Identification of oxalic acid from <i>Persicaria chinensis</i> as a repellent against isopods

The need for eco-friendly pest control has grown with increasing concerns over toxicity of synthetic pesticides. Repellents offer a nonlethal alternative for crop protection. Here, we report the identification of naturally occurring organic acids as repellents for agricultural pests. We evaluated the repellent activity of methanolic extracts of 12 Persicaria species against pillbug. All extracts showed significant activity, with that from P. chinensis being the most effective. Bioassay-guided isolation from P. chinensis shoots revealed oxalic acid as the principal active compound. Oxalic acid and related dicarboxylic acids exhibited concentration-dependent repellency, indicative of the influence of both acidity and molecular structure on the activity. Oxalic acid was detected in all species and was generally more abundant in the shoots, partially correlating with the repellent strength. This study reveals a previously unrecognized defensive role of plant organic acids and highlights their potential as safe, biodegradable agents for pest management.