Evaluation of Contact Toxicity and Repellency of the Essential Oil of
Transcription
Evaluation of Contact Toxicity and Repellency of the Essential Oil of
VECTOR CONTROL, PEST MANAGEMENT, RESISTANCE, REPELLENTS Evaluation of Contact Toxicity and Repellency of the Essential Oil of Pogostemon cablin Leaves and Its Constituents Against Blattella germanica (Blattodae: Blattelidae) XIN CHAO LIU,1 QIYONG LIU,2 HAN CHEN,1 QI ZHI LIU,1 SHI YAO JIANG,1 AND ZHI LONG LIU1,3 J. Med. Entomol. 52(1): 86–92 (2015); DOI: 10.1093/jme/tju003 ABSTRACT The aim of this research was to evaluate contact toxicity and repellency of the essential oil of Pogostemon cablin (Blanco) Bentham leaves against German cockroaches (Blattella germanica) (L.) and to isolate any active constituents. Essential oil of P. cablin leaves was obtained by hydrodistillation and analyzed by gas chromatography (GC) and gas chromatography–mass spectrometry (GC-MS). Twenty-three components were identified in the essential oil, and the main constituents were patchoulol (41.31%), pogostone (18.06%), a-bulnesene (6.56%), caryophyllene (5.96%), and seychellene (4.32%). Bioactivitydirected chromatographic separation of the essential oil led to the isolation of pogostone, patchoulol, and caryophyllene as active compounds. The essential oil of P. cablin leaves exhibited acute toxicity against male B. germanica adults with an LC50 value of 23.45 lg per adult. The constituent compound, pogostone (LC50 ¼ 8.51 lg per adult) showed stronger acute toxicity than patchoulol (LC50 ¼ 207.62 lg per adult) and caryophyllene (LC50 ¼ 339.90 lg per adult) against the male German cockroaches. The essential oil of P. cablin leaves and the three isolated constituents exhibited strong repellent activity against German cockroaches at a concentration of 5 ppm. The results indicated that the essential oil of P. cablin leaves and its major constituents have good potential as a source for natural insecticides and repellents. KEY WORDS pogostone, patchoulol, caryophyllene Introduction German cockroach, Blattella germanica (L.), is an important pest of homes, restaurants, and commercial food processing facilities worldwide. They are a major public health concern in hospitals, kitchens, and food manufacturing plants because they are able to carry a variety of bacteria and other pathogenic organisms. They are the mechanical vectors to a few pathogens that can cause disease such as food poisoning, typhoid, and pneumonia (Brenner 1995). Currently, control of cockroach populations is primarily dependent on continued applications of residual insecticides, such as propoxur, acephate, dimethyl 2, 2-dichlorovinyl phosphate (dichlorvos), and pyrethroids and stomach poisons, such as hydramethylnon, fipronil, and sulfluramid as well dusts, such as boric acid, silica aerogel, and diatomaceous earth (Wang and Bennett 2006). The repeated use of synthetic pesticides may disrupt naturally occurring biological control systems, result in insecticide 1 Department of Entomology, China Agricultural University, 2 Yuanmingyuan West Rd., Haidian District, Beijing 100193, China. 2 State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing 102206, China. 3 Corresponding author, e-mail: [email protected]. resistance, affect nontarget organisms, contaminate food, present an occupational risk for workers, and are sometimes expensive to procure (Isman 2006, Regnault-Roger et al. 2012). These problems have highlighted the need for the development of new types of selective cockroach-control alternatives. From this point of view, botanical pesticides, including essential oils, are promising because they are effective, environmentally friendly, easily biodegradable, and often inexpensive. Moreover, herbal sources give a lead for discovering new insect control agents (Regnault-Roger et al. 2012). Repellents may play an important role in certain situations or areas where