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Article

The Acaricidal Activity of Essential Oil Vapors and Its Effect on the Varroa Mite Varroa destructor

by
Nikoletta G. Ntalli
1,2,*,
Maria Samara
1,
Theodoros Stathakis
1,
Myrto Barda
1,
Eleftheria Kapaxidi
3,
Elektra Manea-Karga
4,
Sofia Gounari
5,
Georgios Goras
6,
Konstantinos M. Kasiotis
4 and
Filitsa Karamaouna
1
1
Laboratory of Efficacy Evaluation of Pesticides, Scientific Directorate of Pesticides Control and Phytopharmacy, Benaki Phytopathological Institute, 8 Stefanou Delta Str., 14561 Athens, Greece
2
Analytical Chemistry and Pesticides Laboratory, Department of Agriculture Crop Production and Rural Environment, University of Thessaly, 38446 Volos, Greece
3
Laboratory of Acaralogy and Agricultural Zoology, Scientific Directorate of Entomology and Agricultural Zoology, Benaki Phytopathological Institute, 8 Stefanou Delta Str., 14561 Athens, Greece
4
Laboratory of Pesticides’ Toxicology, Scientific Directorate of Pesticides Control and Phytopharmacy, Benaki Phytopathological Institute, 8 Stefanou Delta Str., 14561 Athens, Greece
5
Laboratory of Apiculture, Institute of Mediterranean & Forest Ecosystems, ELGO DHMHTRA, 11528 Athens, Greece
6
Laboratory of Sericulture and Apiculture, School of Plant Sciences, Agricultural University of Athens, Iera Odos Str. 75, 11855 Athens, Greece
*
Author to whom correspondence should be addressed.
Agriculture 2025, 15(13), 1379; https://doi.org/10.3390/agriculture15131379
Submission received: 25 April 2025 / Revised: 22 June 2025 / Accepted: 26 June 2025 / Published: 27 June 2025
(This article belongs to the Section Crop Protection, Diseases, Pests and Weeds)
Browse Figure
Versions Notes

Abstract

Νatural compounds such as lactic, acetic, formic, and oxalic acid and thymol are currently registered for use against Varroa destructor in apiaries in Europe. Complex botanical extracts are yet to be authorized, despite their beneficial ecofriendly profile and advantages in terms of resistance management. This study examined the fumigant activity of the essential oil (EO) of oregano, clove, lavender, dittany, bay laurel, sweet orange, peppermint, blue gum, and lemon balm against V. destructor in laboratory bioassays (Petri dishes). The most effective EOs were those of Origanum vulgare, Syzygium aromaticum, and Origanum dictamnus. These three EOs yielded 33.75% carvacrol, 58.64% eugenol, and 69.77% carvacrol and exhibited significant activity from 18 h of exposure to 0.0013 μL/cm until 48 h of exposure to 0.0068 μL/cm3. Origanum vulgare’s first calculated LC50 value was 0.003 μL/cm3 after 24 h of mites’ exposure to EO vapors. The LC50 values stabilized for oregano, clove, and dittany at 0.001, 0.002, and 0.002 μL/cm3 of 24 h exposure, respectively. This first indication of fumigant miticidal activity in Petri dishes is a promising first step before scaling up to field experiments.

