Fig. 1.

—Life cycle of the wheat stem sawfly, Cephus cinctus Norton. (A) After overwintering in diapause in a senesced wheat stem, a prepupa metamorphoses in late spring or early summer. The pupal stage lasts 10–12 days, after which the newly eclosed adult chews a hole in a frass plug left by the larva to emerge from the stem. (B) The adults can mate immediately after emergence, either on the wheat stubble or on new host stems. The short-lived females oviposit 30–40 eggs before dying in 7–10 days. (C) Newly deposited eggs in the stem lumen, usually from multiple females, hatch in 5–10 days. The neonate larvae feed on the parenchyma lining the stem interior. As the larvae grow through four to five larval instars they forage on the stem lining throughout the stem by boring through the nodes. The duration of larval feeding can range from 3 to 8 weeks. (D) Within the stem, cannibalism leads to a single surviving larva that migrates to the base of the stem at plant senescence and ripening. The larva girdles the interior of the ripened stem wall, cutting a groove that encircles the entire stem. Wind or gravity causes the weakened stem to break and lodge, leaving the unharvested wheat head on the soil. Below this groove, the larva makes a frass plug before migrating to the base of the stem near the crown. Within a thin hibernaculum, the prepupa remains protected in obligate diapause from late summer through to warming the following spring. This period of inactivity can last >9 months. Image created by Megan L. Hofland and Norma J. Irish, Department of Land Resources and Environmental Sciences, Montana State University.