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The present experiment was conducted at a constant temperature of 25 ± 0.5 °C, 70 ± 5 per cent relative humidity and 14L: 10D photoperiod on French bean, Phaseolus vulgaris cv. contender plants in the Biocontrol Laboratory of the Department of Entomology, Dr YS Parmar University of Horticulture and Forestry, Nauni, Solan, Himachal Pradesh, India. The study revealed that Encarsia formosa exhibited a Type II functional response both on the bases of parasitism and host kill with third and fourth nymphal instars of greenhouse whitefly. The functional response parameters i.e. handling time (Th), attack rate (a), effectiveness of parasitoid (a/Th) and the maximum parasitization rate (K) on total host kill by the parasitoid on third nymphal instar was 0.575 h, 0.037 h−1, 0.064 and 41.684, respectively whereas with fourth nymphal instar, handling time (Th), attack rate (a), effectiveness of parasitoid (a/Th) and the maximum parasitization rate (K) was 0.518 h, 0.044 h−1, 0.086 and 46.317, respectively. The area of discovery of the parasitoid with third nymphal instars decreased from 0.12 to 0.09 and with fourth instar it decreased from 0.14 to 0.09 with the increase in the density of the parasitoid from 2 to 8 for both the nymphal instars (third and fourth), respectively. The mutual interference coefficient with fourth instar was highest (m = 0.285) as compared to third instar nymphs (m = 0.166). It shows its effectiveness against the greenhouse whitefly. Hence, it can be utilized as one of the component of an integrated pest management programme of greenhouse whitefly, T. vaporariorum under protected cultivation. [ABSTRACT FROM AUTHOR]