Introduction

The global population is currently about 7.3 billion. The United Nations (UN) estimates that by 2050, that number will grow to 9.7 billion. Africa will experience the largest population growth, followed by Asia (McNabb 2019). As part of its Sustainable Development Goals agenda, the UN announced in September 2015 that it drastically reduced global food losses and cut back on food waste worldwide by 2030 (Sheahan and Barrett 2017). Accordingly, it can be said that post-harvest storage technology is the most important issue of food production, which can engage in food security in different ways to reduce post-harvest loss; these ways provide enough food for consumption to improve our food security (Kiaya 2014). In addition to being used immediately after harvest, some agricultural products are kept in warehouses for future use or export. Various biotic and abiotic factors lose many stored products (Jayakumar et al. 2017). The maximum post-harvest losses of cereal grains in most developing nations are approximately 50–60% of cereal grains lost during storage (Kumar and Kalita 2017). In addition, stored grain insects cause damage to 20%–25% of the grains (Rajashekar et al. 2012). Approximately 12%–15% of the wheat produced in Egypt is also lost, but the main causes are pests, improper storage, and poor transportation (IFPRI 2017). Moreover, in Egypt, post-harvest losses were estimated at 20% of the total wheat produced yearly (McGill et al. 2015).

In Egypt, the rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae) is the most notorious and damaging storage insect pest known (Saad et al. 2018). Due to grain weight loss brought on by insect feeding, this insect pest infestation in stored grain results in quantitative damage. In addition, it causes qualitative damage attributable to the loss of nutritional, aesthetic, and industrial values. By feeding on seed embryos, the insect also decreases germination under favorable conditions; S. oryzae can result in a loss of cereal by 12: 20% and as high as 80% (Gad et al. 2020). Early detection of infestation and removal of the potentially infested organic source, physical and mechanical control (i.e., aeration, reduction or raise the temperature, and modified atmosphere in large grain stores/silos) (Fields et al. 2001), chemical control (i.e., inert dust, insecticide application, and fumigants) (Morrison et al. 2019; Nayak et al. 2020), and additionally planting insect-resistant genotypes and several types of radiation are all part of the rice weevil management strategy (Pal et al. 2021; Hossain, et al. 2021; Fawki and Yousery 2022).

Most notably, inert dust is used as diluents and carriers for dust insecticides like fine sand, lime, bentonite, specific types of kaolin clay, and Diatomaceous calcium oxide, kaolinite, and attapulgite, which are used as diluents or carriers in the formulation of pesticides. However, inert dust also has various other industrial and agricultural applications. Moreover, these inert materials exhibit insecticidal properties when used alone to protect stored grain against insects (Subramanyam and Roesli 2000; Kundu et al. 2018). For example, bentonite (calcium aluminosilicate) is a naturally occurring rock significantly characterized by the property of absorbing water and by capacity for base exchange (Kutlić et al. 2012). Recently, many researchers have used this mineral as a natural insect barrier for stored product storage (Kundu et al. 2018; Constanski et al. 2016; Bhanderi et al. 2014). Another inert dust, DE, mainly consists of fossilized DE deposits from the sea or freshwater. Therefore, they consider their major advantages, such as minimal toxicity to mammals, stability (Maceljski and Korunic, 1972), and effective insecticidal action. However, inert dust has certain unfavorable effects on grain, such as negatively affecting the physical and mechanical properties of the grain. Furthermore, because DE-treated grain is abrasive and could damage milling machinery, the industry is hesitant to accept it. Therefore, reducing the DE dosage could minimize the negative effect on the grain. To address these issues, research is being conducted to develop new DE formulations with enhanced insecticidal activity at a lower dosage with no adverse effect on grain quality and to create an innovative grain protectant composition that combines DE with conventional insecticides (Arthur 2004a; Athanassiou and Korunic 2007).

The suitability of using pyrolysis products, i.e., biochar, against insects has been recently tested as environmentally friendly insect control agents (Sayed et al. 2018). More than ever, there is an urgent need to develop environmentally safe pest control methods.

