AbstractThe emergence of insecticide resistant insect pests is of significant concern worldwide. The whitefly,Bemisia tabaci, is an important agricultural pest and has shown incredible resilience developing resistance to a number of chemical pesticides. Entomopathogenic fungi such asIsaria fumosoroseaoffer an attractive alternative to chemical pesticides for insect control, and this fungus has been shown to be an effective pathogen ofB. tabaci. Little is known concerning the potential for the development of resistance toI. fumosoroseabyB. tabaci. Five generations of successive survivors ofB. tabaciinfected byI. fumosoroseawere assayed withI. fumosorosea. No significant differences in susceptibility toI. fumosorosea, number of ovarioles, or ovipostioning were seen between any of the generations tested. Effects ofI. fumosoroseaand cell-free ethyl acetate fractions derived from the fungus on theB. tabacifat body, ovary, and vitellogenin were also investigated. These data revealed significant deformation and degradation of ovary tissues and associated vitellogenin by the fungal mycelium as well as by cell-free ethyl acetate fungal extracts. These data indicate the lack of the emergence of resistance toI. fumosoroseaunder the conditions tested and demonstrate invasion of the insect reproductive tissues during fungal infection.