Toxidade de misturas binárias de óleos essenciais de espécies de eucalipto para Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) e interação com o organismo não-alvo Beauveria bassiana

Abstract

The fall armyworm Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae) is a polyphagous insect that poses highly destructive potential. The control of S. frugiperda is mainly carried out through the application of synthetic insecticides and genetically modified plants. However, the indiscriminate use of these management tactics has led to the selection of resistant insect populations. Thus, this study aimed to determine the effect of the interaction of binary mixtures of essential oils (EOs) from Corymbia citriodora Hook (Myrtaceae) (formerly Eucalyptus citriodora), Eucalyptus staigeriana Labill (Myrtaceae), and Eucalyptus globulus Branch (Myrtaceae) on S. frugiperda, and to evaluate the interaction between the EOs and their binary mixtures (C. citriodora and E. staigeriana) with the non-target organism Beauveria bassiana (Bals) Vuill (Hypocreales: Cordycipitaceae) (Boveria Turbo SC®, Vittia). The doses used for the essential oils (EOs) of C. citriodora and E. staigeriana were 0, 10, 18, 32, 56, and 100 µg of EO/larva, while for E. globulus, the doses used were 0, 20, 32, 50, 80, and 120 µg of EO/larva. Acetone was used as a negative control. Once the doseresponse values of the EOs were determined, the effect of the mixture and the classification of the interaction between them were studied. For this, binary combinations of the DL25 values of the EOs, previously determined, were made. The EOs were toxic to S. frugiperda in this sequence: C. citriodora (DL50 35.98 µg of EO/larva) < E. staigeriana (DL50 41.46 µg of EO/larva) < E. globulus (DL50 48.33 µg of EO/larva). The binary mixtures of the EOs of C. citriodora and E. staigeriana; C. citriodora and E. globulus demonstrated an additive effect. While the mixture of essential oils (EOs) from E. globulus and E. staigeriana resulted in an antagonistic effect on the survival of S. frugiperda caterpillars. Regarding compatibility with B. bassiana, the binary mixture of EOs from C. citriodora and E. staigeriana was not compatible. The results found in this research demonstrated the potential of the EOs, as well as the binary mixtures of C. citriodora + E. staigeriana and C. citriodora + E. globulus when applied against S. frugiperda caterpillars. On the compatibility for B. bassiana, the results indicate the need for new studies in semi-field conditions.