Fumigant and repellent properties of sesquiterpene-rich essential oil from Teucrium polium subsp. capitatum (L.)

Abbas Khani, Monireh Heydarian

Department of Plant Protection, Faculty of Agriculture, University of Zabol, Zabol, Iran

Fumigant and repellent properties of sesquiterpene-rich essential oil from Teucrium polium subsp. capitatum (L.)

Abbas Khani*, Monireh Heydarian

Department of Plant Protection, Faculty of Agriculture, University of Zabol, Zabol, Iran

Objective:To test fumigant and repellent properties of sesquiterpene-rich essential oil from Teucrium polium subsp. capitatum (L.).Methods:The fumigant toxicity test was performed at (27±1) ℃, (65±5)% relative humidity, and under darkness condition and 24 h exposure time. The chemical composition of the isolated oils was examined by gas chromatographymass spectrometry.Results:The major compounds were α-cadinol (46.2%), caryophyllene oxide (25.9%), α muurolol epi (8.1%), cadalene (3.7%) and longiverbenone (2.9%). In all cases, considerable differences in mortality of insect to essential oil vapor were observed in different concentrations and exposure times. Callosobruchus maculatus (C. maculates) (LC50=148.9 μL/ L air) was more susceptible to the tested plant product than Teucrium castaneum (T. castaneum) (LC50=360.2 μL/L air) based on LC50values. In the present investigation, the concentration of 3 μL /mL acetone showed 60% and 52% repellency against T. casteneum and C. maculatus adults, respectively.Conclusions:The results suggests that sesquiterpene-rich essential oils from the tested plant could be used as a potential control agent for stored-product insects.

ARTICLE INFO

Article history:

Received 10 July 2014

Received in revised form 15 August 2014

Accepted 15 October 2014

Available online 20 December 2014

Callosobruchus maculatus

Fumigant toxicit

Gas chromatography-mass

spectrometry

Repellency

Terpenoids

Tribolium castaneum

1. Introduction

The invasion of food products by insects contribute greatly to the loss of quality and quantity. The cowpea weevil,Callosobruchus maculatus(C. maculatus) F. (Coleoptera: Bruchidae), and the rust red flour beetle,Tribolium castaneum(T. castaneum) (Herbst) (Coleoptera: Tenebrionidae), are among the most widespread and destructive stored product pests throughout the world. They cause significant losses of stored products, particularly in tropical and warm temperate regions[1].

Chemicals and fumigants play a vital role in controlling this problem but they have been known to cause serious toxicological and environmental problems. Persistent development of resistance is a serious threat to the future use of these materials, and consequently, there is an urgent need to develop affordable, safe and sound pest control agents and techniques[2]. Researchers are now focused on finding alternative insecticides which will be effective, environmentally friendly, biodegradable, safer and cheaper than existing ones. Plant oils, as an important natural resource of insecticides, are generally considered broadspectrum and safe for the environment because the array of compounds they contain quickly biodegrade in the soil[2-4]. Their lipophilic nature facilitates their interference with basic metabolic, biochemical, physiological and behavioral functions of insects[4].

The genusTeucriumbelongs to the family Lamiaceae (Labiatae), and consists of about 300 species, most of which are found in the dry and stony places of the hills and deserts of Mediterranean countries, South Western Asia, Europe and North Africa[5].Teucrium polium(T. polium) subsp.

capitatumL. is a perennial, pubescent, aromatic plant, 20-50 cm high, white or grey hairs on stems, with greengrayish leaves and white flowers.T. polium(locally called kalpooreh) is one of the wild-growing flowering species and is abundantly found in Iran. Various biological activities have been reported forT. polium, such as antiphytoviral[6], antibacterial[7], antifungal[8], repellent[9,10] and insecticidal properties[11,12].

Phytochemical investigations have shown thatTeucriumgenus contains various compounds such as terpenoids, flavonoids and iridoids[13]. The results of Bezicet al[6] showing that the major compounds inT. poliumessential oil were the sesquiterpene hydrocarbons β-caryophyllene and germacrene D. However, there have been some variations in the constituents of this oil from different countries, and a chemo-geographical variation has been observed in essential oil composition of this species[14].

