Effect of weather parameters on population dynamics of grasshoppers infesting Tuberose, Agave amica (Medikus) Thiede and Govaerts

Introduction

Tuberose (Agave amica (Medikus) Thiede and Govaerts), commonly known as the "Queen of Fragrance" or "Fragrance of the Night," is a night-blooming plant native to Mexico (Iftikhar et al., 2023) [2] . It is a perennial species that belongs to the family Asparagaceae, exhibiting a monocotyledonous nature and a bulbous structure (Thiede and Govaerts, 2017) [14] . The plant's common name derives from the Latin word tuberosa and the French tubéreuse, referring to its swollen, tuberous root system (Singh et al., 2015) [12] . Tuberose (A. amica) is cultivated commercially in tropical and subtropical regions for cut flower production, the floriculture trade, and as a source of oil (Sadhukhan et al., 2022) [11] . Known locally as Rajnigandha or Nishigandha, tuberose is a versatile plant that thrives in pots, borders, and beds. It is highly valued for its wide range of uses. The flowers are prized for making artistic garlands, floral ornaments, bouquets, buttonholes, and gajras, as well as for the extraction of essential oils. Tuberose is also a popular cut flower, not only used in floral arrangements but also for its individual florets, which impart a powerful fragrance to bouquets and boutonnieres. Additionally, the long flower spikes are excellent as cut flowers for table decorations, adding beauty and fragrance to any setting. The delightful fragrance of its flowers is one of the key reasons tuberoses is so cherished in the floral industry. Tuberose is commercially cultivated in countries like India, China, Bangladesh, Mexico, and others. In India, it is grown in states such as West Bengal, Karnataka, Tamil Nadu, Maharashtra, Uttar Pradesh, and the northeastern region. The total area under tuberose cultivation in India is approximately 21.31 lakh hectares, with a production of around 197,000 tonnes in 2023-24. Of this, 96,510 tonnes were loose flowers, and 100,850 tonnes were cut flowers in the 2022-23 period (Agriwelfare, 2024). Renowned for its aromatic flowers, tuberose is a significant ornamental and commercial crop. However, it is highly susceptible to various pests that cause extensive damage. With the effects of climate change, the dynamics of pest populations have shifted, leading to the emergence of new pest threats and increased incidences (Pal and Chakravarthy, 2020) [9] . Understanding these changes is crucial for developing effective pest management strategies. Grasshoppers are particularly destructive to tuberose, targeting young leaves and flower buds (Mandal et al., 2018) [6] . Their feeding activity results in both aesthetic and physical damage, reducing the commercial value of the plants. Damage is most pronounced during the rainy season, with affected plants losing their visual appeal and elegance (NHB, 2024) [8] . Given the importance of minimizing pest impact, this study was undertaken to examine the influence of weather parameters on the population dynamics of grasshoppers infesting tuberose. By understanding these relationships, the findings aim to support the development of sustainable pest management practices for tuberose cultivation.

Materials and Methods

The non-replicated field experiment comprising 72 quadrats each of 3 x 3 sq. m size was laid to investigate succession of major insect pests of Tuberose at the Research Farm of Department of Entomology, College of Agriculture (VNMKV), Latur (MS) during 2023-24. The popular tuberose variety, Phule Rajani was sown at the spacing of 100 x 30 cm in 72 quadrats July 8 th , 2023, as per the package of practices recommended by the Directorate of Floriculture, Pune. The field experiment was conducted under pesticide-free conditions. The succession of grasshoppers on tuberose were determined by recording observations on all the plants from three quadrats, twice in each meteorological week. The population of grasshoppers was then calculated per plant. The statistical analysis of the data on population of grasshoppers on tuberose and weather parameters were carried out by simple correlation and multiple regression using WASP 2.0 software developed by ICAR Research Complex, Goa.

