Pest Management Science Pest Manag Sci 64:857–862 (2008)

Larvicidal activity of Kaempferia galangarhizome phenylpropanoids towards threemosquito speciesNam-Jin Kim,1 Sang-Gi Byun,2 Jang-Eun Cho,1 Keun Chung2 andYoung-Joon Ahn1∗1School of Agricultural Biotechnology, Seoul National University, Seoul 151-921, Republic of Korea2Division of Bio-Resources Technology, College of Agriculture and Life Sciences, Kwangwon National University, Chuncheon 200-701,Republic of Korea

Abstract

BACKGROUND: This study was aimed at assessing the toxicity of ethyl cinnamate and ethyl p-methoxycinnamate(EMC) identified in Kaempferia galangal L. (Zingiberaceae) rhizome and another 12 known compounds to third-instar larvae from laboratory-reared Culex pipiens pallens Forskal, Aedes aegypti L. and Ochlerotatus togoiTheobald and field-collected C. pipiens pallens (Jinhae colony). Results were compared with those for fenthionand temephos.

RESULTS: Ethyl p-methoxycinnamate was the most toxic of the test compounds to larvae of the threemosquito species (LC50 12.3–20.7 mg L−1) but less toxic than either fenthion (0.0096–0.021 mg L−1) or temephos(0.0039–0.0079 mg L−1). Ethyl cinnamate and 3-carene were highly active against C. pipiens pallens larvae (24.1and 21.6 mg L−1) but less toxic to A. aegypti and O. togoi larvae (ca 40 and 60 mg L−1 respectively). The toxicityof these compounds to larvae from the Jinhae colony of C. pipiens pallens was almost the same as their toxicityto the laboratory-reared larvae, although the larvae from the colony exhibited low levels of resistance to fenthion(resistance ratio 9.1) and temephos (5.8).

CONCLUSION: Kaempferia galanga rhizome-derived materials, particularly ethyl p-methoxycinnamate, meritfurther study as potential mosquito control agents for protection of humans and domestic animals from vector-borne diseases and nuisance caused by mosquitoes. 2008 Society of Chemical Industry

Keywords: botanical insecticide; mosquito larvicide; Kaempferia galanga; Zingiberaceae; ethyl cinnamate; ethylp-methoxycinnamate

1 INTRODUCTIONThe northern house mosquito, Culex pipiens pallensForskal, and the yellow fever mosquitoes, Aedesaegypti L. and Ochlerotatus togoi (formerly Aedestogoi) Theobald, are widespread and serious disease-vectoring insect pests. Mosquito larval abatementworldwide has been principally achieved throughthe use of organophosphates such as fenthionand temephos, insect growth regulators such asdiflubenzuron and methoprene and bacterial larvicidessuch as Bacillus thuringiensis Berl. H–14 and Bacillussphaericus Meier & Neide.1,2 Although they are stillthe most effective larvicides, their repeated use hasdisrupted natural biological control systems, ledto resurgences of mosquitoes3 and resulted in thedevelopment of resistance.4,5 Increasing levels ofresistance to the commonly used insecticides havecaused multiple treatments and excessive doses,raising serious human health and environmental

concerns.2,4,5 Additionally, some organophosphorusand carbamate insecticides will be phased out inthe near future in the United States by the USEnvironmental Protection Agency (EPA), under the1996 Food Quality and Protection Act.6 Theseproblems indicate the need for the development ofselective control alternatives for mosquito larvae.

Plants, particularly higher plants, have potentialas natural insecticides for mosquito larval controlbecause they constitute a potential source of bioactivechemicals7 and because some are selective, biodegradeto non-toxic products and have few harmful effects onnon-target organisms and the environment.8–10 Thesepotential new mosquito larvicides can be applied tobreeding places in the same manner as the mosquitolarvicides currently used. In part, because certainplants and their constituents meet the criteria ofminimum risk pesticides,11 much effort has beenfocused on them as potential sources of commercial

∗ Correspondence to: Young-Joon Ahn, School of Agricultural Biotechnology, Seoul National University, Seoul 151-921, Republic of KoreaE-mail: yjahn@snu.ac.kr(Received 16 May 2007; revised version received 28 November 2007; accepted 3 December 2007)Published online 6 March 2008; DOI: 10.1002/ps.1557

2008 Society of Chemical Industry. Pest Manag Sci 1526–498X/2008/$30.00

N-J Kim et al.

