Efficacy of different plant-derived smoke on the adult mortality of rice weevil, (Sitophilus oryzae L.) at different time intervals

Introduction

Wheat (Triticum aestivum L.) holds the position of being the second most vital cereal crop in India, following rice. It plays a crucial role in the human diet, serving as a significant source of protein-surpassing maize, rice, and several other staple grains in protein content. However, during storage, agricultural products, including wheat, are vulnerable to infestation by a wide range of pests-over 600 species of beetles, 70 species of moths, and approximately 355 mite species. These infestations result in considerable quantitative and qualitative losses. In India alone, insect damage to stored grains is estimated to account for about 6.5% of total stored produce. Among the various pests that infest stored wheat, the rice weevil (Sitophilus oryzae L.) is considered one of the most destructive. Belonging to the family Curculionidae (order: Coleoptera), the rice weevil attacks key cereal crops such as wheat, rice, sorghum, barley, and maize-both in the field and during storage. The reddish-brown adult rice weevils and their white, legless grubs are internal feeders that cause significant damage to stored cereal grains, both in terms of quantity and quality. In recent years, the use of smoke from various plant leaves has been explored as a potential method for managing stored grain pests. This traditional approach is gaining renewed interest, especially given the limitations of chemical insecticides, which include environmental pollution, development of pest resistance, high toxicity to mammals, and rising application costs. These challenges have driven the search for safer, more costeffective alternatives. Plant-based products, particularly those containing bioactive compounds or secondary metabolites, show promise as natural insecticides. In fact, more than 2, 000 plant species worldwide have been identified to possess insecticidal properties, offering a rich resource for developing environmentally friendly pest management solutions.

Materials and Methods

The current study was conducted in the research laboratory of the Department of Entomology at Sam Higginbottom University of Agriculture, Technology and Sciences, Prayagraj, Uttar Pradesh, India.

Insect culture, Sitophilus oryzae L.

Adult Sitophilus oryzae specimens used in the study were collected locally from wheat grains that had been naturally infested during storage. For rearing purposes, plastic containers with a capacity of 1 kilogram were used. The openings of these containers were covered with muslin cloth to allow proper ventilation. Healthy, disinfected wheat grains were used as the rearing medium. Approximately 500 grams of wheat grains were placed in each container, and around 100 adult weevils were introduced. The muslin cloth was then secured with a rubber band to keep the containers sealed while still permitting airflow. These containers were maintained under controlled conditions at 32 ± 2 °C and 70 ± 5% relative humidity to promote weevil development.

After 45 days, newly emerged adult weevils (2-3 days old from the F1 generation) were collected and used to artificially infest the experimental wheat samples for further study.

Collection of plants leaves

The fresh leaves of plants i.e. Neem, eucalyptus, curry, bay leaves, orange peel and clove & camphor were collected from the SHUATS campus, the 250 gm of all leaves were dried naturally at room temperature (32-35 °C), to avoid sun light for induce damage of active compound by Uv-ray.

Treatments

The experiments were conducted on susceptible wheat variety SHUATS-W10 under laboratory conditions. The treatments were consist of dried neem leaves, eucalyptus, curry leaves, orange peel, bay leaves, clove & camphor along with chemical, Coragen (100 mg/kg wheat grains) and control (untreated) seeds.

Methodology:

The experiments were conducted by taking storage receptacles such as plastic containers. The treated wheat grains (100g) were kept in the receptacles in three replications, separately at ambient temperature.

