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The present investigation on the impact of population regulating factors on Bemisia tabaci (Gennadius) infesting soybean crop (var. PK-416) was carried out at the experimental area of Research Farm, Department of Entomology, CCS HAU, Hisar during Kharif 2017. The whitefly population and nymphal parasitization by Encarsia spp. were observed on three leaves from 10 randomly selected plants at ten-day intervals from June to September. The peak population of whitefly adults i.e., 19.7 per leaf was recorded from 31^st July to 9^th August, 2017 when temperature ranged from 26.6 ºC to 34.2 ºC and relative humidity ranged from 70.0 to 90.0 per cent. The nymphal population i.e., 24.4 per lead was found maximum from 10^th to 19^th August, 2017 at temperature ranging from 26.4 ºC to 35.6 ºC and relative humidity ranging from 61.0 to 87.0 per cent. Maximum nymphal parasitization of B. tabaci by Encarsia spp. on soybean (28.4%) coincided with the peak population of whitefly nymphs. Correlation analysis revealed the impact of weather factors on whitefly adult and nymphal population which showed significant negative correlation with maximum temperature [(r = -0.62), (r = -0.59)] and positive with morning relative humidity [(r = 0.62), (r = 0.57)], respectively.

 Keywords: Soybean, Bemisia tabaci, peak activity, Encarsia spp., weather parameters, correlation.