A rudimentary chamber is constructed in the stem, and the weevils overwinter in this chamber as fifth instar larvae. Pupation of the overwintering larva occurs the following year in early June. There is one generation per year. The snout is very narrow and protrudes forward from the head, which is small in relation to the rather large, almost globose body. The black stem weevil overwinters as an adult in soil, plant residue, sod and weed clusters, and begins to emerge and feed on volunteer sunflower as soon as the plants reach the early seedling stage.
Females deposit eggs under the epidermis of the stem.
Larvae emerging from these eggs tunnel in the pith area of the stem, pupate and emerge as adults in early August. Little or no Apion adult activity is observed for about two weeks in late July and early August. Apion adults emerging in August also feed on the leaves and stems of the plant, but as the plant matures and the leaves begin to die, the adults move under the bracts of the sunflower heads where they can be observed feeding until the plants are harvested. The average number of weevils per plant can then be calculated. When surveying for stem weevils, the scout must move through the field slowly to avoid having the adult stem weevils drop to the soil and 'play dead' as they typically will do if care is not taken during survey and counting efforts.