EJBR2021v11i3art267


ISSN 2449-8955 
European Journal  

of Biological Research 
Research Article 

 

European Journal of Biological Research 2021; 11(3): 267-273 

DOI: http://dx.doi.org/10.5281/zenodo.4670508  

Fumigant toxicity and repellency of citronella grass 

essential oil (Cymbopogon nardus (L.) Rendle)  

to German cockroaches (Blattella germanica L.) 

Robby Jannatan*, Resti Rahayu 

Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Andalas, 25163 West Sumatra, 

Indonesia 

* Corresponding author: Phone: +6285263681541, E-mail: robbyjannatan@sci.unand.ac.id 

Received: 26 January 2020; Revised submission: 01 March 2021; Accepted: 06 April 2021 

 

https://jbrodka.com/index.php/ejbr 

Copyright: © The Author(s) 2020. Licensee Joanna Bródka, Poland. This article is an open access article distributed under the 

terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/) 

ABSTRACT: Citronella grass (Cymbopogon nardus (L.) Rendle) is a tropical plant that can develop as an insect 

pest fumigant and repellent, especially for the control of the populations of German cockroaches (Blattella 

germanica L.). The research aims to investigate the fumigation toxicity and repellency of citronella grass 

essential oil against German cockroach males and nymphs. Fumigation toxicity and repellency tests are the 

protocol that uses in the present research. The field populations of cockroaches collected in Indonesia from 

several locations. The essential oil of citronella grass is not fumigant. In contrast, the citronella grass essential oil 

effectively repels the cockroach, and the repellency ranges from 65.72–100.00% at 1 hour and still effective after 

24 hours. The citronella grass essential oil can develop as a repellent product than as a fumigant to the German 

cockroach pest. 

Keywords: Citronella; German cockroach; Repellent; Fumigant; Indonesia. 

1. INTRODUCTION 

The German cockroach was the common household pest in Indonesia and has been resistant to 

synthetic insecticides [1-2]. It will be more challenging to control German cockroach populations if 

resistance to insecticides grows. Therefore, to control German cockroach populations, we need new 

insecticide alternatives, such as plant essential oils. It is possible to use essential oils as a toxicant, 

repellent, and antifeedant [3], with a non-toxic or low toxicity effect to mammalian and easily degrade in 

the environment [4-5]. One of the tropical plants that produce essential oils is citronella grass 

(Cymbopogon nardus (L.) Rendle). 

The citronella grass essential oil is toxic to German cockroach males and nymphs using the contact test 

[6]. Another strategy uses to control German cockroach populations is using the fumigation method. The 

public has widely used the fumigation technique to control insect pests. The fumigation method's advantage is 

that the insecticides quickly penetrate the insect body via the trachea and leave a little residue in the 

environment [7]. 



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European Journal of Biological Research 2021; 11(3): 267-273 

Repellent use to repel and prevent cockroaches comes to human settlements and public buildings. 

Some essential oil components were repellent to cockroaches at a laboratory scale [8-9]. The citronella grass 

essential oil has several compounds repellent to agricultural pests [10] and maybe repellent to urban pests. 

Investigation the Citronella grass essential oil as a fumigant and repellent is a good source of alternative 

insecticide to control German cockroach populations in the tropical area. Therefore, this study aims to 

determine the fumigation toxicity and the level of repellency of citronella grass essential oil against German 

cockroaches males, and nymphs. 

2. MATERIALS AND METHODS 

2.1. Provision of German cockroach populations 

The Vector Control Research Unit (VCRU), Universiti Sains Malaysia, Malaysia, provided a 

susceptible population of German cockroaches as a World Health Organization (WHO) standard population. 

The field cockroach populations used in the present research were collected in Indonesia from four locations 

(Table 1). The cockroach populations were reared in Animal Physiology Laboratory, Biology Department, 

Universitas Andalas, Indonesia. The rearing process was conducted in photoperiod 12:12 at a temperature of 

26–28oC, the cockroaches feed with cat food and water ad-libitum [11]. The cockroach sex and stage used in 

this study were male and nymphs. 

 

Table 1. The information of sources and collection years of German cockroach populations. 

Population Collection location 
Collection 

years 

Resistant level history 

Propoxur Permethrin Fipronil 

VCRU-WHO Penang 2007 Susceptible Susceptible Susceptible 

HHB-JKT* Jakarta 2007 High Extremely high High 

KRS-BDG* Bandung 2007 Low Low Low 

PLZ-PDG Padang 2014 - - - 

RMH-PYK Payakumbuh 2015 - - - 

*the information of German cockroach resistance [1]. 

