ARS entomologist John Armstrong (left) and Jerry Vriesenga, president of Dole
Food Company Hawaii, discuss hot-forced-air treatment for papayas that have
been partially tree-ripened.
Heated Air Blasts Papaya Pests
Fresh, juicy papayas from Hawaii can be kept free of live fruit flies with a
packinghouse procedure from ARS and the
University of Hawaii.
Once used only on the islands of Hawaii and Kauai, the hot-forced-air
technique today is on-line at packinghouses on the islands of Oahu and Molokai
as well. It is credited with easing entry to profitable mainland U.S. markets
and rescuing jobs that might otherwise have been lost.
Hawaii's papaya growers produced about 42 million pounds of the
sweet-tasting fruit, worth about $17 million, in 1996. They specialize in two
varietiesthe golden-fleshed Kapoho Solo and Sunrise, a reddish-orange
"Commercially grown papayas from Hawaii are so carefully checked that
it's unlikely fly-damaged fruit would make it to a mainland supermarket,"
says ARS entomologist John W. Armstrong at Hilo, Hawaii. "Our
hot-forced-air process is simply extra insurance."
Called a quarantine treatment, hot-forced-air is one of three federally
approved techniques. The treatment is similar to another option, called vapor
heat, but differs in that vapor heat uses humidity differently. Another
approach, irradiation, requires equipment not yet available in Hawaii.
Hot-forced-air kills three different kinds of crop-damaging fruit
fliesthe Mediterranean fruit fly, oriental fruit fly, and melon fly.
The female Mediterranean fruit fly, shown here on a coffee fruit, can deposit
eggs 2-3 millimeters deep in papayas.
At the packinghouse, papayas are placed in a chamber typically made of
stainless steel. Hot air, forced over the surface of the fruit for at least 4
hours, heats it to 117oF. Then the fruit is cooled for about an
Heat-treating papayas ensures that pestiferous fruit flies can't hitchhike
to vulnerable farms, orchards, and backyard gardens on the U.S. mainland.
Each of the three fly species, already ensconced in Hawaii, "could
readily adapt to the warm, mild climates of California, Florida, or other
Sunbelt States and wreak agricultural havoc," says Armstrong. Medfly, for
instance, "ranks as one of the world's worst agricultural pests, capable
of attacking the fruit of more than 300 different kinds of plants."
The 1995-96 outbreak of medfly in southern California cost an estimated $13
The medfly, oriental fruit fly, and melon fly each employ the same extremely
successful mode of attack, says Armstrong.
"Females use their tubelike ovipositors to pump tiny eggs into the
flesh of ripening fruits and vegetables. Young maggots, or larvae, hatch from
the eggs. They use the fruit or veggie for food and housing and turn it into a
decaying, unmarketable mess. The developing larvae drop to the ground, form
their next lifestagea pupawhile in the soil, and later emerge as
To garner regulatory approval, Armstrong and colleagues tested the
hot-forced-air technique with a research-size chamber at the ARS Tropical
Fruit, Vegetable, and Ornamental Crop Research Laboratory in Hilo. Their
experiments began in 1987 and required more than a quarter-million fresh
papayas, plus some 1.8 million laboratory-reared fruit flies.
Michael Williamson (center), professor of biosystems engineering at the
University of Hawaii, Monoa, and Jerry Vriesenga (right), president of Dole
Food Company Hawaii, monitor papayas delivered by Dole employee Chris Awa for
hot-forced-air treatment. Use of lattice-bottom containers ensures uniform
heating during treatment.
Armstrong did the work with Steven A. Brown of ARS at Hilo; James D. Hansen,
now with ARS at Wapato, Washington; Edward T. Uyeda of USDA's Animal and Plant
Health Inspection Service and Benjamin K.S. Hu, now retired from that agency;
Michael R. Williamson, professor of biosystems engineering with the University
of Hawaii, Manoa; and Paul M. Winkelman of Quarantine Technologies
International, Ltd., Honolulu.
ARS has registered the process with the U.S. Patent and Trademark Office.
The University of Hawaii has filed a patent application for the hot-forced-air
Sunrise Packers on Kauai started using hot-forced-air in 1993. A new
packinghouse for Kauai, expected to be up and running in 1998, will boast two
new hot-forced-air units.
Hawaii Fruit Growers on Molokai chose hot-forced-air in 1997 for their
first-ever papaya shipments to the U.S. mainland. Those sales were so
successful that the co-op is now building a second unit.
Dole Food Company Hawaii on Oahu now has mainland U.S. markets for fresh
papaya as well, thanks to two hot-forced-air chambers that the company
installed in 1997. Dole converted 600 acres of no-longer-profitable sugarcane
fields to papaya.
Bill Pfeil (left), manager of Hawaii Papaya Growers, and ARS entomologist John
Armstrong assess quality of papayas after hot-forced-air treatment.
"We've rehired or newly hired more than 80 people to work in papaya
production," says Dole Food Company Hawaii president, Jerry D. Vriesenga,
"and we expect to hire many more as the project grows."
Hot-forced-air also zaps medflies and oriental fruit flies that might be
concealed in grapefruit and oranges, according to experiments by Armstrong and
co-workers. They tested a total of about 6,500 Marsh White and Marsh Red
grapefruit, plus navel and Valencia oranges, with funds from the California
"What Works in Hawaii Is also Good in Texas"
Their technique would serve as an alternative process, should medfly or
oriental fruit flyperhaps stow aways in luggage or parcels of illegal
fruitever gain a foothold in mainland citrus groves.
By Marcia Wood,
Agricultural Research Service Information Staff, 800 Buchanan St., Albany, CA
94710; phone (510) 559-6070.
JJohn W. Armstrong and Steven A. Brown
are at the USDA-ARS Tropical Fruit, Vegetable, and
Ornamental Crop Research Laboratory, P.O. Box 4459, Hilo, HI 96720; phone
(808) 959-9138, fax (808) 959-4323.
"Heated Air Blasts Papaya Pests" was published in the
January 1998 issue of Agricultural Research magazine. Click
here to see this issue's table of contents.