Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/3/2010
Publication Date: 4/1/2011
Citation: Siegel, J.P., Kuenen, L.P. 2011. Variable development rate and survival of navel orangeworm (Amyelois transitella, Lepidoptera: Pyralidae) on pistachio. Journal of Economic Entomology. 104(2):532-539. Interpretive Summary: The navel orangeworm (NOW) is a scavenger moth that has several generations per year. This pest was first found in the USA on navel oranges in Arizona and it infests nuts when their hulls have split or have been damaged exposing the shell and/or kernel. Since its appearance in the Sacramento and San Joaquin valleys of California in the late 1940’s, commercially grown almonds, pistachios and walnuts have been infested and this moth is currently the primary pest of pistachios and almonds in California. When females emerge in the spring they mate and continue their life cycle by laying eggs on unharvested nuts or on new-crop split nuts when they become available. New crop pistachios include malformed pea-split nuts (4-8 mm diameter) that occur from mid June through August, and these nuts supported the development and survival of this pest. Its survival was highest on the split mature pistachios that occur from late August through harvest, and overall, its development was fastest on these nuts too. However, other factors such as insecticide exposure and moisture also influence development. Survival also differed among pistachio varieties and these experiments demonstrated that nut stage, age, variety and quality affected the rate of development and survival, indicating that pistachios are a dynamic rather than a static nutrient source for NOW.
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.