the european corn borer progresses through four developmental stages. these are the egg, larva, pupa, and adult. the insect is referred to as a borer in its larval stage and as a moth in its adult stage. the adult moths lay their eggs on corn plants. larva hatch from the eggs. larvae have five instars or sub-stages of development. the larval stage is followed by a period of diapause or hibernation in a pupa. during the pupal stage, the borers progress through metamorphosis in a suspended chrysalis. following this intense period of development, an adult moth emerges from the pupa. the length of the pupal stage is determined by environmental factors such as temperature, number of hours of light, and larval nutrition, in addition to genetics.