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Review

Citrus Limonene as a Potential Source of Biopesticides Against Maize Weevils

by
Yamkela Silwanyana
1,*,
Ayodeji Oluwabunmi Oriola
2,
Gugulethu Mathews Miya
2,
Yiseyon Sunday Hosu
3,
Adebola Omowunmi Oyedeji
2,
Opeoluwa Oyehan Oyedeji
4 and
Simon Kamande Kuria
1
1
Department of Biological and Environmental Sciences, Faculty of Natural Sciences, Walter Sisulu University, P/Bag X1, Mthatha 5117, South Africa
2
Department of Chemical and Physical Sciences, Faculty of Natural Sciences, Walter Sisulu University, P/Bag X1, Mthatha 5117, South Africa
3
Department of Business Management and Economics, Faculty of Economic and Financial Sciences, Walter Sisulu University, P/Bag X1, Mthatha 5117, South Africa
4
Department of Chemistry, Faculty of Science and Agriculture, University of Fort Hare, P/Bag X1314, Alice 5700, South Africa
*
Author to whom correspondence should be addressed.
Agriculture 2026, 16(6), 703; https://doi.org/10.3390/agriculture16060703
Submission received: 2 January 2026 / Revised: 9 February 2026 / Accepted: 13 February 2026 / Published: 20 March 2026
(This article belongs to the Section Crop Protection, Diseases, Pests and Weeds)
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Abstract

The maize weevil is a major postharvest pest of stored maize, causing substantial quantitative and qualitative grain losses and posing a serious threat to food security. In many regions of the world, particularly in developing countries where maize is a staple crop, maize weevil infestations can account for up to 50% of postharvest maize losses annually. Traditionally, synthetic pesticides have been used to manage maize weevils, but their prolonged application has been associated with environmental contamination, pesticide resistance, and adverse health effects in humans and animals. These challenges have inspired the search for safe, eco-friendly, and bioactive alternatives from natural sources. Citrus plants are among the most widely consumed fruits globally, with their peels and leaves constituting a significant proportion of agricultural waste. These waste products are rich in essential oils, particularly limonene, which has demonstrated potent insecticidal properties against maize weevils. Repurposing citrus waste into biopesticides offers a sustainable strategy for mitigating maize weevil infestations, thereby reducing postharvest maize losses and enhancing food safety and security. This review examines the prospects of citrus limonene in the development of safe and effective maize weevil biopesticides, highlighting its major chemical constituents, biological activities, and mechanisms of action.

