Bay Laurel ( Laurus nobilis ) essential oil: contact toxicity, detoxification enzyme inhibition, and antifeedant effects on Plodia interpunctella larvae

Abstract

Plant-derived pesticides such as essential oils provide promising, eco-friendly alternatives for managing pest-related damage in stored products. Increasing attention has focused on compounds with toxic or antifeedant effects for use in integrated pest management systems. This study evaluated the insecticidal activity of Laurus nobilis essential oil (EO) against Plodia interpunctella larvae using a filter paper contact bioassay at three concentrations (0.8%, 1.6%, and 3.2%). Nutritional indices and feeding deterrence were also assessed. The EO was rich in eucalyptol (39.46%), linalool (14%), α-terpinyl acetate (8.93%), and sabinene (7.34%). Toxicity assays showed 52% mortality within 3 h at the highest concentration (0.50 µL/cm2), while 72% mortality was reached after 48 h at 0.25 µL/cm2. Exposure at the LC50 value (0.16 µL/cm2) significantly reduced superoxide dismutase activity (1.423 U/mg protein) and glutathione-S-transferase activity (70 µmol/min/mg protein). Essential oil treatment also negatively affected nutritional indices, with the lowest relative growth rate (−0.24 mg/mg/day) and relative consumption rate (0.17 mg/mg/day) observed at the highest concentration (32 µL/pellet). Feeding deterrence was consistently high across treatments, averaging 97%. Overall, L. nobilis essential oil shows strong potential as a botanical insecticide through its contact toxicity, enzyme inhibition, and suppression of feeding behavior in P. interpunctella larvae.