Acaricidal, Insecticidal, and Nematicidal Efficiency of Essential Oils Isolated from the Satureja Genus

The overuse of synthetic pesticides in plant protection strategies has resulted in numerous side effects, including environmental contamination, food staff residues, and a threat to non-target organisms. Several studies have been performed to assess the pesticidal effects of plant-derived essential oils and their components, as partially safe and effective agents, on economically important pests. The essential oils isolated from Satureja species are being used in medicinal, cosmetic, and food industries. Their great potential in pest management is promising, which is related to high amounts of terpenes presented in this genus. This review is focused on the acute and chronic acaricidal, insecticidal, and nematicidal effects of Satureja essential oil and their main components. The effects of eighteen Satureja species are documented, considering lethality, repellency, developmental inhibitory, and adverse effects on the feeding, life cycle, oviposition, and egg hatching. Further, the biochemical impairment, including impairments in esterases, acetylcholinesterase, and cytochrome P450 monooxygenases functions, are also considered. Finally, encapsulation and emulsification methods, based on controlled-release techniques, are suggested to overcome the low persistence and water solubility restrictions of these biopesticides. The present review offers Satureja essential oils and their major components as valuable alternatives to synthetic pesticides in the future of pest management.


Introduction
Although synthetic chemicals have been considered as the pest management strategy so far, their overuse has led to several side effects. These include soil and groundwater pollution, toxic residues on the food stuffs, pest resistance, outbreak of secondary pests, and harmful effects on non-target organisms such as fish, bees, predators, and parasites [1][2][3][4].
The plant essential oils as low-risk agents are recommended alternatives to chemical pesticides [5,6]. Essential oils are complex mixtures of aromatic and aliphatic compounds, which mainly consist of hydrocarbon monoterpenes, monoterpenoids, hydrocarbon sesquiterpenes, and sesquiterpenoids, and can be made by all plant parts, such as flowers, seeds, leaves, stems, and bark [7]. Essential oils are composed by plants as secondary metabolites with anti-herbivore activity, resulted in critical defense strategies against herbivorous pests along with other significant roles, such as allelopathic plant-plant interactions and attraction of pollinators [8]. Hence, the possibilities of pest resistance indicated that the essential oil of S. sahendica had a significant synergistic effect with entomopathogenic fungus Beauveria bassiana against the cowpea weevil, Callosobruchus maculatus (Fabricius). Table 1. Reported acaricidal, insecticidal, and nematicidal effects of the essential oils isolated from different Satureja species.

Pests
Satureja Species Bioassay and Target Pest Efficiency

S. aintabensis Davis
Contact assay (on treated filter papers) against the adult females of the turnip aphid (Lipaphis pseudobrassicae (Davis)).
Significant toxicity with LC 50 (lethal concentration to kill 50% of tested insects) of 1.7 mg/mL after 1 h [29].

S. bachtiarica Bung
Aqueous suspension of essential oil against the third-and fourth-instar larvae of the Asian malaria mosquito (Anopheles stephensi) and filariasis vector (Culex quinquefasciatus Say).
The larval mortality of 100% at the concentration of 160 ppm after 24 h [30].
Fumigant and repellency assays (by impregnated filter papers in glass vials and Petri dishes, respectively) against the adults of red flour beetle (Tribolium castaneum (Herbst)).

S. cilicica Davis
Contact assay (on treated filter papers) against the Colorado potato beetle (Leptinotarsa decemlineata Say).
The knockdown rate of 100% at the concentration of 20.0 µL/L after 0.5 h [32].
Contact assay (on treated filter papers) against L. decemlineata.
S. hortensis L. Aqueous suspension of essential oil against the larvae of the C. quinquefasciatus.
The mortality of 100% at the concentration of 20.0 µL/L after 24 h [34] Fumigant assay (by impregnated filter papers) against the cotton whitefly (Bemisia tabaci) on the eggplant leaves.
The 100% mortality of adult females at 2.4 mL/cm 3 of essential oil after 24 h [35].
Fumigant assay (by impregnated filter papers) against the adults of B. tabaci on cucumber leaves.
The mortality of 100% at 2 µL/L of essential oil after 12 h [36].
Contact assay (on treated filter papers) against the adults of C. maculatus.
Toxic to the adults with LC 50 values of 5.36 and 6.41 µL/cm 2 on the males and females, respectively [37].
Fumigant assay (by impregnated filter papers) against the adults of C. maculatus.
The 91.2% adult mortality at 60 mL/L and the 94.5% egg mortality at 4.3 mL/L of essential oil after 24 h [38]. Fumigant assay (by impregnated filter papers) against the adults of maize weevil (Sitophilus zeamais Motschulsky).
The 100% mortality at the concertation of 10 µL/L after 96 h exposure time [39].
Significant reduction in the relative growth (0.01 mg/day) and consumption (0.31 mg/day) rates of larvae treated by 0.22 µL/cm 2 of essential oil compared to control (0.05 and 0.10 mg/day, respectively) (p < 0.05) [41]. In-vivo repellent assay (by counting the number of bites on the back of rabbits) against the adult females of A. stephensi.
A protection time of 4.16 h at ED 50 (effective dose) of 5.63 mg/cm 2 [42].

