The predator Wesmaelius navasi (Andréu) (Neuroptera: Hemerobiidae) was recorded as a new species in Egypt. The predator was identified by the Natural History Museum of London, UK. Laboratory experiments were carried out at Department of Plant Protection, Faculty of Agriculture, Zagazig University under constant temperature of 25 ± 1°c and 65 ± 5 % RH. to investigate the effect of some prey species on biological aspects of the predator. These prey species were Hyalopterus pruni (Geoffroy), Schizaphis graminum (Greenbug) and Aphis nerii Boyer. The obtained results indicated that the shortest and longest total larval duration of W. navasi were 14.84 + 0.24 and 21.69 + 0.24 days on H. pruni and S. graminum, respectively. The results showed that, the shortest developmental period was obtained when the larvae of the predator were reared on H. pruni (26.21 +0.40 days), while the longest one was recorded when the larvae were fed on A. nerii (40.50 + 0.54 days). The total consumption aphids during the larval stage varied according to aphid species as it averaged 322.11 ± 8.58, 154.67 ± 5.87 and 125.92 ± 4.49 aphids on H. pruni, S. graminum and A.nerii, respectively. The mean percentages of adults emergence attained 94.74, 87.50 and 80.00 %, with a sex ratio of 61.11, 57.14 and 62.50 % were recorded on H. pruni, S. graminum and A.nerii, successfully. Results indicated an average progeny of 288.45 + 10.88, 238.88 + 15.87 and 179.00 + 3.14 eggs/female when reared on the respective preys: H. pruni, S. graminum and A.nerii. Longevity of female was prolonged (36.63±1.67 days) on S. graminum and was shortened (29.18±1.87 and 29.20 ±1.24 days) on H. pruni and A.nerii, successfully.