Characterization and Determination of the Antibacterial Activity of Baccharis dracunculifolia Essential-Oil Nanoemulsions

The aim of this study was to evaluate the antibacterial activity of nanoemulsions of Baccharis dracunculifolia essential oil. The volatile compounds of the essential oil were identified using gas chromatography-mass spectrometry. The properties of the nanoemulsions (droplet size, polydispersity index, pH, and electrical conductivity) were determined. The antibacterial activities of the essential oil and its nanoemulsions were evaluated using MIC, MBC, and disk diffusion. The microorganisms used were: Gram-positive bacteria (Staphylococcus aureus ATCC 25923, Bacillus cereus ATCC 14579, Streptococcus mutans ATCC 25175, and Enterococcus faecalis ATCC 29212) and Gram-negative bacteria (Pseudomonas aeruginosa ATCC 27853, Klebsiella pneumoniae ATCC BAA-1706, Salmonella enterica ATCC 14028, and Escherichia coli ATCC 25922). The major volatile compounds of the B. dracunculifolia essential oil were limonene (19.36%), (E)-nerolidol (12.75%), bicyclogermacrene (10.76%), and β-pinene (9.60%). The nanoemulsions had a mean droplet size between 13.14 and 56.84 nm. The nanoemulsions presented lower and statistically significant MIC values compared to the essential oil, indicating enhancement of the bacteriostatic action. The disk diffusion method showed that both the nanoemulsions and the essential oil presented inhibition zones only for Gram-positive bacteria, while there were no results against Gram-negative bacteria, indicating that B. dracunculifolia essential oil has a better antimicrobial effect on Gram-positive microorganisms.

Chemical composition and phytotoxic potential of Eucalyptus globulus essential oil against Lactuca sativa and two herbicide-resistant weeds: Avena fatua and Amaranthus hybridus

Weed control in sustainable agriculture requires new bioherbicidal molecules to replace synthetic herbicides that have damaged the environment and generated resistance in weeds. This study was conducted to investigate the chemical composition of Eucalyptus globulus essential oil and to explore its bioherbicidal potential on the germination and radicle growth inhibition. The phytotoxic effects of E. globulus essential oil (1, 10 and 20 μL mL-1) were tested in comparison to those of the synthetic herbicide Glyphosate (1, 10 and 20 μL mL-1) in bioassays of germination and radicle growth of Lactuca sativa and the resistant weeds Avena fatua and Amaranthus hybridus. Gas Chromatography with Flame Ionization Detector and Gas Chromatography-Mass Spectroscopy analysis showed that major monoterpenes comprised 1,8-Cineole (86.94%), α-pinene (7.71%), d-limonene (2.65%), and p-cymene (1.48%). The seed germination and radicle length exhibited different degrees of inhibition in response to the concentration of E. globulus essential oil. At some concentrations, both the Glyphosate herbicide and the E. globulus essential oil demonstrated the same phytotoxicity against the resistant weeds A. fatua and A. hybridus. Essential oil bioactivity Lethal Concentration (LC50) in the majority of cases was lowest for A. hybridus, followed by A. fatua and L. sativa. Based on the results, it can be concluded that E. globulus essential oil possesses phytotoxic potential and could be explored as a bioherbicide for resistant weeds management programs.

Acaricidal property of the essential oil from Lippia gracilis against Tetranychus urticae and a natural enemy, Neoseiulus californicus, under greenhouse conditions

