In vivo and in vitro degradation of juvenile hormone-III in presumptive long-winged and short-winged Gryllus rubens

Abstract

Degradation of exogenous juvenile hormone-III was compared between long-winged and short-winged morphs of the cricket Gryllus rubens during the last stadium. This was done to determine if morph-specific differences in haemolymph juvenile hormone esterase activity, which are thought to be important in morph determination, result in corresponding differences in in vivo hormone degradation. Percentage degradation of racemic or (10-R)-juvenile hormone-III was significantly higher in plasma from the long-winged vs the short-winged morph during the mid-stadium while no differences between the morphs were observed early in the stadium. These results paralleled morph-specific differences in plasma juvenile hormone esterase activity. Similar patterns were obtained in vivo, except for early-stadium, short-winged crickets where hormone degradation was much higher than expected based on haemolymph juvenile hormone esterase activity. When esterase activity in long-winged individuals was inhibited in vivo by a trifluoropropanone derivative, there was a corresponding decrease in in vivo hormone degradation. No morph-specific differences were observed in degree of hormone binding by haemolymph components during either the early or mid-stadium, indicating that variation in hormone binders cannot account for differences between morphs in degree of hormone degradation. Importantly, differences between morphs in hormone degradation were much less than differences in haemolymph juvenile hormone esterase activity. These results collectively document morph-specific covariation in haemolymph juvenile hormone esterase activity and in vivo hormone degradation. However, because differences between morphs in hormone degradation are not large, their functional significance with respect to morph determination remains uncertain.