mosquito larval control products. Previously, thepresent authors reported that a methanolic extractof the rhizome from lesser galangale, Kaempferiagalanga L. (Zingiberaceae), had good larvicidal activityagainst C. pipiens pallens, A. aegypti and O. togoi.12

Kaempferia rhizome contains borneol, 1.8-cineole, 3-carene, (E)-cinnamaldehyde, ethyl cinnamate, ethylp-methoxycinnamate, eucalyptol, kaempferol, methylp-coumaric acid ethyl ester and pentadecane.13,14

This study was aimed at isolating larvicidalprinciples from the rhizome of K. galanga active againstearly third-instar larvae of C. pipiens pallens, A. aegyptiand O. togoi. Also, the larvicidal activity of the isolatedcompounds and another 12 known K. galanga rhizomecompounds towards larvae from the laboratory-rearedand field-collected mosquitoes was compared with thatof the most widely used mosquito larvicides, fenthionand temephos.

2 MATERIALS AND METHODS2.1 Apparatus1H- and 13C-NMR spectra were recorded in deute-rochloroform on an AVANCE 600 spectrometer(Bruker, Karlsruhe, Germany) using tetramethylsi-lane (TMS) as an internal standard, with chemicalshifts given in δ (ppm). UV spectra were obtained inmethanol on a UVICON 933/934 spectrophotometer(Kontron Instrument, Milan, Italy), and mass spec-tra on a JMS-AX 505 WA spectrometer (Jeol, Tokyo,Japan). Silica gel (0.063–0.2 mm) (Merck, Darmstadt,Germany) was used for column chromatography. Pre-coated silica gel plates (silica gel 60 F254, Merck) wereused for analytical thin-layer chromatography (TLC).

2.2 ChemicalsFourteen compounds used in this study were as fol-lows: (+)-borneol, (−)-borneol, (−)-camphene andeucalyptol purchased from Fluka (Buchs, Switzer-land); 3-carene, (E)-cinnamaldehyde, p-methoxy-cinnamic acid, pentadecane, (+)-α-terpineol and (−)-α-terpineol purchased from Aldrich (Milwaukee, WI,USA); 1,8-cineole, ethyl cinnamate and kaempferolpurchased from Wako (Osaka, Japan); and ethylp-methoxycinnamate purchased from Tokyo Chem-ical Industry (Tokyo). Fenthion (98.4% purity) andtemephos (97.3% purity) were supplied by Supelco(West Chester, PA, USA) and Riedel (Seelze, Ger-many) respectively. Triton X-100 was obtained fromShinyo Pure Chemicals (Osaka). All other chemicalswere of reagent grade and available commercially.

2.3 MosquitoesThe stock cultures of C. pipiens pallens, A. aegypti andO. togoi12 were maintained in the laboratory withoutexposure to any known insecticide. Culex pipiens pallenslarvae (designated Jinhae colony) were collected froma small pond at Jinhae (Gyeongnam Province, Korea)in late August 2006. The adult females from the Jinhaecolony showed extremely high levels of resistance to

deltamethrin [resistance ratio (RR) 959], cyfluthrin(RR 370) and permethrin (RR 247), high levels ofresistance to bendiocarb (RR 46) and chlorpyrifos(RR 80) and moderate and low levels of resistanceto S-bioallethrin (RR 25) and λ-cyhalothrin (RR 9)respectively.15 Adult mosquitoes were maintained ona 10% sucrose solution and blood fed on live mice.Larvae were reared in plastic trays (24 × 35 × 5 cm)containing 0.5 g of sterilized diet (40-mesh chick chowpowder + yeast, 4 + 1 by weight). They were heldat 27 ± 1 ◦C and 65–75% relative humidity under a14:10 h light:dark cycle.

2.4 Extraction and isolationAir-dried rhizomes (600 g) of K. galanga were pur-chased from Boeun medicinal herb shop, KyoungdongMarket (Seoul, Korea). They were pulverized andextracted with methanol (2 × 3 L) at room temper-ature for 1 day and filtered. The combined filtratewas concentrated under vacuum at 40 ◦C to yieldca 70 g as a dark-brownish tar. The extract (50 g)was sequentially partitioned into hexane- (31.4 g),chloroform- (0.8 g), ethyl acetate- (1.9 g), butanol-(7.4 g) and water-soluble (9.4 g) portions for subse-quent bioassay. The organic solvent soluble portionswere concentrated to dryness by rotary evaporation at40 ◦C, and the water-soluble portion was freeze dried.For isolation of active principles, 50 mg L−1 of eachK. galanga rhizome-derived material was applied to adirect contact toxicity bioassay.

