A hetero-chitooligosaccharide as plant defense elicitors against spider mites

The increasing challenges of pesticide resistance and environmental degradation in modern agriculture require sustainable pest management strategies. This study investigates the efficacy of a specific type of hetero-chitooligosaccharide called partially deacetylated chitooligosaccharide enriched in D-Glucosamine (DACOS, 85.60% deacetylation), as a plant defense inducer against the two-spotted spider mite, Tetranychus urticae Koch. DACOS is characterized with 85% deacetylation and an average molecular weight of 1092.52.In planta bioassays revealed a concentration-specific suppression of mite performance on DACOS-treated leaves of kidney bean seedlings, with an observed optimum concentration of 80 mg/L for local effects. This concentration reduced mite survival by 30% and fecundity by 59% after six days and this optimum was reproducible across three independent biological replicates using leaf discs from >108 plants. Systemic effects exhibited an observed optimum concentration of 160 mg/L, indicating distinct concentration requirements for local versus systemic defense induction. Behavioral choice assays revealed that DACOS-treated leaves induced 73% mite repellency. No direct acaricidal effects were observed, which confirms the role of DACOS as a plant defense elicitor. Metabolic profiling revealed enriched pathways (e.g., monoterpenoid biosynthesis and alpha-linolenic acid metabolism) that produce volatile organic compounds with repellent properties.These findings suggest that DACOS is an environmentally friendly biostimulant that can enhance plant defense, bypass pesticide resistance, and promote the sustainability of crop production.