Demographic statistics for the ladybeetle Scymnus syriacus Marseul (Coleoptera: Coccinellidae) were investigated when reared on the green citrus aphid, Aphis spiraecola Patch (Homoptera: Aphididae), fed on two host plants: spirea (Spirea sp.) and Thompson orange (Citrus sinensis cv. Thompson) under laboratory conditions (25 Ϯ 1°C, 65 Ϯ 5% relative humidity and 16 h light : 8 h dark). Mean developmental times from egg to adult were 20.32 Ϯ 0.18 and 22.07 Ϯ 0.15 days for spirea and Thompson orange, respectively. The survival rate from egg to adult was higher for spirea (85%) than for Thompson orange (72.5%). The oviposition periods were 41.8 Ϯ 2.47 and 39.71 Ϯ 2.6 days and the total number of eggs per female were 657.6 Ϯ 29.5 and 587.9 Ϯ 32.6 on spirea and Thompson orange, respectively. Fertility life tables were also constructed to compare the effects of host plants. The intrinsic rate of increase (rm) on spirea was higher than that on Thompson orange. Jackknife estimates of rm varied from 0.149 on spirea to 0.133 on Thompson orange. The mean population generation times on these host plants were 38.16 and 40.65 days, respectively. These results indicate that spirea-fed A. spiraecola is more suitable for S. syriacus, producing a higher survival rate and shorter developmental time.