Insecticidal activities of essential oils from leaves of Laurus nobilis L. from Tunisia, Algeria and Morocco, and comparative chemical composition

Insecticidal activities of essential oils from leaves of Laurus nobilis L. from Tunisia, Algeria and Morocco, and comparative chemical composition

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Journal of Stored Products Research 48 (2012) 97e104

Contents lists available at SciVerse ScienceDirect

Journal of Stored Products Research journal homepage: www.elsevier.com/locate/jspr

Insecticidal activities of essential oils from leaves of Laurus nobilis L. from Tunisia, Algeria and Morocco, and comparative chemical composition Jouda Mediouni Ben Jemâa a, *, Nesrine Tersim a, Karima Taleb Toudert b, Mohamed Larbi Khouja c a

Laboratoire de Protection des Végétaux, INRAT, Rue Hedi Karray, Université de Carthage, 2080 Ariana, Tunisia Faculté des Sciences Biologiques et des Sciences Agronomiques, Université Mouloud Mammeri, BP 17, Tizi-Ouzou, Algeria c Laboratoire d’Ecologie et d’Amélioration Sylvo-Pastorale, INRGREF, Rue Hedi Karray, Université de Carthage, 2080 Ariana, Tunisia b

a r t i c l e i n f o

a b s t r a c t

Article history: Accepted 10 October 2011

Laurus nobilis essential oils from Tunisia, Algeria and Morocco were analyzed for their chemical composition and assessed for their repellent and toxic activities against two major stored product pests: Rhyzopertha dominica and Tribolium castaneum. The three oils showed quantitative rather than qualitative differences in their chemical compositions. 1,8-cineole, linalool and isovaleraldehyde, were identified as the major common compounds whereas, a-pinene, a-terpineol, eugenylmethylether, b-pinene, spathulenol and b-myrcene were also well represented in all three oils. Results showed that L. nobilis essential oils were repellant and toxic to adults of R. dominica and T. castaneum. Repellent and fumigant toxicities were highly dependent upon insect species and oil origin. In filter paper tests, L. nobilis essential oil from Morocco was more effective compared to Tunisian and Algerian oils. RD50 values were respectively 0.013 ml/cm2, 0.036 ml/cm2 and 0.033 ml/cm2 for R. dominica versus 0.045 ml/cm2, 0.139 ml/cm2 and 0.096 ml/cm2 for T. castaneum. Moreover, fumigant activity tests showed that both R. dominica and T. castaneum were more susceptible to L. nobilis essential oil from Morocco than that from Algeria or Tunisia. The corresponding LC50 values were respectively 68, 99 and 113 ml/l air for R. dominica against 172, 194 and 217 ml/l air for T. castaneum. Our work clearly vindicates interest in the efficacy of essential oils from plants of Mediterranean origin both as insecticides and repellents against stored product pests. Ó 2011 Elsevier Ltd. All rights reserved.

Keywords: Laurus nobilis Repellency Fumigation 1,8-cineole Mediterranean region Maghreb countries

1. Introduction Historically, cereal production has always been an important component of Tunisian agriculture. Durum wheat is the major crop and the most widely cultivated cereal (Latiri et al., 2010). Insects are the main problem in stored grains because they affect quantity and quality (Madrid et al., 1990). The lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and the rust-red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) are among the most important stored-grain pests in Tunisia and North Africa (Jarraya, 2003). T. castaneum is one of the key pests of stored products and stored grains throughout the world (Sinha and Watters, 1985). It is one of the most common insect pests worldwide of flour mills, grocery shops, and warehouses (Garcìa et al., 2005). In addition, the lesser grain borer, R. dominica (F.), is one of the most

* Corresponding author. Tel.: þ216 71235317, þ216 97 652 174 (Cell); fax: þ216 71752897. E-mail address: [email protected] (J. Mediouni Ben Jemâa). 0022-474X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jspr.2011.10.003

important internal feeders of stored grain (Chanbang et al., 2007). It is a major primary pest of stored products (Rees, 1995). Several methods based on techniques such as fumigant action and repellent activity of a broad-spectrum of insecticides have been attempted to control insect pests in storage. Use of fumigants is the most economical tool for managing stored grain insect pests (Mueller, 1990). However, repellents could be used to provide protective bands around grain bulks or incorporated into packaging materials to inhibit invasion by pests (Cox, 2004). The continuous use of broad-spectrum pesticides and fumigants to prevent losses in stored grains has led to numerous problems related to environmental and human health concerns. Thus, continued searching for systems of grain protection that target the pest species more accurately is needed (Cox, 2004). In this context, plant extracts including essential oils can play an important role in protecting grains against insect infestations (Regnault-Roger, 1997; Isman, 2000; Bakkali et al., 2008; Batish et al., 2008). Essential oils exhibit various insecticidal properties; they may have a fumigant activity (Shaaya et al., 1997) and may also act as repellents (Saim and Meloan, 1986).

