Biological Control of the Bulb Mite, Rhizoglyphus robini, by the Predatory Mite, Hypoaspis aculeifer, on Lilies: Predator-Prey Interactions at Various Spatial Scales

Abstract

Experiments in closed jars with lily bulbs showed that the predator, Hypoaspis aculeifer, can suppress populations of its prey, the bulb mite Rhizoglyphus robini, to very low levels. When the bulbs were decomposed into scales, the prey was suppressed earlier, supposedly because of increased accessibility to the sites where bulb mites reside. Repeating the experiment in open jars also led to strong suppression of the prey population: the predators did not leave the jars until almost all prey was eaten. To assess the possibility for biological control of bulb mites in lilies at a larger spatial scale, experiments were carried out in closed plastic bags filled with lily bulb scales and vermiculite, as is common practice in lily bulb propagation. The results showed that H. aculeifer was able to suppress its prey to very low densities, but probably due to a more complex spatial structure (i.e. vermiculite), prey suppression took longer. The results of these small- and large-scale population experiments suggest that local predator-prey interactions are very unstable despite the presence of refuges and spatial complexity. At which spatial scale complexity becomes large enough to cause spatial decoupling of the predator-prey interactions and thereby promote predator-prey persistence rather than prey extinction, will be the subject of future investigations.