The Entomotoxic Fungal Lectin <i>Marasmius oreades</i> Agglutinin Disrupts the Midgut Epithelium of Colorado Potato Beetle Larvae

Fungal lectins, with their specific glycan-binding activity, represent promising biopesticide candidates. This study investigates the potential of six fungal lectins to control Colorado potato beetle (CPB) larvae (<i>Leptinotarsa decemlineata</i>). <i>In vitro</i> feeding trials with recombinant lectins were performed to evaluate their individual toxicity. <i>Marasmius oreades</i> agglutinin (MOA) caused significantly higher mortality than the other lectins, whereas <i>Coprinopsis cinerea</i> lectin 2 (CCL2) and <i>Aleuria aurantia</i> lectin (AAL) completely inhibited weight gain. Functional analysis of MOA mutants revealed that both carbohydrate-binding and proteolytic domains are essential for toxicity. MOA binds to midgut glycoproteins in CPB larvae, disrupting midgut epithelium. Histology and ultramicroscopy showed that MOA causes loss of apicobasal polarity and detachment of basal lamina. No acute toxicity of lectins against adult European honeybees (<i>Apis mellifera</i>) was found; however, significant sublethal effects on larval development were observed. MOA shows promise as a selective bioinsecticide for sustainable CPB control with minimal nontarget effects.