The essential oil from the leaves of Lippia gracilis was investigated for fumigant and residual activity against Tetranychus urticae (Acari: Tetranychidae) and Neoseiulus californicus (Acari: Phytoseiidae). The results were compared to eugenol, Ortus^® and Azamax^®, as positive controls. Gas chromatography (GC) and GC/mass spectrometry analysis enabled the identification of 28 compounds, accounting for 99.1 ± 0.6% of the essential oil. The major constituents were carvacrol (61%), p-cymene (11%) and thymol (11%). Mites were more susceptible to the oil in fumigant tests than in residual tests. Among the components, thymol and β-caryophyllene had the greatest fumigant and residual toxicity against T. urticae, respectively. The role of selected constituents (carvacrol, p-cymene, thymol, limonene, β-pinene, 1,8-cineole, terpinolene and β-caryophyllene) in the acaricidal properties of the L. gracilis essential oil is also discussed. Fumigant and residual effects of Lippia oil were more selective than eugenol with regard to a natural enemy of T. urticae, Neoseiulus californicus. Experiments under greenhouse conditions demonstrated greater toxicity of the Lippia oil in comparison to the positive control at 24, 48 and 72 h after treatment. The results suggest that Lippia oil is a good candidate for the formulation of a botanical acaricide for the integrated management of T. urticae.

Acaricidal and repellent activity of terpenoids from seaweeds Collected in Pernambuco, Brazil

n-Hexane and dichloromethane extracts obtained from Laurencia dentroidea (Rhodophyta) and Canistrocarpus cervicornis (Phaeophyta) were investigated for their acaricidal and repellent properties against Tetranychus urticae under laboratory conditions. The two extracts displayed moderate toxicity and good repellent proprieties, and were significantly more toxic (36-fold) than the positive control (eugenol), whereas eugenol was tenfold more repellent than either seaweed extract. The sesquiterpenoid elatol (1) was isolated from L. dentroidea and the diterpenoid seco-dolastane (4R,9S,14S)-4alpha-acetoxy-9beta, 14alpha-dihydroxydolast-1(15),7-diene (2) from C. cervicornis, the chemical structures of which were characterized by NMR spectroscopic data (1H and 13C) and by comparison with literature data. These compounds exhibited moderate toxicity, but a high degree of repellent activity against T. urticae. The findings suggest that marine natural products, specifically terpenes, can be employed for the development of new pesticides and become prototype agrochemical agents.

Acaricidal and Repellent Activity of Terpenoids from Seaweeds Collected in Pernambuco, Brazil

n-Hexane and dichloromethane extracts obtained from Laurencia dentroidea (Rhodophyta) and Canistrocarpus cervicornis (Phaeophyta) were investigated for their acaricidal and repellent properties against Tetranychus urticae under laboratory conditions. The two extracts displayed moderate toxicity and good repellent proprieties, and were significantly more toxic (36-fold) than the positive control (eugenol), whereas eugenol was tenfold more repellent than either seaweed extract. The sesquiterpenoid elatol (1) was isolated from L. dentroidea and the diterpenoid seco-dolastane (4 R,9 S,14 S)-4α-acetoxy-9β,14α-dihydroxydolast-1(15),7-diene (2) from C. cervicornis, the chemical structures of which were characterized by NMR spectroscopic data (1H and 13C) and by comparison with literature data. These compounds exhibited moderate toxicity, but a high degree of repellent activity against T. urticae. The findings suggest that marine natural products, specifically terpenes, can be employed for the development of new pesticides and become prototype agrochemical agents.

Essential Oil Composition and Acaricidal Activity of Schinus Terebinthifolius from Atlantic Forest of Pernambuco, Brazil against Tetranychus Urticae

The compositions of the essential oils from unripe (UFr) and ripe (RFr) fruits of Schnus terebinthifolius were analyzed by GC and GC/MS. The major compound identified in both oils was limonene (UFr = 44.1 ± 1.3%; RFr = 31.8 ± 1.2%), followed by α-phellandrene (15.7 ± 0.4%) in the UFr oil and thujene (21.7 ± 0.9%) in the RFr oil. Repellent and toxicity activities of the two oils were also evaluated, and the results compared with eugenol. The UFr oil was more active in the fumigation tests (LC50 = 1.46 μL/L of air), whereas the RFr oil was more active in the sealed dishes (SD) than open dishes (OD) contact assay (LC50 = 3.04 μL/cm2) and not significantly different from eugenol. Both oils exhibited significant repellent activity comparable with that of eugenol. The results suggest that the repellent activity of these oils in association with its toxicity could be a great advantage for the integrated management of T. urticae.

