Discrimination between Beauveria bassiana Strains Isolated from Agriopis bajaria (Lepidoptera: Geometridae)

1 Plant Protection Institute, BG-2230 Kostinbrod, Bulgaria
2 Agricultural University, BG-4000 Plovdiv, Bulgaria


DRAGANOVA, S. and I. LECHEVA, 2002. Discrimination between Beauveria bassiana strains isolated from Agriopis bajaria (Lepidoptera: Geometridae). Bulg. J. Agric. Sci., 8: 43–48

Three isolates of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuill. (Deuteromycotina: Hyphomycetes) were compared and discriminated by their biochemical profiles and virulence to three insect species. Strains have been isolated from dead larvae of Agriopis bajaria Denis & Schiff. (Lepidoptera: Geometridae) collected from a natural population of the pest in a plum ecosystem.
It has been studied biochemical profiles of the strains based on the utilization of 18 carbohydrates. Glucose, sucrose, trehalose and maltose were acidified at high degree in opposite to arabinose, rhamnose, inulin and dulcitol that were acidified slightly. The differences between the isolates according to the utilization of 18 carbohydrates were estimated by application of statistical methods ANOVA/MANOVA. It has been proved differences between strains 257–14 and 311 and between strains 311 and 312 as well at significance level p = 0.0046 and p = 0.0001, respectively. Isolates 257–14 and 312 could not be distinguished by their biochemical profiles (p = 0.5207) but they could be discriminated by their virulence.
Virulence of B. bassiana isolates have been examined to the third – fourth instar larvae of the initial host (A. bajaria), to the fifth – sixth instar larvae of Galleria mellonella L. (Lepidoptera: Pyralidae) and to adults of Acanthoscelides obtectus Say (Coleoptera: Bruchidae). According to the values of median lethal time (LT50), used as a measure of the virulence, the isolate 311 was more virulent to caterpillars of A. bajaria than the isolate 312, but it was less virulent than the isolate 257–14. The LT50 – values calculated for the isolate 257–14 varied within a narrow confidence interval from 4.086 to 5.048 days, for the isolate 311 – from 7.836 to 8.447 days and for the isolate 312 they were from 9.028 to 10.450 days, respectively. Strains could be distinguished by their virulence to G. mellonella larvae as well. The isolate 257–14 was more virulent than the isolate 311 and the isolate 312 was not virulent to the caterpillars of the host. Calculated values of LT50 in experiments with adults of A. obtectus showed that the strain 257–14 was less virulent than strains 311 and 312. It has been found a significant difference between examined strains.

Key words: Beauveria bassiana strains, carbohydrate utilization profiles, virulence, Agriopis bajaria, Galleria mellonella, Acanthoscelides obtectus