In this study, the effectiveness of DE, bentonite, and biochar alone and when uploaded with pirimiphos-methyl to form three specks of dust formulations against adults of S. oryzae was tested using laboratory bioassays. In addition, the impact of the three dust materials on seed germination and bulk density was evaluated.

Materials and methods

Tested insects

Adult Sitophilus oryzae (L.) rice weevil cultures were acquired from normal laboratory cultures. S. oryzae was grown on the sterilized hole. The temperature, relative humidity, and photoperiod were all set to 27 °C ± 1 °C, 70% ± 5%, and 12:12 light/dark, respectively, for insect rearing and all experimental procedures. The adults who participated in the trials ranged in age from 2 to 3 weeks.

Diatomaceous earth (DE)

A commercial formula of DE was from Al-Ahram Mining Company, Giza Governorate, Egypt. The chemical compositions were as follows: SiO2 (46.37%), TiO2 (0.37%), AlO3 (8.04%), Fe2O3 (1.23%), MnO (0.10%), MgO (1.68%), CaO (17.72%), Na2O (1.00%), K2O (0.66%), P2O5 (1.68%), Cl (0.79%), SO3 (2.31%), and L.O.I (17.68%).

Bentonite

A commercial formula of bentonite was from Al-Ahram Mining Company, Giza Governorate, Egypt. The chemical compositions were as follows: SiO2 (55.0%), TiO2 (0.2%), A2lO3 (20.0%), Fe2O3 (7.1%), MnO (0.01%), MgO (0.6%), CaO (3.7%), K2O (2.4%), P2O5 (0.8%), and L.O.I (10.2%).

Preparation of biochar

Biochar was prepared from the pruning residue of Ziziphus spina-christi trees grown in the forestry research sector of Antoniades botanical garden, Alexandria. After about three months of air drying in the open air, the pruning branches were maintained at room temperature. The branches were debarked and sawn into suitable pieces. Wood samp les were put in crucibles, covered with a tight-fitting lid, and pyrolyzed in a muffle furnace with limited oxygen. The pyrolysis temperature was raised to 500 °C at approximately 15 °C/min and held for 60 min. The biochar was then ground and stored in sealed bags until use after being allowed to cool to room temperature. The elemental analysis of biochar was conducted using SEM/EDX (Equipment: SEM Type Zeiss EVO50—EP equipped with X-ray Type INCA 450 Stream/Mics).

Biochar was ground to pass through sieves in the nano range then, the particle size of DE, bentonite, and biochar was measured using SEM as shown in Fig. 1(a), (b), and (c).

Fig. 1
figure 1

Particle sizes as measured using SEM for DE (a), bentonite (b), and biochar (c)

Full size image

FTIR

The distribution of the functional groups on the surfaces of biochar, bentonite, and DE was identified using the FT-IR technique. Bruker Tensor 37 spectrometers were used in the range of 400–4000 cm−1 using the technique of KBr pellet as 1.0 mg of samples was added to 100 mg KBr pressed and then exposed to infrared radiation (Wu et al. 2012; Guo and Chen 2014).

Insecticide formulations

Pirimiphos-methyl (95%), as a technical grade sample of pesticides, was obtained from the National Company for Agrochemicals Production, Egypt. The formulations of Pirimiphos-methyl (0.5%) carried on talc powder, DE, bentonite, and biochar were prepared by dispersing 0.01 g Pirimiphos-methyl in 10 ml n-hexane and applying it to 2.0 g of talc, DE, bentonite, and biochar. After being homogenized with a magnetic stirrer for 10 min, the mixtures were left overnight in a laboratory setting before evaluation using the method of (Athanassiou and Korunic 2007).

Bioassay technique

The bioassay was performed on adults by mixing the three tested materials and their formulations with whole wheat.

Selecting a series of concentrations of Pirimiphos-methyl formula and talc as a positive control different concentrations of all tested materials were applied in jars containing 20 g wheat. Twenty adults were used per replicate, and they closed tightly. They were then shaken manually for 2 min to obtain an even distribution. Each concentration had three replicates, and the control was untreated wheat. The mortality was recorded 7 days after applications. Probit analysis was done according to Finney (Finney 1971). In addition, the synergistic effects between dust and Pirimiphos-methyl formulas were evaluated by a co-toxicity coefficient (CTC), where (CTC) = LC50 of pirimiphos-methyl/LC50 of the pirimiphos-methyl formulation according to Sun and Johnson (1960).

