versión On-line ISSN 0718-5839
Chilean J. Agric. Res. vol.71 no.2 Chillán jun. 2011
Chilean Journal of Agricultural Research 71(2) April-June
Chemical constituents and toxicity of Agastache foeniculum (Pursh) kuntze essential oil against two stored-product insect pests
Componentes químicos y toxicidad del aceite esencial de Agastachefoeniculum (Pursh) Kuntze contra dos plagas de insectos de productos almacenados.
1Young Researchers Club, Islamic Azad University, Ardabil branch, P.O. BOX: 467, Ardabil, Iran. *Corresponding author (Asgar.firstname.lastname@example.org).
The uncontrolled use of synthetic insecticides is a great hazard for the environment and consumers. Essential oils were introduced as low toxic agents against mammals and non-targeted insects. In this study, essential oil from aerial parts of blue giant hyssop (Agastache foeniculum [Pursh] Kuntze) (Lamiaceae) was isolated by the water steam distillation method with a Clevenger apparatus, and its chemical composition was studied by gas chromatography mass spectrometry. The toxicity of A. foeniculum essential oil against red flour beetle, Tribolium castaneum (Herbst), and lesser grain borer Rhyzopertha dominica (F.) was evaluated by fumigation at 24, 48, and 72 h exposure times. Estragole and 1,8-cineole were identified as major constituents of the A. foeniculum oil. Fumigation bioassays revealed that A.foeniculum oil had strong insecticidal activity on experimental insects. Rhyzopertha dominica was more susceptible than T. castaneum for all exposure times. Insecticidal activity varied with essential oil concentration and exposure time. Probit analysis showed that increased exposure time and essential oil concentration increased mortality. These results indicated that A. foeniculum essential oil can be applied in the management of stored-product insects to decrease the detrimental effects of synthetic insecticides.
Key words: Blue giant hyssop, fumigation, Rhyzopertha dominica, Tribolium castaneum.
El uso incontrolado de los insecticidas sintéticos causa gran peligro para el medio ambiente y los consumidores. Los aceites esenciales se presentan como agentes tóxicos leves contra mamíferos e insectos no objetivo. En el presente estudio, el aceite esencial de las partes aéreas del hisopo gigante azul (Agastache Foeniculum [Pursh] Kuntze) (Lamiaceae) se aisló por el método de destilación al vapor de agua, utilizando un aparato de Clevenger y se estudió su composición química mediante cromatografía de gases y espectrometría de masas. La toxicidad del aceite esencial de A. foeniculum se evaluó por métodos de fumigación a las 24, 48 y 72 h contra el escarabajo rojo de la harina (Tribolium castaneum (Herbst)) y el barrenador menor de granos (Rhyzopertha dominica (F.)). El estragol y 1,8-cineole se detectaron como componentes principales en el aceite A. foeniculum. Los bioensayos revelaron que el aceite de A. foeniculum tuvo una fuerte actividad insecticida sobre los insectos experimentales. R. dominica fue más susceptible que T. castaneum en todos los tiempos. La actividad insecticida varió con las concentraciones de aceite esencial y los tiempos de exposición. El análisis Probit mostró que la mortalidad aumenta con el incremento del tiempo de exposición y la concentración del aceite esencial. Estos resultados indican que el aceite esencial del A. foeniculum podría ser aplicable al manejo de insectos de productos almacenados con el fin de disminuir los efectos perjudiciales de la utilización de insecticidas sintéticos.
Palabras clave: hisopo gigante azul, fumigación, Rhyzopertha dominica, Tribolium castaneum.
The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), has long been associated with stored food for human consumption and with a wide range of commodities including grain, flour, peas, beans, cacao, nuts, dried fruits, and spices, although milled grain products such as flour appear to be its preferred food. Its presence in stored foods directly affects both the quantity and quality of the commodity (Campbell and Runnion, 2003). The lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), is a destructive insect pest of stored grains. Both larvae and adults of this insect feed on whole, sound grains and cause extensive damage (Dowdy and McGaughey, 1992).