1. Introduction

Bee populations contribute to plant conservation through pollination, supporting food supply, economic stability, plant diversity, and ecological balance [1]. Beyond pollination, honey production is a key contribution of honey bees, with annual global yields reaching 1.8 million tons [2]. However, in recent years, a decline in honeybee populations has been evidenced, raising worldwide concern [3]. Their health is compromised by climate change, loss of biodiversity, pathogens, predators, and toxic compounds. The most significant biotic challenge for honeybees is the immunosuppression and microbiota modification provoked by the combined effects of the mite Varroa destructor (Anderson and Trueman) (Acari: Varroidae), viruses, pesticides, and malnutrition [4]. The Varroa mite, which triggers Varroosis—the most severe arthropod-borne disease affecting honeybees—feeds primarily on the fat body and can serve as a vector of important honeybee viruses [5].
To address honeybee pests and pathogens in apiculture, veterinary medicines designed for food-producing animals are used. These products undergo scientific evaluation in accordance with human food safety requirements [6]. However, the frequent use of synthetic veterinary medicinal products has led to increased resistance among pests, residue accumulation in honeybee products, and potential human health risks [7]. Seeking more ecofriendly alternatives, the use of plant secondary metabolites has been reported for the control of V. destructor [8,9].
Pest resistance to botanical extracts is difficult to develop due to their complex phytochemistry. Even when botanicals are not directly lethal, they may cause sublethal effects and/or attract or repel pests, which are valuable attributes for traps or deterring pests from inhabiting the hive [9,10,11]. Organic substances such as EOs are soft acaricides [12], and, unlike synthetic pesticides, they do not accumulate in wax [13] or hive products [14,15]. Consequently, they are being studied extensively as potential solutions in apicultural pest control [16,17,18].
Applying botanical extracts to manage Varroa presents challenges, primarily due to the narrow margin between lethal doses for mites and honeybees [19] and the need for application methods that balance efficacy and selectivity. Fumigation involves a two-level system or chamber setup where mites naturally reside in the upper level, separated from the lower chamber; it also includes a material soaked with EO. In most cases, it is the approach considered most fit for purpose (in both lab and field tests) because it enables the molecules to penetrate the target organism’s respiratory system [17]. This study examines the effects of nine different EOs used as fumigants against the mite V. destructor in Petri dishes and their correlative efficacy with the chemical profile. It lays the groundwork for EOs to be tested later under semi-field or open field conditions.

2. Materials and Methods

2.1. Plant Materials

EOs from nine plant species (certain plant parts) were tested, namely Origanum vulgare, Lamiaceae (oregano; stalks, flowers, leaves); Syzygium aromaticum, Myrtaceae (clove; flower buds); Lavandula angustifolia, Lamiaceae (lavender; stalks, flowers, leaves); Origanum dictamnus, Lamiaceae (dittany; stalks, flowers, leaves); Laulus nobilis, Lauraceae (bay laurel; leaves); Citrus sinensis, Rutaceae (sweet orange; peel); Mentha piperita, Lamiaceae (peppermint; stalks, flowers, leaves); Eucalyptus globulus, Myrtaceae (blue gum; leaves); and Melissa officinalis, Lamiaceae (lemon balm; stalks, flowers, leaves). Apart from clove, all EOs were extracted from plant material of the Greek flora. Oregano, lavender, bay laurel, peppermint, lemon balm, and blue gum were collected in Thessaly, while dittany and sweet orange were collected in Crete. The above-ground parts of the aromatic plants were harvested during the flowering stage from several sites in Greece. Voucher specimens were deposited in the Department of Ecology, School of Biology, Aristotle University of Thessaloniki, Greece. They were air-dried at room temperature away from light and then stored in paper bags in a dark, cool place until use.

2.2. Isolation of EOs

The dried plant samples were ground and then subjected to water distillation for 3 h using a Clevenger apparatus (Winzer, Laborglastechnik, Wertheim, Germany) following the European Pharmacopoeia guidelines. For each aromatic plant, 100 g were placed in a 2000 mL glass flask with 1000 mL of distilled water. The isolated EOs were dried over anhydrous Na2SO4 and kept in dark glass vials with Teflon-sealed caps at −20 ± 0.5 °C until use. The yield of each EO was averaged over three replicates.

2.3. EO Analysis

The crude EOs were diluted in n-hexane (1:50, v/v, n-hexane obtained from Thermo Fisher Scientific, Waltham, MA, USA), and analyses were performed using a Shimadzu Nexis GC 2030 gas chromatograph (Shimadzu Corporation, Kyoto, Japan) equipped with an AOC-6000 autosampler and a Shimadzu GCMS-TQ8040 NX triple quadrupole. Data acquisition and processing were performed using LabSolutions GCMS solution software, version 4.52. Samples were injected using a multimode injector inlet in splitless mode through a Shimadzu ultra-inert inlet liner with glass wool frit. The injection volume was 1 µL. The injector temperature was kept at 250 °C. A MEGA 5-HT (MEGA S.r.l., Legnano, Italy) column (30 m length × 0.25 mm i.d. × 0.25 µm film thickness) was used.
The oven temperature program was as follows: 45 °C for 1 min, before it was ramped linearly to 250 °C at 5 °C/min and kept at that temperature for 5 min. The total run time was 47 min. The instrument worked at a constant flow of 1.4 mL/min, using the full-scan mode of the mass spectrometer. Helium (99.999% purity) was used as the carrier gas. The transfer line and the ion source—operated in electron impact—were maintained at 250 °C and 230 °C, respectively. The detector voltage was set at 0.4 kV (relative to the tuning result). The solvent delay was 3 min. The identification of the compounds was performed by comparison of the experimental mass spectra with those provided by the NIST 2017 mass spectra library.

