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In this study, we analyzed the components of Mentha spp. essential oils (EOs) and evaluated their major constituents and binary combinations against Reticulitermes dabieshanensis. We also determined the activities of esterases (ESTs), glutathione S-transferases (GSTs), and acetylcholinesterase activity (AChE) in treated insects. According to our findings, the most effective oils were those obtained from M. citrata (with the major constituent linalool constituting 45.1%), M. piperita (menthol, 49.1%), and M. spicata (carvone, 69.0%), with LC50 values of 0.176, 0.366, and 0.146 μL/L, respectively. The LC50 values were recorded for linalool (0.303 μL/L), followed by menthol (0.272 μL/L), and carvone (0.147 μL/L). The insecticidal potency increased with binary mixtures of major active constituents, with carvone strongly synergizing the toxicity of linalool and menthol against R. dabieshanensis. Compared to the control, except for M. citrata treated with no difference in α-NA or GST activity, the activities of ESTs and GST in other treatment groups were significantly increased. Additionally, our results found that Mentha spp. EOs and their major constituents inhibited the activity of AChE in vivo and in vitro. Finally, we performed a structure-based virtual screening of linalool, menthol, and carvone to identify that linalool had the greatest potential to bind to the active site of AChE. The present study suggests that Mentha spp. EOs could provide an additional approach for the management of termites over synthetic insecticides. [ABSTRACT FROM AUTHOR]

The utilization of new plant-based fumigants is one of the most important green control methods for safe storage and protection of grain. The rusty grain beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), is a common stored grain pest that causes a great loss of stored grain every year. This study determined that, Schizonepeta tenuifolia Briq. spike (SS) powder had strong fumigant insecticidal effectiveness against C. ferrugineus. Moreover, the volatile eluates (VEs) of SS extracted with Porapak™ Q adsorbent at a flow rate of 600 mL/min exhibited higher insecticidal activity against C. ferrugineus adults than the larvae; the VEs LC 50 of C. ferrugineus adults were 14.93%− 24.83% of those of C. ferrugineus larvae. The temperature, not the age of C. ferrugineus adults, significantly influenced the fumigation effect of SS VEs; at relatively low temperature (15 ℃) the SS VEs showed quicker and more efficient fumigant activity than at a high temperature (30–35 ℃). In addition, S. tenuifolia VEs showed better fumigation effects against Oryzaephilus surinamensis (Coleoptera: Silvanidae) and Sitophilus oryzae (Coleoptera: Curculionidae) compared to Tribolium castaneum (Coleoptera: Tenebrionidae). The four most abundant components of SS volatiles analyzed by GC-MS were pulegone (62.62%), isomenthone (18.34%), 2-isopropyl-2,5-dimethylcyclohexanone (2.45%), and isopulegone (1.32%), in order by their peak area ratio. Toxicity testing of the two compounds with the largest proportion indicated that only pulegone had insecticidal activity against C. ferrugineus adults with a LC 50 (8.90 mL/L) at 72 h. Consistent with VEs, temperature also greatly affect the fumigant activity of pulegone and at low temperature (15 ℃) the pulegone showed more quick and effective insecticidal activity against C. ferrugineus adults. We further found that both VEs and pulegone can inhibit carboxylesterase (CarE), peroxidase (POD), and superoxide dismutase (SOD) in vivo and in vitro, especially the inhibition rate of carboxylesterase, which reached 84.87% and 63.82% at 24 h in vivo, which suggested that the fumigant insecticidal activity of SS VEs and pulegone may partly be mediated by affecting the detoxification and metabolism enzyme system of C. ferrugineus. Therefore, both S. tenuifolia and pulegone can be used as botanical fumigant to potentially control stored grain pests. • The powder and volatile eluates of Schizonepeta tenuifolia spike (SS) had fumigant insecticidal activity against rusty grain beetle (Cryptolestes ferrugineus). • Pulegone, the SS volatiles component showed good fumigation effect against Cryptolestes ferrugineus. • Low temperature significantly enhanced the fumigation effect of SS volatile eluates and pulegone against Cryptolestes ferrugineus. • SS volatile eluates and pulegone could significantly inhibit carboxylesterase activity. [ABSTRACT FROM AUTHOR]

