1 Introduction

Wheat (Triticum aestivum L.) comprises one of the most important staple cereal crops farmed in Egypt since ancient times. Cereals are stored for future use as food and seed for additional crop production in the following season. One of the many insects that attack wheat seeds while they are being stored is Sitophilus oryzae (L.) (Coleoptera: Curculionidae), a major pest also known as the rice weevil [1, 2]. This pest damages several crops, including wheat, rice, maize, and split peas, by consuming stored seeds, cereals, and milled grains causing significant economic losses [3, 4]. In addition, one of the most prominent pests in the world is Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), a secondary pest that attacks stored products and seeds [5]. This amplifies the significance of S. oryzae and T. castaneum in the long-term storage of wheat seeds. To prevent financial loss, it is crucial to control these insects.

Numerous fumigants and other synthetic pesticides are frequently employed to manage these pests. However, excessive usage of synthetic pesticides has led to a number of serious issues, including insect resistance. The preservation of stored cereals is becoming more and more problematic due to the pesticide resistance [6]. Some stored-cereal insect species have been shown to be pesticide-resistant in a number of nations, including Egypt [7]. Pesticide efficacy is compromised by pesticide resistance, which has become more prevalent in recent years [8]. In many regions of the world, stored grain insects have a severe problem with cypermethrin, pirimiphos-methyl, and malathion resistance [9, 10]. In some nations, there are alarming indications of widespread phosphine resistance in various species of stored grain insects in several countries, which may have contributed to control failures in some instances [11, 12]. This led, in the Egypt, to a search for newer dust formulation which might replace conventional chemicals.

One potential approach for protecting stored products is the use of nanoparticle formulations [13,14,15,16]. Nanoparticles have special characteristics such as a high surface-to-volume ratio, high reactivity, and improved catalytic and biological activities [17]. They have the capacity to damage insects by breaking through their cell membranes [18, 19]. Additionally, this makes them beneficial for a variety of uses, such as agriculture [20]. The metal silver (Ag) was discovered much earlier and was mostly used in oriental medicine and currency, not much else. Every year, about 500 tons of AgNPs are produced [21, 22]. According to a different source, every year, around 320 tons of silver nanoparticles (AgNPs) are produced for usage in food products, biosensing, and nanomedical imaging [23, 24]. This makes AgNPs the most commercialized nanomaterial.

The application of nanoparticles in medicine has made this subject more significant. AgNPs have unique mechanical and visual properties in addition to their antiseptic, antibacterial, and insecticidal qualities. AgNPs can pass right through cell membranes. AgNPs have attracted the attention of scientists due to their potential as antibacterial agents [25]. Furthermore, artichoke extract [26], olive leaf extract [27], and Cicer arietinum L. green leaf extract [28] were used to create synthetic AgNPs that have antibacterial activities.

Despite the fact that a modest amount of Ag can be useful and promote plant growth and development [29], its cytotoxic effects make it appear as though it could play a significant role in reducing the number of pests, i.e., when silver nanoparticles (AgNPs) combined with malathion, it effectively control the red flour beetle, T. castaneum, infestation [30]. In the process of soil bioremediation, silver is important [31]. The effects of AgNPs on seed germination, plant development, photosynthetic efficiency, and the prevention of microbial growth inside the plant body are all favorable [32].

Lemna minor L., known as duckweed, water lentils, or water lenses, is an eco-friendly macrophyte that is found all over the world [33] and used for the treatment of chemicals in the environment [34]. It is a kind of floating aquatic plant that is classified into five genera: Wolffia, Landoltia, Spirodela, Lemna, and Wolfiella. L. minor and L. gibba, two species of duckweed, are both naturally present in Egypt [35, 36]. Most common duckweed species reproduce asexually, without flowers or seeds. Duckweed is the highest land plant that can reproduce the quickest, while Lemna can treble its weight in a day. It has a long growth season, great productivity, large fertilizer absorption, easy handling, and easy harvest. Each hectare of duckweed yields about 55 tons of dry matter annually [37].

Bio-nanotechnology is a new field that combines biological materials with chemical and physical operations to create nanosized particles. The biological production of NPs using plants is a relatively novel technology. The synthesis of metal NPs using plant extracts is inexpensive and has the potential to replace the production of NPs commercially [38]. Enzymes, amino acids, proteins, carbohydrates, polyphenols, alcoholic substances, vitamins, alkaloids, and polysaccharides are a few examples of biological components and their combinations that decrease metal salts and contribute to the creation and stabilization of metallic NPs [39,40,41,42].

It is still important to research the precise process through which AgNPs are created. When AgNPs are produced, the biomolecules in the L. minor extract act as capping and reducing agents.

