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Juvenile hormone (JH) Ill esterase and JH I l l epoxide hydrolase activity was found in the integument, midgut, fat body, and brain during last instar development of the tobacco hornworm, Manduca sexta. JH esterase activity was primarily located in the cytosol in these tissues while the majority of the JH epoxide hydrolase activity was found in the microsomes. A prewandering (on day 3) and postwandering (on day 8) peak in plasma JH Ill esterase activity occurs in the last instar of gate I M. sexta. The JH esterase activity profile in integument, midgut, fat body, and brain followed a similar pattern to that of the plasma. The only exception to this was the absence of the postwandering, prepupal (on day 8) JH esterase peak in the fat body. The topical application of the juvenoid, (RS)-methoprene, failed to induce fat body JH esterase activity but increased activity in the plasma, integument, midgut, and brain in M. sexta prepupae. These results indicate that the source of plasma JH esterase activity is not always the fat body as previously hypothesized. The developmental profile of tissue JH epoxide hydrolase activity was also similar to that of J H esterase suggesting that both enzymes may be regulated partly by the same factors and that JH epoxide hydrolase may also have an important, previously unrecognized functional role in JH regulation and insect metamorphosis. Multiple isoelectric forms of tissue-specific JH esterases and JH epoxide hydrolases were found in integument, midgut, fat body, and brain. The JH esterases in these tissues had isoelectric points more acidic than that for plasma. Tissue a-naphthyl acetate esterase, developmental profiles, and inhibitor sensitivity to 3-(octylthio)-l , I ,l-trifluoropropan-2-one differed sig-

Juvenile hormones (IH)-l and -111 were metabolized in egg homogenates by two primary routes, ester hydrolysis and epoxide hydration, during embryogenesis of the tobacco hornworm, Manduca sexta (L.). The duration of embryogenesis was 3.5 days at 27OC. Preovipositional and newly oviposited eggs had the highest rate of JH metabolism, which was reduced by day 1 and remained unchanged thereafter. The decline in JH metabolism was the result of a decrease by one-half in the JH esterase activity. JH epoxide hydrolase activity remained unchanged throughout embryogenesis. Ester hydrolysis averaged 1.9 times faster for JH-l than JH-Ill and epoxide hydration 6.6 times faster for JH-Ill than JH-I. There was a sixfold increase in the a-naphthyl acetate (a-NA) esterase activity during the time in embryogenesis when the JH esterase activity was declining or at low levels. Developmental, inhibitor, substrate specificity, gel filtration, and isoelectric focusing studies indicated that the egg JH esterase has some specificity for JH, compared with a-NA, and in part is similar to the hemolymph JH esterase of the adult female. The possible functional role of JH metabolism during embryogenesis is discussed.

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