The virulence of entomopathogenic fungi against Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) and their conidial production using solid substrate fermentation

Abstract

The virulence of five isolates of Beauveria bassiana, five of Isaria fumosorosea and four of Lecanicillium muscarium from Brazil was determined on whitefly Bemisia tabaci biotype B lifestages on bean leaves under laboratory conditions. The conidial yield (on cadavers or parboiled rice), surface hydrophobicity and enzyme activity were also determined. The isolates of B. bassiana and I. fumosorosea were the most virulent against nymphs (71–86% mortality within 8d), with LT50 values ranging from 3 to 4d after treatment with 107conidia/mL (150conidia/mm2). Spore production on nymph cadavers reached 4–8×105conidia/insect. The L. muscarium isolates demonstrated low virulence toward nymphs. After spraying eggs with 1×108conidia/mL (1674conidia/mm2) of B. bassiana and I. fumosorosea, most nymphs hatched, but then 40–70% of these nymphs were infected by indirect exposure of conidia on the leaves. Adults exposed to treated leaf disks (150conidia/mm2) were more susceptible to I. fumosorosea than to B. bassiana. The enzyme activity (Pr1) and the relative conidial surface hydrophobicity were not correlated with any virulence parameter measured for either B. bassiana or I. fumosorosea. In addition, the highest conidial yields on parboiled rice using solid-state fermentation (4.9–11.4×109conidia/g) were achieved by isolates of I. fumosorosea CG1228 and B. bassiana CG1229. I. fumosorosea CG1228 was highly virulent against whitefly nymphs and adults as well as attained high spore production on insect cadavers and parboiled rice. Our results indicate that I. fumosorosea CG1228 has desirable attributes for the development of a mycoinsecticide against B. tabaci biotype B.