Juvenile hormone metabolism during embryogenesis in the tobacco hornworm, Manduca sexta (L.)

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Abstract
Juvenile hormones (JH)‐I and ‐III 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 27°C. 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‐I than JH‐III and epoxide hydration 6.6 times faster for JH‐III than JH‐I. There was a sixfold increase in the α‐naphthyl acetate (α‐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 α‐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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