Andean Plants Essential Oils: A Scented Alternative to Synthetic Insecticides for the Control of Blowflies

SIMPLE SUMMARY: Blowflies play a key role in the transmission of foodborne diseases and cause myiasis. With their repellent and insecticidal properties, essential oils (EOs) from aromatic plants can control such insects. However, because of their strong odour, they are often unsuitable for protecting food or places. In this work, the EOs of two Andean plants, Aloysia citrodora and Bursera graveolens, known for their pleasant odour, were analysed from a chemical and sensory point of view, and their bioactivity against the blowfly Calliphora vomitoria was assessed in comparison with the highly effective, but bad-smelling, Allium sativum EO. The behavioural test showed that the A. citrodora EO was more repellent than the A. sativum EO and that, on the contrary, the B. graveolens EO was attractive to C. vomitoria. The toxicity tests showed that the EOs of both Andean plants have a clear insecticidal effect against blowfly eggs and adults. In terms of contact with adult flies, the A. citrodora EO was about twice as toxic as the A. sativum EO. ABSTRACT: Blowflies are vectors of microorganisms and human pathogens, and their maggots cause myiasis in vertebrates and infest and spoil meat and fish products. Essential oils (EOs) from spices were proven to be a safer and more sustainable alternative to synthetic insecticides for the control of blowflies and are suitable for protecting food from such pests. However, some EOs are not acceptable for environmental or topical applications due to their strong, unpleasant odour. In this study, we measured the acute toxicity and the repellence of two EOs extracted from the Andean plants Aloysia citrodora Palau and Bursera graveolens (Kunth) Triana and Planch., both known for their pleasant odour, against the blue blowfly Calliphora vomitoria (L.) (Diptera: Calliphoridae). We also compared their bioactivity with that of the Allium sativum L. EO, which is very effective but bad-smelling. The A. citrodora EO was mainly rich in oxygenated monoterpenes, the most abundant of which were geranial (26.8%) and neral (21.0%). The B. graveolens EO was chiefly composed of monoterpene hydrocarbons, mostly represented by limonene (46.2%). According to the sensory description, the best odour profile was associated with the A. citrodora EO, while the olfactory expression of the EO from B. graveolens was negatively affected by a strong odour of “mouldy lemon”. The behavioural test showed that the A. citrodora EO was more repellent than that of A. sativum and, on the contrary, that the B. graveolens EO was attractive. The toxicity tests showed that the EOs of both Andean plants have a clear toxic effect on the C. vomitoria eggs and adults. In terms of ovicidal activity, there were no significant differences among the effects of the three tested EOs. On the adult flies, the toxicity of the two EOs of the Andean plants was much lower than that of A. sativum (LC(50) fumigation = 1.86 μL EO L(−1) air; LC(50) ingestion = 8.10 μL EO mL(−1) gel) both by fumigation (LC(50) = 23.66 and 25.30 μL EO L(−1) air for A. citrodora and B. graveolens, respectively) and ingestion (LC(50) = 36.65 and 44.97 μL EO mL(−1) gel for A. citrodora and B. graveolens, respectively), while, by contact, the A. citrodora EO (LD(50) = 0.27 μL EO insect(−1)) was more toxic than the A. sativum EO (LD(50) = 0.46 μL EO insect(−1)).