Changes in biosynthesis and degradation of juvenile hormone during breeding by burying beetles: a reproductive or social role?

Burying beetles, Nicrophorus orbicollis, depend on the location of an unpredictable resource, a small vertebrate carcass, for reproduction. When they discover a carcass, they undergo a correlated rapid rise in titers of juvenile hormone (JH) in the hemolymph and ovarian development. This study investigates the regulation of the changes in JH during breeding in both male and female burying beetles and the role of JH in ovarian development. JH biosynthesis by the corpora allata (CA), measured in vitro, increased in females within an hour of their discovery of a carcass and increased later in males. After returning to low rates as oviposition began, JH biosynthesis rose again 3 days later in females but not in males. Neither the ovaries nor testes synthesized JH. There was a concomitant fall in JH esterase activity within 12 h of discovery of the carcass in both males and females. Although the rise in JH titers and biosynthesis and the fall in JH esterase is correlated with ovarian development, application of methoprene or JH III in the absence of a carcass did not result in vitellogenin uptake by the oocytes. Therefore, we conclude that, in spite of the rapid rise in JH before oviposition, it is not sufficient to regulate vitellogenin synthesis and/or its uptake by the ovaries. We suggest that its role has been preempted to organize social behavior and coordinate parental behavior between mates.