We attempt to quantify the impact of future climate change on the developmental dynamics of onion thrips in Slovenia. Monthly averaged results of simulations of future climate from four different general circulation models (GCMs) were projected to local scale by empirical downscaling. The GCM simulations were based on two emission scenarios (IPCC SRES A2 and B2). Local estimates of monthly averaged air temperatures for five locations in Slovenia were adjusted for an additional four emission scenarios (SRES A1T, A1F1, A1B, and B1) using a pattern scaling technique. They were further transferred to a daily scale using a first-order autoregressive model. A simple degree-day model, based on data reported in the literature, was used to relate the development of onion thrips to temperature. Potential changes in the period with favorable developmental conditions for onion thrips (i.e., temperatures above the lower developmental threshold) and in the number of generations per season were estimated with regard to the expected future climate change in Slovenia. The changes are influenced by the magnitude of temperature increase, its asymmetry within the year, and present climate conditions. Using this approach, one can obtain quantitative estimates of the impact of climate change on the developmental dynamics of an insect pest, but one must be fully cognizant of all the assumptions made in the procedure, which introduce uncertainties in the final results. Further research is needed to evaluate the plausibility of such simplified projections.