In the present study, the chemical components of essential oils fromT. poliumsubsp.capitatum(Lamiaceae) aerial parts was determined, and the repellent and insecticidal activity of it was tested against the adult stages of the stored-products pests,T. castaneumHerbst (Coleoptera: Tenebrionidae) andC. maculatusF. (Coleoptera: Bruchidae).

2. Materials and methods

2.1. Insect material

C. maculatusandT. castaneumwere reared in plastic containers (20 cm length, 14 cm width, and 8 cm height, covered by a fine mesh cloth for ventilation) containing bean grain and wheat flour mixed with yeast (10:1, w/w), respectively. The culture was maintained in the dark, in a growth chamber set at (27±1) ℃ and (65±5)% relative humidity. All experiments were carried out under the same environmental conditions.

2.2. Plants and essential oils

Aerial parts (leaves and flowers) ofT. poliumwere collected in Kashmar (35o14’ N, 58o28’ E; 1 100 m a.s.l.) located in Khorasan Razavi province, Iran, from May to July 2010. Essential oil extraction was done following the method described by khaniet al[15]. The extracted oil was dehydrated with anhydrous sodium sulphate (10 min) and immediately stored in airtight glassware in refrigerator at 4 ℃).

2.3. Gas chromatography (GC)-mass spectrometry

The essential oils was analyzed on a gas chromatograph mass spectrometer (GC-mass) (Shimadzu-17A-QP5050, Japan) following the method described by khaniet al[15]. The GC column was DB-5 (30 m×0.25 mmid., 0.25 μm film thickness). The column oven temperature was set at 60 ℃for 3 min, and then increased to 260 ℃ at a rate of 5 ℃/min. Injector and detector temperatures were 230 ℃ and 245 ℃, respectively. The GC mass analysis was carried out with the same characteristics as used in GC. The ionization energy was 70 ev with a scan time of 1s and mass range of 40-500 amu.

2.4. Fumigant toxicity

Fumigant toxicity of the oil on adults of each species (1-7 days old of undefined sex) determined following the method described by khaniet al[15]. Lethal effect assessed in glass vials (60 mL) at concentrations of 166.66, 250, 333.33, 416.67 and 450 μL/L air forT. castaneumand concentrations of 5, 50, 83.33, 166.66, 250 and 416.67 μL/L air forC. maculatus. Each concentration was replicated four or eight times with ten individuals per each replicate. Mortality was determined 24 h after exposure. When no signs of leg or antennal movement were observed, insects were considered dead. The treatment bottles were monitored for 48 h after recording the data, and no affected insect recovered.

To evaluation 50% lethal doses (LC50) after an exposure time of 24 h, the concentrations of the essential oils causing 10% to 90% mortality were used. Data obtained from each dose response bioassay were subjected to probit analysis. LC50values were determined by log-probit regression using SPSS 16.0 for Windows[16].

2.5. Repellency bioassay

Repellency was assessed as described by Fieldset al[17]. The repellency tests were consisted of two clear plastic chambers (65 mL volume) joined to either side of a central main chamber with the same size by a small tubing (2 cm long and 3 mm in diameter). Concentrations of the test solutions were 0.2, 0.5, 1 and 3 μL of essential oil in 1 mL acetone. One milliliter of each solution was applied on 40 seeds of wheat forT. castaneumand 20 seeds of bean forC. maculatus. In the control, the food was treated with 1 mL acetone only. The treated and control seeds were kept for 20 min to evaporate the solvent completely, and placed in the center of treated and control chambers respectively. Three replications were used for each concentration. Fifty nonsexed adults of each species (1-7 days old) were introduced into the center of each main chamber. Central chamber was covered by plastic screen but the treated and control chambers were covered by lids and the whole setup was left in darkness. After 24 h, the number of beetles at each chamber was counted and the percentage repellency (R) values were computed using the formula of Liuet al[18]:

where C is the number of insects in control, E is the number of insects in oil treated chamber and T is the number of total released insects.

2.6. Statistical analysis

Statistical analysis of the mortality and repellency data was performed by one-way analysis of variance (ANOVA) with apost-hocTukey test using SPSS version 16.00. Normality of data was tested using, Kolmogorov-Smirnov test, a nonparametric test. The results were expressed as mean±SE, and considered significantly different at P< 0.05.

