Introduction

Potato, Solanum tuberosum, is one of the most important tuber crop for food. It ranks fifth in the world among the most important staple foods (Orlando et al. 2020). It is third in terms of consumption and fourth in terms of production of tuberous crops (Bahar et al. 2021). In 2017, Egypt's potato production was around 4.33 million tons from a harvested area of approximately 163,939 hectares (FAO 2020). Egyptian potatoes are locally consumed, processed, or exported. Potato is the largest horticultural export, with about 561,400 tons of potato exported in 2020 (El-Din et al. 2022). Like all other crops, potatoes are infested by various insect pests at various stages of growth, which is a limiting factor in the economic cultivation of this crop. Whiteflies are the most destructive pest among the sap feeders, causing damage to the crop's foliage at the vegetative stage (Bojan 2021). More importantly, it is their ability to transmit many plant viruses (Fiallo-Olivé et al. 2020). Essential oils (EOs) have been known for insecticidal activity against a large variety of insects, herbivores, and microorganisms, having some attracting pollinators (Argyropoulou et al. 2022; Meena et al. 2022). Previous studies have shown their contact toxicity and repellency, with additional action as antibacterial, antifungal, antioxidant, insecticidal, antifeedant, fumigant, miticides, oviposition deterrent, nematocidal and growth regulatory (Li et al. 2022; Singh and Pandey 2021; Sahu and Singh 2022). The important challenges for applying EOs in agriculture are attributed to their poor solubility in water, rapid environmental degradation and limited physical stability (Abdelaal et al. 2021). Extending potential applications have been widely considered. Toxicity of EO-based CEs and NEs was tested on several insects of agricultural and medical interest such as sweet potato whitefly (Bolandnazar et al. 2020), aphids (Heydari et al. 2020), Cotton bollworms (Moustafa et al. 2015), stored-product beetles (Adak et al. 2020a, b; Hossain et al. 2019).

The objectives of this study were to identify the main constituent compounds of peppermint and eucalyptus essential oils, prepare CE and NE of both peppermint and eucalyptus essential oils, and evaluate their efficiency against the whitefly, B. tabaci, in potato cultivars during seasons 2021 and 2022, also, to study the role of weather conditions on the emulsion's toxicity against the tested insect and, finally, to study the effect of these emulsions on the chemical components of potato leaves.

Materials and methods

Tested materials

Peppermint is an essential oil obtained from Mentha piperita L. and eucalyptus essential oil obtained from Eucalyptus globulus. Both essential oils were purchased from El-Gomhoria Chemical Company, Cairo, Egypt. The oils were kept at 4 °C until experimentation. Oil emulsion efficacy was evaluated compared with Imidacloprid as a standard pesticide on the population of Bemisia tabaci. Sunclopride ® Imidacloprid 35% S.C was obtained from El-Nasr Company for Intermediate Chemical, Giza, Egypt; it was applied at the rate of 75 gm/100 L water.

Gas chromatography–mass spectroscopy (GC–MS) analysis

The chemical composition of peppermint and eucalyptus essential oils was performed using Trace GC-TSQ mass spectrometer (Thermo Scientific, Austin, TX, USA) with a direct capillary column TG–5MS (30 m × 0.25 mm × 0.25 µm film thickness). The column oven temperature was initially held at 50 °C and then increased by 5 °C/min to 250 °C hold for 2 min, increased to the final temperature 300 °C by 30 °C/min and hold for 2 min. The injector and MS transfer line temperatures were kept at 270, 260 °C, respectively; helium was used as a carrier gas at a constant flow rate of 1 ml/min. The solvent delay was 4 min, and 10 µl of each sample was dissolved in 1ml hexane. The diluted samples of 1 µl were injected automatically using Autosampler AS1300 coupled with GC in the split mode. EI mass spectra were collected at 70 eV ionization voltages over the range of m/z 50–650 in full scan mode. The ion source temperature was set at 200 °C. The components were identified by comparison of their mass spectra with those of WILEY 09 and NIST 14 mass spectral database (Abd El-Kareem et al. 2016). The analyses repeated three times for each essential oil.

