Pathogenicity of Isaria sp. (Hypocreales: Clavicipitaceae) against the sweet potato whitefly B biotype, Bemisia tabaci (Hemiptera: Aleyrodidae)

The pathogenicity of a naturally occurring entomopathogenic fungus, Isaria sp., found during natural epizootics on whiteflies in the Lower Rio Grande Valley of Texas, against the sweet potato whitefly, Bemisia tabaci (Gennadius) biotype B, was tested under laboratory conditions (27 °C, 70% RH and a photoperiod of 14:10 h light:dark). Exposure of second-, third- and fourth-instar nymphs to 20, 200, and 1000 spores/mm 2, on sweet potato leaves resulted in insect mortality. Median lethal concentrations for second-instar nymphs (72–118 spores/mm 2) were similar to those for third-instar nymphs (101–170 spores/mm 2), which were significantly more susceptible than fourth-instar nymphs (166–295 spores/mm 2). The mean time to death was less for second instars (3 days) than for third instars (4 days) when exposed to 1000 spores/mm 2. Mycosis in adult whiteflies became evident after delayed infections of sweet potato whitefly caused by this fungus. These results indicate that Isaria sp. is pathogenic to B. tabaci nymphs, and to adults through delayed infections caused by this fungus. Its low lethal concentrations and high virulence against B. tabaci make this fungus a promising biocontrol agent to control whitefly.