Understanding the relationship between above and below ground herbivores and how this interaction is mediated by nutrition can lead to the development of more efficient insect management methods. In this study we evaluated the effect of four different nitrogen levels on the interaction between darkwinged fungus gnats (DWFG), Bradysia impatiens, and silverleaf whitefly (SLWF), Bemisia tabaci biotype B, on poinsettias and their combined effect on plant performance. Plants were infested one week after transplant with whiteflies, fungus gnats or both (except for the controls). All plants were grown using and ebb and flow system and they were arranged on a split plot (main plot=nutrition; sub plot=insect infestation). The effects on SLWF were measured by evaluating developmental time, survivorship, and F1 oviposition. For DWFG we measured larvae and pupae numbers remaining in the soil, adult emergence and immature distribution within the pot (top and bottom soil layer). Herbivore impact on plant performance was evaluated by measuring plant dry weight (leaves, stems and roots), total number of leaves, photosynthesis and amino acid content. SLWF oviposition was not affected by DWFG presence or nitrogen level. DWFG emergence and larvae numbers were not influenced by SLWF presence but adult emergence was affected by nitrogen level, with DWFG emergence being highest at 150 and 250 ppm of N. Most immature DWFG were found on the bottom soil layer. Overall, the presence of SLWF and DWFG did not affect total dry weight, number of leaves and photosynthesis rate of poinsettias.