An alternative fumigant to methyl bromide called phosphine has been found to be almost 100% effective against insects when combined with high levels of oxygen, a U.S. Department of Agriculture (USDA) scientist has discovered.

It is hoped the oxygen-phosphine combination will be an environmentally friendlier option than methyl bromide, which is being phased out globally because it destroys the atmospheric ozone.

U.S. Agricultural Research Station entomologist Yong-Biao Liu, tested phosphine fumigation under high levels of oxygen against four insects and at different life stages: western flower thrips adults and larvae, leafminer pupae, grape mealybug eggs, and Indianmeal moth eggs and pupae.

Liu said it was important to test fumigation on a range of insect types and life stages for which quarantine treatments are needed.

“Oxygen enhanced the phosphine toxicity significantly for all life stages tested. This has not been reported previously, and the findings have potential to be used to develop more effective phosphine fumigation treatments for pest control.

"The magnitude of toxicity enhancement will likely vary depending on the insect species and their life stage," said Liu whose research station is based at Salinas, California.

The study showed that in 5-hour fumigations with 1,000 ppm (parts per million) phosphine at 5°C, control of western flower thrips on lettuce increased from 80-98% when oxygen was increased from 21 -40%. When the oxygen level was increased to 80%, mortality of western flower thrips reached 99%.

Western flower thrips are a common pest of fruits and vegetables in the U.S. 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.

He also found that  oxygenated phosphine fumigation was also effective in controlling leafminer pupae, grape mealy bug eggs, and Indianmeal moth eggs and pupae.

Phosphine has been used for more than 80 years as a fumigate to control pests in stored products. However, many insects especially at the egg and pupal stages are very tolerant to phosphine and it can take more than 10 days of treatment to control them.

The new treatment will help speed up this process and control insects more quickly.

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