Insecticidal Activity of Monoterpenoids Against Motschulsky and Herbst: Preliminary Structure-Activity Relationship Study.

To contribute to the search for effective substances in pest control, this study describes the fumigant and contact toxicity against and of four essential oils (EOs) and some of their major chemical constituents. The EOs from , , and were obtained by steam distillation and chemically characterized using GC-MS. In the development of research, some monoterpenoids were isolated from the EOs, others were purchased commercially, and some were synthesized from the most active monoterpenoids present in EOs. The main components in the EOs were dill ether (28.56%), α-phellandrene (25.78%) and carvone (23.67%) for , piperitone oxide (30.40%) and pulegone (25.91%) in , pulegone (37.40%) and p-menth-3-en-8-ol (11.83%) for , and dihydrotagetone (32.13%), myrcene epoxide (19.64%) and β-myrcene (5.30%) for . The results highlight the fumigant action (LC) and contact toxicity (LD) of EO from against (LC of 4.8 µL/L air and LD of 6.5 µg/insect) and (LC of 7.0 µL/L air and LD of 5.81 µg/insect). Among the chemical constituents evaluated, R-carvone piperitone oxide and R-pulegone stand out for their insecticidal potential against (LC between 3.0 and 42.4 µL/L, while LD between 14.9 and 24.6 µg/insect) and (LC between 2.2 and 4.8 µL/L, while LD between 4.8 and 13.1 µg/insect). Preliminary structure-activity analysis suggests that the presence of the carbonyl group with conjugated double bonds in cyclic monoterpenes is important for the insecticidal potential exhibited.