Zapping Sweetpotato Weevils
Entomologist Guy Hallman
sweetpotatoes for reaction
to irradiation quarantine
treatment against sweetpotato
Irradiation has yet another useful application.
In the United States, the sweetpotato is best known as
a holiday treat that goes with turkey or ham when families gather for
Thanksgiving. What many Americans may not know is that the versatile
vegetable is the world's fifth-most-produced food crop, with more than
133 million metric tons harvested worldwide every year. That translates
to about 47 pounds for every person on the planet, though we in the
United States consume only 4 pounds each, on average.
But the popular sweetpotato is threatened by the sweetpotato
weevil, Cylas formicarius elegantulus. Although the pest is widely
distributed throughout sweetpotato-growing regions of the world, areas
that do not have itsuch as the southwestern United States, around
the Mediterranean, and parts of Latin America and Africaunderstandably
quarantine against it, to prevent its spread.
The weevils cause serious damage by laying their eggs
at the base of plants in the field. The larvae that hatch burrow into
the roots, causing them to rot. Among food plants, C. formicarius
attacks only sweetpotatoes and continues to damage roots after they
have been harvested and put in storage.
Gassing with methyl bromide has been the only method to
control sweetpotato weevils on market-bound roots, but it usually damages
them. Furthermore, methyl bromide is being phased out for most uses
because it is thought to damage the stratospheric ozone layer that provides
protection from ultraviolet light.
From the spring of 1999 to April 2000, Guy Hallman, an
entomologist at ARS' Kika de la
Garza Subtropical Agricultural Research Center in Weslaco, Texas, studied
irradiation as a postharvest treatment to meet quarantine regulations
for interstate shipment of roots that can harbor sweetpotato weevils.
Exposure sterilizesbut doesn't killthem. The insects may
remain on the roots until they die in a few weeks, but they can't reproduce
and they do only negligible damage.
To prevent the spread of weevils, irradiation is being
used by growers in southern Florida to treat boniato-type sweetpotatoes
shipped out of state. These white-fleshed sweetpotatoes are popular
with Caribbean and other immigrants living in the United States and
also represent a valuable export.
Hallman previously worked with irradiation to curb fruit
flies, but he says that his work on this weevil stands out. "It's
the first time irradiation is being used as a quarantine treatment against
an adult insect," he says. "That's significant. Because the
insects aren't killed, inspectors must have complete confidence in the
treatment. Otherwise, finding live adults would be cause for rejecting
In 2000, the first year the technique was used to treat
boniatos, 175 metric tons were irradiated and shipped. By 2001, the
total had grown to 189 metric tons, and it's expected to reach 200 metric
tons by the end of 2002. Irradiation has the potential to treat a significant
share of the world's sweetpotatoes.By Alfredo
Flores, Agricultural Research Service Information Staff.
This research is part of Crop Protection and Quarantine,
an ARS National Program (#304) described on the World Wide Web at www.nps.ars.usda.gov.
J. Hallman is with the USDA-ARS Kika
de la Garza Subtropical Agricultural Research Center, 2413 E. Hwy.
83, Weslaco, TX 78596; phone (956) 447-6313, fax (956) 447-6345.
"Zapping Sweetpotato Weevils" was published in the April 2003 issue of Agricultural Research magazine.