SEASONAL DIFFERENCES IN METHYL FARNESOATE ESTERASE-ACTIVITY IN TISSUES OF THE SPIDER CRAB LIBINIA-EMARGINATA

Methyl farnesoate (MF), an unepoxidated form of insect JH III, is pres ent in Crustacea. MF is synthesized by the mandibular organs and is de graded to farnesoic acid (FA) by peripheral tissues. In this study we investigated MF degradation by esterases in hepatopancreas, ovary, tes tes and hemolymph of the spider crab Libinia emarginata collected at d ifferent times of the year to determine seasonal differences. The conv ersion of MF to FA varied among the tissues. In the summer, the hepato pancreas showed the greatest esterase activity (52.8% conversion in fe males and 59.16% in males), and it was twice as high (28.86%) in ovari es than in the testes (12.16%), but was low in the hemolymph of both s exes (10.84% in males, and 6.97% in females). In the fall, the convers ion of MF to FA was significantly reduced in all tissues (ovary 8.55%, testes 6.21%, hepatopancreas 10.22%, hemolymph 3.96%). Eyestalk ablat ion of animals in the fall restored MF esterase activity to summer lev els. When tissues from these animals were incubated with OTFP, a speci fic inhibitor of JH esterase, MF metabolism was significantly reduced. These results suggest that MF esterase activity depends on direct ind uction by MF, and its degradation is by a specific esterase(s).