Emulsion preparation

Oil-in-water coarse emulsions PCE and ECE were prepared by stirring (5% essential oil: 10% tween 80: 85% distilled water v/v) at approximately 4000 rpm for 20 min. Nanoemulsions were prepared by ultrasonication of the coarse emulsion at 20Mz for 30 min, and each emulsion was carried out in triplicates (Sugumar et al. 2013). The emulsions were stored at 4 °C.

Nanoemulsions characterization

Nanoemulsions PNE and ENE were characterized by measuring the particle size and polydispersity index (PDI) by photon correlation spectroscopy using Zetasizer Nano-ZS (Malvern Instruments, UK) and then kept for further experiments. The measurements were taken in triplicate to ensure statistical significance, and the results were calculated as the mean ± standard error (S.E.).

Experimental area

A field experiment was carried out during the subsequent growing potato season 2021 and 2022 at the Plant Protection Research Station (PPRS) at Qaha, Qalyubia Governorate, Plant Protection Research Institute, Egypt (PPRS), located at 29.1 km (44 min) of Cairo. Latitude: 30 1719.14 N Longitude: 31 1151.33 E. It is in the rich farmland of the southern part of the Nile Delta and is characterized by well-irrigated canals leading off the Delta Barrage. The experimental area was about 396m2 and was cultivated with potato, Solanum tuberosum (Spunta), on the 18th of September in both seasons. Treatments were arranged in a split-plot-plot randomized complete blocks design (RCPD) divided into six treatments (each treatment replicated three times): (1) the control treatment (sprayed with water); (2) bioinsecticide PCE; (3) PNE; (4) ECE; (5) ENE; and (6) the plots Imidacloprid (positive control), considered as the reference at rate 75 g/100 L water. Each plot covered an area of 21 m2 (7 × 3 m) and contained 33 plants (three rows of 11 plants were cultivated with a spacing of 0.60 m). The treated plots were separated from each other by untreated rows as a barrier to prevent overlapping treatments. Two successive sprays were made, the first on November 1st and the second on November 10th for both years 2021 and 2022.

Sampling methods

One hundred potato leaves were randomly selected and transferred into paper bags for examination by the stereomicroscope once weekly, from 45 days after planting until harvesting. Inspection of plant leaves was carried out before spraying (pretreatment) and after 3, 7 and 10 days after treatments, respectively. The percentage of nymphs per treatment was calculated according to Henderson's and Tilton's formula (Henderson and Tilton1955).

Weather Factors

Weather data for the seasons 2021 and 2022 at Qaha, Qalyubia Governorate, Egypt (Latitude: 30 17 19.14 N Longitude: 31 11 51.33 E), were collected by the Central Laboratory of Agricultural Climate, Agriculture Research Center, Dokki, Giza, Egypt.

Relationships between some phytochemical components of potato leaves and density of B. tabaci pest

Some phytochemical components (total soluble proteins, total carbohydrate, total phenolic contents and peroxidase activity) in the leaves of potato plants were determined to explain the relationship between biochemical components of plant organic matter (nitrogen, phosphorus and potassium) and infestation with B. tabaci during the plant growth period. The analysis of leave samples was conducted in the Department of Insect Physiological, Plant Protection Research Institute, Agricultural Research Centre.

Estimation of total soluble protein

Total soluble protein content was determined by the (Bradford 1976) method. Absorbance was measured at 595 nm.

Estimation of total carbohydrate

Preliminary hydrolysis to convert polysaccharides into monosaccharides was performed by using 2.5N HCl. The total carbohydrate content was estimated by the phenol–sulfuric acid method (Dubois et al. 1956).

Estimation of total phenolic content

The fresh leaves were extracted as IAA extraction; the 0.5 ml extract, 0.5 ml carbonate and distilled water were added to each tube, shaken and allowed to stand for 60 min. The optimal density was determined at 725 nm using a spectrophotometer (Singleton and Rossi 1965; Diaz and Martin 1972).

Estimation of peroxidase enzyme activity

Peroxidase activity was established at 26 °C with a spectrometer (PD-303UV) at 470 nm using guaiacol and H2O2 (Ponce et al. 2004).

