Experimental Studies on Predation: Predation and Cyclamen-mite Populations on Strawberries in California.

A native predatory mite, Typhlodromus sp., normally gives good control of the cyclamen mite, Tarsonemus pallidus Banks, in older plantings of strawberries in California. But because of delay in entrance of the predator, control is only sporadic in second-year plantings. In field trials, stocking of strawberry plantings with the predator late in the first or early in the second year, gave consistent control. The commercial feasibility of the method is still under investigation. The results have significance in relation to theories of population dynamics, a field in which there have been few controlled experiments. Some recent work on vertebrate predation has been Interpreted as more generally applicable to all predation than is iustified. Conclusions minimizing the role of such predation in the regulation of prey populations is not transferrable to the field of biological control of insects, for example. Typhlodromus Sp. is a specific predator of cyclamen mite, and its biology is closely correlated with that of its prey, on which its reproduction depends. It can, however, utilize honeydew and other liquid foods for survival during very low densities of the prey. At such low densities the strawberry plant provides maximum protection for the cyclamen mite; and this, together with spatial factors, insure that the pest will not be entirely eliminated by its predator. Under such circumstances, effective predation is not, as some ecologists have postulated, self-annihilative. Rather, the data indicate fairly regular, reciprocally dependent oscillations of predator and pest (prey) populations, with the pest held to economically unimportant levels. Predation may be superimposed over all other mortality causes.