S. khuzestanica Jamzad
In vivo mosquito repellents assay for human skin (from elbow to wrist) against the adults of A. stephensi.
Significant reduction in the number of mosquito bites compared to the control group (p < 0.01) [51].
Toxicity assay (by impregnated potato leaves in Petri dishes) on the adults of L. decemlineata.
Significant mortality of the fourth-instar larvae and adults with LC 50 values of 23.36 and 167.96 ppm, respectively [52]. Fumigant and repellent assays (by impregnated filter papers in glass vials and Petri dishes, respectively) against the adults of T. castaneum.
Fumigant assay (by impregnated filter papers) against the fourth-instar larvae of T. absoluta.
Aqueous suspension of essential oil on the fourth-instar larvae of common house mosquito (Culex pipiens L.).
Repellent assay (by treated green bean leaves in Petri dishes) on the Western flower thrips (Frankliniella occidentalis).
Contact assay (topical application) against the fruit fly (Drosophila suzukii (Matsumura)).  Significantly toxic with KT 50 value (time to 50% knockdown) of 36.06 min at 60 µL of essential oil concentration [56]. Repellent assay (by treated filter papers in Petri dishes) against the nymphs of kissing bug (Triatoma infestans Klug).

S. rechingeri Jamzad
Fumigant and repellency assays (by impregnated filter papers in glass vials and Petri dishes, respectively) against the adults of T. castaneum.
Fumigant assay (by impregnated filter papers) against the fourth-instar larvae of T. absoluta.

S. sahendica Bornm
Fumigant assay (by impregnated filter papers) against the adults of C. maculatus.
The mortality of 100% at concertation of 10 µL/L after 96 h exposure time [39].
Contact assay (on treated filter papers) against L. decemlineata.
S. spinosa L. Aqueous suspension of essential oil on the fourth-instar larvae C. pipiens.
S. thymbra L. Aqueous suspension of essential oil on the fourth-instar larvae C. pipiens.
Significant adulticidal toxicity (LC 50 = 13.92 µL/L after 12 h) and reduction in the larval and adult emergence and egg production compared to control groups (p < 0.05) [60]. Fumigant (by impregnated filter papers on the adults) and aqueous suspension (on the larvae) assays on African malaria mosquito (Anopheles gambiae Giles).
The 100% mortality of adults and larvae at 32.2 µg/mL and 3 mg/mL of essential oil respectively, after 24 h [61].
Spraying on grape leaves against the nymphs and female adults of the vine mealybug (Planococcus ficus (Signoret)).

S. khuzestanica
Fumigant (by impregnated filter papers) and repellency assays (by treated leaf discs) against T. urticae in Petri dishes.

S. sahendica
Fumigant assay (by impregnated filter papers) against T. urticae on bean leaf discs.

S. thymbra
Fumigant assay (by treated cotton wick) on the adults of the Mediterranean tick (Hyalomma marginatum).
The 100% paralysis of the second-stage juveniles (J2) of both species at the concentration of 2000 µL/L after 96 h [68].

