The predator Amblyseius swirskii and entomopathogenic fungus Beauveria bassiana are important biocontrol agents of Trialeurodes vaporariorum. The effect of either untreated or treated second instar nymphs of T. vaporariorum by B. bassiana DEBI008 (1×10⁵ conidia/ml) with four time intervals; 0, 24, 48 and 72 h on some biological parameters in A. swirskii at 25±1°C, 60–70°RH and a photoperiod of 16:8 h (L: D) was investigated under laboratory condition. In this study, some biological parameters such as searching time, feeding time and predation rate of A. swirskii were evaluated. Data analysis showed that searching time of the predator was increased on treated second instar nymphs of greenhouse whitefly in comparison with untreated second instar nymphs and two other parameters, feeding time and predation rate were decreased. These parameters were strongly affected by fungus presence and by increasing of infection time from 0 to 72 hours in T. vaporariorum and had significant differences. B. bassiana DEBI008 affected behavioral parameters in the predatory mite, enabling it to detect and avoid treated greenhouse whiteflies. Determination of behavioral parameters in A. swirskii when untreated or treated nymphs of greenhouse whitefly, T. vaporariorum are present, is important in control of T. vaporariorum by these two biocontrol agents in concomitant use.