ECDYSONE 20-HYDROXYLATION AND 3-EPIMERIZATION IN LARVAE OF THE GYPSY-MOTH, LYMANTRIA-DISPAR L - TISSUE DISTRIBUTION AND DEVELOPMENTAL-CHANGES

The potential for ecdysone metabolism was determined for various larva l tissues of the gypsy moth, Lymantria dispar. Homogenates of fat body , midguts, and Malpighian tubules, taken on different days during the second half of the fifth instar, were incubated with [H-3]ecdysone, an d the products were analyzed by reversed-phase and normal-phase HPLC, All tissues showed conversion to 20-hydroxyecdysone, and midguts also produced 3-epiecdysone. Ecdysone 20-monooxygenase (E20MO) activity in the fat body increased from a low level on day 5 to a peak on day 11, coinciding with the peak in the hemolymph ecdysteroid titer on the pen ultimate day of the instar, Midguts and Malpighian tubules showed E20M O activity only during the last 3 or 4 days of the instar, with the hi ghest activity also occurring on the penultimate day, For the midguts, the appearance of the E20MO coincided with the transition from larval to pupal tissue, No activity was detected in larval midguts, 3-Epiecd ysone formation, however, was mainly found in larval midguts, with onl y marginal activity detectable in pupal midguts. (C) 1997 Elsevier Sci ence Ltd.