1. Introduction

The maize weevil, Sitophilus zeamais (Motschulsky, 1855) (Coleoptera: Curculionidae), is one of the most destructive postharvest pests of stored maize, a staple food in many parts of the world [1,2]. Its infestation leads to significant economic losses and food insecurity, particularly in regions where maize is the primary dietary component [3,4]. Maize weevils attack both shelled and unshelled grain, boring into kernels to feed and reproduce, which directly reduces grain weight and quality [5]. Beyond physical damage, their activity contaminates grain with frass, body parts, and metabolic by-products, creating favourable conditions for mould growth and the development of harmful mycotoxins [6,7]. Contamination affects the safety of maize, rendering it unsuitable for human consumption or animal feed and diminishing its market value [8,9]. Maize weevils can be difficult to control because of their high reproductive potential, ability to complete their lifecycle within the grain, and their capacity to adapt to various storage environments [1,10,11].
In many developing countries, where maize is both a staple food and an important source of income, losses caused by maize weevils are particularly severe. Postharvest storage losses for maize due to insects can reach up to 50%, with maize weevils being the primary contributor [12]. These losses remain a major constraint to global food security, particularly in developing countries where storage technologies are limited [13]. In Africa, where traditional storage structures are still widely used, the impact is significant [14]. Estimates indicate that 15–30% of stored maize losses are due to insect infestation, with maize weevils accounting for a significant proportion of this damage [6,15,16]. The resulting damage includes direct grain damage, weight loss, and reduced nutritional value [13,17,18]. Contamination by mycotoxin-producing fungi worsens the problem, leading to substantial economic losses for smallholder farmers and grain traders [19]. For the 70% of southern African smallholders who save seed, maize weevil infestations significantly reduce germination rates [20,21,22]. This damage directly compromises future harvests by hindering successful planting. This underlines the urgent need for effective and sustainable maize weevil management strategies to protect both food security and rural livelihoods.
Historically, synthetic pesticides have been the primary method for controlling maize weevils [23,24]. However, their use raises concerns about toxic residues in food, risks to human and animal health, and environmental contamination [25]. Prolonged pesticide use has driven the evolution of resistant weevil strains, requiring higher doses and more frequent applications, which exacerbate ecological damage [26,27]. The persistence of these chemicals in soil and water causes harm to non-target organisms, disrupts ecosystems, and threatens beneficial insects such as pollinators [28]. Furthermore, chronic exposure to pesticide residues has been linked to serious health problems, including endocrine disruption, neurological disorders, and cancer, contributing to hundreds of thousands of premature deaths annually [24,29].
Considering these challenges, there is increasing interest in biopesticides derived from natural products, including citrus plants, as environmentally friendly alternatives for managing maize weevil [30,31,32]. Citrus peels, particularly from sweet orange (Citrus sinensis L. Osbeck) and lemon (Citrus limon (L.) Burm. f.), are rich in bioactive compounds such as limonene, a monoterpene with strong insecticidal properties [32,33,34]. Limonene is a terpene that makes up nearly 90% of orange and lemon oils and is well-studied for controlling maize weevils with minimal risk to human health [35,36,37]. It shows promising efficacy in targeting these pests by disrupting their respiratory and nervous systems, offering a safe alternative for protecting stored grain [38,39]. Compared to synthetic pesticides, citrus-based biopesticides degrade rapidly in the environment, leave minimal or no residues, and are less likely to trigger resistance development in weevil populations [40].
Given the growing concerns associated with synthetic insecticides, there is increasing interest in plant-derived biopesticides for postharvest pest management. Citrus limonene, a major constituent of citrus essential oils and a readily available compound from citrus processing waste, has been widely reported to exhibit insecticidal activity against stored-product pests, including maize weevils. However, existing evidence is dispersed across studies that differ in experimental design, formulation type, and target endpoints, and many investigations have focused on whole essential oils rather than limonene alone. This review, therefore, aims to synthesise current knowledge on the insecticidal potential of citrus limonene and limonene-rich citrus essential oils against maize weevil, critically evaluating their modes of action, efficacy, formulation challenges, and prospects for sustainable application in postharvest maize protection.
This review, therefore, evaluates citrus limonene as a potential biopesticide against maize weevils by summarising its repellent, fumigant, and contact toxicity. It examines the modes of action and assesses the advantages and limitations of citrus limonene and citrus essential oils high in limonene, compared with synthetic insecticides. Finally, the review identifies research gaps and future directions to help develop sustainable, limonene-based products for postharvest pest management.

2. Materials and Methods

This study is a descriptive literature review aimed at synthesising existing research on the insecticidal potential of citrus limonene and limonene-rich citrus essential oils against maize weevils. The review focuses on summarising the reported toxicological effects, modes of action, and potential applications of limonene from citrus essential oils as a botanical biopesticide, rather than quantitatively comparing effect sizes. Relevant literature was obtained through a comprehensive electronic search of major scientific databases and academic search engines, such as Google Scholar, Scopus, Web of Science, and ScienceDirect. These platforms were selected because they provide broad coverage of peer-reviewed journals in entomology, agriculture, pest management, and natural product chemistry. No restrictions were applied regarding the year of publication in order to capture both foundational and recent studies on citrus-derived insecticidal compounds. An initial search using the terms “citrus limonene” and “maize weevil” yielded approximately 2930 records. A refined search was subsequently conducted using combinations of keywords, including “citrus limonene”, “citrus essential oil”, “biopesticides”, “insecticidal activity”, “maize weevils”, and “Sitophilus zeamais”, which resulted in 545 publications.
The retrieved studies were screened for relevance based on their explicit focus on citrus limonene or limonene-rich citrus essential oils, their insecticidal effects, and their application in the management of maize weevils or other stored-product pests. Duplicate records and studies not directly related to the topic were excluded. Following this screening process, 90 publications were selected for inclusion in the review. The selected literature was analysed descriptively to summarise the reported findings on contact toxicity, fumigant toxicity, repellency, mechanisms of action, and the potential use of citrus limonene as an eco-friendly alternative to synthetic insecticides in stored grain protection. Limitations of the review include potential publication bias, the exclusion of non-English literature, and reliance on electronic databases, which may have resulted in the omission of some relevant studies.

