Acmella oleracea extracts as green pesticides against eight arthropods attacking stored products

Developing sustainable control tools for managing noxious pests attacking stored foodstuffs is a timely research challenge. Acmella oleracea (L.) R. K. Jansen is a crop widely cultivated for its multiple usages on an industrial level. In this study, the extracts prepared with A. oleracea aerial parts were applied on wheat kernels for the management of eight important arthropod pests attacking stored products, i.e., Cryptolestes ferrugineus, Tenebrio molitor, Oryzaephilus surinamensis, Trogoderma granarium, Tribolium castaneum, Tribolium confusum, Alphitobius diaperinus (adults/larvae), and Acarus siro (adults/nymphs). Extraction of A. oleracea was optimized on the base of the yield and content of spilanthol and other N-alkylamides which were analysed by HPLC-DAD-MS. Two concentrations of n-hexane or methanol extracts (500 ppm and 1000 ppm), obtained through Soxhlet extraction, were tested to acquire mortality data on the above-mentioned pests after 4, 8, and 16 h and 1 to 7 days of exposure. Both extracts achieved complete mortality (100.0%) of C. ferrugineus adults. In the case of A. diaperinus adults, mortalities were very low at any concentrations of both extracts. In general, the n-hexane extract was more efficient than methanol extract against almost all species and stages. Considering both extracts, the susceptibility order, from most to least susceptible species/stage, was C. ferrugineus adults > A. diaperinus larvae > C. ferrugineus larvae > T. granarium adults > T. molitor larvae > O. surinamensis adults > O. surinamensis larvae > T. confusum larvae > T. castaneum larvae > A. siro adults > T. molitor adults > A. siro nymphs > T. granarium larvae > T. castaneum adults > T. confusum adults > A. diaperinus adults. Our research provides useful knowledge on the efficacy of N-alkylamides-rich A. oleracea extracts as grain protectants, pointing out the importance of targeting the most susceptible species/ developmental stages.