Several studies have previously investigated the potential effect of various nanoparticles against stored grain insect pests. Belhamel et al. [43] found that using 400 mg/kg of nanostructured alumina dust as a seed protectant resulted in a 100% mortality rate for Stegobium paniceum, 80.64% for Oryzaephilus surinamensis, and 79.41% for Tribolium confusum. A high concentration of TiO2 nanoparticles significantly increased T. castaneum cumulative mortality after exposure durations for 5 days, according to Hilal et al. [44]. When tested against the red flour beetle T. castaneum, a silica-based nanoformulation effectively controlled the insect [45]. At the highest concentration, ZnONPs significantly reduced the viability of S. oryzae and Callosobruchus maculatus [46]. Thus, it would be advised to use the highest active formulation when utilizing nanoparticles in integrated pest management.

The current study focuses on the synthesis of AgNPs made from an aqueous extract of the duckweed plant (for the first time) in order to reduce harmful compounds that are a source of stabilization and reduction, testing the toxicity of AgNPs, assessing their formulation, contrasting the activity with malathion (1% DP) at the recommended dose and control  against T. castaneum and S. oryzae adults that attack stored wheat seeds, and finally its effect on F1-progeny counts of S. oryzae and T. castaneum adults for long-term storage (one year).

2 Materials and methods

2.1 Materials

Fresh aquatic plant, Lemna minor L. (family Lemnaceae) was hand-collected from canals between farms in Rashid City, Beheira Governorate, Egypt. Silver nitrate (99.9% purity) was provided by scientific wholesalers in Cairo, Egypt. Talc powder is a hydrated magnesium silicate has the chemical formula Mg3Si4O10 (OH)2 or H2Mg3 (SiO3)4. It is offered by El-Nasr Co. for Phosphate in Cairo, Egypt. Malathion 1% DP was provided by Kafr El-Zayat Chemical and Pesticides Company, Egypt.

2.2 Culture of insects (rearing)

The rice weevil Sitophilus oryzae and the red flour beetle Tribolium castaneum used in this study were obtained from  Stored Grains and Product pests Research Department, Plant Protection Research Institute, El-Sabahia, Alexandria, Egypt. T. castaneum grew on a 10:1 w/w mixture of wheat flour and yeast, but S. oryzae developed on sterilized wheat grains. The two pests were housed in colonies that were raised at a constant temperature of 30 °C and relative humidity of 75% in a laboratory. Using the protocol of Strong et al. [47], the adults used were 2 weeks after eclosion from the parent colony.

2.3 Plant extract preparation

The whole duckweed (L. minor) aquatic macrophyte was collected (Fig. 1), rinsed with deionized distilled water to get rid of any residues, then dried at 25 ± 2 °C, powdered using small laboratory mill, and sieved to a fine powder before being stored separately for the tests. Eight grams of the dry powder was combined with 200 mL of distilled water to create the aqueous extract, which was then boiled for 15 min at 60 °C while being constantly stirred with a magnetic stirrer. The L. minor extract suspension was allowed to cool for 3 h before being filtered using Whatman No. 1 filter paper. The filtrate was kept in a dark, airtight container, refrigerated at 4 °C, and utilized during a week. HPLC analysis of polyphenolic components from the plant extract was determined using HPLC-Agilent. HPLC and conditions and program properties are illustrated in our previous work [48].

Fig. 1
figure 1

Lemna minor plant floating on water

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2.4 Green synthesis of AgNPs using Lemna minor macrophyte extract

With a few minor modifications, silver nanoparticles (AgNPs) were biosynthesized in accordance with Faisal et al. [49]. In brief, a flask was filled with 90 mL of the 1 mM silver nitrate solution (AgNO3) and 10 mL of the crude L. minor extract. Aluminum foil was used to cover the flask in order to protect the reduced silver ions from light damage because they are extremely light-sensitive. The combined reactants were heated to 60 °C for 45 min on a magnetic stirrer. To ensure appropriate reduction, the solution was left in full darkness for 24 h. AgNPs in the broth cause a change in color from pale brown to dark brown. After a successful reduction process, the solution was centrifuged at 12,000 rpm for 20 min to obtain pure AgNPs. The pellets were washed three times with distilled water (DW) after the supernatant was removed, and then they were dried in an oven at 80 °C. The dried material was mixed with a few drops of ethanol, then powdered and stored at 7 °C. Then, AgNPs were formulated as a dust powder with 1% AgNPs as the active ingredient and 99% talc powder as the carrier component.

