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IV. INSECTS 
FREE AMINO ACIDS IN INSECTS 
P. S. CHEN 
Institute of Zoology and Comparative Anatomy, University of Zurich, Zurich (Switzerland) 
There is a large volume of information on the free amino acids in insects. Especially 
during the last decade, numerous studies have been carried out to analyze the patterns 
of free amino acids in different insects, and the changes of these patterns during 
morphogenetic development. Progress in this particular field of insect biochemistry 
has been facilitated by two important facts. First, insect blood is known to have an 
unusually high amino acid concentration which in some species may be more than 
60 times higher than that in human blood. Second, since the advent of such new 
techniques as microbiological assays and paper partition chromatography, it has 
become possible to follow quantitative changes in those components which are present 
even in extremely low concentrations. 
Recent work in various laboratories has demonstrated clearly that the amino 
acids, in addition to their function as protein constituents, enter into diverse metabolic 
pathways and participate in many activities of living organisms. There is also evidence 
which shows that certain amino acids play a specific role in reproduction and develop- 
ment. However, owing to the large variations found for different insects, evaluation 
of the observed results becomes difficult. The present paper is a review of some of 
the latest studies with an attempt to summarize the available data in an integrated 
manner, especially in relation to taxonomic, embryological, genetical and physiological 
problems. 
OCCURRENCE OF FREE AMINO ACIDS IN DIFFERENT INSECTS 
Patterns of free amino acids and related compounds in 20 insect species are summarized 
in Table I. Most data were obtained from analysis of hemolymph at either larval or 
imaginal stage. In those cases where the amount of hemolymph 1s limited, extracts of 
whole bodies were prepared. It is evident that no direct quantitative comparison 
between various studies can be made, as long as no reliable information concerning 
age and nutritional state of the specimens used is available. This may account for some 
of the contradictory findings of authors who have worked on the same species. In the 
following, a survey of the variations in the free amino acid composition of insects 
belonging to seven different orders (Lepidoptera, Diptera, Coleoptera, Orthoptera, 
Odonata, Hymenoptera and Hemiptera) will be considered. 
Lepidoptera 
Extensive data on Lepidoptera have been reported. By using paper partition chroma- 
tography, CHEN AND KtHN*! demonstrated that 24 freeninhydrin-reav'ting components, 
including y-aminobutyric acid and three peptides, are present in the meal moth 
References p. 132/135 
