Essential Oils Extracted from Different Species of the Lamiaceae Plant Family as Prospective Bioagents against Several Detrimental Pests.

On the basis of the side effects of detrimental synthetic chemicals, introducing healthy, available, and effective bioagents for pest management is critical. Due to this circumstance, several studies have been conducted that evaluate the pesticidal potency of plant-derived essential oils. This review presents the pesticidal efficiency of essential oils isolated from different genera of the Lamiaceae family including Agastache Gronovius, Hyptis Jacquin, Lavandula L., Lepechinia Willdenow, Mentha L., Melissa L., Ocimum L., Origanum L., Perilla L., Perovskia Kar., Phlomis L., Rosmarinus L., Salvia L., Satureja L., Teucrium L., Thymus L., Zataria Boissier, and Zhumeria Rech. Along with acute toxicity, the sublethal effects were illustrated such as repellency, antifeedant activity, and adverse effects on the protein, lipid, and carbohydrate contents, and on the esterase and glutathione S-transferase enzymes. Chemical profiles of the introduced essential oils and the pesticidal effects of their main components have also been documented including terpenes (hydrocarbon monoterpene, monoterpenoid, hydrocarbon sesquiterpene, and sesquiterpenoid) and aliphatic phenylpropanoid. Consequently, the essential oils of the Lamiaceae plant family and their main components, especially monoterpenoid ones with several bioeffects and multiple modes of action against different groups of damaging insects and mites, are considered to be safe, available, and efficient alternatives to the harmful synthetic pesticides.


Introduction
Synthetic chemicals such as carbamates, pyrethroids, organochlorines, and organophosphates have played a principal role in the plant protection strategies against agroindustrial and medicinal arthropod pests within the past and present century. However, there are public concerns all over the world about the negative side effects of detrimental chemicals such as residues on food and in drinking water, acute or chronic toxicity to humans and other non-target organisms, outbreaks of secondary pests by abolishing their natural enemies, and the emergence of pest resistance [1][2][3]. Accordingly, there is an imperative demand to diminish chemical pesticides and reveal safe and potential alternatives.
In recent years, the utilization of biopesticides in pest management has been progressing. Three categories of biopesticides have been identified by the United State Environmental Protection Agency as follows: biochemical biopesticides such as botanical pesticides and other natural compounds,

Genera Species Lethal/SubLethal Effects and Targeted Arthropod Pests
S. pratensis L. Contact and fumigant toxicity against T. castaneum and C. maculatus [67]. S. sclarea L.

