ARS entomologist Robert Mangan hopes that a combination of controlled temperature and an altered mix of oxygen, nitrogen, and carbon dioxide can keep shipped citrus free of live Mexican fruit flies, a quarantine pest in California and Texas. Parts of California's San Diego County are currently under quarantine for this fruit fly. Mangan is proposing the new treatment as an alternative to methyl bromide, the chemical fumigant now being used that will be discontinued by 2001.

He is testing the proposed method on grapefruit at the ARS Crop Quality and Fruit Insects Research Unit in Weslaco, TX. His goal is in-transit treatments against the threat the Mexican fruit fly poses for any citrus crop grown in California or Texas. "We are testing lots of combinations of the gases," Mangan says. "Results are not conclusive, but some combinations appear very effective at killing Mexican fruit flies."

Krista Shellie, a plant physiologist at Weslaco, is testing fruit quality for the quarantine treatments program. Grapefruit hold up well for a number of the proposed treatments.

Even if this approach succeeds, it would be only one of many kinds of methyl bromide alternatives that are needed. "We would expect this approach to be applicable as a treatment against Mexican fruit fly in citrus during processing and containerized shipping," Mangan says. The in-transit period for produce being shipped from production areas is typically 1 to 3 weeks. Mangan's approach would include placing recording devices in multi-ton shipping containers to track the actual gas mixture and temperature over time. That way, inspectors at the receiving port can determine the treatment's integrity.

The specific mixtures of oxygen, nitrogen, and carbon dioxide gases are proprietary information of the project's industry partner, TransFRESH Corp., Salinas, CA. ARS has a Cooperative Research and Development Agreement with TransFRESH to test the new method for 3 years. Under this agreement, researchers will look for the perfect in-transit treatment that will protect citrus, mango, avocado, and other fresh fruit from pests such as Mediterranean, Mexican, Caribbean, and other fruit flies.

"Keeping shipped U.S. produce free of pests is essential to maintain and expand markets here and elsewhere, such as in Pacific Rim countries," Mangan says.

Typically, USDA's Animal and Plant Health Inspection Service requires that a method must kill 99.9968 percent of pests before it can be approved as an official quarantine treatment.