Abstract:The dye Sudan Ⅱ 670 was used to spray on the pine needles for feeding the 4-instar larvae of Dendrolimus punctatus and D. tabulaeformis in the marking test. After the feeding, the fat bodies of the larvae appeared to be of blue colour obviously. Not only the marking blue remained in the fat bodies from larvae to pupae and adults of the present generation,but also they remained in the eggs and newly emerged larvae of the following generation. It can be distinguished by naked eyes. The marking agent does not affect reproduction and lifespan of the pine moth. It appears that this method can be used in the study of insect population dynamics caused by dispersal and migration.