Insecticidal and Antifeedant Activities of Plant Essential Oils Against Spodoptera frugiperda Larvae

The fall armyworm (Spodoptera frugiperda), a highly destructive invasive Lepidopteran pest, poses a serious threat to global agriculture, particularly maize production. Plant essential oils (EOs) represent a promising class of botanical pesticides owing to their diverse bioactivities and low environmental persistence. In this study, we evaluated the insecticidal and antifeedant activities of 40 commercially available EOs against third-instar S. frugiperda larvae. After an initial screening at 4 μL/mL, 10 EOs that caused ≥70% mortality at 72 h were selected for bioassays to estimate LC₅₀ value and chemical analysis by GC-MS. Contact toxicity assays showed that geranium EO had the highest activity (LC₅₀ = 2.105 μL/mL at 72 h), followed by cypress (2.123 μL/mL) and niaouli (2.391 μL/mL), whereas tea tree EO exhibited the lowest activity (3.592 μL/mL). Antifeedant tests revealed that clove EO caused the strongest feeding deterrence at both 24 h (antifeedant indices AFI = 72.8%) and 48 h (AFI = 63.4%), while most other EOs lost their deterrent effect within 48 h. GC-MS analysis of the 10 active EOs identified a complex mixture of monoterpenes, sesquiterpenes, and oxygenated derivatives; major constituents included D-limonene, 4-terpineol, carvacrol, caryophyllene, and longifolene. These results provide laboratory evidence that several plant EOs, particularly geranium, cypress, niaouli, and clove, possess strong insecticidal and antifeedant activities against S. frugiperda larvae, supporting their potential as eco-friendly botanical insecticides.