3. Citrus Limonene: Chemical Classification and Structure

Citrus limonene is a naturally occurring monoterpene, classified under the family of cyclic terpenes, which are distinguished by their characteristic ring-shaped structure. Limonene belongs to the broader class of isoprenoids, consisting of two isoprene units that form a monocyclic monoterpene with the molecular formula C10H16 (Figure 1) [41,42]. Its structure includes a six-membered carbon ring with one double bond, making it a simple yet versatile compound with two main isomeric forms: D-limonene and L-limonene. The D-isomer is also known as the (R) configuration, and the L-isomer is often known as the (S) configuration. However, D and L denote relative configuration, whereas R and S denote absolute configuration [42]. D-limonene, which is found predominantly in citrus essential oils such as those from oranges, exhibits a strong citrus aroma and is the most common form used in industrial applications [43]. Although less abundant, the L-limonene isomer is typically found in certain coniferous plants and possesses a more lemon-like scent [42]. The structural simplicity of limonene, coupled with its unique aromatic properties, has made it a valuable compound in various sectors, including the flavour, fragrance, and pharmaceutical industries [44].
The distinct chemical structure of limonene contributes significantly to its biological activity, especially its role as an insecticidal agent. The hydrophobic nature of limonene allows it to easily penetrate the lipid membranes of insect pests, disrupting cellular processes and leading to mortality [45]. Its cyclic terpene structure, with the presence of reactive double bonds, enhances its ability to interact with the nervous system of insects, causing neurotoxicity and respiratory inhibition [46]. The isomeric form, particularly D-limonene, has been found to be effective due to its higher bioavailability and stronger interaction with insect targets [42]. Additionally, the natural abundance and structural stability of limonene make it an ideal candidate for developing biopesticides, offering a safer and environmentally friendly alternative to synthetic chemicals. The chemical classification and structure of limonene thus play a crucial role in its wide-ranging bioactivity and potential applications in sustainable pest management.
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Figure 1. Limonene structure [47].
Figure 1. Limonene structure [47].
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4. Insecticidal Properties of Citrus Limonene

4.1. Repellent Activity

Citrus limonene has shown strong repellent activity against postharvest insect pests, showing promising efficacy as a natural alternative for pest control [33,48]. The volatile nature of limonene plays a crucial role in its repellent properties, as it quickly diffuses in the air, creating an environment that deters insects from infesting stored grains [49]. Studies have demonstrated that insect pests exposed to limonene vapours exhibit avoidance behaviour, reducing the likelihood of oviposition and grain damage [32,50]. The repellent action of limonene is attributed to its strong citrus aroma and the irritant effects on the sensory organs of the insects, causing them to avoid treated areas. Furthermore, research has indicated that the repellent efficacy of limonene is dose-dependent, with higher concentrations providing prolonged protection against maize weevils [40]. As a naturally occurring compound, limonene offers a safer option compared to synthetic repellents, reducing health risks and environmental impact while effectively protecting stored products.
According to previous studies, limonene exhibited strong repellent activity against maize weevils with a 50% repellent dose (RD50) value of 0.213 mg/cm2 [51]. Similarly, Chaubey [52] reported that limonene has a significant (F = 238.64, p < 0.01) repellence against maize weevil adults. C. aurantium leaf essential oil showed complete repellency (100%) against maize weevils within 3 h, indicating a rapid and promising efficacy repellent response [53]. Similarly, essential oil extracted from orange peels exhibited notable repellent effects, with an LC50 value of 29.51 μL/L air after 24 h of exposure (Table 1), further confirming the behavioural avoidance induced by limonene-rich vapours [54]. Moderate but consistent repellency was reported for peel essential oils of C. aurantifolia and C. reticulata, which recorded percentage repellency (PR) values of 27.5% and 30%, respectively, after 4 h of exposure [55]. In another short-term bioassay, orange peel oil achieved a percentage repellency of 25.70% within 30 min, demonstrating its immediate repellent action against adult maize weevils [56]. Additionally, essential oil derived from the leaves of Citrus bergamia showed a repellent index (RI) of 56.3% after 24 h, indicating sustained repellency over longer exposure periods [57]. Collectively, these findings suggest that limonene exerts encouraging/repellent effects against maize weevils. The observed repellent behaviour underscores the value of citrus limonene as a preventive biopesticide capable of reducing infestation and oviposition in stored maize systems.