S. montana
Immersion of the mixed stages of pine wood nematode (Bursaphelenchus xylophilus Nickle) in aqueous suspension of essential oil.
The 100% mortality of nematodes exposed to a 2 mg/mL solution after 24 h [69].
Spraying of the aqueous suspension of essential oil on B. xylophilus co-cultured with Pinus pinaster shoot.
Significant decrease in the population growth of nematode compared to the control groups (p < 0.05) [70]. Spraying of the aqueous suspension of essential oil on the Columbia root-knot nematode (Meloidogyne chitwoodi Golden) co-cultured with Solanum tuberosum hairy roots.
Significant decrease in the population growth of nematode compared to the control groups (p < 0.05) [71].
Furthermore, as shown in Table 1, in addition to agricultural pests, the acute toxicity and repellent action of Satureja essential oils against larvae and adults of blood-sucking mosquitos that carry pathogenic agents were also approved. For example, high susceptibility of the Asian malaria mosquito (A. stephensi) and the filariasis vector mosquito (C. quinquefasciatus) to the essential oil of S. bachtiarica was reported, in which 100% larval mortality of both insects was attained by the concentration of 160 ppm after 24 h exposure time [30].
The identified compounds in the essential oils of Satureja species are categorized in the monoterpene hydrocarbon, monoterpenoid, sesquiterpene hydrocarbon, sesquiterpenoid, and phenylpropanoid groups (see Table 3). Indeed, the majority of recognized compounds are in the monoterpene group, with lower molecular weight than others, and only three compounds belong to other categories. There is sufficient evidence that the monoterpenes, especially monoterpenoids, have high pesticidal properties, and some novel and reliable outcomes in this field are shown in Table 3. For example, the toxicity of thymol, as one of main components in several species of the Satureja genus, was reported against the African cotton leafworm (Spodoptera littoralis Boisduval), the bed bugs (Cimex lectularius L.), the Colorado potato beetle (Leptinotarsa decemlineata Say), the granary weevil (Sitophilus granarius (L.)), the green peach aphid (Myzus persicae (Sulzer)), and the root-knot nematode (Meloidogyne javanica (Treub) Chitwood) [73,76,77]. It can be concluded from these studies that the presence of higher total monoterpenoid content of essential oils had a positive correlation with their pesticidal activity [78][79][80][81]. Thus, the acaricidal, insecticidal, and nematicidal effects of Satureja essential oils may be related to the high amounts of compounds listed in Table 3. It was also demonstrated that the phenolic monoterpenoids such as thymol with CH(CH 3 ) 2 functional group displayed significantly higher pesticidal effects compared to other terpenes, such as carvacrol and eugenol with CH 3 and OCH 3 functional groups, respectively [82,83]. However, the synergistic acaricidal, insecticidal, and nematicidal effects of minor components such as αand β-pinene, camphor, menthol, sabinene, and thujene should also be considered [84][85][86][87]. For instance, the synergistic insecticidal action of terpenes that have methyl functional groups such as p-cymene and limonene with borneol is another consideration already reported by Pavela [83]. p-cymene and limonene with borneol is another consideration already reported by Pavela [83]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].
The inhibition of acetylcholine esterase and insecticidal activity on the rice weevil (Sitophilus oryzae (L.)) [87]. p-cymene and limonene with borneol is another consideration already reported by Pavela [83]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].
The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae p-cymene and limonene with borneol is another consideration already reported by Pavela [83]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].
The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87]. p-cymene and limonene with borneol is another consideration already reported by Pavela [83]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].
The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87]. p-cymene and limonene with borneol is another consideration already reported by Pavela [83]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].
The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87]. Fumigant and contact toxicity, and acetylcholine esterase inhibition activity against the German cockroach (Blattella germanica (L)) [89].
The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].

β-Myrcene
The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].
Terpinene-4-ol C10H18O 154.25 The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].
Terpinene-4-ol C10H18O 154.25 The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87]. The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].
Sesquiterpene hydrocarbon The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].
Sesquiterpene hydrocarbon The inhibition of acetylcholine esterase and insecticidal activity on S. oryzae [87].

Modes of Action of Essential Oils and Their Components
The acetylcholinesterase (AChE) is actively involved in metabolic conversion of 'acetylcholine' in the synaptic cleft of arthropods and has two catalytic and peripheral target sites. The insect-specific cysteine residue positioned at the acetylcholinesterase active site is a proposed target site for developing insecticides to reduce off-target toxicity [94]. On the other hand, inhibition of pest-specific acetylcholinesterase will decrease the risk of utilized pesticides on non-target organisms, such as mammals [94]. Some essential oils and compounds are reported to bind with these target sites to inhibit the AChE action [95][96][97]. Park et al. [26] revealed that the essential oil of S. montana had significant AChE inhibitory activity against the fruit fly (Drosophila suzukii (Matsumura)), along with high toxicity. The inhibition of AChE leads to acetylcholine accumulation, hyperactivity, paralysis, and death of the pest. Along with terpenes, the well-known phenylpropane estragole has also shown AChE inhibitory effects [98,99]. It should be noted that the AChE inhibition can occur in both contact and fumigation methods of used essential oils [100,101]. Octopamine, as a neurotransmitter, neuromodulator, and hormone, is one of the important biogenic amines in invertebrates and is released at times of high energy demands [102]. Octopamine receptor alteration is considered as another mode of action of essential oils or their components [103]. The blockage of gamma-amino butyric acid (GABA) and nicotinic acetylcholine (nAChR) receptors has also been documented in some studies [97,104].
Beside the neurotoxic modes of pesticidal action of essential oils and compounds, there are several studies indicating enzymatic and non-enzymatic effects. The destructive effects of essential oils and their compounds on esterases and glutathione S-transferases (GSTs) as imperative detoxifying enzymes in arthropod pests are reported [88,105,106]. Disruption of the function of detoxifying enzymes may reduce the probability of pest resistance [107], and this has been clearly depicted by essential oils and their components. Farahani et al. [27] showed that the essential oil of S. khuzestanica had adverse effects on cytochrome P450 monooxygenases (P450, responsible for the oxidative metabolism of a variety of xenobiotics and endogenous compounds) function of two spotted spider mites (Tetranychus urticae Koch), along with toxic and repellent activities. The adverse effects of these agents on digestive enzymes such as lipases, proteases, α-amylases, α-glucosidases, and β-glucosidases were also reported [106], which can be very effective in reducing the nutritional efficiency of pests. Effects on energy reservoirs of the pest by decreasing the protein, glucose, and triglyceride contents and disrupting the action of immunological and hematological parameters are the other reasons to approve the multiple modes of action of these eco-friendly bio-pesticides [108,109].

