§ 5.112 RESPIRATION IN DIAPAUSE 183 



the 18-somite stage in their development; but the effect is delayed 

 until the adult stage, when the diapause hormone, D, is secreted. 

 Other (univoltine) races of Botnbyx have only one generation per 

 year, and this always undergoes diapause, unless the source of D 

 in the suboesophageal glands is removed at the pupal stage 

 (Fukuda, 1953). 



Much experimental work in Japan has proved that the source of 

 the diapause hormone is in the suboesophageal ganglion of the 

 adult, and that the brain can inhibit its secretion if the circum- 

 oesophageal connectives remain intact. It is possible that the brain 

 may even stimulate secretion of D, after the moth has been 

 influenced by long day length to lay diapause eggs (Fukuda, 1953). 

 The following series of experiments are typical : 



(1) If the suboesophageal ganglia are removed from late larvae 

 after they have been exposed to long summer days (which normally 

 induce the laying of diapause eggs) all the resulting females lay 

 eggs which will not diapause, owing to the lack of D. 



(2) If the brain is removed at pupation from specimens that 

 have been exposed as embr3^os to short spring days (which should 

 result in their all laying non-diapause eggs) they turn into moths of 

 which only 14 per cent lay such eggs, while 36 per cent lay 

 diapause eggs, and the rest lay mixed batches. The increase in 

 diapause eggs is interpreted as being due to removal of the inhibit- 

 ing action of the brain, which leaves the suboesophageal ganglia 

 free to secrete D. It may also show the lack of sufficient stimulus to 

 cause all the females to lay only diapause eggs. 



(3) If isolated abdomens of specimens that should lay non- 

 diapause eggs are used as hosts, the type of eggs actually formed in 

 them can be influenced by transplants, as follows : 



(a) Brain or prothoracic gland transplanted alone has no effect. 



(b) Brain and suboesophageal ganglia, joined by their con- 

 nectives, have no effect if taken from a moth which has 

 been climatically determined to lay non-diapause eggs, 

 and in which the brain was therefore inhibiting the secre- 

 tion of D. 



(c) Suboesophageal ganglia transplanted alone, or severed from 

 the brain and therefore not inhibited by it, result in the laying 



