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Carbonyl Sulfide: Possible Alternative
Fumigant to Replace Methyl Bromide
United States growers produce more than $1.5 billion worth of
dried fruits and nuts each year. Not only do consumers in the United
States and abroad love these commodities, but so do a wide range of insect
pests. Currently, 100 percent of stored dried fruits and nuts are treated
with methyl bromide or phosphine to rid them of these pests.
Methyl bromide is scheduled for elimination in 2001, and phosphine is
also under attack because of human health concerns and pest resistance.
There is no viable replacement for either fumigant.
"But we've found a possibility," says ARS entomologist J.
Larry Zettler. At the ARS Horticultural Crops Research Laboratory in
Fresno, California, he and colleagues James G. Leesch and Richard Gill
have been testing carbonyl sulfide to control pests in storedproducts.
"This compound was effective against five species of insects that
attack stored commodities," Zettler says. "We think it has
potential as a replacement fumigant of dried fruits and nuts."
The compound, he says, is a colorless, odorless, tasteless gas similar
to carbon disulfide and carbon dioxide. Although it has been known since
1867, carbonyl sulfide was just recently patented by the Australians to
control insects and mites in postharvest commodities.
"Carbonyl sulfide is environmentally friendly, has good
commodity penetration and aeration qualities, and can be toxic in a short
exposure or at a reduced dose for a longer period. Also, it doesn't harm
seed germination," Zettler reports.
Although the compound is patented as a grain fumigant, Zettler and
colleagues have shown that it may be effective in fumigating other
commodities as well. It is still experimental, and is not yet used in the
United States since it has not been registered by the U.S. Environmental
Protection Agency.
The five species of insects that succumbed to carbonyl sulfide in
laboratory tests include: the confused flour beetle (Tribolium
confusum), cigarette beetle (Lasioderma serricorne), sawtooth
grain beetle (Oryzaephilus surinamensis), dried fruit beetle
(Carpophilus hemipterus), and the navel orangeworm (Amyelois
transitella).
Life stage susceptibility varied for the confused flour beetle--the
most tolerant (hardest to kill) species--with the egg and pupal stages
being most difficult to kill, requiring a larger dose of the chemical over
a 24-hour period.
"Our research showed that toxicity of carbonyl sulfide is not
always immediate in some insects," Zettler explains. "Since
time required to kill the pest depends on dose, higher doses than we used
may likely kill the pests more quickly."
On the downside, Zettler says that although carbonyl sulfide is a
relatively stable molecule, under some conditions it can undergo a variety
of reactions that could negatively affect commodities.
Zettler and colleagues at Fresno plan further studies on the
phytotoxicity of this chemical and its effects on insect pests to fully
assess its viability as a replacement fumigant of dried fruits and nuts.
[April 1996 Table of Contents]
[Newsletter Issues
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Last Updated: October 7, 1996
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Last Modified: 01/30/2002
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