Endocrine Activities and Photoperiodic Sensitivity during Prediapause Period in the Phytophagous Lady Beetle, Epilachna vigintioctopunctata.

Abstract

Epilachna vigintioctopunctata ceased to feed and entered diapause after 16 day's vigorous feeding in short-day photoperiods. Diapause could be prevented by the change from a short day to a long day before the 5th day of adult life. If the photoperiodic change occurred later, the beetle entered diapause even in a long day. Therefore, the prediapause period was divided into two stages. The secretory material in the neurosecretory cells of the pars intercerebralis changed in quantity corresponding to these stages. A small amount of the material represented the stage sensitive to a photoperiodic change, the scattering of small agregates of the material the stage insensitive to a photoperiodic change, and a large amount of the material the early stage of diapause. Throughout these stages, the corpora allata were small in size as compared with those of long-day beetles. These correlations were also found in adults reared on sliced potato which did not enter diapause in spite of their ovarian degeneration in short days. The response of prediapause beetles to a juvenile hormone analogue (ZR-515[○!R]) showed that the latter triggered the ovarian development but failed to induce yolk deposition. Another factor, possibly the neurosecretory material from the brain, was nesessary for the full ovarin development.