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Neoseiulus californicus (McGregor) is a relatively effective phytoseiid predator against spider mites reported from the Americas (North and South), Africa, the Mediterranean basin, and Japan. This study was a collaborative effort to identify and mass-rear a strain of N. californicus that is more efficacious under arid conditions than the standard commercial strain from California (USA). N. californicus strains were collected in arid areas worldwide. Discriminant analysis performed with 30 morphological variables allowed for their separation. The performance of these strains under arid conditions and on selected host plants was evaluated in laboratory and semi-field trials. Development and survival of eggs and juveniles differed among strains and humidities. Female performance (survival, oviposition) was influenced by strain but not by humidity. The Californian reference strain was superior to all others, when considering both adaptation to dry conditions and power of population increase at low humidities. Whole potted plant trials (cucumber, strawberry, and pepper) confirmed this result. Field trials were conducted to compare this new product to the standard commercial strain of Phytoseiulus persimilis Athias-Henriot. To identify possible influence of symbiotic bacteria on strains of N. californicus general primers for the 165 rDNA gene were used in a PCR. Among other bacteria, a Spiroplasma, closely related to the one found in various arthropods, was detected in two strains, and it was further characterized. No influence on the host's developmental time, fecundity, and sex ratio could be detected. To provide this product at an affordable cost for European growers an economic rearing and delivery system for N. californicus was developed and its marketing potential in Europe and neighboring countries was estimated.