Encarsia pergandiella develops in a strange way. Unlike most parasitoid species, they are autoparasitoids. This means females develop on whitefly immatures and males develop on immature parasitoids. This means males are parasitoids of other parasitoids, including females of their own species!
The fertilization process is a female decision. The female stores the male sperm for later fertilization of eggs.
All bees and wasps, including parasitoid wasps are haplodiploid. This means not all eggs have to be fertilized to develop. Unfertilized eggs become males, which are haploid. Fertilized eggs become female, and are diploid. In autoparasitoids, placement is also important in sex development. Female eggs can only develop on whitefly larvae. This makes the whitefly a primary host, meaning that the wasp generally places its eggs on this host. The humans from the Aliens movies are the primary host for the aliens.
Male wasps can only develop on wasp larvae. This makes the wasp larva the secondary host. The secondary host can be female wasps of the same species or other parasitoid species developing on the whitefly. If the aliens also had secondary hosts, then they would lay the male eggs on the aliens developing in the humans.
Female autoparasitoids can choose to lay female or male eggs on the basis of environmental conditions. Pretty sophisticated behavior for a wasp the size of a speck of dust, huh?!