Cecropia moths overwinter as pupae inside cocoons and emerge as adults ready to mate and lay eggs on host plants such as wild cherry the following spring. It is adaptive for eggs to be laid as soon as trees have leaves and there is larval food available. Cecropia has a bimodal emergence curve. Most adults emerge in May and probably receive a selective advantage most years. But some adults do not emerge until later in the summer ad, in years of late frosts, they have a selective advantage. This bimodal emergence curve is likely maintained in the population by