CC BY-NC-ND 4.0 · Planta Medica International Open 2020; 07(03): e114-e121
DOI: 10.1055/a-1186-2400
Original Papers

Biological Activity of Matricaria chamomilla Essential Oils of Various Chemotypes

1  Department of Pharmaceutical Chemistry, University of Vienna, Vienna, Austria
,
Jürgen Wanner
2  Kurt Kitzing Co., Wallerstein, Germany
,
Nurhayat Tabanca
3  USDA-ARS, Subtropical Horticulture Research Station, Miami, USA
,
Abbas Ali
4  National Center for Natural Products Research, University of Mississippi, University, MS, USA
,
Velizar Gochev
5  Department of Biochemistry and Microbiology, “Paisii Hilendarski”-University of Plovdiv, Plovdiv, Bulgaria
,
Erich Schmidt
1  Department of Pharmaceutical Chemistry, University of Vienna, Vienna, Austria
,
Vijay K. Kaul
6  CSIR – Institute of Himalayan Bioresource Technology, Palampur, Himachal Pradesh, India
,
Virendra Singh
6  CSIR – Institute of Himalayan Bioresource Technology, Palampur, Himachal Pradesh, India
,
Leopold Jirovetz
1  Department of Pharmaceutical Chemistry, University of Vienna, Vienna, Austria
› Author Affiliations
 

Abstract

The essential oil of Matricaria chamomilla L., which is commonly used for medicinal and cosmetic purposes, can be differentiated between several chemotypes. In the current study, six essential chamomile oil samples of various origins (four of commercial sources, one of cultivation, one of wild collection) were examined regarding their composition and biological activities, i. e., antibacterial, antifungal, mosquito repellent, and larvicidal effects. GC-MS analyses revealed that the samples largely varied in composition and could be attributed to various chemotypes. In contrast to the other two samples, the four commercial samples were unusually high in trans-β-farnesene. The overall antimicrobial effects were only moderate, but it could be shown that a higher content in α-bisabolol and a smaller in α-bisabolol oxides A and B had a positive effect on overall activity. All samples had a biting deterrent effect comparable to DEET. Higher concentrations of (Z )- and (E )-spiroethers improved larvicidal activity, whereas trans-β-farnesene had the opposite effect. In conclusion, the importance of α-bisabolol for the biological activity of chamomile essential oil could be demonstrated.


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Introduction

German chamomile [Matricaria chamomilla L., syn. Matricaria recutita L., Chamomilla recutita (L.) Rauschert, Asteraceae] is among the most valued medicinal plants worldwide. The dried flower heads as well as the essential oil are used as a medicinal drug (Matricariae flos and Matricariae aetheroleum [1] against a broad spectrum of symptoms in the form of tisanes, baths, inhalations, and mouthwashes [2]. Therapeutic indications include inflammatory conditions, bacterial infections, and lesions of the skin and mucosa (e. g., oral cavity, gastrointestinal tract, and respiratory tract), spasms, and ulcers of the gastrointestinal tract as well as insomnia and nervous disposition [2].

Phytochemical analyses have revealed that besides flavonoids (e. g., apigenin, luteolin) and their glycosides as well as coumarins (e. g., herniarin, umbelliferone), the essential oil can be considered crucial for the biological activities of chamomile flowers [3]. The essential oil is notably used in pharmaceutical and cosmetic preparations for its antibacterial [4], antifungal [5], antioxidant [6], and anti-inflammatory [7] [8] properties. The essential oil is mainly comprised of oxygenated sesquiterpenes of the bisabolane type. The blue colour typical for the majority of chamomile oil samples originates from chamazulene, an artefact of the distillation process derived from the nonvolatile sesquiterpene lactone matricin [7].

Within the species M. chamomilla, a chemical polymorphism regarding essential oil composition was first shown by Schilcher [9] and has been substantiated by several studies [10] [11] [12] [13] [14].

In the present study, the compositions of four commercial chamomile essential oil samples as well as a cultivated one and one sample of wild-growing populations were analysed regarding their composition, and antibacterial and anticandidal effects. Moreover, samples from Serbia, Hungary, South Africa, and India were evaluated against biting deterrent and larvicidal activities against Aedes aegypti L. Up to now, the influence of chemotype on biological activities of chamomile essential oils has not been evaluated thoroughly, which was another aim of our study.