insecticide application is not practical or feasible (Nalyanya et al. 2000, Jung et al. 2007). Moreover, highly repellent insecticides, such as pyrethrum, are useful as flushing agents in areas of low visibility to determine relative abundance of cockroaches (Liu et al. 2011). Thus, many essential oils and their components have been screened for repellent activity against cockroaches with some showing potential further development (Ngoh et al. 1998, Appel et al. 2001, Peterson et al. 2002, Paranagama and Ekanayake 2004, Yoon et al. 2009, Liu et al. 2011, Oz et al. 2013). During our mass screening program for new agrochemicals from wild plants and Chinese medicinal herbs, essential oil of patchouli, Pogostemon cablin (Blanco) Bentham (Family: Labiatae) leaves were C The Author 2015. Published by Oxford University Press on behalf of the Entomological Society of America. V For Permissions, please e-mail: [email protected] January 2015 LIU ET AL.: CONTACT TOXICITY AND REPELLENCY OF P. CABLIN found to possess insecticidal and repellent activity against the German cockroach, B. germanica. Patchouli (P. cablin) is native to Malaysia and India and was imported into China for perfume and medicine centuries ago. Currently, patchouli occurs across southern China, including Fujian, Guangdong, Guangxi, Hainan, and Taiwan Province (Editorial Committee of Flora Republicae Popularis Sinicae 1977). It can be used for cooking in some uncommon dishes and snacks for the purposes of adding the flavor layers and increasing nutritional value. The medicinal properties of P. cablin leaves are well known in China (Jiangsu New Medical College 1985). The essential oil of P. cablin leaves exhibited high insecticidal and repellent activity against several insects and mites, e.g., urban ants [Camponotus melanoticus Emery, Camponotus novogranadensis Mayr, and Dorymyrmex thoracicus Gallardo (Albuquerque et al. 2013)], Formosan subterranean termites [Coptotermes formosanus Shiraki (Zhu et al. 2003) and Nasutitermes corniger (Motschulsky) (Lima et al. 2013)], the obliquebanded leafroller (Choristoneura rosaceana Harris) and the cabbage looper (Trichoplusia ni Huebner) (Machial et al. 2010), sweetpotato whitefly [Bemisia tabaci (Gennadius) (Yang et al. 2010)], Spodoptera littoralis (Boisduval) (Pavela 2005), and house dust mite, Dermatophagoides farinae Hughes (Wu et al. 2010). The essential oil also exhibited strong larvicidal activity against Culex pipiens pallens (L.) (Park and Park 2012). However, no studies have been carried out to examine the potential of P. cablin for the management of German cockroaches. Thus, we decided to investigate insecticidal and repellent activity of the essential oil against German cockroaches and to isolate any active constituents from the essential oil. Materials and Methods Plant and Extractions. Dried leaves of P. cablin (5 kg, harvested from Hainan Province) were purchased at Anguo Chinese Herbs Market, Hebei Province, China, and ground to a powder in lab. The plant was identified by Dr. Liu QR (College of Life Sciences, Beijing Normal University, Beijing 100875, China), and a voucher specimen (CAU-CMH-Guanghuoxiang2013-07-003) was deposited at the Department of Entomology, China Agricultural University, Beijing, China. Each portion of the powder was subjected to hydrodistillation using a modified Clevenger-type apparatus for 6 h and extracted with n-hexane. The solvent was evaporated at 40 C using a BUCHI Rotavapor R-124 vacuum rotary evaporator (BUCHI, www.buchi. com). Anhydrous sodium sulfate was used to remove water after extraction. The essential oil was stored in airtight containers in a refrigerator at 4 C for subsequent experiments. Gas Chromatography and Mass Spectrometry. Components of the essential oil of P. cablin leaves were separated and identified by gas chromatography–flame ionization detection (GC-FID) and gas chromatography–mass