Effect of smoke on the mortality of Rice weevil

The study was designed to evaluate the impact of smoke from various plant materials on the mortality of adult rice weevils (Sitophilus oryzae) under controlled laboratory conditions. Treatments included smoke generated from burning (T 1 ) neem leaves, (T 2 ) eucalyptus leaves, (T 3 ) curry leaves, (T 4 ) orange peel, (T 5 ) bay leaves, (T 6 ) a mixture of clove and camphor, and (T 7 ) a chemical control using Coragen at 10 mg. Smoke from each plant material was produced using a smoke-generating device. Freshly emerged adult rice weevils were used for the experiment, with 50 insects introduced into each conical flask containing 100 grams of wheat grains. Each treatment was replicated three times. After releasing the insects, smoke was introduced into the flasks using the smoker. The flask openings were then sealed tightly with cotton plugs and covered with aluminum foil to retain the smoke. Separate sets of flasks were prepared for different exposure durations-24, 48, 72, and 96 hours-to assess the effect of smoke over time. This setup helped determine how varying exposure periods influenced the mortality rate of S. oryzae.

Number of dead insects Percent mortality = × 100 Total number of insect release

Statistical Analysis

The data collected during the experiment were analyzed statistically using the Analysis of Variance (ANOVA) method, following a Completely Randomized Design (CRD). Wherever necessary, data transformations were applied to meet the assumptions of ANOVA. The standard error of the mean (SEm) was calculated for each treatment, and the critical difference (CD) at the 5% level of significance was computed to compare treatment means where significant differences were observed.

Results and Discussion 1. Effect of plant-based smoke on mortality of Rice weevil, Sitophilus oryzae in wheat grains during the month of November

The data obtained on the effect of smoke on insect mortality in stored wheat is presented in table-1 and figure-1. It was evaluated from the data that smoke of (T 6 ) Clove & Camphor with mortality percentage 32.67% was found to be superior which was followed by neem leaves smoke.

Percent mortality of Rice weevil, Sitophilus oryzae without smoke under air tight conditions in wheat grain

The mortality of adult Rice weevil, Sitophilus oryzae was observed without passing any smoke under air tight conditions at different interval of time period and the data obtained is presented in table-2 and figure-2 The data showed that without smoke, no any insect mortality was occurred after 24 hours whereas 1.33 and 1.33 percent mortality at 48 hours and 72 hours and 0.67 percent mortality after 96 hours without smoke under air tight conditions on wheat grains.

Discussion

The findings of the present study clearly demonstrate the significant insecticidal effects of plant-derived smokes on the mortality of adult Sitophilus oryzae in stored wheat grains. Among all the treatments, the smoke generated from Clove and Camphor (T 6 ) consistently exhibited the highest mortality rates across both November and February trials, indicating its superior efficacy. This may be attributed to the presence of bioactive compounds such as eugenol in clove and camphor, which are known for their strong fumigant and insecticidal properties. Nonetheless, even with this decline, treated samples still exhibited notably higher mortality than untreated controls. Furthermore, the negligible mortality observed under airtight conditions without smoke reinforces the fact that the observed effects were due to the action of plant smokes rather than oxygen depletion or container conditions alone. These findings support the hypothesis that smoke from certain plant materials possesses strong bioactivity against storage pests and can serve as a low-cost, eco-friendly alternative to chemical fumigants. Plant-based smokes offer the added benefits of low toxicity to humans, minimal environmental impact, and ease of application in rural settings. However, further research is needed to understand the exact mechanisms of toxicity, residual effects on grain quality, and the potential for scaling up these practices under field or warehouse conditions.

Conclusion

The primary aim of this study was to evaluate the effectiveness of natural, plant-based smoke treatments in controlling rice weevil (Sitophilus oryzae) populations in stored wheat. The results demonstrated that smoke derived from certain plant materials possesses notable insecticidal properties against the weevils. Among all treatments, smoke from clove and camphor consistently produced the highest mortality rates in both the November and February trials, followed by neem and eucalyptus leaf smoke. Mortality increased with longer exposure times in sealed conditions, highlighting the cumulative toxic effects of the smoke on adult insects. These findings indicate that botanical smokes-particularly those from clove & camphor and neem leaves-can offer an effective and environmentally friendly alternative to synthetic fumigants such as Coragen. This method provides a more sustainable approach to managing rice weevil infestations, with reduced risks to human health and the environment compared to conventional chemical pesticides.

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