Seasonal incidence of invasive thrips, Thrips parvispinus (Karny) infesting chilli

Introduction

Chilli (Capsicum annuum L.), often referred to as the "wonder spice," holds significant importance as a commercial spice and vegetable crop. Originating from Latin America, it was introduced to Asia, including India, by Portuguese traders around 450-500 years ago (Berke and Sheih, 2000) [3] . Since then, it has become a staple in Indian agriculture and cuisine, used as a vegetable, spice, condiment, and in medicinal preparations. Globally, major chilli-growing countries include India, Thailand, China, Bangladesh, and Pakistan, with India leading in production. In 2022-23, India cultivated green chillies over 413,000 hectares, yielding 4.495 million tonnes, alongside significant production of capsicum and dry chillies (Anonymous, 2024a) [1] . Major chilli-growing states such as Andhra Pradesh, Maharashtra, and Gujarat contribute over 70% of the country's acreage, with Gujarat alone producing 27,270 tonnes of chillies from 14,060 hectares (Anonymous, 2024b) [2] . Chilli cultivation faces significant challenges from biotic stresses, particularly insect pests, which reduce yield potential and total production. Among these, thrips (Scirtothrips dorsalis Hood and Thrips parvispinus Karny) are notorious for inflicting severe damage. Thrips feed on plant tissues, causing leaf curling, necrosis, flower drop, and fruit distortion, leading to yield losses of up to 74% (Patel and Gupta, 1998; Sridhar et al., 2021) [9,12] . T. parvispinus, an invasive species recently reported in major chilli-growing regions of India, has emerged as a significant pest, capable of replacing native S. dorsalis due to its competitive edge and adaptability. This species causes widespread damage to flowers and fruits, with losses reported as high as 100% in severely infested areas (Lodaya et al., 2022) [7] . The lifecycle and reproductive strategies of thrips, including parthenogenesis and rapid multiplication, make them formidable pests. Environmental factors such as temperature, humidity, and rainfall further influence their population dynamics and distribution. This study focuses on understanding the seasonal incidence of invasive thrips (T. parvispinus) in chilli crops.

By elucidating its population dynamics and correlating them with environmental factors, the research aims to provide critical insights for developing integrated pest management strategies, thereby safeguarding chilli production and enhancing agricultural sustainability.

Materials and Methods

The experiment on seasonal incidence of invasive thrips in chilli was conducted at the Department of Entomology, Anand Agricultural University, Anand (Gujarat), in the month of October, 2022 and September, 2023 during kharifrabi, 2022-23 and 2023-24, respectively. For the purpose, seedlings of local cultivar (VNR 332) were transplanted at spacing of 60 x 60 cm in the 12 x 12 m plot. All standard agronomical practices were followed to raise the chilli crop only except insecticidal applications. The plot was divided into four equal quadrates of 6.0 x 6.0 m. From each quadrate, five plants were randomly selected and observed at weekly interval starting from one week after transplanting till the termination of chilli crop. From each selected plant, three twigs and flowers from the upper, middle and lower canopy were shaken/tap gently over a white paper (A4 size) which subsequently covered with transparent sheet to restrict the movement of thrips. Invasive black thrips that fell on the white paper were counted with the help of a magnifying glass. The number of healthy and damaged fruits per quadrate were recorded at each picking and percent fruit damage was worked out. The weight of healthy and damaged fruits was also recorded. The invasive thrips data obtained were correlated with abiotic parameters viz., maximum (MaxT) and minimum (MinT) temperature, morning (RH1) and evening (RH2) relative humidity, evaporation (EP), morning vapour pressure (VP1) and evening vapour pressure (VP2), bright sunshine (BSS), rainfall (RF) and wind speed (WS). The data obtained during the investigation were used to work out correlation coefficient with help of SPSS software.

Results

Incidence of invasive thrips infesting chilli First year (Kharif-rabi, 2022-23)

The data on the infestation caused by invasive thrips on chilli twig during kharif-rabi 2022-23 are detailed in Table 1 and portrayed in Figure 1. It evident from the data that the population of invasive thrips started from 7 days after transplanting (DAT) i.e., 43 rd 1].

