Synergistic Insecticidal Effects of Ethanol Leaf Extracts of Azadirachta indica (neem), Laurus nobilis (Bay Leaf) and Hyptis suaveolens (Bush Mint) against Adult American Cockroach (Periplaneta americana)

This study evaluated the insecticidal activity of ethanol leaf extracts of Azadirachta indica (Neem), Laurus nobilis (Bay leaf), and Hyptis suaveolens (Bush mint), including their synergistic combinations, against adult Periplaneta americana. Qualitative phytochemical screening showed high levels of alkaloids, terpenoids, phenols, and saponins in Neem; abundant flavonoids and essential oils in Bay leaf; and rich terpenoids and saponins in Bush mint. Bioassays conducted on 200 adult cockroaches revealed clear concentration- and time-dependent effects. Neem was the most potent single extract, achieving 10 (100%) knockdown and 8 (80%) mortality at 20 mg/mL within 6 h, with knockdown increasing from 4 (40%) at 1 h to 10 (100%) at 6 h. Bay leaf and Bush mint showed moderate activity, each producing a maximum of 6 (60%) mortality at 20 mg/mL after 6 h, with knockdown reaching 8 (80%)–9 (90%). Synergistic treatments significantly enhanced efficacy: the Neem + Bay leaf combination at 15 mg/mL achieved 10 (100%) knockdown and 8 (80%) mortality, outperforming individual extracts; Neem + Bush mint reached 9 (90%) knockdown and 7 (70%) mortality. The triple combination evaluated at 5 mg/mL produced rapid knockdown (8 [80%] at 6 h) but did not exceed the mortality of the Neem + Bay leaf mixture. Statistical analyses supported these trends, with strong positive correlations between concentration/time and mortality (r ≈ 0.93–0.98, p < 0.05) and significant differences among treatments by ANOVA (p < 0.05). Overall potency ranked as: Neem + Bay leaf > Neem > Neem + Bush mint > Bay leaf ≈ Bush mint > triple combination. These findings support neem-based synergistic botanicals as eco-friendly alternatives for household cockroach control.