THE FUNCTION OF CORPUS ALLATUM IN THE LAST LARVAL INSTAR 

 OF 3IETAB0LIC INSECTS 



Функция corpus allatum в последнем личиночном возрасте насекомых с полным 

 превращением 



V. J. А. NOVÄK and Е. ÖERVENKOVÄ 



(Biological Institute and Entomological Laboratory of Czechoslovak 

 Academy of Sciences, Praha, Czechoslovakia) 



It has been known since the time of the discovery of the juvenile hormon 

 (JH) or neotenin by Wiggle s wort h in 1935, that the function of corpus 

 allatum in the last larval instar is different from that in all preceding instars 

 this change being the immediate cause of metamorphosis. This was proved 

 experimentally for the first time by Wigglesworth (1935, 1936 etc.) in his 

 well known experiments on Rhodnius prolixus Stal. It was shown, that the 

 implantation of an active с allatum (from some of the younger instars or from 

 imago) into the last larval instar results in the development of supernumerary, 

 giant larvae and thus in preventing or postponing the metamorphosis. 

 Analogous circumstances were found by many other authors subsequently 

 in all insect orders where they had been looked for seriously. 



However, the opinions on the character and cause of the mentioned change 

 in the function of corpus allatum have been rather different so far. So, according 

 to Wigglesworth (1948, 1952, 1954 etc.) the с allatum stops completely 

 the JH production or even actively eliminates the small quantities of JH 

 persisting in the blood and tissues. As a reason for this supposition the negative 

 results of experiments with the simultaneous implantation of several с allata 

 from the nymphs of the late fifth (last) instar of Rhodnius into the same at the 

 beginning of the fifth instar are given. Similar opinions have been uttered 

 by most of the other authors. One of the few exceptions is Piepho (1951 etc.), 

 who admits the possibihty of production of a certain JH quantity in the last 

 larval instar which he supposes to be the reason of the development of pupa, 

 whereas the complete absence of JH in pupal period should result in the deve- 

 lopment of imago. 



As to the cause of the supposed cession of the JH production in the last 

 larval instar determining the beginning of the metamorphosis in the given 

 species or of the "counting of instars" as called by Wigglesworth (1948), 

 it was seen by Wigglesworth, B. Scharrer (1952, 1958 etc.) and many 

 other authors in nervous impulses from the brain. As the chief reason for this 

 supposition, beside of the conclusions based on morphology (c. f. e. g. the 



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