1260 P. S. CHEN 
ZOLLINGER®!; CHEN*), The values per unit body weight show, however, a maximum 
at 72h of age (BENz?*). As to total concentration in the larval hemolymph, there is 
a rapid decrease as development proceeds (HADORN AND STUMM-ZOLLINGER®!; 
CHEN AND Haporn?®). For individual amino acids, glutamic acid, alanine, glycine, 
serine, leucine/isoleucine and valine/methionine decrease steadily, whereas glutamine, 
threonine, arginine, lysine, cystine, histidine, f-alanine and asparagine exhibit a 
maximum at 72 h. Tyrosine and proline increase continuously, especially as the time 
of pupation approaches (CHEN*®.) In the pupal stage the total contents of free ninhy- 
drin-reacting components are rather low and fall off slightly. Quantitative changes 
of individual amino acids during pupal development have been given by BENz}’. 
In contrast to Drosophila, inthe mosquito larvae (Culex pipiens) both total quantities 
of ninhydrin-positive substances per unit body weight and total blood concentration 
remain largely unchanged throughout development*’. Among all substances identified, 
tyrosine and proline show a distinct increase, whether the values are expressed per 
individual or per wg N. The total quantity and total concentration of free amino acids 
are lower in pupal stage and show a continuous decrease. For Calliphora augur (HACK- 
MAN®®) as well as C. quinquefasciatus and A. aegypti (MICKS AND ELLIs!*9) it was also 
found that the pupae contain comparatively less free amino acids than the larvae. 
MIcks AND EL Lis!’ reported that in the mosquito species studied by them, the amino 
acid concentration was relatively constant during pupal development. In C. pipiens 
it was further noticed that several amino acids (tyrosine, glutamic acid, glutamine, 
valine) exhibit a slight increase at the early pupal life®®. A similar situation was re- 
corded for Calliphora erythrocephala (AGRELL!) and Ephestia kiihniella (CHEN AND 
Ktun*!). Such fluctuations reflect most likely the histolytic process at this particular 
developmental period. 
For Bombyx mori, DENUCE AND ZUBER*’, by paper electrophoresis, observed that 
during the fifth instar glycine, alanine and serine decrease gradually, histidine in- 
creases rapidly, whereas arginine and lysine remain constant. Since no peptide was 
detected in the hemolymph, the two authors concluded that protein synthesis in this 
insect takes place in the silk gland. DRILHON AND BuSNEL*® noted that 1o days after 
cocoon formation there was again a steady increase of free amino acids. FUKUDA ef al. 
reported that at the end of fifth instar glycine, threonine, proline, serine and tyrosine 
in the hemolymph were used by the silk glands for protein synthesis. Glycine, alanine 
and serine are known to be the main amino acids of silk fibroin. Tracer studies showed 
that these three amino acids could be synthesized from pyruvate, although this com- 
pound has not been found in the body fluid nor in the silk glands’: ®°. 
Another morphogenetic process which should be considered is moulting. In a recent 
paper ZIELINSKA AND LAsKowsKaA!” identified in the moulting fluid of the fourth 
instar and prepupae of Bombyx mori alanine, arginine, aspartic acid, asparagine, 
cystine, phenylalanine, glycine, glutamic acid, histidine, leucine, lysine, methionine, 
proline, serine, threonine, tyrosine, valine, as well as N-acetylglucosamine and glucos- 
amine. PASSONEAU AND WILLIAMs!48 reported that the early moulting fluid of the 
giant silkworm Platysamia cecropia contains more proteins and less non-protein N, 
and the reverse is true for the late moulting fluid. N-Acetylglucosamine was also 
identified. The high proteolytic and chitinolytic activity of such fluid indicates the 
enzymatic digestion of endocuticle during the process of moulting!®. 
References p. 132/135 
