Chemical characterization, fumigant toxicity and antifeedant activity of essential oils of four indigenous plants against Rhyzopertha dominica (Coleoptera: Bostrychidae)

ABSTRACT


Introduction
The most significant crop in the world, wheat serves as the main protein

Source of essential oils and extraction protocols
The EOs tested in the present study

Rearing of Rhyzopertha dominica
The lesser grain borer R. dominica  Positive values expressed a feeding deterrent effect and negative values expressed a feeding stimulant effect.

Data analysis
Statistical analysis of the toxicity data was performed using Probit analysis to estimate the LC 50 (LDP line, http://www.ehabsoft.com/ldpline/).One-    In studied the antifeedant activity of some EOs against T. castaneum and S. oryzae and found that all tested EOs had an antifeedant activity against both tested insects.

Conclusion
Our findings indicated that the tested EOs could be a promising tool against the lesser grain borer, R. Funding: There is no fund for this study Data Availability: The data used to support the findings of this study will be available from the corresponding authors upon request.

Compliance with ethical standards
Ethical approval and consent to participate: We declare that we do not have human participants, human data or human tissue involved in the study.
Consent to publish: All authors consent to the publication of the manuscript.

Competing interests:
The authors declare that they have no conflict of interest.

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source in developing and impoverished nations (Grote et al., 2021).Wheat must be stored properly both during the yearround storage of wheat grains and during transportation between wheat producers and consumers.Due to the summer's high temperatures and humidity, which are ideal for the growth of pests that feed on stored goods, wheat grains become more vulnerable to protection (Abouelatta et al., 2022).One of the main pests of products that are stored is the lesser grain borer, Rhyzopertha dominica (Coleoptera: Bostrychidae).If preventive measures are not taken, insect infestation during storage can result in a frustrating weight loss of stored wheat in less than six months (Abouelatta, et al., 2022; Abo Arab et al., 2022).Synthetic pesticides and fumigants are largely used to control this pest, but their use has resulted in environmental disruption, rising application costs, pest resurgence, pest resistance to pesticides, lethal effects on non-target organisms, and direct toxicity to users (Pangnakorn, 2018).Therefore, natural insecticides, fumigants, and feeding deterrents make sense substitutes for synthetic pesticides.One potentially significant source of these substitute control strategies is phytochemicals.The essential aromatic components that give a plant its unique flavor or odor are found in essential oils (EOs), which are byproducts of secondary metabolism in plants (The use of essential oils (EOs) derived from various aromatic plants to control stored-product insects has been the subject of an increasing number of studies due to their complex mechanism of action, to which insects find it extremely difficult to become resistant MS) and to examine the fumigant insecticidal properties of the essential oils derived from four commonly found aromatic plants in Egypt against adults of R. dominica.
were violet absolute, Viola odorata, neroli absolute, Citrus aurantium, parsley oil, Petroselium crispum, and marjoram, Origanum majorana, they were purchased from Hashem Brothers Company, Giza, Egypt.For the extraction of violet absolute and neroli absolute, about 10 kg of violet herb and 5 kg fresh bitter orange flowers were placed separately in a still (50 L capacity), and extraction was done using hexane solvent.A 30 L of hexane was added to the herb inside the still to cover the whole herb.After 2 h, hexane was withdrawn for the concentration step till 5 L with a greenish color.The previous process was repeated twice with different soaking times, i.e., 2h and 12 h.remove all the solvent and to obtain the concrete (which contains absolute and wax) under 50 ºC and vacuum -1 bar.After 24 h, the concrete was dissolved in ethyl alcohol 99% undercooling and filtered 5 times to ensure complete wax removal.Next, all the solvent (ethyl alcohol which contains absolute) was transferred to the final concentration apparatus at 70 ºC and -1 bar (vacuum) to remove the ethyl alcohol and obtain the violet absolute only (Holst, 2020).The obtained violet absolute was filtered twice using filter paper and kept in the fridge.Parsley and marjoram oils were extracted from airdried parsley and marjoram herbs for 24 h.About 15 kg of the air-dried herb were loaded in a still (50 L capacity), and direct water steam passed through the herb inside the still at 120 ºC and 1.5 bars for 1.5 h to a condenser using cold water to condense the steam that carries oil inside (Holst, 2020).After distillation, oil was separated from water by a glass separator, and the oil obtained was filtered twice and kept in the fridge.Phytochemicals profile of the essential oils The essential oil constituents for each test plant.The model (HP5890) was manufactured in the USA and used an HP column (60 meters by 0.25 millimeters, 0.25 μm film thickness) (HP-5ms).The temperature was 60°C at start and reached a maximum of 250 °C for 65.3 minutes.The temperature of the injector was 240 °C.Using the apparatus software, relative percentage amounts were computed from the total area of the peaks.All compounds were identified by comparing the mass spectra data with those stored in a computer library ( of 14 days old.Vials were immediately closed with their screw tapes containing the treated filter paper discs.The vials were left in the same laboratory conditions mentioned above.The same steps were repeated for the control, except for treating the filter paper discs with pure acetone.Each treatment was repeated three times for each evaluation period.Assessments of mortality were recorded after 12, 24, and 48 h postexposure.Mortality data were corrected by the Abbott formula (Abbott, 1987).Antifeedant activity of the essential oils A paste of wheat flour and distilled water at a 1:1 ratio was made, and the dough was rolled into thin round discs (2 mm thickness and 30 mm diameter).The wheat flour discs were then dried in a hot air oven.Separately, wheat flour discs were treated with aliquots of 100 µL (1/10 of the amount applied in the fumigation test) of each EO at different concentrations, i.e., 125, 250, 500, and 1000 mg/L.The wheat flour discs treated with acetone alone served as a control.After evaporation of the solvent, the wheat flour discs were weighed and placed separately in Petri dishes (1.5 cm height and 9 cm diameter).Ten R. dominica adults (7-14 days old) were placed onto the treated wheat flour discs.The experiment was carried out in triplicates (n= 3 x 10).After 72 h, the remaining wheat flour discs were weighed again, and mortality of insects was recorded.Nutritional indices (Huang and Ho 1997) were estimated as follows: Feeding deterrence index (FDI) (%): where: C = the consumption of control discs and T = the consumption of treated discs.

