Differentially acetylated chitosan oligosaccharides 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 DACOS, 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 1 kDa. In planta bioassays revealed a dose-dependent suppression of mite performance on DACOS-treated leaves of kidney bean seedlings, with peak efficacy occurring at 80 ppm. This concentration reduced mite survival by 30% and fecundity by 59% after six days. In addition to the local effects, mite survival and fecundity were also reduced on untreated leaves of the same seedlings, confirming that the effect of DACOS on plant defense is systemic. 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 α-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.