Pesticidal Potential of Essential Oils Against Callosobruchus maculatus Fab. (Coleoptera: Bruchidae) under Laboratory Conditions

Zakia Panhwar1, Arfan Ahmed Gilal1*, Lubna Bashir Rajput1, Jamal-U-Ddin Hajano2, Shafique Ahmed Memon3, Naimatullah Koondhar4, Muhammad Ibrahim Kubar1

1Department of Entomology, Faculty of Crop Protection, Sindh Agriculture University, Tando Jam.

2Department of Plant Pathology, Faculty of Crop Protection, Sindh Agriculture University, Tando Jam.

3Department of Entomology, Faculty of Agriculture, Lasbela University of Agriculture Water and Marine Sciences, Pakistan.

4Department of Plant Pathology, Faculty of Agriculture, Lasbela University of Agriculture Water and Marine Sciences, Pakistan.

Abstract | Pulse beetle, Callosobruchus maculatus Fab. is a serious, multi-voltine and most destructive cosmopolitan pest in Asian and African countries on various pulses. Considering the target specificity of botanicals and less hazardous than synthetic insecticides, essential oils of orange (Citrus sinensis L.), lemongrass (Cymbopogon citratus Stapf.), eucalyptus (Eucalyptus globulus Labill.) and peppermint (Mentha piperita L.) were evaluated against C. maculatus adults. Each oil was applied at 0.1, 0.5, and 1.0ml doses on the filter paper. A long glass cylinder divided into three (A, B, and C) sections, supplied with 20g cowpea seeds at ends was used in the study. Ten freshly emerged male and female C. maculatus adults were released separately in the middle of B with the help of aspirator as treated (with oil) and untreated filter were placed at A and C sections, respectively. The number of adults were counted at A and C after 24 and 48 h to calculate the repellent efficacy and mortality percentage. All the essential oils showed pesticidal potential with orange and lemongrass found to be more effective in causing mortality of both male and female C. maculatus, whereas the peppermint and eucalyptus were found to be more repellent. The pesticidal potential of all oils increased with increasing doses and exposure timings. Maximum mortality and repellency of females after 48 h was recorded in orange oil (100.00±0.00%) and peppermint oil (90.00±0.00%), respectively, both applied at rate of 1.0ml dose, whereas maximum mortality and repellency of males after 48 h was also recorded in orange oil (96.67±3.33%) and peppermint (90.00±0.00%), respectively, applied at rate of 1.0ml dose. After 48 h, the lowest (0.008) and highest (0.095) LD50 values against C. maculatus female were recorded for orange and eucalyptus essential oils, respectively. The lowest (0.030 ml) and highest (0.057) LD50 values against C. maculatus males were also recorded for orange and eucalyptus essential oils, respectively. Thus, all the essential oils were found equally effective against both male and female C. maculatus. Therefore, it is suggested that the essential oils of orange or peppermint may be applied in the warehouses against C. maculatus to restrict their damage.

Novelty Statement | The essential oils of orange, lemongrass, eucalyptus, and peppermint were evaluated at 0.1, 0.5, and 1.0ml doses against adult male and female C. maculatus. All the essential oils were found effective to cause mortality and repellence in both the sexes with maximum mortality and repellency recorded in orange and peppermint oils, respectively. Pesticidal potential of all oils increased with increasing doses and exposure time against both the sexes of C. maculatus.

Article History

Received: February 07, 2023

Revised: November 08, 2023

Accepted: November 30, 2023

Published: December, 09, 2023

Authors’ Contributions

ZP conducted the experiments and write initial draft. AAG, LBR and JH conceived the idea and design the experiment. NK help in conduct of experiments. MIK and SAM help analyse and presentation of data. AAG help in designing the study and finalized the manuscript.