spectrometry (GC-MS) using a Agilent 6890N gas chromatograph connected to an 87 Agilent 5973N mass selective detector (www.agilent. com). The same column and analysis conditions were used for both GC-FID and GC-MS. They were equipped with capillary column with HP-5MS (30 m by 0.25 mm, df ¼ 0.25 lm). The GC settings were as follows: the initial oven temperature was held at 60 C for 1 min and ramped at 10 C/min to 180 C where it was held for 1 min, and then ramped at 20 C/min to 280 C and held there for 15 min. The injector temperature was maintained at 270 C. The samples (1 ll, diluted to 1% with acetone) were injected, with a split ratio of 1:10. The carrier gas was helium at flow rate of 1.0 ml/ min. Spectra were scanned from 20 to 550 m/z at two scansper second. Most constituents were identified by GC by comparison of retention indices with those of the literature or of authentic compounds available in our laboratories. The retention indices were determined in relation to a homologous series of n-alkanes (C8–C24) under the same operating conditions. Further identification was made by comparison of their mass spectra with those stored in NIST 05 (Standard Reference Data, Gaithersburg, MD) and Wiley 275 libraries (Wiley, New York, NY) or with mass spectra from literature (Adams 2007). Relative percentages of the individual components of the essential oil were obtained by averaging the GC-FID peak area% reports. Bioassay-Directed Fractionation. The crude essential oil of P. cablin leaves (20 ml) was chromatographed on a silica gel (Merck 9385, 1,000 g) column (inside diameter: 85 mm, length: 850 mm) by gradient elution with a mixture of solvents (n-hexane, n-hexaneethyl acetate). Fractions (500 ml each) were collected and concentrated at 40 C, and similar fractions according to thin layer chromatography (TLC) profiles were combined to yield 12 fractions. Fractions (4–5, 8–9) that possessed contact toxicity, with similar TLC profiles, were pooled and further purified by preparative silica gel column chromatography (PTLC) until to obtain the pure compound for determining structure as caryophyllene (1, 65 mg), patchoulol (2, 145 mg), and pogostone (3, 98 mg). The structure of the compounds was elucidated based on high-resolution electron impact MS and nuclear magnetic resonance. 1H and 13 C NMR spectra were recorded on Bruker Avance DRX 500 instruments using CDCl3 as solvent with tetramethylsilane as internal standard. EIMS were determined on a ThermoQuest Trace 2000 mass spectrometer at 70 eV (probe). The 1H- and 13C-NMR and MS data of the constituents were matched with previous reports (Liu et al. 2013b, Yi et al. 2013). Insect Cultures and Rearing Conditions. German cockroaches tested in this study were from a laboratory culture (State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, CDC, China), nonresistant to conventional insecticide, that were maintained under a photoperiod of 12:12 (L:D) h at 26–28 C, and 70–80% relative humidity (RH). All colonies were kept in plastic tanks at room temperature. Unsexed nymphs used in repellency testing were 1-wk old from hatching. Adult males for contact toxicity testing were 5–10 d post molt. Specimens used for 88 JOURNAL OF MEDICAL ENTOMOLOGY this study were collected form a synchronously reared laboratory colony of insecticide susceptible German cockroaches. Cockroaches were supplied ad libitum with Purina No. 5012 Rat Chow (Laboratory Animal Centre, Chinese Academy of Medicinal Sciences, Beijing 100021), and water was provided in glass tubes with cotton stoppers. Topical Application Bioassay. Range-finding studies were run to determine the appropriate testing concentrations (Zhu et al. 2012). Groups of 10 adult male cockroaches were anaesthetized with carbon dioxide for 15 s before treatment. A serial dilution of the essential oil (7.0–1.3%, five concentrations) and pure compounds (10–0.6%, 6 concentrations) was