Bio-efficacy of novel insecticides against yellow stem borer, Scirpophaga incertulas (Walker), in basmati rice

Introduction

Rice (Oryza sativa L.) is the most important staple cereal crop in Asia, providing food security and sustaining the livelihoods of millions of people. It plays a crucial role in the agricultural economy of many Asian countries. However, rice production is significantly affected by a wide range of insect pests, among which stem borers are considered one of the most destructive due to the severe yield losses they cause (Badari et al., 2023; Tagliapietra et al., 2024) [1,7] . Among the stem borer complex, the yellow stem borer, Scirpophaga incertulas (Walker) (Lepidoptera: Crambidae), is recognized as the most economically important species in irrigated and rainfed lowland rice ecosystems of South and Southeast Asia (Newton & Dixon, 1990) [5] . The larval stage causes damage by boring into rice stems and feeding internally on the growing tissues. This concealed feeding habit protects the larvae from natural enemies and reduces the effectiveness of contact insecticides, making the pest difficult to control. During the vegetative stage, larval feeding results in the formation of "dead hearts," whereas infestation during the reproductive stage causes "white ears" or "white heads," characterized by unfilled panicles. These symptoms substantially reduce productive tillers and grain yield, often without obvious external signs during the early stages of infestation (Dale, 1994; Savary et al., 2000) [3,6] . The incidence and severity of yellow stem borer have increased with the adoption of high-yielding rice varieties, intensive nitrogen fertilization and continuous rice cultivation throughout the year (Heong et al., 2015) [4] . Excessive nitrogen application enhances larval survival, while asynchronous planting and overlapping cropping seasons ensure continuous host availability. In addition, changing climatic conditions, particularly higher temperatures and humidity, have been associated with increased survival, faster development and more generations of the pest, thereby aggravating crop damage. Chemical insecticides have long been the principal method for managing yellow stem borer. However, their indiscriminate and repeated use has led to several challenges, including insecticide resistance, pest resurgence, ecological imbalance and adverse effects on beneficial organisms (Heong et al., 2015) [4] . Consequently, Integrated Pest Management (IPM) has emerged as a sustainable strategy that combines cultural practices, resistant cultivars, biological control agents and the need-based application of selective insecticides. Furthermore, recent advances in pheromone-based monitoring, parasitoid conservation and molecular studies on the biology and ecology of S. incertulas have provided new opportunities for developing environmentally safe and economically viable management strategies. Therefore, a comprehensive understanding of the pest's biology, ecology, damage symptoms and management approaches is essential for designing effective and sustainable control measures against the yellow stem borer in rice (Dale, 1994) [3] .

Materials and Methods

Experimental Site

A field experiment was conducted during the Kharif 2025 season at the Crop Research Centre (CRC), Sardar Vallabhbhai Patel University of Agriculture and Technology (SVPUAT), Modipuram, Meerut, Uttar Pradesh, India. The experimental site is situated at 29°01′ N latitude and 77°45′ E longitude, with an elevation of 237 m above mean sea level, representing the Western Plain Zone of Uttar Pradesh. The study was carried out under field conditions in an untreated rice crop, where yellow stem borer infestation occurred naturally, to evaluate the performance of insecticidal treatments under prevailing pest pressure.

Crop Establishment

The experiment was conducted using the basmati rice variety Pusa Basmati-1509. Twenty-one-day-old seedlings were transplanted during the fourth week of July 2025 (transplanting date: 28 July 2025) at a spacing of 20 × 15 cm. The crop was raised following the recommended agronomic practices of SVPUAT, Meerut. A fertilizer dose of 120:60:40 kg N:P₂O₅: K₂O ha⁻¹ was applied according to the recommended agronomic practices of SVPUAT. Insecticidal treatments were applied throughout the crop season to permit natural infestation of yellow stem borer.

Sampling Method and Recording of Yellow Stem Borer Dead heart and white ear infestation

Each treatment in the form of spraying was applied twice during the crop season. Observation on infestation of yellow stem borer as 'Dead Heart' and 'White Ear Head' were recorded on 5 randomly selected hill from three central rows at one day before, 7, 14 and 21 days after each spray / spread application. The percentage infestation was calculated using the following formulae:

Meteorological Observations

Weekly meteorological data, including maximum temperature (°C), minimum temperature (°C), mean temperature (°C), morning relative humidity (%), evening relative humidity (%), mean relative humidity (%) and rainfall (mm), were obtained from the Agro-meteorological Observatory, Department of Soil Science, SVPUAT, Modipuram, Meerut. Weather data corresponding to each Standard Meteorological Week were used to study their relationship with yellow stem borer incidence.

Statistical Analysis

The relationship between yellow stem borer efficacy of insecticide was analysed using ANOVA

Result

The efficacy of different novel insecticides against yellow stem borer was evaluated based on the incidence of dead heart and white ear head following two insecticidal sprays during Kharif 2025. Significant differences among the treatments were observed at all post-treatment observation intervals.

Effect of insecticides after the first spray

Discussion

The present study demonstrated that all the tested insecticides significantly reduced yellow stem borer infestation compared with the untreated control, with Chlorantraniliprole 18.5% SC proving to be the most effective treatment, followed by Flubendiamide 39.35% WG and Virtako.

The superior performance of Chlorantraniliprole may be attributed to its translaminar activity and its unique mode of action on insect ryanodine receptors, resulting in rapid feeding cessation and effective control of concealed stem-boring larvae (Lahm et al., 2009) [9] . Flubendiamide also exhibited excellent efficacy due to its prolonged residual activity and effectiveness against lepidopteran borers (Tohnishi et al., 2005) [12] . Similar findings have been reported by Singh et al. (2017) [11] , Prasad et al. (2019) [10] and Chinnadurai et al. (2021) [8] , who observed that diamide insecticides provided superior control of Scirpophaga incertulas and significantly reduced dead heart and white ear incidence compared with conventional insecticides. Therefore, Chlorantraniliprole 18.5% SC may be recommended as an effective component of integrated pest management (IPM) programmes for sustainable management of yellow stem borer in basmati rice.

Conclusion

The present study demonstrated that all the evaluated insecticides significantly reduced yellow stem borer infestation in basmati rice compared with the untreated control. Among the tested treatments, Chlorantraniliprole 18.5% SC proved to be the most effective, recording the lowest dead heart and white ear head incidence after both insecticidal sprays, followed by Flubendiamide 39.35% WG and Virtako (Thiamethoxam 1% + Chlorantraniliprole 0.5%). These findings indicate that among the insecticides evaluated under the present experimental conditions of Scirpophaga incertulas due to their high efficacy against concealed larval stages and prolonged residual activity. The study suggests that Chlorantraniliprole 18.5% SC can be effectively incorporated into integrated pest management (IPM) programmes for sustainable management of yellow stem borer in basmati rice. Adoption of this insecticide in combination with appropriate cultural and biological control practices will help minimize yield losses, reduce dependence on repeated insecticide applications and promote environmentally sustainable rice production under the agro-climatic conditions of western Uttar Pradesh.

References

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