Plant-based bioactive compounds for grain storage: a comprehensive review

Abstract

The post-harvest loss of grain is a global concern, especially for developing countries where food security is a big challenge. Botanical plants are called green pesticides, which can affect various insect pests in different ways. Essential oils have a broad range of bioactivity when it comes to combating agricultural pests. Moreover, spices are potential alternatives to preserve grains from insect infestations due to their different characteristics (repellent, deterrent, and insecticidal). The aim of this review is to provide an overview of plant-based products, including their mode of action, bioactive components, and targeted pests and insects for grain storage.

Keywords:

• Botanicals
• bioactive compound
• insecticidal
• toxicity and mode of action

Reviewing Editor:

• M. Luisav Escudero-Gilete, Universidad de Sevilla, Spain

SUBJECTS:

• Food Additives & Ingredients
• Food Chemistry
• Food Engineering
• Food Laws & Regulations
• Botany

1. Introduction

Grain post-harvest loss is a global concern, ­especially for developing countries where food security is a big challenge (Kumar & Kalita, 2017). Red Flour Beetle (Tribolium castaneum) (Herbst) (Coleoptera:Tenebrionidae), and maize weevils (Sitaphilus zeamais) (Coleoptera:Curculionidae) (Wilson et al., 2008) are insects that have significantly reduced grain quality and quantity during storage (Pugazhvendan et al., 2012). Farmers use synthetic insecticides to keep insects away from their grains. Synthetic chemicals can contaminate water and soil, are hazardous to non-target insect species, and are ineffective against insects that are resistant to phosphine (Sousa et al., 2009). To alleviate these problems, botanical pesticides are getting more emphasis than ever before due to the increasing problems associated with the use of toxic synthetic pesticides (Pugazhvendan et al., 2012). Botanical pesticides are easily broken down by detoxifying enzymes and disintegrate quickly in plant systems, the air, and moisture due to their easy breakdown properties. Due to their rapid breakdown, botanical pesticides show less persistence in the environment and are less toxic to non-target creatures (Lengai et al., 2020). As a result, the utilization of plant-based botanical products, such as oil, powder, and leaves, is safer for the environment and human health (Boate & Abalis, 2020; Farooqui et al., 2005).

Essential oils are secondary metabolites of plants and are applied as indigenous pesticides for post-harvest management of grains. Essential oils from spices have aromatic properties that attract or repel insects, and their chemical constituents serve as defense materials against pests and insects (Meena & Lal, 2019). Because of this, essential oils have a broad range of bioactivity when it comes to combating agricultural pests.

Plants are thought to be abundant in bioactive compounds, which have been used naturally to control insects (Silva et al., 2013). Varied parts of plants, such as leaves, stems, flowers, and seeds, as well as varied product forms, such as extracts, oils, powders, and spices, can be used to produce botanical bioactive chemicals that can be employed to manage pest infestations (Meena & Lal, 2019). For instance, some bioactive compounds are quircetin, quinolone, quinolone-4-carbidehyde, quinolone-3-carldehyde, osajin, lupalbeginen, scandinon, sphaerobioside, genistein, prenylated isoflavones, carvacrol, safole, linalool, R-linalool, 2-heptanol, 4-terpenenol, carvane, thujone, and limonene (Soujanya et al., 2016).

Various researchers have documented the use of insecticides derived from plants. To use botanicals for insecticidal purposes, there is a lack of comprehensive data regarding various plants and their bioactive chemicals, modes of action, and targeted pests and insects. Thus, future studies will look at why some plants have a more insecticidal nature than others. The aim of this review is to provide an overview of plant-based products, including bioactive components, their modes of action, and targeted insects for grain storage.

2. Plant-based botanical materials

In spite of acting as natural grain protectants, botanical chemicals also function as antifeedants, attractants, nematicides, fungicides, repellents, insecticides, toxicants, insect growth regulators, allelopathic agents, biopesticides, and chemosterilants by inhibiting the growth and development of insects, acting as a promising source for novel pest control agents (Souto et al., 2021; Trivedi et al., 2018). Because they are thought to pose less of a risk to the environment and human health than synthetic pesticides, botanical pesticides have become progressively more attractive (De Oliveira et al., 2014; Feng & Zhang, 2017). In addition, according to Lal et al. (2017), plants like neem (Azadirachta indica), bach (Acorus calamus), phoolakri (Lantana camara), draik (Melia azadarach), kali mirch (Piper nigrum), and basuti (Adhatoda zeylanica) that are biodegradable, non-residual, equally effective, and readily available may work better to control insect pests without negatively impacting the quality of grains and ecosystems. Therefore, natural chemicals extracted from plants and their secondary products are substituting synthetic pesticides. In addition, they are effective against pests that resist chemical pesticides, are targeted, and have less persistence in the environment (Meena & Lal, 2019). Due to such reasons, plants are extensively used to prevent the proliferation of a variety of storage pests (Obeng-Ofori et al., 1998; Singh, 2017). Plant materials, including leaves, bark, seed powders, and oil extracts, have been used as admixtures with stored grains to reduce seed damage, insect oviposition, and adult emergence (Bakkali et al., 2008; Singh, 2017). Furthermore, they are applied to reduce egg hatchability, postembryonic development, and progeny generation in insects (Asawalam & Adesiyan, 2001; Singh, 2017).

