Plutella xylostella cause considerable harm to the production of broccoli, Chinese cabbage, cabbage and cauliflower. The control of P. xylostella is mainly performed using commercial insecticides, which have even led to the emergence of resistant populations. Two easily available natural products found in different plants essential oil, thymol and eugenol, stand up as possible novel agents to control this pest. In this work a series of alkylated and acylated derivatives of eugenol and thymol were synthesized and screened for antifeedant, larvicidal and ovicidal activities against P. xylostella. The results of biological activities assays suggest that the novel 1,1’-[1,8-octanediylbis(oxy)]-bis(4-allyl-2-methoxy-benzene) (5) was the most toxic in the larvicidal test. Compounds 1-butoxy-2-isopropyl-5-methyl-benzene (8) and hexanedioic acid 1,6-bis(2-isopropyl-5-methyl-phenyl)-ester (10) were the most toxic in the ovicidal assay. The compound 8 presented the most antifeedant activity. Most of the compounds obtained were more active than commercially available insecticidal deltamethrin and azadirachtin.

Amides have been recognized as potent insecticidal natural products but, despite their variety of targets and mechanisms of action, their metabolic fate in insects is virtually unknown. The currently accepted hypothesis is that specialist herbivores are capable of biotransforming xenobiotics rendering them more polar and excretable while generalist insects do not have comparable capacity. The leaves from Piper tuberculatum, rich in insecticide amides, were offered to two insect species found on Piper leaves under natural conditions and also to four generalist grasshoppers in order to compare their capacity of biotransforming xenobiotics. The amides 1-7 were identified in the P. tuberculatum leaves and their corresponding carboxylic acids 8-13 were detected in frass samples of two host insects suggesting that these species promote the amides hydrolysis. The four generalist grasshoppers when offered P. tuberculatum leaves, starved to death after 72 h, indicating a strong antifeedant activity of P. tuberculatum leaves.

Essential oils from the leaves, stems, flowers and fruits of Melaleuca leucadendra growing in the state of Pernambuco, Brazil, were analyzed using gas chromatography-mass spectrometry (GC-MS). The effects of the oils and their major constituent were evaluated on the agricultural pests Tetranychus urticae and Plutella xylostella in different stages of development. The analysis revealed a M. leucadendra chemotype rich in (E)-nerolidol (81.78 ± 0.90 to 95.78 ± 1.20%). P. xylostella was more susceptible to the oils and major constituent than T. urticae. The fruit oil was 1.5-fold more toxic than the leaf oil to T. urticae eggs. (E)-Nerolidol was 5.5-fold and 4.5-fold more toxic to T. urticae adults than the leaf and fruit oils, respectively. Azamax® used as the positive control was more efficient than the oils and (E)-nerolidol against T. urticae. However, the oils and (E)-nerolidol were more toxic to P. xylostella than Azamax®.

Abstract In the laboratory, were evaluated the effects (residual contact and feeding deterrence) of the essential oils from the leaves of Piper aduncum, Lippia sidoides and Schinus terebinthifolius, as well as eleven selected constituents and binary blends of oils in different proportions against 3rd instar larvae of Plutella xylostella (L.). The Piper oil demonstrated the greatest toxicity (LC50 = 0.31 µL/mL) and feeding deterrence (DC50 = 1.08 µL/mL) between oils tested. Dillapiole (LC50 = 1.01 µL/mL; DC50 = 1.10 µL/mL) and carvacrol (LC50 = 6.03 µL/mL; DC50 = 0.075 µL/mL) demonstrated the greatest toxicity and feeding deterrence between constituents tested, respectively. Based on the fractional effects indices for the blends, a synergistic interaction was found for the blend of the Lippia and Schinus oils at a proportion of 75 and 25%, respectively. The present findings indicate that this blend could be used in the control of P. xylostella, as the literature reports populations resistant to the active ingredient in the positive control, Premio®. Further studies are needed for the development of a new botanical insecticide based on the active ingredients in oils from L. sidoides and S. terebinthifolius to improve efficiency, stability and the cost-benefit in the control of P. xylostella.

