Guy J. Hallman


An ionizing irradiation quarantine treatment of 165 Gy was approved by the California Department of Agriculture against sweetpotato weevil, Cylas formicarius elegantulus (Summers), infesting sweetpotatoes from Florida. The first commercial shipment was made in May, 2000. At ≥400 Gy, `Picadito' white-fleshed sweetpotatoes sometimes showed noticeable discoloration of cooked flesh. Therefore, there is not a large margin between the minimum absorbed dose required for quarantine security (165 Gy) and the minimum dose which might cause objectionable loss to commodity quality (about 400 Gy); it can be expected that the absorbed dose range absorbed by sweetpotatoes irradiated on a full pallet when the minimum target dose is 165 Gy will be 165-500 Gy. To be safe, sweetpotatoes should be irradiated in smaller units than pallet loads, which could result in higher processing costs compared with irradiation on standard pallets. This is the first instance of an irradiation quarantine treatment being approved and used against a non-fruit fly where live adults can be found by inspectors and indicates a significant advance in the transfer of this promising quarantine treatment technology. Sweetpotato weevil adults irradiated with a target absorbed dose of 150 Gy (maximum absorbed dose was 165 Gy) lived for 32 days, while at 32 days unirradiated weevils had suffered 57% mortality.

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