prepared in acetone. Aliquots of 2 ml of the solution were dispensed from an Arnold Automatic Micro-applicator (Burkard, Ricksmanworth, England) and applied to the dorsal thorax of individual insects. Controls were determined using acetone. Both treated and control cockroaches were then transferred to glass vials (10 insects per vial) and kept in incubators (26–28 C, 75% RH, and a photoperiod of 12:12 (L:D) h). Mortality of cockroaches was observed at 24 h posttreatment. Five replicates were carried out for all treatments and controls. Results from all replicates were subjected to probit analysis using the PriProbit Program V1.6.3 to determine LC50 (median lethal concentration) values (Sakuma 1998). Positive control, pyrethrum extract (25% pyrethrin I and pyrethrin II) was purchased from Fluka Chemie. Repellent Assays. Circular white filter paper No. 40 (9 cm in diameter, Whatman International Ltd., Maidstone, England), divided in two halves, were used (Liang et al. 2013). One of the halves was treated with 0.5 ml of acetone; the other half was treated with 0.5 ml acetone solutions of essential oils or compounds. Each essential oil was assayed at two concentrations of 5 and 1 ppm (w/v) after preliminary experiments. After solvent evaporation (2 min), each treated half disc was then attached lengthwise, edge-to-edge, to a control half-disc with adhesive tape to form a full disc. Precautions were taken so that the attachment did not prevent the free movement of the insects from one half to another, but a small distance between the filter-paper halves was left to prevent seepage of the test samples from one half to the other. Each filter paper was then placed in a Petri dish (diameter 9 cm) covered with polytetrafluoroethylene to prevent insects from escaping. The Petri dish had a seam orientated in one of four randomly selected directions to avoid any incidental stimuli affecting the distribution of insects. The orientation of the seam was changed in replicates. Ten nymphs of cockroaches were released in the middle of each filter-paper circle, and a plastic cover with some small holes was placed on the Petri dish. Five replicates were used. Counts of the insects present on each filter paper disc half were made after 1 h and subsequently at hourly intervals up to the fourth hour. No significant difference was detected between the repellency of acetone impregnated and plain filter papers in tests designed to check any possible influence of acetone on the insects. The average of the counts was converted to percentage repellency (PR) as PR ¼ 2 (C 50). Vol. 52, no. 1 Where C is the percentage of insects on the untreated half. The averages were then categorized according to the following scale (Ferrero et al. 2007, Zhang et al. 2011, Liu et al. 2013a): Class Percent repulsion 0 I II III IV V >0.01–0.1 0.1–20 20.1–40 40.1–60 60.1–80 80.1–100 PR was analyzed using analysis of variance (ANOVA) and Tukey’s tests after transforming them into arcsine percentage values. Permethrin was used as a positive control, because it has been widely used in the survey of cockroach population density in China (Liu et al. 2011). Permethrin were purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO). Results The yield of the essential oil of P. cablin leaves (yellow) was 0.33% (v/w based on fresh weight), while its density was determined to be 0.93 g/ml. In total, 23 components from the essential oil of P. cablin were identified, accounting for 96.65% of the total oil. The principal constituents of P. cablin essential oil were patchoulol (41.31%), pogostone (18.06%), a-bulnesene (6.56%), caryophyllene (5.96%) and seychellene (4.32%; Table 1). The essential oil of P. cablin exhibited contact activity against male cockroaches with an LC50 value of 23.45 lg per adult (Table 2). The constituent compound, pogostone (LC50 ¼ 8.51 lg per adult), showed stronger acute toxicity than