Chemical Constituents of the Essential Oil Extracted from Elsholtzia densa and Their Insecticidal Activity against Tribolium castaneum and Lasioderma serricorne

Storage pests pose a great threat to global food security. Here, we found that the essential oil (EO) extracted from E. densa possesses obvious effects against the insects that threaten stored-products. In this work, we investigated the chemical constituents of the essential oil extracted from Elsholtzia densa, and their insecticidal (contact and fumigant) toxicity against Tribolium castaneum and Lasioderma serricorne. A total of 45 compounds were identified by GC-MS, accounting for 98.74% of the total EO. Meanwhile, 11 compounds were isolated from the EO, including limonene, β-caryophyllene, ρ-cymene, trans-phytol, α-terpineol, linalool, acetophenone, 1,8-cineole, ρ-cymen-7-ol, 1-O-cerotoylgly-cerol, and palmitic acid. Furthermore, acetophenone, ρ-cymen-7-ol, and 1-O-cerotoylgly-cerol were isolated for the first time from Elsholtzia spp. The results of the bioassays indicated that the EO had the property of insecticidal toxicity against T. castaneum and L. serricorne. All of the compounds showed different levels of insecticidal toxicity against the two species of insects. Among them, 2-ethyl-1H-imidazole had no insecticidal toxicity against T. castaneum, but possessed fumigant and obvious contact toxicity against L. serricorne. ρ-Cymen-7-ol had beneficial insecticidal toxicity against the two species of insects, and fumigant toxicity against L. serricorne. ρ-Cymen-7-ol (LD(50) = 13.30 μg/adult), 1-octen-3-ol (LD(50) = 13.52 μg/adult), and 3-octanol (LD(50) = 17.45 μg/adult) showed significant contact toxicity against T. castaneum. Acetophenone (LD(50) = 7.07 μg/adult) and ρ-cymen-7-ol (LD(50) = 8.42 μg/adult) showed strong contact toxicity against L. serricorne. ρ-Cymene (LC(50) = 10.91 mg/L air) and ρ-cymen-7-ol (LC(50) = 10.47 mg/L air) showed powerful fumigant toxicity to T. castaneum. Limonene (LC(50) = 5.56 mg/L air), acetophenone (LC(50) = 5.47 mg/L air), and 3-octanol (LC(50) = 5.05 mg/L air) showed obvious fumigant toxicity against L. serricorne. In addition, the EO and its chemical compounds possessed different levels of repellent activity. This work provides some evidence of the value of exploring these materials for insecticidal activity, for human health purposes. We suggest that the EO extracted from E. densa may have the potential to be developed as an insecticidal agent against stored product insect pests.