Study On Host Selection Mechanism Of Xylosandrus Germanus (Blandford)

Xylosandrus germanus (Blandford) (Coleoptera:Scolytidae) is one of polyphagous ambrosia beetles, it can attack more than 120 families of coniferous and broad leaved tree. The host behavior and mechanism of Xylosandrus germanus adult female were studied in this dissertation.The results are as follows:(1) The preference of Xylosandrus germanus adult females for various plants was observed by selective and non-selective experiment in the laboratory. The adult females did not excavated entrance holes in Citrus reticulata, Hibiscus syriacus, Prunus cerasus and Prunus armeniaca. The adult females excavated entrance holes, but didn't colonized in Camellia sinensis, Prunus persica, Zizyphus jujuba and Prunus ceraseidos. While the females could colonize in Vitis vinifera, Malus Pumila, Pyrus sorotina, Carya Nutt, Castanea mollissima and Eriobotrya japonica. The females could produce offsprings in semi-artificial diets made of different plant powder, which were V. vinifera, P. persica, Pinus Linn, P. sorotina, C. reticulate and Z. jujube.(2) Antennae sensilla of Xylosandrus germanus adult were observed with scanning electron microscope (SEM). The results showed that the types of sensilla and their distribution patterns are similar in females and males. 5 distinct types of sense receptor were observed, including sensilla trichodea, sensilla chaeticum, sensilla basiconica and bud-shaped sensilla, of which sensilla triehodea was the dominant sensilla types that occupied 80%, while sensilla chaeticum were the least number, only 1 sensillum. Most of the sensilla were distributed on the club of the antenna that occupied 85%, the sensilla were mainly distributed on the two distal segment of the club that occupied 73%, while less sensilla on scape and funicle, only about 6% and 9%, respectively.(3) The olfactory responses of Xylosandrus germanus adult female to plant extract were tested with the Y-tube olfactometer and EAG. The results showed Xylosandrus germanus adult female was attracted by the extracts of V. vinifers, P. sorotia, P. cerascidos, P. persica, P. cerasus, Carya Nutt, P. armeniaca, E. japonica, and Pinus Linn. The females were not attacted by extracts of C. reticulata and H. syriacus. When plant extracts were measured by EAG, the response of P. ceraseidos extract was the maximum, followed by Pinus Linn, and then was V. vinifers and P. persica. When plant extracts were measured by Y-tube olfactometer, the response of V. vinifers extract was the largest, followed by P. ceraseidos, P. persica and Pinus Linn. Meanwhile, the results of the EAG experiments showed that the response of C. reticulata and H. syriacus was the minimum. The results of Y-tube olfactometer experiments showed that C. reticulata and H. syriacus had the repellent effect to Xylosandrus germanus adult female.(4) The EAG and olfactory of Xylosandrus germanus adult female to ethanol and a-pinene were increased with their concentrations. 100% ethanol and 100% a-pinene elicited the strongest EAG response among all the concentrations of ethanol and a-pinene, while 10% ethanol and a-pinene exhibited less EAG responses. 100% and 90% ethanol and a-pinene exhibited the strongest olfactory responses. The olfactory responses of 20% ethanol and a-pinene were the lowest. There was no olfactory response in olfactory test of 10% ethanol and a-pinene.The results showed that Xylosandrus germanus adult female could release aggregation by the Y-tube olfactometer test. The peak of aggregation pheromone releasing was one day after female colonization. The aggregation pheromone were mainly produced in the midgut and hindgut of the female. The indoor and outdoor experiments indicated that a-pinene, ethanol and aggregation pheromone regulated and controlled host selectivity, and ethanol and aggregation pheromone played the key role. When ethanol, a-pinene and aggregation extracts were mixed, the lure of 3 kinds of components were better than 2 kinds of components, which were better than 1 kind of component. Of 3 kinds of components, the lure of ethanol and aggregation pheromone extract were all better than that of a-pinene.