New Test To Identify Screwworm
The same technology that brought pregnancy test kits home is now being used
to help identify larvae of the screwworm, Cochliomyia hominivorax, in
the field. The test can differentiate them from those of a related screwworm,
C. macellaria, which is not harmful to cattle.
A new test developed by ARS
scientists at the Midwest Livestock Insects Research Laboratory in Lincoln,
Nebraska, makes quick work of a complex identification process to distinguish
screwworm larvae from close relatives in the fly family.
The test is expected to be used at airport terminals and other ports of
entry to identify suspicious insects found on dogs, horses, and other animals
which can carry screwworm larvae. Currently, specimens must be viewed in a lab
under microscopes by trained entomologists.
Called an ELISA, for enzyme-linked immunosorbant assay, the test will make
it easier for scientists and agricultural officials in developing countries to
identify and track screwworm infestations and accidental re-introductions and
to positively identify laboratory populations quickly and easily.
Little or no training is required to use the kit. Just crush a suspect larva
in a small container and add a few drops of the kit's enzyme. If the sample
turns a distinctive blue color, the larva was a screwworm.
"This test is important because the screwworm larva and its close
relatives can be easily confused in the primary larval stages," says ARS
entomologist Steve R. Skoda. "This test allows anyone to make a positive
identification so steps can be taken to prevent an accidental
Before its eradication in the 1970s, screwworm was one of the most serious
insect pests of the domestic livestock industry. It devastated livestock
populations across the southern United States and in Mexico, costing cattle
producers hundreds of millions of dollars each year.
The adult female lays her eggs in living tissue, and the larvae hatch and
feed on the wound, creating an opportunity for bacterial infections. Other
females lay more eggs in the infected wounds and continue the cycle. Many
screwworm-infested animals die.
The screwworm has been eradicated from the United States, Mexico, and part
of Central America to Nicaragua. It still persists in Costa Rica and
Panama.--By Dawn Lyons-Johnson,
Agricultural Research Service Information Staff.
Steve R. Skoda is at the
USDA-ARS Midwest Livestock
Insects Research Laboratory, University of Nebraska, 305 Plant Industry,
P.O. Box 830938, Lincoln, NE 68583-0938; phone (402) 437-5267, fax (402)
"New Test To Identify Screwworm Larvae" was published in
the September 1998 issue of Agricultural Research magazine. Click here to see this
issue's table of contents.