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Results

In the present study, the chemical compositions of four commercial essential oil samples, a sample of cultivated plants as well as a sample of collected wild plants were elucidated by means of simultaneous GC-FID and GC-MS. [Table 1] presents the results of the GC-FID and GC-MS analyses. In total, 114 compounds could be identified, amounting to 84.5–95.5%. All samples had a low content in monoterpenes (>3%) except for sample D from India (11.9%, with>2% β-pinene and linalool) and sample F (6.6%) but were dominated by sesquiterpenes (50–84%). While samples A, C, and D were mainly composed of sesquiterpene hydrocarbons, notably (E)-β-farnesene, oxygenated sesquiterpenes prevailed in samples B and F (α-bisabolol oxides A and B, α-bisabolone oxide A) as well as sample E (main compound α-bisabolol). The latter had also notably high concentrations of azulenes (21.8%) and spiroethers (16.9%), not only compared to the other samples (<10%) but also other samples from Hungary [15]. As both α-bisabolol [8] [16] and chamazulene [17] [18] [19] proved to possess anti-inflammatory and highly antioxidant properties [14] [17] [20], this combination is highly preferable for pharmaceutical and cosmetic use.

Table 1 Chemical composition determined by simultaneous GC-FID and GC-MS of six essential oil samples of M. chamomilla L. of various origins.

