PREY AND PREDATOR EMIGRATION RESPONSES IN THE ACARINE SYSTEM TETRANYCHUS-URTICAE-PHYTOSEIULUS-PERSIMILIS

Some of the processes that influence the emigration of prey and predatory mites from bean plants were investigated experimentally. The emigration of the prey depends on the damage they cause to the plants and on predator density. The predator''s emigration rate is a decreasing function of prey density, and does not change (or it slighlty decreases) when prey and predator numbers are increased, maintaining the same prey/predator ratio. The probability of emigration of the predators is independent of their own density when prey are absent and density dependent when prey density is kept constant. Of the variability in the predator''s instantaneous rate of emigration in the different experiments, 43% is accounted for by a 2-parameter, negative exponential function of capture rate (number of prey eaten per predator and per unit of time).