Bulk density

According to Subramanian and Viswanathan (2007), the ratio of the sample’s mass to its total volume is referred to as the free and compact bulk density (kg/m3). It was determined by filling a 500 mL graduated cylinder with untreated and treated wheat with LC50 DE, bentonite, and biochar. Also, the bulk density was determined for the three formulations. An average of five replications is recorded.

Germination test

The wheat seeds were treated with the LC50s of DE, bentonite, and biochar and then stored for ten days. Germination was performed for the treated and untreated seeds. According to Liu et al. (2006), 20 wheat seeds were gathered and submerged in water for 24 h, with four duplicates of each treatment. The filtered, swollen seeds were then incubated at room temperature in the dark on a moistened thin cotton sheet in a nine cm Petri dish. Water was applied to the seedlings as needed. The germination test was re-determined for each formulation by the same steps. After 7 days, the number of seedlings was counted, and the germination percentages were calculated.

Data analysis

The significant differences among data were determined by means ± SE. One-way analysis (ANOVA) at the probability level of 0.05% was used to measure the statistical significance of mean variations between treatments and controls and Tukey’s HSD test using a Co-Stat program.

Results

Characterization of DE, bentonite, and biochar

Particle sizes

Figure 1a, b, and c shows the particle sizes distribution for DE, bentonite, and biochar respectively. As shown in the figures, the particle sizes for all materials were full in the nano-range, as the particle sizes for DE ranged between 18.94–24.14nm and bentonite ranged between 20.96–24.14nm while the particles of biochar ranged between 26.23–35.46nm.

FTIR

The function groups that are distributed on the surfaces of the three materials are shown in Fig. 2 which confirms the presence of different organic and inorganic groups.

Fig. 2
figure 2

FTIR spectrum for diatomaceous earth ( ) bentonite ( ) and biochar ( )

Full size image

Elemental analysis of biochar

Figure 3 shows the elemental composition of biochar prepared from Ziziphus spina-christi trees. Like all types of biochar, Carbon is the main element followed by Oxygen with traces of other elements such as Magnesium, Phosphorus, Potassium, and Calcium which may contribute to its effectiveness.

Fig. 3
figure 3

Elemental analysis of biochar prepared from Ziziphus spina-christi trees

Full size image

Toxicity Bioassays

After being exposed for 10 days, DE, bentonite, and biochar were found to be toxic to S. oryzae. Table 1 presents the LC50 values; statistical analysis indicated a significant difference between all treatments. DE was the most effective material (LC50 3.198 g/kg) followed by biochar (LC50 3.709 g/kg), but bentonite was least effective with LC50 3.979 g/kg. Table shows that the pirimiphos-methyl (0.5%) achieved an LC50 0.530 g/kg.

Table 1 Comparative toxicity of some inert dusts after 10 days exposer periods against S. oryzae
Full size table

Bulk density

In the laboratory examination of the wheat’s free and compact bulk densities after being treated with LC50s of dust, as listed in Table 2, the DE slightly affected wheat-free bulk density. Still, both bentonite and biochar reduced free bulk density. However, all the tested materials decreased compact bulk density. The three formulations decreased the free bulk density without significant difference between the formulations of DE and biochar, but the formulation of bentonite caused the most significant decrease, the same results were obtained for the compact bulk density with significant differences between the three formulations and the formulation of bentonite caused the most significant decrease in compact bulk density.

Table 2 Effect of LC50 dusts treatments on bulk density of wheat grains
Full size table

Germination test

Table 3 shows the germination percentages of wheat treated with LC50 values of DE, bentonite, and biochar after 10 days. Data revealed that in all tested materials, there is no significant difference between treated seeds with DE, bentonite, and biochar compared to untreated seeds after seven days of germination. No significant difference in the germination percentage observed with the formulation of bentonite, while both the formulations of DE and biochar caused a significant decrease in the germination percentage compared to the other treatments.

