The aim of this investigation was to develop an easier and cheaper alternative method for the rearing of the predatory phytoseiid mites, Phytoseiulus persimilis (Athias-Henriot) and Neoseiulus californicus (McGregor), as biological control agents of Tetranychus urticae Koch under plastic tunnel conditions in the Egyptian new reclaimed area, to satisfy the need of the private sector. The castor (Ricinus communis L.) shrub was the species tested because it appears to be a less expensive to grow and more tolerant alternative host plant to the common bean, Phaseolus vulgaris L., which is usually preferred by its growing incidentally as a weed in such locations. However, such proposed host plant have got an efficient alkaloid marked by its insecticidal and insectistatic effect. The biology of both predators and their prey were studied under laboratory condition at a mean temperature of 26 °C ± 2. and 70% ±1 rel. humidity. The estimated life table parameters for P. persimilis and N. californicus when preyed on T. urticae using the green or red leaves of the 2 castor cultivars were only slightly below the reproductive rate when T. urticae was reared on beans. Therefore, the utilization of both red and green castor leaves is usually recommended as a less expensive alternative than the common bean for the mass rearing of both of the phytoseiids predators, P. persimilis and N. californicus, on T. urticae. The total alkaloid ricinine amounted in the leaf crude extract powder 88 and 66 mg /g in red and green leaves of castor bean respectively. Ricinine percentage yield in both cultivars reached 0.59% in green and 0.49% in red leaves respectively.