In vitro effect of the juvenile hormone 



Experiments with tissue homogenates of active and diapausing beetles 

 showed the same differences in oxygen consumption as are observed with 

 intact insects. 



Addition of the 4 active cc. allata per "beetle equivalent" to these homo- 

 genates to our surprise resulted in a remarkable stimulation of cellular meta- 

 bohsm (Tab. 2). An increase of 12— 140% луаз observed in four series of experi- 

 ments (de Wilde & Stegwee, 1958). 



We can now add to these observations the results of our experiments with 

 extracts of abdomens of male adult H. cecropia. These extracts, made by 

 means of the ether-methanol technique described by Williams (1956) have, 

 according to various authors, in many respects the properties of the juvenile 

 hormone. 



Injection of 2 mm^ of the crude extract into allatectomized female beetles 

 resulted in an increase in Oa-uptake varying from 15 — 875% lasting for 3—11 



days. 



Also the effect of this substance on succinate oxydation by tissue ho- 

 mogenates (Tab. 3) bears resemblance to that of the corpora aUata. It is 

 tempting to think that this in vitro test for juvenile hormone activity could 

 be of great use in any attempt at concentration and purification of this subs- 

 tance. 



Summary 



Diapause in the Colorado beetle is primarily a short-day effect. By rearing 

 the beetles under different photoperiods, a predictable percentage of diapause 

 may be obtained in each generation. 



Beetles in diapause show several phenomena characteristic of deficiency 

 of the corpora allata (Pseudo-allatectomy). This was tested in experiments 

 with exstirpation and reimplantation of the corpora allata in both sexes. 

 These experiments show that the behaviour changes, the arrest of oogenesis 

 and the low rate of respiration characteristic of diapause are all under the direct 

 control of the corpora allata. 



This humoral effect is on a subcellular level. Succinate oxydation by homo- 

 genates of diapausing beetles is significantly stimulated by addition of 2 — 4 

 active corpora allata per beetle equivalent. Small doses of a juvenile hormone 

 concentrate prepared from the abdomens of male cecropia silkworms have the 

 same effect, in vitro as well as in vivo. This may be a valuable test for assaying 

 the juvenile hormone. 



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