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The Mediterranean laurel Laurus nobilis L. (Lauraceae) is an evergreen shrub up to 2.15 m height commonly named bay laurel. It is native to the southern Mediterranean region and widely cultivated in Europe and the USA as an ornamental plant. In North African countries (Tunisia, Algeria, Morocco), bay laurel is a common species. Rodríguez-Sánchez et al. (2008) indicated that L. nobilis is common in the Atlas Mountains in Morocco. In Algeria, laurel shrubs are present in the alder forests distributed throughout the wetland complexes of Annaba- El Kala and Guerbès-Senhadja, the coastal interdunal ridges, the riparian alder forests developed along wadies and the lake margins (Belouahem-Abed et al., 2011). In Tunisia, it grows at the edges of rivers, on mountains and on wet cliffs, but is scarce. It also grows in the humid and sub-humid bioclimatic areas, especially in Ain Draham, Tabarka, and Cap-Bon (Pottier-Alapetite, 1979). It is grown commercially for its aromatic leaves in Algeria and Morocco where commercial production centres of L. nobilis are widespread (Demir et al., 2004; Barla et al., 2007). The biological activities and phytochemistry of L. nobilis have previously been extensively investigated. L. nobilis is mainly used in the flavouring industry and could be used as botanical biopesticide in postharvest crop protection (Kivçak and Mert, 2002). In this context, Papachristos and Stamopoulos (2002) reported that L. nobilis essential oil has a repellent action against the bean weevil Acanthoscelides obtectus (Say). Correspondingly, Saim and Meloan (1986) and Andronikashvili and Reichmuth (2002) indicated that L. nobilis essential oil was highly repellent to the rust-red flour beetle T. castaneum (Herbst) and Cosimi et al. (2009) reported that L. nobilis essential oil was repellent to Sitophilus zeamais (Motschulsky), Cryptolestes ferrugineus (Stephens) and Tenebrio molitor (L.). Andronikashvili and Reichmuth (2002) also indicated that L. nobilis essential oil was strongly toxic to the rust-red flour beetle T. castaneum, and Rozman et al. (2007) reported the fumigant activity of naturally occurring compounds of the essential oils of L. nobilis and some other plants against three stored product beetles: T. castaneum, Sitophilus oryzae (L.) and R. dominica (F.). The chemical composition of bay laurel essential oils from different origins has been studied by different researchers. In all cases, 1,8-cineole was the major component with percentages ranging between 31.4% and 56% (Pino et al., 1993). Accordingly, Yalçin et al. (2007) reported that essential oil from L. nobilis leaves is characterized by a high content of 1,8-cineole. Moreover, Zola et al. (1977) reported that essential oils extracted from bay laurel showed substantial consistency regarding their chemical composition. Similarly, Sangun et al. (2007) indicated that the chemical compositions of essential oils from laurel leaves collected from different regions in Turkey were similar according to qualitative and quantitative analysis and they had a high content of 1,8cineole. Interestingly, Ozcan and Chalchat (2005) point out that minor qualitative and major quantitative variation of some compounds of L. nobilis essential oils occur with respect to localities of collection. In Tunisia and Algeria, a comparative study conducted by Marzouki et al. (2002) indicated that laurel essential oils presented as major common compounds 1,8-cineole, linalool, a-terpinyl acetate, methyl eugenol, sabinene and (E)-caryophyllene. Recently, Marzouki et al. (2009) reported that L. nobilis essential oils from Tunisia and Algeria did not reveal differences in their chemical composition. The two oils contained the major constituents in variable proportions. 1,8-cineole represented 31.0% of the oil in Tunisian samples and only 17.0% in Algerian oil. In Morocco, Derwich et al. (2009) reported that the major component of L. nobilis essential oil was 1,8-cineole, other predominant components were a-terpinyl acetate, sabinene and limonene. To the best of our knowledge, no other reports are available on the comparative chemical composition of essential oils from bay

laurel leaves collected from Tunisia, Algeria and Morocco. Thus, the objectives of this work were (1) to investigate and compare the chemical composition of Tunisian, Algerian and Moroccan L. nobilis essential oils and (2) to assess their fumigant and repellent proprieties as control alternatives against the two stored product beetles R. dominica and T. castaneum. 2. Materials and methods 2.1. Insects Adults of R. dominica were reared on whole wheat, while T. castaneum adults were reared on wheat flour at 25  1  C and 65%  5% relative humidity (r.h.). Adult insects of mixed sex, 7e14 days old, were used for bioassays tests. 2.2. Plant material Laurus nobilis leaves were collected in February 2010 from the nursery of the experimental station of INRGREF at Ariana, Tunis, Tunisia (36 500 N; 10140 W), from Tizi-Ouzou, Algeria (36 430 N; 4 030 E) and from Marrakesh, Morocco (31380 N; 8 00 W). The harvested material was air-dried at room temperature (20e25  C) for one week and then stored in cloth bags. 2.3. Essential oils extraction and chemical analysis The essential oils were extracted by hydrodistillation of dried plant material (100 g of each sample in 500 ml of distilled water) using a modified Clevenger-type apparatus for 4 h. The oils were dried over anhydrous sodium sulphate and stored in sealed glass vials at 4e5  C prior to analysis. Yields were averaged over four experiments and calculated according to dry weight of the plant materials. The essential oils were analyzed using an Agilent-Technologies 6890 N Network GC system equipped with a flame ionization detector and HP-5MS capillary column (30 m  0.25 mm, film thickness 0.25 mm; Agilent-Technologies, Little Falls, CA, USA). The injector and detector temperatures were set at 220  C and 290  C, respectively. The column temperature was programmed from 80  C to 220  C at a rate of 4  C/min, with the lower and upper temperatures being held for 3 and 10 min, respectively. The flow rate of the carrier gas (Helium) was 1.0 ml/min. A sample of 1.0 ml was injected, using split mode (split ratio, 1:100). All quantifications were carried out using a built-in data-handling program provided by the manufacturer of the gas chromatograph. The composition was reported as a relative percentage of the total peak area. The identification of the essential oils constituents was based on a comparison of their retention times to n-alkanes, compared to published data and spectra of authentic compounds. Compounds were further identified and authenticated using their mass spectra compared to the Wiley version 7.0 library. Major compounds (5%) and other predominant components (0.5e5%) were marked in bold form when tabulating the data. 2.4. Bioassays tests 2.4.1. Repellency bioassay Repellency assays of L. nobilis essential oils were carried out according to the experimental method described by Jilani and Saxena (1990) at 25  1  C and 65%  5% r.h. Whatman filter papers (diameter 8 cm) were cut in half. Test solutions were prepared by dissolving 2, 4 and 6 ml of L. nobilis essential oil in 1 ml acetone. Each solution was applied to half a filter paper disc as uniformly as possible with a micropipette. The other half of the