2.5 Characterization of the biosynthesized AgNPs

The characterization of AgNPs was completed in the Central Laboratory of the Faculty of Pharmacy and Faculty of Science at Alexandria University, Egypt. A UV/VIS spectrophotometer (943UVA 1002F, Spectronic Helios alpha, Thermo, UK) was used, according to Behzadi et al. [48], to determine the optical characteristics of the produced AgNPs over a 200–750 nm scan range. Energy dispersive X-ray (EDX) scanning electron microscopy (JSM-IT200, JEOL, Japan) was used to study the morphology of dried AgNPs as described by Ramazanli and Ahmadov [27]. The sample was put under vacuum pressure on the metal disc. Element analysis has also been done in SEM analysis. The analysis of FTIR (Fourier-transform infrared spectroscopy) spectra by following the technique as provided by Mahmoud et al. [50] was done using SPECTRUM 10 (Perkin-Elmer, USA); the analyzed liquids were combined with KBr to prepare solid disks for FTIR scanning. The device’s adjustment range was 450–4000 cm−1 with a resolution of 8 cm−1. The resulting spectrum was interpreted based on each active group’s vibration pattern to investigate the functional groups act as capping agents on AgNPs’ surface, as well as functional groups involved for reducing AgNPs. In order to measure the zeta potential, the nanomaterial is sonicated in deionized water for almost 30 min, and a cuvette containing 20 µL of the dispersed solution is used to measure the zeta potential. The procedure is repeated three times to get the average zeta potential value (Nano ZS, Malvern Panalytical, UK) to assess the physical stability, and the surface charges of AgNPs were negatively or positively charged.

2.6 Contact toxicity bioassay

The contact toxicity technique was used to evaluate the insecticidal activity of the green-synthesized AgNPs and its toxic effect against two selected pests, Tribolium castaneum and Sitophilus oryzae [51]. A stock suspension of AgNPs (300 mg/L) was prepared with DW and sonicated for 30 min. After that, DW was used to dilute the stock solution and create concentrations 75, 150, 225, and 300 mg/L of AgNPs. They were applied within a 9-cm-diameter glass Petri dish and distributed equally over the dish’s whole surface. The solution was left to dry at room temperature, leaving a thin layer on the dishes’ floors. After the solvent had evaporated, 20 of each insect species were separately placed in each Petri dish. A total of three replicates of each treatment were made. The number of dead insects was counted and the mortality rate was calculated after treatment for 24, 48, and 72 h. The LC50 values were calculated using Finney [52].

2.7 Efficacy of formulated green-synthesized AgNPs 1%DP seed treatments on adult mortality and emergence of Tribolium castaneum and Sitophilus oryzae

The study was carried out at the Department of  Stored Grains and Product pests Research, Plant Protection Research Institute, Agricultural Research Center, Sabahiya, Alexandria, Egypt, at a laboratory environment of 28 ± 2 °C and a relative humidity of 70 ± 5%. To assess the effectiveness of formulated green-synthesized AgNPs 1% dust powder as seed treatments, freshly harvested certified seed (Misr 2) was used for each treatment. According to Qi and Burkholder [53], wheat seeds were mixed with a formulation of 1% dust powder of green-synthesized AgNPs 1% dust powder and malathion (1% DP). After 12 months of storage, the tested formulation’s impact on adult mortality and the number of progeny was assessed.

Green synthesized AgNPs (1% DP) and malathion (1% DP) were applied to wheat seeds in various concentrations (0.025, 0.05, 0.1, and 0.2 g/100 g seeds), with a recommended concentration of 0.1 g/100 g seeds. Every concentration was mixed with wheat seeds. One hundred grams of wheat seeds were divided into three equal duplicates in glass jars for each concentration. Following treatment, 10 pairs of newly emerging adults of S. oryzae and T. castaneum were introduced to each jar, infecting the treated wheat seeds. Every week, mortality was recorded for 2 weeks, and the overall number of progeny was counted at 6 weeks, and 3, 6, 9, and 12 months after treatments.

2.8 Progeny production counts

After the mortality count on day 14, all adults, both dead and alive, were taken from the jars, and seeds were placed in the same conditions for an additional 6 weeks, as well as for 3, 6, and 12 months post-treatment in order to determine the production of progeny. The Aldryhim formula was used to calculate the percentage reduction in progeny production based on the count of immature and adult emerging individuals in the treated seeds and controls [54].

$$\mathrm{Reduction\;in\;progeny \%}=\frac{{\text{No}}.\mathrm{\;of\;adults\;in\;control}-\mathrm{ No}.\mathrm{\;of\;adults\;in treatment }}{{\text{No}}.\mathrm{\;of\;adults\;in\;control}}\times 100$$

2.9 Seed germination percentage

After 6 and 12 months of storage, germination tests were performed on wheat seeds treated with the formulated green-synthesized AgNPs (1% DP) and malathion (1% DP) based on [53] with minor modifications. Sixty seeds were divided into three replicates for each treatment and placed on a Petri dish with cotton layers rather than filter paper that had been soaked in tap water. Four days later, the germination of seeds was recorded. The results of the germination test for all treatments and the control were recorded using the following formula for estimating the percentages of germination [55].

