Change of Photoperiodic Sensitivity with Fat Body Development during Prediapause Period in the Twenty-Eight-Spotted Lady Beetle, Henosepilachna vigintioctopunctata FABRICIUS (Coleoptera : Coccinellidae)

Abstract

When adult beetles were reared normally on host plant foliage under a short day, they lost sensitivity to a long photoperiod after the 6th day of adult life, ceased feeding and entered diapause on about the 17th day. Fat bodies, including those surrounding the brain, developed markedly to fully occupy the body cavity during this period. If the amount of feeding was limited to 35-40% of normal, the fat body development was delayed and photoperiodic sensitivity to a long day was maintained until the 12th day of adult life. Furthermore, limited feeding after photoperiodic sensitivity was lost, causing an elongation of the prediapause period. In adults which responded to the photoperiodic change to a long day, paraldehyde fuchsin positive materials in the neurosecretory cells in the pars intercerebralis decreased and the diameter of the corpus allatum increased, showing a high activity of the brain-corpus allatum endocrine system. While in the adult showing no response, the neurosecretory cells and corpus allatum showed appearances of decreased activity. It was concluded from these results that the neurosecretory cells in the pars intercerebralis lose their sensitivity to the long photoperiod in the course of the fat body development in adults exposed to a short day, and they enter diapause when the neurosecretory cells become more inactive.