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Population dynamics of Tetranychus urticae and Galendromus occidentalis on bent-cane greenhouse roses
This study was conducted to examine the ability of the predacious mite G. occidentalis to limit population density of T. urticae infesting roses in the greenhouse, Washington state university, Pullman, U.S.A. Population fluctuations of T. urticae, G. occidentalis, and Macrosiphum euphorbiae were assessed for over two years on greenhouse roses through time series data. During the first half of experiment a stratified random sampling was performed (from May 2000 to May 2001) and the presence/absence and randomized sampling method was utilized during second half (from June 2001 to September 2002). Populations of T. urticae and G. occidentalis were estimated by R-functions or discrete prey-predator equations. During 121 weeks there were six population fluctuations of T. urticae, G. occidentalis and M. euphorbiae. The variation of G .occidentalis was closely associated with that of T. urticae but G. occidentalis did not overexploit T.urticae. The predicted populations of both mites were explained by above equations. M. euphorbiae and T. urticae might be compete for limited resource in the greenhouse rose and the movement of G. occidentalis was inhibited by the honeydew of M. euphorbiae. Therefore, M. euphorbiae showed negative relationship with T. urticae and G. occidentalis from the results of non-linear regression analysis. Although the relationship between T. urticae and G. occidentalis was negative it was unlikely to present complete biological control of T. urticae on greenhouse roses. It might be necessary an integrated management strategy to control T. urticae in bent-cane greenhouse roses.
