Juvenile hormone degradation in adult wing morphs of the cricket, Gryllus rubens

Juvenile hormone-III metabolism was compared between adult wing morphs of the cricket Gryllus rubens to determine if variation in hormone degradation could be responsible for the dramatic fecundity differences between female morphs. As in other insects, hormone was degraded almost exclusively to juvenile hormone acid in dilute hemolymph in vitro, while significant quantities of juvenile hormone acid, diol and acid-diol as well as more polar metabolites were produced in vivo within 1 h after injection of racemic hormone. Activities of the degradative enzyme juvenile hormone esterase in hemolymph ranged from 4 to 14 nmol/min/ml serum during the first 10 days of adulthood in each morph of each sex. Activities were similar to values reported in other adult orthopterans and were substantially lower than those in last-stadium G. rubens. The 70 min in vivo half-life of racemic hormone injected into day 5-6 short-winged females was significantly higher than that of mid-last-stadium G. rubens and was similar to values reported in adult Diploptera panctata, Locusta migratoria and Manduca sexta. The amount of (10-R)- or racemic hormone degraded in vivo within 1 h after injection was strongly correlated with hemolymph juvenile hormone esterase activity in individual day 5-7 but not day 2-3 adults. This indicates that the hemolymph esterase contributes significantly to in vivo metabolism of exogenous hormone during some periods in adults. Midgut, fat body and ovaries exhibited significant activities of both juvenile hormone esterase and epoxide hydrolase, indicating that the hydrolase may contribute to tissue-specific and to whole cricket hormone metabolism. Importantly, no major differences were observed between adult wing morphs with respect to (1) percentage racemic or (10-R)-juvenile hormone-III degraded in vivo, (2) developmental profiles of hemolymph juvenile hormone esterase activity or (3) activities of juvenile hormone esterase or epoxide hydrolase in various non-hemolymph tissues. These data (1) provide no evidence that hormone metabolism differs significantly between adult morphs and (2) contrast with the importance of differential hormone degradation in morph induction during the juvenile stage.