Seasonal incidence of grapevine thrips (Scirtothrips dorsalis Hood), along with its natural enemies

Introduction

Grape (Vitis vinifera L., 2n = 38), a perennial vine belonging to the family Vitaceae, originated in the Mediterranean region. It was domesticated approximately 6,000-8,000 years ago in the Transcaucasia area from wild populations of V. vinifera subsp. sylvestris. In India, grape was introduced around 1300 AD from Iran and Afghanistan (Bose et al. 1999) [3] . Presently, it is one of the most commercially important fruit crops. Globally, grape production is led by China (12.67 million tons), followed by Italy, France, Spain, USA, and Türkiye. India ranks 9 th in grape production with about 3.90 million metric tons from 176,000 hectares. Maharashtra contributes approximately 70.67% (2.47 million MT) to the national output (PIB, 2 nd Adv. Estimate, 2021-22) [1] , with major grape-producing districts including Nashik, Sangli, Satara, Kolhapur, Ahilyanagar, and Pune. The national average productivity is 22.1 t/ha, while progressive vineyards under intensive management often achieve 30-35 t/ha. Grapes are mainly consumed as fresh fruit and are also processed into raisins, juice, wine, seed oil, and value-added products like anthocyanin capsules and pomace powders (Sharma and Shabeer Ahammad, 2019) [15] . They are rich in antioxidants such as resveratrol, and are a source of essential nutrients including vitamin C (3.68 mg/100 g), potassium (175.72 mg/100g), and iron (0.267 mg/100g) (Yadav et al. 2009) [16] . In India, over 85 insect pest species have been recorded on grapes (Mani et al. 2008) [9] , while 459 species have been documented globally (Reddy, 2019) [12] , including members of Hemiptera, Lepidoptera, and Coleoptera. Key insect pests in Indian vineyards include thrips (Scirtothrips dorsalis, Rhipiphorothrips cruentatus), flea beetles (Scelodonta strigicollis), mealybugs (Maconellicoccus hirsutus), shot hole borer (Xyleborus crassiusculus), grapevine girdler (Sthenias grisator), and leaf rollers (Sylepta lunalis) (Atwal & Dhaliwal, 2005) [2] . Among these, thrips have emerged as a major constraint in recent years. In India, Scirtothrips dorsalis Hood, Rhipiphorothrips cruentatus Hood, and Thrips hawaiiensis Morgan are reported on grapevines (Butani, 1979; Rahana et al. 2022) [4,11] . S. dorsalis feeds on the lower surface of leaves, flowers, and berries, causing leaf curling, silvery patches, and scablike fruit damage, which severely reduces marketability by over 90% (Kulkarni et al., 2007) [7] .

In Maharashtra, particularly in Nashik district, grape farmers struggle with effective thrips man, while progressive vineyards under intensive management often achieve 30-35 t/ha. Grapes areagement due to the lack of detailed data on their seasonal incidence and population dynamics. Thrips populations are strongly influenced by climatic factors like temperature, humidity, rainfall, and sunshine hours, which directly affect incidence timing and severity (Rienth et al. 2021) [14] . Therefore, the present study was undertaken to assess the seasonal incidence of Scirtothrips dorsalis Hood on grapevines along with its natural enemies, monitor associated weather parameters and analyze their correlation. This study aims to provide grape growers with climate-resilient, economically viable, and scientifically validated pest management strategies, thereby reducing yield losses and improving fruit quality and export potential.

Materials and Methods

The occurrence and seasonal incidence studies of thrips (Scirtothrips dorsalis Hood) (Thripidae: Thysanoptera) were carried out at Onion and Grape Research Station, Pimpalgaon Baswant. The observations were initiated after pruning in October 2024. A small plot of two rows including 24 grapevines each row was kept unprotected. Among them ten vines were selected randomly. Out of these 10 randomly selected vines, ten shoots per vine were tapped to record the thrips population per meteorological week such weekly observation as per Standard Meteorological Week commencing from October pruning to till harvesting were continued. (Duraimurugan and Jagadish, 2004) [5]. The thrips population was correlated with weather parameters viz., maximum temperature, minimum temperature, morning and evening relative humidity, rainfall and sunshine hour to quantify the impact of abiotic factors on the incidence levels of thrips. The data of weather parameters was obtained from Automatic Weather Station (AWS) of Onion and Grape Research Station, Pimpalgaon Baswant.

