Hawaii—blue skies, balmy breezes, beautiful flowers, and bountiful exotic fruit. Things that the mainland dreams of and wants. But one thing the mainland doesn't want is Hawaii's wide range of pests. Movement of exotic fruit from Hawaii is regulated to keep these pests—including the Mediterranean fruit fly, the melon fly, and the oriental fruit fly (a trio known as Trifly)—from the mainland. The litchi fruit moth and the mango weevil are among other pests found in Hawaii that are unwelcome on the mainland.

But amended regulations will allow some of Hawaii's tropical produce, with the help of irradiation, to move safely and more freely to the mainland.

"As early as 1956, Agricultural Research Service (ARS) scientists proposed irradiation as a quarantine treatment for Hawaii-grown fruits," reports John W. Armstrong. He is with the ARS Tropical Fruit, Vegetable, and Ornamental Crop Research Laboratory in Hawaii. "Nothing much came of the work for years because at the time we still had ethylene dibromide (EDB) and we also had methyl bromide. These chemicals were the first choice of export fruit industries because they were considered relatively safe, effective, and inexpensive."

But EDB was banned in 1984 and methyl bromide will be gone in 2001. The ARS research staff in Hawaii has been preparing for these possibilities for years. Armstrong and colleagues have been studying alternative measures to chemical fumigation since the 1970s. They've developed, tested, and successfully used vapor heat, forced hot air, hot-water immersion, and cold treatments. The nonhost status of crops was investigated to see if some fruits and vegetables could escape fumigation if no quarantine pests were found.

And they resurrected the idea of irradiation.

"The use of irradiation as a quarantine treatment against fruit flies was delayed by the lengthy process required to get approval from the Food and Drug Administration (FDA). FDA needed assurance that irradiation is a safe, effective treatment for fresh fruits," Armstrong says. "And, ARS showed the treatment was effective."

"Some fruits can't tolerate irradiation; it can alter the quality, depending on the dose. From a database that we had accumulated since 1956, we developed a generic dose of irradiation that would kill fruit flies without damaging the quality of the fruit," Armstrong says.

Based on this work, FDA approved irradiation as a quarantine treatment for fruit and vegetables in 1986, and in 1987, USDA's Animal and Plant Health Inspection Service (APHIS) issued regulations supporting irradiation treatment to disinfest papaya.

But even though approval has been granted, industry and the public are still cautious about accepting irradiation. Armstrong says that in the late 1980s, a combined federal and state program to construct an irradiation facility in Hawaii failed for lack of industry and public support and sufficient construction funds. This facility had been proposed primarily for the papaya industry to demonstrate the use of irradiation.

But in 1995, ARS joined forces with the Hawaii Department of Agriculture (HDOA), Hawaii export industries, and APHIS to revisit the issue of using irradiation as a quarantine treatment. The commercial feasibility of using irradiation needed to be proven.

"APHIS granted HDOA a special permit to ship untreated fruit from Hawaii to Chicago. There the fruit was irradiated and dispersed to grocery stores in a number of states," Armstrong reports.

Armstrong's lab sent infested fruits to Chicago along with those from HDOA to show that the recommended dose of irradiation provided quarantine security by killing pests in the fruit. Infested fruits, which were shipped only during the winter months and under secure conditions that prevented insects from escaping, were returned to the lab after irradiation.

"Our lab also tested the recommended irradiation treatment for Mediterranean fruit fly, melon fly, and oriental fruit fly against the Malaysian fruit fly, which became established in Hawaii in the early 1980s," Armstrong says. "Our tests showed that the recommended treatment was more than adequate to kill or prevent adult emergence of the Malaysian fruit fly."

Consumer acceptance of the irradiated fruit was excellent. A company specializing in irradiation facilities plans to build a quarantine treatment plant in Hawaii in the near future.

In July 1997, APHIS published amended regulations that now allow papayas, carambolas, and litchis from Hawaii to be irradiated either in Hawaii or in areas of the mainland United States where fruit flies can't survive winter conditions.

Under the new regulations, litchis must be inspected and declared free of the litchi fruit moth and other plant pests, then either irradiated or treated with hot water (a treatment also developed by Armstrong's lab) to kill potential fruit flies. So, while allowing Hawaii growers to move their produce, the new regulations also protect the U.S. mainland from unwanted pests.

"Irradiation is another tool we can use to disinfest fresh fruits before moving them through export market channels," Armstrong says. "But, we need to be aware that it is not a silver bullet, because some fruits can't tolerate irradiation."