Future atmospheric CO2 concentrations are predicted to increase, and directly affect host plant phenology, which, in turn, is assumed to mediate the performance of herbivorous insects indirectly as well as the abundance and epidemiology of plant diseases. In a 4-year field experiment, spring wheat (Triticum aestivum L. cv. Triso) and spring oilseed rape (Brassica napus L. cv. Campino) were grown using a mini- free-air CO2 enrichment (FACE) system, which consisted of a control (CON), an ambient treatment (AMB) and FACE treatments. The CON and AMB treatments did not receive additional CO2, whereas the FACE plots were moderately elevated by 150μLL-1 CO2. The impact of elevated CO2 was examined with regard to plant phenology, biomass, leaf nitrogen and carbon, abundance of insect pest species and their relative population growth by either direct counts or yellow sticky traps. Occurrence and damage of plants by pathogens on spring wheat and oilseed rape were directly assessed. Disease infestations on plants were not significantly different between ambient and elevated CO2 in any of the years. Plant phenology, aboveground biomass, foliar nitrogen and carbon concentrations were also not significantly affected by CO2 enrichment. In contrast, the abundance of some species of insects was significantly influenced by elevated CO2, showing either an increase or a decrease in infestation intensity.