Technical Abstract: A series of laboratory and field studies were conducted using two lines of navel orangeworm (NOW) reared on different stages of new crop and mummy pistachios. This study demonstrated the potential importance of malformed pistachios (pea splits) to the population dynamics of NOW, because these nuts, which are available as early as mid June, supported NOW development and survival. Overall, the development rate on new crop pistachios is fastest on mature nuts, 422.3 ± 123 degree-days (DD)°C, but other factors such as exposure to insecticide residue also sped development, although survival decreased. Development took the longest on unharvested nuts (mummies) baked at 90°C for 24 h, 2,664.7 ± 131.4 DD°C. In most trials development was variable and two generations could develop at the fastest rate before the slowest individual completed development, which in turn calls into question the concept of discrete generations. Generally, survival was highest on mature pistachios and other stages of new crop nut and lowest on mummies collected in May. It was also higher on the new varieties ‘Lost Hills’ and ‘Golden Hills’ (24.7% and 32.0%, respectively) than on the most extensively planted variety, ‘Kerman’ (13.3%). In our trials both the rate of development and survival were dependent on nut stage, age, variety and quality, indicating that pistachios are a dynamic rather than a static nutrient source for NOW.