Comparison of air and ground insecticide coverage and duration of control for navel orangeworm ( Amyelois transitella Walker) (Lepidoptera: Pyralidae) in California tree nuts

Abstract BACKGROUND Insecticide application is necessary to control navel orangeworm ( Amyelois transitella ) in California tree nuts. Coverage is problematic because of height, and application timing can be problematic due to logistical challenges combined with grower reaction time. Bioassays using contact toxicity were conducted to characterize both spray coverage and the duration of control for air application for a period of 14–28 days, and contrast air application with ground sprays. RESULTS Ground application caused higher mortality than air application at a critical height of 3.7–4.3 m, and its duration of control was superior, based on higher mortality at 21 days. In one study, the mortality resulting from ground application remained constant at 89% for 21 days, whereas the average mortality for air application fell to 62%, although this was still satisfactory. There was a rapid decline in contact toxicity between 4 and 7 days after application by air. The mortality observed with air application did not depend on the water volume used because there was no difference between 93.5 L ha −1 and 280.6 L ha −1 . CONCLUSION The focus of this study on contact toxicity is the first step toward establishing a baseline for this route of exposure in tree nuts, and additional baselines are needed for adulticidal and ovi‐larvicidal activity. Air application was capable of providing high initial mortality but its duration needs to be extended. Improving coverage and application timing will become more important as California phases out the use of synthetic insecticides and makes the transition to insecticides solely dependent on ingestion toxicity. Published 2026. This article is a U.S. Government work and is in the public domain in the USA.