Variable developmental rate and survival of navel orangeworm (Lepidoptera: Pyralidae) on pistachio

A series of laboratory and field studies were conducted using two lines of navel orangeworm, reared on different stages of new crop and mummy pistachios, Pistacia vera L. This study demonstrated the potential importance of malformed pistachios (pea splits) to the population dynamics of navel orangeworm, because these nuts, which are available as early as two months before mature nuts, supported navel orangeworm development and survival. Overall, the developmental rate on new crop pistachios is fastest on mature nuts, 422.3 +/- 123 degree-days (DD, degrees C), but other factors such as exposure to insecticide residue also sped development, although survival decreased. Development took the longest on unharvested nuts (mummies) dried at 90 degrees C for 24 h, 2664.7 +/- 131.4 DD. 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. Survival 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, like almonds, Prunus dulcis (Mill.) D. A. Webb, are a dynamic rather than a static nutrient source for navel orangeworm.