Abstract
The uric acid concentration in the fat body and haemolymph of the lepidopteran, Manduca sexta (L.) (tobacco hornworm) was determined for each day between pupation and adult eclosion. Uric acid levels in the fat body remained at about 0.5 μmol/mg dry wt until 16 days after pupation (day 16), then decreased rapidly to <0.1 μmol/mg by adult emergence on day 19. The concentration in the haemolymph increased significantly on day 11, peaked at 2.5 μmol/ml on day 15, and decreased rapidly thereafter. The concentration of ecdysteroid in the haemolymph, measured by RIA, increased starting at day 2 and peaked at 7 μg/ml on day 6. This was followed by a gradual decline to low concentrations at adult emergence. HPLC was used to determine changes in the amounts of ecdysone and 20-hydroxyecdysone in the haemolymph. Pupae injected with 20-hydroxyecdysone beginning on day 13, 14 or 15 showed a 3–10-fold increase in uric acid concentration in the fat body on day 19 as compared to controls. However, exogenous 20-hydroxyecdysone administered after day 16 had no effect on the temporal release of uric acid from the fat body. Electron microscopy was used to examine fat body cells for the presence of uric acid-containing granules during the pupal-adult transformation.
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