Modulation of female grasshoppers’ reproductive behaviour by nitric oxide and juvenile hormone

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The sexual behaviour of female Ch. biguttulus grasshoppers changes with age, oocyte cycle and mating experience (for a description see Wirmer et al. 2010). Immediately after their imaginal molt, females reject all male mating attempts (“primary rejection”). Within a few days, females enter the state of “active copulatory readiness”, a state of high receptivity recognized by singing in response to male stridulation, orientation and active walking towards the partner. After mating, females assume the state of “secondary rejection” which lasts for several days and may end with another period of “copulatory readiness”.

Previous studies on various grasshopper species implicated two signalling systems in the control of female reproductive states, nitric oxide/cGMP signalling in the brain and juvenile hormone (JH) released from the corpora allata. Ch. biguttulus females that are injected with the nitric oxide synthase inhibitor aminoguanidine respond longer and more frequently to male calling songs (Weinrich et al. 2008) while grasshopper females that lack JH remain in a rejective state and do not stridulate (Loher 1962).



We evaluate the effects of NO and juvenile hormone JH on reproduction related behaviors of female grasshoppers and particularly look for interactions in the brain and/or the corpora allata or for simultaneous regulation of both substances by upstream systems. We assess female responsiveness to male calling songs after diverse treatments that interfere with JH titers or NO production. Cellular sources and targets of NO as well as the distribution of neuroactive signals thought to control JH synthesis are investigated by immunocytochemistry. In contrast to previous beliefs that the corpora allata are regulated by the brain, we demonstrated the presence of neurons that project from the corpora allata to the protocerebrum, suggesting a more complex bi-directional information flow between brain and neurosecretory organs.