The most active hexane-soluble fraction (12 g) waschromatographed on a 70 × 5.5 cm silica gel column(600 g) and eluted with a gradient of hexane and ethylacetate [(10 + 1 (1.1 L), 7 + 3 (1.5 L), 5 + 5 (1 L) and3 + 7 (1 L) by volume] and finally with methanol (1 L)to provide 22 fractions (each about 250 mL). Columnfractions were monitored by TLC, and fractions withsimilar Rf values on the TLC plates were pooled. Spotswere detected by spraying with 10% sulfuric acid andthen heating on a hot plate. The bioactive fractions4–5 (670 mg) were pooled and chromatographed onthe preparative TLC plates under benzene and hexane(1 + 1 by volume) to give active compound 1 (87.5 mg,Rf = 0.43). The bioactive fractions 6–7 (5.27 g) werepooled and recrystallized in methanol and water (6+4)at −4 ◦C to yield compound 2 (2.11 g).

2.5 BioassayA direct contact toxicity bioassay12 was used toevaluate the toxicity of K. galanga rhizome-derivedmaterials to early third-instar larvae from laboratory-reared C. pipiens pallens, A. aegypti and O. togoiand field-collected C. pipiens pallens. Each compoundin methanol was suspended in distilled water withTriton X-100 (20 µL L−1). Groups of 20 mosquitolarvae were separately put into paper cups (270 mL)containing each test compound solution (250 mL).The toxicity of each test compound was determinedwith 4–6 concentrations ranging from 1 to 200 mgL−1. Fenthion and temephos served as standards for

858 Pest Manag Sci 64:857–862 (2008)DOI: 10.1002/ps

Mosquito larvicidal activity of Kaempferia galanga

comparison in larval toxicity tests. Controls receivedmethanol–Triton X-100 solution.

Treated and control larvae were held at the sameconditions as used for colony maintenance. Larvalmortalities were determined 24 h post-treatment.Larvae were considered to be dead if they did not movewhen they were prodded with fine wooden dowels. Alltreatments were replicated 3 times.

2.6 Data analysisThe LC50 values were calculated by probit analysis.16

A resistance ratio (RR) was calculated according tothe formula RR = LC50 of larvae from the field-collected C. pipiens pallens colony/LC50 of larvae fromthe laboratory-reared strain. Larvicidal activity wasconsidered to be significantly different when 95%confidence limits of the LC50 values failed to overlap.The susceptibility ratio (SR) was determined as theratio of LC50 of A. aegypti or O. togoi larvae/LC50 ofC. pipiens pallens larvae, as previously described.17

3 RESULTS3.1 Bioassay-guided fractionation and isolationFractions obtained from the methanolic extract ofK. galanga rhizomes were bioassayed against earlythird-instar larvae from C. pipiens pallens, A. aegyptiand O. togoi by direct contact application (Table 1).Significant differences in larvicidal activity in fractionsof the extract were observed, and they were used toidentify peak activity fractions for the next step in thepurification. After 24 h exposure, the hexane-solublefraction was most toxic to larvae of the three mosquitospecies. Moderate and weak larvicidal activity wasobserved in the chloroform- and ethyl acetate-solublefractions respectively. No mortality was produced fromthe butanol- and water-soluble fractions at 200 mgL−1. There was no mortality in the methanol–TritonX-100 treated controls.

Direct contact toxicity bioassay-guided fraction-ation of K. galanga rhizome extract afforded twoactive principles identified by spectroscopic analyses,including MS and NMR, and by direct compari-son with authentic samples. The two active princi-ples were the phenylpropanoids ethyl cinnamate (1)and ethyl p-methoxycinnamate (2) (Fig. 1). Ethyl p-methoxycinnamate (2) was identified on the basis

of the following evidence: colourless needles; UV(methanol) λmax nm: 286; EI-MS (70 ev), m/z (rel.int.): 206 [M]+ (100, base peak), 178 (21), 161(97), 134 (76), 133 (54), 118 (13), 77 (10); 1H-NMR (deuterochloroform, 600 MHz): δ 1.32 (3H,t, J = 7 Hz), 3.84 (3H, s), 4.25 (2H, q, J = 7 Hz),6.31 (1H, d, J = 16 Hz), 6.90 (2H, d, J = 9 Hz),7.47 (2H, d, J = 9 Hz), 7.64 (1H, d, J = 16 Hz);13C-NMR (deuterochloroform, 150 MHz): δ 14.5d, 55.6 d, 60.5 d, 114.5 d ×2, 116.0 d, 127.4 s,130 d ×2, 144.4 d, 161.5 s, 167.5 s. The struc-ture of ethyl cinnamate (1) was determined simi-larly.