J. Mediouni Ben Jemâa et al. / Journal of Stored Products Research 48 (2012) 97e104 Table 1 Percentage composition of Laurus nobilis essential oils collected from Tunisia, Algeria and Morocco (Major and predominant compounds marked in bold form). Components

RT

KI

Tunisia

Algeria

Morocco

Isohexane Pentane Isovaleraldehyde Cyclopentane 1,3-pentadiene Heptanen a-thujene a-pinene Camphene b-phellandrene b-pinene b-myrcene L-phellandrene a-phellandrene D3-carene a-terpinene 1,8-cineole b-Ocimene g-terpinene Trans-sabinene hydrate a-terpinolene 2-norbornanone Linalool Cis-sabinene hydrate 1-terpineol 2-cyclohexen-1-ol Camphor Tepinene 4-terpienol Tepinen-1-ol a-terpineol 2-pinen-10-ol Esdragole Cis-geraniol Linalyl acetate Pulegone Vertiverol Endobornyl acetate a-fenchyl acetate 1-bornyl acetate 2-undecanone Phenol 2-carene Camphene Eugenol Nerylacetate g-phenylpropyl acetate Geraniol acetate b-elemene Eugenylmethylether a-gurjunene Trans-caryophyllene b-caryophyllene Trans-b-caryophyllene a-guaiene Cinnamyl acetate Iso-eugenol a-caryophyllene Epizonaren Aromadendrene Ethyl-cinnamate Cinnamic acidethyl ester Cyclodecene Germacene-D b-selinene Naphtalene a-berganotene Methyl cis-isoeugenol Eremophilene Lepidozene Germacrene a-amorphene b-elemene D-cadinene

2.06 2.14 2.27 2.5 2.62 3.29 8.65 8.88 9.27 10.13 10.19 10.61 11 11.01 11.16 11.38 12.05 12.07 12.68 12.96 13.57 13.60 14.28 14.64 14.67 14.71 15.39 16.30 16.31 16.33 16.72 16.84 16.85 17.70 18.45 18.03 18.1 19.29 19.30 19.31 19.48 19.92 21.11 21.14 21.33 21.36 21.57 21.86 22.15 22.67 22.61 22.87 22.89 22.91 23.34 23.47 23.63 23.74 23.79 23.91 23.99 24 24.08 24.41 24.53 24.55 24.66 24.77 24.79 24.79 24.99 25.20 25.09 25.41

636 663 701 716 724 766 921 930 945 977 980 995 1006 1006 1010 1014 1029 1030 1045 1050 1063 1064 1080 1087 1087 1089 1111 1125 1125 1126 1189 1196 1197 1229 1257 1264 1266 1292 1288 1293 1297 1312 1358 1357 1367 1368 1376 1386 1398 1415 1414 1426 1426 1428 1443 1448 1455 1459 1461 1467 1468 1469 1471 1486 1489 1490 1494 1499 1499 1500 1508 1518 1511 1526

0.35 0.47 9.65 0.11 e 0.03 0.22 2.52 0.41 3.85 1.39 0.30 e e 0.11 0.11 24.55 0.04 0.26 0.14 e 1.20 17.67 e e 0.08 2.66 e e 1.47 1.29 0.14 e 0.10 0.69 e e e 0.40 e 0.09 0.30 e 7.21 2.18 e e 0.08 0.08 12.40 e e 0.27 e 0.10 e e 0.08 e e e e 0.08 e e 0.27 e

0.33 2.14 8.82 0.10 e 0.03 0.44 4.58 0.25 5.71 1.95 0.87 e 0.11 0.42 0.28 34.62 0.28 0.22 0.08 0.15 e 12.57 e 0.04 e e 0.92 e e 0.90 e 0.12 0.08 0.41 e e 0.15 e e e 1.73 e 8.91 e e 0.09 e 0.31 2.84 0.10 e e 0.74 0.8 e e e 0.06 0.23 e 0.11 e 0.18 0.04 0.19 0.19

0.67 e e e 0.17 0.10

e 0.39 e 0.19 e 0.09

0.41 e 10.47 e 0.02 e 0.33 4.31 0.42 e 1.92 0.80 0.19 e 0.19 0.32 38.86 e 0.62 0.30 0.20 e 9.45 0.08 e e e e 1.52 e 5.83 e e 0.14 e 0.05 0.08 e e 0.52 0.06 e 5.62 e 1.42 0.13 e e 0.16 3.93 e 0.05 e e e 0.06 0.03 e e e 0.25 e e e 0.18 e e 0.16 e e 0.1 e e e

