Screening of rice varieties for susceptibility to Sitophilus oryzae (L.) under laboratory conditions

Introduction

Stored grain insect pests are an important constraint to the safe preservation of food grains, particularly in tropical and subtropical regions. Among the major pests associated with stored cereals, the rice weevil, Sitophilus oryzae (L.), is considered one of the most destructive primary pests of stored grains. It attacks a wide range of cereals, including rice, wheat, maize and sorghum and can cause considerable quantitative and qualitative losses during storage (Atwal and Dhaliwal, 2015) [4] . The pest is capable of developing within intact grains, allowing infestation to remain unnoticed during the early stages of storage. The developing larvae feed within the grain, while adults also contribute to grain damage through feeding, thereby reducing grain quality and weight. Infestation by S. oryzae can adversely affect both the quantity and quality of stored grain. The feeding activity of the insect reduces the nutritive value of grains, particularly through damage to the germ and endosperm and may also reduce seed viability (Gvozdenac et al., 2020) [9] . In addition to direct feeding damage, insect infestation can favour the development of secondary pests and microorganisms, contributing further to deterioration and contamination of stored grains (Okram and Hath, 2019) [13] . The high reproductive capacity and internal development of S. oryzae make its management particularly difficult once the infestation becomes established. Therefore, preventing infestation at the storage stage is important for minimizing post-harvest losses. The degree of infestation by S. oryzae may vary considerably among different grain varieties. Recent studies have shown that rice variety and grain form influence the development, reproduction and damage caused by S. oryzae, highlighting the importance of varietal screening to identify less susceptible rice varieties (Chekol, 2025; Borah and Ahmed, 2026) [6,5] . Varietal resistance or comparatively lower susceptibility is considered an important component of stored-grain pest management because the use of less susceptible varieties can reduce pest development and associated losses (Ashamo, 2006) [3] . Host plant resistance also offers an economical and environmentally compatible approach for reducing damage caused by storage pests, particularly where access to modern storage and chemical protection measures is limited (Abebe, 2009) [1] .

Hence, identifying rice varieties that show comparatively lower infestation and grain loss can contribute to the development of effective strategies for managing S. oryzae during storage. Previous studies have demonstrated differences among cereal varieties in their response to rice weevil infestation, indicating the importance of varietal screening for identifying suitable grain types for storage. However, the response of rice varieties may differ depending on the conditions under which the insect is allowed to infest the grain. The study was undertaken to assess the variation in response of the selected rice varieties to S. oryzae and to identify varieties showing comparatively lower susceptibility based on these parameters.

Materials and methods

Experimental site and Location:

The experiment was carried out utilizing the facilities of the Entomology Laboratory, Barrister Thakur Chhedilal College of Agriculture and Research Station, Bilaspur, during January -March 2026.

Mass rearing and maintenance of test insects

The initial culture of Sitophilus oryzae was obtained from infested wheat grains collected from the local market, Bilaspur. The insects were initially reared on wheat and polished rice grains and subsequently maintained on polished rice grains to acclimatize the culture to the host grain used in the experiment. Such host conditioning helps to minimize short-term changes in insect behaviour and biology associated with a change in host grain (Dobie, 1974) [7] . Fresh rice grains were periodically provided, while frass and grain dust were removed to maintain suitable conditions for insect development. Newly emerged adults were transferred to fresh rice grains to maintain a uniform culture, while overcrowding was avoided as it may adversely affect reproductive activity (Sano, 1967) [14] . Adults obtained from the maintained culture were used for the varietal screening experiments.

Experimental details

The experiment was conducted under two laboratory conditions with a mean temperature of 25±3.1°C and mean relative humidity of 60±9%. The study was conducted from January to March 2026. It comprised two types of behavioural assays, viz., free choice and no choice tests. Eight different polished rice varieties (Table 1) were procured from the local market, Bilaspur. The moisture content of the rice varieties ranged from 12.46 to 13.47%.

Free choice test

The relative preference of Sitophilus oryzae among the eight different varieties of rice grains was observed in the free choice test. About 30 grams of each rice variety were taken separately in small containers and arranged equidistantly in a circular pattern within the tray (Swamy et al., 2025) [20] . Thirty pairs of newly emerged adults were released at the centre of the tray such that they would get an equal chance to choose the grains of their choice. Males and females were identified based on the rostrum structure. The male rostrum is relatively short, wide and less curved, whereas the female rostrum is relatively long, smoother, slender and more curved. Immediately after the adult release, the tray was covered with muslin cloth and secured tightly with the help of a thread to avoid insect escape. The adults were carefully removed after seven days and the grains were transferred into separate plastic containers.

