Citrus Under Protective Screen (CUPS) production system excludes the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, vector of Huanglongbing (HLB), and large predators. However, small pests and beneficial arthropods such as predatory mites may enter the CUPS. Predatory mites from the family Phytoseiidae attack several economically important pests, especially phytophagous mites common in CUPS. The species assemblage, abundance, and distribution of phytoseiid mites in CUPS and open-air (control) were investigated in Ray Ruby grapefruit from 2018 to 2020. Foliar sprays of chemicals for pest suppression were used in both systems and evaluated for effect on predatory mite populations. In the 2 production systems, a significant peak in the phytoseiid mite population was observed in February 2019 and 2020. This increase coincided with the blooming period of grapefruit, which likely provided pollen as an alternative food. A total of 2,234 specimens of 11 species were identified. Amblyseius tamatavensis Blommers and Typhlodromalus peregrinus (Muma) were dominant in both systems. Amblyseius tamatavensis was slightly more abundant in CUPS (50% of total specimens) than T. peregrinus (47%), while T. peregrinus was prevalent (82%) in open-air compared with A. tamatavensis (16%). Shannon index and evenness were significantly higher in CUPS, but species richness was similar. Chlorpyrifos with abamectin and oil, cyantraniliprole with spirodiclofen, copper, and oil as well as pyridaben alone reduced phytoseiid populations between 87% and 96%. Fenbutatin oxide mixed with copper reduced phytoseiids by 48% in open-air only. Our results demonstrate phytoseiid survival, reproduction, and contribution to biological control in CUPS, despite high temperature and humidity.