Statistical analyses

Data were statistically analyzed by the significance of mean differences between treatments and controls. Statistical comparisons were made by a twice-analysis design. Firstly, with one-way complete block and least significant difference significant difference (LSD05) at P < 0.05 (LSD05). A second analysis by variance (split-split-plot ANOVA) and at the 0.05% probability level, Main, sub, and sub-subplot means separation was tested with Tukey’s multiple range tests at a 95% confidence level via Co-Stat software. The data were calculated by date, and the data were analyzed for each year separately to study the effect of weather data (temperature, precipitation, specific humidity and wind speed) on the efficacy of tested emulsions; the simple correlation (r) and the regression (b) were calculated between each of the weather factors and the revealed mean nymph reduction percentage. The significance level was set at P < 0.05.

Results

Chemical composition of peppermint and eucalyptus essential oils

The essential oils of both peppermint and eucalyptus components were identified by GC–MS. The main constituents of peppermint and eucalyptus oils are shown in Table 1 and Fig. 1; peppermint oil has 16 components, representing 99.83% of the essential oil, many oxygenated monoterpenes and sesquiterpene derivatives. The main components discovered in this fraction were levomenthol (33.81%), p-menthone (22.33%), menthyl acetate (8.89%), l-menthone (8.28%), and eucalyptol (8.27%). Among them, the significant two components of peppermint are levomenthol and p-menthone. Eucalyptus oil has 30 components described that represent 97.77% of the essential oil. The main components were eucalyptol (27.78%) followed by alpha-terpinene (19.78%) and α-terpineol acetate (18.37%).

Table 1 Chemical component (%) of peppermint and eucalyptus essential oils
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Fig. 1
figure 1

GC–MS analysis of peppermint (A) and eucalyptus (B) essential oil

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Nanoemulsions characterization

Data of all these nanoemulsions preparations are based on the nanometric size range (Table 2 and Fig. 2); the PNE droplet size distribution was 114.5 nm with PDI 0.27. The ENE droplet size distribution was 145.8 nm with PDI 0.69.

Table 2 The characterization of the nanoemulsion peppermint oil and eucalyptus oil formulations
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Fig. 2
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Droplet size distribution of prepared PNE (A) and ENE (B) essential oils

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Efficacy of tested emulsions on reduction % of B. tabaci (nymph) infesting potato plants

The average number of B. tabaci nymphs infesting potato leaves before the application was 15.00 to 18.66 nymphs per plant during the 2021 summer season experiment, while the average number increased from 23.16 to 26.66 nymphs per plant during the 2022 summer season experiment, respectively. For the first and second post-treatment, observations across the three post-treatments in seasons 2021 and 2022 show differences (P < 0.05) in whitefly infestation levels, among treatments and Imidacloprid as a positive control. The numbers of nymphs per plant and reduction percentages of infesting potato plants as influenced by 5% P (CE, NE) and 5% E (CE, NE), which were applied to potato plants in two consecutive sprays during season 2021, are tabulated in Table 3. During the whole duration of the study, we found a significant difference between all treatments compared with the control and between all treatments and Imidacloprid treatment. The second spray was more effective than the first spray. After the first spray, during season 2022, the field experiment revealed similar data to the season 2021 field experiment as shown in Table 4 and Fig. 3. Generally, the toxicity decreased with increasing time after spraying. Also, the second spray was more effective than the first spray. P (CE, NE) revealed more effectiveness against B. tabaci nymphs, followed by E (CE, NE). A three-way ANOVA was performed on the mean reduction percentage of nymph with treatments, sprays and time samples as the factors. Table 5 shows no significant differences between three tested independent variations (treatments, sprays, time samples), but significant differences were found between time samples and treatments. Significant differences were also found among time samples and sprays. No significant differences were observed between treatments and sprays.

Table 3 Efficacy of P (CE, NE) and E (CE, NE) against whitefly on potato field during season 2021
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Table 4 Efficacy of P (CE, NE) and E (CE, NE) against whitefly on potato field during season 2022
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Fig. 3
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Average daily temperature (°C) (A), precipitation (cm) (B), specific humidity at 2 meters (g/kg) (C), and wind speed at 2 meters (m/s) (D) 2 recorded in Qaha, Qalyubia Governorate Egypt, during field trials, in 2021 and 2022. All data were collected by Central Laboratory of Agricultural Climate, Agriculture Research Center, Dokki, Giza, Egypt

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Table 5 Effects of treatments and their interactions on whitefly nymphs in 2021 and 2022
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Weather Factors