According to Mosta et al. (2019), the insecticidal properties of three commonly available benzoates are examined (Ethyl Benzoate, Ethyl Benzoate, and Vinyl Benzoate) against the cotton aphid, Aphis gossypii Glover, and its lacewing predator and Chrysoperla carnea Stephens. According to previous author, methyl benzoate exhibited the highest contact toxicity against A. gossypii nymphs and adults when compared to ethyl benzoate and vinyl benzoate. Furthermore, methyl benzoate is a food-safe natural product (Mostafiz et al., 2021) used to control insect pests and mites, which causes contact toxicity such as spotted wing drosophila, tobacco hornworms, brown marmorated stink bugs, diamondback moths, red imported fire ants, whiteflies, aphids (Mostafiz et al., 2018) and also its fumigation toxicity in P. interpunctella has been examined and methyl benzoate is extracted from fermented apple juice and recognized to possess insecticidal and repulsive properties against a variety of insect species (Mostafiz et al., 2021) benzoate is also against to non-targeted organism for example, Tetranychus urticae Koch (Acari: Tetranychidae) (Mostafiz et al., 2020). Additionally, the effectiveness of three botanical repellents (sweet flag (Acorus calamus), black pepper (Piper nigrum), and clove (Syzygium aromaticum)) against adult storage grain pests, specifically the pulse beetle, was assessed and results showed that, sweet flag rhizome extract exhibits much higher maximum repellency (90.07%) than clove (80.13%) and black pepper (83.51%) respectively (Madavi et al., 2022).

2.1. Essential oils

Essential oils (EOs) from aromatic plants in Lauraceae, Myrtaceae, Asteraceae, and Piperaceae families are often suggested as potential sources of insecticidal compounds (Karla et al., 2024). Significant amounts of biologically active chemicals, such as Eos, which are environmentally friendly, are found in natural plants. Hikal et al. (2023) conducted that, from 16 selected EOs, EOs of Nano emulsions patchouli (Pogostemon cablin) and honeysuckle (LC50 (Lonicera caprifolium) killed mosquitos’ larvae more effectively than the other oils (100% mortality) at 24 hours after treatment. Similarly, EOs are safe, natural, and environmentally friendly and are used against mosquito larvae instead of synthetic chemicals (Patel et al., 2023). EOs from plants like Lantana camara Linn (family Verbenaceae) can be used as an environmentally friendly pesticide for controlling storage pests, offering an effective solution for controlling noxious weeds (Aisha et al., 2024). According to the previous work, the effect of EOs obtained from L. camara leaves on the three storage pests: Tribolium castaneum, Lasioderma serricorne, and Callosobruchus chinensis, showed strong fumigant, contact, and repellent properties against various insects, with LC50 values of 16.70 mg/L for T. castaneum, 4.141 mg/L for L. serricorne, and 6.24 mg/cm2 for C. chinensis. However, EOs from different plants have varied effects on different insects. On a range of insects, EOs exhibit the following properties: repellant, insecticidal, antifeedant, growth inhibitor, oviposition inhibitor, ovicide, and growth-reducing (Pugazhvendan et al., 2012). EOs extracted from Mentha piperita repels ants, flies, lice, and moths’ and is effective against Callosobruchus maculatus and Tribolium castanum, and the oils of Zingiber officinale rhizomes and Piper cubebaberries are showing insecticidal and anti-feeding activities against Tribolium castaneum and Sitophilus oryzae (Hikal et al., 2017). According to the previous authors, oils isolated from the above-mentioned plant species exhibit anti-insect activity against Ceratitis capitata and Triatoma infestans. Oils extracted from eucalyptus are used to protect T. granarium, S. granaries, and C. maculatus from wheat, sorghum, sesame, and sunflower (Yadav et al., 2008) due to 1,8-cineole, citronellal, citronellol, citronellyl acetate, p-cymene, eucamalol, limonene, linalool, α-pinene, ϒ-terpinene, α-terpineol, alloocimene, and aromadendrene components (Hikal et al., 2017). Oil extracted from neem is also used to protect wheat from R. dominica, S. oryzae, and T. castaneum (Kemabonta & Falodu, 2013).