2.4. Varroa Mite Collection

Adult female V. destructor mites were collected from untreated A. mellifera colonies maintained at the Agricultural University of Athens. The combs selected for this purpose were those containing a high proportion of sealed brood. After being carefully removed from the hives, the adult bees present on the combs were brushed off. The brood combs were then placed in a transport box and taken to the laboratory of Efficacy Control of Pesticides at Benaki Phytopathogical Institute, where they were kept at a temperature of 34 °C, which mimics the brood nest conditions within a hive. Under these conditions, bees emerged carrying Varroa mites on their bodies. Mites were separated from the brood cells using a paintbrush and examined under a stereomicroscope for their vitality. Active mites were transferred to 9 cm Petri dishes (5 per dish) for the bioassays.

2.5. Acaridical Activity Bioassays

The screening bioassay was conducted at two different concentrations, where most of the EOs exhibited activity, ensuring comparable fumigant results among experimental treatments, i.e., 0.0013 and 0.0068 μL EO/cm3. The three most effective EOs (oregano, clove, dittany) were used in concentration–response bioassays, calculating LC50 values. The test concentrations for the concentration response were 0.0002, 0.0004, 0.0008, 0.0017, 0.0034, and 0.0068 μL EO/cm3 in Petri dishes. Mortality was assessed after 18, 24, and 48 h of exposure to EO vapors.
In all bioassays, the test solutions were prepared in dimethyl sulfoxide (DMSO) and Tween 20 in water (2% and 0.3% v/v, respectively) and were vortex-mixed to overcome solubility issues. Carriers and water were used as controls. The test solution was applied on folded filter paper, which was placed on the underside of the lid of the Petri dish to avoid contact with the mite individuals and act through its vapors. To prevent possible malnutrition during the bioassays, the mites were supplied with five honeybee pupae. Directly after the application was completed, five Varroa mite adults were placed in each Petri dish, which was then sealed with parafilm. The natural mortality in the carriers (DMSO, Tween 20) never exceeded 5–10%, and it did not differ statistically from the water control. Mites were deemed dead if unresponsive to probing. In parallel, the acute toxicity effect in terms of mortality was assessed on the test honeybee pupae. Metamorphosis of the pupae to adults was recorded within 48 h.
The Petri dishes were kept in a chamber under controlled environmental conditions, 33 ± 1 °C in fully dark conditions, to simulate a honeybee colony and maintain pupae survival both in the treatment and non-treatment replications. Every EO treatment was replicated five times, in two sets of bioassays (repetitions in time).

2.6. Statistical Analysis

Corrected mortality (acaricidal activity) was assessed with the Schneider Orelli formula [20] [(mortality % in the treatment − mortality % in the control)/(100 − mortality % in the control)] × 100, by eliminating the natural mortality of the control. Since mites’ mortality in carrier control was not significantly different from that in plain water, corrected mortality data were expressed as the percentage death increase over water control. The data were analyzed by a two-way repeated ANOVA, with time as a repeated factor and replication of the experiment as an independent factor. Because there was no significant time interaction, means were averaged over time and analyzed as a whole for each assessment time point separately. Statistical variations between different EOs are represented with different letters (Duncan, p < 0.05) for each separate assessment time point (18, 24, and 48 h of exposure). LC50 values for every assessment time point were calculated using the log-logistic equation [21]. For the statistical analysis, SPSS version 29.0.0.0 was used.