Essential oil composition and acaricidal activity of Schinus terebinthifolius from Atlantic Forest of Pernambuco, Brazil against Tetranychus urticae

The compositions of the essential oils from unripe (UFr) and ripe (RFr) fruits of Schinus terebinthifolius were analyzed by GC and GC/MS. The major compound identified in both oils was limonene (UFr = 44.1 +/- 1.3%; RFr = 31.8 +/- 1.2%), followed by alpha-phellandrene (15.7 +/- 0.4%) in the UFr oil and thujene (21.7 +/- 0.9%) in the RFr oil. Repellent and toxicity activities of the two oils were also evaluated, and the results compared with eugenol. The UFr oil was more active in the fumigation tests (LC50 = 1.46 microL/L of air), whereas the RFr oil was more active in the sealed dishes (SD) than open dishes (OD) contact assay (LC50 = 3.04 microL/cm2) and not significantly different from eugenol. Both oils exhibited significant repellent activity comparable with that of eugenol. The results suggest that the repellent activity of these oils in association with its toxicity could be a great advantage for the integrated management of T. urticae.

Volatile constituents of two species of Protium from the Atlantic rainforest in the state of Pernambuco, Brazil

The chemical composition of the essential oils from Protium giganteum and P. aracouchine was determined, for the first time, using GC-MS analysis. From the oil of P. giganteum, 32 components were identified, representing 93.9% of the oil, and from P. aracouchine, 29 components, representing 97.8% of the oil. Among the compounds identified in the P. giganteum oil, 93.6% were sesquiterpenes, with beta-caryophyllene (26.0 +/- 0.8%), globulol (9.3 +/- 0.2%), alpha-cadinol (7.0 +/- 0.5%), alpha-humulene (6.4 +/- 0.1%) and germacrene D (6.2 +/- 0.3%) as the major components. Among the 29 compounds identified in the P. aracouchine oil, 95.9% were sesquiterpenes as well, with spathulenol (31.8 +/- 1.6%), alpha-cis-bergamotene (8.8 +/- 0.2%) and viridiflorol (9.7 +/- 0.7%) as the major components.

Acaricidal activity against Tetranychus urticae and essential oil composition of four Croton species from Caatinga biome in northeastern Brazil

Volatile components of essential oils from the leaves and stems of Croton jacobinensis, C. rhamnifolius, C. muscicapa and C. micans, which are medicinal plants found in the Caatinga biome of northeastern Brazil, were analyzed using GC and GC/MS. The acaricidal activity of these oils against Tetranychus urticae was evaluated using the fumigation method. Oil yields from the Croton species ranged from 1.1 +/- 0.0 to 0.6 +/- 0.0%, w/w, for leaves and 0.7 +/- 0.0 to 0.1 +/- 0.0% for stems. Sesquiterpenoids were dominant in all oils, except the stem oil from C. rhamnifolius, which exhibited a high monoterpene content, and the leaf and stem oils from C. muscicapa, which were rich in phenylpropanoids. The major volatile components of the leaf and stem oils from C. jacobinensis were (Z)-alpha-atlantone (24.3 +/- 0.4%) and trans-isolongifolanone (22.8 +/- 0.5%), respectively. The most abundant constituents detected in C. rhamnifolius were alpha-cedrene epoxide (23.3 +/- 0.1%) and caryophyllene oxide (21.9 +/- 0.0%) in the leaf oil, and camphor (16.6 +/- 0.5%) and tricyclene (12.8 +/- 0.1%) in the stem oil. Foenicolin was the main compound identified in the leaf (50.6 +/- 0.2%) and stem (72.7 +/- 0.6%) oils of C. muscicapa, while alpha-bulnesene (32.9 +/- 0.2%) and guaiol (17.9 +/- 0.7%) were the principal components of C. micans oils. These oils exhibited a high degree of toxicity in the fumigation assay. The stem oils from C. jacobinensis and C. rhamnifolius exhibited high lethality rates, with LC50 values of 0.3 and 0.2 microL/L of air after 24 h, respectively. The results suggest the potential use of stem essential oil, especially from C. rhamnifolius and C. jacobinensis, for the integrated control of Tetranychus urticae.

