Toxicity of essential oils and pure compounds of Lamiaceae species against Spodoptera frugiperda (Lepidoptera: Noctuidae) and their safety for the nontarget organism Trichogramma pretiosum (Hymenoptera: Trichogrammatidae).
The fall armyworm (FAW) Spodoptera frugiperda is a key pest of countless cultures of economic importance. FAW control is still mostly achieved by using synthetic chemicals and genetically modified plants, which can cause adverse effects on nontarget organisms. In this sense, secondary metabolites are an inexhaustible source of bioactive substances. Thus, this study investigated the insecticidal activity of essential oils (EOs) of plants of the Lamiaceae family against FAW. The EOs from Hyptis marrubioides (LD50 = 18.49 μg/larvae) and Ocimum basilicum (LD50 = 38.21 μg/larvae) were toxic to FAW in topical bioassays. The majority of compounds of H. marrubioides were identified as β-thujone (41.50%) and α-thujone (15.82%), while for O. basilicum, linalool (35.68%) and 1,8-cineole (16.03%) were the major substances. The pure compounds linalool (survival probability = 28.1%), α-thujone (survival probability = 24.5%) and 1,8-cineole (survival probability = 40.4%) were employed in a new bioassay; although all substances were toxic to FAW, the toxicity was less than that observed for EOs from H. marrubioides (survival probability = 9.5%) and O. basilicum (survival probability = 2.1%). These results suggest that there is more than one active substance in the EOs or else, there is synergism and/or an additive effect between the substances. With regard to the experiment conducted with the parasitoid Trichogramma pretiosum, the EOs from H. marrubioides and O. basilicum were classified as harmless according to the IOBC criteria, so they are safe for this parasitoid and have potential to be used in programs of integrated FAW pest management the natural enemy T. pretiosum.