$$\mathrm{Germination\;Percentage \%}=\frac{\mathrm{Total\;germinated\;seeds }}{\mathrm{Total\;seeds}}\times 100$$

2.10 Data analysis

The lethal concentration (LC50) was calculated from the toxicity data using a Probit analysis, for 24, 48, and 72 h. All data were subjected to a one-way analysis of variance (ANOVA) followed by least significant difference (LSD) at 0.05 level of probability [56] to estimate the significance of variations in treatment mean values at probability (P < 0.05). The mortality rate was calculated and corrected using the following formula [57]:

$$Corrected\;mortality=\frac{(\mathrm{Mortality\%\;of\;treated\;insects}-\mathrm{ Mortality\%\;of\;control })}{(100-\mathrm{Mortality\%\;of\;control}) }\times 100$$

3 Results and discussion

3.1 Biosynthesized of AgNPs by L. minor plant aqueous extract

The change in color of the colloidal solution from light brown to dark brown suggests the production of AgNPs (Fig. 2). These were in reaction to the aqueous extract’s bioactive component content like vanillic acid (8595.24 µg/g), benzoic acid (4841.3006 µg/g), quercetin (906.07 µg/g), resveratrol (495.419 µg/g), ferulic acid (324.79 µg/g), rutin (199.92 µg/g), p-hydroxy benzoic acid (181.67 µg/g), rosmarinic acid (155.28 µg/g), ellagic acid (122.61 µg/g), and o-coumaric acid (122.18 µg/g) as shown Table 1 and Fig. 3 of HPLC analysis.

Fig. 2
figure 2

Change in color of the reaction mixture during the formation of AgNPs

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Table 1 Phytochemical compounds identified in aqueous extract from L. minor plant
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Fig. 3
figure 3

HPLC chromatograms of the identified phytochemical compounds in the aqueous extract from L. minor biomass

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There have been various bioactive substances or allelochemicals found in L. minor plants [58]. Flavonoids and fatty acids substances were present in L. minor plant extract [59]. Twelve amino acids, lignin, sugars, amino acids, dipeptides, flavonoids, biflavonoids, fatty acids, together with three organic acids (p-coumaric, cinnamic, and sinapic acids) were identified in L. minor extract [60], phytol, campesterol, loliolide, dihydroactinediolide, ascorbic acid, vanillic acid, 2,3-dihydroxybenzoic acid; caffeic acid, chlorogenic acid, esculetin; esculin, and fraxetin were also reported [61, 62].

3.2 Structural characterization of Ag-NPs

3.2.1 UV/Visible analysis

The UV–Vis spectrum of AgNPs appeared to change in color of the colloidal solution from light brown to dark brown as the AgNPs were produced in the reaction mixture as a result of the AgNPs’ surface plasmon vibrations being activated. The formation of the AgNPs shown in Fig. 4 was observed using a UV–Vis spectrophotometer with a wavelength range of 200 to 750 nm. The UV–Vis spectra showed a single, strong peak at 450 nm. Previous studies have also shown that silver nanoparticles are responsible for peaks between 410 and 460 nm [63, 64].

Fig. 4
figure 4

UV–vis absorption spectra of colloidal AgNPs synthesized using Lemna minor

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3.2.2 Scanning electron microscope analysis of AgNPs

A scanning electron microscope (SEM) was employed to investigate the morphology, size, and crystalline nature of AgNPs. Figure 5, a magnified SEM image, shows that the majority of the particles are spherical in shape and that their sizes range from 29.42 to 52.30 nm, with an average size of 40.56 nm. Furthermore, the AgNPs were not in close contact in the aggregated condition, indicating that the capping agent was stabilizing the AgNPs.

Fig. 5
figure 5

SEM image of the synthesized AgNPs by L. minor plant aqueous extract were taken at × 40,000 magnification (20 kV)

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However, the abovementioned results are in agreement with the findings of a lot of scientists on various plant species, i.e., a spherical shape with a diameter of 38–62 nm for AgNPs was synthesized using Mangifera indica peel aqueous extract [65]. Additionally, spherical particles with a size distribution ranging from 10 to 25 nm were synthesized using a Moringa oleifera leaf aqueous extract [66]. Spherical particles with a size distribution ranging from 7.12 to 18.8 nm were synthesized using an olive leaf extract [27]. Moreover, spherical particles with a size distribution ranging from 6.11 to 9.66 nm were synthesized using a Cicer arietinum leaf aqueous extract [28]. Additionally, it was claimed that an aqueous extract of Malvaviscus arboreus leaves could be used to successfully biosynthesize spherical AgNPs with a mean diameter of 21.8 nm [67]. It was shown that synthetic AgNPs are spherical in nature and have an average size of about 80 nm using an aqueous extract of Azolla pinnata [68]. Due to their small size, biosynthesized nanoparticles are expected to have better insecticidal action.

