Phenotypic plasticity is a mechanism where different phenotypes are expressed from a genotype allowing individuals to survive variable environments. Diet-induced phenotypic plasticity was observed in the developmental time and size at maturity of the specialist predatory mite Phytoseiulus persimilis. As a preliminary study, we investigated variations in developmental time and size at maturity of P. persimilis under intermediate diet restriction of 10 and 20 spider mite (Tetranychus urticae) eggs using enclosed rearing cells. Analysis of covariance using consumption as a covariate showed no difference in the developmental time of P. persimilis between the different prey densities. Additionally, the size at maturity of P. persimilis given different prey densities was similar from the Wilcoxon rank sum test. However, when given 20 prey eggs, a relatively high variation was found in the consumption rate of both female and male P. persimilis. The findings of this study are essential for designing our later studies on the influence of diet restriction and lifespan of P. persimilis. This study also expands our understanding of the viability and adaptability of P. persimilis under food stress.