Keywords

Bruchid beetle, Callosobruchus, Mortality, Repellence, Stored grain

Copyright 2023 by the authors. Licensee ResearchersLinks Ltd, England, UK. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Corresponding author: Arfan Ahmed Gilal

aagilal@sau.edu.pk

To cite this article: Panhwar, Z., Gilal, A.A., Rajput, L.B., Hajano, J.D., Memon, S.A., Koondhar, N. and Kubar, M.I., 2023. Pesticidal potential of essential oils against Callosobruchus maculatus Fab. (Coleoptera: Bruchidae) under laboratory conditions. Punjab Univ. J. Zool., 38(2): 201-210. https://dx.doi.org/10.17582/journal.pujz/2023.38.2.201.210

Introduction

The pulse beetle, Callosobruchus maculatus Fab. (Coleoptera: Bruchidae) is commonly known as cowpea weevil. It is a serious, multi-voltine and most destructive cosmopolitan pest of pulses like cowpea, lentils, black gram, green gram, and chickpea in Asian and African countries (Boeke et al., 2004; Muntaha et al., 2017). The damage of C. maculatus starts from the standing crop in the field and the same will carry with the produce even during the storage in godowns (Ahuchaogu and Ojiako, 2020; Seth et al., 2017). During storage, C. maculatus can cause 100% damage of pulse seeds (Gbaye et al., 2011), whereas its average losses can range between 20-30 and 5- 10% in tropical and temperate countries, respectively (Kiradoo and Srivastava, 2010). Muntaha et al. (2017) reported that C. maculatus causes up to 10% damage to stored chickpea and up to 90% loss to stored gram. Pulse beetle infestation also invites secondary organisms such as rot organisms mostly fungi which leads to mycotoxin contamination, which create further degradation of legume grains. Seeds infested by pulse beetle thus become unhealthy for the consumption with poor germination percentage due to quantity and quality losses and fungal growth (Bhalla et al., 2008). Various management tools such as physical, biological, botanical, and chemical methods are utilized to minimize bruchids infestation, hence reduce grain losses (Rahman and Sabiha, 2018). However, to overcome the bruchid’s infestation and protect stored legumes, insecticides are the most common method. Despite the direct and rapid control of bruchids by synthetic pesticides, many reasons i.e., pest resurgence, resistance, persistence, effects on non-target organisms, high cost, residual environmental impacts make insecticides an unsuitable option (Elhag, 2000). Additionally, stored legumes should not be treated with insecticides as detrimental residues of toxic chemicals may cause serious effects on human health during consumption. Therefore, many other conventional and plant-based control methods are considered more safer and secure than insecticides (Weaver and Subramanyam, 2000). Natural insecticides that are extracted from plants contain several bio-active compounds and are generally known as bio-insecticides (Bai et al., 2019; Buxton et al., 2020; Peeyush et al., 2011). Plants produced huge variety of chemicals i.e., phenolics, steroids, terpenoids and alkaloids that are used by plants for their protection and also possessed important insecticidal and medicinal properties (Hamada et al., 2018; Hamad et al., 2019; Hussein et al., 2017). Various essential oils have repellent compounds that repel targeted insects by affecting their touch, taste, and smell senses. Generally, repellent effect of essential oils prevent pest from achieving their targeted site (Choochote et al., 2007; Haq et al., 2021; Nerio et al., 2010). Therefore, present study was conducted to evaluate the efficacy of some botanical oils i.e., lemongrass oil (Cymbopogon citratus), eucalyptus oil (Eucalyptus globulus), peppermint oil (Mentha piperita) and orange oil (Citrus sinensis) against C. maculatus.

Materials and Methods

Study location

The experiments were carried out at Stored Grain Research Laboratory, Department of Entomology, Sindh Agriculture University, Tandojam during 2022.

Collection and rearing of Callosobruchus maculatus

Callosobruchus maculatus were obtained from the culture that was already managed at the laboratory as further rearing was done in cowpea seeds. The F1 generation adults obtained from the culture were then utilized for the experiment to determine the repellence and mortality of various essential oils against them.

Essential oils

Four essential oils were purchased from Chiltan pure international, an ISO certified company and used in the study mentioned below:

1. Lemongrass (Cymbopogon citratus Stapf.)
2. Eucalyptus (Eucalyptus globulus Labill.)
3. Peppermint (Mentha piperita L.)
4. Orange (Citrus sinensis L.)

