Lethal effects of essential oils from eight Iranian pharmaceutical plants against two stored-product lepidopterans and their chemical composition

To produce high-quality food and minimize risks from chemical applications, employing economically viable alternative methods without chemical-related drawbacks is vital. Plant essential oils (EOs) have garnered attention as potential insect pest control agents. The current study examines the lethal effects of plant EOs on the Mediterranean flour moth (Ephestia kuehniella Zeller) and the Indian meal moth (Plodia interpunctella (Hübner)).

This study examined the fumigant toxicity of eight Iranian pharmaceutical plant EOs: sweet wormwood (Artemisia annua), black cumin (Elwendia persica), Shirazi thyme (Zataria multiflora), costmary (Tanacetum balsamita), galbanum (Ferula gummosa), myrtle (Myrtus communis), lemon (Citrus × limon) and marjoram (Origanum majorana) against eggs, first instar larvae, and adults of P. interpunctella and E. kuehniella. Insects were maintained under controlled conditions at 27 ± 2 °C, 60 ± 5% R.H., and a photoperiod of 14L:10D. Gas Chromatography-Mass Spectrometry (GC-MS) was employed to identify the compounds present in the tested plant EOs. The lethal concentration (LC) values were estimated using probit analysis based on data obtained from preliminary and main bioassays.

The predominant compounds (in term of %) identified in the EOs were as follows: A. annua: Camphor (41.388), 1,8-Cineole (13.431); E. persica: α-Terpinolen (31.622), Limonene (14.524), Propanal, 2-methyl-3-phenyl- (13.180); Z. multiflora: Carvacrol (60.593) and Terbutaline, tris (trimethyl silyl) ether (11.229); T. balsamita: Carvone (42.607), (‒)-Thujanone (17.600); F. gummosa: β-Thujene (34.234), β-pinene (22.371); M. communis: δ-3-Carene (30.549), 1,8-Cineole (19.580), Carvacrol (13.987); C. limon: Limonene (55.131), and O. majorana: (‒)-Terpinen-4-ol (34.138), γ-Terpinene (15.494). EOs exhibited comparable ovicidal activity against the eggs of both species. Notably, A. annua EO displayed the highest efficacy, with LC50 values of 58.12 μl/L air for E. kuehniella and 51.55 μl/L air for P. interpunctella. For E. kuehniella, the EOs of M. communis, Z. multiflora, and F. gummosa followed suit in terms of efficacy, while E. persica, O. majorana, T. balsamita, and C. limon EOs demonstrated the lowest ovicidal activity. Conversely, regarding P. interpunctella, the EOs of M. communis, F. gummosa, Z. multiflora and E. persica exhibited the next highest efficacy, whereas T. balsamita, O. majorana, and C. limon EOs displayed the least ovicidal activity. Eggs of P. interpunctella exhibited slightly greater sensitivity compared to those of E. kuehniella. The EOs of M. communis and A. annua demonstrated the highest efficacy against first instar larvae of both species, with estimated LC50 values of 84.19 and 76.64 μl/L air, respectively. Following closely, EOs of A. annua and F. gummosa exhibited notable effectiveness against first instar larvae of E. kuehniella, while EOs of M. communis and Z. multiflora showed similar efficacy against first instar larvae of P. interpunctella. Conversely, the EOs of C. limon, T. balsamita, O. majorana and E. persica displayed the least larvicidal activity against E. kuehniella larvae, whereas the EOs of O. majorana and E. persica demonstrated the lowest efficacy against P. interpunctella larvae. Consistent with the findings concerning the eggs, the first instar larvae of P. interpunctella demonstrated slightly greater sensitivity compared to those of E. kuehniella. The EOs exhibited similar lethal effects against adults of both species. Notably, M. communis EO exhibited the highest lethality against male and female adults of both species, followed by EOs of A. annua, E. persica and Z. multiflora. Conversely, EOs of C. limon, T. balsamita, F. gummosa and O. majorana displayed the least lethal effect. Interestingly, female adults showed greater tolerance compared to male adults. Moreover, similar to the observations with eggs and first instar larvae, adults of P. interpunctella displayed slightly greater sensitivity than those of E. kuehniella.

The study findings highlight the significant lethal effects of various plant EOs, indicating promising alternatives to hazardous chemical pesticides. Iran's rich pharmaceutical plant flora contains diverse compounds, including volatile ones like EOs, which can be explored for their medicinal, insecticidal, fungicidal and other properties. The availability of formulations derived from complete plant EOs or their active components (i.e. insecticides, acaricides, fungicides and herbicides) in the market suggests the potential for developing more potent and environmentally friendly biorational pesticides through dedicated research in this field.