Second year (Kharif-rabi, 2023-24)

Infestation caused by invasive thrips during kharif-rabi 2023-24 are detailed in Table 2 and depicted in Figure 2. It evident from the data that the population of invasive thrips started from 7 th DAT i.e., 38 th SMW (0.20 thrips/twig). Subsequently, the population gradually increased and attained its first peak at 70 th DAT in December, 2023 i.e., 47 th SMW (8.00 thrips/twig) and second peak at 84 th DAT in December, 2023 i.e., 49 th SMW (8.20 thrips/twig). Afterward, the population of invasive thrips fluctuate and at 6 th SMW it reached upto 8.00 thrips/twig. In case of, the data recorded on the infestation caused by invasive thrips on flowers, the population of invasive thrips started from 42 nd DAT i.e., 43 rd SMW [1.40 thrips/flower]. Then, the population gradually increased and attained its first peak at 70 th DAT in November i.e., 47 th SMW (9.40 thrips/flower) and second peak at 105 th DAT in December, 2023 i.e., 52 nd SMW (10.60 thrips/flower) as depicted in Figure 2. Subsequently, the population of invasive thrips gradually decreased upto 5 th SMW then afterand reached to 7.40 thrips/flower at 147 th DAT in February it again increase in reached to 7.40 thrips/flower at 6 th SMW. The seasonal incidence of T. parvispinus was studied during kharif-rabi 2022-23 and 2023-24. Based on two years study, it can be concluded that the activity of invasive thrips on chilli twigs was started from first week after transplanting (WAT) the crop and gradually increased in subsequent weeks, which observed throughout the cropping period. The appearance of T. parvispinus in chilli flowers was observed on sixth week after transplanting (42 DAT) and remained up to crop termination. Moreover, the peak incidence was noticed on the chilli plants at fruit maturation period from tenth to sixteen weeks after transplanting. The chilli crop carried higher thrips population at peak flowering stage as it feeds on pollen of the flowers.

Correlation matrix of the relationship between weather parameters and incidence of invasive thrips

In nature, the population of insect-pests is never truly stable. The rise and fall of the population density of any organism depends on many abiotic factors like temperature, rainfall, humidity etc. To measure the effect of various weather parameters on the population of invasive thrips on chilli, simple correlation was worked out. The correlation data between invasive thrips incidence with weather parameters during kharif-rabi, 2022-23 and 2023-24 are presented in Table 3.

First year (Kharif-rabi, 2022-23)

The correlation analysis of thrips per twig with various weather parameters was worked out during kharif-rabi, 2022-23 and the data obtained are presented in Table 3. In 2022-23, thrips per twig showed highly negative correlation with morning vapour pressure (r=-0.67 ** ) and showed negative correlation with minimum temperature (r=-0.51 * ) and evaporation (r=-0.53 * ) whereas, there was no significant relation with maximum temperature, morning and evening relative humidity, evening vapour pressure, bright sunshine hours, rainfall and wind speed. The data on correlation analysis of thrips infesting flowers with various weather parameters recorded during kharif-rabi, 2022-23 are presented in Table 3. Maximum temperature exhibited a significant negative correlation (r = -0.52*) with thrips on flower, suggesting that higher temperatures may be associated with reduced thrips presence per flower. Whereas, all other weather parameters (maximum Temperature, morning and evening Relative humidity, morning and evening vapour pressure, evaporation, bright sunshine hours, rainfall, wind speed) have no significant influence on thrips per flower.

Second year (Kharif-rabi, 2023-24)

Thrips population on twig exhibited a highly significant negative correlation with maximum temperature (r = -0.57**), minimum temperature (r = -0.81**), morning vapour pressure (r = -0.89**), evening vapour pressure (r = -0.75**) and rainfall (r = -0.56**) whereas, morning and evening relative humidity, evaporation, bright sunshine hours and wind speed showed no significant correlation with thrips on chilli twigs. During 2023-24, the invasive thrips population highly negatively affected by maximum temperature (r= -0.81**), minimum temperature (r=-0.56*) and morning vapour pressure (r=-0.60**). Whereas, it showed significantly positive correlation with evening relative humidity. Furthermore, remaining weather parameters viz., morning relative humidity, evening vapour pressure, evaporation, bright sunshine hours, rainfall and wind speed did not have any correlation with invasive thrips.