In a partial regression analysis for the application period during the 2020–2021 season, Table 6 and Fig. 4 display the key findings. The data indicated a significant positive relationship between temperature and all treatment sample correlations, ranging from r = 0.804 to 0.868. Specific humidity also showed positive correlations with r = 0.839 to 0.857 values. However, the wind speed had a significant positive effect, with r values ranging from 0.759 to 0.839. Precipitation showed positive but no significant correlations, with r values ranging from 0.371 to 0.438. The 2021–2022 applications revealed specific humidity showed a significant negative correlation with all treatment “r” values ranging from − 0.856 to − 0.773, indicating a strong inverse relationship. On the other hand, the relationship between temperature and all treatments was negative but non-significant, with correlation coefficients ranging from − 0.606 to − 0.331, suggesting a weaker association. Wind speed exhibited a significant positive correlation with all treatments, with correlation coefficients ranging from 0.840 to 0.772, indicating a strong positive relationship between wind speed and the treatments studied. However, the correlations between wind speed and precipitation were positive but non-significant, suggesting that there may be little to no relationship between wind speed and precipitation in this context.

Table 6 Simple correlation of the three main weather factors on each of the weather factors and the revealed mean nymph reduction percentage of the tested emulsions in 2021 and 2022
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Fig. 4
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Damaged leaves of potato plants infected with whitefly Bemisia tabaci, A treated with PNE, B treated with ENE and C yield after applications during season 2022

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Effects of tested emulsions on phytochemical components of potato leaves

The growth components parameters of potato plants after being treated with tested emulsions are tested in Table 7. Both CEs showed a slight decrease in protein levels. The ECE, PNE and ENE increased total plant carbohydrates, respectively. ENE increased phenolic compounds. All treatments decreased nitrogen plants' contents. ECE and ENE increase phosphorus and PCE, PNE and ENE increase potassium contents. We can conclude that the use of EO and its emulsions is more effective in controlling B. tabaci.

Table 7 Effects of peppermint and eucalyptus oils course and nanoemulsions on growth components and peroxidases of potato plant in the field
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Effects of tested emulsions on peroxidase enzyme

Determination of the potato plant antioxidant enzyme peroxidase after being treated with essential oils CE and NE, in these studies, is shown in Table 7. The ENE most affected in the enzyme activities was 621.00 (∆ O.D./min/g) followed by PCE, PNE and ECE 521.66, 521.66 and 515.33(∆ O.D./min/g), respectively.

Discussion

The goal of the current study evaluates the efficacy of the CEs and NEs of peppermint and eucalyptus oils as a potential botanical insecticide to control whitefly, Bemisia tabaci pest in Qaha, Qalyubia Governorate, Egypt. The efficacy of tested emulsions in this study was less than that of the conventional synthetic insecticide, Imidacloprid, in managing the B. tabaci on potato fields. However, the use of peppermint and eucalyptus oil as a biopesticide to control insects plays a role in protecting the environment from pollution. The present result was in concordance with the previous studies (Heydari et al. 2020; Rajkumar et al. 2020; Beigi et al. 2018; Buleandra et al. 2016). From GC–MS analysis of the peppermint oil, the main components were levomenthol, p-menthone menthyl acetate, l-menthone and eucalyptol. According to the studies of (Hamad Al-Mijalli et al. 2022), the main compounds identified in the peppermint essential oil were menthone (29.24%), levomenthol (38.73%), menthol (2.71%) and eucalyptol (6.75%). (El-Lateef Gharib and Silva 2013) determined that p-menthone (36.3%) is one of the highest contents in peppermint oil. Eucalyptus oil’s main components were eucalyptol, alpha-terpinene and α-terpineol acetate. Many researchers found that the eucalyptol is the main component in eucalyptus oil (Abelan et al. 2022; Adak et al. 2020a, b).