4.2. Fumigant Activity

The fumigant properties of limonene-rich essential oils make limonene an effective insecticidal compound against maize weevils, especially in enclosed storage environments. Due to its high volatility, limonene easily vaporises, allowing it to penetrate deep into grain masses where it can interact with pests [60,61]. Recent studies have shown that fumigation with limonene vapours promisingly reduces the population of maize weevils, leading to increased mortality rates among both adult weevils and their larvae [48,62]. Limonene’s fumigant activity has also been reported to be effective when applied in combination with other natural compounds, enhancing its insecticidal effects [63]. However, its efficacy may vary depending on environmental factors such as temperature and humidity [64]. Higher temperatures enhance limonene evaporation but reduce persistence [48]. Also, high humidity may lower insecticidal effectiveness by reducing vapour penetration and increasing grain moisture [36]. Despite these variations, the use of limonene as a fumigant offers a promising alternative to synthetic fumigants, which pose significant health and environmental hazards.
The fumigant activity of limonene against maize weevils has been reported, further supporting its potential as a biofumigant for stored-grain protection. Kim and Lee [58] investigated the insecticidal properties of limonene-rich citrus essential oil and concluded that limonene was highly effective as a fumigant against adult weevils, recording an LC50 value of 0.122 mg/cm3. Similarly, Liao et al. [62] reported a strong fumigant toxicity of limonene against maize weevils, with a 50% lethal concentration (LC50) of 22.90 μL/L air after 24 h of exposure, indicating rapid and potent fumigant action. Supporting these findings, Oyedeji et al. [47] assessed the fumigant efficacy of limonene-rich essential oil extracted from orange peel and reported an LC50 value of 80.01 mL/L air against maize weevils, confirming the effectiveness of citrus limonene in fumigation toxicity assays. In addition, Fouad and da Camara [55] demonstrated that essential oils from C. aurantifolia and C. reticulata, characterised by high limonene content, showed considerable fumigant effects against maize weevils (Table 1). Although variations in LC50 values are evident among studies, these differences are likely attributable to factors such as oil composition, limonene concentration, exposure duration, and experimental conditions. Such variability may also be influenced by differences in exposure time, fumigation chamber volume, temperature, and air circulation, all of which affect the volatility and dispersion of limonene vapours. Nonetheless, these studies collectively provide growing evidence that limonene is a key contributor to the fumigant toxicity of citrus essential oils. They also highlight its promise as a natural alternative to synthetic fumigants in postharvest pest management.