patchoulol (LC50 ¼ 207.62 lg per adult) and caryophyllene (LC50 ¼ 339.90 lg per adult) against the male German cockroaches (Table 2). At a concentration of 5 ppm, the essential oil and the three isolated compounds as well as the positive control, permethrin, showed strong repellent activity (Class V) against the German cockroaches after 1-h exposure (Table 3). Repellency of the essential oil, patchoulol, caryophyllene, and permethrin decreased to Class III after 4-h exposure, whereas pogostone had Class IV repellency against cockroaches (Table 3). At a lower concentration of 1 ppm, the essential oil of P. cablin and the three isolated constituents exhibited moderate repellent activity (Class III) against the German cockroaches after 1-h exposure, whereas the positive control, permethrin, exhibited only Class II repellency (Table 4). Moreover, at 4-h exposure, the essential oil of P. cablin and the constituents, caryophyllene and pogostone, still had Class II repellent activity against the German cockroaches, whereas no repellent activity of the positive control, permethrin, was observed (Table 4). Caryophyllene (1, Fig. 1), colorless oil, 1HNMR (CDCl3, 500 MHz) d (ppm): 5.00 (1H, s, H-12), 4.88 (1H, s, H-12), 2.90 (1H, dd, J ¼ 4.1 and 10.7 Hz, H-9), 2.64 (1H, d, J ¼ 9.1 Hz, H-2), 2.33–2.37 (1H, m, H-11), January 2015 LIU ET AL.: CONTACT TOXICITY AND REPELLENCY OF P. CABLIN 2.28 (1H, dd, J ¼ 3.6 and 8.4 Hz, H-10), 2.09–2.15 (2H, m, H-7, H-11), 1.72–1.74 (1H, m, H-5), 1.69 (1H, br. s, H-3), 1.65–1.67 (1H, m, H-6), 1.62 (1H, br. s, H-3.), 1.44 (1H, d, J ¼ 2.8 Hz, H-6), 1.36–1.39 (1H, m, H-10), 1.23 (3H, s, H-15), 1.03 (3H, s, H-13), 1.01 (3H, s, H-14), 0.99 (1H, br. s, H-7); 13CNMR (CDCl3, 125 MHz): d (ppm): 151.8 (C-1), 112.8 (C-12), 63.8 (C-9), 59.9 (C-8), 50.7 (C-5), 48.9 (C-2), 39.7 (C-3), 39.1 (C-7), 34.0 (C-4), 30.2 (C-10), 29.9 (C-14), 29.8 (C-11), 27.2 (C-6), 21.6 (C-13), 17.0 (C-15). EI-MS m/z: 222 (Mþ, 6), 121 (60), 109 (66), 107(65), 93 (100), 91 (73), 81 (51), 79 (90), 69 (60), 55 (43), 43 (63), 41 (82), 39 (31), 27 (17). Patchoulol (2, Fig. 1), white solid, 1H NMR (300 MHz, CDCl3þCCl4): d (ppm): 0.80 (3H, d, J ¼ 6.6 Hz, H-15), 0.86 (3H, s, H-14), 1.04 (3H, s, H12), 1.06 (3H, s, H-13), 1.11–1.55 (9H, m), 1.55–1.75 (1H, m), 1.80–2.00 (3H, m). 13C NMR (CDCl3, 125 MHz): d (ppm): d 75.6 (C-1), 43.7 (C-9), 40.1 (C-11), 39.1 (C-4), 37.6 (C-2), 32.7 (C-6), 28.9 (C-10), 28.6 (C-8), 28.1 (C-3), 26.9 (C-7), 24.6 (C-5), 24.4 (C-12, C-13), 20.7 (C-14), 18.6 (C-15). EI-Ms: m/z 222 Table 1. Chemical constituents of the essential oil of P. cablin leaves No. Compounds Monoterpenoids a-Pinene b-Pinene b-Thujene 2-Carene b-Phellandrene Fenchol Borneol Pinocarvone 4-Terpineol a-Terpineol Sesquiterpenoids b-Patchoulene Caryophyllene a-Guaiene Seychellene c-Gurjunene b-Selinene b-Guaiene a-Bulnesene Spathulenol Caryophyllene oxide Patchoulol Others Cinnamaldehyde Pogostone Total identified 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 RIa 931 981 975 1,001 1,027 1,116 1,160 1,162 1,175 1,189 1,382 1,420 1,437 1,458 1,479 1,485 1,487 1,506 1,578 1,585 1,672 1,266 1,720 Content (%) 4.36 0.48 0.55 0.11 0.35 0.75 0.66 0.32 0.24 0.19 0.71 73.98 2.39 5.96 3.24 4.32 2.79 3.65 2.14 6.56 0.57 1.05 41.31 18.31 0.25 18.06 96.65 a RI, retention index as determined on a HP-5MS column using the homologous series of n-hydrocarbons. 