Role of the brain in photoperiodic regulation of juvenile hormone biosynthesis in the brown-winged green bug Plautia stali

We investigated the roles of the brain in photoperiodic regulation of juvenile hormone (JH) biosynthesis in Plautia stali (Heteroptera: Pentatomidae). Within 4 days after transferring the adults from short-day to long-day conditions, the biosynthesis of juvenile hormone III skipped bisepoxide became higher than that under short-day conditions. When the corpus cardiacum–corpus allatum complex (CC–CA) was coincubated with different regions of the brain, JH biosynthetic activities were inhibited by a middle part of the brain, i.e., the brain excluding the optic lobes, extirpated from short-day and long-day females. Backfills from the CC–CA revealed three groups of somata in the middle part of the brain: 15–18 pairs of somata were stained in the pars intercerebralis, 9–10 pairs were stained in the pars lateralis, and five pairs were stained on the nervi corporis cardiaci 2. These results suggest that inhibitory molecules of JH biosynthesis are produced in the middle part of the brain, regardless of photoperiod, but their release is suppressed under long-day conditions, leading to an increase in JH biosynthetic activities. Further, some neurons with somata in the pars intercerebralis, in the pars lateralis, or on the nervi corporis cardiaci 2 might be involved in photoperiodic regulation of JH biosynthesis.