Assessment of the Bio-pesticidal Activity of Bay Leaf (Laurus nobilis) Extract against Adult American Cockroach (Periplaneta americana)

Cockroach infestation poses significant public health risks due to their role in pathogen transmission. This study evaluated the bio-insecticidal activity of Laurus nobilis (bay leaf) ethanolic extract against 240 adults Periplaneta americana under laboratory conditions. Sixty adult cockroaches each were exposed to three extract concentrations (T1: 1.5 g/m², T2: 1.0 g/m², T3: 0.5 g/m²) and a control for 8 hours. Phytochemical screening of the extract revealed the presence of alkaloids, flavonoids, tannins, phenols, saponins, glycosides, steroids, terpenoids, coumarins and abundant essential oils, all of which are bioactive metabolites known to contribute to insect toxicity. Mortality, knockdown time (KT₅₀, KT₉₀) and lethal dose (LD₅₀, LD₉₀) were assessed. By 8 hours, all treatments achieved 100% mortality, whereas the control showed 0% mortality. Treatment T1 exhibited the fastest toxic action, with cumulative mortality increasing to 25% by 4 hours, KT₅₀ = 2.80 hours and KT₉₀ = 5.60 hours. Treatment T2 produced moderate effects, recording 20% mortality at 4 hours, KT₅₀ = 4.10 hours and KT₉₀ = 7.90 hours. Treatment T3 showed slower initial activity (0–15% deaths at 1–4 hours) but reached complete mortality by 8 hours, with KT₅₀ = 5.50 hours and KT₉₀ = 10.20 hours. LD₅₀ values were lowest for T1 (11.20 mg/cm²), followed by T2 (17.00 mg/cm²) and T3 (23.80 mg/cm²), while LD₉₀ followed the same trend (T1: 25.30, T2: 33.50, T3: 40.70 mg/cm²). ANOVA indicated significant differences among treatments (F = 16.42, p = 0.001), with Tukey HSD confirming T1 as significantly more effective than T2 and T3. The strong insecticidal performance is attributed to the synergistic action of terpenoids together with phenolic compounds and flavonoids that induced oxidative stress, neurotoxicity and metabolic disruption in cockroaches. These findings demonstrate dose-dependent and time-dependent bio-pesticidal effects of L. nobilis extract, supporting its potential as a natural, eco-friendly alternative to synthetic insecticides for sustainable cockroach management.