Experimental studies on acarine predator–prey interactions: the effects of predator density on immature survival, adult fecundity and emigration rates, and the numerical response to prey density (Acarina: Phytoseiidae)

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Abstract
Laboratory experiments revealed that increasing the density of the immature instars of Phytoseiulus persimilis had little effect on their survival rates. However, due to the high prey requirements of the immature instars of Amblyseius degenerans and the tendency for underfed individuals of this species to become cannibalistic, their survival rates decreased with increasing predator density. Increasing predator density reduced the fecundity of P. persimilis and caused its numerical response to prey density to reach plateaux at increasingly lower levels of fecundity as the predator density increased. In contrast, increasing predator density did not affect the fecundity of A. degenerans to such an extent and its numerical response appeared eventually to reach maximum levels when sufficient prey were available. The emigration rates of P. persimilis tended to increase with increasing predator density whereas those of A. degenerans increased or decreased depending on the density of the predators and the prey.