3. Results

3.1. Chemical composition of essential oils

The chemical composition of the essential oils ofT. poliumsubsp.capitatumaerial parts (leaves and flowering heads) is presented in Table 1. The major compounds were α -cadinol (46.2%), caryophyllene oxide (25.9%), α muurolol epi (8.1%), cadalene (3.7%), longiverbenone (2.9%), carotol (2.7%) and diethyl phthalate (2.5%) in the essential oils ofT. poliumsubsp.capitatumaerial parts.

Table 1 Chemical composition of essential oils of T. polium aerial parts (leaves and flowering heads).

3.2. Fumigant toxicity

The mortality increased significantly with rising concentrations (Figure 1) (F4,27=24.16; P=0 forT. castaneumand F5,35=30.13; P=0 forC. maculatus). Results indicated that the oil of tested plant was significantly more toxic againstC. maculatusthanT. castaneum, as inferred by the confidence intervals of LC50(Table 2). Based on LC50(Table 2) and fumigant toxicity experiments (Figure 1), the oil ofM. communisdisplayed strong insecticidal activity againstC. maculatus(LC50=148.9 μL/L air), but revealed fewer activity againstT. castaneum(LC50=360.2 μL/L air) (Figure 2, Table 2).

Figure 1. Lethal effect of essential oil from T. polium aerial parts on T. castaneum and C. maculatus after 24 h.

Table 2 Efficiency of essential oil extracted from T. polium against T. castaneum and C. maculatus adults.

Figure 2. Mortality probit line and 95% confidence limits for T. castaneum and C. maculatus after 24 h exposure to essential oil extracted from T. polium aerial parts. LC50point is shown by the star sign.

3.3. Repellent activity

T. poliumessential oil moderately repelledT. castaneumandC. maculatusin the tested concentrations and the repellency for these two insects was not statistically different in all concentrations (t=-0.8,df= 22,P=0.43) (Table 3). The test showed that the repellency was concentrationdependent and the repellency increased significantly with increasing concentration of essential oil in all cases. In the present investigation, the concentration of 3 μL/mL acetone showed 60% repellency againstT. casteneumbeetle while it was 24.7% repellency at lower concentration 0.2 μL/mL acetone (F3,11=52.38; P=0). Also the repellency forC. maculatuswas obvious when compared to the lowest concentration and the highest one (20% and 52% respectively) (F3,11= 5.03;P=0.3).

Table 3 Percent repellency (mean±SE) of the essential oil from T. polium on T. castaneum and C. maculatus adults.

4. Discussion

Essential oils ofT. poliumssp.capitatumhave been the subject of many studies. According to the plant origin studied, the amounts of main constituents differed notably[19]. Important differences were found with regard to the major constituents of the essential oils of five populations ofT. capitatumgrown in Portugal. τ-cadinol (24.1%) and α-cadinol (9.8%) were the major compounds in the oil from one population, whereas δ-cadinene (9.8%) and E-caryophyllene (4.6%) or α-muurolol (6.0%) was the major constituents in the other population[20]. Conversely α-pinene (7.7%), sabinene (11.2%) and β-pinene (10.3%) were the main compounds in the other sample[20]. α -pinene (28.8%), β-pinene (7.2%) and p-cymene (7.0%) were the main components of the essential oil ofT. poliumssp.capitatumfrom Corsica, France[21]. Menichiniet al[22] reported carvacrol (10.1%), (E)-β-caryophyllene (9.8%), α -cadinol (4.5%) and verbenone (3.7%) were the most abundant components inT. poliumssp.capitatumfrom Greece. In the oil ofT. poliumssp.capitatumfrom Crete, Italy, the most abundant compounds were (E)-β-caryophyllene (10.1%) and the monoterpene, carvacrol (9.6%)[23]. The dominant constituents of the aerial parts ofT. poliumssp.capitatumcollected during the flowering period from Serbia were sesquiterpenes, germacrene D (31.8%), transcaryophyllene (8.8%) and bicyclogermacrene (6.2%), and monoterpenes, linalool (14.0%) and β- pinene (10.7%)[24]. While the essential oil from Bulgaria was characterized by a high percentage of monoterpenes, β-pinene (26.8%), α -pinene (9.3%) and limonene (6.4%), and the sesquiterpene, germacrene D (17.7%)[24].

