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

Abstract

Peel oils from Citrus aurantifolia and C. reticulata cultivated in the Northeast of Brazil were analyzed by GC-FID (Gas Chromatography with Flame Ionization Detection) and GC-MS (Gas Chromatography Mass Spectrometric Detection). Their insecticidal activities and both of the enantiomeric forms of the main constituent limonene [(R)-(+)-Limonene) and (S)-(-)-Limonene)] were evaluated against Sitophylus zeamais under laboratory conditions. Results were compared with deltamethrin (K-obiol 25 CE) as a positive control. Chromatographic analysis of Citrus oils showed limonene as the main constituents, with 38.9% in C. aurantifolia and 80.2% in C. reticulata. Peel oil of C. reticulata proved to be more toxic than C. reticulata oil towards S. zeamais adult by contact, ingestion and fumigant tests (LC50 = 71.18 µL mL-1 LC50 = 1.52 µL g-1, LC50 =41.92 µL L-1 air, respectively). Non-significant difference was found between (R) and (S)-Limonene in contact and fumigant tests. However, (R)-Limonene in ingestion test exhibited higher toxicity against S. zeamais than the (S)-Limonene. Deltamethrin was much more toxic in contact and ingestion bioassays than Citrus oils and two enantiomeric forms of limonene. Repellent bioassay also revealed that C. reticulata oil was more repellent than C. aurantifolia. In the repellency test, S. zeamais adult was more susceptible to (S)-Limonene than the (R)-Limonene at a lower concentration. The results of this study suggested that, in addition to behavior effect on S. zeamais, the Citrus oils affected by different ways, i.e., via the cuticle, digestive and respiratory systems, and the two enantiomeric forms of limonene showed different insecticidal properties.