A study was conducted for two consecutive years (2016–17 and 2017–18) to understand the relative role of weather parameters and humid thermal ratio (HTR) on population dynamics of thrips, T. tabaci, in bulb onion. Counts were made at five randomly selected spots, consisting of five plants in each spot. Results revealed that the highest peak of 65 thrips per plant was observed during fourth standard meteorological week (SMW). Further, irrespective of the years, higher numbers of thrips were observed during third to sixth SMW. Correlation analysis showed a significant positive correlation (r = 0.587*) with HTR and a significant negative correlation with maximum temperature (r = –0.628*) and minimum temperature (r = –0.566*). The linear and logarithmic regression analysis between HTR and thrips population had explained 50 % of variation. Thus, the present study suggests that apart from temperature, prevailing humid thermal ratio during the growth period could have an impact on occurrence of thrips in bulb onion.