Insecticide application on western bean cutworm eggs and response of predators to treated eggs

Western bean cutworm, Striacosta albicosta, is a major pest of corn and dry beans. Current treatment recommendations suggest pesticide application after egg eclosion while in early instars, yet before larvae move into ears.  However, both eggs and larvae may be present in the field, therefore targeting both stages would be more effective. To evaluate for potential ovicidal properties, we tested five commonly used insecticides at their low and high labeled rates by applying them to white (younger) and tan (older) S. albicosta egg masses in a manner replicating aerial application. Egg hatching and larval mortality in each egg mass were recorded every 4-5 days for two weeks after application.  No evidence was found to suggest that any of the insecticides tested possessed ovicidal properties. However, residual larvicidal effects were present dependent on insecticide type and egg age upon application. To test for potential negative impacts on natural enemies of S. albicosta, individuals from two species of ladybird beetles (Coleoptera: Coccinellidae) were given a choice between treated and untreated egg masses. Time-lapse videos were recorded using Dino-Lite cameras for 24-hours to observe ladybird preference or avoidance behavior of treated vs. untreated egg masses and other behaviors indicating health, such as time spent disoriented. Evidence suggests that ladybirds are unable to detect and avoid treated egg masses and exposure to treated egg masses causes sublethal effects. It is important to consider not only the effectiveness of each insecticide, but also impacts on natural predators valuable to the biological control of S. albicosta.