AN ACARINE PREDATOR–PREY POPULATION INFESTING STORED PRODUCTS

Populations of the stored product mite Tyrophagus putrescentiae (Schrank) and its predator Blattisocius dentriticus (Berl.) were propagated in two experimental universes. Although the predator determined the size of the prey populations, the densities of both species fluctuated with peaks of abundance occurring every 6 to 8 weeks. A number of factors modified, to some extent, the role of "predator searching" as a mechanism controlling both the average densities and fluctuations in abundance of the two species. With large fluctuations in the abundance of the prey there was a pronounced cycle in the age structure of the predator and prey populations. The larger stages of the prey were largely immune to attack by the predator. Individuals of the predator developed to about one-half their normal size when the prey were scarce. The combination of immune stages of the prey and adjustment of predators to scarcity of prey ensured the coexistence of the predator–prey system. Contamination of experimental populations by psocids was one of the major hazards in rearing the populations for extended periods.