Acaricidal Activity against Tetranychus Urticae and Essential Oil Composition of Four Croton Species from Caatinga Biome in Northeastern Brazil

Volatile components of essential oils from the leaves and stems of Croton jacobinensis, C. rhamnifolius, C. muscicapa and C. micans, which are medicinal plants found in the Caatinga biome of northeastern Brazil, were analyzed using GC and GC/MS. The acaricidal activity of these oils against Tetranychus urticae was evaluated using the fumigation method. Oil yields from the Croton species ranged from 1.1±0.0 to 0.6±0.0%, w/w, for leaves and 0.7±0.0 to 0.1±0.0% for stems. Sesquiterpenoids were dominant in all oils, except the stem oil from C. rhamnifolius, which exhibited a high monoterpene content, and the leaf and stem oils from C. muscicapa, which were rich in phenylpropanoids. The major volatile components of the leaf and stem oils from C. jacobinensis were ( Z)-α-atlantone (24.3±0.4%) and trans-isolongifolanone (22.8±0.5%), respectively. The most abundant constituents detected in C. rhamnifolius were #aL-cedrene epoxide (23.3±0.1%) and caryophyllene oxide (21.9±0.0%) in the leaf oil, and camphor (16.6±0.5%) and tricyclene (12.8±0.1%) in the stem oil. Foenicolin was the main compound identified in the leaf (50.6±0.2%) and stem (72.7±0.6%) oils of C. muscicapa, while α-bulnesene (32.9±0.2%) and guaiol (17.9±0.7%) were the principal components of C. micans oils. These oils exhibited a high degree of toxicity in the fumigation assay. The stem oils from C. jacobinensis and C. rhamnifolius exhibited high lethality rates, with LC50 values of 0.3 and 0.2 μL/L of air after 24 h, respectively. The results suggest the potential use of stem essential oil, especially from C. rhamnifolius and C. jacobinensis, for the integrated control of Tetranychus urticae.

Insecticidal Activity against Bemisia Tabaci Biotype B of Peel Essential Oil of Citrus sinensis var. pear and Citrus aurantium Cultivated in Northeast Brazil

The fumigant action of peel essential oils of Citrus sinensis var. pear (pear orange = PO) and C. aurantium (bitter orange = BO) from the northeast of Brazil were evaluated against Bemisia tabaci biotype B and compared with eugenol as a positive control. The oil concentration in the PO at 8.5 μL/L of air caused 97% mortality, while the oil concentration of BO at 9.5 μL/L of air caused 99% mortality. However, the LC50 estimates for both oils (LC50 = 3.80 μL/L of air for PO and LC50 = 5.80 μL/L of air for BO) did not differ from each other, but they did when compared with eugenol (LC50 = 0.20 μL/L of air). Regarding their effects on oviposition, the Citrus oils showed concentration-response dependence, reducing the number of eggs as the concentration increased, which was not observed for eugenol. The minimum concentrations of the oils that caused a significant reduction in the egg lay were 3.5 and 7.0 μL/L of air for BO and PO, respectively. These results suggest that oils from PO and BO peels may be promising as models to develop new insecticides that might be applied into the integrated management of whiteflies.

