Study On Resistance Of Different Tree Species (Variety) To Holcocerus Hippophaecolus (Lepidoptera: Cossidae)

Holcocerus hippophaecolus Hua, Chou, Fang et Chen (Cossidae, Lepidoptera) is the insect pest appeared in "Three Norths Areas" of China in recent ten years. It damaged the seabuckthorn forest to death about 160 thousand hm2. The disaster become the main restricting factor. In recent years, studies and reports of H. hippophaecolus focused on biology and zoology, species and suppression function of natural enemies, development and utilization of sexual pheromone, countermeasures both at forest management and chemical control etc. Howerver, the study on insect-resistant mechanism of seabuckthorn has not been mentioned before, which plays important role to explore the causes of population eruptive, therefore provides scientific evidence for regional control of H. hippophaecolus.The study was carried out by adopting the methods both bioassay in wild and observation in laboratory. We probe resistance levels of different tree species to H. hippophaecolus and analyse relationships among morphological structure, organizational structure and resistance mechanism by using method of tissue anatomy. The major findings are as follows:(1)Combine artificial infection in cage and natural infection in wild, aiming for the baring-egg frequency and ovipositing rate of H. hippophaecolus at different tree species, then giving corresponding weight based on the correlation coefficient among them, so as to construct a new Integrated Damage Index as indicators for setting resistance levels. There were four levels: i Immune tree species (Hippophae salicifolia, Hippophae rhamnoides subsp. yunnanensis Rousi, Ulmus pumila, Prunus persica, Malus pumila and Prunus armeniaca); ii High resistance tree species (Elaeagnus angustifolia, XiuyisikeXzhongguoshaji, Lengguo, Xiaguang, Leiguo and Taiyang); iiiLow resistance tree species(Ayaganka, Wulangemu, Wulangemu X Zhongguoshaji, Yousheng, Chuyi and Pyrus sorotina); ivSusceptible tree species (Hunjin, Hippophae rhamnoides L. subsp. sinensis Rousi and Chengse).(2)Seabuckthorn varieties with different resistance levels, some of whose trunks were covered by green cloth while others were not, were planted under a controlled natural condition. Then the experiment taking the landing rate of H. hippophaecolus on different hosts as index, was carried out to observe the host selection behavior of H. hippophaecolus which was used by different treatments. The results showed that size of landing rate are completely consistent with the divided resistance levels. Besides, it can be proved that olfactory plays a decisive role in the host selection process of H. hippophaecolus, which reflects that host selection mechanism of H. hippophaecolus is greatly linked to its hosts. Additionally, it is showed that the difference of host volatiles affecting the selection behavior of H. hippophaecolus is the key factor.(3) The experiment on removing antennae indicates that antennae is an important part of the sensory system of H. hippophaecolus, and there are various types of sensilla implicating olfaction and gestation that are very important in host location and identification distributed on the terminal of antenna. Remove the antennae completely, H. hippophaecolus can not accept the stimulation of host volatiles because of missing olfactory function, which lead to the indeterminacy of its host selection. Further more, it suggests that the olfaction plays an important role in host selection.(4) The study on relationship between bark morphology and insect resistance of seabuckthorn indicates that the damaging behavior of H. hippophaecolus has nothing to do with hosts'bark color, stomata size, roughness, but is associated with their compaction degree and crack size.(5)The relationship between the damage degree of H. hippophaecolus and the difference of tissue characteristics of tree trunk and one-year-old branches was investigated. The multiple regression analysis shows that vessel density, wood ray width, lignification cell radius and Cortex sclerotic cell thickness of the tree trunks and annual branches of different seabuckthorn species (varieties) are not closely correlated with the resistance of H. hippophaecolus...