Abstract

Many, if not all, decapod crustaceans produce methyl farnesoate (MF), a compound structurally related to insect juvenile hormone. MF was studied in the crayfish Orconectes virilis by measuring its synthesis by the mandibular organ (MO) and its levels in the hemolymph. Incubation of MO from this species with [3H]methionine resulted in the production of radiolabeled MF. Over half of this product was released into the culture medium, suggesting that the MO is the in vivo source of MF found in the hemolymph. Hemolymph levels of MF were measured in male and female crayfish. This compound was elevated in vitellogenic females, suggesting that MF has a role in the regulation of vitellogenesis. MF levels were further studied in some crayfish by analyzing individual hemolymph samples obtained twice weekly over 4 weeks. Some crayfish had no detectable MF (<0.25 ng/mL) in any sample obtained during this period. Samples from other crayfish showed rapid variations in MF levels, some samples having substantial amounts of MF (1 to 6 ng/mL). Eyestalk ablation caused hemolymph levels of MF to increase from <0.5 ng/mL for intact animals to 2 and 14 ng/mL for unilaterally and bilaterally ablated animals, respectively. These data indicate that MF levels are negatively regulated by the eyestalk.

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