4.3. Contact Toxicity

Citrus essential oils rich in limonene exhibit strong contact toxicity against maize weevils, making limonene an effective compound for direct application on infested grains [65]. When applied topically, limonene-rich biopesticide penetrates the insect’s cuticle, disrupting cell membranes and leading to dehydration and death [66]. Contact toxicity studies have shown that even at low concentrations, limonene can induce high mortality rates among adult maize weevils, suggesting its potential as an effective treatment for stored grains [45]. Toxicity assays have reported that the median LC50 of limonene and limonene-rich essential oils is relatively low, highlighting their potency. Unlike conventional contact insecticides, limonene poses minimal risk to non-target organisms and is considered safe for human exposure, making it a suitable option for integrated pest management strategies in postharvest grain protection [65,67].
Several studies have demonstrated the strong contact toxicity of limonene against the maize weevil, highlighting its potential as an effective biopesticidal compound. Yıldırım et al. [68] evaluated the toxicity of selected monoterpenes against maize weevils and reported that limonene exhibited pronounced contact toxicity, with a median lethal concentration (LC50) of 15.06 μg/cm2. Similarly, Kim and Lee [58] investigated the insecticidal activity of limonene and found it to be the most potent compound tested, recording an LC50 value of 0.187 mg per adult weevil, further confirming its strong contact insecticidal efficacy. In agreement with these findings, Fouad and da Camara [55] demonstrated that essential oils derived from C. aurantifolia and C. reticulata, in which limonene was the major constituent, were highly effective in contact toxicity assays against maize weevils (Table 1). These results suggest that limonene plays a key role in the insecticidal activity of citrus essential oils. However, variability in toxicity has been reported across studies, likely reflecting the differences in oil composition, limonene concentration, extraction methods, and bioassay conditions. For instance, Oyedeji et al. [47] reported a higher LC50 value of 95.63 μg/adult when using limonene-rich essential oil from C. sinensis in contact toxicity assays against maize weevils. Despite this variability, the growing body of evidence consistently supports limonene as a major bioactive component responsible for its contact toxicity against maize weevils.

5. Mechanism of Action of Citrus Limonene on Maize Weevils

5.1. Neurotoxic Effects on the Nervous System

The primary molecular mechanism through which citrus limonene, derived from orange and lemon, is proposed to exert insecticidal activity involves neurotoxic effects on the maize weevil’s nervous system. Limonene-rich essential oil, as a prospective biopesticide, acts as a neurotoxic agent by interfering with the GABA (gamma-aminobutyric acid) receptor pathways, which are critical components of insect neural signalling [69,70]. GABA receptors regulate the flow of chloride ions across neuronal membranes and play an essential role in maintaining inhibitory signals within the nervous system [71]. Growing evidence from insect neurophysiology studies suggests that when limonene interacts with these receptors, it may inhibit the normal flow of chloride ions, thereby disrupting synaptic transmission. Such disruption is thought to result in neuronal hyperexcitation, where reduced inhibitory control leads to the continuous firing of nerve signals [72]. Consequently, maize weevils may experience neuromuscular dysfunction, manifesting as paralysis, and ultimately death (Figure 2). The reported affinity of limonene-rich essential oils, particularly D-limonene, for neural targets supports its proposed neurotoxic action, highlighting its potential as a biopesticide against maize weevils [73,74].

5.2. Volatility and Respiratory Disruption

The volatile nature of limonene is considered a key factor contributing to its insecticidal efficacy as it facilitates entry into the respiratory system of maize weevils. Due to its high vapour pressure, limonene readily evaporates and can interact with the insect tracheal system, potentially disrupting respiration [75]. Upon inhalation, limonene vapours are believed to penetrate the spiracles (respiratory openings), where they may cause irritation and partial obstruction within the tracheal tubes [76]. This process can lead to respiratory distress, impairing gas exchange that is essential for cellular respiration and energy production (Figure 2). Disruption of respiratory function is therefore suggested to contribute to insect mortality while also accelerating the onset of toxic effects. This rapid mode of action is advantageous for pest control as it reduces the exposure time required to achieve notable mortality in maize weevils [74].

