Less Irradiation Would Still Stop Fruit Pests

By Jim De Quattro
April 15, 1997

Irradiation could become more practical as a quarantine treatment to prevent fruit flies from spreading via shipments of grapefruit and other produce, according to studies at the Agricultural Research Service.

Irradiation--exposure to safe, very low levels of gamma ray energy--interrupts the insects’ development. They can’t reach adulthood and produce offspring.

ARS scientists say it may be possible to reduce the irradiation amounts by half or more. If further studies confirm this, irradiation could be done more quickly and on fruits that can be damaged by the gamma ray doses now used. Lowering the dose would make irradiation more feasible as an alternative to fumigation by methyl bromide, a chemical scheduled to be phased out by 2001.

Irradiation takes only a few minutes and leaves no residue. The fruit or other produce can be shipped immediately. And with a faster, cheaper treatment, the fruit could arrive sooner at the supermarket--with more of its harvest quality intact.

For two years, Hawaiian papayas and other tropical fruits have been approved for shipping to the Chicago area. Exposure to 250 Grays (Gy) of gamma rays ensures that no oriental or Mediterranean fruit flies that may be hidden inside the fruit will survive to adulthood. But the irradiation amount needed to obtain this exposure level could damage orange, mango, grape, avocado and other fruits in a commercial shipment.

The ARS scientists found, however, that irradiation at only 16 Gy stopped development of Mexican fruit flies in lab dishes. The studies used 100,000 Mexican fruit fly eggs, larvae and pupae. More recently, tests with a few thousand grapefruit indicate 50 Gy may be adequate to halt Mexican fruit flies hiding inside the fruit.