Abstract

CHAN-CUPUL, Wilberth et al. In vitro development of four Paecilomyces Fumosoroseus isolates and their pathogenicity on immature whitefly. Agrociencia [online]. 2010, vol.44, n.5, pp.587-597. ISSN 2521-9766.

The use of chemical insecticides in the management of whitefly (Bemisia tabaci) (Gennadius) causes serious damage to the environment and has generated populations resistant to conventional products. A promising alternative is biological control by using entomopathogenic fungi. In the present study the in vitro development and pathogenicity of four native strains (Pf-Tim-Tiz Pf, Pf-Hal, Pf-Rg), as well as a commercial (Pae-sin) of Paecilomyces Jumosoroseus (Wize) Brown & Smith were evaluated in eggs and first instar nymphs of Bemisia tabaci (Gennadius). The variables to assess the in vitro development were: daily growth rate of the colony (TCD), sporulation and spore germination rate (TGE). The pathogenicity of the strains was determined by dipping the leaves of Capsicum chinense, which contained the immature stages of B. tabaci in a conidial suspension 1×10⁷ spores mL^-1. The TCD of the strain Pae-sin (1.63 mm d^-1) was higher (p<0.05) than that of Pf-Hal (1.40 mm d^-1) and Pf-Rg (1.35 mm d^-1). Sporulation was not different (p> 0.05) between native isolates and the commercial strain. The TGE was higher (p<0.05) in Pf-Rg (22 % h^-1) than that observed in other native strains and Pae-sin (11.91 to 12.50 %). All fungi were more pathogenic in nymphs than in eggs; the mortality of eggs and nymphs ranged from 29.8 to 45.5 % and from 51.4 to 74.5 %. With the data of mortality in nymphs, mean lethal time (TL₅₀) and the area under the curve of cumulative mortality (ABCMA) were calculated. The lowest values of TL₅₀ and the highest of ABCMA were observed in the strain Pae-sin with 3.2 d and 311.93 units and in Pf-Hal with 3.7 d and 301.93 units. The analysis of the results indicates that there was no clear relationship between the in vitro development capacity of the isolates and their virulence on B. tabaci immature stages.

Keywords : Bemisia tabaci; biological control; entomopathogenic microorganisms.