It is difficult to determine the diapause intensity and health status of diapausing insects while these are overwintering. However, this can be achieved by measuring certain biochemicals in insects’ bodies thereby providing useful information for population forecasting. By reviewing the literature on the biomolecules of diapause insects, we here summarize: 1) methods for correlated studies; 2) changing patterns of certain biochemicals including sugar, polyol, fat and protein; 3) the factors, including temperature, diapause intensity and their interactions, that influence the content of these biochemicals. During the overwintering period, glycogen, which serves as primary energy storage, can be transferred into a series of small antifreeze molecules, including trehalose, glucose/fructose, plycerol, sorbitol/mannitol, inositol, fatty acids and amino acids. These biomolecules can protect diapausing insects by stabling membrane structures and maintaining protein function. Glycogen showed the following four trends during diapause: 1) first decrease and then increase; 2) first increase and then decrease; 3) continuous increase and continuous decrease. The function of fat is similar to glycogen. Because temperature is necessary for internal biomolecule synthesis and transformation it is essential that insects that go through a relatively deep intensity diapause are able to detect external temperature fluctuations. These results provide a novel approach to predicting insect population trends.