99

Table 1 (continued) Components

RT

KI

Tunisia

Algeria

Morocco

b- isoprpyl

26.04 26.15 26.17 26.80 26.89 26.92 27.09 27.35 27.36 27.49 27.71 27.94 27.94 28.12 28.19 28.43 18.48 28.51

1554 1558 1558 1587 1591 1592 1599 1612 1612 1625 1626 1636 1636 1644 1646 1658 1660 1661

0.05 e 0.28 1.12 e e 0.11 e 0.09 e e 0.23 e 0.12 e 0.50 e 0.70 87.84

e e 0.24 1.66 e 0.47 0.13 0.13 e 0.08 e

e 0.14 e 0.16 0.23 e e e e e 0.04

0.09 0.12 0.07

e e e

0.15 e 96.9

e e 89.75

Elemicin Benzene Spathulenol Globulol Caryophyllene epoxide Veridiflorol Ledol D-gurjunene Allo spathullenol b-maaliene b-gurjunene Caryophyllene Isospathulenol g-cadinene 2-naphthalenemethanol a-cadinol Ledene Total

e Not detected. RI, KI were respectively Retention Index and Kováts Index calculated on a HP-5MS capillary column (30 m  0.25 mm  0.25 mm).

filter paper was treated with acetone alone as a control. The treated and control half discs were air-dried under a fan to evaporate the solvent completely. Treated and untreated halves were attached to their opposites using adhesive tape and placed in Petri dishes. Twenty adult (7e14 days old) beetles of mixed sex were released at the centre of each filter paper disc. The dishes were then covered and sealed with Parafilm. Four replications were used for each concentration. Observations on the number of insects present on both the treated and untreated halves were recorded after 1, 3, 5 and 24 h. Four trials were made for each concentration to test for homogeneity ratio (1:1) by applying the c2-test. 2.4.2. Percentage repellency (PR) and median repellent dose (RD50) Numbers of R. dominica and T. castaneum present on the treated and untreated portions of the experimental paper halves were recorded after various periods of exposure. Percentage repellency (PR) was calculated according to Nerio et al. (2009) as follows:

PR ¼ ½Nc  Nt=ðNc þ NtÞ  100: Nc was the number of insects on the untreated area after the exposure interval and Nt was the number of insects on the treated area after the exposure interval. Four replications were used for each concentration. The mean number of insects on the treated portion of the filter paper was compared with the number on the untreated portion. Results were presented as the mean of percentage repellency  the standard error. Probit analysis (Finney, 1971) was then used to calculate the median repellent dose RD50 (dose that repelled 50% of the exposed insects). 2.4.3. Fumigant activity bioassay To assess fumigant toxicity of L. nobilis essential oils, 2 cm diameter filter papers (Whatman No. 1) were impregnated with the different oil doses 2, 3, 4, 5 and 6 ml. The impregnated filter papers were then attached to the screw caps of 38 ml Plexiglas bottles to give calculated fumigant concentrations of respectively 52.63, 78.95, 105.3, 131.6 and 157.9 ml/l air. Caps were screwed tightly on the vials, each of which contained 10 unsexed adults (7e14 days old). Each concentration and control was replicated four times. Mortality was recorded hourly until death. When no leg or antennal movements were observed, insects were considered dead. Bioassays were designed to assess respectively median lethal

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Table 2 Rhyzopertha dominica: repellent effect of three L. nobilis essential oils to adults after different exposure times in the filter paper test. Data tested by applying the c2-test; total number of insects for each concentration was 80; TEO: Tunisian Essential Oil; AEO: Algerian Essential Oil; MEO: Moroccan Essential Oil. Dose (ml/cm2)

Trial

Number of beetles on each half after each exposure 1h

TEO

0.04

0.08

0.12

AEO

0.04

0.08

0.12

MEO

0.04

0.08

0.12

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

3h

5h

24 h

Tr

Un

c2

c2r

c2s

Tr

Un

c2

c2r

c2s

Tr

Un

c2

c2r

c2s

Tr

Un

c2

1 0 7 1 2 5 7 1 2 1 1 1 8 2 4 3 1 1 3 4 0 0 1 0 1 1 2 1 1 0 1 2 0 0 0 0

19 20 13 19 18 15 13 19 18 19 19 19 12 18 16 17 19 19 17 16 20 20 19 20 19 19 18 19 19 20 19 18 20 20 20 20

16.25 20.05 1.85 16.25 12.85 5.05 1.85 16.25 12.85 16.25 16.25 16.25 0.85 12.85 7.25 9.85 16.25 16.25 9.85 7.25 20.05 20.05 16.25 20.05 16.25 16.25 12.85 16.25 16.25 20.05 16.25 12.85 20.05 20.05 20.05 20.05

