Sustainable Solutions for Wheat Grain Protection: Evaluation of Inert Materials against Rice Weevil (Sitophilus oryzae L.)

Introduction

Grains, a staple food worldwide, are packed with essential nutrients that nourish the body. Beyond their dietary value, whole grains offer a range of health benefits, including improved cholesterol management, weight control, and blood pressure regulation. Studies have shown that consuming whole grains significantly reduces the risk of developing chronic conditions such as diabetes and heart disease [1].

Despite their nutritional value and health benefits, grains suffer from significant post-harvest losses, particularly during storage. Minimizing these losses is crucial for ensuring global food security and maintaining access to this essential source of nutrients for future generations [2, 3].

Post-harvest grain losses, primarily caused by insect pests like the rice weevil, jeopardize global food security. Conventional pest management strategies often rely on chemical insecticides and fumigants, which pose environmental, health, and resistance concerns, motivating the quest for sustainable alternatives.

Despite the effectiveness of chemical pesticides in controlling insect pests, their widespread reliance poses several critical challenges, including the emergence of resistant insect pests [4, 5] environmental contamination [6], and potential human health risks [7].

Inert dusts and ash effectively control stored grain pests through physical disruption, influenced by material type, species susceptibility, concentration, exposure time, and dust adherence [8, 9, 10, 11, 12].

Strong empirical evidence supports the effectiveness of this approach. Applying ash to stored seeds has demonstrably reduced pest damage by up to 80% and inhibited offspring production in pulse beetles (9, 10).

The toxicity of wood ash from Acacia polyacatha willd and Hymenocardia acida Tul against adult maize weevils Sitophilus zeamais Mostch increased with higher concentration and treatment time on stored maize grains [13].

The mortality rates of adult Cowpea seed beetle Callosobruchus maculatus L and the pulse beetle Callosobruchus chinensis L reached 100% at high concentrations of kaolin dusts, ranging from 0.2-1% [14].

A study by Aldryhim [15] demonstrated that silica dusts effectively control wheat weevils Sitophilus granarius L. and Confused floor beetles Tribolium confusum Duv, with higher concentrations and longer exposure times leading to increased mortality and reduced offspring production. Notably, wheat weevils were more susceptible to silica than confused floor beetles.

Shams, et al. [12] further investigated the insecticidal efficacy of diatomaceous earth (DE) against wheat weevils S. granarius and cowpea seed beetles Callosobruchus maculatus. They found that DE, primarily composed of silica, exhibited concentration-dependent mortality rates, with higher concentrations and longer exposure times leading to more effective control. Interestingly, cowpea seed beetles showed greater sensitivity to DE compared to wheat weevils.

Abdelgaleil, et al. [16] evaluated the effectiveness of zeolite inert dusts against S. granarius and S. oryzae. Zeolite treatment at 500 mg/kg resulted in mortality rates of 43.5% and 50.3%, respectively. Synergistic effects were observed when zeolite was combined with insecticides, leading to higher mortality rates. All treatments provided effective protection against insect damage and weight loss for 90 days.

Astuti, et al. [17] investigated the insecticidal activity of five types of ash against R. dominica. Giant bamboo leaves ash and rice husks ash demonstrated superior efficacy, significantly reducing mortality, hindering reproduction, and delaying population growth. Their effects extended to subsequent generations, impairing growth and reducing adult weight. Additionally, treated rice grains showed significantly lower damage compared to untreated controls, therefore giant bamboo leaves ash and rice husks ash hold promise as environmentally friendly alternatives to chemical insecticides for stored product pest control. Gvozdenac, et al. [18] further supported this notion by demonstrating the feasibility and effectiveness of inert dusts for small- scale farmers in protecting their stored crops from insect infestations.

This experiment investigates the efficacy of kaolin dust, silica dust, and apple ash against the rice weevil (Sitophilus oryzae) by assessing their impact on cumulative mortality rates, grain weight loss, damage percentage, and adult emergence under controlled laboratory conditions (26±1°C temperature and 60±5% relative humidity).