89 (Mþ, 70), 207 (25), 161 (41), 138 (100), 125 (70), 98 (97), 43 (67), 41 (82). Pogostone (3, Fig. 1), colorless oil, 1HNMR (CDCl3, 500 MHz): d (ppm): 5.92 (1H, d, J ¼ 0.75 Hz), 3.13 (3H, d, J ¼ 0.75 Hz), 3.07 (2H, t, J ¼ 7.64 Hz), 1.64 (1H, m), 1.54 (2H, m), 0.95 (3H, d, J ¼ 6.52 Hz), 0.93 (3H, d, J ¼ 6.52 Hz); 13CNMR (CDCl3, 125 MHz): d (ppm): 208.3 (C-6), 181.3 (C-3), 168.8 (C-1), 160.9 (C-5), 101.5 (C-4), 99.5 (C-2), 39.7 (C-7), 32.9 (C-8), 27.8 (C-9), 22.4 (C-10), 22.4 (C-11), 20.6 (C-12); EI-MS m/z: 224 (Mþ, 11), 209 (12), 181 (37), 168 (100), 153 (73), 85 (17), 55 (21), 43 (41). Discussion GC-MS results showed the major constituents in P. cablin essential oil were patchoulol, pogostone, a-bulnesene, and caryophyllene (Table 1). Great variations were observed in chemical composition of the essential oils derived from various cultivation regions and harvesting times (Luo et al. 2003, Guo et al. 2004, Hu et al. 2006). Two chemotypes, patchoulol-type and pogostone-type, were suggested based on the chemical compositions. The pogostone-type oil contains rich oxygenated components, especially pogostone and poor nonoxygenated composition with patchoulol (Luo et al. 2003). However, besides the two typical chemotypes, an interim type of P. cablin essential oil was also developed based on characteristics of 10 investigated peaks in GC profiles (including b-patchoulene, caryophyllene, a-guaiene, seychellene, b-guaiene, d-guaiene, spathulenol, patchouli alcohol, and pogostone; Hu et al. 2006). Thus, for practical use, it is necessary to standardize the essential oil of P. cablin leaves because great variations were observed in chemical composition of the essential oils derived from different cultivation regions. The essential oil of P. cablin leaves and the three constituent compounds exhibited contact activity against male cockroaches (Table 2). When compared with the positive control, pyrethrum extract (25% pyrethrin I and pyrethrin II, LC50 value of 1.70 lg per adult), the essential oil of P. cablin leaves was 14 times less toxic (LC50 value of 23.45 lg per adult) to adult male cockroaches (Table 2). Among the three constituent compounds, pogostone exhibited strongest acute toxicity and stronger toxicity than the essential oil against male B. germanica adults. It is suggested that pogostone maybe a major contributor to the acute toxicity of the essential oil of P. cablin leaves. Moreover, compared with pyrethrum extract, pogostone exhibited only one-fifth level of acute toxicity against Table 2. Contact toxicity of the essential oil and its isolated components from P. cablin leaves against male cockroach adults Compounds Patchoulol Pogostone Caryophyllene Crude oil Pyrethrum extract LD50 (mg per adult) 95% Fiducial limits Slope 6 SE v2 207.62 8.51 339.90 23.45 1.70 19.92-24.43 102.13-143.51 302.84-374.32 59.21-70.46 1.16-3.78 5.67 6 0.56 5.91 6 0.58 5.23 6 0.47 6.10 6 0.59 4.23 6 0.47 10.36 12.23 13.40 11.40 6.80 90 JOURNAL OF MEDICAL ENTOMOLOGY Vol. 52, no. 1 Table 3. Repellency (PR) after two exposure times for P. cablin essential oil and its isolated constituents against the nymphs of B. germanica at a concentration of 5 ppm Treatment 1h 2h P. cablin Patchoulol Pogostone Caryophyllene Permethrin 80.8 6 3.6b 82.9 6 2.5a 90.2 6 2.9a 81.2 6 2.7a 88.9 6 3.2a V V V V V 3h 73.1 6 3.7ab 69.5 6 2.7b 82.6 6 3.3a 73.4 6 2.5ab 75.4 6 2.6ab IV IV V IV IV 4h 56.6 6 5.7b 58.7 6 2.5b 70.9 6 2.3a 70.6 6 2.8a 66.5 6 5.3ab III III IV IV IV 47.6 6 4.7bc 40.5 6 2.6c 62.4 6 3.8a 55.2 6 2.5ab 49.3 6 2.6b III III IV III III Means within a column followed by the same lower case letter are not significantly different (P < 0.05, ANOVA and Tukey’s tests). Table 4. Repellency (PR) after two exposure times for P. cablin essential oil and its major constituents against the nymphs of B. germanica at a concentration of 1 ppm Treatment 1h 2h P. cablin Patchoulol Pogostone Caryophyllene Permethrin 46.1 6 3.4a 47.7 6 1.8a 51.5 6 3.2a 53.1 6 2.2a 28.1 6 3.0b III III III III II 3h 38.4 6 3.5a 42.7 6 1.4a 45.5 6 2.7a 43.3 6 3.7a 20.2 6 2.6b II III III III II 34.5 6 4.3e 24.3 6 1.1d 37.9 6 2.2a 37.9 6 2.2a 14.1 6 2.2e 4h II II II II I 23.1 6 3.7ab 13.1 6 4.7b 22.9 6 2.5ab 27.5 6 2.6a 0 II I II II - Means within a column followed by the same lower case letter are not significantly different (P < 0.05, ANOVA and Tukey’s tests). 14 13 H 6 5 4 H 9 1 12 8 11 10 Caryophyllene (1) Fig. 1. 