External marking and behavior of early instar Helicoverpa armigera (Lepidoptera: Noctuidae) on soybean

Helicoverpa armigera Hubner (Lepidoptera: Noctuidae) is a pest of major agricultural crops, such as soybean and cotton. A better understanding of larval movement is important for its integrated management and resistance management. Studies with neonates through second instar larvae are still limited by the difficulties involving the handling and observation of these instars. Many studies require marking larvae, and most research involving marking is focused on moths. However, our study investigated aspects of larval behavior of the second instar of H. armigera on soybean plants. The dyes luminous powder red and Sudan Red 7B were tested as external larval markers. Both dyes successfully marked the larvae for most of 1 stadium (48 h) without deleterious effects, and are useful for short-period behavioral studies. Luminous powder red was selected for the H. armigera larval behavior study on soybean because of ease of detection during both day and night. Second instar on-plant movement was consistent, independent of the d period (morning, afternoon, evening). In general, larvae established their feeding site within a few hours of release, and remained feeding on soybean leaves. Second instar behavior suggests that management by nocturnal insecticide application, based on H. armigera larval movement, would not have an advantage over daytime application.