Abstract: The sub-lethal effects of spirodiclofen on the functional response of the predatory coccinellid Cryptolaemus montrouzieri Mulsant, a potential biological control agent of mealybugs, were investigated, using adult females of Planococcus citri (Risso) as prey. The experiment was conducted in varying densities (2, 4, 8, 16, 32, 64 and 128) of P. citri at 28 ± 1 °C, 60 ± 10% r.h., and a photoperiod of 16 L:8 D. The results of logistic regression analysis suggest a type II functional response in both the control and all insecticide concentrations. Comparison of functional response curves revealed that the tested insecticide markedly decreased the mean number of preys consumed by C. montrouzieri. The search rates found for predators decreased when exposed to increasing sub-lethal concentrations of spirodiclofen (from LC10 up to LC30). The handling times of female ladybirds exposed to insecticide were in all cases lower than in the control treatment. The maximum handling time and the minimum attack rate were observed in LC10. The adverse effect of spirodiclofen on C. montrouzieri must be considered in integrated pest management programs.