Evaluation of benzaldehyde derivatives from Morinda officinalis as anti-mite agents with dual function as acaricide and mite indicator

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS virus with 12-30% fatality rate. Despite severity of the disease, any medication or treatment for SFTS has not developed yet. One approach to prevent SFTS spreading is to control the arthropod vector carrying SFTS virus. We report that 2-methylbenzaldehyde analogues from M. officinalis have a dual function as acaricide against Dermatophagoides spp. and Haemaphysalis longicornis and indicator (color change) against Dermatophagoides spp. Based on the LD 50 values, 2,4,5-trimethylbenzaldehyde (0.21, 0.19, and 0.68 μg/cm³) had the highest fumigant activity against D. farinae, D. pteronyssinus, and H. longicornis, followed by 2,3-dimethylbenzaldehyde (0.46, 0.44, and 0.79 μg/cm³), 2,4-dimethylbenzaldehyde (0.66, 0.59, and 0.95 μg/cm³), 2,5-dimethylbenzaldehyde (0.65, 0.68, and 0.88 μg/cm³), 2-methylbenzaldehyde (0.95, 0.87, and 1.28 μg/cm³), 3-methylbenzaldehyde (0.99, 0.93, and 1.38 μg/cm³), 4-methylbenzaldehyde (1.17, 1.15, and 3.67 μg/cm³), and M. officinalis oil (7.05, 7.00, and 19.70 μg/cm³). Furthermore, color alteration of Dermatophagoides spp. was shown to be induced, from colorless to dark brown, by the treatment of 2,3-dihydroxybenzaldehyde. These finding indicated that 2-methylbenzaldehyde analogues could be developed as functional agent associated with the arthropod vector of SFTS virus and allergen.