Fruits Damaged due to T. parvispinus (On number base)

The data on fruit infestation by invasive thrips based on numbers reveals important trends over different pickings during the kharif-rabi 2022-23 and 2023-24 growing seasons as mentioned in Table 4. In 2022-23, fruit damage started relatively high at 18.76% during the first picking and peaked during the second picking, where damage increased to 21.59%. Following this, there was a slight decline, with damage percentages of 20.40 and 20.79% during the third and fourth picking, respectively. As the season progressed, the damage percentage showed some stabilization, recording 21.34% in the fifth picking, and then decreased to 19.54% during the sixth picking. Interestingly, damage levels remained relatively stable during the seventh picking, with 20.24% recorded, and finally decreased to 18.35% in the eighth picking. The mean fruit damage for the 2022-23 seasons stood at 20.13%, reflecting consistent damage across the pickings, particularly in the early to mid-season. In contrast, the 2023-24 season exhibited lower fruit damage percentages overall, starting at 12.06% during the first picking. Damage levels gradually increased as the season progressed, with the second picking recorded 17.62% and the third picking showed 20.13%. The fourth picking experienced a slight decrease to 18.06%, followed by fifth picking at 17.75%. In, sixth picking damage stabilized around 20.04% and seventh picking recorded with highest damage 21.66%. Thereafter, damage was slightly decreased to 20.42% in the eighth and final picking. The overall mean damage for the 2023-24 season was relatively lower than in the previous year, at 18.47%. The pooled data, which average the damage percentages across both seasons, provided further comprehensive overview. The first picking showed a mean damage of 15.41%, followed by 19.61% in the second picking. Fruit damage remained higher in third picking i.e., 20.27% damage, whereas it remained more or less similar from fourth to sixth pickings, with mean percentage ranging from 19.43 to 19.79%. The highest pooled damage occurred during the seventh picking, where 20.95% was recorded, before dropping to 19.38% during the final picking. The pooled mean across all pickings and both years was 19.30%, indicated that thrips-induced fruit damage was most significant during the mid-season pickings (second to sixth), necessitating consistent pest management throughout these critical periods. The trends in this data highlighted the necessity for early and continued management of invasive thrips population, as damage tends to peak during the middle of the picking cycle.

Fruits Damaged due to T. parvispinus (On weight base)

The data on fruit infestation by invasive thrips based on weight reveals important trends over different pickings during the 2022-23 and 2023-24 growing seasons. In 2022-23, fruit damage started relatively high at 16.95% during the first picking and peak damage (20.56%) recorded in second picking. Followed by a slight decline, with damage percentages of 19.58 and 19.74% during the third and fourth picking, respectively. As the season progressed, the damage percentage showed some stabilization, and recorded 20.37% damage in the fifth picking, which was further declined to 18.47% during the sixth picking. Interestingly, damage levels remained relatively stable during the seventh picking, with 18.71% recorded, and finally decreased to 17.21% in the eighth picking. The mean fruit damage for the 2022-23 season stood at 18.95%, reflecting consistent damage across the pickings, particularly in the early to mid-season. In contrast, the 2023-24 season exhibited lower fruit damage percentages overall, starting at 11.13% during the first picking. Damage levels gradually increased as the season progressed, with the second picking recording 16.34% and the third picking showing 18.57%. The fourth picking experienced a slight decrease to 16.99%, followed by 16.37% in the fifth picking. In, sixth picking damage stabilized around 18.65% whereas, seventh picking recorded with highest damage 20.15%. Then, damage levels declined to 18.83% in the last picking. The overall mean damage for the 2023-24 season was lower (17.13%) than in the previous year. The pooled data, which averages the damage percentages across both seasons, provides a more comprehensive overview. The first picking showed a mean damage of 14.04%, followed by 18.45% in the second picking. Chilli crop recorded with 19.08% damage in third picking. Thereafter, fruit damage remained moderate through the fourth to sixth pickings, with mean percentages ranging from 18.36 to 18.56%. The highest pooled damage occurred during the seventh picking with 19.43% damage, before dropping to 18.02% during the final picking. The pooled mean across all pickings and both years was 18.04%, indicating that thrips-induced fruit damage was most significant during the mid-season pickings (second to sixth), necessitating consistent pest management throughout these critical periods.