5.3. Oxidative Stress and Disruption of Detoxification Pathways

Citrus limonene-rich essential oil has also been associated with the induction of oxidative stress in insects, which is considered an additional mechanism contributing to its insecticidal activity against maize weevils (Figure 3). Studies suggest that limonene can interfere with detoxification enzymes, particularly cytochrome P450 monooxygenases, which are essential for metabolising and neutralising xenobiotic compounds [77,78,79]. Inhibition of these enzymes may reduce the insect’s detoxification capacity, resulting in the accumulation of reactive oxygen species (ROS) [79]. Elevated ROS levels are known to induce oxidative stress, leading to cellular damage through lipid peroxidation, protein denaturation, and DNA fragmentation [31,78]. Such oxidative damage is likely to weaken cellular integrity, disrupt physiological processes, and contribute to metabolic failure, ultimately resulting in insect mortality [80].

5.4. Cell Membrane Penetration and Lipid Disruption

Another proposed mechanism underlying the insecticidal activity of citrus limonene is the ability to penetrate and disrupt lipid membranes in maize weevil cells. Due to its hydrophobic (lipophilic) properties, limonene can readily integrate into the lipid bilayer of cell membranes, increasing membrane permeability [81,82]. This interaction may compromise membrane integrity, making cells more vulnerable to environmental stress and chemical damage. Increased membrane permeability is believed to facilitate the leakage of ions and essential metabolites, disrupting osmotic balance and potentially leading to cell lysis [83]. By weakening cellular membranes, limonene is thought to enhance its overall toxic effects and contribute to a cascade of metabolic disturbances within the insect (Figure 3). When considered together, these neurotoxic, respiratory, oxidative, and membrane-targeting effects illustrate a multifaceted mode of action. This supports the potential of citrus limonene and limonene-rich essential oils as a safer, natural alternative to conventional synthetic insecticides for maize weevil management.
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Figure 3. Mechanisms of action of citrus limonene against maize weevils, illustrating limonene-induced detoxification and cell membrane disruptions.
Figure 3. Mechanisms of action of citrus limonene against maize weevils, illustrating limonene-induced detoxification and cell membrane disruptions.
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6. Prospects of Citrus Limonene as a Potential Biopesticide

Citrus limonene shows considerable potential as a biopesticide due to its broad-spectrum insecticidal activity and favourable environmental profile. Limonene and limonene-rich citrus essential oils, particularly from orange and lemon sources, have demonstrated insecticidal activity against maize weevils, indicating their possible application in postharvest pest management systems [25,84]. Its natural origin and relatively low toxicity to humans and non-target organisms align with the growing demand for safer, more sustainable alternatives to synthetic pesticides. In addition, limonene’s biodegradability and limited environmental persistence reduce the risk of long-term soil and water contamination, supporting its suitability for environmentally responsible pest control strategies [37]. Although the precise, species-specific mechanisms of action against maize weevils remain insufficiently validated, insecticidal effects observed in limonene-rich citrus essential oils are generally associated with neurophysiological disruption and respiratory impairment, as inferred from studies on other insect taxa [70].
Beyond its bioactivity, citrus limonene offers sustainability advantages through the valorisation of citrus processing waste. Citrus peels, a major by-product of the juice and food industries, are rich sources of limonene and are often discarded or underutilised. Transforming these into biopesticidal products is a cost-effective and eco-friendly approach that aligns with circular economic principles. This approach provides practical storage solutions for regions where citrus farming and maize production coexist.
To further capitalise on the insecticidal potential of citrus limonene, researchers have explored innovative formulation strategies and synergistic combinations with other natural compounds. Nano-emulsions and microencapsulation technologies have shown promise in improving limonene stability, limiting rapid volatilisation, and enabling controlled release. This, therefore, extends its persistence and efficacy in pest management systems [85]. Encapsulation allows for more targeted delivery and may reduce the quantity of active ingredient required while maintaining insecticidal performance [86]. In addition, combining limonene-rich citrus essential oils with synergists such as piperonyl butoxide or other aromatic plant oils has been reported to enhance toxicity against resistant pest populations [87,88]. These strategies also help mitigate variability in limonene content across citrus species and extraction methods. Continued development of standardised, optimised formulations could therefore facilitate a broader adoption of citrus limonene-based products for sustainable postharvest pest management.