2.2. Powders

Similarly, powders obtained from plant parts are also used as insecticides. Red and black pepper powders are used to reduce the activity of pests like granarius and R. dominica from wheat grain during storage. The results of research conducted by Ashouri and Shayesteh (2010) and, Soujanya et al. (2016) showed that when the powders of red and black pepper were applied to stored wheat grain, both immature and adult granarius and R. dominica pests died within 15 days. Table 1 summarizes the effects of various plant-based powders and oils on reducing insect pest activities in different stored grains. Powders derived from neem kernel and leaves are effective against R. dominca, S. oryae, T. granarium, C. chinensis, and C. maculatus of wheat, sorghum, cowpeas, and maize grains (Kemabonta & Falodu, 2013). Costus root powder was effective against T. Granarium of wheat (Girish & Jain, 1974; Jilani & Haq, 1984). In addition, eucalyptus, sarifa, and lantana powders are used to protect maize and paddy from S. Cereaella (Soujanya et al., 2016; Yadu et al., 2000). The leaves and flowers of Croton heliotropiifolius, Duguetia furfuracea, Magonia pubescens, Senna obtusifolia, Senna occidentalis, and Vernonia scabra have a good pesticide irritation effect as compared to synthetic insecticides via modifying the behavior of S. zeamais species (Silva et al., 2013). Nasiru et al. (2016) pointed that the leaf powders of Tamarindus indica, Azadirachta indica, and Jatropha curcas showed insecticidal activities by controlling the growth and reproduction of maize weevils (Sitophilus zeamais). According to the previous authors, adult mortality of T. indica, A. indica, and J. curcas at different concentrations of admixture with maize grain during storage was 97%, 66%, and 40%, respectively. Powders from Chenopodium ambrosioides leave and aframomum melegueta seed have shown a significant effect on death rate of cowpea weevil callosobruchus maculatus within 144 hours storage time of cow pea pulse (Chougourou et al., 2016). Powders of abeyi (Maesa lanceolata) seed and bekenisa (Croton macrstachyus) leaf, both 5% w/w admixtures with teff (Eragrostis teff), 50% w/w, were used to boost germination ability, reduce weight loss, and induce maize weevil and angoumois pest mortality (Kidanu et al., 2018). In addition to the botanical properties of the powder used, teff can also reduce the movement of the pests since it reduces the void space between the grains. Due to this, teff can also reduce the growth of the pests when it admixed with other grains. Generally, plants are applied in different forms, like oil, powder, and extract from different plant parts, as indicated in Table 1. Each product has a toxic effect on specific storage insects or pests. Powder extracted from neem kernels and their leaves can prevent R. dominca and S. oryae, T. granarium, C. chinensis, and C. maculatus from growing in wheat, sorghum, cowpeas, and maize, but that does not mean that it can control other stored insects or pests. Therefore, these indicated that to apply botanical plants for pest control, it is better to understand the types and properties of insects and types of stored grains.

Table 1. Different plants and their products act as insecticide in stored grains.

Type of plant	Product types	Targeted insect/pest	Types of grain	References
Neem kernel and leaves	Powder	R. domincaand, S.oryae, T. Granarium, C. chinensis, and C. maculatus	Wheat, sorghum cowpeas, maize	(Kemabonta & Falodu, 2013)
Dharek kernel	Powder	T. castaneum and R.dominica	–	(Singh, 2017)
Costus root	Powder	T. Granarium	Wheat	(Girish & Jain, 1974; Jilani & Haq, 1984)
Garlic and pine	Oil	T. Castaneum and c. Maculates	Stored grain	(Maia & Moore, 2011)
Daturaalba, calotropis procera, chromol aenaodorata	Powder	R. Dominica	Rice	(Fatope et al., 2008; Patel et al., 1993)
Neem	Oil	R. Dominica, S. Oryzae, T. Castaneum and C. Chinensis	Wheat plus	(Kemabonta & Falodu, 2013)
Eucalyptus, Sarifa, and Lantana	Leaf powder	S. Cereaella	Maize and paddy	(Soujanya et al., 2018; Yadu et al., 2000)
Neem and black pepper	Extracts	R. Dominica	Wheat	(Kemabonta & Falodu, 2013)
Jatropha seed, Mustard	Powder	S. Oryzae	Wheat maize	(Kakde et al., 2014)
Mustard	Oil	S. oryzae R. Dominica	Wheat maize	(Kakde et al., 2014; Reddy et al., 1999)
Castor and Linseed	Oil	C. Chinensis, S. Oryzae R. Dominica C. Maculatus	Pea seed	(Ali & Mohammed, 2013)
Sesame, Sunflower	Oil	T. Granarium and S. Granaries C. Maculatus	Wheat and Sorghum	(Bhargava & Meena, 2002; Saxena & Singh, 1994; Yadav et al., 2008)
Eucalyptus	Oil	S. Oryzae, C. Maculatus	Wheat, pigeon pea	(Kumawat & Naga, 2013; Singh et al., 2017)