Table 3 Effect of LC50 dusts treatments on germination of wheat grains after storage period 10 days
Full size table

Discussion

Fourier transforms infrared analysis results show the differences in functional groups distribution on the surfaces of DE, bentonite, and biochar as shown in Fig. 1. Stretching vibration of the O-H group was recorded for three materials at the bands centered around 3400 cm−1, which was associated with the hydrogen-bonded O-H group for carboxylic and phenolic compounds (Cantrell et al. 2012; Pasieczna-Patkowska and Madej 2018; Tatzber et al. 2007). The presence of methyl and methylene groups in DEs between 2800 and 3000 cm−1 and 2514 cm−1, respectively, for CH3 and CH2, confirms the aliphatic substitution of aromatic rings (Pasieczna-Patkowska and Madej 2018). Peaks recorded for the three materials between 1600 cm−1 and 1800 cm−1 may refer to C = O for lactones or carboxyl carbonate (Morterra and Low 1982; Zawadzki 1989) or the vibration of C = C in aromatic compounds (Morterra et al. 1988). The carbonyl group for ketones may confirm biochar only at wavelength 2300. Moreover, the presence of ring stretching C = C was established in the biochar by the peak near 1560 cm−1 (Abdulrazzaq et al. 2014). Bands between 1420 and 1450 cm−1 present in the spectra for three materials correspond to aliphatic C-H groups (Cantrell et al. 2012; Tatzber et al. 2007). The peaks recorded for three types in the range 1000–1240 cm−1 are assigned to the stretching C-O group in phenolic, alcoholic, and carboxylic compounds (Hergert 1960; Varsanyi 1969). Moreover, peaks near 1000 cm−1 can be attributed to asymmetric Si-O stretching observed for bentonite and DEs (Socrates 2004). The peaks observed in the range of 400–600 cm−1 (Xue et al. 2013) found in all types may confirm the presence of variations in organic matter, such as carbonate and silicates. Moreover, three materials confirmed the presence of aromatic rings by the bands in the range 700–900 cm−1, which were assigned to bind C-H out of the aromatic plane (rings with more substitutions) (Gómez-Serrano et al. 1999; Keiluweit et al. 2010).

The dust type and concentration both affected the mortality of stored product beetles. The dust examined can be in the following order: DE > biochar > bentonite. Our results agree with those of (Ciobanu and Drosu 2009; Q Al-Naqib and Al-Iraqi 2006). The three dusts have different insecticidal properties, which might be related to variances in their chemical and physical characteristics; these were most probably particle size distribution, active surface and oil absorption, dust moisture content, and SiO2 concentration (Mahdi and Khalequzza 2006).

Inert dust leaves no harmful residues on cereals’ surfaces; hence, applications could be carried out in either storages, silos, or mills. Hard wheat treated with 50 or 300 ppm DE had no effect on milling, analytical, rheological, or baking quality, and these doses had no effect on the properties for making pasta, according to (Korunic et al. 1996), whereas 100–900 ppm on barley showed no differences in malting quality characteristics.

Several suggested inert dust modes of action have been expanded. These are as follows: (1) Dust embedded between cuticular segments increases water loss through the abrasion of the cuticle; (2) dust absorbs water from the insect’s cuticle; (3) insects die from ingesting the dust particles; (4) dust absorbs the epicuticular lipids of arthropods, resulting in excessive water loss through the cuticle; and (5) the film of dust on the cuticle inhibits breathing through the plugging of the spiracles. Excessive water loss or desiccation is thought to cause death (Chiu 1939; Subramanyam and Roesli 2000; Al-Naqib and Al-Iraqi 2006; Baliota and Athanassiou 2020). Due to its high capacity to absorb oil, biochar may also work against insects in the same way that inert dust does (Yang et al. 2020; Huang et al. 2021), and biochar is recognized as having a high ability to absorb water (Yi et al. 2020; Li and Tan 2021). As a result, it can absorb water from insect cuticles. Based on the SiO2 content, which results in desiccation upon contact with bentonite (55.0%), DEs (46.37%), and other test materials, the insecticidal values are also determined. SiO2 is the primary component and is also referred to as highly absorbed water. As observed by the FTIR analysis of DE, biochar, and bentonite, the surface hydrophilic functional groups (mainly–OH and–COOH) can absorb water from insect bodies, as (Li and Tan 2021) described. Biochar and SiO2 are the main components known as highly absorbed water.

