Toxicological Activity of Some Plant Essential Oils Against Tribolium castaneum and Culex pipiens Larvae

In the present work, essential oils (EOs) from Schinus terebinthifolius (ripe and unripe fruits and leaves), Origanum majorana (air-dried aerial parts), and Psidium guajava (leaves) were assayed for their insecticidal activity against red flour beetle (Tribolium castaneum) and Culex mosquito larvae (Culex pipiens). Several components were identified in the EOs using Gas chromatography–mass spectrometry (GC/MS), of which Δ-3-carene (25.9%), γ-terpinene (19.4), and γ-elemene (7.1%) were the major ones in S. terebinthifolius ripe fruits, α-pinene (48.9%), germacrene D (12.9%), and α-thujene (7.7%) in S. terebinthifolius unripe fruits, γ-elemene (11.7%), spathulenol (10.1%), β-elemene (9.2%), and p-cymene (9.1%) in S. terebinthifolius leaves, α-pinene (25.5%), (E)-caryophyllene (15.7%), (E)-nerolidol (16.7%), and cedran-8-ol (8.8%) in P. guajava leaves, and terpinen-4-ol (21.7%), γ-terpinene (16.5%), and sabinene (10.1%) in O. majorana air-dried aerial parts. The lethal concentration (LC50) was calculated for tested EOs at different time periods (after 6, 12, 24, 48, and 72 h). After 6 h of treatment, the LC50 was 33.3 and 6.8 µg/L air for S. terebinthifolius ripe and unripe fruits, respectively, and >40 µg/L air for EOs of S. terebinthifolius leaves, O. majoranaair-dried aerial parts, and P. guajava leaves. After 24 h of treatment, the LC50 was 4.2, 40, and 6.1 µg/L air for EOs of S. terebinthifolius ripe fruits and leaves, O. majorana leaves, and P. guajava leaves, respectively. On the other hand, the LC50 values decreased when the exposed period was increased to 72 h, and were