FUNCTIONAL RESPONSE OF THREE SPECIES OF PHYTOSEIIDAE (ACARINA) TO PREY DENSITY

Abstract Experiments were carried out on excised leaves to determine the form of the functional response curve of the phytoseiid predators Amblyseius largoensis (Muma), A. concordis (Chant), and Typhlodromus floridanus (Muma), to increases in density of the prey, Oligonychus punicae (Hirst). The curve for each species was curvilinear to a plateau from prey densities of 1 to 70/arena, the average number killed/24 hours at the plateau being 8.5/female for A. largoensis, 5.5/female for A. concordis, and 2.0/female for T. floridanus. From prey densities of 70–300/arena, there was an accelerated rise to another plateau, in which the average number of prey killed in a 24 hour period was double that of the first plateau.Detailed analysis of A. largoensis at a density of 200 prey/arena showed the effect to be due to a stimulation–interference component, which resulted in the predator killing several prey in close succession because of increased prey contact, and because total utilization of each was minimal. During a 1 hour period, A. largoensis captured an average of 1.25 prey/predator at a prey density of 35/arena, while at a prey density of 200/arena, 3.87 prey/predator were captured. More than four times longer was spent feeding on the first prey at a density of 35 than at a density of 200 prey/arena. During the time that the predator was hungry, it was stimulated to capture and kill interfering prey that bumped into it.The functional response curve of the three predators increased in magnitude when waterproofed paper arenas were used. Four possible reasons for this increase are discussed: reduced number of prey eggs for consumption by T. floridanus; lack of webbing, which interferes with searching; increased prey activity; and dehydration of prey, affecting their relative palatability to the predator.