 

2.2. Provision of citronella grass essential oil 

The Research Institute for Spices and Medicinal Plants K.P. Laing, Solok, West Sumatra, Indonesia, 

provided the citronella grass essential oil. The concentration of essential oil used in the fumigant toxicity test 

was 100%. The amount of essential oil used in the repellency test was 0.57 mg/cm2 and was a sub-lethal 

concentration and not killing the cockroaches during observation. The oil concentrations were determined 

from the preliminary test. The components of citronella grass oil were not determined in the present research, 

the main components volatility of the oil that have been reported were geraniol (35.7% of total volatiles), 

trans-citral (22.7%), cis-citral (14.2%), geranyl acetate (9.7%), citronellal (5.8%) and citronellol (4.6%) [12]. 

2.3. Fumigant toxicity test  

The test of fumigant toxicity of citronella grass essential oil to German cockroaches was referred from the 

previous study [9] with some modifications. This test used a plastic container (volume: 1 liter) and a cotton ball 

(diameter: 1 cm). The cotton ball injected with 100 µl essential oil using a micropipette. It is then suspended with 

yarn in the middle of the plastic container's top to prevent the cockroaches from being in direct contact with 



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European Journal of Biological Research 2021; 11(3): 267-273 

essential oil. The plastic container's top inside wall was smeared with Vaseline and petroleum oil solution to prevent 

cockroaches escape during observation. The top of the container was covered with gauze. About ten individuals 

from each German cockroach’s population were placed into the plastic container. The mortality of the cockroaches 

was observed every 24 hours until 96 hours after treatments. Each treatment was replicated three times. 

2.4. Repellency test 

The repellency test of citronella grass essential oil to German cockroaches was referred from the previous 

study [9] with some modifications. The filter paper (diameter: 15 cm) was divided into two parts. Part 1 filled with 

essential oil as much as 0.57 mg/cm2, and part 2 was only filled with ethanol as much as 0.57 mg/cm2. The 

concentrations used were obtained from the preliminary test and were a sub-lethal concentration (did not paralyze 

or killed the cockroaches). Therefore, the movement of cockroaches can observe during the treatment. The 

filter paper dried at room temperature for 24 hours until the ethanol evaporated. Both of the papers were 

placed into a petri dish (same diameter as filter paper). The inside wall of the petri dish was smeared with 

Vaseline and petroleum oil solution to prevent the cockroach escape during observation. About ten 

individuals from each population of German cockroaches were placed in the center of the petri dish. 

Distribution and movement of the cockroaches were observed every one hour until 24 hours after 

treatment. Each treatment was replicated three times. 

2.5. Data analysis 

Each cockroach population's lethal time was analyzed using Probit Regression Analysis in Polo-PC 

computer software [13] to determine the lethal time 50% (LT50) of cockroaches. The susceptibility status of 

each cockroach’s population was determined by calculating the ratio resistance (RR50) by comparing the 

LT50 between the field population and the standard strain. The ratio resistance was grouped into four 

categories (RR50 < 2 indicates susceptible, RR50 ranged from 2–5 indicates the presence of low resistance, 

RR50 ranged from 5–10 indicates a moderate level of resistance, and RR50 > 10 demonstrates high 

resistance) [14]. The effectiveness of citronella grass essential oil can be determined if more than 90% of the 

cockroaches died in less than six hours of observation [15]. To determine the repellency value of citronella 

grass essential oil was used the formula: Repellency (%) = 100 - (T × 100/N) [16], T = number of individuals 

distributed in the treatment paper filter, N = number of individuals distributed in the ethanol paper. The 

repellency value (RV) of citronella grass essential oil was determined from criteria: not repellent: RV < 0.1%, 

very low repellent: RV 0.1–20%, low repellent: RV 20.1–40%, repellent: RV 40.1–60%, high repellent:  

RV 60.1–80%, very high repellent: RV 80.1–100% [11]. The lethal time 90% (LT90) and repellency effect of 

citronella grass essential oil between standard population and field populations of German cockroaches were 

determined using Analysis of Variance (ANOVA) and Duncan Multiple Range Test 5%. 

3. RESULTS 

3.1. Fumigation toxicity test 

The lethal time 90% (LT90) of male German cockroaches in standard population was occurred at 11.43 

hours and in field population at 65.00 hours until 107.03 hours. The LT90 of nymph was slower than male in 

the standard population. However, the mortality of nymph field populations faster than males. In general, the 

mortality of cockroaches did not occur at 6 hours in each experimental population. The LT90 of male and 

nymph of German cockroaches were significantly different between standard and field populations (Table 2). 