No choice test

One hundred grams of each rice variety were placed in separate plastic containers with three replications and ten pairs of newly emerged adult weevils were released into each container. The plastic container was covered with muslin cloth and secured with a tight rubber band. Three replications were used. The adult weevils were removed after one week in both tests. The containers were kept at ambient room temperature till the observations were completed.

Observations recorded 2.4.1 Progeny emergence

The number of newly emerged adult weevils was recorded from 35 DAI (days after infestation) and subsequently at intervals up to 65 DAI. Emerged adults were counted and removed to prevent further breeding. The adult emergence data were recorded to assess the relative preference of the different rice varieties for S. oryzae.

Per cent weight loss

Per cent weight loss was determined by weighing the rice grain after removing the frass by sieving. The percentage loss in grain weight was calculated by using the formula suggested by Adams and Schulten (1978) [2] .

Where, OW = Original weight of grains on a dry matter basis and CW = Current weight of grains on a dry matter basis. Observations on per cent weight loss were recorded at 65 DAI (days after infestation).

Statistical analysis

The data obtained from the experiment were subjected to statistical analysis using a Completely Randomized Design (CRD) with the help of OPSTAT statistical software. Appropriate transformations were applied to the data. The data were analysed using analysis of variance (ANOVA) and treatment means were compared using Duncan's Multiple Range Test (DMRT) at the 5% level (Duncan, 1955) [8] . As the present study was conducted under free choice conditions, varietal selection may have been influenced by volatile compounds emitted from different rice varieties (Sathiyaseelan and Balaji, 2025) [15] . The difference in the number of progeny emergence indicates that the varietal characteristics play an important role in oviposition success and subsequent weevil development, as reported by Marsadi and Yuliadhi (2025) [12] . Similarly, Zhang et al. (2023) [21] reported that variation in metabolic and detoxification enzyme activities plays a major role in the developmental duration and population growth of the rice weevil across different rice cultivars. In milled rice, variations in the grain characteristics such as kernel hardness and nutrient composition influence the successful development and adult emergence of Sitophilus oryzae (Swamy et al., 2022; Sharma et al., 2024) [19,16] .

Results and Discussion

No choice test

The data demonstrated in Rice varieties differ in their susceptibility to S. oryzae, owing to differences in physical and biochemical characteristics of the grains. Such varietal differences can influence weevil survival, development, progeny production, grain damage and weight loss. Therefore, screening different rice genotypes is important for identifying relatively resistant varieties and understanding their potential for reducing storage losses. The higher progeny emergence observed in Dubraj in the present study is consistent with the findings of Songer and Yadu (2022) [17] , who reported that Dubraj Selection-1 (21.66 adults/30g), an improved selection derived from the traditional Dubraj rice, was found to be more susceptible to the rice weevil. Swarna (3.33) recorded the lowest adult emergence, which is in accordance with the results obtained from no choice test. A previous study by Srivastav et al.

(2026) [18] reported 27.66 F 1 progeny from PB 1121, in the present study, the variety PB 1121 appeared to be comparatively tolerant among tested varieties with 16.00 progeny. Kiran et al. (2020) [11] recorded 4.00 F 1 adults in MTU 1010 (paddy) and classified it as a moderately resistant variety, this is in contrast with the present findings of free choice test. This variation may be attributed to differences in the experimental methodology and conditions, as they evaluated 10g paddy grains with 8 females and 4 males. Furthermore, a previous study by Hasaranga et al. (2018) [10] reported that milled rice supported significantly higher infestation and progeny emergence of S. oryzae than paddy, which may explain the observed data in the present investigation. A similar study within the same range of progeny emergence observed in the present study was reported by Ashamo (2006) [4] , who found that the elite variety ITA 117 recorded the highest number of progeny (55.00), while ITA 212 recorded the lowest (9.00).