 

Experimental set-up, data collection and analysis

Following the study of Lee et al. (2020) and Park et al. (2018), a long glass cylinder (500 ml, 32 cm height, 2.75 cm diameter) trap was manufactured with slight modifications (Figure 1). The cylinder connected with feeding dishes divided into three sections (A, B, C), where the one end was covered with muslin cloth for ventilation and prevention of C. maculatus from escaping during the entire duration of experiment. Method of Jo et al. (2013) and Khaskheli et al. (2021) was used to evaluate repellency of the of essential oils. In this experiment, three doses of essential oils i.e., 0.1, 0.5, and 1.0ml were used against both adult males and females of C. maculatus. The respective dose of the individual oil was applied on a filter paper, thereafter, it was then allowed to air-dry for 20 minutes. Afterwards, the treated filter paper with respective dose of a particular oil was placed between section A and B of the glass cylinder, whereas control filter paper without any oil was kept between B and C (Figure 1). Ten freshly emerged F1 adults (males or females) were released separately in the middle of section B with the help of an aspirator. The face of glass cylinder was closed with a fine muslin cloth at the end of section C to ensure the ventilation inside it. The entire experiment was conducted at the temperature of 30±2 °C with 55±5% R.H. The completely randomized design was used to setup the experiment where three replications were managed for each essential oil treatment. A separate glass cylinder was used for each treatment, whereas cylinder was thoroughly cleaned and wiped using tissue paper after performing each replication.

The data were collected by counting the number of insects at sections C and A after 24 and 48 h of the application of essential oils.

The percentage repellency of the essential oils was calculated using the equation given below:

Where, Nc is the number of insects in C section, and Na is the number of insects in section A.

The percentage of mortality was calculated by using the following equation:

Analysis of variance was used to analyse the obtained data on mortality and repellency of essential oils for C. maculatus males and females, whereas means with significant differences were separated using the Least Square Difference (LSD) at 5% probability. All the analysis were performed using STATISTIX 8.1 computer software. Moreover, SPSS version 21, IBM Corp. was used to perform Probit analysis for the calculation of LD50 values for various essential oils for their insecticidal potential against C. maculatus.

Results and Discussion

Insecticidal potential of essential oils against Callosobruchus maculatus females

Figure 2 shows the results regarding the percentage mortality of C. maculatus females after 24 h application of various essential oils applied at various doses. A highly significant difference was recorded among various essential oils applied at various doses (F= 9.17, P < 0.001) to elicit the C. maculatus female mortality. According to the results, significantly the highest mortality (86.67±3.33%) after 24 h of application was recorded in orange oil applied at 1.0ml dose, followed by 83.33±3.33 and 10.00±0.00% mortality recorded in lemongrass and peppermint essential oils, respectively, both applied at 1.0ml dose. Moreover, in eucalyptus essential oil treatment, the highest mortality (20.00±5.77%) of C. maculatus females was recorded at 0.5ml dose, whereas the lowest mortality (6.67±3.33%) was recorded in 0.1 ml peppermint oil.

 

 

The mortality percentage of C. maculatus showed an increasing trend due to the application of various doses of essential oils after 48 h, exhibiting highly significant (F= 12.98, P < 0.001) difference among various treatments (Figure 3). According to the results, significantly the highest (100.00±0.00%) mortality percentage of C. maculatus after 48 h at 1.0ml dose was recorded in orange oil, followed by lemongrass (96.67±3.33%), whereas the lowest mortality was recorded in peppermint (10.00±5.77%) at 0.1ml dose. Moreover, the maximum mortality of female C. maculatus in orange oil (86.67±3.33%) and lemongrass (73.33±3.33%) was recorded at 0.5ml dose.

Figure 4 shows the results regarding the repellency percentage of C. maculatus females due to the application of different doses i.e., 0.1, 0.5 and 1.0ml after 24 h. Different essential oils showed significant difference (F = 16.76, P =< 0.001) in their potential to repel C. maculatus females. The highest repellency percentage was recorded in peppermint (83.33±3.33%) and eucalyptus (63.33±3.33%), whereas the maximum repellency of the females in orange oil (26.67±6.67%) was recorded at 0.1ml dose and lemongrass oil (40.00±5.77%) at 0.5ml dose. Moreover, orange (13.33±3.33%) and lemongrass (16.67±3.33%) oils exhibited the lowest repellency when applied at 1.0ml dose.