Controlling these insects and other stored-product pests relies heavily on gaseous fumigants. Although effective synthetic insecticides such as methyl bromide or phosphine are available, there is a global concern about their negative effects causing ozone depletion, environmental pollution, toxicity to non-target organisms, and pesticide residues (Lee et al., 2004; Isman, 2006). There is an urgent need to develop safe alternatives with the potential to replace toxic fumigants, and still be effective, economical, and convenient. Natural compounds of plant origin are biodegradable, often of low mammalian toxicity, and pose a low danger to the environment if used in small amounts (Papachristos and Stamopoulos, 2002; Ayvaz et al., 2008). There has recently been a growing interest in research as to possibility of using plant extracts as alternatives to synthetic insecticides. Essential oils are complex mixtures comprised of a large number of constituents in variable ratios (Van Zyl et al., 2006). Furthermore, they are volatile and can act as fumigants for stored-product protection. Plant essential oils have had insecticidal (Tapondjou et al., 2002; Negahban et al., 2007; Park et al., 2008), antifungal (Razzaghi-Abyaneh et al., 2008), nematicidal (Oka et al., 2000), virucidal (Schuhmacher et al., 2003), and anti-bacterial (Kotan et al., 2008) effects. This is mainly because essential oils are easily extractable, eco-friendly i.e., biodegradable, easily catabolized in the environment, and do not persist in soil and water (Isman, 2000; 2006). All these properties of essential oils permit their use even in sensitive areas such as schools, restaurants, hospitals, and homes. In spite of the widespread recognition that many plants possess insecticidal properties, only a handful of pest control products directly obtained from plants are used because the commercialization of new botanicals can be hindered by a number of issues (Isman, 1997).
Blue giant hyssop, Agastache foeniculum (Pursh) Kuntze, is a species of perennial plant of the mint family (Lamiaceae). It is native to the southwestern and eastern US and central Asia. This flowering plant is very attractive to bees and butterflies and commonly used as garnish for fruit salads, iced tea, desserts, and anise-flavored spices. This species is a candidate for large-scale, domestic cultivation as an aromatic plant with a wide variation in essential oil composition and content (Ayers and Widrlechner, 1994). The Agastache genus has received considerable attention for its variation in essential oil content and composition (Charles et al., 1991).
This paper describes a laboratory study carried out to assess the potential of essential oil as an insecticide. This study investigates fumigant toxicity of the essential oil from aerial parts of A. foeniculum against T. castaneum and R. dominica under laboratory conditions.
MATERIALS AND METHODS
Plant material, extraction, and analysis of essential oil
Aerial parts from 1.5 cm from the top of A. foeniculum were collected at flowering stage from plants grown on the experimental farm of the Department of Horticulture, University of Urmia, Urmia, Iran. This material was air-dried in the shade at room temperature (26 to 28 °C) for 14 d. The essential oil was isolated from dried plant samples by hydrodistillation with a Clevenger-type apparatus. Extraction conditions were: 50 g of air-dried sample, 1:10 plant material:water volume ratio, 4-h distillation. Anhydrous sodium sulfate was employed to remove water after extraction. Extracted oils were stored in a refrigerator at 4 ºC.
The constituents of A. foeniculum essential oil were analyzed by gas chromatography mass spectrometry (GC-MS) (Thermo-UFM, Italy). The GC-MS conditions were as follows: capillary column pH-5 (10 m × 0.1 mm, film thickness 0.4 µm); helium as carrier gas (0.5 mL min-1); oven temperature program initially at 60 °C rising to 285 °C; and injector and detector temperatures of 280 °C. The identification of individual compounds was based on the comparison of their relative retention index with those of original samples on a capillary column (Davies, 1990).
