| Chinese white pine bark beetle (Dendroctonus armandi Tsai and Li) is arguable the most destructive insect of Chinese white pine in Qingling Mountains (Pinus armandi Fr. (Pinaceae)), which primarily attacks healthy Chinese white pine trees aged 30 years or more and often reaches epidemic proportions and causes widespread mortality of trees in both natural and managed forest ecosystems. The volatiles of P. armandi play important roles in the behavior of D. armandi, such as host selection, attack, oviposition and reproduction. Antenna is the major organ of the insects to detect host volatiles and electroantennogram (EAG) techniques have been widely used in chemical ecology to identify olfactory active compounds and characterise antennal receptor neurons, therefore, to better understand the mechanism of the dispersal and aggressive behavior of D. armandi, a detailed research on the EAG response of D. armandi to the volatiles of P. armandi is required.In this research, female and male D. armandi was tested to the 11 major monoterpenes from the P. armandi, and the volatile oil from needles and phloem of P. armandi, by the technique of EAG. The results are as follows:(1) All the monoterpene tested includingα-phellandrene, (S)-(?)-β-pinene, (R)-(+)-α-pinene, (S)-(?)-α-pinene, (?)-camphene, 3-carene,β-myrcene, (S)-(?)-limonene, (+)-camphene, (R)-(+)-limonene and bornyl acetate, could evoke the EAG response of the male and female D. armandi at an indefinite concentration, within those compounds,α-phellandrene, (S)-(?)-β-pinene, (S)-(?)-α-pinene share the lowest threshold dose while (R)-(+)-limonene and bornyl acetate the highest.(2) There's sexual dimorphism available in the EAG response of the D. armandi to P. armandi. Female insects were more sensitive to (S)-(?)-α-pinene,(?)-camphene andα-phellandrene, while males more responsive to (R)-(?)-α-pinene, (+)-camphene and 3-carene. For the 2 monoterpenes: (S)-(?)-β-pinene and (?)-camphene, males were more responsive in lower concentrations in EAG response, while females was more responsive in higher.(3) Concentration contributes significant influence in EAG response of the male and female D. armandi. In the low concentration stimulus, D. armandi was more sensitive to (S)-(?)-β-pinene,α-phellandrene, (S)-(?)-α-pinene, with the concentration reached 100μg/μL, the most responsive monoterpene was changed intoα-phellandrene,(?)-camphene in female andα-phellandrene, (R)-(+)-α-pinene and (+)-camphene in males.(4) Pooled data analysis indicates that there was significant difference between all three stereoisomers in this research. Both females and male showed significant difference in two stereoisomers, ((+)-Camphene and (?)-Camphene; (R)-(+)-Limonene and (S)-(?)-Limonene) while the other stereoisomers ((R)-(+)-α-pinene and (S)-(?)-α-pinene) could evoke significant difference in males but not in females (P<0.01).(5) It is also manifested that the EAG responses of the female D. armandi to the volatile oil were significant higher the males, and the invaded volatile could evoke higher EAG response. When the concentration of the volatiles oil was below 0.1μg/μL, there was no significant difference between females and males, but as the concentration was above 1μg/μL, there is significant difference between the 2 sexes either to the volatile from invaded or healthy P. armandi (0.01 |
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