Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 4, 2009
Publication Date: August 1, 2010
Citation: Kuenen, L.P., Siegel, J.P. 2010. Protracted Emergence of Overwintering Amyelois Transitella (Lepidoptera: Pyralidae) from Pistachios and Almonds in California. Environmental Entomology. 39(4):1059-1067. Interpretive Summary: The navel orangeworm (NOW) is a major insect pest of almonds and pistachios in California. Under field conditions, spring-time NOW emergence from almonds had at least three emergence peaks whereas only a single peak was seen among NOW emerging from pistachios. The single peak emergence from pistachios was confirmed in a laboratory study; large sample size plus degree-day modeling showed that emergence would have lasted until mid-July, a full four months after emergence began. This indicates that late-emerging NOW adults can infest new crop nuts, supporting the perspective that orchard sanitation standards are not stringent enough and dispelling the concept of discrete NOW generations even early in the growing season.
Technical Abstract: The navel orangeworm, Amyelois transitella, is the primary insect pest of pistachios and almonds in California. Four years of research (2002-2006) were conducted in Madera and Kern counties to elucidate the pattern of emergence of the overwintering population. Springtime emergence from unharvested (mummy) nuts was protracted (as long as 600 degree-days Celsius from January 1 of each year) and in 2004 and 2006 extended as late as mid-July. The population structure, sex ratio, and timing of emergence differed between pistachios and almonds. Pistachio populations had a significantly greater (P < 0.001) proportion of late stage individuals compared to almonds, 85.7%, vs. 34.1%. The sex ratio of adults emerging from pistachio mummies was significantly skewed (P < 0.001) with a ratio 57:43 male:female while it was 50:50 in almond mummies. Emergence from mummies held outdoors (variable temperature) began in early March and continued through early June in both pistachios and almonds. The adult emergence pattern from pistachios contained a single emergence peak while emergence from almonds occurred in multiple peaks. These same patterns occurred when mummies were held at constant temperature, and the emergence peak from pistachios occurred sooner. The impact of these findings on understanding NOW population dynamics and current control recommendations is discussed.