3. Results

3.1. EO Yields and Chemical Composition Analysis

The plant parts used for EO isolation, along with the average EO yields, are presented in Table 1. The EO yields are expressed in mL per 100 g of dry plant weight, and they ranged from 0.1 to 13% (v/w). Among the aromatic plants studied, the highest EO yield was obtained from S. aromaticum, followed by O. vulgare and L. nobilis, with yields of 13, 3.1, and 1.97% (v/w), respectively. The lowest yields (0.3 and 0.1%) were recorded from C. sinensis and M. officinalis. The Origanum dictamnus, L. angustifolia, and M. piperita yields ranged from 0.96 to 1.65% (v/w).
Table S1 displays the identified compounds, ordered by their elution time from a MEGA-5 HT column, along with retention index (RI) and relative percentages in each EO’s total composition. The identified constituents were predominantly monoterpenes and sesquiterpenes, including hydrocarbons and oxygenated compounds.
The number of compounds varied per EO, with O. vulgare, O. dictamnus, and C. sinensis yielding 22 identified components; E. globulus yielded 21 components; L. angustifolia and L. nobilis yielded 19 components; M. officinalis yielded 18 components; S. aromaticum yielded 16 components; and M. piperita yielded 11 components.
According to Table 2, the EO of O. vulgare was characterized by high concentrations of p-cymene, thymol, and carvacrol, present at 10.13%, 33.47%, and 33.75% of total content, respectively. The Syzygium aromaticum EO had significant levels of eugenol, β-caryophyllene, and eugenyl acetate, comprising 58.64%, 11.49%, and 13.17%, respectively. The EO of L. angustifolia contained linalool and linalyl acetate at relative amounts of 32.17 and 24.21% of total content, correspondingly. The EO of O. dictamnus comprised high levels of p-cymene and carvacrol found at relative amounts of 10.03 and 69.77% of total content, respectively. The EO of M. officinalis was characterized by the significant presence of citronellal and geraniol found at relative amounts of 41.67 and 27.69% of total content. The EO of E. globulus was dominated by eucalyptol at a relative amount of 69.38% of the total content. The EO of L. nobilis was distinguished by the significant presence of methyl eugenol, linalool, and α-terpinyl acetate found at a relative amount of 19.44, 16.67, and 15.95% of the total content, respectively. L-menthon and L-menthole, found at a relative amount of 16.11 and 46.11% of the total content, respectively, were the key components of the M. piperita EO. Lastly, the EO of C. sinensis was dominated by limonene (relative amount of 88.49% of total content).

3.2. Miticide Screening Test and Activity Against V. destructor

According to the screening bioassay results, as depicted in Figure 1, all EOs showed activities from 24 h of exposure to both concentration levels. Origanum vulgare, S. aromaticum, O. dictamnus, and M. officinalis exhibited the optimum activity from 25 to 50% within 48 h at the test concentration of 0.0013 μL/cm3. This effect was even more pronounced at a concentration of 0.0068 μL/cm3, reaching almost 100% activity after 48 h of mites’ exposure to EO vapors. Listing the EOs in descending order of miticidal activity, considering results from 48 h post-bioassay initiation, the list is as follows: Mentha piperita, E. globulus, L. nobilis, M. officinalis, L. angustifolia, and, lastly, C. cinensis. Among these EOs, the vapors of E. globulus were the most active at 0.0013 μL/cm3 (slightly over 50%) but did not differ at 0.0068 μL/cm3. We considered the “most effective EOs” as those that exhibited significant activity starting from 18 h of exposure to 0.0013 μL/cm3 to 48 h of exposure to 0.0068 μL/cm3. Therefore, three EOs, namely O. vulgare, S. aromaticum, and O. dictamnus, were employed in concentration–response bioassays for the calculation of LC50 values.

3.3. Miticide Concentration Response Test and LC50 Values of O. vulgare, S. aromaticum, and O. dictamus Against V. destructor

The LC50 values of the three most effective EOs displaying significant miticidal activity in the tested concentration range are presented in Table 2. Concentration and time response relationships were established. Specifically, the calculated LC50 values for O. vulgare, S. aromaticum, and O. dictamnus after 48 h of exposure to the EO vapors in the Petri dishes were 0.001, 0.002, and 0.002 μL/cm3 in the Petri dishes, respectively. In the previous two exposure periods, namely 24 and 18 h, S. aromaticum and O. dictamnus did not establish 50% mortality even at the highest tested concentration. Origanum vulgare was the fastest to take effect among the three EOs, with an initial LC50 value calculated at 0.003 μL/cm3 in the Petri dish after 24 h of exposure to the vapors.
No acute toxicity, such as mortality, was observed in honeybee pupae for any of the EOs tested. Metamorphosis to adults was recorded for most pupae within 48 h.

