Seasonal incidence of yellow thrips in relation to weather parameters on chilli

Introduction

Chilli (Capsicum annuam L.) is an important spice as well as commercial vegetable crop grown all over India. It is an essential ingredient of Indian curry, which is characterized by tempting colour and titillating pungency (Reddy et al. 2011) [11] . In India, green chilli is cultivated in an area of 292 thousand hectares with annual production of 2955 thousand metric tonnes during 2015-16 (Berke & Sheih, 2000) [2] . Chilli accounts for 40 per cent of the total spices exported from India and 23 per cent in terms of value. Although, the crop has got great export potential besides huge domestic requirement, a number of limiting factors have been attributed for low productivity (Reddy et al. 2011) [12] . Chilli is widely grown in states among them occurrence of viral diseases as well as ravages caused by insect pets are significant ones (Gundannavar et al. 2007) [5] . Chilli is known to be affected by 57 insect and non-insect pests of which thrips, Scirtothrips dorsalis are most destructive sucking pests and are considered as major pest (Berke & Sheih, 2000; Reddy & Puttaswamy, 1984) [1,10] . Chilli thrips affected leaves curl "upward" resulting in a typical damage known as 'leaf curl syndrome' (Sarkar et al. 2013) [15] . Economic yield loss may be 11-75% quantitatively and 60-80% qualitatively in the event of serious infestation (Ghosh et al. 2009) [3] . Since there is great variation in different agro climatic conditions of various regions; the pests show varying trends in their distribution, incidence, nature and extent of damage to the crop. Besides, there may also be some known and unknown factors contributing a key role in determining the incidence and dominance of a particular pest or pest complex (Meena & Kanwat, 2010; Patel et al. 2009) [7,9] . Knowing the peak period of pest infestations could help in taking pest management tactics more effectively with less incorporation of highly toxic chemical substances in the field. Keeping above aspects in mind, the present investigation was aimed to study on the seasonal incidence yellow thrips in relation to various weather parameters like rainfall, temperature, relative humidity etc.

Materials and Methods

The present investigations was carried out during summer 2022-23 and Rabi 2023-24 at experimental farm, Department of Entomology, VNMKV, Parbhani. The chilli variety Parbhani Tejas was grown on an area of 100 m 2 by adopting the spacing of 60 x 45 cm following the recommended package of practices. One week of after transplanting, an observation for yellow thrips was recorded on weekly basis till last picking. Ten plants from plot were randomly selected and tagged. Observation of nymph and adult of thrips recorded from six leaves per plant, two each from upper, middle and lower canopy of the plant. Mean of sucking pests worked out as population per three leaves per plant. The data pertaining to seasonal incidence were correlated with weather using WASP 2.0 software.

Results and Discussion

The data of seasonal incidence of yellow thrips, S. dorsalis during summer 2022-23, graphically presented in Figure 1 revealed that infestation of yellow thrips commenced from about 15 days after transplanting and recorded 0.70 thrips per three leaves in 5 th standard metrological week (SMW). Steady increase was observed in thrips population in subsequent period, from 3.6 to 12.20 thrips per three leaves from 6 th SMW to 9 th SMW. The peak activity of yellow thrips was observed in 10 th SMW with counting 14.10 thrips per three leaves. After the peak, population start declining from 11.40 thrips per three leaves to 1.8 thrips per three leaves in 22 nd SMW. In agreement with these findings, Samanta et al. (2017) [14] recorded the highest mean thrips population (6.15 per leaf) in the 15 th and 17 th SMW. Further, Ghosh et al. (2018) [4] observed peak thrips incidences of 6.71 and 5.77 thrips per two leaves during the 12 th and 14 th SMW for 2015-16 and 2016-17, respectively. The data graphically shown by Figure 2 revealed that infestation of yellow thrips, S. dorsalis during Rabi 2023-24 commenced from about 15 days after transplanting and recorded 0.2 thrips per three leaves. Steady increase was observed in thrips population in subsequent period, from 1.8 to 14.4 thrips per three leaves from 39 th SMW to 46 th SMW. The peak activity of yellow thrips was observed in 47 th SMW with counting 15.7 thrips per three leaves. After that population start declining from 10.50 thrips per three leaves to 1 thrips per three leaves in 2 nd SMW. These observations align closely with those of Meena and Tayde (2017) [8] , who reported the presence of yellow thrips starting in the rainy season at the 38 th SMW with an average of 0.38 insects per plant, reaching a peak of 6.38 insects per plant by the 45 th SMW. Similarly, Jayewar et al. (2018) [6] noted peak thrips populations at 12.36 and 9.86 thrips per leaf during the 43 rd and 47 th SMW for the 2016-17 and 2017-18 seasons. The correlation coefficients between weather parameters and the population of yellow thrips during the summer 2022-23 are presented in (Table No. 1). The relationship between the yellow thrips population on chilli and various weather parameters showed positive but non-significant correlations, maximum temperature (r=0.286) and morning relative humidity (r= 0.037) were weakly associated with yellow thrips, indicating a mild positive response. Negative but non-significant correlations were found with rainfall (r= -0.125), minimum temperature (r= -0.338), evening relative humidity (-0.072) and wind speed (r= 0.364) suggesting minimal influence from these factors. Zainab et al. (2016) [16] noted a non-significant positive correlation between thrips populations and maximum temperature, while negative correlations were observed with rainfall, morning relative humidity, evening relative humidity, and minimum temperature. These results align with our findings of minimal influence of temperature and humidity on yellow thrips populations. The correlation coefficients between weather parameters and the population of yellow thrips during the Rabi 2023-24 are presented in (Table No. 1). Yellow thrips showed a significant positive correlation with maximum temperature (r= 0.446*), indicating that higher temperatures favour their population growth. Minimum temperature had a significant negative correlation with yellow thrips (r= -0.605*), suggesting that lower night-time temperatures reduce their numbers. Rainfall (r= -0.385), morning relative humidity (r= -0.015), evening relative humidity (r= -0.414), and wind speed (r= -0.428) showed weak, non-significant negative correlations with chilli thrips, implying limited negative effects from these factors. These observations are in line with studies by Ghosh et al. (2018) [4] , who also found a significant positive correlation between thrips populations and maximum temperature and negative correlations with minimum temperature. The multiple regressions were worked out between weather parameters with yellow thrips population during summer 2022-

