Species of Aphytis Howard (Hymenoptera: Aphelinidae) are the most effective natural enemies of armored scale insects (Homoptera: Diaspididae). Classification based on the morphology of adult wasps is difficult. The possibility of using morphological characteristics of developmental stages in the systematics of this genus is explored. The developmental stages of A. chilensis Howard are described. The ovarian egg is double-bodied, whereas the deposited egg is stalked. The larva passes through 3 instars. First-instar larvae have 4 pairs of spiracles; the 2nd and 3rd instars have 8 pairs. The cephalic skeleton, respiratory system and various integumentary structures of the 3rd-instar larva are described. The morphology of the pupa was studied with light and scanning electron microscopy. At 28 .+-. 1.degree. C, egg development takes 2-3 days, larval development (including the prepupal period) 10-12 days and pupal development 6-7 days. The theoretical threshold of development is 14.1.degree. C and a thermal constant of 270.2 day-degrees for the completion of development was determined.