3.2 Larvicidal activity of test compoundsThe toxicity to early third-instar larvae from C. pipienspallens of 14 test compounds and two mosquitolarvicides (fenthion and temephos) was evaluatedby comparing the LC50 values estimated from thedirect contact application (Table 2). Responses variedaccording to the compound tested. On the basis of 24 hLC50 values, ethyl p-methoxycinnamate (12.3 mg L−1)was the most toxic compound, followed by 3-carene(21.6 mg L−1) and ethyl cinnamate (24.1 mg L−1).These compounds were less active than either fenthion(0.0096 mg L−1) or temephos (0.0039 mg L−1). (E)-Cinnamaldehyde and p-methoxycinnamic acid weremoderately toxic. The other nine compounds wereineffective at the concentration tested.

The toxicity of the test compounds and twomosquito larvicides to third-instar larvae from theJinhae colony of C. pipiens pallens was comparedwith toxicity to the laboratory-reared larvae (Table 2).

O

O

1

O

O

O

2

Figure 1. Structures of ethyl cinnamate (1) and ethylp-methoxycinnamate (2).

Table 1. Toxicity of each solvent fraction derived from a methanolic extract of Kaempferia galanga rhizome to early third-instar larvae from the three

mosquito species during a 24 h exposure

LC50 (mg L−1) (95% CL)

Material Culex pipiens pallens Aedes aegypti Ochlerotatus togoi

Methanol extract 36.5 (28.2–46.5) 30.4 (28.2–33.3) 49.4 (39.4–61.2)Hexane fraction 28.3 (27.2–29.3) 27.9 (27.0–29.0) 40.4 (38.9–41.8)Chloroform fraction 44.2 (40.2–48.8) 40.9 (39.4–42.3) 53.0 (40.8–68.2)Ethyl acetate fraction 165.8 (144.9–188.2) 133.7 (118.9–149.5) 142.5 (125.8–161.8)Butanol fraction >200 >200 >200Water fraction >200 >200 >200

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Table 2. Toxicity of Kaempferia galanga rhizome compounds and two mosquito larvicides to early third-instar larvae from laboratory-reared and

field-collected Culex pipiens pallens during a 24 h exposure

Laboratory-reared larvae Field-collected larvae

Compound Slope (± SE) LC50 (mg L−1) (95% CL) Slope (± SE) LC50 (mg L−1) (95% CL) RRb

(+)-Borneol >100 >100(−)-Borneol >100 >100(−)-Camphene >100 >1003-Carene 4.7 (±0.36) 21.6 (17.6–26.4) 4.6 (±0.77) 15.3 (13.1–18.1) 0.71,8-Cineol >100 >100(E)-Cinnamaldehyde 4.6 (±0.57) 48.4 (40.0–57.6) 7.9 (±0.98) 49.1 (44.8–53.7) 1.0Ethyl cinnamatea 4.7 (±0.60) 24.1 (18.7–30.5) 4.3 (±0.50) 28.4 (24.5–32.2) 1.2Ethyl p-methoxycinnamatea 3.3 (±0.40) 12.3 (9.0–16.7) 5.8 (±1.12) 18.8 (13.9–23.1) 1.5Eucalyptol >100 >100Kaempferol >100 >100p-Methoxycinnamic acid 5.7 (±0.70) 44.0 (39.6–48.8) 2.8 (±0.53) 54.3 (42.5–72.3) 1.2Pentadecane >100 >100(+)-α-Terpineol >100 >100(−)-α-Terpineol >100 >100Fenthion 1.7 (±0.19) 0.0096 (0.0068–0.0134) 1.8 (±0.29) 0.087 (0.066–0.120) 9.1Temephos 2.9 (±0.35) 0.0039 (0.0031–0.0046) 2.7 (±0.31) 0.0225 (0.0185–0.0282) 5.8

a Compounds identified in this study. The other compounds were described by Kiuchi et al.13 and Namba.14

b Resistance ratio. See Section 2.6.

