Seasonal incidence of yellow stem borer (Scirpophaga incertulas Walker) and its relationship with weather parameters in basmati rice

Introduction

Rice (Oryza sativa L.) is a staple food crop for over half of the world's population and is widely cultivated globally. Rice is grown under diverse conditions. India is the largest rice growing country and India has officially overtaken China as the world's top rice producer (Devi and Varma, 2022) [3] . India now produces around 150 million metric tons per year, whereas China's output is around 145 million metric tonnes (Anonymous 2026) [1] . Rice cultivation requires a warm and humid atmosphere, which also promotes insect survival and growth. In India, it accounts for 52% and 55% of total food grain and cereal production, respectively. It is produced in several ecosystems, including flooded, irrigated, rainfed lowland and upland areas (Jasrotia et al., 2019) [6] . Over a hundred insect species are thought to have caused significant damage to rice crops. The majority of them are minor and intermittent, resulting in occasionally economic losses. Certain insects have a considerable impact on rice development and yield, making them a major pest. Rice stem borers, which belong to the Lepidoptera order, are extremely damaging pests. In India, 18 Pyralidae stem borer species and three Noctuidae species have been identified. The yellow stem borer (Scirpophaga incertulas Walker) is a highly damaging and widespread monophagous insect pest in the Indian subcontinent. YSB infests rice plants during the cropping season (Baskaran et al., 2019) [2] . According to Sharma et al., (2018) [2] , yellow stem borer (Scirpophaga incertulas Walker) causes yield losses in rice ranging from 20 to 70%. This pest can be identified in fields by "dead heart" or "white ear" in vegetative hills and panicles during reproductive phases, caused by larval feeding and inter-nodal penetration. Abiotic conditions including temperature, humidity, and rainfall impact insect populations, either directly or indirectly (Jasrotia et al., 2019) [6] . Climate change will impact insect behavior, distribution, and abundance, resulting in more annual generations, higher winter survival rates, and earlier appearance of most insects (Patel and Singh, 2017) [8] . Insect pest management involves studying insect incidence, population distribution on crops, and conducting regular field surveys. Seasonal incidence studies improve insecticide application planning by identifying peak activity and insectfree periods during crop growth. Insect pest populations fluctuate based on both abiotic (rainfall, relative humidity, temperature) and biotic (natural enemies) components of a given area. This study aims to investigate how abiotic conditions influence the population build-up of yellow stem borer (Scirpophaga incertulas Walker) populations.

Materials and Methods

The field experiment on rice (Pusa Basmati-1509) was conducted during Kharif, 2022 at the Crop Research Centre, Chirori, Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut (U.P.) in randomized block design (RBD) with three replications. The standard weekly average data on temperature, relative humidity, rainfall, rainy days and sunshine hours during growing season were recorded at meteorological observatory located at the Crop Research Centre of Sardar Vallabhbhai Patel University of Agriculture Technology, Meerut (U.P.) for the year, 2022. The rice crop was grown in Kharif, 2022 and average weekly weather observations were recorded during July to October of the year. The plot size for seasonal incidence of yellow stem borer (Scirpophaga incertulas Walker) was 6 x 4.5 m². Observations were recorded on dead hearts and white ear heads of yellow stem borer, Scirpophaga Incertulas (Walker). Five hills per plot were selected randomly from separated plot grown for seasonal incidence of yellow stem borer (Scirpophaga incertulas Walker). The selected hills were observed regularly after transplanting till the harvesting of the crop at weekly interval and meteorological data was recorded simultaneously from the meteorological observatory. Maximum dead heart percent infestation was observed during the vegetative phase and maximum white ear head percent infestation was highest during the reproductive phase of the crop growth period. The infected tillers of the hills were removed each time after the observation was taken. The data collected on the pest population was correlated with the maximum temperature, minimum temperature, morning relative humidity, evening relative humidity and rainfall to study the effect of these variables on seasonal incidence of yellow stem borer (Scirpophaga incertulas Walker). Calculation of the percentage infestation of yellow stem borer (Scirpophaga incertulas Walker) were done by using the following formula. The data recorded during the course of investigation were also analysed with the help of computer software "OPSTAT" developed by O.P. Sheoran, CCS HAU, Hisar.

Percent dead hearts =

Results and Discussion

Data showed that the incidence of yellow stem borer (Scirpophaga incertulas Walker) appeared firstly in 32 th standard week and continued till the 44 th standard week (Table 1). The incidence of yellow stem borer (Scirpophaga incertulas Walker) recorded as dead heart and white ear heads ranged from 2.43 to 6.55 percent during Kharif, 2022. The incidence of yellow stem borer (Scirpophaga incertulas Walker) was increased gradually in last week of August and reached its peak (6.55 percent dead heart) during 37 th standard week the weather parameters like temperature, relative humidity and rainfall ranged from 24.7 to 34.7℃, 64.9 to 86.3%, 109.5 mm, respectively. The highest white ear heads infestation was 6 percent recorded during 42 th standard week. The yellow stem borer incidence suddenly decreased after last week of week of October i.e., 43 th and 44 th standard week this might due to no emergence of new leaves.

The correlation between infestation of yellow stem borer with weather parameters are presented in table 1 and figure 1. The correlation matrix indicated that there was a nonsignificant positive correlation with maximum temperature (r = 0.105), evening relative humidity (r = 0.411) and nonsignificant negative correlation with minimum temperature (r =-0.003), morning relative humidity (r =-0.242) and rainfall (r =-0.155). Morshed et al. (2020) [7] reported that the non-significant positive correlation with maximum temperature and non-significant negative correlation with minimum temperature. Guru-Pirasanna-Pandi et al. (2021) [4] had reported the negative correlation with minimum temperature and rainfall. Jastoria et al. (2019) had also reported the non-significant positive correlation with maximum temperature and non-significant negative correlation with minimum temperature. Hatwar et al. (2021) [5] found that the infestation by yellow stem borer showed non-significant positive correlation with maximum temperature and non-significant negative correlation with minimum temperature, morning relative humidity and rainfall. Rana et al. (2017) [9] who had also reported that the positive correlation with evening relative humidity. Shilpa et al. (2018) [10] reported negative correlation with rainfall.

Conclusion

The present study revealed that the yellow stem borer (Scirpophaga incertulas Walker) remained active from the 32 nd to the 44 th standard week during Kharif 2022, with peak dead hearts (6.55%) and white ear heads (6.0%) infestations occurring during the 37 th and 42 nd standard weeks, respectively. Pest incidence showed non-significant positive correlations with maximum temperature and evening relative humidity, and negative correlations with minimum temperature, morning relative humidity, and rainfall. These findings provide valuable information for timely monitoring and effective pest management in basmati rice.

References

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