48.05

54.40 **

62.80 **

57.60 **

80.05

80.20 **

80.05

80.20 **

26.45

30.80 **

0.05

5.60 NS

0.25

4.10 NS

48.05

49.60 **

45.05

46.20 **

39.20

40.60 **

76.05

76.40 **

64.80

65.40 **

64.80

66.20 **

61.25

61.60 **

51.20

51.80 **

45.00

47.00 **

64.80

65.40 **

57.80

58.20 **

45.00

46.20 **

80.05

80.20 **

76.05

76.40 **

12.85 20.05 16.25 20.05 16.25 16.25 5.05 20.05 20.05 20.05 20.05 20.05 3.25 0.85 0 0 12.85 9.85 5.05 12.85 20.05 9.85 16.25 20.05 12.85 12.85 16.25 5.05 9.85 12.85 16.25 7.25 16.25 12.85 20.05 12.85

80.05

61.60 **

18 20 19 20 19 19 15 20 20 20 20 20 6 12 10 10 18 17 15 18 20 17 19 20 18 18 19 15 17 18 19 16 19 18 20 18

69.20 **

80.05

2 0 1 0 1 1 5 0 0 0 0 0 14 8 10 10 2 3 5 2 0 3 1 0 2 2 1 5 3 2 1 4 1 2 0 2

68.45

61.25

20.05 12.85 12.85 20.05 12.85 20.05 20.05 9.85 20.05 20.05 20.05 20.05 0.25 1.85 3.25 0.25 16.25 12.85 9.85 7.25 16.25 20.05 12.85 16.25 12.85 9.85 12.85 16.25 16.25 16.25 12.85 12.85 20.05 20.05 20.05 16.25

65.80 **

36 **

20 18 18 20 18 20 20 17 20 20 20 20 9 13 6 11 19 18 17 16 19 20 18 19 18 17 18 19 19 19 18 18 20 20 20 19

64.85

61.25

0 2 2 0 2 0 0 3 0 0 0 0 11 7 14 9 1 2 3 4 1 0 2 1 2 3 2 1 1 1 2 2 0 0 0 1

61.25

62.00 **

8 13 9 6 9 8 2 2 0 1 4 4 13 2 9 10 2 0 6 0 2 1 3 0 5 3 6 7 4 6 7 10 6 4 3 5

12 7 11 14 11 12 18 18 20 19 16 16 7 18 11 10 18 20 14 20 18 19 17 20 15 17 14 13 16 14 13 10 14 16 17 15

0.85 1.85 0.25 3.25 0.25 0.85 12.85 12.85 20.05 16.25 7.25 7.25 1.85 12.85 0.25 0 12.85 20.05 3.25 20.05 12.85 16.25 9.85 20.05 5.05 9.85 3.25 1.85 7.25 3.25 1.85 0 3.25 7.25 9.85 5.05

c2r

c2s

0.85

6.20

48.05

26.80 **

48.05

50.80 **

1.85

14.95 *

51.25

56.20 **

57.80

59 **

18.05

20.00 **

8.45

12.35 **

24.2

25.40 **

Data tested by c2-test for homogeneity of 1:1 ratio; ** Means for treated (Tr) and untreated (Un) halves significantly different at P < 1%; * Means significantly different at P < 5%; NS: means not significantly different (P < 5%).

concentration (LC50 values) (dose that kill 50% of the exposed insects) and median lethal time (LT50 values) (time that kills 50% of exposed insects). 2.5. Data analysis One-way analysis of variance using Statistica (Statsoft, 1998) was performed on the data. A Duncan test was applied to the means to detect significant differences of repellency among concentrations and oils at the 0.05 percent level. Data are presented in tables as means with standard errors. Probit analysis (Finney, 1971) was conducted to estimate median repellent dose (RD50), median lethal concentrations (LC50) and median lethal time (LT50 values) with their 95% fiducial limits; RD, LC and LT values were considered significantly different when their respective 95% fiducial limits did not overlap.

Algeria and Morocco respectively, representing 87.84%, 96.9% and 89.75% of the total content (Table 1). Oils yields determined on the basis of leaf dry matter weight were respectively 0.584%, 0.46% and 0.655%. Qualitatively, the oils obtained from the three countries were found to have similar compositions; the main common compounds were 1,8-cineole, linalool and isovaleraldehyde. Thus the collection locality (country) does not have a major effect on chemical composition of the essential oils but does influence the relative essential oil contents. Oils constituents were present in variable proportions. Nevertheless, some components were only present in one or the other of the oils. In this respect, 2-carene (5.62%), 4-terpienol (1.52%) and 1-bornyl acetate (0.52%) were only present in the Moroccan oil while pentane (2.14%), phenol (1.73%) and terpinene (0.92%) were at high levels only in Algerian oil. Tunisian oil is characterized by the presence of camphor (2.66%), terpinene-1-ol (1.47%), 2norbornanone (1.20%) and eremophilene (0.67%) (Table 1).