Larvae from the Jinhae colony exhibited low levels ofresistance to fenthion (RR 9.1) and temephos (RR5.8). The toxicity of the compounds tested to larvaefrom the colony was almost the same as that to thelaboratory-reared larvae.

The larvicidal activity of 14 test compoundstowards early third-instar larvae from A. aegyptiwas compared with that of fenthion and temephos(Table 3). Based on 24 h LC50 values, ethyl p-methoxycinnamate (18.9 mg L−1) was the mosteffective compound but was less toxic than eitherfenthion (0.019 mg L−1) or temephos (0.0079 mgL−1). Moderate to weak activity was produced from

3-carene, (E)-cinnamaldehyde, ethyl cinnamate and p-methoxycinnamic acid (39.5–61.0 mg L−1). The othernine compounds were ineffective.

Toxic effects on early third-instar larvae from O.togoi in direct contact application of the test com-pounds and two mosquito larvicides were exam-ined (Table 4). As judged by 24 h LC50 val-ues, ethyl p-methoxycinnamate (20.7 mg L−1) wasmost toxic but less effective than either fenthion(0.021 mg L−1) or temephos (0.0071 mg L−1). Mod-erate to weak larvicidal activity was obtained from3-carene, (E)-cinnamaldehyde, ethyl cinnamate andp-methoxycinnamic acid (44.1–68.4 mg L−1). No

Table 3. Toxicity of Kaempferia galanga rhizome compounds and two mosquito larvicides to early third-instar larvae from Aedes aegypti during a

24 h exposure

Compound Slope (± SE) LC50 (mg L−1) (95% CL) SRb

(+)-Borneol >100(−)-Borneol >100(−)-Camphene >1003-Carene 3.4 (±0.48) 60.0 (50.5–70.7) 2.81,8-Cineole >100(E)-Cinnamaldehyde 2.9 (±0.44) 51.3 (38.2–66.1) 1.1Ethyl cinnamatea 4.4 (±0.62) 39.5 (34.4–44.4) 1.6Ethyl-p-methoxycinnamatea 4.3 (±0.48) 18.9 (16.3–21.6) 1.5Eucalyptol >100Kaempferol >100p-Methoxycinnamic acid 2.5 (±0.41) 61.0 (49.8–76.8) 1.4Pentadecane >100(+)-α-Terpineol >100(−)-α-Terpineol >100Fenthion 2.0 (±0.25) 0.019 (0.014–0.026) 2.0Temephos 4.3 (±0.56) 0.0079 (0.0058–0.0107) 2.0

a See Table 2.b Susceptibility ratio = LC50 of A. aegypti larvae/LC50 of C. pipiens pallens larvae.

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Table 4. Toxicity of Kaempferia galanga rhizome compounds and two mosquito larvicides to early third-instar larvae from Ochlerotatus togoi during

a 24 h exposure

Compound Slope (± SE) LC50 (mg L−1) (95% CL) SRb

(+)-Borneol >100(−)-Borneol >100(−)-Camphene >1003-Carene 7.9 (±1.17) 56.7 (51.5–63.5) 2.61,8-Cineole >100(E)-Cinnamaldehyde 3.4 (±0.40) 46.9 (39.1–55.1) 1.0Ethyl cinnamatea 3.4 (±0.64) 44.1 (35.1–59.3) 1.8Ethyl p-methoxycinnamatea 6.9 (±0.86) 20.7 (18.8–22.6) 1.7Eucalyptol >100Kaempferol >100p-Methoxycinnamic acid 6.2 (±0.83) 68.4 (62.9–74.6) 1.6Pentadecane >100(+)-α-Terpineol >100(−)-α-Terpineol >100Fenthion 1.7 (±0.32) 0.021 (0.012–0.041) 2.2Temephos 4.7 (±0.62) 0.0071 (0.0054–0.0094) 1.8

a See Table 2.b Susceptibility ratio = LC50 of O. togoi larvae/LC50 of C. pipiens pallens larvae.

larvicidal activity was observed with the other ninecompounds.

3.3 SusceptibilityThe SR varied according to mosquito species andcompound tested (Tables 3 and 4). High SR wasobserved in 3-carene. Moderate SR was producedby ethyl cinnamate, ethyl p-methoxycinnamate, p-methoxycinnamic acid, fenthion and temephos, andvery little with (E)-cinnamaldehyde (SR = 1).