Spices that have different chemical compounds can be extracted from different plant parts such as bulb, flowers, fruits, seeds, barks and rhizomes and used as insecticides. During grain storage, spice is used in the form of extract, powder, essential oil, or as is. Essential oils are complex combinations of 20-60 chemical molecules derived from many forms of spices that impart characterstic odor and flavor to leaves, flowers, fruits, seeds, barks, and rhizomes (Meena & Lal, 2019). Due to their repellant, deterrent, and insecticidal properties, spices increase insect mortality and lower the number of biting insects in stored grains (Meena & Lal, 2019, Babatunde, 2015). Spices derived from black pepper seed powders are effective against cowpea bruchid, Tribolium castanuem, on stored finger millet, reduce the growth and infestation of rice weevils and boll weevils, demonstrate toxicity, and significantly reduce the oviposition and emergency of C. subinotatus adults (Nelso & Ntonifor, 2011). Babatunde (2015) and Solomon and Azare (2019) reported that, the use of dried powders of ginger, chili pepper (Capsicum annum), and scale leaves of onion (Allium cepa) are applied to control pests in the field.

Table 2 summarizes the effects of various spices from different plant parts, their chemical components and effects in different pests. The toxicity of a spice in the form of essential oils indicated neurotoxic action with hyperactivity, hyperextension of the legs and abdomen and rapid knock-down effect or immobilization in insects (Boate & Abalis, 2020; Prowse et al., 2006; Zhao et al., 2013). Essential oil from garlic is applied to the bodies of insects, which alters locomotion activity, muscle contractions, and paralysis, resulting in a toxic effect on the insect’s nervous system due to its allicin content. Garlic essential oil, when applied to insects, can cause alterations in locomotion, muscle contractions, and paralysis, causing a toxic effect on the nervous system due to its allicin content (Hamada et al., 2018). Boate and Abalis (2020) and Chaubey (2012) reported that oils of Zingiber officinal rhizomes and Piper cubebaberries showed insecticidal and antifeedant activities against T. castaneum and S. oryzae.

Table 2. Different types of spices with their chemical compounds and characteristics.

Type of spices	Parts used	Chemical compound	Characteristics	Reference
Zingiber	Rhizome	Gingerol, gingeberne, α–zingiberene, citral, vitamin C, β carotene, flavonoids and tannins	Mortality of C. chinensis and repellent against T. castaneum	(Hamada et al., 2018, Rizvi et al., 2016)
Garlic	Bulb	Sulphur-containing compounds (allicin, alliin, and ajoene, citral, geraniol, linalool, α phellandrene and β- phellandrene.	Larvicidal against Spodoptera litura, Ovipositional inhibition against Sitotroga cerealella, Ovicidal against Spodoptera littoralis	(Hamada et al., 2018, Rizvi et al., 2016; Plata-Rueda et al., 2017)
Pepper	Fruit	Piperine, piperidine, piperettine, β- pinene and α-pinene and β-caryophyllene, linalool oxide and α-terpineol	Larvicidal against S. oryzae, Corcyra cephalonica, acaricidal and larvicidal against T. castaneum	(Elgayyar et al., 2001; Khani et al., 2012; Upadhyay & Jaiswal, 2007)
Nutmeg	Seed	Sabinene (32.1), myristicene (2.6%), α-Pinene (13.6%), β-Pinene (12.9%) and terpinen-4-ol.	Larvicidal against second stage larvae of Toxocara canis, inhibits oviposition and adult emergence against C. maculatus, Mortality against S. oryzae adults.	(Kalpana & Sumithra, 2013; Parthasarathy et al., 2008)
Turmeric	Rhizome	Curcumene 5%, curcuminoids, turmerone, zingiberene and cineole.	Adulticide against T. castaneum and S. Zeamais and other storage pest, Contact and fumigant toxicity against R. dominica, S. oryzae and T.castaneum adult weevils, Repellent against T. castaneum	(Gangwar & Tiwari, 2017, Mallavarapu et al., 1995; Wagner et al., 2016)
Caraway	Fruit & Seed	(R)-Carvone (37.9%), D-limonene (26.5%), α-pinene (5.2%) and cis-carveol (5.0%).	Antitermitic activity against Reticulitermes speratus, Contact toxicity against S. zeamais and T. castaneum adults, adulticidal activity against S. oryzae and T. castaneum, ovicidal, larvicidal and adulticidal against C. maculatus, nematicidal activity against Meloidogyne javanica	(Fang et al., 2010; Sahaf et al., 2007)
Clove	Flower and bud	Eugenol (49–87%), β-caryophyllene (4–21%), eugenyl acetate (0.5–21%), methyl eugenol, flavonoids, galloyltannins, phenolic acids and triterpenes.	Fumigant toxicity against S. zeamais and eggs of T. castaneum, S. oryzae	(Elgayyar et al., 2001; Hamada et al., 2018)
Coriander	Seed and leaf	Linalool (57.1%), trans-anethol (19.8%), c-terpinene (3.8%) and geranyl acetate (3.2%).	Larvicidal against T. confusum and C. maculatus, contact toxicity on Diaphorina citri adults, larvicidal against Culex quinquefasciatus, Fumigant activity against S. oryzae adults, C. chinensis	(Knio et al., 2008; Mann et al., 2012; Zoubiri & Baaliouamer, 2014)
Cumin	Fruit	Caryophyllene oxide (6.1%), α-pinene (4.8%), geranyl acetate (4.1%) and âcaryophyllene (3.4%).	Fumigant toxicity against C. maculatus adults, inhibits the growth and fecundity potential of Bactrocera zonata	(Abdul et al., 2011; Farooqui et al., 2005)
Star anise	Dried fruit	Trans-Anethole (94.05%), Limonene (1.74%), Estragole (1.45%), α-trans-Bergamotene (0.72%) and Linalool (0.31 %)	Effective control against adults and eggs of T. Castaneum and suppressed F1 progeny production.	(Farooqui et al., 2005; Ho, 1995)