4. Discussion

The composition of the investigated EOs is highly consistent with the relevant literature. Specifically, for O. vulgare and O. dictamnus, the major components in this study, namely pinenes, cymenes, terpinenes, thymol, and carvacrol, were also identified by several researchers not only in the Mediterranean [22,23,24] but on a global scale [25,26]. For S. aromaticum EO, eugenol and caryophyllene emerged as the principal components, in line with Teles et al. [27], while for L. angustifolia EO, linalool and linalyl acetate accounted for more than 50% of its composition, in agreement with the results reported by Dong et al. [28]. Eucalyptus globulus EO was characterized by the preponderance of the bicyclic ether of eucalyptol (1,8-cineol), although fluctuations in its abundance have been reported [29,30]. Mentha piperita EO was dominated by menthol and menthone, a fact corroborated by several studies [31], while C. sinensis was dominated by limonene [32], and the composition of L. nobilis was in agreement with the work conducted by Peris and Blázquez [33]. In the same context, the oxygenated monoterpenes, geraniol and citronellal, were the major chemicals of M. officinalis EO, with the literature presenting high variability in the abundance and key constituents of this EO [34,35], potentially related to the plant growth stages.
From a bioactivity viewpoint, the miticidal activity of Italian oregano against V. destructor has been previously demonstrated under an acute toxicity protocol [16]. Our study confirmed that O. vulgare EO was among the most effective EOs, exhibiting fumigant toxicity against V. destructor. Among the three most effective treatments—O. vulgare, S. aromaticum, and O. dictamnus—O. vulgare was the fastest to exhibit miticidal activity through its vapors, with an LC50 of 0.003 μL/cm3 in Petri dishes 24 h post-bioassay initiation. At 48 h, O. vulgare achieved an LC50 value of 0.001 μL/cm3, indicating significant varroacidal efficacy. Syzygium aromaticum and O. dictamnus followed with LC50 values of 0.002 μL/cm3 at 48 h. Consequently, this is the first report of the fumigant activity of O. vulgare and S. aromaticum against V. destructor in Petri dishes.
In accordance with our findings, considering the international literature, the miticidal activities of O. vulgare and S. aromaticum EOs in a glass-vial-based residual bioassay (extensively used to detect pesticide toxicity and resistance in arthropods) were found to be the most effective out of the twenty-two natural products tested for their acute toxicity on V. destructor [36]. Özüiçli and Baykalir (2024) dissolved S. aromaticum in glycerin before soaking on strips, which were then placed between frames, and S. aromaticum exhibited significant efficacy against the Varroa mite in this field study [37]. Li et al. (2017) [38] examined the effects of S. aromaticum on the enzyme activities and respective physiological reactions of V. destructor and found that the bioactivity of glutathione-S-transferase increased significantly after low-dosage (0.1 μL) exposure but decreased at a higher dosage (1.0 μL). At the same time, the activities of superoxide dismutase and Ca2+-Mg2+-ATPase were significantly elevated after the application of treatments [38]. Maggi et al. (2012) proved that V. destructor body size is directly correlated to the activity of S. aromaticum EO [39]. Upon systemic administration of S. aromaticum diluted in syrup and placed in feeders for bees, it was found to be an attractant for the Varroa mite [40]. This study contains the first mention of Origanum dictamnus being an effective fumigant against V. destructor. Its substantial activity might be, to some extent, correlated to the high contents of carvacrol, as in O. vulgare, a very potent miticide against V. destructor with an LC50/4h value of 106.10 µg/mL (5.31 mg carvacrol/L air volume) [41]. In our study, S. aromaticum, O. vulgare, and O. dictamnus exhibited similar miticidal activity, containing monoterpene phenols as major compounds but different chemical profiles considering specific ingredients.