Laboratory bioassays on fumigation, ovicidal and oviposition deterrence activity of the essential oil from Indigofera suffruticosa and its constituents [eugenol, (E)-asarone, dill apiole, (Z)-asarone, thymol, (E)-nerolidol and safrole] against Tetranychus urticae were carried out. Components of Indigofera leaf oil were characterized by gas chromatography (GC) ad mass spectrometry (GC-MS), which revealed the identification of 17 components, representing 97.7 ± 0.6% of the total oil, with a high percentage of phenylpropanoids (89.9 ± 0.5%), among which eugenol (45.6 ± 0.4%) and (E)-asarone (17.4 ± 0.2%) were major constituents. The ovicidal activity and oviposition deterrence tests revealed that the essential oil as well as its main compounds affected the oviposition and hatchability of mite eggs. Eugenol and thymol were the most potent compounds and were approximately 225-fold more potent than the oil. The acaricidal action exerted by sesquiterpenes and phenylpropanoids of the leaf oil is also discussed. The results suggest that the Indigofera oil and selected components associated with ovicidal activity and oviposition deterrence can serve as the basis for a promising agent that could be used in the formulation of a product for use against the T. urticae.

RESUMEN El objetivo del presente estudio fue evaluar el potencial insecticida de los aceites esenciales de los frutos maduros y no maduros de la planta Schinus terebinthifolius y comparar los efectos tóxicos de mezclas artificiales con los constituyentes seleccionados de estos aceites [limoneno, (E)-nerolidol, α-terpineol, β-terpineol, terpinoleno, α-pineno y β-pineno] en el barrenador de grano pequeño, Rhyzopertha dominica. La susceptibilidad de la plaga a los aceites aumentó con el tiempo. No se encontró diferencia estadísticamente significativa entre los aceites en los períodos de tiempo evaluados (24, 48 y 72 h). Rhyzopertha dominica fue más susceptible al limoneno, terpinoleno, α-pineno y β-pineno. Entre las mezclas artificiales completas, ensayadas en las proporciones caracterizadas químicamente, solamente la preparada con los componentes del aceite de fruta madura demostró toxicidad al mismo nivel que el aceite esencial. El análisis de los constituyentes reveló que el limoneno y el α-terpineol contribuyeron más a la toxicidad del aceite de fruta madura, mientras que unicamente el limoneno contribuyó a la toxicidad del aceite de fruta no madura. Los presentes hallazgos demuestran que la toxicidad de los aceites de frutas maduras y no maduras no puede atribuirse únicamente a la toxicidad individual de los constituyentes, sino también a la proporción en que se encuentran estos compuestos y al tipo de interacción entre estos.

ABSTRACT The aim of the present study was to evaluate the insecticidal potential of the essential oil from ripened and unripened fruit of the plant Schinus terebinthifolius and compare the toxic effects of artificial blends made with selected constituents of these oils [limonene, (E)-nerolidol, α-terpineol, β-terpineol terpinolene, α-pinene and β-pinene] on the lesser grain borer, Rhyzopertha dominica (family -order). No statistically significant difference was found between the oils in the time periods tested (24, 48 and 72 h). Rhyzopertha dominica was more susceptible to limonene, terpinolene, α-pinene and β-pinene. Among the complete artificial blends tested at the proportions identified chemically, only that prepared with the constituents of the ripened fruit oil demonstrated toxicity on the same level as the essential oil. The analysis of the constituents revealed that limonene and α-terpineol contributed most to toxicity of the ripened fruit oil, whereas only limonene contributed to the toxicity of the unripened fruit oil. The present findings demonstrate that the toxicity of the ripened and unripened fruit oils cannot be attributed only to the individual toxicity of the constituents, but also the proportion at which these compounds are found and the types of interactions among the compounds.

ABSTRACT Essential oils from the leaves of two species of the genus Ocotea that occur in the Atlantic Forest in the state of Pernambuco, Brazil, were analyzed using gas chromatography-mass spectrometry. The acaricidal activity of these oils as well as 11 selected components and blends were evaluated in fumigation and residual contact tests against the two-spotted spider mite (Tetranychus urticae). Sixty-seven constituents were identified, totaling 97.3 ± 0.3% and 97.8 ± 0.5% of the oils from O. duckei and O. glomerata, respectively. Sesquiterpene was the dominant class. The compounds β-caryophyllene (18.6 ± 0.1%) and aromadendrene (17.3 ± 0.6%) were the main constituents of the oils from O. duckei and O. glomerata, respectively. Acaricidal action varied depending on the method employed, species and chemical nature of the selected constituents. The mites were susceptible to the oils and chemical constituents using the fumigation method. The O. duckei oil was respectively 2.5-fold and 1.5-fold more toxic than the O. glomerata oil using the fumigation and residual contact methods. Among the selected constituents, β-caryophyllene was the most toxic, independently of the method employed. The individual toxicity of the selected compounds and their blends as well as the role of these constituents in the overall toxicity of the essential oils are also discussed.