Abstract Plutella xylostella (L.) is responsible for considerable vegetable crop losses in the metropolitan region of Manaus, Brazil. In recent decades, essential oils have been investigated as an alternative to synthetic insecticides. The genusPiperis widely distributed in Amazonia and essential oils from these plants have insecticidal properties. This study describes the chemical composition of the essential oils fromPiper capiterianumandPiper krukoffiias well as the lethal and sublethal effects onP. xylostella. The phytotoxicity of the oils on the host plant was also evaluated. Globulol was the major constituent of theP. krukoffiioil ando-cymene was the major constituent of theP. capitarianumoil. The oil fromP. capiterianumexhibited greater toxicity to larvae and eggs. This oil also presented greater repellant action, feeding deterrence and mild phytotoxicity to the host plant (Brassicae oleraceae). The findings suggest that this oil can be used in the preparation of a formulated insecticide for the management ofP. xylostellain different development phases. However, further studies are needed to evaluate the effect of this oil on crops under field conditions as well as non-target organisms and determine the cost-benefit ratio of a product formulated withP. capitarianumoil.

Chemical analysis involving gas chromatography coupled to mass spectrometry of the essential oils of red and orange flowers from E. velutina revealed a predominance of phenylpropanoids in both samples. However, qualitative and quantitative differences were found in the compositions. (E)-Asarone (16.22 ± 0.23%) and (E)-caryophyllene (12.22 ± 0.11%) were identified as the major constituents of the essential oil from the red flowers, whereas (E)-caryophyllene (41.72 ± 1.65%) and eugenol (20.99 ± 0.21%) were identified as the major constituents of the oil from the orange flowers. Seventeen fatty acids were characterized in the red and black seeds. The fatty acid composition in the two chromatic variations had a high degree of similarity. Oleic acid (41.56 ± 1.33% and 46.12 ± 1.90% in the red and black seeds, respectively), palmitic acid (15.39 ± 0.16% and 12.33 ± 0.41%) and behenic acid (9.95 ± 0.14% and 12.10 ± 0.42%) were identified as the main fatty acids. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) enabled identifying significant differences in the chemical profile of the essential oils from the red flower and orange flower varieties of E. velutina. In contrast, PCA and HCA analysis revealed no significant differences in the fatty acid profile of the red and black seeds.

Óleos essenciais das folhas e frutos de Eugenia langsdorffii foram analisados por CG-FID (cromatografia gasosa com detecção através de ionização por chama) e CG-EM (cromatografia gasosa com detecção por espectrometria de massas) e exibiram alta percentagem de sesquiterpenos. epi-Longipinanol (13,6 ± 0,1%) e γ-eudesmol (12,3 ± 0,2%) foram os componentes principais do óleo das folhas, enquanto que 10-epi-γ-eudesmol (35,7 ± 0,3%) e 1,10-di-epi-cubenol (15,6 ± 0,3%) foram majoritários no óleo dos frutos. Estudo comparativo da toxicidade por fumigação e contato residual desses óleos foi conduzido. O óleo das folhas (dose letal média, LC50 = 1,7 µL L-1 de ar) foi 1,7 vezes mais tóxico do que o óleo dos frutos por fumigação, e 1,8 vezes menos tóxico por contato residual. O controle positivo (eugenol) foi muito mais tóxico no bioensaio de fumigação do que os óleos de Eugenia. Entretanto, o efeito de contato residual do óleo dos frutos (LC50 = 12,25 µL mL-1) foi apenas 6,7 vezes menor do que o do eugenol. A função exercida por terpenóides na propriedade acaricida dos óleos de E. langsdorffii também foi discutida.

Leaf and fruit essential oils of Eugenia langsdorffii were analyzed by GC-FID (gas chromatography with flame ionization detection) and GC-MS (gas chromatography with mass spectrometric detection), featuring a high percentage of sesquiterpenes. epi-Longipinanol (13.6 ± 0.1%) and γ-eudesmol (12.3 ± 0.2%) were the principal components of the leaf oil, whereas 10-epi-γ-eudesmol (35.7 ± 0.3%) and 1,10-di-epi-cubennol (15.6 ± 0.3%) were the major constituents of the fruit oil. A comparative study to assess fumigant and residual contact toxicities of the oils was conducted. The leaf oil (lethal concentration average, LC50 = 1.7 µL L-1 of air) was 1.7 times more toxic than the fruit oil and 1.8 times less toxic by residual contact. The positive control (eugenol) was much more toxic in the fumigation bioassay than Eugenia langsdorffii oils. Nevertheless, the residual contact effect of the fruit oil (LC50 = 12.25 µL mL-1) was just 6.7 times smaller than that of eugenol. The role of terpenoids in the acaricidal property of the E. langsdorffii essential oils was also discussed.