3.2.3 Energy-dispersive X-ray (EDX) analysis of AgNPs

The elemental analysis of AgNPs was performed using an EDX coupled to an SEM. The presence of Ag was verified by the Ag peak in the EDX spectrum. AgNPs demonstrated a high signal (18.41%) as well as a characteristic optical absorption peak at 3 kV owing to metallic silver due to surface plasmon resonance (SPR), which confirmed the UV–Vis data, as shown in Fig. 6. Two additional significant signals in the EDX spectroscopy for C (25.37%) and O (34.24%) indicate that the extracellular components of L. minor extracts effectively capped the AgNPs on the nanoparticle surface. Additionally, C and Cu signals are derived from the carbon-coated copper grid used in SEM sample preparation and EDX analysis. Additionally, there are additional indications on the particle surfaces, including Na, Ca, N, Mg, Al, Si, P, S, Cl, and K, which could be chemical components in L. minor [61, 62, 69]. The EDX pattern reveals unequivocally that the AgNPs are crystalline in form as a result of Ag ion reduction by using L. minor extract. The findings obtained agree with other results obtained by utilizing different plants that also exhibit similar types of findings [70,71,72].

Fig. 6
figure 6

EDX spectrum showing elemental composition analysis of AgNPs

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3.2.4 Fourier-transform infrared spectroscopy (FTIR)

Fourier-transform infrared spectroscopy (FTIR) was used to determine the potential L. minor secondary metabolites involved in the extract and AgNO3 reduction processes. The FTIR spectra of the AgNPs showed that the particles were potentially active, with functional groups spanning from 450 to 4000 cm−1 (Fig. 7). The spectrum clearly shows the intense peaks situated at 3436, 2074, 1634 cm−1, and below 583 cm−1. The significant FTIR peaks correspond to the amide I and II, as well as the -OH stretch of alcohols and phenolic compounds found in L. minor extract. The peak of absorption at 1634 cm−1 might be attributed to protein -NH scissoring (amide I) [73, 74]. Furthermore, the peak of absorption at 3436 cm−1 is similar to that observed for -OH stretching of plant extracts, including alcohols and phenolic chemicals [74,75,76,77]. The absorption band at 2074 cm−1 may be classified as an alkynes group characteristic [78]. These results show that carbonyl groups in proteins strongly attach to metals, indicating that proteins may have also formed a layer with bioorganics to protect interactions with phytosynthesized NPs. In order to prevent agglomeration during the synthesis of AgNPs, we can infer that some biological elements of the L. minor extract, such as proteins and metabolites, served a dual purpose of bio-reduction and stabilization. This led to the stability of the AgNPs in the medium [79]. Similar results were found by Khandel et al. [80], who synthesized AgNPs from the lichen Parmotrema tinctorum in their study. In order to create bioactive AgNPs, an aqueous extract of M. arboreus leaves [67] and Mentha pulegium leaves was used [81].

Fig. 7
figure 7

FTIR image of biosynthesized AgNPs from L. minor plant extract

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3.2.5 Zeta potential measurement

The ζ-potential was utilized to assess the surface condition and stability of the biogenic AgNPs. The highly negative value of the ζ-potential keeps the nanoparticles from conglomerating together, which refers to the stability of the colloid AgNPs. However, nanoparticles that have a significantly lower negative charge can enter the cell more readily [59,60,61]. The biosynthesized AgNPs had a zeta potential of − 27 mV, as shown in Fig. 8. This result showed that the AgNPs were evenly widespread and consistently stable. Therefore, with good colloidal nature, it may conclude that using biological techniques enables the production of stable nanoparticles free of stabilizers. Previous studies have documented the ζ-potential values of AgNPs synthesized from diverse materials [28, 71, 82].

Fig. 8
figure 8

Zeta potential data of green-synthesized AgNPs

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3.3 Contact toxicity bioassay

The results of the residual film technique used to assess the contact toxicity of green synthesized AgNPs against T. castaneum and S. oryzae, are presented in Table 2 and 3 and Figs. 9 and 10. The comparative toxicity as a speed of action (initial effect) after 24 h of treatment and as a long-acting (residual) effect after 48 and 72 h of treatment of green-synthesized AgNPs against adults of S. oryzae is illustrated in Table 2 and Fig. 9, the LC50 values of synthesized AgNPs were the most toxic to adults of S. oryzae with LC50 values of 6.79, 6.30, and 6.08 μg/ml after 24, 48, and 72 h, respectively.

