Trogoderma spp. including Trogoderma versicolor are important insect pests whose larvae damage different stored products and stuffs of both plant and animal origin. Trogoderma versicolor is a quarantine species for Bulgaria.
Bioassays were conducted with larvae from a laboratory population of T. versicolor with wheat varieties of foreign origin stored at the former Plant Protection Institute, Bulgaria.
The virulence of 5 isolates of the entomopathogenic fungus Beauveria bassiana was investigated in laboratory experiments. Active larvae (L2-4) of T. versicolor were treated with conidial suspensions at concentrations 1-2х107 conidia/ml and the dead larvae were put into a humid chamber. The larval mortality was estimated as a percentage of the cumulative daily mortality due to mycosis, corrected with the control mortality. The virulence of the fungal isolates was evaluated according to the values of the median lethal time (LT50), calculated by probit analysis.
The results showed that the larvae were susceptible to mycosis caused by the tested B. bassiana isolates except for the re-isolate 513reTgrBb. The larval mortality caused by isolate 687Bb was 1.11% on the 6th day after the treatment and it rose to 98.89% and 100% on the 7th and 10th day, respectively. Isolate 689Bb was the most virulent to the larvae with LT50 values 3.420 (2.994 – 3.905) days (Р < 0.05).