Species of Aphytis Howard (Hymenoptera: Aphelinidae) are the most effective natural enemies of armored scale insects (Homoptera: Diaspididae). Their classification, based on the morphology of adult wasps, is difficult. The studies herein were intended to explore the possibility of using morphological characteristics of developmental stages in the systematics of this genus.

The developmental stages of A. chilensis Howard, the generotype of Aphytis, are described. The ovarian egg is double-bodied, whereas the deposited egg is stalked. The larva passes through three instars, each of which differs markedly in shape and size of the mandibles. First-instar larvae have four pairs of spiracles; the second and third instars have eight pairs, viz., one pair in the mesothoracic segment and one in each of the first seven abdominal segments. The cephalic skeleton, respiratory system, and various integumentary structures of the third-instar larva are described. The morphology of the pupa was studied with light and scanning electron microscopy.

At 28 ± 1° C, egg development takes 2 to 3 days, larval development (including the prepupal period) 10 to 12 days, and pupal development 6 to 7 days. Rearings under various constant temperatures gave the theoretical threshold of development as 14.1° C and a thermal constant of 270.2 day-degrees for the completion of development.