Cyclotides Enable the Oral Activity of Neuroactive Peptides against Lepidopteran Pests

Abstract Farmers face shrinking crop-protection options due to climate change, resistance, regulations, and demand for residue-free food. Peptides and proteins are attractive solutions because they are potent, specific, and degrade into harmless amino acids. Venom-derived peptide neurotoxins show strong potential as bioinsecticides, but their poor oral activity limits use in sprayable formulations. We show that plant cyclotides, kalata B1 and B2, dramatically enhance the oral efficacy of venom-derived neurotoxins against major lepidopteran pests. Their effects are synergistic, increasing activity by two to 3-fold beyond additivity, and in some cases, enabling complete mortality at doses where either component alone is ineffective. The proposed mechanism involves cyclotides selectively disrupt the lepidopteran midgut barrier, allowing neurotoxins to cross into the hemocoel and act on the nervous system. Microscopy confirms midgut damage, and the D-form of kalata B1 retains activity, indicating an achiral, lipid-mediated interaction. These results establish cyclotides as enablers of peptide-based bioinsecticides against selected important crop pests.