Comparative toxicity of Helosciadium nodiflorum essential oils and combinations of their main constituents against the cabbage looper, Trichoplusia ni (Lepidoptera)

The chemical composition of the essential oils from the aerial parts of Helosciadium nodiflorum Apiaceae), obtained from two different localities in Italy, were analyzed by gas chromatography/mass spectrometry (GC/MS). Sample 1 (collected from Sulmona) was dominated by phenylpropanoids (49.1%) with myristicin (49.1%), (Z)-β-ocimene (19.0%), limonene (7.8%) and terpinolene (7.1%) as major constituents. Sample 2 (collected from Colfiorito) was mainly composed of monoterpene hydrocarbons (58.7%) and the main compounds of the oil were limonene (40.6%), myristicin (24.3%), dillapiol (9.4%) and β-pinene (5.5%). In order to determine relationships between the chemical composition and insecticidal activity of the oils, comparative and synergistic interactions of the main constituents of H. nodiflorum essential oils were investigated in third-instar larvae of the cabbage looper, Trichoplusia ni, via a contact toxicity bioassay. In the case of sample 1, myristicin was identified as a major active principle while in sample 2, limonene, myristicin and dillapiol were main insecticidal constituents. Several combinations of these compounds were synergistic when topically applied, especially myristicin and (Z)-β-ocimene, or limonene.