 

 

An increase in the repellency of C. maculatus was recorded at 48 h of the application of various doses of essential oils, however, there was a significant difference (F= 26.19, P < 0.001) among various oils applied at various doses (Figure 5). The highest repellency (90.00±0.00%) was recorded in peppermint and eucalyptus (80.00±0.00%) at 1.0ml dose, whereas the maximum repellency in lemongrass and orange oils was recorded as 30.00±00 and 13.33±3.33%, respectively, all applied at 0.1ml dose. Moreover, the lowest repellency was recorded in lemongrass (3.33±3.33) due to rise in mortality percentage at 1.0ml dose.

Overall repellency and mortality of C. maculatus females due to the application of various doses of different essential oils are given in Figure 6. The results confirmed a highly significant difference among various essential oils regarding their potential to cause mortality (F= 394.77, P < 0.001) and repellency (F= 220.21, P < 0.001) of C. maculatus females. Significantly, the highest overall mortality of female C. maculatus (80.56±3.57%) was recorded in orange oil, whereas the mortality percentage recorded in lemongrass (61.67±6.12%), eucalyptus (21.11±1.59%), and peppermint (10.56±1.51%) was significantly different from each other. Moreover, significantly the highest (66.11±3.63%) repellency of C. maculatus females was recorded in peppermint oil, followed by 48.89±5.11 and 25.00±3.16% repellency observed in eucalyptus and lemongrass oils, respectively. Moreover, the lowest (14.44±2.46%) repellency percentage of C. maculatus females was recorded in orange oil treatments.

 

Insecticidal potential of essential oils against Callosobruchus maculatus males

Figure 7 shows the results regarding the percentage mortality of C. maculatus males after 24 h application of various essential oils applied at various doses. A highly significant difference was recorded among various essential oils applied at various doses (F= 7.33, P= 0.0002) to elicit the C. maculatus male mortality. According to the results, significantly the highest mortality (86.67±3.33%) after 24 h of application was recorded in orange oil applied at 0.5 and 1.0ml doses. Moreover, the maximum mortality in lemongrass, and peppermint oils was recorded as 43.33±3.33% and 20.00±0.00%, respectively, both applied at 1.0ml dose, whereas in eucalyptus, the highest mortality (20.00±0.00%) was recorded at 0.5 and 1.0ml doses. Overall, the lowest mortality i.e., 6.67±3.33% was recorded in peppermint oil applied at 0.1ml dose.

 

The mortality percentage of C. maculatus showed an increasing trend due to the application of various doses of essential oils after 48 h, with highly significant (F= 16.19, P < 0.001) difference among various treatments (Figure 8). According to the results, significantly the highest (96.67±3.33%) mortality percentage of C. maculatus males after 48 h was recorded in orange oil applied at 1.0ml dose, followed by lemongrass oil (86.67±3.33%) when applied at 0.5 and 1.0ml doses. Moreover, the maximum mortality of C. maculatus males in eucalyptus oil (23.33±3.33%) was recorded at 0.1ml dose. Overall, the lowest mortality was recorded in peppermint (10.00±0.00%) at 0.1ml dose.

 

 

Figure 9 shows the results regarding the repellency percentage of C. maculatus males due to the application of 0.1, 0.5, and 1.0ml doses of essential oils after 24 h. Different essential oils showed significant difference (F= 4.37, P= 0.0041) in their potential to repel C. maculatus males as the highest (76.67±3.33%) repellency percentage was recorded in peppermint and eucalyptus at 1.0ml dose. Moreover, the maximum repellency of the males in orange oil (13.33±3.33%) and lemongrass (16.67±3.33%) when recorded at 0.5 and 1.0ml doses. Overall, the orange oil exhibited the lowest repellency (6.67±3.33%) when applied at 0.1ml dose and lemongrass (16.67±3.33%) when applied at 0.5 and 1.0ml doses.

An increase in the repellency of C. maculatus was recorded at 48 h of the application of various doses of essential oils with a significant difference among various oils (F= 21.07, P < 0.001) applied at various doses (Figure 10). The highest repellency (90.00±0.00%) of C. maculatus males was recorded in peppermint and eucalyptus oil (80.00±0.00%), applied at 1.0ml dose. The maximum mortality in lemongrass and orange oils was recorded as 36.67±3.33 and 6.67±3.33%, respectively, both applied at 0.1ml dose. Overall, the lowest repellency was recorded in orange oil (3.33±3.33%) at 1.0ml and lemongrass (10.00±0.00%) at 0.5ml dose due to rise in mortality percentage in the respective treatment oils.

