Bioactivity of Different Chemotypes of Oregano Essential Oil against the Blowfly Calliphora vomitoria Vector of Foodborne Pathogens

Blowflies play a substantial role as vectors of microorganisms, including human pathogens.The control of these insect pests is an important aspect of the prevention of foodborne diseases,which represent a significant public health threat worldwide. Among aromatic plants, spices essential oils (EOs) are the most suitable to protect food from insect pests. In this study, we determined thechemical composition of three oregano EOs and assessed their toxicity and deterrence to ovipositionagainst the blowfly Calliphora vomitoria L. The chemical analyses showed that the EOs belonged tothree chemotypes: one with a prevalence of carvacrol, the carvacrol chemotype (CC; carvacrol, 81.5%),and two with a prevalence of thymol, the thymol/p-cymene and thymol/?-terpinene chemotypes(TCC and TTC; thymol, 43.8, and 36.7%, respectively). The bioassays showed that although allthe three EOs chemotypes are able to exert a toxic activity against C. vomitoria adults (LD50 from0.14 to 0.31 µL insect-1) and eggs (LC50 from 0.008 to 0.038 µL cm-2) as well as deter the oviposition (Oviposition Activity Index, OAI, from 0.40 ± 0.04 to 0.87 ± 0.02), the bioactivity of oreganoEOs significantly varies among the chemotypes, with the thymol-rich EOs (TCC and TTC) overalldemonstrating more effectiveness than the carvacrol-rich (CC) EO.