Neural mechanisms conroling adult diapause in insects

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The present study was performed with an aim to investigate neural mechanisms underlying reproductive diapause in the blow fly, Protophormia terraenovae. In vitro synthetic activities of juvenile hormones (JH) were examined using a radiochemical assay in diapause females and reproductive females. JH synthetic activities increased in females reared under diapause-averting conditions and remained low in previtellogenic females reared under diapause-inducing conditions. A decrease in the JH production rate is a cause of diapause induction. JH synthetic rate after removal of the pars intercerebralis (PI) and pars lateralis (PL) neurons suggested that these neurons do not directly mediate changes in the JH production rate, but regulate ovarian development cooperatively with some unknown allatostatic and allatotropic factors. Morphological and electrical properties of PI and PL neurons were examined by intracellular recording and staining. Three types of PI and two types of PL neurons were identified. Among these neurons, one PI neuron showed significant differences in spike durations and one PL neuron in spike heights between diapause-inducing and diapause-averting conditions. FMRFamide, β-pigment-dispersing hormone, corazonin and cholecystokinin-like peptides were immunocytochemically revealed in the PI or PL neurons. FMRFamide and cerebral lobes weakly suppressed JH biosynthetic rates in vitro. The present study morphologically and electrophysiologically characterized PI and PL neurons, and showed candidates for factors controlling JH synthetic rates in neural mechanisms for reproductive diapause in P.terraenovae.