 

 

Overall repellency and mortality of C. maculatus males due to the application of various doses of different essential oils are given in Figure 11. The results confirmed a highly significant difference among various essential oils regarding their potential to cause mortality (F= 563.90, P < 0.001) and repellency (F= 418.71, P < 0.001) of C. maculatus males. Significantly, the highest overall mortality of C. maculatus (80.00±4.20%) was recorded in orange oil, whereas the mortality percentage recorded in lemongrass (70.00±4.78%), eucalyptus (18.89±1.11%), and peppermint (15.56±1.66%) was significantly different from each other. Moreover, significantly the highest (70.00±3.02%) mortality of C. maculatus males was recorded in peppermint oil, followed by eucalyptus (66.11±3.04%) and lemongrass (20.00±2.43%) essential oils. Overall, the lowest repellency (9.44±2.06%) of C. maculatus males was recorded in orange essential oil.

Overall effect of essential oils on mortality of C. maculatus male and female

The comparative analysis of various essential oils indicated all the oils were found equally effective (F= 1.12, P =0.2918) to cause mortality of both male and female C. maculatus. However, orange oil and eucalyptus were found relatively more toxic against females, whereas lemongrass and peppermint were more lethal against males (Figure 12).

 

Overall effect of essential oils on repellency of C. maculatus male and female

The comparative analysis of various essential oils indicated that all the oils were found equally effective (F= 1.47, P =0.2268) to cause repellency of both male and female C. maculatus. However, peppermint oil and eucalyptus showed relatively more repellent potential against males, whereas lemongrass and orange were more effective against females (Figure 13).

Lethal dose (LD50) of essential oils against Callosobruchus maculatus females and males

Table 1 describes the results regarding the LD50 values calculated for various essential oils used against female of C. maculatus. It was evident from the results that LD50 values of all the essential oils were time dependent, instead of dose dependent as LD50 values decrease at the data observation of 48 h from 24 h. Among all the essential oils, the lowest LD50 values after 24 h were recorded in orange [0.012 ml (0.000-0.046)], followed by lemongrass [0.070 ml (0.002-0.147)] and peppermint [0.108 ml (0.002-0.238)], whereas the eucalyptus showed the highest LD50 values of 0.198 ml (0.071-0.337) against C. maculatus females. After 48 h, the lowest [0.008 (0.001-0.019) and highest [0.095 ml (0.054-0.136) LD50 values were recorded for orange and eucalyptus essential oils, respectively. Moreover, LD50 values recorded for lemongrass and peppermint treatment were 0.068 ml (0.029-0.097) and 0.033 ml (0.000-0.133), respectively.

 

Table 1: LD50 values of various essential oils against Callosobruchus maculatus females.

Essential oil	H	LD50 (ml)	FL 95%	Slope ± SE	χ2	Probability
Eucalyptus	24-h	0.198	0.071-0.337	1.010±0.105	35.684	< 0.001
	48-h	0.095	0.054-0.136	1.885±0.139	27.762	< 0.001
Lemon grass	24-h	0.070	0.002-0.147	1.629±0.138	94.411	< 0.001
	48-h	0.068	0.029-0.097	2.536±0.254	33.723	< 0.001
Peppermint	24-h	0.108	0.002-0.238	1.012±0.108	66.581	< 0.001
	48-h	0.033	0.000-0.113	1.128±0.133	89.602	< 0.001
Orange	24-h	0.012	0.000-0.046	0.996±0.152	25.692	0.001
	48-h	0.008	0.001-0.019	1.142±0.206	13.719	0.056

 

Table 2: LD50 values of various essential oils against Callosobruchus maculatus males.