Compound

RI#

Sample/provenance

A/Hungary

B/South Africa

C/Serbia

D/India

E/Hungary

F/India

hexanal

800

tr

ethyl 2-methyl butanoate

848

0.1

0.1

0.1

0.3

ethyl isovalerate

851

tr

(Z)-3-hexenol

852

tr

0.1

hexanol

862

tr

tricyclene

930

0.3

α-pinene

941

tr

tr

1.2

0.1

isopropyl 2-methylbutanoate

943

tr

tr

tr

0.1

0.2

3-buten-2-one

948

0.5

camphene

957

1.5

tr

isoamyl propanoate

964

0.1

sabinene

980

0.1

tr

0.5

6-methyl-5-hepten-2-one

984

tr

0.1

tr

tr

0.1

0.5

β-pinene

985

tr

2.3

6-methyl-5-hepten-2-ol

989

tr

myrcene

991

tr

0.1

0.1

2-pentylfuran

994

0.1

0.1

tr

yomogi alcohol

997

tr

0.1

0.1

0.4

0.4

octanal

1001

0.1

0.1

tr

0.1

0.1

(Z)-3-hexenyl acetate

1003

tr

δ-3-carene

1017

tr

α-terpinene

1023

tr

tr

p-cymene

1031

0.1

0.1

0.2

1.6

0.1

0.2

limonene

1035

0.1

0.1

tr

0.1

tr

0.1

(Z)-β-ocimene

1036

0.1

tr

0.1

0.1

0.1

1,8-cineole

1038

0.1

1.0

0.3

0.3

(E)-β-ocimene

1050

0.6

0.2

0.6

0.2

0.3

0.9

(E)-2-octenal

1055

tr

3-methyl-2-cyclohexen-1-one

1055

tr

artemisia ketone

1062

0.3

0.4

0.6

0.1

0.5

2.0

γ-terpinene

1065

0.1

tr

0.2

tr

0.2

0.9

1-nonen-3-ol

1067

tr

octanol

1068

0.1

tr

0.1

(Z)-sabinene hydrate

1072

tr

tr

(Z)-linalool oxide

1076

tr

artemisia alcohol

1086

0.1

0.1

0.1

0.5

0.6

(E)-linalool oxide

1092

tr

(Z)-3-hexenyl propanoate

1098

tr

0,1

isoamyl 2-methylbutyrate

1101

0.1

linalool

1102

2.2

0.1

0.1

nonanal

1102

0.1

0.1

tr

acetate of yomogi alcohol

1111

tr

hexyl isobutanoate

1146

tr

(E)-pinocarveol

1150

0.1

4-acetyl-1-methyl-cyclohexene

1155

tr

camphor

1154

0.3

(E)-chrysanthemol

1160

0.1

0.1

(E)-2-nonenal

1165

0.2

lavandulol

1167

0.2

isoborneol

1167

0.1

artemisyl acetate

1169

tr

0.2

0.2

borneol

1177

0.1

0.2

terpinen-4-ol

1186

0.1

0.3

hexyl butanoate

1189

tr

α-terpineol

1198

tr

1.8

0.2

0.2

decanal

1204

tr

γ-terpineol

1204

0.3

4,8-dimethyl-7-nonen-2-one

1227

0.1

(Z)-3-hexenyl-2-methylbutanoate

1231

tr

tr

(Z)-3-hexenyl-3-methylbutanoate

1234

0.1

0.1

4,8-dimethyl-3,7-nonadien-2-one isomer 1

1238

0.3

benzyl propanoate

1258

0.1

geranial

1274

0.1

4,8-dimethyl-3,7-nonadien-2-one isomer 2

1275

0.4

1.2

methyl geranate

1275

0.1

0.3

0.3

lavandulyl acetate

1288

tr

(E,E)-2,4-decadienal

1319

tr

δ-elemene

1352

0.2

α-copaene

1359

0.1

caprinic acid

1360

0.3

0.4

0.1

0.6

0.5

benzyl isovalerate

1398

0.1

tetradecane

1399

0.1

β-elemene

1406

0.2

0.1

0.2

0.2

0.1

0.2

α-isocomene

1411

0.2

0.3

0.4

0.3

2,5-dimethoxy-p-cymene

1423

0.3

(Z)-β-farnesene

1434

0.7

(E)-β-caryophyllene

1442

0.2

0.2

0.3

0.4

0.1

0.1

(E)-α-bergamotene

1448

0.3

geranyl acetone

1453

0.2

(E)-β-farnesene

1460

38.5

18.7

38.4

24.1

3.3

7.2

(Z,Z)-α-farnesene

1475

1.0

dihydrosesquicineole

1479

0.2

0.2

0.3

0.6

0.4

1.4

allo-aromadendrene

1486

0.1

0.2

0.1

γ-curcumene

1490

0.1

0.8

0.1

(Z,E)-α-farnesene

1497

0.6

0.6

(E,Z)-α-farnesene

1496

0.6

0.4

0.9

pentadecane

1499

0.1

0.2

germacrene D

1503

2.3

1.4

3.1

1.0

0.5

1.6

(E,E)-α-farnesene

1510

5.8

1.3

5.6

4.5

0.2

0.8

bicyclogermacrene

1518

1.9

1.2

2.0

0.4

1.1

β-bisabolene

1519

1.5

(Z)-γ-bisabolene

1529

0.5

β-sesquiphellandrene

1535

0.5

γ-cadinene

1537

0.2

0.1

0.1

δ-cadinene

1539

0.2

0.3

0.4

0.2

tr

0.1

trans-γ-bisabolene

1544

0.3

isohumbertiol B

1546

0.1

(Z)-nerolidol

1551

tr

(E)-α-bisabolene

1552

2.7

(E)-nerolidol

1568

0.2

1.4

0.4

0.2

0.8

0.2

(E)-dendrolasin

1580

0.2

0.5

0.1

0.2

0.1

spathulenol

1602

0.7

5.7

0.6

0.7

0.8

caryophyllene oxide

1610

0.1

τ-cadinol

1661

0.4

0.8

0.3

0.2

0.2

0.5

α-bisabolol oxide B

1676

3.9

12.1

5.8

5.9

3.1

17.0

α-bisabolol

1703

1.2

1.9

11.5

5.7

38.3

6.2

(E,E)-farnesol

1704

5.6

epi-α-bisabolol

1705

0.5

α-bisabolone oxide A

1707

3.0

8.5

2.8

5.2

0.1

7.3

(E,Z)-farnesol

1728

4.0

chamazulene

1763

1.3

4.4

8.0

0.6

21.6

6.8

α-bisabolol oxide A

1770

24.1

6.9

6.3

6.0

1.0

25.0

guajazulene

1808

0.2

phytol

1848

0.3

1.1

0.3

0.5

(Z)-spiroether

1887

5.5

10.4

1.3

2.6

0.1

6.0

(E)-spiroether

1900

0.6

1.6

0.2

0.3

16.8

0.6

palmitic acid

1954

0.3

Sum

94.2

84.5

91.7

90.9

95.5

92.2

"tr" = trace, "–" = not detectable.