Importantly, O. vulgare showed no adverse toxicity effects on honeybees in this study, consistent with previous reports for thyme, savory, and spearmint EOs’ toxicity to worker honeybees, not differing significantly from that of the control treatments (acetone and water) [42]. In contrast with our findings, S. aromaticum appears in different experimental protocols to have some inhibitory effects on A. mellifera (MICs of 32–64 μg/mL) [43].
Our results are in accordance with Aglagane et al. (2022), who reported that the L. nobilis EO’s EC50 on V. destructor was 5.470 µL/Lair [44]. In our study, using a similar experimental protocol of fumigant activity, L. nobilis EO tested at 0.0068 μL/cm3 exhibited a miticidal activity of almost 50%. In this regard, it has been proven that L. nobilis, treated on experimental colonies during three seasons, two consecutive autumns, and one spring, exhibited activity of 76.7 to 65.2%, with no abnormal deaths recorded in adult bees [45].
In another study, L. angustifolia distributed on sheets of papier-mâché traced on the frames of the brood chamber inside the hive exhibited significant toxicity against V. destructor, while E. globulus EO did not show consistent parasite control using the same experimental protocol [46].
Interestingly, according to our findings, C. sinensis EO has the least potent effect on V. destructor, as similarly described by Bava et al. (2021) [47] but with a different experimental protocol assessing acute toxicity based on incubating mites inside vials previously filled with the tested essential oil. As regards reports on the EO of Mentha sp., when tested with a fumigation protocol on V. destructor mites, it exhibited 47.5% toxicity, while honeybee toxicity was only 6.2% on the same assessment date and at the same test concentration [17]. Melissa officinalis employed at 15, 20, and 25 μL/L air induced oxidative/nitrosative stress and mortality of V. destructor without causing high mortality in A. mellifera [48]. In the same study, carvacrol (24.97%) and γ–terpinene were found to be the major components, contrary to our findings identifying citronellal and geraniol.
Mixtures of terpenes have been reported to be more potent insecticides than individual compounds [49,50]; therefore, such synergies can be the driving force behind the fumigant activity observed in this work. Dambolena et al. (2016) reviewed terpenes in the context of controlling insects of importance, demonstrating quantitative structure–activity relationship (QSAR) insights [51]. A potential underlying mechanism is the competitive inhibition of acetylcholinesterase, where, in the case of ketonic terpenes, the carbonyl group has a role in structural interplay.
Plant secondary metabolites like lactic acid, acetic acid, formic acid, oxalic acid, and thymol have already been registered for use in apiaries in Europe, but complex botanical extracts are yet to be authorized. However, using complex extracts rather than single compounds in apiaries could be a very promising resistance management tool. In fact, in this study, we evidence similar activities exhibited by EOs of totally different chemical profiles. Based on our results, our future research will focus on semi-field/field efficacy trials including comparisons with formulated commercial miticides. Formulation studies could help enhance residual life and subsequent efficacy, thus aiding progress towards the development of botanicals for sustainable varroa management.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agriculture15131379/s1, Table S1: Chemical and percentage contents a of essential oils (EOs) of the plants Origanum vulgare, Syzygium aromaticum, Lavandula angustifolia, Origanum dictamnus, Melissa officinalis, Eucalyptus globulus, Laurus nobilis, Mentha piperita, and Citrus sinensis.

