Radiation-Induced Changes in Melanization and Phenoloxidase in Caribbean Fruit Fly Larvae (Diptera: Tephritidae) as the Basis for a Simple Test of Irradiation

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Abstract
First instars of the Caribbean fruit fly, Anastrepha suspensa (Loew), were irradiated with 0, 5, 10, 20, 50, 75, 100, and 150 Gy doses from a Cs-137 source, and observed for whole body melanization as late third instars. Control larvae rapidly melanized, whereas larvae irradiated at ≥20 Gy failed to show typical melanization after freezing and thawing. Assays of phenoloxidase in control and irradiated larvae showed greatly decreased enzyme activity at ≥20 Gy and substantial reduction at lower doses. Larvae were also irradiated on the 1st d of each instar, and phenoloxidase activity was determined when they became late third instars. Larvae irradiated on the 1st d of the first instar and on 1st d of the second instar had ≈90% or greater reduction in phenoloxidase activity as late third instars. Larvae irradiated on the 1st d of the third instar had ≈50% reduction in phenoloxidase activity at the time they became late third instars leaving the food to pupate. A simple spot test for phenoloxidase was developed that produced a red color with a crushed control larva and no color with a larva irradiated at ≥25 Gy. The radiation induced changes in melanization and phenoloxidase activity, and a simple spot test may serve as tests for irradiation treatment of Caribbean fruit fly larvae.

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