2.3. Plant-based insecticides and their toxicity on non-target organisms compare with commercial pesticides

As discussed in Sections 2 and 2.1, the toxicity effect of plant-based insecticides on non-targeted organisms is addressed to some extent. Furthermore, some additional recent findings have been reported about the nature of the toxicity of plant-based insecticides or pesticides on non-targeted pests or insects; thus, considering this and comparing it with commercial pesticides is important. Recently, it has become obvious that botanical pesticides are the best alternative to synthetic pesticides to control insects and other pests in agriculture due to their safety to non-targeted organisms and environmental friendliness (Esmaeily et al., 2014). Therefore, after knowing the adverse effects of synthetic pesticides on the environment and other non-target organisms, the researchers have grown interested in botanical pesticides because they are biodegradable and do not leave residues in plant systems (Haritha et al., 2021). In addition, by lowering the usage of synthetic pesticides, there are chances of improving the quality of agricultural products and environmental conditions, avoiding harm to non-target and beneficial organisms like bees and other pollinators. This leads to the use of botanical pesticides in the storage of agricultural products, sustainable agriculture, and house gardens in developing countries. However, synthetic or commercial pesticides have adverse effects on non-targeted organisms such as fish, amphibians, birds, mammals, honeybee pollinators, reptiles, and vertebrates (Gibbons et al., 2016). Human beings are non-targeted organisms; therefore, plant-based chemicals are preferable to synthetic ones due to their different properties. For example, spices are known for their medicinal properties due to their bioactive phytochemicals, including phenolic compounds, carotenoids, sterols, terpenes, alkaloids, and glucosinolates, which possess strong antioxidant capacity. Spices, based on their composition, exhibit varying levels of antibacterial and antioxidant activity (Table 3), making them effective antimicrobial agents and free-radical scavengers (Husain et al., 2019; Husain & Pandey, 2015). Therefore, spices possess therapeutic properties and beneficial pharmacological effects on animals, as well as potential protection against diseases in humans (Islam et al., 2021). Additionally, spice is used to reduce the risk of non-communicable chronic diseases associated with oxidative stress and inflammation (Pistollato & Battino, 2014). The phytochemicals from spices appear to be responsible for the therapeutic effect, and they provide a diversity of health benefits such as anticancer, anti-inflammatory, antibacterial, antiviral, and antioxidant effects (Bower et al., 2016; Herrera et al., 2020; Opara & Chohan, 2014). These indicated that if plant-based compounds or chemicals are encouraged and used as insecticidal and pesticidal agents, directly or indirectly, human beings will get different benefits than non-targeted organisms. For example, cumin has different properties such as antibacterial, antimicrobial, stimulant, antispasmodic, digestive, anti-inflammatory, wound-healing, astringent, constipating, diuretic, revulsive, galactogogue, uterine, and nerve stimulants, and due to these properties, it is used for treating rectal issues, loose stools, gastric issues, providing iron, and promoting a healthy immune system (Mehdizadeh et al., 2017). Fenugreek is a carminative, tonic, aphrodisiac, emollient, antibacterial, used in the treatment of vomiting, fever, anorexia, and colonitis, and utilized as a sedative, astringent, digestive, stomach tonic, diuretic, emetic, expectorant, lactating agent, and tonic (Acharya et al., 2008; Beyzi et al., 2017). Cinnamon has an antipyretic, hypothermic, antiseptic, astringent, anti-inflammatory, digestive, diuretic, carminative, aphrodisiac, deodorant, expectorant, febrifuge, and stomachic properties and it is used as Treatment of intestinal disorders, joint inflammation, menstrual issues, anorexia, inflammation, salivation, and tuberculosis ulcers, as well as in gastric and digestive recipes (Khan et al., 2013). Cardamom, has a Gastroprotection, stimulant, tonic, diuretic, carminative, digestive, expectorant, and cardiotonic properties, and is commonly used in various pharmaceutical preparation (Abu-Taweel, 2018; Kandikattu et al., 2017). Cloves, Cell strengthening, anti-infectious, antiviral, antibacterial, antidiabetic, sedative, antithrombotic, analgesic, ophthalmic, digestive, carminative, stomachic, stimulant, antispasmodic, expectorant, rubefacient, aphrodisiac, appetizer, and emollient properties (Kundu et al., 2014). Black pepper has Antihypertensive, anti-alzheimer’s, antidepressant, antiplatelets, anti-inflammatory, antioxidant, antipyretic, antitumor, antiasthmatic, analgesic, and antimicrobial (Kumar Paswan et al., 2021). The previus authors aslo exihibit that, Nutmeg and mace have a antimicrobial properties with healrt benefits of Flavor pudding and fruit pie, and as a ground state in various baked goods, including cakes, cookies, pies, chocolate, and garam masala.

