Increased mortality of Acanthoscelides obtectus by alkane-grown Beauveria bassiana.

R. CRESPO; M. P. JUÁREZ; G. DAL BELLO; S. PADÍN; CALDERÓN FERNÁNDEZ G.; N. PEDRINI

BIOCONTROL (DORDRECHT)

SPRINGER

Año: 2002 vol. 47 p. 685 - 696

1386-6141

The effect of alkane-growth induction of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Deuteromycotina: Hyphomycete), on the ability to kill the bean weevil Acanthoscelides obtectus Say (Coleoptera: Bruchidae), was tested. Adult insects were sprayed with an 0.01% Tween 20 aqueous suspension of 4 x 106 conidia/ml. The performance of fungi grown in complete agar medium containg glucose as carbon source (FS0) was compared to that of alkane-grown fungi (FS1) with n-hexadecane as the only carbon source. Mortality was significantly increased (p <0.05) from 22 ± 4.5% to 44 ± 11.4% at day 7, and from 26 ± 5.5% to 60 ± 7.1% when measured at day 14 after treatment with FS0 or FS1 respectively. The insect epicuticular hydrocarbons were analysed by capillary gas chromatography (CGC), they were all saturated, major components ranged from 27 to 29 carbons in their skeleton. A variety of methyl-branched isomers of C27 were the prevailing structures, and nC27 was the major straight chain component. Whole insect hydrocarbons were qualitatively identical to those of the epicuticular surface. Oleic, linoleic and palmitic acids accounted for almost 88% of the fungal fatty acids, irrespectively from the carbon source used for growth, however, the unsaturated/saturated ratio diminished markedly from 4.32 (FS0) to 2.47 (FS1). These results indicate that alkane-growth induction might be a tool to improve mycoinsecticide development.