All of the commercially available samples were found to have a remarkably high content of trans-β-farnesene (18.7–38.5%) compared to sample E from the wild collection in Hungary (3.3%) and sample F from North India (7.2%). Among the reasons for these unusually high levels, the developmental stage of the harvested plants as well as the use of vegetative plant parts [21] can be discussed. These results are supported by a study by Su et al. who showed that the activity of (E )-β-farnesene synthase, and thus (E )-β-farnesene production, is influenced by the plant part investigated (highest in leaves, lowest in disc flowers) and the developmental stage of the plant (highest in semi-opened flowers, lowest in fully opened flowers) amongst other factors like distillation time [22].

In [Table 2], the results of the antimicrobial activity screening are given. As demonstrated before, chamomile essential oil exerts antibacterial effects [4] [20], particularly against gram-positive bacteria like Staphylococcus aureus as well as anticandidal activity [14] against Candida albicans. However, gram-negative bacteria, especially Pseudomonas aeruginosa, were less susceptible. In this respect, this result was predictable as P. aeruginosa is protected against terpenoids and other chemicals by its outer membrane and specific efflux mechanisms [23]. Compared to other essential oils, the overall antimicrobial activity was mediocre, but our findings go along with those of Satyal et al. [14]. While our findings corroborate previous findings concerning the antibacterial effects of pure α-bisabolol [24], there is also evidence for a negative effect of α-bisabolol oxides A and B on antimicrobial activity as shown by samples A and F.

Table 2 Minimal bactericidal/fungicidal concentrations (µg/mL) of six essential oils of M. chamomilla L. of various origins.

Test strain

Essential oils

Controls

A

B

C

D

E

F

Ac

Ci

Ce

Na

Va

S. aureus ATCC 6538

4000

2000

2000

4000

2000

8000

0.5

0.125

0.125

0.063

0.5

E. coli ATCC 25922

4000

2000

4000

2000

2000

8000

0.5

0.25

0.25

0.125

0.25

S. abony ATCC 6017

4000

2000

4000

2000

2000

8000

0.5

0.5

0.5

0.5

0.5

P. aeruginosa ATCC 9027

4000

4000

8000

4000

4000

8000

32

1.0

2.0

4.0

8.0

Am

Fl

It

Ke

Vo

C. albicans ATCC 10231

2000

2000

2000

2000

2000

4000

0.25

0.25

0.25

0.023

0.016

Ac=amoxicillin, Ci=ciprofloxacin, Ce=cefazolin, Na=nalidixic acid, Va=vancomycin; Am=amphotericin B, Fl=fluconazole, It=itraconazole, Ke=ketoconazole, Vo=voriconazole.

The in vitro K&D system used in this study specifically quantified the mosquito biting deterrent properties of five essential oils of M. chamomilla. Biting deterrent indices (BDI) of the essential oils against Aedes aegypti are given in [Fig. 1]. All the essential oil samples showed biting deterrent activity above the negative control ethanol, and the activity of all samples was similar to DEET at 25 nmol/cm2. A high content in α-bisabolol as well as monoterpenes might have a positive influence on biting deterrence, but the differences were minimal.

Zoom Image
Fig. 1 Biting deterrent indices (BDI) of five essential oils (10 µg/cm2) of Matricaria chamomilla L. from various parts of the world against female A. aegypti. Ethanol was the solvent control and DEET at 25 nmol/cm2 was used as positive control. Mean BDI falling between 1/2 length of 95% CI and 1 are statistically similar to DEET.

Data on the toxicity against the larvae of A. aegypti is presented in [Table 3]. The toxicity of sample B (South Africa) with an LD50 of 2.9 ppm was significantly higher than all the other samples, followed by sample F (India) with an LD50 of 8.2 ppm. Samples A (Hungary), C (Serbia), and D (India) exhibited similar mortalities with LD50 values of 60.5, 49.3, and 45.4 ppm, respectively. Sample E was not included in these assays. The high toxicity of samples B and F might be explained by its relatively high content in spiroethers (12.0 and 6.6%, respectively). Polyines (or polyacetylenes), especially those found in the genus Artemisia, have been known to possess high larvicidal activity for a long time [25]. In contrast, higher yields of sesquiterpene hydrocarbons, especially (E)-β-farnesene, had a negative effect on toxicity in Aedes larvae in this study.

Table 3 Toxicity of essential oils of M. chamomilla from various parts of the world against 1-day-old larvae of A. aegypti 24 h post-treatment.