3. Results 3.2. Repellent activity tests 3.1. Chemical composition of L. nobilis essential oils The essential oil compositions (%) of L. nobilis leaves collected from Tunisia, Algeria and Morocco, as determined by GC and GC/MS analysis, are listed in Table 1. Fifty one, fifty five and forty compounds were identified from the essential oils from Tunisia,

Repellency tests results are shown in Tables 2e4 while Table 5 gives the calculated median repellent dose (RD50) values. Chi-square analysis indicated that the three essential oils showed significant pest repellent activity to R. dominica and T. castaneum adults. Oils were repellent even at low concentrations

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101

Table 3 Tribolium castaneum: repellent effect of three L. nobilis essential oils to adults after different exposure times in the filter paper test. Data tested by applying the c2-test; total number of insects for each concentration was 80; TEO: Tunisian Essential Oil; AEO: Algerian Essential Oil; MEO: Moroccan Essential Oil. Dose (ml/cm2)

Trial

Number of beetles on each half after each exposure 1h

TEO

0.04

0.08

0.12

AEO

0.04

0.08

0.12

MEO

0.04

0.08

0.12

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

3h

5h

Tr

Un

c2

c2r

c2s

Tr

Un

c2

4 8 5 3 3 4 2 4 1 3 4 2 3 1 1 2 2 3 1 1 1 1 1 1 3 1 0 1 2 1 1 1 1 0 0 1

16 12 15 17 17 16 18 16 19 17 16 18 17 19 19 18 18 17 19 19 19 19 19 19 17 19 20 19 18 19 19 19 19 20 20 19

7.25 0.85 5.05 9.85 9.85 7.25 12.85 7.25 16.25 9.85 7.25 12.85 9.85 16.25 16.25 12.85 12.85 9.85 16.25 16.25 16.25 16.25 16.25 16.25 9.85 16.25 20.05 16.25 12.85 16.25 16.25 16.25 16.25 20.05 20.05 16.25

20.00

23.00 **

8 12 7 6 7 9 10 5 5 3 2 4 5 6 9 5 4 5 6 7 2 3 1 1 5 1 1 2 2 3 2 1 2 2 1 3

12 8 13 14 13 11 10 15 15 17 18 16 15 14 11 15 16 15 14 13 18 17 19 19 15 19 19 18 18 17 18 19 18 18 19 17

0.85 0.85 1.85 3.25 1.85 0.25 0 5.05 5.05 9.85 12.85 7.25 5.05 3.25 0.25 5.05 7.25 5.05 3.25 1.65 12.85 9.85 16.25 16.25 5.05 16.25 16.25 12.85 12.85 9.85 12.85 16.25 12.85 12.85 16.25 9.85

36.45

37.20 **

45.00

46.20 **

54.45

55.20 **

54.45

55.20 **

64.85

65.00 **

61.25

62.40 **

61.25

61.60 **

72.25

72.60 **

c2r

c2s

2.45

6.80 *

4.05

7.15 *

33.80

35.00 **

11.25

13.60 **

16.25

17.20 **

26.45

55.20 **

48.05

50.40 **

51.25

51.80 **

51.25

51.80 **

24 h

Tr

Un

c2

10 14 9 11 9 10 13 7 7 5 9 10 10 11 8 12 9 8 7 11 5 6 9 11 6 3 4 3 4 3 5 4 4 2 2 4

10 6 11 9 11 10 7 13 13 15 11 10 10 9 12 8 11 12 13 9 15 14 11 9 14 17 16 17 16 17 15 16 16 18 18 16

0 3.25 0.25 0.25 0.25 0 1.85 1.85 1.85 5.05 0.25 0 0 0.25 0.85 0.85 0.25 0.85 1.85 0.25 5.05 3.25 0.25 0.25 3.25 9.85 7.25 9.85 7.25 9.85 5.05 7.25 7.25 12.85 12.85 7.25

c2r

c2s

Tr

Un

c2

0.85

3.75 NS

0.05

3.95 NS

4.05

7.15 **

0.05

1.95 NS

1.25

3.20 *

4.05

8.80 **

28.85

30.20 **

28.85

29.40 **

39.25

40.20 **

15 16 10 9 12 9 14 9 11 12 13 10 12 15 6 14 10 12 14 9 10 7 8 11 9 8 7 9 6 7 5 9 6 4 4 5

5 4 10 11 8 11 6 11 9 8 7 10 8 5 14 6 10 8 6 11 10 13 12 9 11 12 13 11 14 13 15 11 14 16 16 15

5.05 7.25 0 0.25 0.85 0.25 3.25 0.25 0.25 0.85 1.85 0 0.85 5.05 3.25 3.25 0 0.85 3.25 0.25 0 1.85 0.85 0.25 0.25 0.85 1.85 0.25 3.25 1.85 5.05 0.25 3.25 7.25 7.25 5.05

c2r

c2s

5.05

12.55 *

0.85

4.60 NS

1.85

2.95 NS

2.45

12.40 *

1.25

4.35 *

0.85

2.95 *

2.45

3.20 *

8.45

10.40 *

22.05

22.80 **

Data tested by c2-test for homogeneity of 1:1 ratio; ** Means for treated (Tr) and untreated (Un) halves significantly different at P < 1%; * Means significantly different at P < 5%; NS: means not significantly different (P < 5%).