Per cent weight loss 3.2.1 Free choice test

Under free choice condition, varieties Dubraj (3.56%) and MTU 1010 (3.52%) recorded the highest per cent weight loss at 65 DAI, which were statistically at par, indicating that they are the most preferred. Followed by Jeeraphool (2.94%), which was statistically at par with HMT (2.82%). Variety HMT and Pusa Basmati 1121 (2.57%) were also statistically at par. Vishnubhog and Swarna recorded 2.23% and 1.53% weight loss, respectively. Among all the tested varieties, Mahamaya (0.70%) recorded the least weight loss percentage, suggesting it was the least preferred variety (Table 2). Similar observations were reported by Swamy et al. (2025) [20] , who found that the highly susceptible genotype (BPT 2841) recorded 2.40% weight loss, whereas the resistant genotype (Baptala Mahsuri) recorded only 0.49% weight loss. The lower weight loss in resistant genotypes was associated with reduced weevil population and progeny development. Although the absolute values differ from those obtained in the current study, the overall trend of greater weight loss in susceptible varieties is consistent between studies. Under free choice condition a study by Marsadi and Yuliadhi (2025) [12] recorded a higher weight loss in red rice (7.68%) and a lower weight loss in white rice (4.57%). The present investigation dealt with polished white rice, so the weight loss percentage was in a similar range as that of their observation.

No choice test

Per cent weight loss of rice grains differed significantly among the tested rice varieties at 65 DAI, as shown in Table 3. Dubraj (4.04%) variety showed the highest weight loss and was superior to all other varieties, indicating that it was the most susceptible host among the eight tested rice varieties. Jeeraphool (3.85%) recorded the second highest weight loss and was statistically at par with Dubraj. Also, Jeeraphool was statistically at par with MTU 1010 and HMT. Varieties MTU 1010 (3.74%) and HMT (3.71%) exhibited intermediate weight loss and were statistically at par with each other. Vishnubhog recorded 3.53% weight loss, which was statistically at par with MTU 1010 and HMT, while Mahamaya (3.37%) exhibited significantly lower grain weight loss than the more susceptible varieties, it was also statistically at par with Vishnubhog. The lowest weight loss was recorded in Swarna (2.57%) and Pusa Basmati 1121 (2.63%), both of which were statistically at par, indicating comparatively greater resistance to damage caused by S. oryzae (Table 3).

Rice varieties differ in their susceptibility to S. oryzae, owing to differences in physical and biochemical characteristics of the grains. Such varietal differences can influence weevil survival, development, progeny production, grain damage and weight loss. Therefore, screening different rice genotypes is important for identifying relatively resistant varieties and understanding their potential for reducing storage losses. (Sharma et al., 2024) [16] These findings are comparable with those of Songer and Yadu (2022) [17] , who reported Dubraj Selection-1 as the most susceptible variety, with 6.66% weight loss, while MTU 1001 showed the lowest weight loss (1.00%). Basmati -370 (1.33%), MTU 1010 (1.33%), Swarna (2.33%) and HMT (2.66%) also exhibited relatively low weight loss. Although the magnitude of weight loss differed between the two studies, the observed differences are likely attributed to variation in experimental conditions. Another similar study reported significant variation in paddy grain weight loss among rice genotypes infested by rice weevil. The lowest weight loss was recorded in JGL (0.4%), while the highest was exhibited by JGL 11118 (7.43%). The variety MTU 1010 recorded 0.86% weight loss (Kiran et al., 2020) [11] . Similarly, significant variation in grain weight loss among basmati paddy genotypes was reported by Srivastav et al. (2026) [18] . The highest grain weight loss was observed in PB-1 (24.04%). While PB-370 (6.57%) showed the lowest. Variety PB 1121 exhibited 11.43% grain weight loss. The data difference observed in the present study may be attributed to the use of polished rice over paddy and variation in experimental conditions.

Conclusion

None of the tested rice varieties showed complete resistance to S. oryzae. Under the free choice test, Mahamaya recorded the lowest progeny emergence (1.33) and grain weight loss (0.70%), whereas under the no-choice test, Swarna showed the lowest progeny emergence (15.33) and weight loss (2.57%). Dubraj was the most susceptible variety, recording the highest progeny emergence (56.67) and grain weight loss (4.04%) under no choice conditions. Dubraj also recorded the highest weight loss (3.56%) in free choice conditions, while MTU 1010 recorded the highest progeny emergence (27.67) under the free choice test. The relative rankings differed between the two test conditions, showing that varietal response depended on whether host choice was available. Within the scope of this laboratory study, the screening indicated that the Dubraj variety is comparatively more susceptible to rice weevil attack under storage conditions.

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