Hormonal stimulation of the brain for its control of oögenesis in Phormia regina (Meigen)

Abstract

Neck ligation experiments revealed that a head factor(s) is required for the regulation of oögenesis in liver-fed Phormia regina. After neck ligations were performed hourly from 7 to 12 h after the onset of liver feeding, the percentage of flies containing vitellogenic ovaries increased steadily from 0 to 70% when ovaries were examined at 48 h after the onset of liver feeding. Thus, this 5 h period delineated the gate interval for cephalic involvement. Transection of either the cervical ventral nerve cord or the cardiac-recurrent nerve, of already liver-fed flies, did not affect oögenesis. Transection of either of the same two nerves, prior to liver feeding, also did not affect oögenesis. This lack of neural involvement, before and after a liver meal, indicates that a hormonal factor(s) is most likely involved in the initiation and execution of the cephalic regulation of oögenesis in P. regina. Transection of cervical tracheal trunks greatly suppressed oögenesis indicating that an adequate air supply to the head (i.e. the brain) is essential for the normal production/secretion of the cephalic factor(s). In liver-fed flies, neck-ligation suppressed oögenesis could not be reversed by a topical application of methoprene (a juvenile hormone analogue). This suggests that neck-ligation may alter factors, other than juvenile hormone, that are also important for normal oögenesis. Indeed, the same ligation was found to lower the haemolymph ecdysteroid and vitellogenin titres. Proper titres of both are known to be essential to oögenesis. The lack of neural regulation in oögenesis is incorporated into our previously developed working model and is included in the discussion to provide an overview of the factors regulating oögenesis in P. regina.