Orange spiny whitefly (OSW), Aleurocanthus spiniferus (Quaintance, 1903) (Hemiptera, Aleyrodidae) is a new quarantine pest of Croatia. It is a polyphagous insect which infest plant species belonging to 38 plant families, but the main hosts are plants of the genera Citrus, Pyrus and Vitis. In Croatia, A. spiniferus was first found in 2012. on ornamental potted orange seedlings (Citrus x aurantium L) in one nursery garden in Split. After indentification, this pest was eradicated. During the 2018. the presence of OSW was reported in Dubrovnik –Neretva valley, in Vitaljina. This pest continued to spread through the area of Konavle and the presence of OSW on the island of Hvar was recorded, what presents high phytosanitary risk to various agricultural crops. The characteristics of this pest have not been studied in Croatia. Accordingly, the aim of this article is to present the biology of pest in field conditions in Vitaljina from July to December, 2019. Inside the nursery, an insectarium without temperature and humidity regulation was placed, in which a mandarin seedling Citrus Unshiu Marc 'Owari' was placed. To determine the life cycle, a mandarin seedling was artificially infected with 50 individuals of adult. Also, the period of presence of all developmental stages of pests on the leaf was determined. Sampling was performed every 7-10 days during the growing season and once a month during the dormant period. During the research and monitoring of the life cycle of the insect during August, depending on the climatic conditions, the embryonic development of Aleurocanthus spiniferus lasted 12-15 days, the development of the larvae 36 - 43 days and the "puparium" for 12-17 days. The total development from egg to adult form lasted 60-75 days. In early October, the adult emerged, ending the life cycle.