Results and Discussion Population dynamics of grasshoppers

The population dynamics of grasshoppers on A. amica (tuberose) was studied during 2023-2024. During the course of the investigation, the weather parameters-rainfall, minimum temperature, maximum temperature, before noon relative humidity, and afternoon relative humidity-ranged from 0.00 to 179.5 mm, 11.78 °C to 20.22 °C, 23.22 °C to 29.86 °C, 70.28% to 97.57%, and 35.25% to 61%, respectively. The first incidence of grasshoppers on tuberose was observed in the 33 rd SMW (Standard Meteorological Week) of 2023, with 0.11 grasshoppers per plant. The peak population occurred in the 47 th SMW of 2023, with a population level of 0.23 grasshoppers per plant. At the maximum population level of grasshoppers, the prevailing weather factors were as follows: rainfall 0.00 mm, minimum temperature 20.17 °C, maximum temperature 29.21 °C, before noon relative humidity 77.46%, and afternoon relative humidity 36.80% (Table 1 and Fig. 1). The results of present investigation are in congruence with the findings of Kumar et al. (2023) [4] who revealed that the highest grasshopper incidence was recorded in the 40 th SMW with 4.22 percent infestation in little millet. Khan et al. (2022) [3] exhibited that the maximum grasshopper population on maize was recorded in the 7 th SMW (0.40 per plant). The seasonal average of the grasshopper population on maize was 0.17 per plant. Rawat et al. (2021) [10] showed that the highest grasshopper infestation (26.67 percent) in finger millet was recorded and the maximum infestation (33.33 percent) of grasshoppers in barnyard millet was recorded at Gaja Farm. Sreedhar et al. (2020) [13] evidenced that grasshoppers were associated with chrysanthemum crop right from the seedling stage to maturity stage. Kumar et al. (2020) [5] revealed that percentage damage of surface grasshoppers in maize appeared in the 10 th SMW (1.26 percent) and reached its peak (3.21 percent) in the 22 nd SMW. Manjunatha et al. (2019) [7] reported that the grasshopper's population was observed throughout the cropping period with a peak population (0.90 no. per plant) in the first fortnight of August as well as October.

Correlation between incidence grasshoppers and weather parameters

The results in respect of simple correlations between population of grasshoppers infesting tuberose and weather parameters during 2023-24 are presented in Table 2. The data revealed that minimum temperature (r = -0.570*) and maximum temperature (r = -0.509*) had a significantly negative correlation with the population of grasshoppers. Meanwhile, afternoon relative humidity (r = 0.529) exhibited a significantly positive correlation with the population of grasshoppers, while before noon relative humidity (r = 0.353) showed a non-significant positive correlation. However, rainfall (r = -0.072) showed a nonsignificant negative correlation with the population of grasshoppers. More or less similar results were reported by Kumar et al. (2020) [5] who demonstrated that grasshoppers infesting rabi oat exhibited a highly significant positive correlation with maximum and minimum temperature (r = 0.06**, r = 0.73**) and sunshine (hrs.) (r = 0.40*). While, highly significant negative correlation with morning relative humidity (r = -0.58**) and non-significant positive correlation with rainfall (r = 0.26) and non-significant negative correlation with evening relative humidity (r = -0.03). Manjunatha et al. (2019) [7] indicated that grasshopper population infesting castor had positive significant relation with maximum temperature (r =0.701*) and wind speed (r =0.749*).

Regression studies

Weather based multiple linear regression model was developed in respect of incidence of grasshoppers (Y) as a dependent variable and weather parameters (B1 to B5) as independent variables and presented in Table 3. The regression equation worked out is as follow.

Y=0.361 +(0.000) x B1+ (-0.009) x B2+(0.000) x B3+ (-0.001) x B5+ (0.001) x B6+0.041

The regression equation revealed that various weather parameters had profound influence on the incidence of grasshoppers on tuberose. The coefficient of determination (R2) was 0.347, which designated that different weather parameters accounted 34.7 percent variability in the population of grasshoppers.

Conclusion

In conclusion, the study on the population dynamics of grasshoppers infesting tuberose revealed that grasshopper populations are most abundant during the 47 th Standard Meteorological Week of 2023. The weather parameters significantly affect their population, with higher afternoon relative humidity promoting grasshopper populations, while increasing temperatures (both minimum and maximum) lead to a decrease in their numbers. Morning relative humidity and rainfall had limited or negligible effects on the grasshopper population. These findings highlight the importance of weather factors in grasshopper population dynamics and provide valuable insights for the development of effective pest management strategies in tuberose cultivation.

Acknowledgement

AcknowledgementThe authors express their gratitude to the Head of the Department of Entomology, College of Agriculture (VNMKV), Latur, for designing the research, providing the necessary facilities, and offering financial support.

References

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