Essential oil	H	LD50 (ml)	FL 95%	Slope ± SE	χ2	Probability
Eucalyptus	24-h	0.139	0.089-0.187	0.767±0.103	11.453	0.120
	48-h	0.057	0.024-0.093	0.669±0.105	6.175	0.520
Lemon grass	24-h	0.051	0.019-0.083	1.721±0.164	23.351	0.001
	48-h	0.032	0.002-0.067	1.674±0.201	33.095	< 0.001
Peppermint	24-h	0.069	0.023-0.117	1.343±0.123	26.913	< 0.001
	48-h	0.040	0.005-0.076	1.816±0.200	35.515	< 0.001
Orange	24-h	0.094	0.064-0.121	2.999±0.258	30.619	< 0.001

 

Table 2 describes the results regarding the LD50 values calculated for various essential oils used against male of C. maculatus. It was evident from the results that LD50 values of all the essential oils were time dependent, instead of dose dependent as LD50 values decrease at the data observation of 48 h from 24 h. Among all the essential oils, the lowest LD50 values after 24 h was recorded in lemongrass oil [0.051 ml (0.019-0.083)], followed by peppermint [0.069 ml (0.023-0.117)] and orange [0.094 ml (0.064-0.121)], whereas the eucalyptus showed the highest LD50 values of 0.139 ml (0.089-0.187) against C. maculatus After 48 h, the lowest [0.030 ml (0.001-0.064) and highest [0.057 ml (0.024-0.093) LD50 values were recorded for orange and eucalyptus essential oils, respectively. Moreover, LD50 values recorded for lemongrass and peppermint treatment were 0.032 ml (0.002-0.067) and 0.040 ml (0.005-0.076), respectively.

The current study was undertaken on the insecticidal potential of four essential oils i.e., orange oil, lemongrass, eucalyptus, and peppermint at three different doses i.e., 0.1, 0.5, and 1.0ml to determine their mortality and repellent efficacy against adult male and female C. maculatus. The obtained results indicated that essential oils of orange and lemongrass were found more effective to cause mortality of both male and female C. maculatus, whereas the peppermint and eucalyptus were found to be repellent towards both adults. Moreover, the mortality or repellence of C. maculatus adults increased with increasing dose of essential oils and their exposure timings. Among essential oils, orange oil showed highest mortality in females and males followed by lemongrass, whereas the highest repellence of males and females was recorded in peppermint oil, followed by eucalyptus. Moreover, among all tested doses of various essential oils, 1.0ml was proved to more effective as compared to 0.1 and 0.5ml, as the highest mortality or repellence of C. maculatus males and females was recorded after 48 h of the exposure.

Many studies have been reported to determine the insecticidal activity of essential oils against C. maculatus. De Souza et al. (2019) investigated the essential oil of lemongrass (C. citratus) against C. maculatus. The changes in the behaviour and high mortality were observed in male and female C. maculatus. Behavioural changes has led to reduction in the acetylcholinesterase activities in both sexes, β-esterase in females and decrease triacylglycerol in mated and unmated females. Kéita et al. (2001) also found males more susceptible than females when treated with essential oils of Ocimum basilicum and O. gratissimum. Similarly, Ojebode et al. (2016) investigated the potency of the essential oils i.e., A. indica, C. sinensis, and C. citratus against C. maculatus and other stored product pests. The highest mortality was observed in C. sinensis on first day of application followed by A. indica and C. citratus. Cymbopogon citratus also caused hundred percent mortality of adult within one h of exposure, whereas C. sinensis showed 100 percent mortality after three h of exposure. According to the study of Jayakumar et al. (2017) five essential oils i.e., nutmeg, eucalyptus, camphor, rosemary, and wintergreen showed 100 percent mortality against C. maculatus. The highest mortality of C. maculatus after 96 h of exposure was observed in citrodora (96 percent) and lemongrass oil (92 percent) at 5% concentration (Raja and William, 2008). Omotoso et al. (2020) found that essential oil of lemongrass has strong mortality and repellent effect against C. maculatus as reduction in egg laying, 80 percent mortality and 66 percent repellency was recorded on treated cowpea within 24 h of exposure. However, the beetle mortality and repellency were time and concentration dependent. Similarly, essential oil of lemongrass was capable to cause 100 percent mortality after 1-h of exposure, whereas orange oil (Citrus sinensis) exhibited 100 percent mortality after 3rd h of exposure against C. maculatus (Ojebode et al., 2016). Saeidi (2015) evaluated the efficacy of plant extract of Eucalyptus camaldulensis and Eucalyptus globulus and found that E. globulus was more effective against C. maculatus after 72-h of exposure. Ekeh et al. (2013) study reported that application of Citrus sinensis oil suppress C. maculatus population for moderate time of storage. While evaluating the insecticidal potential of peppermint oil the obtained results reveal that the most susceptible stage of C. maculatus was egg. Moreover, the application of peppermint oil has greater effect on male as compared to female and can significantly decrease the fecundity, survivorship, and mating frequency of next generation (El-Nagar et al., 2012).

