The impact of defoliation by fall armyworm, Spodoptera frugiperda (J. E. Smith), on the photosynthetic rates of injured, individual wheat, Triticum aestivum L., leaves and the impact of different spatial patterns of artificial insect defoliation on photosynthesis of remaining leaf tissue of injured, individual wheat leaves were evaluated in this study. Photosynthesis, stomatal conductance, transpiration, and chlorophyll a fluorescence were recorded in the flag-leaves of wheat plants 1 and 24 h after defoliation in 2003 and at 1 h, 24 h, 7 d, and 14 d after defoliation in 2004. Photosynthesis of injured leaves was not significantly affected by any defoliation treatment (i.e., control, natural, and artificial). Similarly, we did not observe interactions between defoliation treatments and time after defoliation. Stomatal conductance was significantly affected by time after defoliation and by the interaction between defoliation treatment and time after defoliation. However, in general, our results showed that wheat responded similarly to insect defoliation and artificial defoliation, which, therefore, may be used to simulate leaf mass consumption. Spatial defoliation patterns had a significant effect on photosynthetic parameters of injured leaves, but responses were dependent on plant developmental stages. The chlorophyll a fluorescence data revealed no significant effects from any defoliation pattern on the photochemical efficiency of the injured leaf. No significant interactions between defoliation patterns and time after defoliation were observed. Our findings reveal that the spatial pattern of defoliation in wheat affects photosynthetic and other gas exchange responses, which suggests that when simulating insect defoliation in wheat, researchers need to be cognizant of the defoliation pattern to adequately simulate insect defoliation.