The virulence of the Isaria fumosorosea strain (Ifu13a) against different plant sap-sucking insects such as Jacobiasca formosana Paoli (Hemiptera: Cicadellidae), Aphis gossypii Glover (Hemiptera: Aphididae), Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), and Stephanitis nashi Esaki et Takeya (Hemiptera: Tingidae) in laboratory condition at 21 ± 1°C temperature and 78 ± 5% relative humidity was determined. We found that the Ifu13a strain had excellent potential to control the target insects. The mortality of the tested insect species ranged from 81 to 100% in the concentration of 1 × 108 conidia/ml. However, the lowest mortality of 33% was observed in the concentration of 1 × 105 conidia/ml against the S. nashi population. Median lethal times (LT50) were obtained from a regression-probit value which indicated 4.1, 4.1, 4.8, and 7.3 days at a concentration of 1 × 108 conidia/ml, whereas, median lethal concentration dosages (LC50) were calculated as 3.9 × 103, 6.8 × 104, 3.0 × 104, and 6.9 × 105 conidia/ml against J. formosana, A. gossypii, B. tabaci, and S. nashi, respectively. The present study showed that the Ifu13a fungal strain is highly pathogenic to the target insects, and it can be used as a biocontrol agent against plant sap-sucking insect species under favourable weather conditions.