Developing novel markers for tracking dispersal of navel orangeworm in California orchards

Navel orangeworm Amyelois transitella (Lepidoptera: Pyralidae) is the primary insect pest in California almonds, pistachios, and a serious pest in walnuts. This pest is particularly problematic as it can infest all three crops when they are vulnerable in the fall during harvest and is considered a strong flyer. Populations can disperse between crops as nuts develop which is staggered starting with almonds followed by pistachios and then walnuts. Currently there are limited tools to trace inter-orchard movement for this pest. Understanding navel orangeworm movement between orchards is crucial for refinement of IPM strategies. Here, we investigate the isotopic markers nitrogen-15 and rubidium absorption by navel orangeworm in field conditions. Almond and pistachio trees were treated with a water only control as well as two rates each of nitrogen-15 enriched ammonium nitrate and rubidium chloride. The two rates for nitrogen-15 were 1 g/L and 2 g/L, and rubidium at 50 g/L and 100 g/L . All treatments were externally applied from April-June of 2023. To monitor the absorption of these markers in plant and insect tissues, leaf, nut, and insect samples were collected. All samples were analyzed to determine the abundance of nitrogen-15 and rubidium. Refinement of these techniques is necessary, but they offer a novel tool to potential track movement of important insect pest.