Abstract: Field test on the control of pine caterpillars (Dendrolimus tabulaeformis & D. spectabilis) with Diflubenzuron were conducted on Western Hill, Beijing and Hopei province in 1982—1984. The insecticides were applied 1. with LV and ULV spraying, the dosages used were 1, 1.5, 2.0, 3.0g. Per mu, and 2. with traditional spraying, the dosages used were 10,20, and 50ppm. More than 70% control was achieved with both methods. Even with 4th and 5th instar larvae, control of more than 70% can still be achieved at the dosage of 2g/mu. The larvae died slowly, but the amount of food taken was reduced. The body weight and the size of the larvae were also reduced. At the dosage of 2g/mu, the residual effect can last for more than 20 days.