Essential oil

Aedes aegypti

LC50 (95% CI)*

LC90 (95% CI)

χ2

DF

Sample A (Hungary)

60.5 (54.2–67.8)

99.9 (86.3–124.4)

59.8

48

Sample B (S. Africa)

2.9 (2.6–3.2)

4.4 (3.9–5.2)

54.6

48

Sample C (Serbia)

49.3 (43.2–56.6)

103.4 (85.7–135.3)

79.3

48

Sample D (India)

45.4 (40.3–51.1)

81.7 (69.9–102.5)

67.6

48

Sample F (India)

8.2 (7.4–9.0)

12.6 (11.3–15.6)

52.2

48

Permethrin**

0.0034 (0.003–0.0038)

*LC50 and LC90 values are in ppm, 95% CI=confidence interval.


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Discussion

Since 1973 [9], the chemical polymorphism of German chamomile regarding its essential oil has been established. Originally, Schilcher [10] proposed four chemotypes based on varying contents in sesquiterpene compounds: Type A, mainly found in Central, South, and East Europe, is dominated by bisabolol oxide B, Type B (South America) by bisabolol oxide A, and Type C by α-bisabolol, while Type D is composed of comparable quantities of these three sesquiterpenes. Additionally, a variant low in matricin (prochamazulene) was mentioned. This classification has been used by many authors [13] [15] [26] [27], however, Type A and B have been interchanged. Later, Horn et al. [28] could identify four chemotypes as follows: Type I dominated by α-bisabolol and matricin, Type IIa by α-bisabolol oxide A and matricin, Type IIb by α-bisabolol oxide B and matricin, and Type III high in α-bisabolone oxide but devoid of α-bisabolol and matricin. Horn et al. [28] as well as Massoud and Franz [29] [30] also elucidated the genetically controlled mechanisms for the formation of α-bisabolol and its derivatives as well as chamazulene and identified the responsible genes, thus assigning genotypes to the chemotypes. As some of these chemotypes form locally distinct populations, they could also be termed “chemodem” [31]; however, this term is rarely used in literature. Moreover, some authors suggested spiroether [14] [32] and trans-β-farnesene [14] chemotypes; however, Satyal et al. [14] analysed the essential oil of the aerial parts. Interestingly, the European Pharmacopoeia differentiates between only two chemotypes, one rich in α-bisabolol (10–65%) and one dominated by bisabolol oxides (29–81%) [1].

Considering that a high trans-β-farnesene level might also be ascribed to a premature harvesting or use of stems and leaves, the samples in the current study could be characterised as follows: Sample A (Hungary) is a representative of the α-bisabolol oxide A/matricin type, and sample E (Hungary) is typical for the α-bisabolol/matricin type, both of which are commonly found in Hungary [15]. Sample F (North India) can also be attributed to the α-bisabolol oxide A/matricin type (though also rich in α-bisabolol oxide B), which is apparently common for this region [33] as well as the Ganges plains [34]. Sample B (South Africa) might represent the α-bisabolol oxide B/matricin type, whereas sample C (Serbia) could be an example of Schilcher’s Type D, which is prevalent in this geographical region [35] [36]. Sample D (India) might also be attributed to Type D, even though it is also rich in α-bisabolone oxide and poor in chamazulene. However, the limited data on used cultivars, harvesting, and essential oil production of the commercial samples should be pointed out.

In conclusion, our study could demonstrate that the quantitative differences regarding the chemical composition of M. chamomilla essential oils crucially influence biological activities such as antimicrobial, insect repellent, and larvicidal effects. To our knowledge, this is the first published study that directly compared chamomile essential oils of different provenance and chemotype in this respect. Regarding essential oil composition, essential oils of chemotypes rich in α-bisabolol, chamazulene, and spiroethers should be preferred over chemotypes dominated by trans-β-farnesene and α-bisabolol oxides for use in pharmaceutical and cosmetic products as these compounds have been shown once more to have positive effects on various activities of chamomile essential oil.


