Disruption of juvenile hormone receptor binding in tobacco cutworm larvae by Gladiolus gandavensis extract

Abstract

Tobacco cutworm (Spodoptera litura [Fabricius]) is a destructive insect pest distributed in densely cultivated parts of Asia and Australia. This insect shows an explosive increase in its population in summer. Furthermore, tobacco cutworm larvae are very difficult to control because of their strong resistance to commonly applied chemical insecticides. To identify alternative pesticides that circumvent toxic effects to the environment and the threat of insecticide resistance, we aimed to examine plant extracts with insect growth regulatory activity targeting juvenile hormones (JHs). Using RNA sequencing and de novo transcriptome assembly, S. litura cDNA sequences of the JH receptor methoprene-tolerant (Met) and steroid receptor coactivator (SRC) were determined and used to generate yeast two-hybrid bait and prey plasmids. The JH/JH analog-mediated binding of Met and SRC was measured by assaying β-galactosidase activity. In the plant extract activity assay, we tested 1,628 plant extracts in transformants bearing Met and SRC. We identified 67 plant extracts with high JH disruptor (JHD) activity in tobacco cutworm, of which Gladiolus gandavensis extract showed the highest JHD activity. Plant-based JHDs might serve as a viable and sustainable alternative to chemical pesticides to control tobacco cutworm infestations in the field.