Tribolium castaneum was bred in glass containers (1 L) containing wheat (Triticum aestivum L.) flour. The mouth of the containers was covered with a fine mesh cloth for ventilation and to prevent the beetles from escaping. Rhyzopertha dominica was bred on whole-wheat in similar containers. Cultures were maintained in an incubator at 27 ± 2 °C and 60 ± 5% RH in the dark. Parent adults were obtained from laboratory stock cultures maintained at the Entomology Department, University of Urmia, Iran. Adult insects, 1 to 7 d old, were used for fumigant toxicity tests. All experimental procedures were carried out under the same environmental conditions as the cultures.
The fumigant bioassays were conducted as described by Negahban et al. (2007) with only slight modifications. Concentrations of 10 to 48 µL L-1 and 4 to 32 µL L-1 of the oil were used for T. castaneum and R. dominica, respectively. Each concentration was dissolved in 200 µL acetone (solvent) and applied to filter paper strips (4 × 5 cm, Whatman N° 1), which were air-dried for 2 min. Treated filter papers were placed at the bottom of 1-L glass jars. Twenty insect adults were placed in small plastic tubes (3.5 cm diameter and 5 cm height) with open ends covered with cloth mesh. Tubes were hung at the geometrical centre of the glass jars and then sealed with air-tight lids. Thus, there was no direct contact between the oil and the insects. In the control jars, only acetone was applied on the filter papers. Jars were kept in the incubator and mortality was determined after 24, 48, and 72 h after exposure began. Each experiment was replicated three times for each concentration. Insects were considered dead when no leg or antennal movements were observed.
Mortality percentages were calculated by the Abbott correction formula for natural mortality in the untreated control (Abbott, 1925). To equalize variances, insect mortality percentages were transformed by the squared root of the arcsin. Experiments were arranged in a completely randomized design and data were analyzed by ANOVA. Lethal concentration (LC50 and LC95) was estimated by probit analysis whereas lethal time (LT50 and LT95) values were obtained with SPSS software (SPSS, 2001). The means were separated by the Tukey test at the 5% level.
Chemical analysis of the essential oil determined that estragole (94.003%) and 1,8-cineole (3.334%) were the predominant components (Table 1). Agastache foeniculum oil revealed a strong toxicity against the insects. A 50% lethal concentration for T. castaneum and R. dominica at 24 h exposure time were 22 and 14 µL L-1, respectively. Rhyzopertha dominica was most susceptible and T. castaneum was most tolerant for all exposure times (Table 2A). LT50 values (the time needed to kill 50% of the population) were 12.47 h for T. castaneum and 10.05 h for R. dominica at the highest concentrations (42 µL L-1 for T. castaneum and 32 µL L-1 for R. dominica) (Table 2B). The susceptibility of both insects increased with exposure time and concentration, and LC50 values decreased within 72 h (Table 2 and Figure 1). On the other hand, the increased susceptibility of the two insects was associated with the increase of the different oil concentrations and exposure time. For example, T. castaneum showed LC50 = 22 µL L-1 24 h after fumigation, and this value decreased to 13 µL L-1 within 72 h.
Table 2. Result of probit analysis to calculate LC50, LC95 (A), and LT50, LT95 (B) values. LT values and their corresponding information were calculated at the highest concentrations (42 µL L-1 for Tribolium castaneum and 32 µL L-1 for Rhyzopertha dominica).
The most promising botanical groups are Meliaceae, Rutaceae, Asteraceae, Annonaceae, Lamiaceae (e.g. A. foeniculum), Aristolochiaceae, and Malvaceae (Regnault-Roger, 1997). Purple giant hyssop, Agastache rugosa (Fisch. & C.A. Mey.) Kuntze, essential oil has been evaluated for insecticidal and nematicidal activity (Kim et al., 2003; Choi et al., 2007), and A. foeniculum essential oil indicated strong fumigant toxicity against T. castaneum and R. dominica in the present study. These insects are from different insect families, thus confirming the wide toxicity range of this essence.