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Table 2. The Lethal time 90% (LT90) of male, and nymph of German cockroach, and the effectiveness category of 

citronella grass essential oil used fumigant toxicity test. 

Stages Population LT90 (Hours) Effectiveness category 

Male 

VCRU-WHO 11.43 Ineffective 

HHB-JKT 72.95* Ineffective 

PLZ-PDG 74.72* Ineffective 

RMH-PYK 107.03* Ineffective 

KRS-BDG 65.00* Ineffective 

Nymph 

VCRU-WHO 37.73 Ineffective 

HHB-JKT 22.50ns Ineffective 

PLZ-PDG 48.70* Ineffective 

RMH-PYK 53.74* Ineffective 

KRS-BDG 53.74* Ineffective 

The LT90 values were followed by (*) sign that significantly difference between standard population (VCRU-WHO) and field population 

used Duncan New Multiple Range Test 5%. 

 

The German cockroach's susceptibility level to citronella grass essential oil was moderate for males, 

with RR50 varying from 6.81–9.10 folds. In comparison, in field populations with RR50, the nymph's 

susceptibility level was still susceptible from 1.45–1.46 folds (Table 3). 

 

Table 3. The susceptibility status of citronella grass essential oil against German cockroaches male and nymph in 

fumigation toxicity test. 

Stages Population LT50 (Hours) RR50 (Folds) Susceptibility status 

Male 

VCRU-WHO 6.77 1.00 RR50 <2 Susceptible 

HHB-JKT 50.14 7.41 5<RR50<10 Moderate resistant 

PLZ-PDG 55.35 8.18 5<RR50<10 Moderate resistant 

RMH-PYK 61.58 9.10 5<RR50<10 Moderate resistant 

KRS-BDG 46.09 6.81 5<RR50<10 Moderate resistant 

Nymph 

VCRU-WHO 17.13 1.00 RR50<2 Susceptible 

HHB-JKT 12.45 0.73 RR50<2 Susceptible 

PLZ-PDG 24.97 1.46 RR50<2 Susceptible 

RMH-PYK 24.82 1.45 RR50<2 Susceptible 

KRS-BDG 24.82 1.45 RR50<2 Susceptible 

Note: LT50 (Lethal Time 50%) = the time of 50% cockroaches mortality; RR50 (Resistance Ratio 50) = LT50 field population/LT50 

standard population. 

 

3.2. Repellency test 

The repellency of citronella grass essential oil differed between German cockroaches stages and sexes at 

one-hour observation. The result was high in females (87.96–100.00%) and followed by nymphs (82.01–96.30%) 

and males (65.72–83.33%). After 24 hours, this repellency test was decreased in males (57.14–65%), in females 

of the Bandung population, KRS-BDG (82.01%), and nymphs (57.14–83.33%). 

 

 



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Table 4. The repellency (%) of citronella grass essential oil to male, female and nymph of German cockroaches at 24 

hours of observation. 

Strains Male (%) Female (%) Nymph (%) 

VCRU-WHO 69.05±10.31 100.00±0.00 93.00±14.00 

HHB-JKT 57.14±0.00 ns 100.00±0.00 ns 83.33±14.43 ns 

PLZ-PDG 84.26±8.01 ns 91.67±14.43 ns 73.68±15.91 ns 

RMH-PYK 79.63±8.02 ns 100.00±0.00 ns 73.68±15.91 ns 

KRS-BDG 59.79±27.87 ns 82.01±22.24 ns 57.14±0.00 ns 

Note: The repellency values followed by signs (ns) was  not significantly difference between standard and field populations in male, 

female and nymph of German cockroaches used ANOVA test 5%. 

 

4. DISCUSSION 

The citronella grass essential oil is not effective in killing the German cockroach population using the 

fumigation toxicity test. We assume that German cockroaches field populations have the same physiological 

responses to citronella grass essential oil. Citronella grass essential oil as a fumigant cannot poisonous to the 

nervous system of cockroaches. The compound of citronella grass essential oil is dominated by citronella at 

35.97% [10]. Some studies also reported the dominated compound of citronella grass oil varied among the 

cultivated varieties of citronella grass plant. Citronella grass essential oil from Sri Lanka and Indonesia dominated 

by 40.5–60.7% of citronellal, whereas the oil from India contained the small amounts of citronellal (17.2–33.2%) 

[17]. Previous research reported that the citronellal is tested to a cockroach in the fumigant method and did not 

cause mortality [18]. 