7. Limitations of Citrus Limonene as a Potential Biopesticide

Despite its prospects, citrus limonene offers a compelling alternative to synthetic pesticides; however, its use as a biopesticide against maize weevils faces several significant challenges. One of the foremost issues is the high volatility and rapid degradation of limonene when exposed to open environments [78]. Limonene’s volatility allows it to evaporate quickly, which diminishes its contact efficacy and fumigant properties, particularly in grain storage settings where prolonged residual activity is desired [42]. The chemical instability of limonene is further exacerbated by environmental factors such as elevated temperatures and exposure to ultraviolet (UV) light, both of which can accelerate its breakdown [65]. This rapid degradation limits its effective duration of action, requiring frequent reapplications, which may not be economically viable for large-scale pest control. Additionally, the short-lived nature of limonene’s insecticidal effect poses a challenge in integrated pest management strategies where sustained pest suppression is critical.
Beyond issues of volatility, there are additional concerns related to phytotoxicity and standardisation that limit the practical application of citrus limonene as a biopesticide. At higher concentrations, limonene can exhibit phytotoxic effects, potentially causing physical damage to the surface of stored grains, such as discolouration or pitting, which in turn can reduce the quality and market value of the affected produce [89,90]. This risk of phytotoxicity complicates the formulation process, as careful dosing is required to balance efficacy against pest insects while minimising harm to the commodity itself. Moreover, the content and composition of limonene can vary across different citrus species, as well as due to factors like growing conditions, harvest time, and extraction methods [42,46]. Such variability can lead to inconsistencies in the efficacy of limonene-based products, making it challenging to standardise their use as reliable biopesticides. Addressing these limitations would require advanced formulation techniques, such as microencapsulation, to stabilise limonene and reduce its phytotoxic effects. Additionally, further research is needed to develop standardised extraction and application protocols.

8. Conclusions and Recommendations

Citrus limonene is a promising bioactive compound with demonstrated insecticidal activity against maize weevils, a major postharvest pest of stored maize. The growing body of evidence from existing studies indicates that limonene is believed to exhibit multiple modes of action, including repellent, fumigant, and contact toxic effects, supporting its potential use in postharvest pest management. Compared with conventional synthetic insecticides, limonene-based products offer advantages such as biodegradability, reduced environmental persistence, and lower risks to human health and non-target organisms. The abundance of limonene in citrus processing by-products further presents an opportunity for waste valorisation and the development of more sustainable pest control approaches.
Despite these advantages, several challenges limit the widespread application of citrus limonene under real storage conditions. High volatility, rapid degradation, and variability in limonene content across citrus species and extraction methods affect consistency and efficacy. In addition, concerns related to phytotoxicity and the lack of commercially standardised formulations remain significant constraints. Importantly, most available studies focus on whole citrus essential oils rather than isolated limonene, creating uncertainty regarding its standalone performance.
Future research should therefore prioritise the development of stable, standardised limonene formulations using advanced delivery systems such as nano-encapsulation and slow-release technologies. Greater emphasis is also needed on evaluating long-term efficacy under diverse storage environments and assessing compatibility with integrated pest management strategies. Further investigations into non-target effects and environmental safety will be essential to support responsible application. Addressing these gaps will strengthen the scientific basis for citrus limonene as a viable, eco-friendly alternative to synthetic insecticides in postharvest maize weevil management.

Author Contributions

Conceptualization, Y.S. and A.O.O. (Ayodeji Oluwabunmi Oriola); methodology, Y.S.; validation, A.O.O. (Ayodeji Oluwabunmi Oriola), A.O.O. (Adebola Omowunmi Oyedeji), and S.K.K.; formal analysis, O.O.O. and G.M.M.; investigation, Y.S.; resources, S.K.K. and Y.S.H.; writing—original draft preparation, Y.S.; writing—review and editing, Y.S., A.O.O. (Adebola Omowunmi Oyedeji) and S.K.K.; visualization, G.M.M. and O.O.O.; supervision, S.K.K.; project administration, Y.S.H.; funding acquisition, Y.S.H., S.K.K. and A.O.O. (Adebola Omowunmi Oyedeji). All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Research Foundation (grant number SRUG22052715195).