Thymus kotschyanus
Camphene ( Terpenes which are large and diverse natural hydrocarbons are commonly classified according to the number of isoprene units C 5 H 8 , to hemi-(one unit), mono-(two units), sesqui-(three units), di-(four units), ses-(five units), tri-(six units), tetra-(8 units), and polyterpenes (n units) [85]. Although the majority of these compounds are found in plant essential oils, the more complex terpenes, such as lanosterol, exist in animals. Furthermore, each terpene can be oxygenated and modified to terpenoid hydrocarbons [86,87]. In general, there are high amount of terpenes in the essential oils of the Lamiaceae family. The main components in the essential oils of the Lamiaceae plants from acyclic, cyclic, and bicyclic monoterpenes; monoterpenoids; sesquiterpenes; sesquiterpenoids; and phenylpropanes' groups [88] possess promising pesticidal properties against several arthropod pests (Table 3 and Figure 1).   Table 3 summarizes the bioactivity of the main components identified in the essential oils of Lamiaceae as a pesticide agent against insect pests. It has been found that the monoterpenoids had more fumigant toxicity than monoterpenes against the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) [90]. The ketone, aldehyde (such as camphor, carvone, fenchone, and menthone), and epoxide (such as 1,8-cineole and limonene oxide) derivatives of monoterpenoids have also been found to be more toxic than alcohol and ester groups (such as borneol, linalool, and menthol) [90]. The essential oil of Salvia leriifolia Benth (Lamiaceae) showed the highest insecticidal activity as fumigant and contact agents against adults of C. maculatus, S. oryzae, and T. castaneum [100]. It was indicated that among eight terpenes including 1,8-cineole, carvacrol, eugenol, menthone, linalool, limonene, β-pinene, and α-pinene, the cyclic monoterpenoids carvacrol and menthone had the most fumigant toxicity against the cowpea weevil, C. maculatus [101]. In another study, the fumigant and contact toxicities of eugenol (a phenylpropanoid), ρ-cymene and α-pinene (monoterpenes), and menthone, α-terpinene, and terpinen-4-ol (monoterpenoids) were evaluated against T. castaneum adults. Terpinen-4-ol and α-terpinene as cyclic terpenes had the most fumigant toxicity followed by menthone, ρ-cymene, α-pinene, and eugenol [96]. In contrast, eugenol was the most toxic compound in the contact bioassay. The fumigant toxicity of some essential oils' components was evaluated against bed bugs (Cimex lectularius L.) and it was found that cyclic  Table 3 summarizes the bioactivity of the main components identified in the essential oils of Lamiaceae as a pesticide agent against insect pests. It has been found that the monoterpenoids had more fumigant toxicity than monoterpenes against the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) [90]. The ketone, aldehyde (such as camphor, carvone, fenchone, and menthone), and epoxide (such as 1,8-cineole and limonene oxide) derivatives of monoterpenoids have also been found to be more toxic than alcohol and ester groups (such as borneol, linalool, and menthol) [90]. The essential oil of Salvia leriifolia Benth (Lamiaceae) showed the highest insecticidal activity as fumigant and contact agents against adults of C. maculatus, S. oryzae, and T. castaneum [100]. It was indicated that among eight terpenes including 1,8-cineole, carvacrol, eugenol, menthone, linalool, limonene, β-pinene, and α-pinene, the cyclic monoterpenoids carvacrol and menthone had the most fumigant toxicity against the cowpea weevil, C. maculatus [101]. In another study, the fumigant and contact toxicities of eugenol (a phenylpropanoid), -cymene and α-pinene (monoterpenes), and menthone, α-terpinene, and terpinen-4-ol (monoterpenoids) were evaluated against T. castaneum adults. Terpinen-4-ol and α-terpinene as cyclic terpenes had the most fumigant toxicity followed by menthone, -cymene, α-pinene, and eugenol [96]. In contrast, eugenol was the most toxic compound in the contact bioassay. The fumigant toxicity of some essential oils' components was evaluated against bed bugs (Cimex lectularius L.) and it was found that cyclic monoterpenoids thymol and carvacrol had much more fumigant toxicity than bicyclic monoterpenoids camphor and 1,8-cineole, cyclic monoterpene limonene, bicyclic monoterpene α-pinene, and phenylpropanes cinnamaldehdye, citronellic acid, eugenol and methyl eugenol [93]. Consequently, although the high insecticidal effects of monoterpenes, monoterpenoids, sesquiterpenes, sesquiterpenoids, and phenylpropanes has been reported, on the one hand, the monoterpenoids, especially cyclic monoterpenoids, showed the most toxic effects. On the other hand, minor structural differences cause major alterations in the toxic effects. However, susceptibility of the considered pests can be affected by the synergistic effects of other minor components [102].
Apart from insecticidal activity, the acaricidal efficacy of essential oils extracted from some Lamiaceae species have also been reported. The acaricidal effects of the essential oils of S. hortensis, Mentha pulegium L., Mentha viridis L., R. officinalis, and Z. multiflora was demonstrated against Tetranychus turkestani Ugarov and Nikolskii (Acari: Tetranychidae) [41]. Some of the constituents of R. officinalis essential oil were toxic against Tetranychus urticae Koch. (Acari: Tetranychidae) on bean and tomato plants. However, a synergistic effect among the active and inactive constituents was observed when they were mixed with each other [103].
Since larva is the damaging stage of insects, evaluating the larvicidal effect of essential oils is of great importance. For example, the larvicidal potential of essential oils of different Lamiaceae species has been reported in literature studies. The oil of Mentha piperita L. (Lamiaceae) was found to be an effective larvicidal agent against the housefly, Musca domestica (L.) (Diptera: Muscidae) [104]. The essential oil of M. piperita had higher larvicidal pupicidal than M. citrata Ehrh oil in contact and fumigant applications against M. domestica [105]. Similar results were obtained by the essential oil of M. piperita which had the most promising larvicidal against Anopheles stephensi Liston and Aedes aegypti L. (Diptera: Anophelinae) among 25 tested plant essential oils [106]. The larvicidal effects of M. piperita essential oil with a high quantity of bioactive monoterpenes were also reported on the M. domestica and An. stephensi larvae [107]. In other research with pure components, larvicidal effects of fifty constituents from terpene, terpenoid, and phenylpropanoid groups against Culex quinquefasciatus Say were assessed and it was demonstrated that carvacrol and thymol as cyclic monoterpenoids were the most toxic against larvae among all tested components [89].

