Repellent activity of herbal essential oils against Aedes aegypti (Linn.) and Culex quinquefasciatus (Say.)

Abstract

1. Introduction

Mosquitoes are the most important of insects in terms of public health importance which transmit a number of diseases such as dengue, chikungunya, Japanese encephalitis, filariasis and malaria, causing millions of deaths every year. Aedes aegypti (Ae. aegypti) and Culex quinquefasciatus (Cx. quinquefasciatus) are major urban vectors of dengue fever, dengue haemorrhagic fever, chikungunya and Japanese encephalitis. Mosquito bites may also cause allergic responses including local skin reactions and systemic reactions such as urticarial. Personal protection is one approach to prevent mosquito bites[1]–[3]. Most common mosquito repellents available contain N,N-diethyl-3-methylbenzamide or also called DEET that has shown strong protection from mosquitoes. However, it may exert toxic reaction under some circumstances and age groups and damage plastic, synthetic materials, thus the alternative new products need to be explored[4]–[8].

Plant essential oils in general have been recognized as important natural resources of insecticides because some are selective, biodegrade to non-toxic products and have few effects on non-target organisms and environment[9]. Many research insect repellents derived from plant extract, such as Eucalyptus citriodara (E. citriodara), Syzygium aromaticum, Cymbopogon nardus, Cymbopogon citratus (C. citratus), Curcuma longa, Zingiber officinale (Z. officinale), Azadirachta indica, Ageratum houstonianum, Pogostemon cablin, Albizzia amara, Ocimum basilicum, Zanthoxylum piperitum, Anethum graveolens, Kaempferia galangal, Aristolochia bracteata, Cardiospermum halicacabum, Clausena anisata and Vetiveria zizanioides, have been studied as possible mosquito repellents and have demonstrated good efficacy against Aedes spp., Culex spp. and Anopheles spp[4],[10]–[22].

In the present, most insecticides are non-selective and can be harmful to other organisms and environment. There is a need to develop new formulations for controlling mosquitoes in an environmentally safer way, using biodegradable and target-specific insecticides against them[23]–[24]. Therefore, the present study aimed to investigate the mosquito repellent of eight essential oils: Cananga odorata (C. odorata), Syzygium aromaticum, Z. officinale, C. citratus, Cymbopogon nardus, E. citriodara, Citrus reticulate and Ocimum basilicum against Ae. aegypti and Cx. quinquefasciatus.

2. Materials and methods

2.3. Repellent activity

Volunteers for testing are students of the Plant Production Technology Section, Faculty of Agricultural Technology, KMITL, and test times was determined by normal feeding times for each mosquito species. The Ae. aegypti testing time was between 8.00 am to 4.00 pm, while the Cx. quinquefasciatus testing time was 6.00 pm to 12.00 pm.

Before application of the repellents, the arms of three human volunteers were washed and cleaned thoroughly with distilled water. Both arms were covered with rubber sleeve with a window area of 3 cm×10 cm. On the ventral part of forearm, the left arm for treatment and the right arm for control. A total of 0.1 mL of test repellent was applied to the treatment area of left forearm of each volunteer and used the olive oil and coconut oil as a negative control and Kor Yor 15^® insect repellent lotion (containing DEET 25.63%) as a positive control. After applying the test repellent, the volunteer was instructed not to rub, touch or wet the treated forearm. The right forearm, which acted as a control was not treated and was exposed for up to 30 seconds to mosquito cage (30 cm×30 cm×30 cm) contained 250 nulliparous female mosquitoes (5 to 7 day-old). If at least two mosquitoes landed on or bit the arm, the repellency test was then continued. The test continued unit as least two bites occurred in a three-minute period. If no mosquitoes bit or landed during the three-minute period, the arm was withdrawn from the cage. The repellency test period was carried out every 30 min until fewer than 2 mosquitoes bit or land during the three-minute study period at which time the repellency test was stopped. The time between application of the repellents was recorded as the protection time.

For comparison, a percentage of mosquito biting was calculated for each test using the following formula[25]–[26]:

Where B is the total number of biting by the end of the test. The test was carried out 3 times per sample.

