Variable Development Rate and Survival of Navel Orangeworm (Lepidoptera: Pyralidae) on Wheat Bran Diet and Almonds

A series of laboratory and field studies were conducted using three lines of navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), reared on wheat bran diet and almonds, Prunus dulcis (Mill.) D.A.Webb, at constant and fluctuating temperature. The duration of development on wheat bran diet at constant temperature differed significantly among the three lines. Development was as much as 40% faster at constant temperature than at fluctuating temperatures, consequently the developmental duration determined at constant temperature was not an absolute measure. When the maximum temperature in fluctuating regimes exceeded 43 degrees C, survival decreased by 50% compared with the constant temperature control. In almonds held at constant temperature, the developmental rate on new-crop nuts was variety-dependent and was fastest on 'Nonpareil' almonds and slowest on the experimental selection '23-122'. Development and survival were also variety-dependent on unharvested (mummy) almonds, and navel orangeworm average emergence was earliest from Nonpareil and latest from 'Carmel' nuts, differing by 529 degree-days, whereas survival was the highest on 'Butte', 35.7%, and the lowest on Carmel nuts, 7.2%. In our trials, both the speed of development and survival depended on host age, variety and quality, indicating that almonds were a dynamic rather than a static nutrient source for navel orangeworm. Identifying the factors responsible for variation in development and survival will give insight into improving control strategies.