Author Contributions

Conceptualization, N.G.N. and F.K.; methodology, N.G.N., M.S., M.B., T.S., F.K., E.K., S.G., G.G., E.M.-K. and K.M.K.; software, N.G.N., K.M.K. and F.K.; validation, N.G.N., K.M.K. and F.K.; formal analysis, N.G.N. and K.M.K., investigation, N.G.N.; resources, N.G.N., K.M.K. and F.K.; data curation, N.G.N., E.M.-K. and K.M.K.; writing—original draft preparation, N.G.N., writing—review and editing, N.G.N., M.S., M.B., T.S., F.K., E.K., S.G., G.G. and K.M.K.; visualization, N.G.N.; supervision, N.G.N. and K.M.K.; project administration, N.G.N., K.M.K. and F.K.; funding acquisition, K.M.K. All authors have read and agreed to the published version of the manuscript.

Funding

Financial support has been provided by the Partnership for Research & Innovation in the Mediterranean area (PRIMA: grant number 1812/PLANT-B), a program supported by the European Union.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding author(s).

Conflicts of Interest

The authors declare no conflicts of interest.

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Agriculture 15 01379 g001
Figure 1. Screening bioassay results regarding the acaricidal activity of various EOs at two concentrations, (A) 0.0013 and (B) 0.0068 μL/cm3 in Petri dishes, and under three EO vapor exposure periods, namely 18, 24, and 48 h. Each figure bar represents an average of ten replications, presented with standard deviations. Bars marked with the same small letter, for each separate assessment time point, are not statistically different according to Duncan’s test (p < 0.05).
Figure 1. Screening bioassay results regarding the acaricidal activity of various EOs at two concentrations, (A) 0.0013 and (B) 0.0068 μL/cm3 in Petri dishes, and under three EO vapor exposure periods, namely 18, 24, and 48 h. Each figure bar represents an average of ten replications, presented with standard deviations. Bars marked with the same small letter, for each separate assessment time point, are not statistically different according to Duncan’s test (p < 0.05).
Agriculture 15 01379 g001
Table 1. Aromatic plant species’ yield in essential oils.
Table 1. Aromatic plant species’ yield in essential oils.
Plant SpeciesPlant Part Used for
Water Distillation		Yield a
(mL/100 g of dw)
1Origanum vulgare (oregano)stalks, flowers, leaves3.1 ± 0.01
2Syzygium aromaticum (clove)flower buds13 ± 0.5
3Lavandula angustifolia (lavender)stalks, flowers, leaves 1.1 ± 0.1
4Origanum dictamnus (dittany)stalks, flowers, leaves0.96 ± 0.01
5Laurus nobilis (bay laurel)leaves1.97 ± 0.01
6Citrus sinensis (sweet orange)peel0.3 ± 0.2
7Mentha piperita (peppermint)stalks, flowers, leaves1.65 ± 0.02
8Eucalyptus globulus (blue gum)leaves0.71 ± 0.03
9Melissa officinalis (lemon balm)stalks, flowers, leaves0.10 ± 0.03
a expressed in dry weight (dw); values represent means (±standard deviation) of three replicates.
Table 2. Concentration–response bioassay and respective calculated LC50 values, R2 values (fitness), Standard Error, and confidence limits (95%) of the three most effective essential oil vapors, namely Origanum vulgare, Syrigium aromaticum, and Origanum dictamnus, against Varroa destructor calculated for three exposure periods in laboratory conditions.
Table 2. Concentration–response bioassay and respective calculated LC50 values, R2 values (fitness), Standard Error, and confidence limits (95%) of the three most effective essential oil vapors, namely Origanum vulgare, Syrigium aromaticum, and Origanum dictamnus, against Varroa destructor calculated for three exposure periods in laboratory conditions.
Origanum vulgareLC50 (μL/cm3 Petri)R2St. ErrorCl95%
18 h>0.0068n.a.n.a.n.a.
24 h0.0030.9920.00030.002–0.005
48 h0.0010.9400.00130.000–0.002
Syzygium aromaticumlC50 (μL/cm3 Petri)R2n.a.n.a.
18 h>0.0068n.a.n.a.n.a.
24 h>0.0068n.a.n.a.n.a.
48 h0.0020.9460.00040.001–0.002
Origanum dictamnusLC50 (μL/cm3 Petri)R2n.a.n.a.
18 h>0.0068n.a.n.a.n.a.
24 h>0.0068n.a.n.a.n.a.
48 h0.0020.9310.00070.001–0.003
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Ntalli, N.G.; Samara, M.; Stathakis, T.; Barda, M.; Kapaxidi, E.; Manea-Karga, E.; Gounari, S.; Goras, G.; Kasiotis, K.M.; Karamaouna, F. The Acaricidal Activity of Essential Oil Vapors and Its Effect on the Varroa Mite Varroa destructor. Agriculture 2025, 15, 1379. https://doi.org/10.3390/agriculture15131379

AMA Style

Ntalli NG, Samara M, Stathakis T, Barda M, Kapaxidi E, Manea-Karga E, Gounari S, Goras G, Kasiotis KM, Karamaouna F. The Acaricidal Activity of Essential Oil Vapors and Its Effect on the Varroa Mite Varroa destructor. Agriculture. 2025; 15(13):1379. https://doi.org/10.3390/agriculture15131379

Chicago/Turabian Style

Ntalli, Nikoletta G., Maria Samara, Theodoros Stathakis, Myrto Barda, Eleftheria Kapaxidi, Elektra Manea-Karga, Sofia Gounari, Georgios Goras, Konstantinos M. Kasiotis, and Filitsa Karamaouna. 2025. "The Acaricidal Activity of Essential Oil Vapors and Its Effect on the Varroa Mite Varroa destructor" Agriculture 15, no. 13: 1379. https://doi.org/10.3390/agriculture15131379

APA Style

Ntalli, N. G., Samara, M., Stathakis, T., Barda, M., Kapaxidi, E., Manea-Karga, E., Gounari, S., Goras, G., Kasiotis, K. M., & Karamaouna, F. (2025). The Acaricidal Activity of Essential Oil Vapors and Its Effect on the Varroa Mite Varroa destructor. Agriculture, 15(13), 1379. https://doi.org/10.3390/agriculture15131379

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