EFFECT OF GAMMA-RADIATION ON PHENOLOXIDASE ACTIVITY IN MEDITERRANEAN FRUIT-FLY (DIPTERA, TEPHRITIDAE) LARVAE

The effect of gamma radiation on the phenoloxidase activity in larvae of the Mediterranean fruit fly Ceratitis capitata (Wiedemann), was exa mined. Phenoloxidase activity was determined by spectrophotometrically measuring the increase in optical density at 490 nn because of the co nversion of L-Dopa to Dopachrome, or by observing the degree of melani zation in larvae killed by freezing. Both methods produced comparable results. In unirradiated larvae, phenoloxidase activity can be detecte d on day 4 (late 2nd instar), and the activity continues to accumulate through day 7 (late 3rd instar). This accumulation was not observed w hen larvae were irradiated with a minimum dose of 40 Gy before the 3rd instar. However, irradiating larvae in which enzyme activity was alre ady high (days 5 and 6) did not remove activity but only reduced the r ate of further accumulation. These results indicate that measuring the activity of this enzyme in C. capitata larvae is a good, sensitive, a nd reliable indicator of irradiation treatment provided that the limit s mentioned above are observed.