In recent ecological studies on the European pine shoot moth, (Rhyacionia buoliana (Schiff.)), where a major objective was to evaluate the influence of different hosts on oviposition preference, larval mortality, insect size, rate of development, and sex ratio, the inadequacy of conventional growth measurements was much too apparent. There was a need to document relatively small differences in larval size and rate of growth on several hosts or from one stand to another. Measurements which showed growth but not weight or volume losses have limited value where the insect under study has a long non-feeding period. Such measurements as body length, and especially head capsule width, obviously belonged in this category. On the other hand, it was felt that dry weight measurements would show both gain and loss. Further, a volume estimate (or body index) would be even more useful, if one could be devised which bore a linear relationship to dry weight. Such an index, while it might involve more than one measurement, nevertheless could be made without destroying the larvae.