4 DISCUSSIONIn the Chinese and Indian Pharmacopoeia, K. galangarhizome has long been used for the treatmentof peptic illness and a remedy for toothache.14,18

Very little work has been done to consider itspotential to manage mosquitoes, although K. galangarhizome extract has been reported to be toxicto larvae of dog roundworm, Toxocara canis.13

Sukumar et al.10 pointed out that the most promisingbotanical mosquito control agents are species inthe families Asteraceae, Cladophoraceae, Lamiaceae(formerly Labiatae), Meliaceae, Oocystaceae andRutaceae, although K. galanga belongs to the familyZingiberaceae. In the present study, K. galangarhizome-derived materials exhibited larvicidal activityagainst third-instar larvae of C. pipiens pallens, A.aegypti and O. togoi.

Various compounds, including phenolics, ter-penoids and alkaloids, exist in plants, and jointlyor independently they contribute to behavioural effi-cacy, such as repellency and feeding deterrence, andphysiological efficacy, such as acute toxicity anddevelopmental disruption, against various arthropodspecies.8,9 Many plant preparations and their con-stituents manifest larvicidal activity against differentmosquito species10,19–21 and have been proposed as

alternatives to the most widely used larvicides. Muchconcern has been focused on determining the dis-tribution, nature and practical use of plant-derivedsubstances that have mosquito larvicidal activity.For example, it has been reported that the isobuty-lamide alkaloids pellitorine, guineensine, pipercideand retrofractamide A derived from the fruits of Pipernigrum L. (Piperaceae) possess potent larvicidal activ-ity against larvae of C. pipiens pallens, A. aegypti andO. togoi, and the N-isobutylamine moiety appears toplay a crucial role in the larvicidal activity.19 Addition-ally, certain plant-derived compounds were found tobe highly effective against insecticide-resistant insectpests.21,22 Guineensine was found to possess remark-able insecticidal activity against a pyrethrin-resistantstrain of Musca domestica L.21

In the present study, the larvicidal principlesof K. galanga rhizome were identified as thephenylpropanoids ethyl cinnamate (1) and ethylp-methoxycinnamate (2). The interpretations ofproton signals of ethyl cinnamate and ethyl p-methoxycinnamate were largely consistent with thoseof Kiuchi et al.13 This is the first report onthe mosquito larvicidal activity of the phenyl-propanoids. Of all the compounds tested, ethyl p-methoxycinnamate exhibited potent larvicidal activitytowards larvae of the three mosquito species, whileethyl cinnamate and 3-carene were highly to mod-erately toxic to mosquito larvae. Introduction ofa methoxy moiety in ethyl cinnamate significantlyincreased the larvicidal activity. Additionally, toxic-ity to larvae from the field-collected C. pipiens pallensof these compounds was almost the same as that tolaboratory-reared C. pipiens pallens larvae, although lar-vae from the colony exhibited low levels of resistanceto fenthion and temephos. These results suggest thatinsecticide mode of action might be different betweenthe phenylpropanoids and organophosphates tested.

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Ethyl cinnamate and ethyl p-methoxycinnamate werefound to possess strong larvicidal activity towards T.canis.13

Variation in mosquito responses to chemicalshas been well noted. For example, A. aegyptiand O. togoi larvae were found to be moretolerant than C. pipiens pallens larvae to pellitorine,guineensine, pipercide and retrofractamide A.19 Inthe present study, responses were dependent onmosquito species and compound tested. A. aegyptiand O. togoi larvae were slightly more tolerant thanC. pipiens pallens larvae to 3-carene, ethyl cinnamate,ethyl p-methoxycinnamate, p-methoxycinnamic acid,fenthion and temephos. Different susceptibilitiesof larvae of the three mosquito species to thecompounds and insecticides might be attributedto differences in one or more physiological orbiochemical characteristics: penetration, detoxifyingenzyme activity and the relative sensitivity to the toxiclesion at the target site.23,24

Results of this study indicate that K. galangarhizome-derived materials, particularly ethyl p-methoxycinnamate, could be useful as mosquito larvalcontrol agents for field populations of mosquitoes.Further research is necessary on issues of their safetyas regards human health, non-target aquatic organismsand the environment. Other areas requiring attentionare larvicide mode of action and formulations forimproving larvicidal potency and stability.

ACKNOWLEDGEMENTSThis work was supported by grants from the PlantDiversity Research Centre of the 21st CenturyFrontier Research Programme (M106KD010024-07K0401-02410) funded by the Ministry of Scienceand Technology and the Ministry of Educationand Human Resources Development of the KoreanGovernment (Brain Korea 21 Project) to YJA.

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