Data Availability Statement

No new data were created or analysed in this study. Data sharing is not applicable to this article.

Acknowledgments

The authors thank the Directorate of Research and Innovation at Walter Sisulu University, National Research Foundation and the Council for Scientific and Industrial Research for their support in developing this work.

Conflicts of Interest

The authors declare no conflicts of interest.

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Agriculture 16 00703 g002
Figure 2. Mechanisms of action of citrus limonene against maize weevils, illustrating limonene-induced neurotoxicity and limonene-induced respiratory disruption.
Figure 2. Mechanisms of action of citrus limonene against maize weevils, illustrating limonene-induced neurotoxicity and limonene-induced respiratory disruption.
Agriculture 16 00703 g002
Table 1. Effects of citrus limonene and limonene-rich essential oils on maize weevils.
Table 1. Effects of citrus limonene and limonene-rich essential oils on maize weevils.
Citrus spp.Plant PartToxicity EffectReference
Repellent Activity
Citrus aurantiumLeavesPR3h = 100%[53]
Citrus sinensisPeelsLC50; 24h = 29.51 μL/L air [54]
Citrus aurantiifoliaPeelsPR4h = 27.5% [55]
Citrus sinensisPeelsPR30min = 25.70%[56]
Citrus bergamiaLeavesRI24h = 56.3%[57]
Citrus reticulataPeelsPR4h = 30% [55]
Fumigation Activity
Citrus sinensisPeelsLC50; 3d = 80.01 mL/L air [47]
Citrus aurantiifoliaPeelsLC50; 24h = 58.51 μL/L[55]
Citrus sinensisPurchasedLC50; 24h = 75.80 μL/L[25]
Citrus sinensisPeelsPM24h = 61.25%[56]
Citrus sinensisPeelsLC50; 24h = 0.12 mg/cm3[58]
Citrus reticulataPeelsLC50; 24h = 41.92 μL/L[55]
Contact Toxicity
Citrus sinensisPeelsLC50; 24h = 95.63 μg/adult[47]
Citrus aurantiifoliaPeelsLC50; 24h = 71.18 μL/mL [55]
Citrus aurantiifoliaPeelsPM3d = 100%[59]
Citrus sinensisPeelsLC50; 24h = 0.19 mg/adult[58]
Citrus reticulataPeelsLC50; 24h = 51.29 μL/mL[55]
LC: lethal concentration; RI, repellency index; PR, percentage repellency; PM, percentage mortality.
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Silwanyana, Y.; Oriola, A.O.; Miya, G.M.; Hosu, Y.S.; Oyedeji, A.O.; Oyedeji, O.O.; Kuria, S.K. Citrus Limonene as a Potential Source of Biopesticides Against Maize Weevils. Agriculture 2026, 16, 703. https://doi.org/10.3390/agriculture16060703

AMA Style

Silwanyana Y, Oriola AO, Miya GM, Hosu YS, Oyedeji AO, Oyedeji OO, Kuria SK. Citrus Limonene as a Potential Source of Biopesticides Against Maize Weevils. Agriculture. 2026; 16(6):703. https://doi.org/10.3390/agriculture16060703

Chicago/Turabian Style

Silwanyana, Yamkela, Ayodeji Oluwabunmi Oriola, Gugulethu Mathews Miya, Yiseyon Sunday Hosu, Adebola Omowunmi Oyedeji, Opeoluwa Oyehan Oyedeji, and Simon Kamande Kuria. 2026. "Citrus Limonene as a Potential Source of Biopesticides Against Maize Weevils" Agriculture 16, no. 6: 703. https://doi.org/10.3390/agriculture16060703

APA Style

Silwanyana, Y., Oriola, A. O., Miya, G. M., Hosu, Y. S., Oyedeji, A. O., Oyedeji, O. O., & Kuria, S. K. (2026). Citrus Limonene as a Potential Source of Biopesticides Against Maize Weevils. Agriculture, 16(6), 703. https://doi.org/10.3390/agriculture16060703

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