A fumigant called phosphine is more effective at controlling insects when it's combined with oxygen, according to findings by a U.S. Department of Agriculture (USDA) scientist. The oxygen-phosphine combination could be an environmentally friendly alternative to methyl bromide for combating pests on harvested fruits and vegetables.

Entomologist Yong-Biao Liu with USDA's Agricultural Research Service (ARS) in Salinas, Calif., found that oxygenated phosphine fumigation effectively controlled several insect pests during laboratory studies. ARS is USDA's principal intramural scientific research agency, and this research supports the USDA priority of promoting international food security.

In the ARS Crop Improvement and Protection Research Unit at Salinas, Liu tested phosphine fumigation under high levels of oxygen against four pests: western flower thrips adults and larvae, leafminer pupae, grape mealybug eggs, and Indianmeal moth eggs and pupae. The four species represent insect types and life stages for which quarantine treatments are needed.

In 5-hour fumigations with 1,000 parts per million of phosphine at 41 degrees Fahrenheit, control of western flower thrips on lettuce increased from 80 percent to 98 percent when oxygen was increased from 21 percent to 40 percent. When the oxygen level was increased to 80 percent, 99 percent of the western flower thrips were killed.

Western flower thrips are a common pest of fruits and vegetables in the United States and are often found on fresh products exported to Taiwan, where it is a quarantined pest. Currently, fresh fruits and vegetables exported to Taiwan are fumigated with methyl bromide to control western flower thrips, but use of methyl bromide is being phased out due to environmental concerns.

Liu used varying concentrations of oxygen at 41 degrees F and 50 degrees F and found that oxygenated phosphine fumigation was also effective in controlling leafminer pupae, grape mealybug eggs, and Indianmeal moth eggs and pupae.

Phosphine has been used for more than 80 years as a fumigant to control pests in stored products. It acts slowly against insects. Many insects, especially at egg and pupal stages, are very tolerant of phosphine, and it may take more than 10 days of fumigation treatment to control them. The new treatment would help speed up this process and control insects more quickly.

Read more about this research in the July 2012 issue of Agricultural Research magazine.