Vigorous young trees growing in the open on good sites may survive a high degree of defoliation while weak trees may die. Mortality is generally higher among young pines growing in shade beneath overstory than among those growing in the open free from shade and competition. Partial defoliation of trees is a common occurrence, i.e., only the leader or a few branches are stripped of needles. Pupation takes place in the cocoon following arrival of warm weather. In an overwintering colony studied in Lee County, prepupae were found in cocoons through May, the first pupa was found in early June.
Adults emerge within a few weeks following pupation.
Eggs are laid in both old and current-year needles. Full-grown larvae move to the duff and soil and spin cocoons. Time required for completion of the entire life cycle is about 2 to 2.5 months. Seasonal activity of the redheaded pine sawfly is determined by climate. In Alabama, climatic conditions favorable for sawfly activity may exist for 8 or 9 months in some years in some localities.