Fumigant toxicity and physiological effects of spearmint (Mentha spicata, Lamiaceae) essential oil and its major constituents against Reticulitermes dabieshanensis

Abstract

This study evaluated the chemical components of spearmint essential oil, and determined individually the efficacy of spearmint EO and its major constituents, and their mutual binary combination against Reticulitermes dabieshanensis. We also evaluated the activities of esterases (ESTs), glutathione S-transferases (GST) and Acetylcholinesterase (AChE) enzymes in treated insects. GC–MS analysis showed that the major constituents of spearmint EO were carvone (52.25 %), limonene (19.78 %), and dihydrocarvone (11.1 %). In fumigant toxicity assay, the spearmint EO achieved a LC50 value of 0.194 μl/L. The three major constituents, carvone, dihydrocarvone, and limonene were most effective against R. dabieshanensis, with LC50 values of 0.074, 0.155, and 2.650 μl/L, respectively. The toxicity assay of binary mixtures of carvone + dihydrocarvone, carvone + limonene and limonene + dihydrocarvone in all the used ratios showed the three major constituents exhibited synergistic effects against R. dabieshanensis. Spearmint EO and its major constituents showed significantly stronger insecticidal efficacies at the high temperature, with rapid insecticidal action. The increased activity of ESTs and GST were observed, but with the decreased activity of AChE in all treatments. In vitro experiments, all treatments showed significant inhibition of AChE activity, except for dihydrocarvone, with IC50 values were 0.871, 2.405, 2.653 and 4.343 μl/mL for limonene, carvone, carvone + limonene and carvone + dihydrocarvone, respectively. The results showed that the insecticidal efficacy of spearmint EO can be attributed to the major component, possibly carvone, with strong AChE inhibition properties. Hence, spearmint EO and its bioactive constituents have the potential to be used as new environmentally safe insecticides for controlling R. dabieshanensis.