EPS overwinter as eggs inserted into the needles of host plants during August and September. Warm temperatures during early spring stimulate egg hatch in late March and early April. Larvae are gregarious, feeding in tightly clustered groups. By mid-May, larvae are fully developed. By mid to late-August, adult sawflies emerge from their cocoons.
Female sawflies emit a sex pheromone which help the males locate females for mating purposes.
Using her saw like ovipositor, the female sawfly deposits overwintering eggs into the slits made in needles. EPS produce a single generation per year. EPS larvae begin and complete their feeding activities before current-year needles are produced. If, however, EPS infestations occur over several successive seasons, it is possible for plant vigor to decline. Overwintering eggs, although small, can be detected without the aid of a hand lens.