Proposed New Formulations for Greenhouse and Field Applications
Although great potential for acaricidal, insecticidal, and nematicidal activity of Satureja essential oils and compounds have been reported, limitations such as susceptibility to light, moisture, oxygen, and temperature may restrict their application in the pest management strategies [5]. Indeed, the use of essential oils and their components in noncrop agriculture in the management of stored product pests, flies, and cockroaches is effective [110]. Additionally, the larvicidal activity of essential oils by treating standing wa-

Modes of Action of Essential Oils and Their Components
The acetylcholinesterase (AChE) is actively involved in metabolic conversion of 'acetylcholine' in the synaptic cleft of arthropods and has two catalytic and peripheral target sites. The insect-specific cysteine residue positioned at the acetylcholinesterase active site is a proposed target site for developing insecticides to reduce off-target toxicity [94]. On the other hand, inhibition of pest-specific acetylcholinesterase will decrease the risk of utilized pesticides on non-target organisms, such as mammals [94]. Some essential oils and compounds are reported to bind with these target sites to inhibit the AChE action [95][96][97]. Park et al. [26] revealed that the essential oil of S. montana had significant AChE inhibitory activity against the fruit fly (Drosophila suzukii (Matsumura)), along with high toxicity. The inhibition of AChE leads to acetylcholine accumulation, hyperactivity, paralysis, and death of the pest. Along with terpenes, the well-known phenylpropane estragole has also shown AChE inhibitory effects [98,99]. It should be noted that the AChE inhibition can occur in both contact and fumigation methods of used essential oils [100,101]. Octopamine, as a neurotransmitter, neuromodulator, and hormone, is one of the important biogenic amines in invertebrates and is released at times of high energy demands [102]. Octopamine receptor alteration is considered as another mode of action of essential oils or their components [103]. The blockage of gamma-amino butyric acid (GABA) and nicotinic acetylcholine (nAChR) receptors has also been documented in some studies [97,104].
Beside the neurotoxic modes of pesticidal action of essential oils and compounds, there are several studies indicating enzymatic and non-enzymatic effects. The destructive effects of essential oils and their compounds on esterases and glutathione S-transferases (GSTs) as imperative detoxifying enzymes in arthropod pests are reported [88,105,106]. Disruption of the function of detoxifying enzymes may reduce the probability of pest resistance [107], and this has been clearly depicted by essential oils and their components. Farahani et al. [27] showed that the essential oil of S. khuzestanica had adverse effects on cytochrome P450 monooxygenases (P450, responsible for the oxidative metabolism of a variety of xenobiotics and endogenous compounds) function of two spotted spider mites (Tetranychus urticae Koch), along with toxic and repellent activities. The adverse effects of these agents on digestive enzymes such as lipases, proteases, α-amylases, α-glucosidases, and β-glucosidases were also reported [106], which can be very effective in reducing the nutritional efficiency of pests. Effects on energy reservoirs of the pest by decreasing the protein, glucose, and triglyceride contents and disrupting the action of immunological and hematological parameters are the other reasons to approve the multiple modes of action of these eco-friendly bio-pesticides [108,109].

