Studies On Cold-hardness And Cold-Tolerant Mechanism Of Dendrolimus Spectablis

Dendrolimus spectabilis Butler is an important leaf-eating pest of coniferous trees in north of china. In order to master its over-wintering larva's cold-hardness mechanism, the paper studies the contents of cold-tolerant substances.The major achievements in this experiment were as follows:1. Instars identification of over-wintering larva:The width of head capsules those larva moult in different instars and generations are measured , the results show that over-wintering larva are mainly fifth instar,and there are 21.2% fourth and 42.6% fifth as well as 18.6% sixth instar.2. The time of larva leaving and ascending tree:In the course of the larva leaving and ascending tree ,we observed that the larvas almost leave tree in the middle ten day period of November and ascend tree in the middle and last ten day period of March.3. The place of over-wintering larva:The place of over-wintering larva is investigated. We find that after the larvas leave tree ,they tend to select 2m below of the trunk that is exposed to the sun and out of the wind. They also survive in the grass, under the stone within 30cm from the stump of the tree.4. Over-wintering larva super-cooling points:The super-cooling points(SCP) are studied .It reduced when the temperature reduced in from October to January and February, which means that the larva' cold-tolerant capacity become strengthened. The SCP changed as follows:October,-8.67 ± 2.32