Table 3. Different botanical bioactive compounds from different plant source with their modes of action.

Types of bioactive	Source/plant	Mode of action	Toxicity	Reference
A-Pinene and bornyl acetate	Aziliaeryngioides (Pau)	Fumigation	Sitophilus granaries (L.) Tribolium castaneum (Herbst)	(Ebadollah & Mahboubi, 2011)
Azadirachtin	Azadirachta indica A. Juss (Meliaceae)	Repellent, antifeedant, nematicidal, sterilant, antifungal, growth regulator	Stored grain pests, aphids	(Morgan, 2009)
Z-asarone	Acorus gramineus (Ogon	Contact	Sitophilus zeamais (Motsch)	(Yingjuan et al., 2008)
Linalool	Ocimum canum (Sim	Antifungal, Repellent	Saccharomyces cerevisiae and Sitophilus oryzae (Linnaeus)	(Germinara et al., 2017)
Eugenol	Ocimum basilicum (Labiatae)	Fumigation or repellent	Pulse beetle (Callosobruchus analis Fabriciuss) and Housefly (Musca domestic	(Mishra et al., 2012)
Carvacrol	Cedrus deodara (Roxb. ex D. Don) G. Don (Pinacea)	Insecticidal	Pulse beetle (Callosobruchus analis.) and Housefly (Musca domestica)	(Park et al., 2003)
(+)-Limonene, myrcene α-phellandrene, α-pinene, bornyl acetate	Chamaecyparis obtuse (Endl.)	Contact	Sitophilus oryzae (Linnaeus) Callosobruchuschinensis (L.)	(Park et al., 2003)
Flavonoids, rotenone isoflavonoids, chalcones, terpenoids Tannins, saponins, steroids, glycosides, and alkaloids	Millettia ferruginea (Hochst.)	Contact	Sitophilus zeamais (Motsch)	(Hiruy & Getu, 2018)
1–8-Cineole	Eucalyptus (Eucalyptus globulus Labiil)	Repellent	Tribolium castaneum (Herbst) and Sitophilus oryzae (Linnaeus)	(Gharsan et al., 2018)
Estragole, (+) fenchone and (E)-anethole	Foeniculum vulgare (Mill)	Contact and fumigation	Sitophilus oryzae (Linnaeus), Callosobruchus chinensis (L.), and Lasioderma serricorne (Fabricius) Sitophilus	(Kim & Ahn, 2001)
Carvone chemotypes LA-13 and LA	Lippia alba (Mill) Lonchocarpus	Contact/and repellent	Sitophilus zeamais (Motsch.) and Tribolium castaneum (Herbst)	(Rajashekar et al., 2012)
Rotenone	Lonchocarpus sp.	Contact/fumigation and repellent	Sitophilus oryzae (L.)	(Bezabih et al., 2022)
Camphor	kilimandscharicum	Repellent	Sitophilus oryzae (L.)	(Jayakumar et al., 2017)
Rotenoids	Tephrosia vogelii	Contact	Sitophilus zeamais	(Koona et al., 2007)
β-Caryophyllene α-humulene cis-Caryophyllene	Lantana camara (L.)	Contact/fumigation and repellent	Sitophilus zeamais (Motsch.) Sitophilus granarius Callosobruchus maculatus (Fabricius)	(Zandi-Sohani et al., 2012)

However, unwanted effects of the excessive use of synthetic pesticides can result in damage to non-target organisms, contamination of food and feed by pesticide residues, a recovery of pests, genetic variety in plants, and adverse effects on biodiversity. Pest management aspects pose economic and environmental challenges due to over-reliance on synthetic pesticides, causing non-target toxicity, residual consequences, and biodegradability issues, necessitating sustainable, cost-effective solutions. On the other hand, botanical pesticide ingredients that work well against a wide range of harmful diseases and pests, are easily obtainable, affordable, quickly biodegradable, and little harmful to beneficiary agents are maybe more significant than anything else. Different plant species have different modes of action against pests and diseases, which can be attributed to differences in their phytochemical composition (Ngegba et al., 2022). Furthermore, the majority of synthetic pesticides react against organisms that are not their intended targets, such as fish, plants, and mammals, posing a risk to consumer health. Moreover, the cost of these products is prohibitive for farmers in developing nations (Multigner et al., 2016; Singh, 2014).