Interestingly, DE or biochar with pirimiphos-methyl was more effective when used together in the formulations than when applied separately. The formulation pirimiphos-methyl (0.5%) with DE reported the highest significance more than the other two formulations (LC50 = 0.082 g/kg). The co-toxicity values were recorded for the three formulations. The DE formula showed the highest effective CTC value was 6.46-fold than pirimiphos-methyl, followed by the biochar formula more active than pirimiphos-methyl about 1.74 bentonite formula achieved activity 0.69-fold. Due to the adsorptive nature of DE, biochar, and bentonite particles, combining inert dust with other chemicals such as insecticides is one of the possible remedies to the consequences of excessive inert dust doses. Indeed, using inert dust as a carrier is a viable alternative for applying insecticides at lower concentrations and combining at least two separate modes of action, namely, desiccation via inert dust and a secondary action dependent on the chemical, e.g., neurotoxic agents, such as pirimiphos-methyl. According to many studies, there is significant potential—possibly even synergism—when commercial inert dust formulations are combined with residual insecticides. (Wakil et al. 2013) reported high mortality of R. dominica in wheat, rice, and corn treated with a combination of DE and thiamethoxam. Also found that the combination of DE and imidacloprid resulted in greater mortality than DE or imidacloprid alone against several stored product insects in wheat, rice, and corn. Applying DE along with two insect growth regulators was more efficient than doing so separately (Chanbang et al. 2007; Chanbang et al. 2007; Awais et al. 2019; 2020).

DE slightly affected wheat-free bulk density, but both bentonite and biochar reduced the free bulk density. However, the compact bulk density decreased for all tested materials. A reduction in bulk density brought on by dust should not significantly impact grain valuation because grain is sold by mass. Furthermore, the concentration of inert materials does not affect the quality of the grain grade. However, when DE is combined with grain, various physical and mechanical qualities of the bulk commodity are harmed: flowability and bulk density are diminished, and visible residues in the grains are obvious (Korunic et al. 1998). (Korunic et al. 1996) found that the application of 300 ppm DE reduced bulk density of the wheat by 4.8 kg/hl. Therefore, in our study, DE, bentonite, and biochar were blended with pirimiphos-methyl insecticide to reduce the negative impacts of DE on bulk density and grain flowability. Our results agree with many researchers (Arthur 2004a, b; Korunic & Rozman 2010; Korunic and Fields 2020).

In conclusion, DE has the potential to negatively affect the bulk density and flowability of grains when combined directly with them. However, by blending DE with other materials, such as insecticides, these negative impacts can be reduced.

Dusts can stick to insects because of the same physical characteristics that make them stick to grain. Particle collection from kernels by the insects moving through DE-treated wheat grains was exactly related to the concentration of DE in the wheat through various concentrations (Collins and Cook 2006; Baker et al. 1976). Therefore, the ability of DEs to adhere to surfaces may be related to insecticide effectiveness and bulk density decrease. Generally, data revealed that in all tested materials, there was no significant difference between treated seeds with DE, bentonite, and biochar compared to untreated seeds after 7 days of germination. Therefore, DE, bentonite, and biochar treatments do not significantly affect germination. Many studies have found that bentonite, DE, and biochar are effective at controlling various stored product insects and have no negative effects on the germination of wheat seeds (Aldryhim 1990; Mahmoud et al. 2010; Yodgorov et al. 2022).

Conclusion

This study suggests that DE, bentonite, and biochar can effectively control insects in stored products without negatively impacting the germination of seeds. The ability of these materials to adhere to surfaces, including insects, may contribute to their insecticidal effectiveness. The concentration of DE in wheat grains was found to be directly related to the collection of particles by insects. However, after 7 days of germination, no significant difference was observed between treated and untreated seeds in terms of germination. This indicates that the use of DE, bentonite, and biochar treatments does not significantly affect the germination process. These findings support the potential of using these materials as effective, environmentally friendly insecticides in pest control strategies for stored products Declarations.