An acarine predator-prey metapopulation system inhabiting greenhouse cucumbers

The two-spotted spider mite ( Tetranychus urticae ) is a serious pest on greenhouse cucumbers, but can be controlled by the phytoseiid predator Phytoseiulus persimilis. The two mite species exhibit considerable fluctuations in overall population densities but within acceptable limits. The system appears to be persistent at a regional (greenhouse) scale in spite of frequent local extinctions (e.g. at individual plants). Experimental evidence indicates that the mites form a metapopulation system characterized by 'shifting mosaic' dynamics. A stochastic simulation model is used to analyse the role played by dispersal in the dynamics and persistence of the system. It shows that demographic stochasticity generates sufficient endogenous 'noise' to counteract the synchronizing effect of density-dependent dispersal, provided dispersal rates are not too high and the system is not too small. Low dispersal rates, on the other hand, increase the risk of local outbreaks of spider mites that may cause destruction of plants.