Mite color alteration and acaricidal activity of 3,7-dimethyl-2,6-octadienal and its structural analogues against the stored food pest mite Tyrophagus putrescentiae.

Acaricidal activities of the active component isolated from Melissa officinalis oil and its structural analogues against Tyrophagus putrescentiae were evaluated using fumigant and contact bioassays. The structure of 3,7-dimethyl-2,6-octadienal purified from M. officinalis oil was elucidated with EI-MS, 1H- and 13C-NMR, 1H-1H COSY, and DEPT-NMR. Based on the LD50 values of 3,7-dimethyl-2,6-octadienal analogues in fumigant and contact bioassays, respectively, 2,4-octadienal showed the highest activity (LD50 = 2.09 µg/cm3 and 11.08 µg/cm2), followed by 3,7-dimethyl-6-octenal (3.60 µg/cm3 and 29.34 µg/cm2), 3,7-dimethyl-2,6-octadienal (6.18 µg/cm3 and 36.17 µg/cm2), 2-octenal (7.45 µg/cm3 and 47.36 µg/cm2) and M. officinalis oil (8.89 µg/cm3 and 23.83 µg/cm2). Comparing the acaricidal activities of the aldehyde group based on the degree of unsaturation, 2,4-octadienal containing two double bonds was more potent than 2-octenal with a single double bond. Based on the acaricidal activities of the methyl group, on the other hand, 3,7-dimethyl-6-octenal containing a single double bond was more acaricidal than 3,7-dimethyl-2,6-octadienal with two double bonds. These results indicate that 3,7-dimethyl-2,6-octadienal analogues are useful to control food mites.