Menthol, one of the main components of peppermint oil, has cholinesterase inhibitory effects and is reactive to nicotinic, 5-hydroxytryptamine (HT3), GABAA, glycine and receptors (Kennedy 2019). Many researchers recorded that the primary component in eucalyptus oil was 1,8-cineole (eucalyptol) (Chaudhari et al. 2021; Chauhan et al. 2018; Bett et al. 2016). They inhibited acetylcholinesterase and binding to gamma-aminobutyric acid (GABAA), nicotinic and muscarinic receptors (Kennedy 2014). It could attribute the components and quantity of essential oil in the same plant species to the differences in processing conditions, such as harvesting time, geographical region, seasonal factors and method of extraction (Pang et al. 2020). Peppermint and eucalyptus oil showed biopesticide effects to control whitefly (Aroiee et al. 2005; Bolandnazar et al. 2018) the difficulty in applying essential oils to control insects on a field scale and under environmental conditions such as oil volatility, poor water solubility and aptitude for oxidation have to be resolved before they can be used as an alternative pest control system (Ibrahim 2020). The nanoemulsions were in the nanometric size ranges; PNE and ENE were 114.5 and 145.8 nm. Smaller droplet sizes lead to NE ranges that may lead to improved emulsion stability, which is a significant factor for many applications. Many researchers found that NEs having a particle size between 10 and 200 nm showed beneficial inputs, such as solubility and permeability (Almadiy et al. 2022; Abdelaal et al. 2021). The PDI value of PNE showed good physical stability of the NE, because of the reduced Ostwald ripening (Hashem et al. 2020), whereas a PDI value of ENE above 0.30 shows heterogeneity of the NE (Nenaah et al. 2022). To whitefly management, a less amount of (EO) NE may be required than bulk EO. Downsizing the oil particles may have allowed it to come into contact with insects, as opposed to EO, which showed its toxic effect. This was consistent with the findings of (Heydari et al. 2020; Barzegar et al. 2018). However, the smallest size of the NE formulation of PNE obtained by (Shaker et al. 2022) was about 66 nm, and the ENE obtained by (Mohammadi et al. 2020) was about 103.9 nm, which is like the present research. Smaller particle size improves the NE penetration through the insect cuticle and plays a critical role in insecticidal activity. Low particle sizes of NEs increase penetration and uptake of EO into the insect tissues. This may improve the biological activity of NEs compared to CEs (Mustafa and Hussein 2020; Adak et al. 2020a, b).

Despite many essential oils estimated as insecticides such as neem oil, orange oil act, only a few researchers have focused on vegetable crops in the field (Isman 2020). There are very few studies on crop systems that have investigated both the effectiveness and the impact of insecticide treatments on the crop in the field. Also, most articles discuss the toxicity of certain essential oils and nanoformulations. The effectiveness of both NE and CE in this study was less than that of the synthetic insecticide Imidacloprid, in managing the major whitefly population in potato fields; however, some level of pest control was promoted compared to non-treat plots. Similarly, positive results were regarded with the NE of Lippia multiflora Mold on the reduction of the cabbage pest, in a very effective effect compared with the synthetic insecticide lambda-cyhalothrin (Tia et al. 2021). The NE of Mentha piperita EO has high contact toxicity on the cotton aphid in laboratory conditions (Heydari et al. 2020).

The analysis of the application periods during the seasons 2020–2021 and 2021–2022 provides relationships between weather variables and the efficacy of tested emulsions. In the 2020–2021 season, a notable moderately positive correlation was identified between temperature, specific humidity, wind speed and the effectiveness of the emulsions. This indicates that higher levels of temperature, humidity and wind speed were associated with increased efficacy of the emulsions. Additionally, a positive but non-significant correlation was found between precipitation and emulsion effectiveness, suggesting a potentially weaker relationship compared to other weather variables.

In contrast, the findings from the 2021–2022 season revealed that The specific humidity was moderate negatively correlated with all treatments, indicating a significant inverse relationship with the treatments being studied. Temperature, on the other hand, showed a negative but non-significant relationship with the treatments, suggesting a weaker association compared to specific humidity. Wind speed exhibited a significant positive correlation with all treatments, highlighting a moderately positive relationship between wind speed and treatment effectiveness. The correlations between wind speed and precipitation, while positive, were non-significant, indicating a lack of substantial relationship between the two variables.