It is noticeable that the chemical composition of IranianT. poliumsubsp.capitatumstudied here was to some extent in accordance with some populations ofT. capitatumgrown in Portugal[20]. Furthermore, it is the first time that globulol and Longiverbenone (vulgarone B) have been characterized inT. poliumoil. These discrepancies might account for geographical variation and explain the probability of the existence of several chemical races within the species.

Results indicated that the oil of tested plant was more toxic but not significantly againstC. maculatusthanT. castaneum, as inferred by the confidence intervals of LC50. A difference in the response of the insect species to the essential oils haspreviously been reported for stored-product insects[15,25,26]. It has been reported that the oil and extract of the tested plant had insecticidal activity against other insects. For example, An LC50of 80 ppm was estimated with the larvae ofMusca domesticain bioassays when the essential oil ofT. poliumwas admixed with artificial diet. Furthermore a reduction of carbohydrase activity of α-amylase, α -glucosidase and β-glucosidase were detected in larval midgut extract[12]. The contact LD50ofT. poliumessential oil against house fly larvae was 0.028 μL/larvae[27]. The LC50of essential oil ofT. poliumfor adults ofC. maculatusandTribolium confusumwere 9.6 μL/L and 35.5 μL/L, respectively[27].

Terpenes have been well documented as active fumigants, repellents, and insecticides toward stored-product insects[4]. The insecticidal activity of the essential oils investigated in our study may be attributed to their having major terpenoids components. There are numerous reports on the toxicity of the essential oils from various plants species with major components similar toT. poliumin our study, such as α -cadinol[28], caryophyllene oxide[29], Longiverbenone (vulgarone B)[30,31], viridiflorol[32-34] which are classified as active toxic compounds.

Furthermore, insecticidal activity of major constitutes of the tested oil were before reported. α-cadinol possessed the strong antitermitic activity with 70% mortality ofC. formosanusShiraki at 10 mg/g dosage for 14 days[35]. In addition, α-cadinol possessed the strong antimite activities.Dermatophagoides pteronyssinusandDermatophagoides farinae, the dominant species of house dust mites, were all killed at a low concentration (6.3 mg/cm2) dosage of α -cadinol after 24 h of exposure[36]. Caryophyllene oxide showed high insecticidal activity (LC50=0.18 mg/L) againstT. castaneum(Coleoptera: Tenebrionidae) adults[37]. LC50value of caryophyllene oxide inCinnamomum osmophloeumleaf essential oil against mosquito species,Aedes albopictuslarvae was 65.6 μg/mL[29]. Caryophyllene oxide inhibited the mitochondrial electron transport chain in mammalian cells[38].

The essential oil assayed was not only active insecticide againstT. castaneumandC. maculatus, but it was also effective repellent. Based on our results, adults of these two beetles were found to be repelled by essential oil tested even at very low concentration. Our results are in accordance with those of Heydarzadeet al[9] who reported the mean repellency percentage ofT. poliumat the highest concentration (3 μL/mL acetone) was 84.9% and 76.1% on males and females ofC. maculatus, respectively. Other study has shown that 35% effective repellent doses ofT. poliumessential oil against adults ofC. maculatusandTribolium confusumwere 6.45 and 2.91 μL/mL acetone, respectively[10]. The strong repellent activity of the tested oil could be due to caryophyllene oxide, one of the main constituent of this oil (>25%). In previous research, this compound has shown to be a powerful repellent towardsT.castaneumwith complete repellency at 0.03 mg/cm2[37].

The essential oil from the plant could become a viable alternative to conventional chemical control strategies. However, further studies need to be conducted in order to evaluate the safety of the oil before practical use in storedproduct insect control.

Conflict of interest statement

We declare that we have no conflict of interest.

Acknowledgments

This research was supported by the University of Zabol, which is greatly appreciated.

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ment heading

10.1016/S1995-7645(14)60169-3

*Corresponding authors: Abbas Khani, Department of Plant Protection, Faculty of Agriculture, University of Zabol, Zabol, Iran.

Tel & Fax: +98-542-2242501

E-mail: abbkhani@yahoo.com or abbkhani@uoz.ac.ir