Table 2 The LC50 values of green synthesized AgNPs on Sitophilus oryzae adults utilizing thin film residue after 24, 48, and 72 h of exposure
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Table 3 The LC50 values of green synthesized AgNPs on T. castaneum adults utilizing thin film residue after 24, 48, and 72 h of exposure
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Fig. 9
figure 9

Ld-P lines of green-synthesized AgNPs efficacy against S. oryzae adults after 24, 48, and 72 h

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Fig. 10
figure 10

Ld-P lines of green-synthesized AgNPs efficacy against T. castaneum adults after 24, 48, and 72 h

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The LC50 values of synthesized AgNPs were 8.64, 7.83, and 7.03 μg/ml after 24, 48, and 72 h, respectively, against the adults of T. castaneum are shown in Table 3 and Fig. 10 in the treatment condition. In light of the current findings on the impact of green-synthesized AgNPs, data showed that S. oryzae was more susceptible than T. castaneum. Additionally, as the exposure period was extended, the LC50 values of S. oryzae and T. castaneum steadily reduced.

In order to demonstrate contact toxicity effects against T. castaneum and S. oryzae after 24 h, the biogenic AgNPs derived from Myriostachya wightiana leaf extracts was used [83]. The mortality rates of 29% and 20.3%, respectively, were observed at a concentration of 50 g. While after 24 h, T. castaneum and S. oryzae insects died at rates of 55.2% and 47.4%, respectively, from the highest dose (150 g).

In order to calculate the LC50 for adults of T. castaneum, the fabricated AgNPs using the chemical reduction method and mixed with wheat grain were used [30]. After 24 and 72 h, they found that the LC50 was 92.25 and 36.84 mg, respectively. The effectiveness of green-manufactured AgNPs was examined by Sedighi et al. [84] using sweet orange peel extract. The results showed that the generated AgNPs’ LC50 values for the filter paper residue tests against the adult T. confusum were 30.62 ppm. The reason for the significantly greater reductions in adult populations could be attributed to the high surface area to volume ratio of nanoparticles. This feature increases the possibility of the formulation coming into contact with adults, as they can pass through insect cell membranes and cause damage to the insects [30].

3.4 Effect of formulated AgNPs and malathion 1% DP seed treatments on adult mortality of S. oryzae and T. castaneum

The findings clearly showed that, as compared to the control, mortality rates for all treatments ranged widely. When compared to treatment with the standard check malathion, which provided 86.67% mortality, Table 4 shows that the maximum mortality of 90% was obtained against S. oryzae at the highest concentration (0.2 g/100 g seed) with the formulated green-synthesized AgNPs seed treatment as dust powder 1% (AgNPs 1% DP).

Table 4 Effect of malathion 1% DP and formulated AgNPs 1% DP on the mortality of S. oryzae
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In the case of T. castaneum, Table 5 shows the treatment with the standard check Malathion was superior, producing 80% mortality at a recommended dose of 0.1 g/100 g seeds, compared to the treatment with AgNPs (1% DP), which caused 73.33% mortality after 1 week of exposure. After 2 weeks of exposure, both concentrations of 0.1 and 0.2 g/100 g seeds of the tested formulation of AgNPs produced 100% mortality of exposed adults of S. oryzae, compared to treatment with the standard check malathion, which caused 96.67% mortality. In the instance of T. castaneum, the formulated AgNPs (1%DP) were superior, providing the greatest mortality of 98.33% with a concentration of 0.2 g/100 g seeds compared to treatment with the standard check malathion, which produced 95% mortality.

Table 5 Effect of malathion 1% DP and formulated AgNPs 1% DP on the mortality of T. castaneum
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3.5 Effect of formulated AgNPs and malathion 1% DP seed treatments on adult emergence of S. oryzae and T. castaneum

All grain protectant concentrations were shown to be considerably superior in terms of reducing adult emergence. The adults that emerged from wheat seeds treated with green-synthesized AgNPs (1% DP) and malathion (1% DP) differed significantly between treatments. As seen in the toxicity trials on adult mortality, the green-synthesized AgNPs (1% DP) treatments outperformed malathion (1% DP). After 6 weeks of treatment, no S. oryzae adult emergence was seen from wheat seeds treated with the formulated green synthesized AgNPs (1% DP) at both concentrations 0.1 and 0.2 g/100 g seeds and malathion (1% DP) at concentration 0.1 g/100 g seeds, as indicated in Table 4. In the case of T. castaneum, AgNPs (1% DP) treatments gave superior performance to malathion (1% DP). No T. castaneum adult emergence was observed from wheat seeds treated with AgNPs (1% DP) at a concentration of 0.2 g/100 g seeds, where the reduction in progeny percentage was 100% for AgNPs (1% DP) at the high concentration. While malathion (1% DP) resulted in few emergences of adults of 2, the reduction in progeny percentage was 96.29% and ranked as the second best treatment after AgNPs (1% DP) after 6 weeks of treatment, as shown in Table 5.