The present study is in agreement with (Jha and Kumar 2017) who reported the weather parameters affect the population dynamics of B. tabaci on tomato crops. Temperature had a negative correlation, while relative humidity had a positive correlation, but wind speed had a non-significant positive correlation. Also, (Pavela and Sedlák 2018) found temperature to be a factor influencing the insecticidal activity of essential oils, which exhibits a significant positive as well as negative gradient of toxicity depending on the sequence of temperature changes. Increases in temperatures can enhance the volatility of tested emulsions, potentially increasing their spread in the air and contact with B. tabaci. Furthermore, low humidity conditions may enhance the retention of essential oils emulsions on plant surfaces, prolonging their residual activity against B. tabaci, balancing humidity levels to maintain optimal conditions for the efficacy of essential oils (de Brito-Machado 2022).

The results showed that sprayed with both tested NEs does not negatively affect total protein levels in potato leaves. Our outcome shows we can control insects in the field without affecting plant protein content; conventional insecticides decrease the total protein accordingly (Siddiqui and Ahmed 2002, 2006). There is a positive correlation between higher protein content and reduction in infested soybean plants which have tolerance to infestation with B. tabaci (Cruz 2016).

Also, the results presented a positive effect of all tested emulsions on carbohydrates in potato plants. (Pandey et al. 2020) found there were no significant differences between carbohydrate content in untreated tomato plants and others treated with PNE.

All treatments did not affect total phenol except ENE which showed a positive effect; recorded maximum total phenolic contents of 2.06 mg/g and therefore activates phenolic compounds production. Increases of phenolic compounds induced in plants are directly toxic to insects or produce toxic secondary metabolites and activate the defensive enzymes (Bhonwong et al. 2009). Our data agree with (Pandey et al. 2020) who found no significant difference between plant PNE and control. Plants use phenolic compounds for a variety of purposes, including growth and development, cell wall thickening, hormone synthesis, pigmentation, reproduction, stress resistance, osmoregulation, UV protection, anti-herbivore and antibacterial activities (Dixon 2001). Also, phenolics play a defensive role against pests and influence insect growth and feeding which has high levels of flavonoids and antibiosis mechanisms that prevented Spodoptera litura larval growth (Mallikarjuna et al. 2004). Plants that contain a high level of phenolic compounds were less infested by the cereal aphid (Wójcicka 2010).

Nitrogen (N), phosphorus (P) and potassium (K) are the major elements in optimizing potato yield. We examined the effect of our tested CEs and NEs on the NPK plant's content. Our data indicated all treatments decreased plant nitrogen contents. There was a significant increase in phosphorus content with plants treated with ECE and ENE. Potato plants treated with PCE exhibited increase in potassium contents. In the potato nutrition literature, it is highlighted that the importance of potassium is evident in obtaining high potato tuber yields (Kumar et al. 2007). Our tested NEs showed a positive effect on plant potassium content. So, it may promote tubers' growth more than untreated plants.

Peroxidases using H2O2 oxidize several substances. The peroxidases are considered a plant defense-responsive system in plants. The biological response of essential oils and their constituents causes oxidative effect by the accumulation of reactive oxygen species (Mousavizadeh and Sedaghathoor 2011). Based on the antioxidant property of essential oils, we evaluated the effect of both PNE and ENE on the increased peroxidase activity in potato leaves. Also, both NEs showed antioxidant activity higher than CEs in plant leaves. So, peroxides act as defense enzymes against whitefly insects in potato fields. Our results agree with those obtained by (Ben-Jabeur et al. 2015) thyme oil applied on leaves of tomato plants inducing plant systemic resistance by causing peroxidase accumulation. PNE and ENE increased plant peroxidases, so these oils may provide insect-resistant plants against B. tabaci on potato fields. (Pandey et al. 2020) evaluated NEs as promoting growth, as they can have significant effects on plant seedlings or as well as on promoting plant growth. The derived from peppermint EO could suppress fungi Alternaria solani growth while promoting tomato plant growth (Pandey et al. 2020). Thymol oil NE exhibited antibacterial activity and promoted soybean plant growth (Kumari et al. 2018).

Conclusion

In conclusion, essential oils, whether in coarse or nanoemulsion forms, present a promising non-chemical alternative for Integrated Pest Management (IPM) to B. tabaci. Adapting application methods and timing to align with prevailing weather conditions is crucial for maximizing the efficacy of essential oils in controlling B. tabaci. Factors such as temperature, humidity and wind speed can influence the performance and persistence of essential oils on potato fields. Therefore, adjusting application techniques accordingly can enhance the coverage and contact of essential oils with the target pest, improving overall efficacy.