| tThe 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)--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 maincompounds of the oil were limonene (40.6%), myristicin (24.3%), dillapiol (9.4%) and -pinene (5.5%). Inorder 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 wereinvestigated 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 compoundswere synergistic when topically applied, especially myristicin and (Z)--ocimene, or limonene |