Green-synthesized AgNPs (1% DP) treatments with concentrations of 0.1 and 0.2 g/100 g seeds were similarly effective and fully inhibited adult emergence even after 3 months of seed treatment, while malathion (1% DP) resulted in 14 adult emergences with a 93.26% reduction in progeny percentage and was scored as the second-best treatment after 3 months of treatment, as indicated in Table 4. In the instance of T. caastneum, the green-synthesized AgNPs (1% DP) represented the first position by providing no adult emergence, and the reduction in progeny percentage was 100%. While malathion (1% DP), which on par with the concentration of 0.1 g/100 g seeds of the green synthesized AgNPs (1% DP), proved to be the second best treatment, which resulted in a few six adults and the reduction in progeny percentage was 90.90%, as shown in Table 5.

At 6 months of seed treatment, the green-synthesized AgNPs (1% DP) completely diminished the population increase of S. oryzae and achieved a 100% reduction in adult progeny at a concentration of 0.2 g/100 g seeds, followed by a concentration of 0.1 g/100 g seeds, which achieved a reduction in progeny percentage of 97.50%. While malathion (1% DP) resulted in few emergences of S. oryzae adults of 42 with a reduction in progeny percentage was 88.33% after 6 months of treatment, as shown in Table 4. In the case of T. castaneum, the green-synthesized AgNPs (1% DP) at concentration 0.2 g/100 g seeds remained the best compound, giving few adult emergences 4 adults and a reduction in progeny percentage was 94.66%, as shown in Table 5. While malathion (1% DP), which is on par with AgNPs (1% DP) at concentrations of 0.1 g/100 g seeds, proved a reduction in progeny percentage of 81.33% with 14 adult emergences.

At 9 months of seed treatment, a similar trend was observed where the least number of adults emerged in the green-synthesized AgNPs (1% DP) at both concentrations of 0.2 and 0.1 g/100 g treated seeds, with 5 and 20 adults of S. oryzae, respectively, with reductions in progeny percentage of 98 and 92%, respectively, followed by malathion (1% DP) at the recommended concentration of 0.1 g/100 g seeds, where 61 adults emerged with a reduction in progeny percentage of 75.60%, as shown in Table 4. In the case of T. castaneum, the green-synthesized AgNPs (1% DP) at a concentration of 0.2 g/100 g seeds remained the best compound, providing a few adult emergences (16 adults) and a reduction in progeny percentage of 71.92%, followed by a concentration of 0.2 g/100 g seeds of AgNPs (1% DP) remained the second compound, providing a few adult emergences 21 adults and reduction in progeny percentage was 63.15% followed by malathion (1% DP) providing 26 adult emergences and a reduction in progeny percentage was 54.38%.

After a year of treatment, the adult number of S. oryzae that emerged from the green-synthesized AgNPs (1% DP) is shown in Table 3, which gave 7 adults at a concentration of 0.2 g/100 g seeds with a reduction in progeny percentage of 95.27% and was still ranked number 1. Malathion (1% DP) provided 53 adults with a reduction in progeny percentage of 64.18%, which was followed by providing 25 adults with a reduction in progeny percentage of 83.10%. Regarding the T. castaneum adults that emerged as indicated in Table 5, the green-synthesized AgNPs (1% DP) provided 24 adults at concentration 0.2 g/100 g seeds with a reduction in progeny percentage of 51.02% and remained ranked number 1 after concentration 0.1 g/100 g seeds of AgNPs (1% DP). Following malathion’s (1% DP), which provided 28 adults with a reduction in progeny percentage of 42.85%, the (1% DP) provided 25 adults with a reduction in progeny percentage of 48.97%.

The current study’s findings are among fewer publications concerning the application of formulated green-synthesized silver nanoparticles as seed protectants, particularly against T. castaneum and S. oryzae. We found that both insects’ mortality rates rose at the highest concentrations and during the longest exposure time of the treatment application. Additionally, parental exposure to the green-produced AgNPs caused the F1 progeny of both insects to significantly and/or completely reduce (100% inhibition), especially at the highest concentrations utilized. The findings of Alif Alisha et al. [30] are completely consistent with our recent research’ findings, which showed that high insecticidal efficiency for T. castaneum control was achieved with AgNPs. Plant-mediated green AgNPs produced by prostrate spurge plants [85] and grey mangrove [86] resulted in increased mortality in S. oryzae, followed by Rhyzopertha dominica and T. castaneum. In addition, it was reported that Callosobruchus maculatus adult and larvae mortality increased by 83% when AgNPs were applied at a rate of 1.00 g/kg of seed [87]. In other work, it was indicated that at a concentration of 50 mg of malathion causes 95% mortality, compared to 75% for AgNPs [30]. Also, the egg production of C. maculatus and T. castaneum was effectively decreased to 18 eggs per female and 85 eggs per female with a concentration of 2000 ppm of AgNPs produced from Azadirachta indica leaf extracts [88]. Likewise, the produced AgNP s from false flax extract caused 60.1% mortality in Oryzaephilus surinamensis and 46.2% mortality in Sitophilus granarius after a 72 h exposure period [89]. Moreover, the green AgNPs formed with the extract of peel sweet orange killed T. confusum at a rate of 83–77% [84]. The AgNPs derived from Moringa oleifera leaf extract had a maximum kill rate against S. oryzae of 100% after 15 days of treatment [90]. Furthermore, the insecticidal activity of AgNPs formed from the extract of the Calotropis procera and C. gigantea leaves against T. castaneum at a high concentration of 1.85 mg/cm2 was reported [5]. It can be concluded that biological nanoparticle production is an environmentally friendly process given the advantages of nanoparticles as biocontrol agents, which have been shown by the previously mentioned research, as well as the fact that when nanoparticles are produced biologically, their concentrations can be lowered with an effective mortality rate.

