The size of prey is critical to the feeding success of any given predator, but the effects of diet packet size have not been studied. We examined the effects of size of packets (Parafilm® domes) of artificial diet and the size of prey eggs on oviposition and mortality rates of Orius insidiosus (Say). Artificial diet was presented to adult female O. insidiosus in 10-, 25- and 50-μL domes for 6 d and rate of oviposition was measured for 24 h. Oviposition was highest after feeding on the 10-μL domes, decreased slightly on the 25-μL domes, and was significantly reduced on the 50-μL domes. The effect of capsule size was negated on the 25-μL and 50-μL diet domes when the diet was supplemented with E. kuehniella egg protein. Predators were also fed eggs of 4 species of Lepidoptera, Ephestia kuehniella Zeller, Plodia interpunctella (Hübner), Helicoverpa zea (Boddie), Spodoptera frugiperda (J. E. Smith), and Heliothis virescens (Fabricius), ranging in volume from 19 ± 1.7 nL (mean ± SD) for P. interpunctella to 108 ± 21.3 nL for H. virescens eggs. Oviposition was highest and comparable on the E. kuehniella, P. interpunctella and H. virescens eggs and significantly less on S. frugiperda and H. virescens eggs. Oviposition positively correlated and mortality negatively correlated with weight-specific protein contents of the eggs, but neither correlated with egg volume. When all species of eggs were extracted and combined with diet in domes of constant size and constant protein content, only extracts of E. kuehniella and P. interpunctella eggs were more active than diet alone.