Abstract:The Cimbicid sawfly Cimbex japonica Kirby is a newly occurred pest in China. In recent years it has caused serious damage to Ulmus pumila in the central part of Shanxi Province. The generation is annual with adults on the wing in early May. No adult male occurred. Each female can lay about 50 eggs. The eggs are laid singly on the edge of the leaf under the upper surface. The feeding peak of the larvae is from mid-May to mid-June. When its larva is full-grown, it goes into the litter or into the furrows in the soft soil 2～3cm in depth, makes a elliptic dark brown cocoon and there spends the winter, changing to a prepupa. Pupation takes place in mid-April. The pest was 90% or over controlled by Cyhalothrin(Karare) at 3000×dilution during the peak of the larval eclosion in mid-May. In mid-April, before the emergence of the adults, digging out the cocoons from the soil under tree crowns and then burning them was also very effective against the pest.