The effect of many essential oils used as insecticides to protect against T. castaneum and R. dominica infestation has been studied, and these beetles have shown susceptibility to some plant-derived chemicals. Experiments have shown that T. castaneum is more tolerant than R. dominica. Sahaf et al. (2007) studied fumigant toxicity of Carum copticum C.B. Clarke (Apiaceae) essential oil against Sitophilus oryzae (L.) (Curculionidae) and T.castaneum observing that S. oryzae (LC50 = 0.91 µL L-1) was significantly more susceptible than T. castaneum (LC50 = 33.14 µL L-1). Chaubey (2007) investigated insecticidal activity of Trachyspermum ammi (L.) Sprague ex Turrill (Apiaceae), Anethum graveolens L. (Apiaceae), and Nigella sativa L. (Ranunculaceae) essential oils against T. castaneum. The death of T. castaneum adults was caused by fumigation with these essential oils. Fumigant toxicity of Vitexpseudonegundo (Hausskn.) Hand.-Mazz. (Lamiaceae) essential oil against T. castaneum and S. oryzae was evaluated by Sahaf et al. (2008). They demonstrated that S. oryzae (LC50 = 31.96 µL L-1) was more susceptible than T. castaneum (LC50 = 47.27 µL L-1). Ogendo et al. (2008) found that, except for the more tolerant T. castaneum, LC50 values for S. oryzae, R. dominica, Oryzaephilus surinamensis (L.) (Silvanidae), and Callosobruchus chinensis (L.) (Bruchidae) adults ranged from 0.20 to 14 mL L-1, 0.01 to 17 mL L-1, and 0.80 to 23 mL L-1 air 24 h after treatment with Ocimum gratissimum L. (Lamiaceae) essential oil, eugenol, and b-(Z)-ocimene, respectively. In the other experiment, it was found that Lavandula stoechas L. (Lamiaceae) essential oil had insecticidal effects on Lasioderma serricorne (F.) (Anobiidae), R. dominica, and T. castaneum. Lasioderma serricorne (LC50 = 3.835 µL L-1) was significantly more susceptible than R. dominica (LC50 = 5.66 µL L-1) and T. castaneum (LC50 = 39.685 µL L-1) 24 h after treatment (Ebadollahi et al., 2010). These findings are similar to the results of this study for sensibility of T. castaneum and R. dominica to plant essential oils and T. castaneum is more tolerant than R. dominica.
Previous studies have shown that, in general, the toxicity of plant essential oils against stored-product pests is related to their major components (Isman etal., 2001; Tapondjou et al., 2002; Singh et al., 2003). Estragole (= methyl chavicol) is a major constituent of A. foeniculum essential oil (Charles et al., 1991; Mazza and Kiehn, 1992), fact which was confirmed in this study. Lopez et al. (2008) reported estragole as an example of toxic fumigant compounds in Coriandrum sativum L. (Apiaceae), Carum carvi L. (Apiaceae), and Ocimum basilicum L. (Lamiaceae) essential oils that are active against insect pests. Another major constituent of A. foeniculum oil, 1,8-cineole, is reported as a toxic agent against some insect pests (Tripathi et al., 2001; Yang et al., 2004; Kordali et al., 2006; Stamopoulos et al., 2007).
According to the results obtained from the current study and previous studies, it can be suggested that A. foeniculum essential oil, or probably its components, can be used to control stored-product insect pests. If cost-effective commercial problems are solved, essential oils obtained from plants can be used as part of integrated pest management strategies. Therefore, large quantities of plant material must be processed to obtain sufficient quantities of essential oils for commercial-scale tests, situation which also requires breeding these plants in great quantities.
I would like to thank M.H. Safaralizadeh, A.A. Pourmirza, H.J. Golizadeh, and S.A. Gheibi for their excellent technical support during the experimental work. I am also grateful for the valuable comments provided by an anonymous reviewer.
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Accepted: 20 December 2010.