Aged Sensibility of Leptinotarsa decemlineata Say (Chrysomelidae, Coleoptera) to Strains of Beauveria bassiana (Bals.) Vuill.
Plant Protection Institute, BG-2230 Kostinbrod, Bulgaria
DRAGANOVA, S., 2000. Aged sensibility of Leptinotarsa decemlineata Say (Chrysomelidae, Coleoptera) to strains of Beauveria bassiana (Bals.) Vuill. Bulg. J. Agric. Sci., 6: 553-559
Virulence of ten strains of Beauveria bassiana (Bals.) Vuill. to larvae and imago of Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) has been studied under laboratory conditions from 1994 to 1999. The virulence of the strains was measured by values of the median lethal time (LT50) calculated by probit analysis. It was established that larvae of the pest showed aged sensibility to a strain 256-1 of B. bassiana (isolated from a larva of L. decemlineata). It was expressed by a highly virulence to the 1st and to the 2nd instar larvae, a weaker lethal effect to the 3rd and to the 4th instar larvae and a low virulence to imago of the pest. The calculated LT50-values varied within fiducial limits (*P < 0.05) from 2.393 to 3.867 (days), from 3.447 to 4.220 (days) and from 7.678 to 8.333 (days), from 10.990 to 11.640 (days) and from 22.220 to 38.430 (days), respectively. Six strains were with a high virulence to the 3rd instar larvae of L. decemlineata and there was not a significant difference between their LT50-values. A strain 256-1 was with the lowest virulence to the 3rd and to the 4th instar larvae of the pest. A strain 224-2 was the most virulent to the 4th instar larvae and it's LT50-values varied within the fiducial limits from 6.261 to 6.486 (days). A strain 224-3 of B. bassiana (isolated from imago of L. decemlineata) was the most virulent to imago of the host. It's LT50-values varied in fiducial limits from 7.980 to 9.354 (days). A strain 269 of B. bassiana (isolated from larvae of Ostrinia nubilalis Hb, Pyralidae, Lepidoptera) was with a low virulence and a strain 257 (isolated from larvae of Agriopis bajaria (Denis & Schiffermuller), Geometridae, Lepidoptera) was not virulent to imago of L. decemlineata. Their LT50-values varied within fiducial limits from 14.400 to 17.870 (days) and from 119.300 to 833.100 (days), respectively.
Key words: virulence, aged sensibility, Beauveria bassiana, Leptinotarsa decemlineata