Five species of entomopathogenic fungi were tested against whiteflies and aphids. Cladosporium spp. showed a high incidence on the two insect species tested (81% of the total isolated species). However, C. uridenicola was the predominant species isolated from both insect species during the two successive seasons of 1998 and 1999. Natural infection by Cladosporium ranged from 18.19 to 44.38% and 16.4 to 45.27% in 1998 and 1999, respectively, according to insect species and the host plant. Statistical analysis revealed a high correlation (R = 0.8759 ± 0.093) between the total investigated and total infected of each insect species during the two successive years of the study. The natural infection of Cladosporium to whitefly life stages was higher on whitefly nymphs (87.8%) than adults (8.08%) and eggs (4.15%) in 1998 and 1999. The results showed that the seasonal distribution of Cladosporium occurred all year around, but rates were higher during the period from June until November which coincided with the high populations of whiteflies and aphids. The weather had a significant effect on infection of insects and had no effect on other fungi species. The laboratory tests showed a higher pathogenicity of the candidate on Aphis gossypii, Aphis craccivora and Bemisia agrentifollii than other reported fungi.