Insecticidal activity against Bemisia tabaci biotype B of peel essential oil of Citrus sinensis var. pear and Citrus aurantium cultivated in northeast Brazil

The fumigant action of peel essential oils of Citrus sinensis var. pear (pear orange = PO) and C. aurantium (bitter orange = BO) from the northeast of Brazil were evaluated against Bemisia tabaci biotype B and compared with eugenol as a positive control. The oil concentration in the PO at 8.5 microL/L of air caused 97% mortality, while the oil concentration of BO at 9.5 microL/L of air caused 99% mortality. However, the LC50 estimates for both oils (LC50 = 3.80 microL/L of air for PO and LC50 = 5.80 microL/L of air for BO) did not differ from each other, but they did when compared with eugenol (LC50 = 0.20 microL/L of air). Regarding their effects on oviposition, the Citrus oils showed concentration-response dependence, reducing the number of eggs as the concentration increased, which was not observed for eugenol. The minimum concentrations of the oils that caused a significant reduction in the egg lay were 3.5 and 7.0 microL/L of air for BO and PO, respectively. These results suggest that oils from PO and BO peels may be promising as models to develop new insecticides that might be applied into the integrated management of whiteflies.

Acaricidal activity against Tetranychus urticae and chemical composition of peel essential oils of three Citrus species cultivated in NE Brazil

The repellency and fumigant toxicities of the peel essential oils of Citrus sinensis var. pêra (LP), C. sinensis var. mimo (LM), and C. aurantium (LL) cultivated in northeast Brazil were evaluated against Tetranychus urticae. Analysis of the oils by GC and GC/MS led to the identification of twenty-eight components, which represented 99.9%, 99.7% and 99.3% of the total constituents of the LP, LM and LL oils, respectively. Limonene was the main component found in all three oils. Other main components were alpha-pinene (1.5% in LP; 1.4% in LM), myrcene (5.7% in LP; 5.9% in LM and 5.6% in LL) and linalool (2.4% in LP; 2.3% in LM and 3.9% in LL). The best repellency action was observed for LM at 2.0%, followed by LL oil and eugenol, both of them at 2.5%. The Citrus oils were less active than eugenol (LC50 = 0.004 microL/L air) and phosphine, which revealed 100% mortality at 2 x 10(-3) g/L (66.7% of the recommended dose). However, the most potent fumigant toxicity was found with LL oil, with an LC50 value of 1.63 microL/L air, followed by the oils from LM and LP with LC50 values of 2.22 microL/L air and 4.63 microL/L air, respectively. The associated fumigant and repellent properties of these Citrus peel oils, particularly those of C. aurantium and C. senensis var. mimo, could be used to advantage for the control of T. urticae.

Acaricidal Activity against Tetranychus urticae and Chemical Composition of Peel Essential Oils of Three Citrus Species Cultivated in NE Brazil

The repellency and fumigant toxicities of the peel essential oils of Citrus sinensis var. pêra (LP), C. sinensis var. mimo ( LM), and C. aurantium ( LL) cultivated in northeast Brazil were evaluated against Tetranychus urticae. Analysis of the oils by GC and GC/MS led to the identification of twenty-eight components, which represented 99.9%, 99.7% and 99.3% of the total constituents of the LP, LM and LL oils, respectively. Limonene was the main component found in all three oils. Other main components were α-pinene (1.5% in LP; 1.4% in LM), myrcene (5.7% in LP; 5.9% in LM and 5.6% in LL) and linalool (2.4% in LP; 2.3% in LM and 3.9% in LL). The best repellency action was observed for LM at 2.0%, followed by LL oil and eugenol, both of them at 2.5%. The Citrus oils were less active than eugenol (LC50 = 0.004 μL/L air) and phosphine, which revealed 100% mortality at 2×10−3g/L (66.7% of the recommended dose). However, the most potent fumigant toxicity was found with LL oil, with an LC50 value of 1.63 μL/L air, followed by the oils from LM and LP with LC50 values of 2.22 μL/L air and 4.63 μL/L air, respectively. The associated fumigant and repellent properties of these Citrus peel oils, particularly those of C. aurantium and C. senensis var. mimo, could be used to advantage for the control of T. urticae.