Proposed New Formulations for Greenhouse and Field Applications
Although great potential for acaricidal, insecticidal, and nematicidal activity of Satureja essential oils and compounds have been reported, limitations such as susceptibility to light, moisture, oxygen, and temperature may restrict their application in the pest management strategies [5]. Indeed, the use of essential oils and their components in non-crop agriculture in the management of stored product pests, flies, and cockroaches is effec-tive [110]. Additionally, the larvicidal activity of essential oils by treating standing water and waterways and their repellent effects on adults may be useful in mosquito management (See Tables 1 and 3 for examples). Due to the disadvantage of low persistence in environmental conditions, the application of essential oils in crop agriculture can be limited [6]. Soft body and sucking pests (viz., aphids, thrips, and mites) are usually controlled by essential oils on crops, particularly under low pest pressure [110]. For example, Western flower thrip and green peach aphid were successfully controlled by the essential oil-based insecticide Ectrol (EcotecTM, California, USA) on lettuce and strawberry. However, partial efficiency was achieved against larger chewing insect pests, such as coleopterans and lepidopterans [110].
Nanoencapsulation based on the controlled release technique has been offered to overcome the lack of persistence restriction of bio-pesticides [111]. In the nanoencapsulation process, the active agent as a solid, liquid, or gas is surrounded by a thin layer of natural or synthesized polymer or a membrane to keep the core active agent from harmful environmental factors [112]. Generally, reducing the amount of active ingredients and minimizing evaporation and its controlled release are main advantages of nanoencapsulation [111]. However, along with above-mentioned advantages, expensive and difficult processes of the creation of nano-formulations should be considered. In the study of Ahmadi et al. [65], encapsulation of S. hortensis essential oil in chitosan-tripolyphosphate nanoparticles improved its ovicidal and adulticidal toxicity against T. urticae. Along with high toxicity, nanoencapsulation of S. hortensis essential oil in chitosan-tripolyphosphate nanoparticles enhanced its persistence so that 80% and 15% mortality was achieved for nano-encapsulated and pure essential oil formulation after 14 days. Usha Rani et al. [113] evaluated the antifeedant activity of pure and silica nanoparticles-based capsulated α-pinene and linalool against the tobacco cutworm (Spodoptera litura F.) and the castor semi-looper (Achaea janata L.). Although both terpenes had significant antifeedant effects, nano-capsule formulation augmented their effectiveness up to 10 and 25 times for A. Janata and S. litura, respectively. The same results regarding the enhancing toxicity and persistence of other essential oils by encapsulation in polymeric and non-polymeric materials, such as poly(ethylene glycol), myristic acid-chitosan, and mesoporous material, were also documented [114][115][116]. The preparation of nano-emulsions is another applicable method to solve the solubility restriction of essential oils in water and is more effective with minute quantities of toxic substances, both in medicinal and agricultural pest management prospects [117,118]. Further, the combination of essential oils with other protectants such as microbial agents may enhance their effectiveness. For example, the combination of S. sahendica essential oil with entomopathogenic fungus Beauveria bassiana augmented its toxicity against cowpea weevil, and insect pest mortality increased from 50% after a 1-day exposure time to 80% after 7 days [28].

Conclusions
Along with antibacterial, antifungal, antiviral, and general importance in medicinal, food, and cosmetic industries [119][120][121], the essential oils isolated from different species of Satureja genus could have great potential in the management of detrimental mite and tick Acari, insects, and nematodes. Pesticidal effects of Satureja species essential oils, which may be commonly related to their main terpenes [67,83,86], were reported as lethal contact and fumigant toxicity to sublethal repellent action, developmental inhibitory effects, adverse effects on the feeding, life cycle, oviposition, and egg hatching, and biochemical disturbances, such as reduction in general esterase content and inhibition of acetylcholinesterase and cytochrome P450 monooxygenases functions (see Tables 1 and 3). Such multiple modes of action of essential oils and their compounds, in addition to reducing pest resistance, can affect a wide range of pests [5,9]. Despite all of the mentioned advantages, high volatility or lack of persistence and insolubility in water are the main restrictions in the commercialization and extensive application of these compounds [110]. Accordingly, their application is principally focused against indoor non-crop pests such as storage pests, flies, and cockroaches [96,114]. Further, the acute toxicity against larvae and repellent activity on the adults of mosquitos that carry pathogens and suck blood were also documented in Tables 1 and 3. However, with micro-and nano-encapsulation on the basis of controlled release techniques, their persistence can be increased [122]. Although nano-emulsification is also a suitable way to dissolve essential oils in water [123,124], it is possible to increase their effectiveness by combined application with microbial control agents, such as entomopathogenic fungi [28]. These less-toxic substances may help in agriculture and environmental protection and can be proposed to countries that apply extreme amounts of synthetic pesticides. However, effects on beneficial and non-target organisms, residues on food products, and more importantly, considering a method for lower cost of Satureja essential oils and their components, should also be investigated in future research.