickly develop resistance to insecticides; moreover, it is vital to understand
the insects biology in order to develop effective biological controls or
chemicals to prevent crop losses. At the Integrated Farming and Natural Resources Research Unit, Greenberg
tested beet armyworm, Spodoptera exigua, to determine how quickly
armyworm larvae consumed five different host plants, and the impact of the
feeding on the insect's fertility and life cycle. His findings can be read in
the July issue of the Annals
of the Entomological Society of America. Cotton, cabbage, pepper, sunflower and pigweed were tested as host plants,
with interesting results. For example, although beet armyworms destroyed the
1995 South Texas cotton crop, pigweed was most nutritional for larvae, as
measured by the weight of the pupae that developed from them. Pupae that
developed from larvae feeding on pigweed weighed 117 milligrams (mg), compared
to 103 mg for those feeding on cotton, even though armyworm larvae feeding on
cotton ate more than those dining on pigweed. And larvae reared on pigweed
developed into females more than 60 percent of the time. Greenberg believes an absence of pigweed in South Texas, where it is
naturally abundant, could cause damaging outbreaks of armyworm infestation in
cotton as the pest moves from its preferred host of pigweed to cotton. Scientists are now finishing a study to determine where the insects prefer
to lay their eggs. With this information, scientists would know where to coat
leaves with insecticides that would kill the armyworms eggs or larvae.
ARS is the U.S. Department of
Agriculture's chief scientific research agency. U.S. Department of Agriculture |