Discussion

T. parvispinus is an invasive pest which cause havoc in recent years; therefore, only one correlation study of researcher was found to compare with present investigations' results. However, it is also compared with earlier findings on chilli thrips, S. dorsalis. Lokare et al. (2024) [8] , as they studied population dynamics of black thrips on chilli during the summer season. They recorded that population of black thrips initiated on 2 nd week of March (11 th SMW) with 0.20 thrips/leaves and reached its peak (13.85 thrips/leaves) on 2 nd week of May (19 th SMW). The variation is observed due to difference of experimental seasons as well as locality and variety. Also they observed non-significant positive association with maximum temperature (r= 0.478) and bright sunshine hours (r= 0.199) with invasive black thrips population, T. parvispinus, whereas non-significant negative correlations with minimum temperature (r= -0.238), morning relative humidity (r= -0.497) and evening relative humidity (r= -0.135). The chilli thrips, S. dorsalis population was negatively correlated with sunshine hours (r=-0.137), and significantly negative with average relative humidity (r=-0.620*) as per reports Borgohain et al. (2024) [4] . They also recorded that rainfall had no significant effect on incidence of pest population in chilli. Reddy et al. (2017) [11] . They recorded the seasonal incidence of S. dorsalis in chilli during kharif and noticed highest thrips population during January 3 rd SMW with 24.82 thrips per five leaves in kharif, 2015-16, while, it was December's last week (52 nd SMW) with 17.01 thrips per five leaves during kharif, 2016-17. Kotresh et al. (2020) [5] recorded peak chilli thrips, S. dorsalis incidence during the 48 th SMW with significant negative correlation with sunshine hours and evaporation. First incidence of thrips, S. dorsalis was noticed in chilli during fourth week of November (47 th SMW) and reached its peak (20.2 thrips/plant) during the second week of April (15 th SMW) by Kumar et al. (2020) [6] . Prathyusha et al. (2021) [10] revealed that occurrence of thrips was started during 35 th SMW and reached the peak during 44 th SMW and population exhibited non-significant positive correlation with maximum temperature.

Acknowledgement

AcknowledgmentThe authors take this opportunity to express gratitude to B.A. College of Agriculture, Anand Agricultural University, Anand, for the provision of research facilities and constant guidance during the course of the investigation. Also, authors are thankful to Dr. R. R. Rachana, Scientist, Division of Insect Systematics, ICAR-National Bureau of Agricultural Insect Resources, P. B. No. 2491, H. A. Farm Post, Bellary Road, Hebbal, Bangalore-560 024, Karnataka, India, for confirming the identity of invasive thrips species infesting chilli as Thrips parvispinus (Karny).

References

1. Anonymous. Indiastat [Internet]. 2024a [cited 2024 Jul 24]. Available from: http://www.indiastat.com/
2. Anonymous. Indiastat [Internet]. 2024b [cited 2024 Jul 24]. Available from: http://www.indiastat.com/
3. Berke T, Sheih SC. Chilli peppers in Asia. Capsicum and Eggplant Newsletter. 2000;19:38-41.
4. Borgohain A, Rajkumari P, Borah N, Borah BK. Seasonal incidence of major insect pests of chilli and their correlation with weather parameters. International Journal of Environment and Climate Change. 2024;14(5):336-341.
5. Kotresh S, Raghuraman M, Srushtideep A. Seasonal incidence of mites and thrips in chilli. Journal of Entomology and Zoology Studies. 2020;8(4):569-572.
6. Kumar S, Awasthi AK, Kerketta A, Shyam R. Seasonal incidence of chilli thrips (Scirtothrips dorsalis Linn.) on chilli and its correlation with different abiotic factors. Journal of Entomology and Zoology Studies. 2020;8(5):779-782.
7. Lodaya JP, Suthar MD, Patel HC, Sisodiya DB, Acharya RR, Raval AT, Trivedi NP, Mohapatra AR. Status of invasive species of thrips, Thrips parvispinus (Karny) infesting chilli grown in middle Gujarat. The Pharma Innovation Journal. 2022;11(3):1298-1302.
8. Lokare OS, Bagde AS, Barve AN, Bandrewar PG, Ghonmode IA, Karande RA, et al. Population dynamics of new invasive black thrips (Thrips parvispinus Karny) infesting chilli under open field conditions. International Journal of Statistics and Applied Mathematics. 2024;SP-9(6):146-148.
9. Century, Biodiversity, Sustainability, Environmental Safety and Human Health, Udaipur, Rajasthan; 1998.
10. Prathyusha P, Dwivedi RK, Pal D, Gulab. Studies on population dynamics of sucking pest complex of chilli and their relation with environmental factors. International Journal of Current Microbiology and Applied Sciences. 2021;10(5):802-808.
11. Reddy AA, Reddy NC, Kumari AD, Rao MA, Reddy NS. Seasonal incidence of thrips and relation to abiotic factors in chilli (Capsicum annuum L.). Journal of Entomology and Zoology Studies. 2017;5(5):88-91.
12. Sridhar V, Chandana PS, Rachana RR. Global status of Thrips parvispinus (Karny, 1922), an invasive pest. The Journal of Research PJTSAU. 2021;49(4):1-11.