Results

Cumulative Mortality Rates of Rice Weevil Adults and Efficacy in Increasing Mortality Ratio by Kaolin, Silica, and Apple Ash on the Eighth Day of Treatment

Figure 1 shows the average cumulative mortality rates of rice weevil adults treated with kaolin, silica, and apple ash at three concentrations (2%, 4%, and 8%) after treatment durations of 1, 2, 4, and 8 days.

Kaolin outperformed both apple ash and silica in causing adult mortality. After one day, only kaolin at 8% concentration showed significant or apparent mortality (13.33%), while apple ash and silica exhibited none. Similar results were observed on the second day. Mortality rate increased with concentration for all treatments. This trend held true throughout the experiment, with higher concentrations leading to greater mortality. Kaolin significantly outperformed silica at all tested concentrations. At day 8, kaolin achieved 13.33%, 16.67%, and 20% mortality at 2%, 4%, and 8% concentrations, respectively, compared to silica’s 3.33%, 6.67%, and 10%.

No significant differences were observed between kaolin and apple ash at 2% and 8% concentrations. Both treatments reached comparable mortalities of 6.67% and 13.33% at these concentrations, respectively.

The tested dusts and ash showed a clear time-dependent and concentration-dependent effect on rice weevil adult mortality. Mortality rates steadily increased with longer treatment durations compared to the untreated control, which reached just 3.33% after four days. Similarly, higher concentrations within each treatment led to greater mortality.

At the highest tested concentration (8%), kaolin and apple ash achieved comparable high mortality rates, with 76.67% for kaolin and 70% for apple ash. These values exhibited no statistically significant difference. However, both significantly outperformed silica dust, which only achieved 26.70% mortality at the same concentration after four days.

Table 1 results reveal a clear positive correlation between increasing adult mortality rate and longer treatment durations. This trend is evident on the eighth day, where all treatments except silica at 2% showed significantly higher mortality compared to the untreated control (6.66%).

Apple ash emerged as the most effective treatment, achieving significantly higher mortality than both kaolin and silica at 2% and 8% concentrations. With an impressive 73.33% mortality at 2% concentration, apple ash significantly outperformed kaolin (53.33%) and silica (10%). Interestingly, no significant difference was observed between apple ash and kaolin at 4% concentration.

The highest overall mortality was achieved with apple ash at 8% concentration, reaching a remarkable 100%. Kaolin and silica followed at 90% and 40%, respectively, demonstrating the potency of apple ash in this experiment.

Click to enlarge

Mean %

70.49 90.66Aa 33.4Bc 87.42Aa 2

80.96 91.98Aa 59.30Bb 91.59Aa 4

89.5 93.34Aa 82.61Ba 92.54Aba 8 91.99 58.44 90.52 Mean%

Powder × concentration =18.56 concentration =10.72 Powder =10.72 LSD0.01 Means followed by the same small letters in the same column are not significantly different at P=0.01. Means followed by the same big letters in the same row are not significantly different at P=0.01. Table 1: Effectiveness of kaolin, silica and apple ash in increasing of adult’s cumulative mortality ratio of the rice weevil S. oryzae on the eighth day after treatment.

The results of Table 1 illustrate the effectiveness of treatment with kaolin, silica, and apple ash in increasing the average cumulative mortality ratio in rice weevil adults after eight days of treatment, using concentrations of 2, 4, and 8%.

Effectiveness in increasing cumulative mortality ratio on the eighth day of treatment% concentration% Apple ash Silica Kaolin Apple ash achieved the highest reduction values at all tested concentrations, with values of 90.66, 91.98, and 93.34% respectively. The values were not significantly different from those of kaolin, which achieved values of 87.42, 91.59, and 92.54% respectively. On the other hand, the lowest effectiveness values were recorded for silica, with reduction values of 33.40, 59.30, and 82.61% for cumulative mortality ratio respectively. There were no significant differences between silica and kaolin when treated with a concentration of 8%. The order of effectiveness, from highest, was as follows: apple ash > kaolin > silica.

