Pathogenicity of Isaria fumosorosea to Bemisia tabaci, with some observations on the fungal infection process and host immune response

- The fungus Isaria fumosorosea IF-1106 infected all sweetpotato whitefly lifestages.
- Scanning electron microscopy revealed several distinct stages of pathogenesis over 7 d.
- Antioxidant and detoxification enzymes were upregulated in infected whiteflies.

Isaria fumosorosea is an important pathogen of whiteflies, and is used as a mycoinsecticide against this pest in many regions of the world. We quantified the pathogenicity of the Chinese isolate IF-1106 against different life stages of sweetpotato whitefly, Bemisia tabaci, on cucumber plants, and describe the infection process and aspects of the host immunological response in the laboratory. The second instar was the most susceptible life stage to infection, with mortality rates at 107 conidia/ml ≈83% after 7 d. Scanning electron microscopy was used to monitor morphological aspects of the infection process. The following stages were observed; conidia adhered on the cuticle of B. tabaci and began to germinate within 6 h of inoculation, appressoria development after 24 h, germ tube penetration within 48 h, emergent hyphae within 72 h, secondary conidiogenesis within 96 h with mass hyphal proliferation occurring on cadavers within 120 h. The activities of endogenous enzymes were evaluated from host homogenate at various intervals post infection. Three enzymes associated with antioxidant activity [superoxide dismutase (SOD), perioxidase (POD), and catalase (CAT)], and two with detoxification [glutathione S-transferase (GSTs) and carboxylesterase (CarE)] were apparently upregulated in second instars infected by I. fumosorosea. Enzyme activities reached peak values at 48-60 h post infection, then decreased to significantly lower than controls in 84 h as mycosis occurred. Our results provide new insights into the pathogenicity and potential physiological response of B. tabaci to this fungal isolate.