Humoral and nervous pathways in photoperiodic induction of diapause in Leptinotarsa decemlineata

Abstract

By means of microsurgical operations combined with photoperiodic treatment the rôle of the different elements of the neuro-endocrine system in the effects produced by long- and short-day induction is investigated. The effect of short day is explained by the inactivity of the medial protocerebral neurosecretory cells, resulting in a lack of activation of the corpora allata. Apparently, these glands need constant activation by the brain hormone. The innervation of the corpus allatum appears to play a rôle at the onset of diapause induction rather than in maintaining diapause. We have found no evidence in favour of an inhibitory ‘diapause hormone’, produced by either the brain or the suboesophageal ganglion. The effect of long day is explained by activation of the medial neurosecretory cells. The brain hormone can activate the corpora allata by way of the haemolymph with the same speed as via the corpora cardiaca. Implanted corpora allata without any nervous connexions can be activated and inactivated repeatedly by manipulating the photoperiod. In producing the behavioural components of photoperiodic response, the corpus allatum does not act by way of the ovaries.