(0.04 ml/cm2) and the 1:1 ratio hypothesis was rejected statistically (Tables 2 and 3). Repellent action was highly dependent upon oil concentration and exposure time. In filter paper tests, Moroccan oil at 0.04 ml/cm2 showed the highest repellent activity against R. dominica adults after the 1-h time interval. Percentage repellency was 87.5% versus 62.5% and 57.5% respectively for Tunisian and Algerian oils. The maximum activity (100% repellency) was observed at the highest concentration (0.12 ml/cm2) after 3 h and 5 h of exposure for Tunisian oil and after 1 h for Moroccan oil (Table 4). Regarding the flour beetle T. castaneum, essential oil from Moroccan laurel strongly repelled adults on filter papers at 0.12 ml/ cm2 at almost all tested exposure times (Table 4). Algerian and Tunisian essential oils exhibited a repellent activity at all concentrations, but especially after the shorter exposure times (1 h, 3 h and 5 h) (Table 4). Interestingly, against T. castaneum, Moroccan oil still showed high repellent activity (72.5%) after the 24-h exposure at 0.12 ml/cm2. The median repellent dose was highly dependent upon insect species and oil origin (Table 5). For both insect species, L. nobilis essential oil from Morocco was more effective compared to the two other oils. The corresponding RD50 values were respectively 0.013 ml/ cm2 for R. dominica and 0.045 ml/cm2 for T. castaneum (Table 5). Briefly, it can be concluded that the repellent effect of the three essential oils on T. castaneum was less evident than on R. dominica (Table 5). The three laurel oils showed significant repellent activity against R. dominica at the highest concentration mainly after 3 h

and 5 h of exposure, while the essential oil of Moroccan origin elicited a strong repellent response against both beetle species at all concentrations and all exposure periods (Tables 4 and 5). 3.3. Fumigant toxicity Table 6 shows results related to fumigant activity of L. nobilis essential oils from the three origins against adults of the lesser grain borer and the rust-red flour beetle. The oils were more toxic to R. dominica than to T. castaneum, both when calculated in terms of concentration (LC50) or exposure (LT50). Probit analysis also showed that both R. dominica and T. castaneum were more susceptible to Moroccan oil than to Algerian or Tunisian oil (Table 6). LT50 values ranged from about 14 to 20 h for R. dominica, and from 43 to 56 h for T. castaneum (Table 6). 4. Discussion This study showed considerable similarity regarding chemical composition of the three essential oils collected from Tunisia, Algeria and Morocco. Results indicated that quantitative rather than qualitative variations in the composition of the essential oils were observed. The three essential oils exhibited a number of common major components in variable proportions. Consequently, insecticidal proprieties were dependent upon geographical origin

102

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Table 4 Percentage repellency (mean  SE) of L. nobilis essential oil against R. dominica and T. castaneum adults after various periods of exposure. Insect

Oil

Exposure time (h)

R. dominica

Tunisian oil

1 3 5 24 1 3 5 24 1 3 5 24 1 3 5 24 1 3 5 24 1 3 5 24

Dose (ml/cm2) 0.04

Algerian oil

Moroccan oil

T. castaneum

Tunisian oil

Algerian oil

Moroccan oil

62.5 88.75 92.5 10 57.5 2.5 5 15 87.5 80 75 47.5 50 17.5 10 25 82.5 37.5 2.5 17.5 87.5 77.5 60 17.5

0.08                        

3.2c,b,a 1.1b,a,a 2.3b,a,a 1.7c,c,a 2.7c,c,b 1.2c,c,b 1.1c,c,b 2.5b,b,a 2.1b,a,a 2.5c,b,a 1.9b,b,a 3.2b,a,a 2.1c,c,b 1.2c,c,b 1.5c,c,b 1.3c,c,b 2.4b,b,a 2.2c,b,a 1.9c,b,a 1.9c,b,b 2.8b,a,a 2.5b,a,b 3.9b,a,b 2.5c,a,b

0.12

77.5  87.5  82.5  47.5  77.5  75  70  80  90  85  75  32.5  67.5  22.5  2.5  10  82.5  45  12.5  12.5  87.5  80  60  32.5 

2.4b,b,a 1.8b,a,a 3.6c,a,a 3.9b,b,a 2.9b,b,b 1.9b,b,a 3.6b,c,a 1.3a,a,a 3.2b,a,a 2.1b,a,a 3.1b,b,a 1.1c,c,a 4.2b,c,b 2.6b,c,b 0.9a,c,b 1.2a,b,b 2.4b,b,a 4.5b,b,b 1.6b,b,b 1.9b,c,b 3.2b,a,b 1.5a,a,b 3.4b,a,b 3.2b,a,a

87.5  100  100  77.5  97.5  90  90  85  100  97.5  87.5  55  75  65  2.5  15  90  82.5  22.5  10  95  80  70  72.5 

4.2a,c,a 0.1a,a,a 0.1a,a,a 3.2a,b,a 1.6a,b,a 1.9a,c,a 1.7a,b,a 2.1a,a,a 0.2a,a,a 1.9a,b,a 2.8a,c,a 3.9a,c,b 2.2a,c,b 2.5a,b,b 1.1b,c,b 1.7b,c,b 2.1a,b,a 2.9a,a,b 3.1a,b,b 2.2a,b,b 1.6a,a,b 1.9a,a,b 2.4a,a,b 1.8a,a,a

For each insect: For each oil and at each exposure time, within columns comparisons were made between percentage repellency of the three tested doses. Values followed by the same letter are not significantly different according to Duncan test at P ¼ 0.05. For each oil and at exposure time, within rows comparisons were made between percentage repellency of the three tested oils for each concentration. Values followed by the same letter are not significantly different according to Duncan test at P ¼ 0.05. Between insects: For each dose and at each exposure time, within rows comparisons were made between percentage repellency of the three tested oils. Values followed by the same letter are not significantly different according to Duncan test at P ¼ 0.05.