Pandey et al. (2014) while evaluating thirty-five essential oils of medicinal and aromatic plants against C. maculatus and C. chinensis found that Adhatoda vasica and Chenopodium ambrosioides L. showed 100% repellency for both insects, whereas Chenopodium sp. oil also caused 100% death of all tested organisms of the two species. Results also confirmed that application of 0.29 and 0.58 μl/ml of Chenopodium oil also showed a promising feeding deterrence with reduced seed damage for the two species. According to Satongrod et al. (2021) essential oil from piperaceae plant family also showed repellent effect against many stored grain pests. Similarly, when Oliveira et al. (2017) treat the Vigna unguiculata seeds with Piper hispidinervum (Piperaceae), they found that it repels insects away from the seeds and resulted in significantly less seed damage. Manju et al. (2019) also evaluated the repellent efficacy of twelve botanicals against C. maculatus and found that P. nigrum and A. indica extracts were more effective to control its population than others in green gram storage. Similarly, oils of castor, neem, and eucalyptus on Cajanus cajan seeds showed longer emergence period as well as no adult emergence, while the application of sunflower take longer time than control (Dinesh and Raj, 2012). Idoko and Ileke (2020) found that essential oil from Aframomum melegueta as the most effective among five oils they evaluated against the pulse beetle. Moreover, the effectiveness of citrus fruit peel extracts (Harshani and Karunaratne, 2021) and Gnidia kraussiana (Kosini et al., 2021) was also evaluated against C. maculatus and were found to significantly affect its oviposition and larvae.

It has been mentioned that essential oils of lemongrass contain majority of terpenes and terpenoids such as10.120-β-pinene and β-mycene; 20.182- Citral (geranial); 19.766-citral (geranial) and citronellal; 20.435- Epoxy-linalooloxide (Furanoid); 22.733- Lavandulyl acetate; 23.338- Neric acid, whereas 10.073- β-pinene and β-myrcene; 10.577- Octanal; 11.812- Limonene; 14.455- Linalool; 13.474- 1-Octanol; 17.516- Decanal were reported as major terpenes and terpenoids in orange oil (Ojebode et al., 2016). Thus, the presence of such huge quantities of terpenes and terpenoids in orange and lemongrass essential oils may be responsible for their more toxic potential against C. maculatus adults. Moreover, Myint et al. (2021) identified eight main constituents in peppermint with menthol being the most abundant (43.29%) and the same may be responsible for its more repellent potential against C. maculatus adults. Myint et al. (2021) also reported comparatively less LD50 values of 0.018 (0.017–0.019) for peppermint essential oil against C. maculatus than essential oil of Syzygium aromaticum.

A recent review on the use of essential oils against C. maculatus indicated that essential oils from 121 plant species belonging to 26 families have shown their insecticidal potential against C. maculatus. Among the plant families, Lamiaceae (30 species) and Asteraceae (22 species) are the two most widely tested families against the C. maculatus as generally terpenoids and sesquiterpenoids classes of chemicals present in these plant essential oils are responsible for the insecticidal properties (Mssillou et al., 2022).

Therefore, in continuation of above studies, all essential oils elicit promising mortality and repellent effect against C. maculatus, but essential oils of orange and lemongrass were found more effective to cause mortality of both male and female C. maculatus, whereas the peppermint and eucalyptus were found to be repellent. Moreover, the mortality or repellence of C. maculatus adults increased with increasing dose of essential oils and their exposure timings.

Conclusions and Recommendations

All the essential oils i.e., orange, lemongrass, eucalyptus, and peppermint exhibited pesticidal potential against male and female C. maculatus by causing their mortality and repellency. Orange and lemongrass oils were found to be more effective and lethal towards both males and females, whereas peppermint and eucalyptus oils were found to be more repellent. The pesticidal potential of all oils increased with increasing doses and exposure timings as the lowest LD50 value was recorded for orange essential oil. Therefore, essential oils of either orange or peppermint may be applied in the warehouses against C. maculatus to mitigate their population growth and grain damage.

Conflict of interest

The authors have declared no conflict of interest.

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