• Illicium verum powder and its volatiles had fumigation activity to Cryptolestes ferrugineus. • Only the volatile component trans -anethole showed effective biological activity. • Estragole could did significantly enhance fumigant efficiency of trans -anethole. • Trans -Anethole affects the beetles acetylcholinesterase activity of nervous system. The safe storage and protection of grain includes the exploitation of plant-based fumigants as a green control technology. This study first determined the fumigant toxicity of 12 traditional Chinese medicinal plants against adults of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), one of the most ubiquitous and pestilent grain storage pests worldwide. Exposure to volatiles released from Illicium verum Hook. f. powder was found to be by far the most lethal. Illicium verum power and its volatiles eluent were then confirmed to be highly effective in killing both larvae and adults of C. ferrugineus. Star anise volatiles also showed good biological activity against Lasioderma serricorne (Fabricius) and Sitophilus zeamais Motschulsky, but not Tribolium castaneum Herbst. No significant differences were found in mortality of the adults of the rusty grain beetle when exposed at different temperatures ranging from 15−35°C. Gas chromatography-mass spectrometry (GC–MS) analysis showed that the main components of the eluent of star anise powder were trans -anethole (62.60%), estragole (23.70%), linalool (3.66%) and d -limonene (2.15%). In the fumigation test using synthetic standards of these four chemicals, only trans -anethole showed effective biological activity with exposure to 30 mL/L trans -anethole for 24 h resulting in 100% mortality of rusty grain beetle adults. Estragole did significantly enhance fumigant efficiency of trans -anethole. We further found that trans -anethole affects the beetles acetylcholinesterase activity, which was inhibited and decreased by 64.48% within 24 h. The results therefore show that trans -anethole, the major component of star anise volatiles contributes to its fumigant toxicity against C. ferrugineus by, at least partly, affecting its insect nervous system. Hence, star anise or its biologically active substances show very good potential to be used as a botanical insecticide to control C. ferrugineus. [ABSTRACT FROM AUTHOR]

Monoterpenes are the major components of essential oils from many aromatic plants, partly contributed to the insecticidal properties of essential oils. In this study, the fumigation activity of 40 pure monoterpenes against fruitfly, Drosophila melanogaster , were evaluated. Results from fumigation tests revealed that terpinolene, 3-carene, eugenol, thymol, carvacrol, isoeugenol, citral, (±)-citronellal, cuminaldehyde, (−)-verbenone, and (+)-pulegone exhibited strong fumigation activity against D . melanogaster . In addition, the (±)-citronellal and (+)-pulegone (aldehydes and ketones) were the most toxic monoterpenes to D . melanogaster with LC 50 values of 0.015 and 0.02 μl/L, respectively. Oxygenated monoterpenes were found to be with higher toxicity as compared with monoterpene hydrocarbons. The present results indicated that (±)-citronellal and (+)-pulegone exhibit a potential for the development of new botanical insecticides against the D . melanogaster , suggesting that further studies of a number of medically important dipterans might be warranted. [ABSTRACT FROM AUTHOR]

• Spearmint EO and its major constituents have toxic effects on R. dabieshanensis. • The toxic efficacy increased with increasing temperature against R. dabieshanensis. • Carvone highly synergized the toxicity of limonene and dihydrocarvone. • All treated termite showed the increased activity of detoxifying enzymes. • Spearmint EO and its constituents inhibited activity of AChE in vivo and in vitro. 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 LC 50 value of 0.194 μl/L. The three major constituents, carvone, dihydrocarvone, and limonene were most effective against R. dabieshanensis , with LC 50 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 IC 50 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. [ABSTRACT FROM AUTHOR]