3. Results

The results of the protection time and the biting percentage of essential oils in olive oil against Ae. aegypti and Cx. quinquefasciatus are shown in Table 2. There were significant differences in repellency among the repellents by mosquito species (P<0.05). The clove oil repellent and citronella grass oil had the best efficiency against Ae. aegypti and Cx. quinquefasciatus, respectively in which the protection time were (76.50±3.00) and (165.00±103.92) min respectively. The essential oil of Z. officinale (ginger oil) and C. citratus (lemongrass oil) had the best efficiency against Ae. aegypti and Cx. quinquefasciatus, respectively in which the biting percentage were 0.80% and 1.00%, respectively.

Table 3 shows the repellency for the essential oils in coconut oil against Ae. aegypti and Cx. quinquefasciatus. There were significant differences in repellency among the mosquito species (P<0.05). The clove oil had the best efficiency against Ae. aegypti [(96.00±15.87) min protection time]. The lemongrass oil and citronella grass oil had the best efficiency against Cx. quinquefasciatus [(112.50±37.00 and (105.00±8.49) min protection time, respectively]. The protection time of eight herbal essential oils in coconut oil against Ae. aegypti was 54 to 96 min (0.90%-1.13% biting rate) and against Cx. quinquefasciatus was 54.00 to 112.50 min (0.90%-1.17% biting rate). The essential oil of C. odorata (ylang-ylang oil) exhibited good efficiency against Ae. aegypti in which the biting percentage was 0.93%. And essential oils of C. odorata (ylang-ylang oil) and E. citriodara (eucalyptus oil) exhibited good efficiency against Cx. quinquefasciatus in which both of the biting percentages were 0.90%.

The Thai Industrial Standards Institute (TISI) standard determines the repellency time against mosquitoes should be >2 h[27]. Some repellents provided nearly 2 h protection against Ae. aegypti and Cx. quinquefasciatus.

4. Discussion

The results of our study showed that the clove oil was effective against Ae. aegypti. The citronella grass oil and lemongrass oil were effective against Cx. quinquefasciatus. The results are similar with report by Tjahjani reported that the clove oil was the most effective against Aedes species (131 min protection time) and the citronella oil and clove oil were effective against Culex species (287 and 287 min protection time, respectively)[4]. Phasomkusulsil and Soonwera have reported that the lemongrass oil was effective against Ae. aegypti, Anopheles dirus and Cx. quinquefasciatus in which the protection time were 72, 132 and 84 min, respectively[28]. Sritabutra and Soonwera have reported that the lemongrass oil exhibited a high protection time of 98.66 and 98.00 min against Ae. aegypti and An. dirus, respectively[29]. The phytochemical constituent of clove and citronella oil are appreciable such as eugenol, citronellal, citronellol, geraniol, citral, α pinene and limonene. These constituents have properties to repellent activity of mosquitoes[30]–[32].

From the results, it showed that the herbal essential oils have a protection time less than Kor Yor 15^® insect repellent lotion (containing DEET 25.63%). Therefore, it may be improved by developing a formulation that would prolong the time of constituents of the oil on the skin. Many researchers have demonstrated improved repellency of repellent products after formulation with a base or fixative materials such as report from Songkro et al., who also reported that effect of glucam P-20, vanillin and fixolide on the mosquito repellent property of citronella oil lotions and found that the lotion containing emulwax and 5% vanillin was the most effective repellent[33]. It provided the longest protection time of 4.8 h, while the lotion containing emulwax and 2.5% glucam P-20 had the shortest protection time of 1 h. Kongkaew et al. have reported that the combination of citronella oil and vanillin provided complete repellency at least 3 h in Anopheles and Culex mosquitoes, a combination of citronella oil and vanillin product demonstrated a comparable protection time against DEET[34]. Kim et al. have reported that the combination of lemongrass oil, xanthoxylum oil and vanillin (1:3:1, v:vo:w) provided 270 min of complete protection time compared with 15% N,N-diethyl-3-methylbenzamide (247.5 min of complete protection time)[35].

The results of this study clearly demonstrated that clove oil, citronella oil and lemongrass oil had high potency to control two species of vector mosquitoes. Hence, the results may contribute to a reduction in the application of chemical in mosquito repellents, which in turn increases the opportunity for natural product for control of vector-borne disease. Further studies on identification of active compounds, toxicity and field trials are needed to recommend the active fraction of these plant extracts for development of eco-friendly for control insect vectors.

Acknowledgments

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