Introduction
Stored-product insects cause significant quantitative and qualitative losses to agricultural commodities worldwide, particularly in dried fruits and nuts. Among these pests, the dried-fruit beetle, Carpophilus hemipterus (L.) (Coleoptera: Nitidulidae), is considered one of the most destructive species due to its high reproductive potential, broad host range, and ability to infest both stored and semi-processed products. Infestation by this beetle not only results in direct feeding damage but also facilitates microbial contamination, leading to reduced market value and potential health risks for consumers. Chemical fumigants such as phosphine and methyl bromide have traditionally been used to control stored-product pests. However, the extensive and prolonged use of synthetic fumigants has led to several serious concerns, including the development of insect resistance, environmental pollution, residues in food products, and adverse effects on non-target organisms and human health. In addition, the phase-out or restriction of some conventional fumigants due to international regulations has intensified the need for safer and more sustainable alternatives in stored-product pest management. In recent years, plant-derived essential oils have gained increasing attention as potential alternatives to synthetic insecticides. Essential oils are complex mixtures of volatile secondary metabolites, primarily terpenoids and phenolic compounds, which exhibit a wide range of biological activities, including insecticidal, repellent, antifeedant, and fumigant effects. Their high volatility, rapid degradation, and relatively low mammalian toxicity make essential oils particularly suitable for use as fumigants in stored-product protection. Pennyroyal (Mentha longifolia L.), a perennial aromatic plant belonging to the family Lamiaceae, is widely distributed in many regions and has been traditionally used for medicinal and culinary purposes. The essential oil of M. longifolia is rich in bioactive compounds such as pulegone, menthone, and 1,8-cineole, which have been reported to possess antimicrobial and insecticidal properties. Several studies have demonstrated the toxicity of pennyroyal essential oil against different insect pests; however, information regarding its fumigant activity against C. hemipterus remains limited. Given the economic importance of C. hemipterus and the growing demand for eco-friendly pest control strategies, evaluating the fumigant toxicity of plant essential oils is of considerable interest. The present study aims to investigate the fumigant toxicity of pennyroyal (M. longifolia) essential oil against adults of C. hemipterus. The findings of this research may contribute to the development of plant-based fumigants as effective and environmentally benign alternatives for the management of stored-product beetles.
Materials and Methods
Adults of the dried-fruit beetle C. hemipterus were collected from a date storage facility in Anbarabad (Kerman Province, Iran) and reared for several generations under controlled laboratory conditions (25 ± 2 °C, 20 ± 10% RH, and darkness) on dates supplemented with watermelon as a moisture source. The aerial parts of M. longifolia were collected from a natural habitat near Rayen (Kerman Province) and the essential oil was extracted by hydrodistillation using a Clevenger apparatus. The obtained oil was stored at −4 °C in dark glass vials until use, and its chemical composition was analyzed by GC–MS. Fumigant bioassays were conducted in sealed plastic containers to evaluate the toxicity of the essential oil against young adult beetles. Preliminary tests were performed to determine the appropriate concentration range, followed by dose–response assays using six concentrations (20–120 µL L⁻¹ air) to estimate LC₅₀ values at 24, 48, and 72 h. Mortality was assessed based on lack of movement in response to gentle probing, corrected using Abbott’s formula, and analyzed by probit regression. LT₅₀ values were determined at selected concentrations (20 and 35 µL L⁻¹) by recording mortality at 6-h intervals up to 72 h under the same environmental conditions.

Results and Discussion
The GC–MS analysis of M. longifolia essential oil identified 16 compounds, with pulegone (63.24%) as the dominant component, followed by 1,8-cineole (9.14%), menthofuran (9.11%), menthone isomers (1.82–4.41%), and piperitenone oxide (1.3–2.53%). Fumigant bioassays showed strong toxicity against adult C. hemipterus, with LC₅₀ values decreasing significantly over time from 35.58 µL L⁻¹ at 24 h to 5.57 µL L⁻¹ at 72 h, and LT₅₀ decreasing with increasing concentration (88.92 h at 20 µL L⁻¹ to 26.64 h at 35 µL L⁻¹). These results confirm a clear dose- and time-dependent fumigant effect. The observed toxicity is likely associated with the high content of volatile monoterpenoids such as pulegone, menthofuran, and 1,8-cineole, which can disrupt insect nervous system pathways, including octopaminergic receptors and acetylcholinesterase. Compared with other plant essential oils reported for C. hemipterus, M. longifolia shows comparable or superior efficacy, with rapid action, broad-spectrum activity against multiple stored-product pests, high volatility, rapid degradation, low mammalian toxicity, and compatibility with integrated pest management strategies.

Conclusion
These findings suggest that M. longifolia essential oil is a promising, eco-friendly fumigant for controlling C. hemipterus, although further research is needed to evaluate its effectiveness under industrial storage conditions and develop controlled-release formulations.