Integration of a Natural Biopesticide into Grain Storage Systems: Insecticidal Toxicity and Antifungal Activity of Mentha Pulegium Essential Oil

Abstract

Post-harvest losses of stored cereals are largely due to insects and phytopathogenic fungi, particularly in developing countries where storage conditions remain precarious. In the context of reducing the use of synthetic insecticides, essential oils are a promising alternative. This study evaluates (i) the insecticidal activity of Mentha pulegium L. (pennyroyal) essential oil against two major pests of stored commodities, Sitophilus oryzae L. and Tribolium castaneum Herbst, by inhalation and ingestion, and (ii) its in vitro antifungal activity against three phytopathogenic fungi, Rhizoctonia spp., Fusarium spp. and Alternaria spp.

The essential oil was extracted by hydrodistillation using a Clevenger apparatus and then characterised by GC-MS. Insecticidal bioassays were performed on adults fed or exposed to different doses of the essential oil; mortalities were corrected using the Abbott formula and the LC₅₀/LD₅₀ estimated by probit analysis. Antifungal activity was studied by direct comparison on PDA medium supplemented with 0.25 and 0.5% (v/v) essential oil.

The essential oil of M. pulegium is dominated by pulegone (≈ 60%) and menthone (≈ 7.5%). When inhaled, it induces up to 100% mortality in both insect species at high doses, with a lower LC₅₀ in S. oryzae (54.20 µL/L of air) than in T. castaneum (93.31 µL/L). When ingested, the LD₅₀ is lower in T. castaneum (46.01 µL/mg of grain) than in S. oryzae (66.02 µL/mg). In vitro, M. pulegium strongly inhibits the mycelial growth of Rhizoctonia spp. (≈ 90%), Alternaria spp. (≈ 85%) and, to a lesser extent, Fusarium spp. (54–66%).

These results confirm the potential of M. pulegium as a natural biopesticide with dual insecticidal and antifungal action for the protection of stored commodities.