Molecular Entomology 2024, Vol.15, No.2, 61-68 http://emtoscipublisher.com/index.php/me 62 various natural plant volatiles, their mechanisms of action against maize pests, and the practical implications for farmers and agricultural stakeholders. 2 Natural Plant Volatiles: Definition and Types Natural plant volatiles are organic compounds emitted by plants that can have various ecological roles, including attracting pollinators, repelling herbivores, and communicating with neighboring plants. These compounds are typically low molecular weight and highly volatile, allowing them to disperse easily through the air. 2.1 Essential oils and their chemical composition Essential Oils (EOs) are concentrated hydrophobic liquids containing volatile chemical compounds from plants. They are typically extracted through steam distillation and are composed of a complex mixture of terpenes, terpenoids, and phenolics. Essential oils are known for their insecticidal, repellent, and growth-reducing effects on various pests. For instance, essential oils from plants in the Myrtaceae, Lauraceae, Lamiaceae, and Asteraceae families have been shown to be effective in pest control due to their neurotoxic effects on insects (Isman et al., 2011). The major constituents of these oils, such as monoterpenes and sesquiterpenes, play a significant role in their bioactivity (Patiño-Bayona et al., 2021). 2.2 Terpenoids, alkaloids, and phenolics in plant volatiles Terpenoids, alkaloids, and phenolics are key classes of compounds found in plant volatiles. Terpenoids, including monoterpenes and sesquiterpenes, are the most common and are known for their roles in plant defense and communication. For example, terpenes like β-pinene, β-myrcene, and linalool have been identified in maize plants and are involved in repelling or attracting pests (Boncan et al., 2010; Piesik et al., 2011). Alkaloids and phenolics also contribute to the defensive properties of plant volatiles, although they are less commonly studied in the context of volatiles compared to terpenoids (Regnault-Roger et al., 2012). 2.3 Volatile organic compounds (VOCs) and their pest-repelling properties Volatile Organic Compounds (VOCs) are a broad category of compounds that include terpenoids, Green Leaf Volatiles (GLVs), and other secondary metabolites. VOCs play a crucial role in plant-insect interactions by acting as repellents or attractants. For instance, maize plants emit VOCs such as (Z)-3-hexenal, (E)-2-hexenal, and methyl salicylate in response to herbivore attack, which can attract natural enemies of the herbivores or repel the herbivores themselves (Mérey et al., 2011). Additionally, fungal VOCs like 1-octen-3-ol have shown potential as biopesticides by repelling pests and inhibiting fungal growth (Herrera et al., 2015). The use of synthetic VOCs in field experiments has demonstrated their ability to modify pest behavior without adversely affecting natural enemies, highlighting their potential in integrated pest management strategies (Lamy et al., 2017). 3 Mechanism of Action of Plant Volatiles on Insect Pests 3.1 Disruption of insect olfaction and behavior Plant volatiles play a crucial role in disrupting the olfactory senses and behavior of insect pests. These volatiles can interfere with the insects' ability to locate their host plants, thereby reducing the likelihood of infestation. For instance, certain volatiles emitted by maize plants in response to herbivore damage can attract natural enemies of the pests, thereby indirectly protecting the plants (Mérey et al., 2011). Additionally, the application of synthetic Herbivore-Induced Plant Volatiles (HIPVs) has been shown to attract beneficial insects such as parasitoids and predators, which can help in controlling pest populations (Simpson et al., 2011). This disruption of olfaction and behavior is a key mechanism by which plant volatiles contribute to pest management. 3.2 Insect repellency and attractant effects Plant volatiles can act as both repellents and attractants for different insect species. For example, a meta-analysis revealed that while attractants significantly increased insect herbivore abundance, repellents did not show a significant effect, possibly due to the limited number of field studies focusing on repellents (Szendrei and Rodriguez-Saona, 2010). Specific volatiles such as S-linalool and (E)-β-caryophyllene have been found to attract predators and parasitoids while repelling certain pests like the rice brown planthopper (Xiao et al., 2012).
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