15 5 O 13 1 OH 12 H 2 3 6 7 11 15 4 H 14 2 7 10 OH 13 9 8 Patchoulol (2) O 2 6 4 7 5 12 8 O 1 O 10 9 11 Pogostone (3) Bioactive compounds isolated from P. cablin essential oil. B. germanica adults (Table 2). In the previous reports, pogostone exhibited strong contact toxicity against the fourth-instar larvae of cabbage butterfly (Pieris rapae L.) with an LC50 value of 32.20 lg/ml (Zeng et al. 2006) and also possessed contact toxicity to the thirdinstar larvae of oriental leafworm (Spodoptera litura F.) and beet armyworm (Spodoptera exigua Hubner) with LC50 values of 1,041.42 mg/liter and 519.48 mg/liter, respectively (Huang et al. 2014). It also exerted significant antifeedant, larvicidal (oral toxicity and contact toxicity), pupicidal, growth inhibitory, and ovicidal properties against insects (Zeng et al. 2006, Huang et al. 2014). The hydrolysate of pogostone was shown to have strong acaricidal activities against the house dustmite (D. farinae Hughes) (Wu et al. 2012). Another major constituent in the essential oil, patchoulol was found to possess strong acute toxicity against several insects, e.g., the booklice (Liposcelis bostrychophila Badonnel) (Liu et al. 2013b), Formosan subterranean termites (C. formosanus Shiraki) (Zhu et al. 2003). It also exhibited pupicidal and repellent activities against three important vector mosquitoes (Aedes aegypti L., Anopheles stephensi Liston, and Culex quinquefasciatus Say) (Gokulakrishnan et al. 2013) and weak larvicidal activity of patchoulol against house mosquito (Cu. pipiens pallens Coquillett) was also observed (Park and Park 2012). At a lower concentration of 1 ppm, the essential oil of P. cablin leaves and the three constituent compounds exhibited stronger repellent activity than the positive control, permethrin, against German cockroach nymphs (Table 4). After 4-h exposure, pogostone and caryophyllene exhibited stronger repellent (Class II) than patchoulol (Class I; Table 4). Repellence of the essential oil of P. cablin leaves has been demonstrated to other insects (Zhu et al. 2003, Yang et al. 2010, Albuquerque et al. 2013, Gokulakrishnan et al. 2013, Zhang et al. 2013). One of the main components, patchoulol also has been demonstrated to possess repellent activity against several other insects (Zhu et al. 2003, Albuquerque et al. 2013, Gokulakrishnan et al. 2013). However, no reports on repellence of pogostone against insects are known at the time this article was written. January 2015 LIU ET AL.: CONTACT TOXICITY AND REPELLENCY OF P. CABLIN The above findings suggest that the essential oil and the major constituent compounds of P. cablin show potential for further development as possible natural insecticides and repellents for cockroaches. However, to develop a practical application for the essential oil and its constituents as novel insecticides and repellents, further research into the safety of the essential oil or compounds to humans is needed. Additional studies on the development of formulations are also necessary to improve the efficacy and stability and to reduce cost. Moreover, field evaluation and further investigations on the effects of the essential oil and its constituent compounds on nontarget organisms are necessary. The essential oil of P. cablin leaves demonstrates strong insecticidal and repellent activity against German cockroaches. The isolated constituents, especially pogostone exhibited strong insecticidal and repellent activity against German cockroaches. Our results suggest the essential oil of P. cablin leaves and the three constituents may be considered for future cockroach management program. Acknowledgments This work was supported by Special Fund for Agro-scientific Research in the Public Interest (grant 201003058). We thank Dr. Liu Quan Ru from the College of Life Sciences, Beijing Normal University, Beijing 100875, for the identification of the investigated medicinal herb. 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