3.6 Effect of green-synthesized AgNPs-treatment seed on germination of wheat seeds

Germination, as defined by Black [91], is the emergence of the first symptoms of growth, i.e., the visible protrusion of the radical. Various factors, including temperature, moisture, seed damage, fungal and insect infestation, and protectant materials, might influence germination. The impact of the formulated green-synthesized AgNP seed treatment as dust powder 1% and malathion (1% DP) on wheat seed germination percentages after 6 weeks, 3, 6, 9, and 12 months of post-treatment is given in Table 6. The results showed that exposure to AgNPs (1% DP) all concentrations of 0.025, 0.05, 0.1, and 0.2 g/100 g seeds had positive significant effects on the germination of wheat seeds during storage; however, the highest germination percentages of 100, 98.67, 96.67, 95, and 93.33% for storage periods of 6 weeks, 3, 6, 9, and 12 months, respectively, were recorded for seeds treated with 0.1 g/100 g seeds. However, treatment with malathion (1% DP) had a marginal effect on seed germination after 6 weeks and had no effect on the germination of wheat seeds after storage for 3 and 6 months, it had a negative effect after 9 and 12 months.

Table 6 Effect of plant-mediated green silver nanoparticle seed treatment on germination of wheat seeds
Full size table

This is consistent with the findings of the prior research study, which showed that green-synthesized AgNPs had a positive effect on seed germination. The synthesized AgNPs had demonstrated significant potential to improve wheat seed germination at a lower dosage of 25 mg/L [92]. In an additional study, the green-synthesized AgNPs increased seed germination, with the greatest germination rate of 95% occurring in plants treated with 20 ppm of the substance [93]. Furthermore, AgNP exposure had significant effects on seed germination in watermelon, maize, and zucchini plants [94]. In addition, the biologically generated AgNPs increased the percentage of seed germination in pearl millet [95]. This could be explained by the fact that NPs are likely designed to penetrate the seed coat and assist in seed germination. According to studies on the effects of NPs on seed germination mechanisms, NPs might be useful for seed water absorption [96].

On the contrary, after applying AgNPs, the germination of wheat seeds was unaffected [97]. Additionally, the AgNPs that formed using the extract of black seeds and prepared at different concentrations had no impact on the rate of germination of wheat seeds [98]. On the other hand, treatment with AgNPs had no effect on seed germination of Vicia faba [99], Arabidopsis thaliana [100], and tomatoes [101]. This might be clarified by the grain coatings’ protective properties, which could include selective permeability. In order to reduce toxicity and exposure to seeds, AgNPs can interact or form complexes with ligands [98].

4 Conclusion

Duckweed (Lemna minor L.) aquatic macrophytes were effectively used for the consistent and easy synthesis of AgNPs, which is an economical and eco-friendly technique using L. minor aqueous extracts. SEM revealed that NPs were pure metallic silver in nature, spherical in shape, and had an average size of 40.56 nm. The optical behavior of colloidal samples as well as the presence of various extract biomolecules were investigated by UV–Vis, the formation of silver nanoparticles was confirmed by the appearance of a characteristic peak at 450 nm in the UV–Vis spectra, and FTIR confirmed that proteins and polyphenolic compounds found in the aqueous extracts of L. minor serve as capping agents during the production process and prevent the reduction of silver particle agglomeration. A negative ζ-potential of − 27 mV was found, indicating that the silver nanoparticle colloidal solution was stabilized. The findings of the bioassay, including the mortality tests, demonstrated that silver nanoparticles showed the highest insecticidal activity against S. oryzae and T. castaneum, as well as a significant positive effect on wheat seed germination during storage. Therefore, Ag NPs have good potential as a seed protective agent if applied with proper safety measures. This work might open the door for the use of nanomaterial-based technologies in the pesticide industry.