The navel orangeworm overwinters primarily in the larval stage in mummy almonds that remain in the trees or on the ground after harvest. In the spring, moths emerge and lay eggs on the mummy nuts in the trees, and these nuts provide the principal food source of the first-generation larvae. Moths of this generation emerge to infest the current year's almond crop during the hullsplit period. Infestations may reach as high as 30 to 50 percent.