Hormonal rhythm and behavioural trends in insects
Circadian rhythmicity in the timing of secretion and release of many of the neurohormones appears to be a common phenomenon in insects. Involvement of hormonal components in the locomotor activity rhythm in cockroaches, crickets etc. has not yet been proved unequivocally eventhough some of the findings along these lines support this. Many of the physiological events in insects occur only once in each individual’s life-time-gated events. Release of eclosion hormone in insects is determined both by a circadian clock and by the developmental competence of the insect. Periodic release ofPTTH which influence the moulting process in larvae has been established to be gated. Induction of prodromal signs of pupation as a result of gated release of PTTH in some insects have been confirmed. Intrinsic neurosecretory cells of cc release a hormone (calling hormone) in a rhythmic fashion which affect the pheromone release and subsequent initiation of calling behaviour in some of the lepidopteran virgin females. Production of proctodone by the epithelial cells of hindgut also follows a rhythm bringing about diapause in some of the insects.