of the oils since the major components of the essential oils determine their biological properties (Hussain, 2009). Previous studies reported that geographical origin, seasonal and maturity variation, genetic variation, growth stages, part of plant utilized and postharvest drying and storage may influence the essential oil composition (Marotti et al., 1994; Hussain et al., 2008; Anwar et al., 2009). Moreover, there are many reports showing the variation in chemical composition of the essential oil with respect to geographical regions (Uribe-Hernandez et al., 1992; SoutoBachiller et al., 1997; Celiktas et al., 2006; Van Vuuren et al., 2007). Uribe-Hernandez et al. (1992) also reported that the essential oil composition varied significantly depending on the locations where the plants grew. Furthermore, climatic factors such as heat and drought were also related to the essential oil profiles (Milos et al., 2001). In addition, Vokou et al. (1993) pointed out that altitude seems to be another important environmental factor influencing the essential oil content and chemical composition. No data are available in the literature comparing the efficacy of L. nobilis essential oils from Morocco, Tunisia and Algeria against stored product pests. However, literature is available describing the

Table 5 RD50 values (ml/cm2) of L. nobilis essential oils from Tunisia, Algeria and Morocco against adults of R. dominica and T. castaneum. Insect R. dominica

RD50a,b

T. castaneum

Slope  SEM c2 RD50a,b Slope  SEM

c2 a b

Tunisian oil

Algerian oil

Moroccan oil

0.036 (0.022 e0.045) 1.18  0.47 1.44 0.139 (0.046 e0.221) 3.84  1.20 0.20

0.033 (0.022 e0.04) 2.87  0.51 1.64 0.096 (0.065 e0.225) 2.23  1.33 0.34

0.013 (0.002 e0.028) 1.18  0.47 1.44 0.045 (0.019 e0.063) 2.94  1.55 0.84

Units RD50 ¼ m/cm2, applied for 24 h at 25  C. 95% lower and upper confidence limits are shown in parenthesis.

pest control potential of this oil from various other Mediterranean regions Italy: Cosimi et al. (2009) against S. zeamais (Motschulsky), C. ferrugineus (Stephens) and T. molitor (L.); Greece: Papachristos and Stamopoulos (2002) against A. obtectus (Say); Turkey: Erler et al. (2006) against Culex pipiens (L.). The results presented in this paper showed significant variation in the repellent and fumigant activities of L. nobilis essential oils with respect to regions. Moroccan oil was more active against R. dominica and T. castaneum compared to Tunisian and Algerian oils. The superior insecticidal potential of Moroccan oil could be attributed to high amounts of the major components; 1,8-cineole (38.86%), isovaleraldehyde (10.47%), linalool (9.45%) and aterpineol (5.83%). In this context, Lee et al. (2003) proved that T. castaneum could be controlled by high doses of several compounds such as 1,8-cineole, 1-fechone and pulegone (only present in Moroccan oil, Table 1). Similarly, Rozman et al. (2007) demonstrated that fumigant activities against R. dominica, T. castaneum and S. oryzae of nine essential oil compounds revealed 1,8-cineole to be the most effective, followed by camphor and linalool. It is also possible that minor components such as g-

Table 6 LC50 and LT50 values of L. nobilis essential oils from Tunisia, Algeria and Morocco against adults of R. dominica and T. castaneum. Insect

Oil origin

LC50 (ml/l air)a,b

LT50 (h)c

R. dominica

Tunisian oil Algerian oil Moroccan oil Tunisian oil Algerian oil Moroccan oil

113.42 98.95 67.9 217.10 193.95 172.37

19.58 17.58 14.25 55.67 51.53 43.05

T. castaneum

a b c

(103.95e123.16) (92.10e105.26) (72.63e89.47) (193.16e345.26) (165.79e298.16) (141.84e288.68)

(14.37e25.7) (12.37e26.7) (9.34e20.16) (49.38e56.12) (46.23e58.92) (39.51e48.21)

Units LC50 ¼ ml/l air, applied for 24 h at 25  C. 95% lower and upper confidence limits are shown in parenthesis. 95% lower and upper confidence limits are shown in parenthesis.

J. Mediouni Ben Jemâa et al. / Journal of Stored Products Research 48 (2012) 97e104

terpinene, 4-terpineol and 1-bornyl acetate may play a key role in the toxicity profile of Moroccan essential oil. To summarize, we can advance that variations in insecticidal activities of the three L. nobilis essential oils against R. dominica and T. castaneum could be related to changes in the amounts of the active components from one region to another. The comparative study revealed that chemical composition varied according to oil origin and that variations were quantitative rather than qualitative. Results of our study compare favourably with other investigations in which L. nobilis essential oil produced significant activity against pest insects. Additionally, as reported in earlier works (Fiorini et al., 1997; Hokwerda et al., 1982; Macchioni et al., 2006), we found 1,8cineole to be the main terpene found in L. nobilis leaf essential oil and thus implicated in the observed insecticidal proprieties. Our work clearly supports interest in the development of essential oils from plants of Mediterranean origin for stored-food pest control. In Maghreb countries, the use of L. nobilis essential oil as a pest control agent will contribute to enhance the economic value of this plant in Morocco and Algeria and to preserve the species in Tunisia. In this context, Boussaid et al. (1998) reported that in Tunisia, L. nobilis is endangered, and is listed for environmental protection. The present study demonstrated that composition of L. nobilis essential oils from Tunisia, Algeria and Morocco showed a similar pattern to those published for other geographical regions, but that the oil from Morocco had higher activity against two major pest species.

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