Results and Discussion

The seasonal incidence of Scirtothrips dorsalis Hood on grapevine was intensively studied under field conditions during the Rabi 2024-25 seasons at Onion and Grape Research Station, Pimpalgaon Baswant. The weekly observations recorded from the 43 rd (2024) to the 13 th (2025) Standard Meteorological Week (SMW) revealed a clear trend of thrips incidence of grapevine. The first incidence of thrips was observed during the 44 th SMW (October 29th to November 4th), with a mean population of 1.2 thrips per shoot. This initial incidence coincided with the emergence of new vegetative shoots after pruning. A steady rise in population was observed in the subsequent weeks reached its peak during the 50 th SMW (December 10th to 16th), and recorded the highest population of 18.6 thrips per shoot. This peak incidence period coincided with the flowering stage of grapevine, which provides tender tissues and floral structures favorable for thrips feeding and oviposition. The incidence then gradually declined as the crop entered the fruit-setting and berry development stages, with the hardening of tissues making them less suitable for thrips survival. The population of coccinellid beetles, known predator of thrips, began appearing from the 44 th Standard Meteorological Week (SMW) of 2024 which was 0.9 beetles per plant and continued till the 5 th SMW of 2025 with 0.7 beetles per plant. The population gradually increased and reached its peak at 50 th (SMW) with 2.8 beetles per plant, suggesting possible predator-prey relationship with thrips. During the peak incidence, specific meteorological conditions were noted: maximum temperature was 28.1 °C, minimum temperature was 10.12 °C, morning relative humidity was 89.5%, evening relative humidity was 69.4%, there was no rainfall, and sunshine hours were slightly reduced. These environmental parameters appeared to support optimal development and survival of thrips. Thrips damage symptoms were observed which as presented in plate.1 These findings are strongly supported by earlier research viz., Kulkarni et al. (2008) [8] observed a population peak of 8-10 thrips per shoot during November and December which coincided with the flowering period. Similarly, Reddy et al. (2019) [13] documented the highest incidence between the 50th and 2nd SMW, with population levels ranging from 8.28 to 8.53 thrips per shoot. Goutham (2009) [6] also reported peak thrips populations between the second week of December and last week of January, under temperature ranges between 29.5 °C and 31.4 °C. The correlation studies conducted between thrips incidence on grapevine and prevailing weather parameters during the rabi season of 2024-25 revealed that temperature and humidity played a crucial role in influencing thrips population. The maximum temperature exhibited a statistically significant negative correlation with thrips incidence at 1% level of significance (r = -0.560**), indicating that lower daytime temperatures favored population buildup. Similarly, minimum temperature showed a non-significant but negative correlation (r = -0.165), suggesting that cooler nights might also contribute to pest proliferation, though not conclusively. Relative humidity emerged as an important factor, with morning relative humidity showing a weak positive correlation (r = 0.253), while evening relative humidity showed a significant positive correlation at 5% level of significance (r = 0.500*), indicating that high evening moisture levels support thrips activity and reproduction. Other weather parameters such as rainfall (r = 0.356) and sunshine hours (r = -0.180) exhibited non-significant correlations, with rainfall displaying a weak positive trend and sunshine hours showing a weak negative trend. These results are in agreement with findings by Kulkarni et al. (2008) [8] , Reddy et al. (2019) [12] and Nagaraj et al. (2017) [10] ,who similarly reported negative correlations between thrips population with temperature, and positive associations with relative humidity. Multiple linear regression models were also carried out for thrips population and weather parameters which were presented in (Table 2). Y = a + bx Y= Incidence of thrips a= Intercept b = Slope x= Weather factor The multiple linear regression analysis was employed to assess the combined effect of various meteorological parameters on the population dynamics of Scirtothrips dorsalis Hood on grapevine during the rabi season of 2024-25. This study indicated that evening relative humidity, rainfall, and sunshine hours would increase the number of thrips by 0.416, 0.300, and 1.677 units respectively. However, among these none were statistically significant at p<0.05, as their p-values were 0.135, 0.138, and 0.159 respectively. Whereas, every unit increase in temperature maximum and temperature minimum as well as morning relative humidity would decrease the incidence of thrips by -381, -583, and -471 respectively. Among these, morning relative humidity showed a statistically significant negative effect (p = 0.029, t-value = -2.413), indicating it had the strongest individual influence among all predictors. The weather parameter during October pruning influenced the incidence of thrips to the extent of 59.30 per cent (R 2 = 0.5930). These findings corroborate the results reported by Reddy et al. (2019) [12] and Goutham (2009) [6] , who similarly observed that climatic factors, especially temperature and humidity, significantly influenced the seasonal incidence of thrips. Hence, the regression analysis confirms that predictive models integrating multiple climatic parameters provide a more reliable approach for forecasting thrips outbreaks and can be instrumental for timely pest management decisions in viticulture.

Regression:

Y= 27.370 -0.381 (X 1 ) -0.583 (X 2 ) -0.471 (X 3 ) + 0.416.(X 4 ) + 0.300 (X 5 ) + 1.677 (X 6 )(R 2 ) = 0.5930

Conclusion

The incidence of Scirtothrips dorsalis Hood on grapevine peaked during the 50th Standard Meteorological Week (December 10 th -16 th , 2024), coinciding with the flowering stage. A similar peak in coccinellid beetle population was also recorded during the same week, indicating a possible predator-prey relationship. Thrips incidence showed a highly significant negative correlation with maximum temperature (r = -0.560**) at the 1% level, and a significant positive correlation with evening relative humidity (r = 0.500*) at the 5% level. Morning relative humidity exhibited a non-significant positive trend, whereas rainfall and sunshine hours had no significant influence on thrips population. Multiple regression analysis revealed that morning relative humidity exerted a statistically significant negative effect (p = 0.029, t = -2.413), indicating it had the strongest individual influence among the weather parameters. The model explained 59.30% of the variation in thrips incidence (R² = 0.5930).

Author Contribution 1. Avhad P.S.¹* contributed to the conceptualization, data collection, experimentation, data analysis, and manuscript writing. 2. M. P. Badgujar² provided overall guidance, research supervision, and critical revision of the manuscript.

Acknowledgement

AcknowledgementI would also like to thank the staff of [Onion and Grape Research Centre, Pimpalgaon Baswant] for providing the necessary facilities and a conducive environment for the smooth conduct of this research. Lastly, I express my heartfelt thanks to my family and friends for their moral support, patience, and encouragement during the entire period of this research journey.

References

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