Abstract: The cytoplasmic incompatibility (CI) is the most common effect of Wolbachia on the reproduction of its arthropod hosts, and the expression of CI differs greatly among different populations. Using the Jiangsu (JS) and Liaoning (LN) populations of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), as experimental materials, 100% infected and uninfected Wolbachia lines were obtained by screening. The present study tried to evaluate some factors influencing the expression of CI in the spider mite by crossing experiment and Real-time quantitative PCR. These factors include age of host, temperature, host genes and Wolbachia density. The 1, 3, 5, 7-day-old virgin males were used to investigate the influence of host age on Wolbachia-induced CI. The results showed no effect of age on CI, suggesting that host age does not reduce the sperm modification induced by Wolbachia. The effect of temperatures (20℃, 25℃ and 30℃) on the CI induced by Wolbachia was also checked. Neither high nor low temperatures influenced the expression of CI. Wolbachia density in males of the JS population, as measured by quantitative PCR using the wsp (surface protein of Wolbachia) gene, was significantly higher than that in the LN population. In addition, in both the JS and LN populations, Wolbachia density increased with the age of male hosts. Wolbachia density also showed no effect on CI. We estimated the variability of CI expression between the JS and LN population of T. urticae was due to the interaction between Wolbachia and host genotypes. The results might provide foundation for understanding the mechanisms of reproductive manipulation induced by Wolbachia.

Key words: Tetranychus urticae, Wolbachia, cytoplasmic incompatibility, age, temperature, bacterial density