Chemical composition and bioactivity of Citrus aurantifolia and Citrus reticulata peel oils and enantiomers of their major constituents against Sitophilus zeamais.

Peel oils from Citrus aurantiifolia and C. reticulata cultivated in northeastern Brazil were analyzed using gas chromatography with flame ionization detection and gas chromatography-mass spectrometry. The insecticidal activity of the oils and both enantiomeric forms of the main constituent – limonene [(R)-(+)-limonene and (S)-(−)-limonene] – was evaluated against Sitophylus zeamais under laboratory condition. The results were compared with deltamethrin as the positive control. Chromatographicanalysis of the Citrus oils demonstrated limonene to be main constituent, accounting for 38.9% of the C. aurantiifolia oil and 80.2% of the C. reticulata oil. Peel oil fromC. reticulata proved to be more toxic to S. zeamais adults in the contact, ingestion andfumigant tests (LC₅₀ = 71.18 μL mL⁻¹, 1.52 μL g⁻¹ and 41.92 μL L⁻¹ of air, respectively) than the C. reticulata oil. A non-significant different was found between (R) and (S)-limonene in the contact and fumigant tests. However, (R)-limonene exhibited greater toxicity against S. zeamais than the (S)-limonene during the ingestion assay. Deltamethrin was much more toxic in the contact and ingestion bioassays than the Citrusoils and the two enantiomeric forms of limonene. The C. reticulata oil was more repellent than C. aurantiifolia. In the repellency test, S zeamais adults were more susceptible to (S)-limonene than (R)-limonene. The results of the present study suggest that theseCitrus oils and the two enantiomeric forms of limonene have toxic effects on S. zeamaisin different ways (i.e., via the cuticle, digestive system and respiratory system) as well as a behavioral effect (repellency).