The Effect of Inert Dusts and Ash on Adult Emergence and Effectiveness in Reducing the Average Percentage of the Adult Emergence Laboratory

From the results in Table 2, it is evident that the most effective tested material in reducing the number of adult emergence resulting from rice weevil infestation was apple ash, which gave the best values compared to both kaolin and silica, with significant or apparent differences and an average of 91.43%. The reduction values ​for ash ranged between 85.16% to 96.02%, depending on the concentration used 2- 8%. Following in importance was treatment with kaolin, with reduction percentages ranging from 65.93% to 89.55%. On the other hand, treatment with silica gave the lowest average reduction percentage for the adult emergence of rice weevil, ranging from -14.01% to 56.40%. The effectiveness in reducing increased with higher concentrations, with average reduction percentages ranging from 55.03% to 80.66%. The ranking of effectiveness starting from the best was: apple ash > kaolin > silica

Means followed by the same small letters in the same column are not significantly different at P=0.01. Means followed by the same big letters in the same row are not significantly different at P=0.01. Table 2: Effects of Kaolin, Silica, and Apple Ash on Rice Weevil Adult Emergence Rate after Laboratory Treatment.

Discussion

The study found that inert dusts, including kaolin, silica dust, and apple ash, significantly increased rice weevil mortality compared to untreated controls. This effect was consistent with the findings of previous research [16, 24, 25]. The mechanism of action involves physical damage to the insect cuticle, disrupting water balance, and potentially obstructing respiratory pores, leading to death.

Our study revealed varying efficacy of inert dusts against rice weevil mortality. Silica dust exhibited the lowest effectiveness, with maximum mortality not exceeding 40%. Conversely, kaolin and apple ash demonstrated superior efficacy, achieving mortality rates of 90% and 100%, respectively. This trend aligns with previous research [26, 27].

In a recent study, researchers evaluated the efficacy of inert dusts, including kaolin, diatomaceous earth, and vermiculite, in controlling adult rice weevils (S. oryzae) and Indian meal moth larvae (P. interpunctella Hubner), the results indicated that kaolin and diatomaceous earth exhibited superior efficacy, achieving mortality rates of 86.7-98% and 86.7-98%, respectively, after two days of treatment at the highest concentrations. Prolonged exposure further enhanced mortality, reaching 100% for both inert dusts after seven days of treatment at lower concentrations. Vermiculite, on the other hand, demonstrated limited effectiveness, with mortality rates ranging from 7-11% at all tested concentrations [18].

A study by Amin, et al. [28] revealed that the mortality rate of adult rice weevils (S. oryzae) increased with higher concentrations and exposure periods. Sulfur powder emerged as the most effective substance, followed by diatomaceous earth, white cement, phosphate rock, zinc powder, animal dung ash, pyrethrum, calcium carbonate, talcum powder, and silica gel. Hiruy [26] demonstrated that inert dusts at rates of 5 to 10% significantly reduced maize weevil infestation (Sitophilus zeamais) compared to untreated controls [26].

Apple ash and kaolin effectively protected wheat grains from rice weevil damage by reducing new adult emergence, weight loss, and damage ratio. These materials killed insects quickly, hindered movement, reduced egg laying sites, and prevented egg adhesion, all contributing to their effectiveness. Higher concentrations further enhanced their impact, aligning with previous research [13, 14, 29].

Studies have shown that ash from various plant species effectively reduced the number of eggs laid by cowpea seed beetle (C. maculatus) and pulse beetle (Callosobruchus chinensis), leading to decreased grain weight loss and offspring production [29, 30]. Additionally, the use of corn cob ash and mustard seed powder significantly increased mortality rates of S. oryzae, Rhyzopertha dominica, Tribolium castaneum, and C. maculatus [31].

Adopting physical control methods like ash and inert dusts, particularly kaolin, is a sustainable and effective approach to safeguard stored grains and seeds from insect damage. Their integration into integrated pest management (IPM) strategies promotes reduced reliance on chemical pesticides, contributing to a more environmentally friendly approach to pest control.

Conclusion

The findings of this study provide compelling evidence that apple ash and kaolin dust exhibit remarkable potential as eco-friendly alternatives to conventional chemical pesticides for managing rice weevil infestations and mitigating their detrimental impact on stored grains. This efficacy stems from their ability to suppress adult emergence, reduce grain weight loss, and minimize damage percentages. Consequently, these inert materials offer promising strategies for integration into integrated pest management (IPM) programs, effectively addressing rice weevil populations while adhering to stringent environmental and human health considerations.