Toxicity of Ocimum basilicum L. (Lamiaceae) essential oil to Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) and its selectivity for Telenomus remus Nixon, 1937 (Hymenoptera: Scelionidae)

Spodoptera frugiperda is an agricultural pest that has spread to several regions, with frequent reports of populations resistant to synthetic insecticides. Consequently, there is an increasing number of studies seeking novel control strategies compatible with beneficial organisms. This study aimed to: (i) evaluate the toxicity of Ocimum basilicum essential oil (EO) to S. frugiperda ; (ii) chemically characterize O. basilicum EO; (iii) determine the toxicity of the EO’s major compound to S. frugiperda ; and (iv) assess selectivity of EO toward Telenomus remus . The EO was toxic to second-instar caterpillars (LD 50 = 13.36 μg of EO/caterpillar). Methyl chavicol was identified as the major compound (86.14%) in EO and exhibited toxicity to S. frugiperda . The EO reduced the emergence of T. remus in the F 2 and F 3 generations when exposed during the egg and pupal stages within the natural host and was classified as harmless to slightly harmful according to the IOBC scale, without affecting parasitism rates. The sex ratio was reduced. The O. basilicum EO caused 100% mortality in adult female T. remus . In conclusion, O. basilicum EO is toxic to S. frugiperda and induces transgenerational effects on T. remus emergence during the egg and pupal stages, while exhibiting high toxicity to adult females. These findings indicate that O. basilicum EO is compatible with T. remus during its immature stages and underscore the need for application strategies that prevent exposure of adult parasitoids in IPM programs. • Basil essential oil and methyl chavicol are toxic to fall armyworm caterpillars. • Stage of exposure determines parasitoid sensitivity to basil oil. • Immature stages tolerate basil oil, whereas adult females are highly sensitive. • Transgenerational effects alter emergence and sex ratio with no loss of parasitism. • Developmental stage shapes parasitoid sensitivity to basil oil.