Chlordecone (CLD), a synthetic pesticide used in the French West Indies from 1972 to 1993, is known as the ‘monster of the Antilles’ due to soil and biomass contamination; it also has high steric hindrance and hydrophobicity, making it problematic (Multigner et al., 2010; Souto et al., 2021); polychlorinated biphenyls (PCBs) used from 1926 to 1970 (Rattner, 2009); and the 1, 1, 1-trichloro-2,2-bis(4-chlorophenyl)-ethane (DDT) used from 1939 to 1962 (Pérez-Criado & Bertomeu Sánchez, 2021) that cause adverse effects to non-targeted organisms; and they are non-volatile and less biodegradable. Even though there is an argument that commercial pesticide active substances in conventional agriculture have different non-target effects than the natural active substances in organic agriculture (Burtscher-Schaden et al., 2022).

2.4. Bioactive compounds and their role on mature and immature insect pests

Bioactive compounds like quircetin, quinolone, osajin, lupalbeginen, scandinon, genistein, carvacrol, safole, linalool, 2-heptanol, 4-terpenenol, carvane, thujone, and limonene are found in various plants (Soujanya et al. 2016). They have a big role in reducing insect pest activity during storage. Pure compounds of osajin, lupalbigenin, scandinon, sphaerobioside, genistein, and prenylated isoflavones derived from Derris scandens Benth Caused 100% toxicity to T. castaneum and C. cephalonica after the 10^th and 15^{th days} of treatment (Soujanya et al., 2016, Usha Rani et al., 2013). Jeon et al. (2013) and Soujanya et al. (2016) conducted research on the contact and fumigant toxicity of the methanolic extract of Ruta chalepensis and found that quinoline (0.057 mg/cm2), quinoline-4-carbaldehyde (0.065 mg/cm2), and quinoline-3-carbaldehyde (0.092 mg/cm2) were most toxic to S. oryzae. Other studies showed that plant extracts of Anagallis arvensis L., Hibiscus rosa-sinensis Linn., and Lapsana communis L. can repel T. castaneum, S. oryzae, and R. Dominica up to 50 -60% after 24 hours (Singh et al., 2017; Soujanya et al., 2016). Decaleside II and sitosteryl–D-glucopyranoside from D. hamiltonii and Peltophorum pterocarpum extracts were tested against S. oryzae and T. castaneum, showing toxicity due to easy penetration into insect cuticle (Soujanya et al., 2016). Rajashekar et al., 2012; Soujanya et al., 2016 demonstrated that the contact and fumigant toxicity of methanolic extract from leaves of Lantana camara against S. oryzae (LC50 - 128 μl/l, LD50 - 0.158 mg/cm²) and T. castaneum (LC50 - 178.7 μl/l, LD50 - 0.208 mg/cm²). Other studies conducted by (Fouad et al., 2014; Khani et al., 2012; Soujanya et al., 2016; Zambare et al., 2012) reported that, petroleum ether extract of P. nigrum and Jatropha curcas at concentrations of 2 ∼ 10 μL/g showed strong inhibition on egg hatchability and adult emergence of C. cephalonica with LC50 values of 12.52 and 13.22 μL/mL, respectively. Similiarly, chloroform extract of Argemone mexicana at 4 ml concentration inhibited 60% egg hatching of C. cephalonica (Khani et al., 2012; Soujanya et al. 2016). Whereas the extracts of Tithonia diversifolia at 1% w/w inhibited egg laying and larval mortality of S. cerealella; potentiality due to the presence of sesquiterpenes, lactones (Soujanya et al. 2016). In general, different bioactive compounds extracted from different plants and their parts have different effect on both immature and mature insect pests.

2.5. Mode of actions of botanical compounds

Green pesticides, derived from botanical plants, are recommended for preventing insect pest infestation in stored grain like maize. These bio-pesticides are environmentally friendly and can be applied in layers, dried, ground, or combined with grain. They are safe for humans and the environment, target-specific, and cost-effective. However, they require repeated treatments for optimal control. Botanical plants can affect various insect pests in diverse ways.

