Chemical composition and bioactivity of Thymus daenensis Celak (Lamiaceae) essential oil against two lepidopteran stored-product insects

Abstract

Chemical composition of the Thymus daenensis essential oil and its toxicity was investigated against the first and third instar larvae and adults of Ephestia kuehniella and Plodia interpunctella. Chemical composition of the volatile oil was studied by gas chromatography–mass spectrometry (GC–MS). Carvacrol (37.0%), thymol (12.8%), β-caryophyllene (7.6%), and geraniol (5.74) were found to be the major constituents of the oil. In fumigant toxicity, the adult stage of E. kuehniella and P. interpunctella (lc₅₀ values of 0.191 and 0.27 μL/L, respectively) were more sensitive to T. daenensis essential oil than first and third instar larvae. In both pests, sensitivity of larvae decreased from first to third instar larvae. However, the first instar larvae of E. kuehniella (lc₅₀=16.30 μL/L) was more sensitive to T. daenensis essential oil than P. interpunctella (lc₅₀=25.32 μL/L) but sensitivity of the third instar larvae of E. kuehniella (lc₅₀=44830 μL/L) was less than P. interpunctella (lc₅₀=3480 μL/L). Repellency of the essential oil in both species was proportional to essential oil concentration. Adults of E. kuehniella with an rc₅₀ value of 0.69 μL/L were more sensitive to repellent effect of the essential oil than adults of P. interpunctella with rc₅₀ value of 6.88 μL/L.

Keywords:

• Ephestia kuehniella
• Plodia interpunctella
• repellency
• fumigant toxicity
• essential oil

Acknowledgement

We are grateful to the research vice presidency of Vali-e-Asr University of Rafsanjan for grant to Dr. Izadi.