The essential oil from the citronella grass is volatile and quickly evaporated into the air. The higher volatile 

compound of citronella oil is geraniol (35.7%) [12], geraniol has low toxicity level to German cockroach [7]. Via 

the tracheal system of cockroaches, the essential oil will penetrate. In a cockroach's body tissue, the chemical 

compounds of essential oil are inserted into spiracles and delivered through the diffusion process. The tracheal 

cockroaches system is derived from the integument as the tubular form and served to exchange gases [19]. 

The octopamine system usually targets the essential oils in insects. The octopamine was a nervous system 

neurotransmitter [4]. We presume that in German cockroaches, the volume of essential oil that reaches the tracheal 

system might not be capable of paralyzing the cockroach in the octopamine system. 

The evaporation point possibly affected the citronella grass essential oil's ineffectiveness against 

cockroaches used the fumigation test. This point affects the volatility of the essential oil compounds entered 

through the trachea during the respiration process. The essential oil compound is more volatile and toxic at the 

high evaporation point than the low point. Insects bodyweight does not influence the toxicity of essential oil in a 

fumigation test, so the differences in body weight between males and nymphs will not affect the toxicity of 

essential oil compounds in the fumigation test [7]. In the present study, we also found that the citronella grass 

essential oil has a low toxicity level and not fumigant to German cockroaches. 

The citronella grass essential oil has a low susceptibility level. It most likely takes a long time for 

cockroaches to develop resistance to citronella grass essential oil because these essential oil compounds are more 

complex than synthetic insecticides. Several chemical compounds containing citronella, nerol, citronellol, 

geranium acetate, elemol, limonene, and citronellil acetate in the composition of citronella grass essential oil [10]. 



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A variety of essential oil chemical compounds can develop physiological resistance more slowly than synthetic 

insecticides commonly resistant to insect pests [3]. 

In Indonesia, German cockroaches are resistant to synthetic insecticides, such as carbamate, pyrethroid, and 

phenylpyrazole. The resistance of German cockroaches to permethrin is extremely high [1], which is very high 

compared to the susceptibility of citronella grass essential oil using the contact [7] and the fumigation method. 

In the repellency test, the fast and erratic movements are German cockroach responses before a one-hour 

observation in this study. When they find the area without essential oil, cockroach's movements become slower, 

so most of them will stay there. The interaction of cockroaches with an insecticide is shown to be irritable and 

marked by rapid motion patterns. It is known as an insect repellent in essential oils when the insects made 

natural movements to keep away from the surface containing insecticide [8]. 

In all-male, female, and nymph of German cockroaches, the repellency of citronella grass essential oil 

generally still effective within 24 hours. Meanwhile, the repellency decreased by the boiling point of the essential 

oil of citronella grass. The essential oil of citronella grass has dominated by citronella [3, 10]. Citronella has a 

121°C boiling point, but apart with a low boiling point can evaporate faster [7]. 
After 24 hours, the repellency of citronella grass essential oil was still higher than 50 percent. The essential oil 

of citronella grass also has a high repellency against Aedes aegypti [20], and Helicoverpa armigera [10]. The 

essential oil of citronella grass can be developed as a repellent for cockroaches. The essential oil product would 

prevent cockroaches in human settlements or public places such as hospitals and restaurants. As a cockroach 

repellent, the citronella grass essential oil was more effective in present research than killing them as a fumigant [21]. 

5. CONCLUSIONS 

Citronella grass essential oil as a fumigant cannot poison the nervous system of cockroaches and ineffective 

in controlling the German cockroach population. Erratic movements and rapid motion patterns show the interaction 

of cockroaches with citronella grass essential oil. The German cockroach makes natural movements to keep away 

from the surface containing citronella grass essential oil. Citronella grass essential oil was more effective to the 

German cockroach population in present research as a repellent than killing them as a fumigant. 

 

Authors' Contributions: RJ contributed to design the research, laboratory works, data analysis, and preparing the 

manuscript. RR contributed to design the research, data interpretation, preparing and editing the manuscript. All author 

approved the final version of the manuscript. 

Conflict of Interest: The author has no conflict of interest to declare. 

Funding: The Directorate General of Higher Education, Ministry of Education and Culture of Indonesia funded this 

research with grant registered number No.030/SP2H/PL/DIT.LITABMAS/II/2015. 

Acknowledgment: We wish to thank the Director and Staff of The Research Institute for Spices and Medicinal Plants KP 

Laing, Solok, Indonesia for the provisioned stocks of citronella grass essential oil and Mr. Rijal Satria (Padang State 

University, Indonesia) for his valuable suggestions. 

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