Relative abundance and population dynamics of chilli thrips Scirtothrips dorsalis (Hood) (Thripidae:Thysanoptera) and its correlation with weather parameters

Thrips, particularly Scirtothrips dorsalis (Hood) (Thripidae: Thysanoptera), are major sucking pests of chilli, with their populations varying throughout crop growth period depending on seasonal conditions. Field experiments were carried out during the rabi and kharif seasons of 2024 in Coimbatore, Tamil Nadu to study the population dynamics of susceptible and resistant chilli plants about weather parameters. In the rabi season, thrips infestation began in the second week of January and continued till March 2024. The peak population was recorded during the flowering stage in the 6th Standard Meteorological Week (SMW), with 4.73 thrips per three leaves in the susceptible entry IC-537583 and 2.73 thrips in the resistant IC-344364 at 75 days after transplanting (DAT). The associated weather conditions included 32 °C maximum temperature, 22 °C minimum temperature, 84 % maximum relative humidity, 41 % minimum relative humidity, 5.0 km/h wind speed, no rainfall and 4.07 sunshine hours. The thrips population declined at crop maturity, with 3.53 thrips in IC-537583 and 1.87 thrips in IC-344364. During the kharif season, initial thrips populations were recorded at the 28th SMW, peaking at the 32nd SMW, with lower populations of 3.73 thrips in IC-537583 and 1.33 thrips in IC-344364, primarily due to heavy rainfall from July to September. Correlation analysis showed that thrips incidence was positively correlated with maximum temperature, sunshine hours and wind speed in the first season. In contrast, minimum temperature, rainfall and relative humidity (both maximum and minimum) had a negative correlation. In the second season, maximum and minimum temperatures, maximum relative humidity and sunshine hours positively influenced the thrips population, whereas minimum relative humidity and rainfall had a negative impact. Multiple regression analysis accounted for 73 % and 64 % variation in thrips population during rabi and 64 % and 48 % during kharif.