For bisexual insects, sex is based on a sex chromosome system. In most species females are XX and males are either XY or XO . In the Hymenoptera, Thysanoptera, some Homoptera , males are produced from unfertilized eggs. The sex ratio of the progeny can often be controlled by insects and may be influenced by environmental factors such as temperature. The eggs are typically quite large relative to size of insect, and contain a lot of yolk, though in some parasitic Hymenoptera whose eggs are placed into the body of their host, the e ggs may not have much yolk .
Eggs come in a great variety of shapes.
The vitelline membrane surrounds the cytoplasm. This is a complex, layered structure with airspaces, and possibly with additional layers of wax . Some eggs have a line of weakness which facilitates the exit of insect at hatching. Also, since the shell is laid down before fertilization, a entry way for the sperm has to be left. This is called the micropyle .