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Materials and Methods

Plant material

Three essential oil samples were purchased from Paul Kaders (Hamburg, Germany): sample A (Lot. nr. 122300/260810, Hungary), sample B (Lot. nr. 12302/260810, South Africa), and sample D (Lot. nr. 122306/260810, India). Sample C (Lot. nr. 38595, Serbia) was purchased from Unterweger (Thal-Assling, Austria). Sample E was prepared in 2009 by Beata Gosztola and authenticated by Prof. Eva Nemeth (Corvinus University, Budapest, Hungary) from plants of a wild-growing population of M. chamomilla. For sample F, the plants were cultivated and harvested by Dr. Virendra Singh at the CSIR-Institute of Himalayan Bioresource Technology (Palampur, India) from April to May 2014, and authenticated by V. K. Kaul. The aerial parts containing 95% flowers were distilled using a Clevenger-type apparatus; the oil yield was 0.1%.


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Essential oil analysis

GC-FID and GC-MS analyses as well as identification and quantification of the compounds were carried out as described earlier [37]. Retention indices [38] were compared to retention indices of reference compounds and from literature data [39] [40] [41] [42] to confirm the peak data. Quantification of compounds was performed using normalised peak area calculations of the FID chromatogram.


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Microbiological assays

The antimicrobial effects of the essential oils were tested against the following strains of microorganisms: S. aureus ATCC 6538, Escherichia coli ATCC 25922, Salmonella abony ATCC 6017, P. aeruginosa ATCC 9027, and C. albicans ATCC 10231, all obtained from culture collections of The National Bank of Industrial Microorganisms and Cell Cultures (NBIMCC, Bulgaria). Nutritional agar, Mueller-Hinton broth and agar as well as Sabouraud dextrose broth and agar were obtained from the National Center of Infectious and Parasitic Diseases (NCIPD, Bulgaria). For positive controls, HiComb MIC test strips were obtained from HiMedia Laboratories Ltd. Antibacterial and anticandidal susceptibility testing was carried out as described in detail previously [43].


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Mosquito bioassays

Both the larvae and adult mosquitoes used in these studies were from the laboratory colonies maintained at the Mosquito and Fly Research Unit at the Center for Medical, Agricultural and Veterinary Entomology, USDA-ARS, Gainesville, Florida. Maintenance conditions and bioassays are described in detail elsewhere [44].

For biting bioassays, two sets of replications, consisting of six treatments (four test compounds, DEET at 25 nmol/cm2, and ethanol-treated organdy as a solvent control) each with five females per treatment, were conducted on two different days using a newly treated organdy and a new batch of females in each replication. Treatments were replicated nine times.

Regarding the larval bioassay, larvae that showed no movement in the well after manual disturbance of water were recorded as dead. A series of 5 concentrations ranging between 125 and 0.98 ppm were used in different treatments to obtain a range of mortality. Permethrin (46.1% cis/53.2% trans; Chemical Service) was used as a positive control. Treatments were replicated ten times for each of the treatments.

Statistical analysesProportion not biting (PNB) and biting deterrence index (BDI) were calculated as described before [44]. A BDI value of 0 indicates an effect similar to ethanol, while a value significantly greater than 0 indicates a biting deterrent effect relative to ethanol. BDI values that were not significantly different from 1 are statistically similar to DEET. BDI values were analysed using SAS Proc ANOVA [single factor: test compound (fixed)], (SAS Institute 2007), and means were separated using the Ryan-Einot-Gabriel-Welsch Multiple Range Test. To determine whether confidence intervals (CIs) include the values of 0 or 1 for treatments, Scheffe’s multiple comparison procedure with the option of CLM was used in SAS. LC50 values for larvicidal data were calculated by using SAS, Proc Probit. Control mortality was corrected by using Abbott’s formula [45]. Toxicity was compared among treatments based on non-overlapping 95% CIs [46].


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Conflict of interest

The authors declare thay they have no conflict of interest.


Correspondence

Dr. Martina Höferl
Department of Pharmaceutical Chemistry
University of Vienna, UZA-2
Althanstrasse 14
1090
Vienna
Austria   
Phone: +43 1 4277 55555   
Fax: +43 1 4277 855555   

Publication History

Received: 16 December 2019
Received: 15 May 2020

Accepted: 18 May 2020

Publication Date:
15 July 2020 (online)

© 2020. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/).

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Fig. 1 Biting deterrent indices (BDI) of five essential oils (10 µg/cm2) of Matricaria chamomilla L. from various parts of the world against female A. aegypti. Ethanol was the solvent control and DEET at 25 nmol/cm2 was used as positive control. Mean BDI falling between 1/2 length of 95% CI and 1 are statistically similar to DEET.