Mode of Pesticidal Action
The mechanism of action of Lamiaceae essential oils and their components on pests is not completely recognized but, based on their diverse lethal and sublethal effects, it is obvious that these natural agents affect in different ways. The difference in the pesticidal potential of these agents could also be related to differences in their structures. For example, the higher toxicity of oxygenated monoterpenes as compared with the non-oxygenated ones could be due to the different structures of these components. Furthermore, according to recent findings, different physiological and behavioral modes of action of essential oils and their components have been reported. For example, inhibition of adenosine triphosphatases (ATPases), acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) [76,96], and distribution in the octopamine and gamma-aminobutyric acid receptors (GABArs) have been documented [112]. Given that octopamine receptors are invertebrates-specific, the use of essential oils in pest management, with this mode of action, can be considered to be safe bioagents for mammals [112]. Some other studies revealed that they can diminish esterase and glutathione S-transferases (GSTs) activities and total carbohydrate, lipid, and protein contents in the pests [73,113]. Detoxifying enzymes such as esterase and glutathione S-transferases have a significant effect on pest resistance before pesticides. Consequently, impairing the function of such enzymes can reduce the likelihood of pest resistance to essential oils [114]. Furthermore, histological changes in the epithelial cells of insects' midguts [115], and even a diminution in the respiration rate of pests have also been reported [116]. Generally, because of the wide pesticidal effects and several modes of action of the essential oils and their derivatives, pests have very few changes to resistant before these safe agents, and therefore they are very valuable in pest management strategies.

Conclusions
The overuse of synthetic chemicals in pest management programs has caused several side effects, such as contamination of drinking water; residues on food; acute or chronic negative effects on mammals and non-target organism including bird, bees, parasitoids, and predators; and the development of pest resistance. Due to this circumstance, researchers have focused on the application of plant-derived essential oils from different plant genera and families in recent years. Although the pesticidal properties of essential oils extracted from different species of Apiaceae, Lamiaceae, Myrtaceae, Rutaceae, Verbenaceae, and Zingiberaceae families have been recognized, the present review focused on the Lamiaceae species based on their availability and diversity. Along with these advantages, plant essential oils generally are nontoxic to mammals and other vertebrates. Furthermore, based on their multiple modes of action, development of pests' resistance against them is very low. Consequently, the Lamiaceae plant essential oils and their components with a wide range of lethal and sublethal effects against different damaging insects and mites in the field, greenhouse and storage conditions, have great potential in pests' management strategies and are considered to be safe, available, and eco-friendly alternatives to the synthetic chemicals. Indeed, the most important issue to be considered for the application of essential oils is their rapid degradation under the influence of air and light, which could be overcome by encapsulation or controlled release techniques. Briefly, the essential oils and their components, as core materials, are protected from adverse environmental factors in these techniques. Emulsifying the essential oils and components through adjuvants is another solution to improve pesticidal efficiency. However, their direct and indirect effects on the other non-target organisms such as honeybees and natural biocontrol agents and the economic aspects must be assessed before commercialization.