Field Evaluation of the Bioactivity of Flonicamid and Flubendiamide and Their Mixtures with the Lemongrass, Cymbopogon citratus, Essential Oil on Fall Armyworm (Lepidoptera: Noctuidae) Infesting Sweet Corn and Dissipation of Chemicals in Seeds and Husks¹

Chemical insecticides are currently the major management means used against Spodoptera frugiperda (J.E. Smith) larvae on sweet corn (Zea mays L. var. saccharata) in Egypt. However, essential oils-based pesticides (EOs) and new insecticides might also be used. As a first report, this study aimed to assess the effectiveness and biochemical impact of lemongrass (Cymbopogon citratus Stapf) EO, flonicamid, and flubendiamide insecticides alone or in combination for managing S. frugiperda on sweet corn under field conditions. In addition, the dissipation of these compounds was determined in corn seeds and corn husks using the QuEChERS method combined with high-performance liquid chromatography (HPLC-DAD). The field efficacy trials showed that flubendiamide alone or in combination with lemongrass EO was more effective than either lemongrass EO or flonicamid alone or combined. Additionally, biochemical analysis revealed that detoxification enzymes may play an important role in S. frugiperda adaptation to flonicamid and flubendiamide. The residues of flonicamid and flubendiamide in corn seeds were undetectable in all treatments. Conversely, corn husks contained high levels of flubendiamide and flonicamid residues after application at high dosages. Interestingly, the dissipation rates of both tested insecticides increased when combined with lemongrass. The half-life values for flonicamid following the applications on corn husks alone or in combination with lemongrass EO were 4.44 and 2.45 d, respectively, while the half-life values for flubendiamide were 1.25 and 2.72 d, respectively. Our results show the potential use of flubendiamide alone or with lemongrass EO for managing S. frugiperda on sweet corn crops.