Pine wood nematode (PWN), Bursaphelenchus xylophilus, is a serious pathogen of pines throughout the world. Previous work indicated that different concentra-tions of α-pinene could affect nematode reproduction, however the mechanism of that influence is not clear. In order to examine the reproductive strategies of PWN in response to the stress of the volatile materialα-pinene, we investigated different aspects of population changes of B. xylophilus under two concentrations of α-pinene. The results show that a high concentration (214.5 mg ml-1) promoted population growth while a low concentration (56.33 mg ml-1) decreased the population. Population structure was analyzed and it was found that a high con-centration of α-pinene decreased the percentage of adults but increased the percentages of larvae and eggs. Furthermore, from the results of an evaluation of sex ratios (female/male), it was determined that a high concentration could elevate sex ratios but a low concentration decreased ratios sharply. These results suggest that the PWN could regulate its population by changing sex ratios under stress ofα-pinene. This study has provided a theoretical basis for the prevention and control of pine wilt disease caused by the pine wood nematode.