Seasonal abundance of whitefly, Bemisia tabaci (Gennadius) vis-à-vis tomato leaf curl disease in relation to weather parameters

Introduction

Tomato (Solanum lycopersicum L.) is one of the most widely cultivated and economically important vegetable crops grown under diverse agro-climatic conditions. Its productivity is constrained by several insect pests, among which whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is considered a major sucking pest (De Barro et al., 2011) [7] . Whitefly causes direct damage by extracting plant sap and indirect damage through the transmission of several plant viruses (Bugti, 2016; Pal et al., 2021) [3,12] . Among these, tomato leaf curl virus (ToLCV), the causal agent of tomato leaf curl disease is one of the most destructive viral pathogens affecting tomato production in tropical and subtropical regions. B. tabaci serves as the principal vector of ToLCV and transmits the virus from infected to healthy plants in a persistent-circulative manner (Uchibori et al., 2013) [18] . The incidence and severity of tomato leaf curl disease are closely associated with the abundance of the whitefly vector and higher vector populations often result in greater disease spread and crop losses (Cohen and Berlinger, 1986) [6] . The population dynamics of whitefly and the development of leaf curl disease are greatly influenced by prevailing weather conditions, including temperature, relative humidity, rainfall, bright sunshine hours and wind speed (Khandare et al., 2019) [9] . Knowledge of the seasonal occurrence of whitefly and its relationship with environmental factors is therefore essential for forecasting pest outbreaks and implementing timely management interventions. Considering the economic importance of tomato leaf curl disease and the role of whitefly as its vector, the present investigation was undertaken to study the seasonal abundance of B. tabaci visà-vis tomato leaf curl disease and their relationship with prevailing weather parameters under field conditions at Anand, Gujarat.

Materials and Methods

The Weekly meteorological data on maximum and minimum temperature, morning and evening relative humidity, bright sunshine hours, rainfall, wind speed, and morning and evening vapour pressure were collected from the Department of Meteorology, B. A. College of Agriculture, Anand Agricultural University, Anand. To determine the relationship between whitefly population, tomato leaf curl disease incidence and prevailing weather parameters, Pearson's correlation coefficients were computed following the procedure described by Steel and Torrie (1980) [16] . Correlation analyses were performed between whitefly population and tomato leaf curl disease incidence as well as between each of these variables and the corresponding meteorological parameters.

Results and Discussion

The week-wise observations on whitefly population and tomato leaf curl disease incidence are presented in Table 1. Whitefly activity commenced from the second week after transplanting (WAT), corresponding to the fourth week of September (40 th Standard Meteorological Week; SMW), with a population of 0.47 whitefly per leaf and persisted throughout the crop season. The population gradually increased and attained an initial peak of 1.70 whiteflies per leaf during the third week of October (5 WAT and 43 rd SMW), followed by a slight decline to 1.43 whiteflies per leaf during the 44 th SMW. Thereafter, it increased and attained a maximum population of 5.50 whiteflies per leaf during the fourth week of December (14 WAT and 52 nd SMW). Subsequently, the population declined gradually and reached 1.90 whiteflies per leaf during the first week of February (5 th SMW). The present findings are in close agreement with Patel et al. (2021) [13] , who reported the onset of whitefly incidence during the 38 th and 39 th SMW with its peak population during the 48 th and 49 th SMW, respectively, in tomato during kharif, 2017-18 and 2018-19. Similarly, Chakraborty (2012) [4] and Pavan et al. (2020) [14] observed a gradual increase in whitefly population after its initial appearance, with peak populations during the 6 th and 7 th SMW, respectively. Chavan et al. (2013) [5] noted higher whitefly infestation at 11 WAT, whereas Koshale (2018) [10] reported whitefly activity at 7 WAT in tomato. Hence, the seasonal trend observed in the present study broadly corroborates earlier findings, with variations in peak activity likely due to differences in agro-climatic conditions, geographical location, transplanting time, cropping season, tomato cultivar and prevailing weather parameters. Tomato leaf curl disease incidence was first observed during the first week of October (41 st SMW) at 0.87% (Table 1) and increased progressively reaching a maximum of 23.06% during the first week of February (5 th SMW). Although whitefly population declined after its peak in late December, disease incidence continued to increase until crop termination. The progressive increase in tomato leaf curl disease incidence observed in the present investigation is in accordance with the findings of Lakshmi et al. (2015) [11] , Koshale (2018) [10] and Anco et al. (2020) [1] , who also reported a gradual increase in tomato leaf curl disease incidence as the crop progressed, with maximum disease incidence recorded during the later stages of crop growth.