Acknowledgement

AcknowledgementsThe authors thank Department of Entomology, College of Agriculture, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani, and Maharashtra for providing facilities.

References

1. Berke T, Sheih SC. Chilli peppers in Asia. Capsicum Egg Plant Newsletter. 2000;19:38-41.
2. Department of Agriculture Cooperation & Farmers Welfare, Ministry of Agriculture & Farmers Welfare. Area and production of horticulture crops -All India, 2017.
3. Ghosh A, Chatterjee ML, Chakraborti K, Samanta A. Field evaluation of insecticides against chilli thrips Scirtothrips dorsalis Hood. Ann Plant Prot Sci. 2009;17(1):69-71.
4. Ghosh M, Bhattacharya S, Mandal S. Seasonal incidence of pests of bell pepper (Capsicum annum var grossum) and their correlation with weather parameters. J Entomol Zool Stud. 2018;6(3):825-830.
5. Gundannavar KP, Giraddi RS, Kulkarni KA, Awaknavar JS. Development of integrated pest management modules for chilli pests. Karnataka J Agric Sci. 2007;20:757-760.
6. Jayewar N, Bhosle B, Bhede B. Short term climatic conditions influencing thrips infesting chilli. J Entomol Zool Stud. 2018;6(5):2459-2463.
7. Meena NK, Kanwat PM. Studies on seasonal incidence and relative safety of pesticides against Coccinellids in okra ecosystem. J Biol Control. 2010;24(2):116-122.
8. Meena RK, Tayde AR. Effect of abiotic factors on the population dynamics of chilli thrips Scirtothrips dorsalis (Hood) in chilli, Capsicum annum L. crop in Allahabad, India. Int J Curr Microbiol Appl Sci. 2017;6(6):2184-2187. https://doi.org/10.20546/ijcmas.2017.606.257
9. Patel BH, Koshiya DJ, Korat DM. Population dynamics of chilli thrips, Scirtothrips dorsalis Hood in relation to weather parameters. Karnataka J Agric Sci. 2009;22(1):108110.
10. Reddy DNR, Puttaswamy S. Pests infesting chilli Capsicum annuum L. in nursery. Mysore J Agric Sci. 1984;18:122125.
11. Reddy KG, Reddy AS, Satiss Babu J, Reddy MC. Adoption of integrated pest management (IPM) in chilli Capsicum annuum L.: A case study in Guntur district of Andhra Pradesh. J Entomol Zool Stud Biol Pharm Technol. 2011;2(2):117.
12. Reddy MC, Reddy KG, Tirupamma K, Siva Reddy KV. Economics of integrated pest management (IPM) in chilli in Guntur district of Andhra Pradesh. Int J Plant Anim Environ Sci. 2011;1(1):140-143.
13. Samanta A, Sen K, Basu I. Incidence study of yellow mite and thrips and their natural enemies in relation to weather parameters on chilli. J Entomol Zool Stud. 2017;5(4):12131216.
14. Sarkar PK, Timsina GP, Vanaldikiandl H, Chakraborty S. Arylpyrrole acaro-insecticide chlorfenapyr: a tool for managing yellow thrips Scirtothrips dorsalis Hood and broad mite Polyphagotarsonemus latus Banks of chilli. J Crop Weed. 2013;9(1):188-192.
15. Zainab S, Sathua SK, Singh R. Study of population dynamics and impact of abiotic factors on thrips, Scirtothrips dorsalis of chilli, Capsicum annuum and comparative bio-efficacy of few novel pesticides against it. Int J Agric Environ Biotechnol. 2016;9(3):451-456. https://doi.org/10.5958/2230-732x.2016.00058.9