none Quantitative essential amino acid requirements of the larvae of parasitic hymenopterous, Pimpla turionellae L. reared on a chemically defined synthetic diet under aseptic conditions were investigated. Dietary levels of leucine, methionine, isoleucine and lysine were found to be critically important for P. turionellae. In the control diet, 50% increase of leucine or isoleucine, or 50% decrease of methionine showed noticable positive effects of adult yield. Furthermore, 50% increase of lysine level retarded development. Dietary levels of arginine, histidine, phenylalanine, tryptophan, threonine and valine were not critically important for the insect and their present amount in the control diet could be taken as optimal.