Abstract: [Objective]The sex ratio is one of the determining factors of the nematode reproduction rate that is key for the pathogenicity, and population expansion of pine wood nematode, Bursaphelenchus xylophilus. This study aims to survey the reproductive tactics of PWN under different cultural conditions for providing a theoretical basis for futher study on the population expansion relatived to reproductive behavior and strategy for prevention and control of pine wood disease.[Method]We investigated the change pattern of PWN female to male ratio under different nutritional conditions and pinene stress by micro-examination.[Result]The sex ratios were biased to females at nutrition-rich conditions and the nematodes exercised a masculinizing effect on the developing larvae in poor nutrition environments. The α-pinene and β-pinene were ableto inhibit the nematode's reproductive rate with low sex ratio at low concentration but promote the rate at high concentration with high sex ratio. The β-pinene might inhibit the reproduction potential with low sex ratio at low and high concentration. The sex ratio was lowest and relatively stable under the mixture stress of low concentration α-pinene and β-pinene.[Conclusion]The PWN sex ratios were biased to females at favorable environmental conditions and the nematodes exercised a masculinizing effect on the developing larvae in uncomfortable environments. Thus we infer that the PWN would control the reproduction rate by modifying the sex ratio to adapt the environment change.

Key words: pine wood nematode, reproductive behavior, reproductive tactics, sex ratio, reproduction ratio