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of the oils themselves, where major and/or minor compounds have been shown to have insecticidal properties against a variety of insect pests including stored grain pests.The essential oils extracted from parsley (P.crispum) were found to be toxic For Plodia interpunctella larvae (Pascual-Villalobos et al., 2015), and stored grain pests (Maroufpoor et al., 2016).In a different study, C. aurantium was toxic against Sitotroga cerealella (Song et al., 2016).Other studies using extracts of V. odorata found that they were not very effective (Saleem et al., 2018).Acetyl esterase inhibition activity of O. Mielecki et al., 2020).Permeabilization is a mechanism by which essential oils can damage both the cell and the cell membrane (Cristani et al., 2007; Nazzaro et al., 2013).
O. majorana achieved higher toxicity against adults.The EOs of O. majorana and C. aurantium were more deterrents for feeding adults.Therefore, the current study may recommend the use of bioactive components of plant-based essential oils as a suitable alternative to synthetic chemical insecticides, reducing the disorders resulting from the heavy use of pesticides.Also, the oil components may be introduced as an element of an integrated pest management program.Author contributions: All authors contributed to the study conception and design.Material preparation, data collection and analysis were performed by Mervat A. Seada, and Ahmed M. Abouelatta.The first draft of the manuscript was written by Mervat A. Seada and Amal Moustafa Hamza and all authors commented on previous versions of the manuscript.All authors read and approved the final manuscript.

Table (
Feeding deterrent indices of EOs of violet (Viola odorata), neroli (Citrus aurantium), parsley (Petroselium crispum), and marjoram (Origanum majorana) against adults of Rhyzopertha dominica fed on flour wheat discs treated with different concentrations of the tested Eos.