Relationship between whitefly population and tomato leaf curl disease incidence

Correlation analysis showed in Table 1 revealed a highly significant positive correlation (r = 0.576**) between whitefly population and tomato leaf curl disease incidence, indicating that an increase in whitefly population was associated with a corresponding increase in disease incidence. The finding is in agreement with Khandare et al. (2019) [9] , Bansode (2020) [2] and Koshale (2018) [10] , who reported significant positive associations between whitefly population and leaf curl disease incidence in tomato.

Relationship of whitefly population and tomato leaf curl disease incidence with weather parameters

The correlation coefficients of whitefly population and tomato leaf curl disease incidence with different weather parameters are presented in Table 2. Whitefly population showed a significant positive correlation with bright sunshine hours (r = 0.533*). In contrast, highly significant negative correlations were recorded with maximum temperature (r = -0.600**), minimum temperature (r = -0.844**), morning vapour pressure (r = -0.843**) and evening vapour pressure (r = -0.675**). Wind speed (r = -0.504*) and evening relative humidity (r = -0.456*) also showed significant negative correlations. However, morning relative humidity (r = 0.151) and rainfall (r =-0.388) exhibited non-significant associations. The present findings are in close agreement with Chavan et al. (2013) [5] and Patel et al. (2021) [13] , who reported significant negative correlations of whitefly population with both maximum and minimum temperatures. Likewise, Patel et al. (2021) [13] observed a significant negative correlation with wind speed. Koshale (2018) [10] also reported a highly significant positive association between whitefly population and bright sunshine hours, while Jahanzaib et al. (2017) [8] observed a non-significant negative association with rainfall. However, Patel et al. (2021) [13] reported a significant positive correlation with relative humidity, differing from the present findings. Such variations may be attributed to differences in agro-climatic conditions, geographical location, crop season, tomato cultivar and prevailing weather conditions. Tomato leaf curl disease incidence exhibited highly significant negative correlations with maximum temperature (r = -0.828**), minimum temperature (r = -0.730**) and morning vapour pressure (r = -0.728**), while evening vapour pressure (r = -0.471*) showed a significant negative correlation. Morning relative humidity (r = 0.228) and bright sunshine hours (r = 0.168) showed non-significant positive correlations, whereas evening relative humidity (r = -0.140), rainfall (r = -0.406) and wind speed (r = -0.167) showed non-significant negative correlations with disease incidence (Table 2). The present results are in agreement with Koshale (2018) [10] , who reported a positive association between bright sunshine hours and tomato leaf curl disease incidence. Likewise, Jahanzaib et al. (2017) [8] observed non-significant negative correlations of disease incidence with rainfall and wind speed. However, Lakshmi et al. (2015) [11] , Singh et al. (2015) [15] , Koshale (2018) [10] , Khandare et al. (2019) [9] and Sujatha et al. (2025) [17] reported positive associations between temperature and disease incidence. These findings differed from the present research. It might be due to different locations, seasonal pattern, cropping period and tomato cultivars.

Conclusion

The present study revealed distinct seasonal variation in the population of whitefly and tomato leaf curl disease incidence during kharif-rabi 2025-26. Whitefly population peaked during the fourth week of December, while disease incidence increased progressively and reached its maximum during the first week of February. A highly significant positive relationship between whitefly population and disease incidence indicated the important role of vector abundance in disease development. Whitefly population and disease incidence showed significant associations with several weather parameters, highlighting the importance of seasonal weather conditions and vector abundance in the progression of tomato leaf curl disease.

Acknowledgement

AcknowledgmentsThe authors gratefully acknowledge the assistance provided by the Departments of Entomology, B. A. College of Agriculture, Anand Agricultural University, Anand during the course of the study.

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