author(s)
Arun Janu, KK Dahiya, Yogesh Kumar and Pritish Jakhar

abstract
Studies were carried out to explore population dynamics and the impact of abiotic factors like maximum temperature, minimum temperature, morning relative humidity, evening relative humidity, average weed speed, sunshine hours and rainfall on the population of thrips, (Thrips tabaci Lindeman) on twenty Bt cotton genotypes at Research Farm, Cotton Section, Department of Genetics and Plant Breeding, CCS Haryana Agricultural University, Hisar during kharif 2014 and 2015. Regression analysis was carried out with SPSS v19 software. In present studies, R2 was found with a range of 0.00 to 0.73 i.e. population of thrips was influenced up to 73.00 per cent by the simple, multiple, hierarchical and stepwise linear regression models under Hisar conditions. Simple linear regression model during 2014 and 2015 revealed that minimum temperature (Tmin) and evening relative humidity (RHe) had higher impact (17.20 and 46.10 per cent) on the incidence of thrips, respectively. In multiple linear regression models, the impact of weather factors on the thrips in Bt cotton during 2014 exerted 58.20 per cent, 71.60 per cent during 2015 role in the thrips population fluctuation. Hierarchical linear regression models revealed that the impact on the fluctuation of thrips population increases with the addition of the influence of weather parameters in both the years. No stepwise linear regression model was observed during 2014. While, two stepwise linear regression models are developed during 2015. The evening relative humidity and rainfall exerted (58.20 per cent) impact in the fluctuation of thrips population in the combination while, evening relative humidity alone explained (46.10 per cent) role in the variation of thrips population on Bt cotton.