128 P. S. CHEN 
that only alanine, serine, leucine, isoleucine, proline and possibly lysine were needed 
for males, and alanine, lysine, leucine and probably isoleucine for females. It is interest- 
ing to notice that, according to this author, this insect is able to synthesize cystine 
and methionine from inorganic sulfate, and to carry out methylation of amino acids 
itself. In ruminants it was also found that cystine and methionine could be formed 
from Na,*°SO, (ref. 24). It is possible that the synthetic ability of these S-containing 
amino acids is due to the symbiotes in these animals. 
For the larval growth of the mosquito Aedes aegypti, GOLBERG AND DEMEILLON*! 
concluded that ten amino acids were important, but instead of valine they added 
glycine. Cystine is needed for the emergence of adult mosquitoes. SINGH AND BRowN?®8 
showed that female adults raised on synthetic diet could lay eggs. The non-essential 
amino acids can be formed by the mosquitoes, although their contents are compara- 
tively lower than in those raised under “natural” condition!®®. A chemically defined 
medium for A. aegypti has been designed by LEA, DimonD AND DELonG!*. 
In connection with the problem of essential amino acids an interesting piece of work 
was done by AUCLAIR AND Ma tats}, who found that the pea strains which were 
susceptible to aphid attacks contain three times more arginine, threonine and valine 
than the resistant strains. Apparently in the latter strains the growth of aphids is 
inhibited due to inadequate supply of essential amino acids (see AUCLAIR?). 
Studies on synthetic medium for insect growth has yielded some information about 
the specific morphogenetic roles of amino acids in addition to their function as protein 
constituents. For instance, LAFoN™’ observed that arginine was essential for pupation 
of Drosophila. According to VANDERZANT AND REISER!’® cystine and glycine were 
needed for normal pupation of the pink boll-worm. For the flour beetle Tvzboliwm 
confusum, LEMONDE AND BERNARD!” observed that the pupal life was doubled if 
lysine was lacking. In the absence of aminoacids such as valine, histidine, tryptophane 
or leucine, pupation did not take place and there was no metamorphosis. In the opinion 
of FrOBIScH’? still another unknown factor is necessary for imaginal differentation. 
The earlier work of WiLson on Dyosophila revealed that proline enhances differentia- 
tion!®®, tryptophan retards histolysis in the pupae!, whereas tyrosine, phenylalanine 
and methionine accelerate moulting!®, !®!. The tripeptide glutathione has most likely 
a stimulating effect on the larval growth of both Drosophila!8 and A edes!®8. A similar 
effect was found for a certain peptide in the yeast and pancreas extracts”! 8. This sub- 
stance 1s probably responsible for the growth-promoting effect of yeast extracts found 
in Phormia regina®®. There is no doubt that different species or even various strains 
of the same species have different nutritional requirements. The problem of insect 
nutrition has been reviewed by LIPKE AND FRAENKEL!8, 
Contents of soluble proteins 
Fluctuations of free amino acids must be related to protein synthesis during develop- 
ment. The patterns of soluble proteins in insect blood have been analyzed by various 
workers. In the larval blood of Drosophila melanogaster at least seven protein fractions, 
and in that of Culex pipiens at least four fractions could be detected*4. Judging from 
their mobility and isoelectric point, they seem to be more related to the serum globu- 
lins!%, 29. KREG" also reached the same conclusion from studies on the blood pro- 
teins in Melolontha sp., Neodiprion sertifer and Lymantria dispar. But CLARK AND 
References p. 132/135 
