Larvae of the federally threatened Euproserpinus euterpe from Walker Basin, Kern Co., CA. and Carrizo Plains, San Luis Obispo Co., CA populations were reared to the pupal and adult stage for the first time. The E. euterpe pupa is described. Mature larvae excavated a subterranean pupal chamber in an unusual (not burrowing solely headfirst) manner, but typical of other species in the sphingid tribe, Macroglossini. Soil depth of pupation ranged from 5 to 11 cm, mean = of 7.14±1.83 cm s.d. cm (n=14) for the Walker Basin population. Pupae were maintained in artificial pupal cells, facilitating observations of development. Multiple-year diapause to three years, predicted based on field observations, was demonstrated in the laboratory. Soil humidity during the fall and winter season appears critical to break pupal diapause. Pupae did not travel through the soil. Adults burrowed to the soil surface after eclosion from the pupa. The wing expansion behavior of adults at the soil surface, along with their vertical, upward wing expansion, are described.