Green insecticides’ efficacy is determined by their ability to destroy cells via reactive oxygen intermediates (ROI), alkylation, and oxidation of protein, lipid, and membrane, inactivation of the channel protein, and distribution of membrane potentials by interacting with the electron transport chain in the mitochondrial membrane, depending on the physiological characteristics of the insect species and types of insecticidal plants (Boate & Abalis, 2020). Plant extract largely harms the cellular structure of the insect midgut epithelium and, to a lesser extent, the gastric caeca, columnar cells, peritrophic membrane, striated border, and longitudinal muscles. This causes storage bug pest mortality as well as loss of nerve cell membrane activity, which leads to nerve function loss, paralysis, and death. Paralysis knockdown is caused by altering the sodium and potassium ion exchange pathways in insect nerve fibers and interfering with normal nerve impulse transmission (Boate & Abalis, 2020). This shows that understanding the type, mode, and action of bioactive botanical compounds can help prevent insecticide resistance in specific insect pests. The sources, modes of action, and toxicity of various botanical bioactive compounds from various plant sources are summarized in detail in Table 3. Fumigation of stored grains with a-pinene and bornyl acetate from aziliaeryngioides (Pau) plant sources is toxic to Sitophilus granaries and Tribolium castaneum (Ebadollah & Mahboubi, 2011). On the other hand, rotenone, a bioactive substance from Lonchocarpus sp., is toxic to Sitophilus oryzae through a combination of mode of actions such as contact, fumigation, and repellant.

2.6. The sub-lethal effects of plant-based insecticides

Insecticides can kill pests when a lethal amount is administered, but to fully understand their impact, sub-lethal effects must also be considered. Because pesticides naturally break down after being applied to crops, insects are frequently exposed to sub-lethal amounts of the chemicals (Desneux et al., 2007; Mostafiz et al., 2020). Historically, acute lethal dosages have been crucial for assessing pesticide toxicity to arthropods. However, sub-lethal effects and direct mortality must also be considered for a comprehensive assessment (Desneux et al., 2007). Furthermore, the study conducted on Apis mellifera L. to assess the toxicity and sublethality of several oils such as andiroba oil, citronella oil, eucalyptus oil, garlic extract, neem oil, and rotenone reveals that only andiroba oil was shown to be non-lethal to adult workers of A. mellifera. Nevertheless, neem oil, garlic extract, and andiroba oil showed acute toxicity to bee larvae. Adult workers of A. mellifera were repelled by all these botanical pesticides (Xavier et al., 2015). However, there have been reports of biopesticides having negative impacts on natural enemies. For example, the biological pesticide spinosad, which originated from the Saccharopolyspora spinosa bacteria, showed an important level of toxicity towards adult parasitoids. Ishii’s Trichogramma chilonis (Hymenoptera: Trichogrammatidae) (Sattar et al., 2011); Hyposoter didymator (Thunberg) (Hymenoptera: Ichneumonidae) (Nozad-Bonab et al., 2021); and Bracon nigricans (Hymenoptera: Braconidae) (Biondi et al., 2012).

3. Conclusion

Botanical pesticides, such as essential oils and plant-based powders, offer a safer and more sustainable alternative to synthetic insecticides for managing pests in grain storage. These natural chemicals extracted from plants have shown effectiveness against resistant pests and have lower environmental persistence. Recently, humans have been highly affected by synthetic pesticides and insecticides due to their toxicity. Thus, spices derived from plants have insecticidal properties and offer health benefits due to their bioactive phytochemicals. Even though botanical plants are a safe option for preventing insect pest infestations in stored grain, repeated treatments may be necessary for optimal control. For non-targeted organisms, botanical plant-based pesticides or insecticides are the best alternatives. Understanding the sub-lethal and lethal numbers of botanical insecticides is also important, and we have to consider preventing non-targeted and killing or reducing targeted insects during integrated pest management of grain storage.

Future outlooks

Further research is required on the effectiveness and modes of action of botanicals as well as the specific physiological characteristics of different insect species, which are crucial before and during grain storage. Furthermore, the maximum and optimum concentrations of botanical insecticides and pesticides are not yet studied and applied aggressively, especially in developing countries, including Ethiopia. There are different potential botanical plants that have been used as traditional medicine due to their bioactive substances, but few reviews have been reported about whether they are or are not preventing pests and insects during grain storage.

Author contributions

ZTA: Conceptualization, Writing–original draft. MAA: Conceptualization, review & editing. BDA: Conceptualization, Supervision, Writing – review & editing.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

No data was used for this review paper.

Additional information

Funding

This review work did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Notes on contributors

Zemenu Tadesse Adimas

Zemenu Tadesse Adimas is a lecturer and young researcher in the department of Food Engineering. His research interest is in food processing, food storage, dairy processing technology and so on.

Mekuannt Alefe Adimas

Mekuannt Alefe Adimas is lecturer and young researcher and also a PhD candidate in the department of Food Engineering. His research interest is food processing, food storage, dairy processing technology, indigenous technologies, Food hygiene and safety and so on.

Biresaw Demelash Abera

Biresaw Demelash Abera is an Assistant professor and a young researcher in the department of Food Engineering. His research interest is in emerging technologies in food processing and safety, food analogs, Food hygiene and safety, Food fortification, Nutrition, and so on.