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- 44.38% and 16.4- 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 during the two successive years of 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 and that coincide with the high population of whiteflies and aphids. The weather had a significant effect on insects infection and had no effect on the others. The laboratory tests showed a high pathogenicity of the candidate on A. gossypii, A. craccivora and B. agrentifollii than other reported fungal.